Spatiotemporally ordered topological transformation in layered double hydroxides enables synergistic mineralization of As^III/Cd^2+

Domain: chemistry
Published: 2026-01-16
Editorial outcome: major_revision

Abstract
The co-contamination of arsenite (AsIII) and cadmium (Cd2+) poses a significant challenge in environmental remediation due to their divergent chemical speciation and transformation pathways. Here, a redox-active layered double oxide (MgMn-LDO) is designed, and achieves adsorption capacities of 821.7 mgg‒1 for AsIII and 1895.6 mgg‒1 for Cd2+ in their coexisting system, presenting a state-of-the-art performance. Unexpectedly, the co-adsorption system not only enhances individual adsorption capacities but also accelerates the adsorption rate by 181‒fold compared to single-component systems. The LDO undergoes a four-stage spatiotemporally ordered topological transformation, which effectively decouples the oxidation of AsIII from the adsorption of Cd2+ and reverses the conventional competitive sequence. This stepwise mechanism ensures preferential oxidation of AsIII to AsV, followed by the alteration of Cd2+ adsorption pathway to isomorphous substitution, expanding diffusion pathways and accelerating As immobilization. Large-scale experiments demonstrate this material’s potential in synergistic remediation As/Cd in mining wastewater and contaminated soils.

Introduction
Arsenite and cadmium co-contamination (AsIII/Cd2+) poses a significant global environmental challenge. However, remediation efforts are hindered primarily by the distinct chemical forms and transformation mechanisms of these two pollutants1–6. To tackle this issue, nano-composite materials have emerged as a promising solution, leveraging their multi-factor adjustability to synchronous AsIII/Cd2+ immobilization7,8. Among these, nano-composite metal oxides with redox activity stand out for their unique advantage in the remediation process, as they can efficiently pre-oxidize the uncharged and highly mobile AsIII into AsV anions9. This transformation not only enhances the immobilization of AsIII but also significantly reduces its toxicity10–12. However, in AsIII/Cd2+ co-contaminated environments, the oxidation capacity of such materials often fails to function fully. The primary reason is that the strong coordination ability of Cd2+ preferentially occupies all of adsorption sites formed by surface hydroxyl (‒OH) groups generated through oxide hydration, including oxidation sites13–15. Moreover, while highly oxidative components (such as MnO2) rapidly convert AsIII to AsV, they may also cause extensive reduction of Mn4+ to Mn2+, leading to structural collapse and secondary pollution from Mn2+ release. Hence, overcoming the competitive inhibition effects of AsIII and Cd2+, while maintaining a balance between oxidative activity and structural stability, remains a significant challenge16,17. The ideal immobilization material should possess spatiotemporally ordered oxidation-adsorption sites and self-stabilizing properties. Through functional decoupling and spatiotemporal matching, they address multiple pollutants in sequence while maintaining stability under complex conditions, thus directing pollutant transformation pathways for efficient and synergistic AsIII/Cd2+ remediation.

Despite decades of research, nano-composite metal oxides still face significant limitations in heavy metal immobilization, with adsorption capacities typically capped at 200 mgg‒1,18–20. These shortcomings arise from structural deficiencies, including insufficient active sites and their poor accessibility and utilization. To overcome these challenges, a structural redesign must prioritize two critical strategies: (1) introducing defects at the atomic scale can drive water dissociation and generate bulk-phase ‒OH groups. This approach leverages the entire nanoparticle volume, rather than just the 20–30% confined to surface regions, leading to a three to five fold enhancement in adsorption performance; (2) developing channel structures with precisely controlled sizes of 2–3 nm is essential. These dimensions are carefully balanced: they are large enough to minimize diffusion resistance and improve active site accessibility, yet compact enough to facilitate the formation of tightly coordinated inner structures upon heavy metal binding. This dual functionality significantly boosts immobilization efficiency. Among various materials, layered double oxides (LDOs) offer promising structural advantages and have demonstrated exceptional performance in immobilizing single heavy metals, such as As, Pb, and Cd21–24. For instance, MgMn-LDO (Mg:Mn=2:1) has previously been reported to exhibit excellent Cd removal efficiency due to the formation of CdCO3 and Cd(OH)2 25. However, the challenge lies in the synchronous immobilization of AsIII/Cd2+, where competitive inhibition during interfacial adsorption significantly diminishes their effectiveness. Fortunately, LDOs possess a unique property: topological transformation, allowing them to revert to the LDH structure26–30. By harnessing this transformation, it becomes possible to spatially and temporally decouple the oxidation process of AsIII from the adsorption process of Cd2+, effectively mitigating the competitive inhibition effect. This innovative strategy can pave the way for overcoming current limitations and achieving efficient synchronous immobilization of AsIII/Cd2+.

In this work, the framework structure of MgMn-LDO (LDO) is successfully constructed through calcination of MgMn-LDH (LDH) precursor. As a result, the adsorption capacity of LDO for AsIII and Cd2+ can reach 821.7 and 1895.6 mgg−1 in co-contamination, presenting a state-of-the-art result (Supplementary Table 1)31,32. Conventional materials such as iron-manganese oxides and graphene nanotubes exhibit adsorption capacities for AsIII rarely exceeding 100 mgg−1 due to their limited active sites33,34. Unexpectedly, compare the adsorption of AsIII or Cd2+ alone, not only was adsorption capacity improved, but rate also increased by 181 times. Kinetics and mechanistic analysis indicate that the quadruple topological transformation of the adsorbent from MgMn-LDH → MgMn-LDO → MgMn-LDO-H2O (LDO(H)) → MgMn-LDH(AsIII) (LDH(AsIII)) → CdMgMn-LDH(AsIII/Cd2+) (Cd-LDH(AsIII/Cd2+)), triggered sequentially by heat, H2O, AsIII, and Cd2+, is the key factor (Fig. 1a). The distinct AsIII oxidation and Cd2+ adsorption energies successfully reversed the usual sequence in AsIII/Cd2+ co-adsorption, causing AsIII oxidation to precede Cd2+ adsorption (Fig. 1b). Through electron transfer between AsIII and Mn4+, the LDO undergoes a topological transformation into an LDH, enabling AsIII/AsV to be deeply fixed within the LDH interlayers. Meanwhile, the original adsorption pathway for Cd2+ is altered, causing Cd2+ to enter the layer via isomorphous substitution, which induces lattice expansion and significantly enlarges the bulk diffusion channels. This multi-level topological transformation plays a central role by not only safeguarding the high reactivity of the adsorbent during the process but also conferring a stable mineralized encapsulation in the final adsorption structure.

Results
AsIII and Cd2+ shifted from remediation targets to mutual adsorption enhancers
Typically, when metal oxides are used to treat multiple heavy metals (such as Cd2+/Pb2+ and Cu2+/Zn2+), their adsorption efficiency tends to be lower compared to treating a single heavy metal35–38. This is especially true for AsIII/Cd2+ co-contaminants, as the primary adsorption sites on metal oxides are the surface hydroxyl groups (‒OH). The strong coordination ability of Cd2+ with these ‒OH groups often significantly hinder the adsorption of AsIII,39. Unexpectedly, although the solution pH value increased with adding LDO calcined at 350°C (Supplementary Figs. 1‒4), the maximum adsorption capacity for AsIII can reach 821.7 mgg⁻1, which is five times the current highest value (Starch‒FeMnO x, 161.29 mgg⁻1)31; and for Cd2+ reach 1895.6 mgg⁻1, which is three times the current highest value (graphene/δ‒MnO2, 644 mgg⁻1) (Fig. 2a,b, Supplementary Figs. 5‒8, and Supplementary Tables 2‒4)40. More importantly, these values are higher than the adsorption capacities of LDO for treating AsIII (691.6 mgg⁻1) and Cd2+ (1723.1 mgg⁻1) individually (Fig. 2c). This anomaly indicates that AsIII and Cd2+ become triggers for mutually enhancing adsorption performance. In addition, the structure of LDO is stable (Supplementary Figs. 9‒13), and its removal efficiency for AsIII/Cd2+ is independent of pH value, coexisting salts, and metal ions (Supplementary Figs. 14–18).

The adsorption of both AsIII and Cd2+ are chemical, with intraparticle diffusion controlling rate, supported by kinetics and fittings. A series of concentrations were used to fit the adsorption process. Specifically, the initial concentration of AsIII remain unchanged and the initial concentration of Cd2+ is = 50, 100, 200, 300, 500, and 600 mg L‒1. All adsorption process follow pseudo-second-order kinetics, with an excellent fit indicated by an R2 value (>0.99) (Fig. 2d and Supplementary Figs. 19‒23 and Supplementary Table 5). The fit results of Weber‒Morris model have been showed in Fig. 2e and Supplementary Table 6. The kinetic adsorption of AsIII and Cd2+ is divided into three stages, including external diffusion, intraparticle diffusion, and equilibrium stages. Among them, intraparticle diffusion is the main rate-controlling step41. As confirmed by the rate constant of the second stage is significantly lower than that of the first stage and R2 2 > R2 1.

The deep-remove of AsIII/Cd2+ co-contaminates remains an unresolved challenge in practical applications42,43. LDO demonstrates deep-remove capabilities in AsIII/Cd2+ co-contaminated systems. As evidenced in Fig. 2f, when the initial concentrations of AsIII/Cd2+ are 0.1/0.1 and 1.5/1.5 mg L‒1, 0.5 g L‒1 of the adsorbent LDO achieves low residual concentrations of AsIII/Cd2+ (AsIII ≤ 4 μg L‒1; Cd2+ ≤ 2 μg L‒1), which meet WHO drinking water standards44,45. Especially, even when the initial concentrations of AsIII/Cd2+ rise to 12.0 mg L‒1, 1.0 g L‒1 of the adsorbent still achieves low residual concentrations with AsIII = 5 μg L‒1 and Cd2+ = 1.8 μg L‒1, which is currently unattainable by other materials.

Owing to the convenient and economical synthesis method (Supplementary Table 7), the LDO can be scaled up for kilogram-scale production (Supplementary Figs. 24 and 25), verifying the high feasibility for practical applications in remediation of wastewater and contaminated soil. Firstly, when LDO was used to treat the mining water from Yiyang in Hunan province (detail information see Supplementary Table 8), the total concentration of As and Cd2+ decreased from 0.257 and 1.153 mg L‒1 to 0.012 and 0.008 mg L‒1, respectively (Fig. 2g), meeting the advisory level of Standard for irrigation water quality of China (GB5084-2021, As ≤ 0.05 mg L‒1, Cd ≤ 0.01 mg L‒1). Additionally, LDO has demonstrated excellent adsorption capacity for AsIII/Cd2+ in domestic wastewater environments (Supplementary Figs. 26‒28). Secondly, when LDO was added the highly contaminated industrial soils located at Changde City, Hunan Province, the concentration of As and Cd in solution leached decreases 89.9% and 91.5%, respectively after remediation (Fig. 2h). Based on the dose-effect relationship, an optimal LDO dosage of 2–3% was identified, offering the best balance between treatment efficacy and LDO consumption (Supplementary Table 9 and detailed discussion). Moreover, the remediation efficiency for heavily contaminated soils remained high across various parameters, including different contamination levels, pH values, and soil types, with removal efficiencies consistently exceeding 87% (Supplementary Tables 10‒12 and detailed discussion). When the dose-effect relationship is not considered, the removal rates of As and Cd still exceeded 85% with a 10% LDO addition for treating high contaminated industrial soils with initial As and Cd concentrations of 700–3100 mg kg−1 (Supplementary Table 13 and detailed discussion). These findings demonstrate the substantial practical potential of in-situ immobilization technique using LDO for the remediation of environments contaminated with heavy metals.

Bulk hydroxylation topology (Topology I and II)
In the treatment of AsIII/Cd2+ using metal oxides, whether at oxidation sites or adsorption sites, the initial chemical reaction involves ligand exchange between AsIII/Cd2+ and the ‒OH groups on the surface of the adsorbent46,47. Thus, the variation in the ‒OH groups of LDO was monitored by X-ray photoelectron spectroscopy (XPS, Fig. 3a). The O 1s spectra of the LDO(H) demonstrates that the O OH content reach 71.8%, far exceeding that of LDH (50.4%) and LDO (36.8%). Meanwhile, the content of lattice oxygen (O L) in LDO(H) significantly reduced to 4.8% compared with that of conventional LDH (18.7%) and LDO (47.6%)48. The reason lies in the formation of metal defects and oxygen defects during the transformation of LDH to LDO triggered by heat (Topology I)49–51. Firstly, metal defects sites promote hydroxylation. The presence of Mg2+ defects can be confirmed by extended X-ray absorption fine structure (EXAFS, Supplementary Figs. 29 and 30 and Fig. 3b). The peak intensity of Mn‒M bonds at 2.73 Å for LDO is weaker than that of LDH, revealing an increased unsaturated metal site. Secondly, the oxygen defects (oxygen vacancy and clusters) can also effectively promote the hydroxylation. The electron paramagnetic resonance (EPR) of LDO shows a stronger signal located at g = 2.003 than that in LDH, demonstrating the presence of much more oxygen vacancies (Fig. 3c)52. In addition, microscopic changes show oxygen vacancies/clusters (Fig. 3d–f and Supplementary Figs. 31–33). LDH has irregular hexagonal nanosheets (40‒80 nm radial, ~20 nm thick). Calcination preserved morphology; hydrolysis distorted LDO(H) into thinner flakes. LDO’s 0.15 nm smaller lattice spacing (vs. LDH) indicates topological rearrangement, exposing defects to affect hydrolysis53. Diffraction ring confirms retained LDH polycrystal structure. These observations indicate high-density oxygen vacancies and vacancy clusters induce localized charge redistribution, enhancing electrostatic interactions with polar water54. In addition, the hydroxylation can be finished in 1 min as confirmed by XRD, where a series of characteristic peaks appeared at 2θ = 18.5, 37.8, 50.8, 58.7, and 62.1° (Fig. 3g). These peaks do not belong to Mg(OH)2 or MnOOH, thus, confirming the formation of LDO(H). The hydroxylation rate of LDO is faster than that of Nano-MgO and commercial MgO (Supplementary Figs. 34 and 35). Moreover, LDH layers uniformly disperse Mg, Mn (Supplementary Fig. 36). Post-calcination, no separate MnOₓ phases beyond vanished peaks, indicating atomic-dispersed Mg2+ and Mn3+/Mn4+ in oxide matrix, supporting oxidation/adsorption site partitioning.

The spontaneous hydroxylation of LDO is also confirmed by density functional theory (DFT) calculations. All the binding energies between metal sites (Mg and Mn) in LDO and H2O or OH− are negative (Mg−OH−: −2.86 eV, Mg−H2O: −1.58 eV, Mn−OH−: −3.32 eV, Mn−H2O: −0.60 eV) (Fig. 3h and Supplementary Figs. 37 and 38). Moreover, metal sites (Mg, Mn) favor OH⁻ over H2O (more negative binding energies), aiding H2O dissociation and LDO hydroxylation. Mn binds OH⁻ stronger than Mg, making it optimal for H2O dissociation. After that, the Gibbs free energy (ΔG) for the hydroxylation of LDO (with a chemical formula of Mg12Mn3O22H8) to LDO(H) (with a chemical formula of Mg12Mn3O30H24) is calculated to be −43.41 eV, which is far lower than that of MgO (with a chemical formula of Mg8O8) to Mg(OH)2 (with a chemical formula of Mg8(OH)16) (−16.10 eV) (Fig. 3i, j and Supplementary Fig. 39). These results reveal that LDO hydroxylates more strongly than MgO. MgO only surface-hydroxylates while LDO fully does so via rich sites/defects. Its 2D structure enables spontaneous bulk hydroxylation via H2O–induced interlayer hydrolysis, activating sites globally. This is key for high adsorption.

Prior oxidation of AsIII triggers Topology III transformation
This process converts LDO back to LDH, thereby altering the adsorption pathway of Cd2+. To explore the sequence of AsIII oxidation and Cd2+ adsorption, the following experiments were conducted. The same mass of LDO was used to treat equal masses of AsIII and Cd2+, but the order of addition of AsIII and Cd2+ was different in condition 1–3 (See Supplementary Information for details). Adsorption solids at 1 and 2 h (Fig. 4a–c): Condition 1 showed only Cd(OH)2 peaks at 2θ = 18.8, 29.7, 35.5, 38.1, 49.3, 56.2, 59.1° (Supplementary Fig. 40). Condition 2 showed LDH peaks 2θ = 11.3, 22.3, 34.7, 38.2, 59.3, 60.1°: AsIII restores LDO to LDH (Supplementary Figs. 41 and 42), with Cd2+ incorporating into LDH lattice without altering its layered structure. Condition 3 solids matched 2, meaning simultaneous AsIII/Cd2+ generates stable LDH. Cd2+ did not affect AsIII adsorption (Supplementary Figs. 43 and 44). Results confirm co-adsorption: AsIII oxidation precedes Cd2+ adsorption, triggering LDO-to-LDH transformation. This topological shift alters Cd2+ adsorption from surface ligand exchange to LDH lattice substitution, as confirmed by time-resolved transmission electron microscopy (TEM) mapping (Fig. 4d, e) and ICP (Supplementary Fig. 45). Mg2+ in Cd-LDH(AsIII/Cd2+) decreased from 23.29% to 8.97%, whereas Cd2+ increased from 15.71% to 31.04%, indicating Cd2+ replaces the Mg2+ via isomorphous substitution with Mg2+ leaching. This is supported by Mg2+ dissolution: Fig. 4f shows Mg2+ increased from 0 to 118 mg L‒1 over 0‒6 h, and from 14 to 34 mg L‒1 as Cd2+ initial concentration rose 10‒200 mg L‒1. Mn leaching was negligible (near zero). As locates in LDH interlayers, shown by increased interlayer spacing with higher adsorption capacity. Fig. 4g shows Cd-LDH(AsIII/Cd2+) interlayer spacing increased from 0.74 to 0.78 nm as time extended 0‒12 h, with adsorption capacity rising from 0 to 99.7 mgg‒1 (Supplementary Fig. 46); simultaneously, spacing increased from 0.73 to 0.77 nm as AsIII concentration rose 10‒500 mg L‒1, with capacity up to 389 mgg‒1 (Supplementary Figs. 47 and 48).

The spatiotemporal order of the oxidation of AsIII and the isomorphous substitution of Cd2+ is further verified through the thermodynamics energy diagrams obtained by DFT calculations. As shown in Fig. 4h, after oxidation of AsIII on LDH(AsIII), the ΔGs for the isomorphous substitution of each Mg2+ cation by each Cd2+ cation are all smaller than 0 eV, indicating this process is spontaneous. In contrast, the ΔGs of isomorphous substituting Mg2+ in LDO(H) by Cd2+ is larger than 0 eV, demonstrating is thermodynamically unfavorable (Fig. 4i). Above all, we prove that the oxidative adsorption of AsIII occurs before the isomorphous substitution of Cd2+.

The electron transfer from AsIII to Mn4+ during adsorption, forming AsV and Mn3+, as confirmed by XPS and XANES. For As, post-adsorption Cd-LDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9 eV (AsV, Fig. 5a); LDO raised AsV to 53.8% (vs. LDH’s 18.0%), showing stronger oxidation55, which also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR, and in-situ Raman (Supplementary Figs. 49‒51). For Mn, XPS shows Mn 2p peaks at 643.1 and 653.8 eV (Mn3+) (Fig. 5b); its proportion in Cd-LDH(AsIII/Cd2+) (84.0%) exceeds LDO’s 35.9%, confirming Mn4+ reduction with AsIII oxidation, as confirmed by XANES. Cd-LDH(AsIII/Cd2+) has a 1.02 eV lower Mn K-edge (lower oxidation state) and an As K-edge 11874 eV peak (AsV, Supplementary Figs. 52 and 53), verifying electron transfer56. To clarify Mn4+/AsIII redox roles in structural reconstruction, we conducted controlled experiments (Fig. 5c): (1) With only AsV/Cd2+, LDO showed no significant topological change, where XRD revealed no LDH peaks, matching LDO. (2) With Na2CO3 alone, LDO formed composite hydroxides (Mg(OH)2·MnOOH) with peaks at 18.5°‒62.1° (no layered order). (3) With electron-donating ascorbic acid, LDO formed LDH (peaks at 11.0°‒59.3°), same as AsIII/Cd2+ co-adsorption: its vicinal diols transfer electrons, reducing Mn4+ to Mn3+ and restoring LDH57. O 1s XPS confirmed LDO → Cd-LDH(AsIII/Cd2+) transformation (M‒OH: 54.2%, OL: 23.4% in product vs. 50.4%/18.7% in LDH; Supplementary Fig. 54). The aforementioned comparative experiments fully demonstrate that AsIII undergoes oxidation by Mn4+ centers and occur electron transfer. The reduction of Mn4+ triggers LDO → Cd-LDH(AsIII/Cd2+) topological transformation via electron transfer.

The topological transformation from LDO to Cd-LDH(AsIII/Cd2+) is accompanied by the intercalation of AsIII and/or AsV and multi-site coordination, which is key to enhancing the removal capacity of AsIII. The adsorption capacities of 821.7 mgg‒1 for AsIII/Cd2+ and 240.0 mgg‒1 for AsV/Cd2+, respectively (Supplementary Fig. 55). Note that AsV/Cd2+ solution need Cd2+ concentration adjustment due to poor solubility. EXAFS probed As coordination: Cd-LDH(AsIII/Cd2+) had As−O (1.23 Å, first shell) and As−M (2.80 Å, second shell) bonds (Fig. 5d). Its As–O coordination number (4.2) and distance (1.68 Å) matched Na2HAsO4 (4.0, 1.68 Å) (Supplementary Table 14), indicating binuclear AsO4 tetrahedrais thermodynamically favored. These tetrahedra bridge MO6 octahedra via corner/edge-sharing, boosting stability and electron transfer between AsIII and Mn4+58,59. This allows As incorporation into layers (not just surface), increasing sorption capacity post-transformation. Though AsV forms similar coordination, it doesn’t transfer LDO to LDH, causing lower adsorption. The coordination of Mn showed Mn‒O (1.47 Å) and Mn‒M (2.64 Å) peaks; Cd-LDH(AsIII/Cd2+) had shorter Mn‒O (1.91 Å vs. 1.92 Å in LDH) and Mn–M (2.91/3.20 Å vs. 3.23 Å in LDH), confirming strong As−Mn interaction (Fig. 5e and Supplementary Table 15). Due to the inherently low affinity between As and MnO2 in binary oxides compared to magnesium oxides, a higher proportion of Mn in the LDO leads to a reduction in adsorption efficiency, as confirmed by that the adsorption capacity decreases with increasing Mn content from Mg:Mn=5:1, 4:1, 3:1, 2:1 (Supplementary Figs. 56–58). Therefore, to balance sufficient oxidation sites (Mn‒OH) and maximize adsorption sites (Mg‒OH), the optimal Mg:Mn=5:1 in the LDO was chosen. DFT calculations characterized adsorption-oxidation processes and active sites. As shown in Fig. 5f, AsIII binding energy on Mn sites in LDO(H) (−1.48 eV) was far more negative than on Mg sites (−0.36 eV), meaning AsIII preferentially adsorbs on Mn sites to drive Mn4+/AsIII redox (forming Mn3+/AsV), converting LDO(H) to LDH(AsIII). With Cd2+, AsIII binding energies on Mn (−1.87 eV) and Mg (−1.60 eV) sites strengthened, boosting AsIII adsorption. AsV binding energies on Mg/Mn/Cd sites were more negative than that of AsIII, confirming stable Cd-LDH(AsIII/Cd2+). However, no electron transfer occurs between Mn4+ and AsV, blocking LDH-forming topological transformation and limiting to low-capacity surface adsorption. Figure 5g shows calculated M‒O bond energies: AsIII (AsO2−) oxidation to AsV (AsO43−) requires O transfer from LDO, necessitating M‒O cleavage. Mn‒O (2.49 eV) is weaker than Mg‒O (2.63 eV), so Mn sites favor O transfer and oxidation60,61. With Cd2+ (partly substituting Mg2+), LDO(H) lattice parameters increase, lowering Mg‒O (2.50 eV) and Mn‒O (2.10 eV) energies. This weakens Mn‒O bonds, aiding AsIII oxidative adsorption. The oxidation of AsIII happens with a chemical formula of AsO2−+2Mn4+→AsO43−+2Mn3+, indicating that the oxidation of one AsIII requires the collaboration of two Mn4+. However, the Mn4+ may not be adjacent to another Mn4+ in one LDO(H) layer since Mn is uniformly dispersed in LDO(H) layer. Therefore, the oxidation of AsIII is likely to occur between two LDO(H) layers and thus facilitating the topological transformation of LDO(H) to LDH. Then the generated AsV binds tightly with two reduced Mn3+, forming a stable structure (Supplementary Fig. 59). Therefore, the subsequent diffusion pathways of AsIII can be divided into two types: (1) directly through the AsV-occupied site (path I) and (2) bypassing this site (path II, Fig. 5h). The diffusion energy barriers of AsIII for paths I and II are calculated by DFT to be 0.60 and 0.41 eV, respectively, as displayed in Fig. 5i. The optimized geometries of the diffusion intermediates are displayed in Supplementary Fig. 60. Therefore, bypassing AsV-occupied site is the favorable pathway for AsIII diffusion.

The presence of Cd2+ triggers Topology IV transformation
The presence of Cd2+ significantly enhances the adsorption rate of LDO for AsIII (Fig. 6a). When LDO is used alone for AsIII adsorption (C0 = 100 mg L–1), it takes 7 h to reach adsorption equilibrium. However, when the introduction of Cd2+ (200 mg L‒1), the adsorption of AsIII by LDO reaches equilibrium in just 10 min. The adsorption rate constant (k) increases from 0.0183 to 3.3200 gh‒1 mg‒1 (Supplementary Figs. 61 and 62 and Supplementary Table 16), representing an approximately 181-fold enhancement. This phenomenon can be attributed to increased oxidation rate and diffusion rate. Cd2+ substitution for Mg2+ changes the local tensile strain within the layers, promoting electron transfer of AsIII‒Mn4+ and AsIII oxidation. The variation in tensile strain can be observed in Raman spectroscopy, where the Mn4+‒O peak progressively shifts to lower wavenumbers from 626.8 to 606.7 cm‒1 as increasing Cd2+ (Fig. 6b), indicating a longer Mn‒O bond is easier to break. The same conclusion can also be drawn from EXAFS, where Mn‒M of Cd-LDH(AsIII/Cd2+) located at 2.64 Å is longer than that of LDH(AsIII) (2.61 Å) in Fig. 6c. The correlation between localized tensile strain and electron transfer was systematically investigated through DFT calculations. Firstly, the Mulliken charge analysis shows that the partial charges of Mn and O are 1.82 e and ‒1.00 e in Mg‒O‒Mn (Fig. 6d), the more electrons are transferred from Mn to O due to the local tensile strain in the structure by Cd substitution, resulting in a charge of Mn and O are 1.86 e and ‒1.02 e, respectively, which demonstrates that Cd substitution promotes the electron transfer of Mn. This charge redistribution is further corroborated by the electron density isosurface calculations (Fig. 6e), which demonstrate that the Mg–Cd distance elongation (3.54 Å vs. Mg–Mg: 3.21 Å) promotes electron delocalization under tensile strain. The integrated crystal orbital Hamilton population (ICOHP) analysis provides additional insight (Fig. 6f)62, showing a reduction in the covalent character of the Mn–O bond (ICOHP: −1.33 to −1.11), which indicates an increased ability of Mn to accept electrons. Together, these results establish a coherent mechanism: Cd2+ induced strain promotes charge delocalization, destabilizes the Mn–O bond, and ultimately facilitates electron transfer from AsIII to transfer to Mn, thereby enhancing the oxidation of AsIII.

The isomorphous substitution of Cd2+ in LDH layers resembles natural mineral isostructural substitution63. Specifically, larger radius induces structural relaxation, lattice expansion, and interlayer spacing variation, as confirmed by XRD patterns (Fig. 7a)64. In 100 mg L–1 AsIII solution, as Cd2+:Mg2+ rises from 1:28 to 1:7, (003) peak of Cd-LDH(AsIII/Cd2+) shifts from 11.6° to 11.2°; HRTEM shows lattice expansion (from 0.21 to 0.27 nm, Fig. 7b) and time-dependent growth (from 0.205 to 0.211 nm, Supplementary Fig. 63)65. Increased spacing reduces AsIII diffusion resistance, boosting its rate. Cd2+ replacing Mg2+ expands Cd‒As‒Mn lattice, modulating AsIII migration via two mechanisms: (i) AsIII distal to Cd2+ has lower activation energy (enhanced diffusion) from relaxed strain; (ii) First-shell AsIII near Cd2+ faces narrowed channels (higher barriers) via charge redistribution (Fig. 7c). Thus, low Cd2+ substitution favors expansion; high levels favor channel narrowing66. To verify this mechanism, the diffusion energy barriers of AsIII in Cd-LDH(AsIII/Cd2+) with Cd2+/Mg2+ molar ratio of approximately 1:28, 1:14, and 1:7 following path I (away from Cd2+) and path II (close to Cd2+) are calculated and displayed in Fig. 7d. The optimized geometries of diffusion intermediates are shown in Supplementary Fig. 64. For Cd2+/Mg2+ = 1:28, the diffusion energy barriers are calculated to be 0.27 eV in path I and 0.42 eV in path II. The diffusion of AsIII along the path away from Cd2+ is significantly easier than that close to Cd2+. With the increasing amount of Cd2+, the diffusion energy barriers of AsIII along path I decreases progressively, reaching 0.24 eV for Cd2+/Mg2+ = 1:14 and 0.20 eV for a ratio of 1:7. On the other hand, the diffusion energy barriers of AsIII along path II is further increased to 0.45 eV for Cd2+/Mg2+ = 1:14 and 0.46 eV for a ratio of 1:7. Therefore, DFT calculations verify that Cd2+ substitution benefits AsIII diffusion by local expansion effect.

Methods
Chemicals
Mg(NO3)2·6H2O, Mn(NO3)2·4H2O, NaOH, Cd(NO3)2·4H2O, H2O2 were purchased from Beijing Innochem Chemical Reagent Company (Beijing, China). Experimental AsⅢ and AsⅤ solution were prepared by dissolving NaAsO2 and Na2HAsO4·7H2O in deionized. As standard stock solutions in HNO3 (National Institute of Metrology, China) were used for preparation and calibration standards. In this work, all reagents were used as received without further purification. All solutions were prepared with deionized water.

Synthesis of MgMn-LDH
MgMn-LDH was synthesized via a traditional co-precipitation method. The Mg(NO3)2·6H2O (1.0 mol) and Mn(NO3)2·4H2O (0.2 mol) were firstly dissolved in 100 mL deionized water. Meanwhile, NaOH (1.92 mol) and H2O2 (1 mL) were also dissolved in another 100 mL deionized water. Then, the two solutions were poured into the colloid mill at the same flow rates with rotating of 210×g at room temperature. The slurry was aged at 60°C for 4 h. The products were washed with deionized and ethanol for three times, respectively, and dried at 60°C drying for 12 h to obtain LDH (Mg:Mn=5:1). Similarly, LDH samples with different ratios (Mg:Mn=2:1, 3:1, 4:1) were synthesized by the same method, except different feeding ratio of Mg/Mn.

Synthesis of MgMn-LDO
MgMn-LDO was obtained by calcined the MgMn-LDH at different temperatures (200, 250, 350, 450, 550, and 650°C) for 3 h in air, with a heating rate of 5°C·min‒1.

Adsorption experiments of AsIII/V/Cd2+
All adsorption experiments were conducted at room temperature using a batch sorption method. A certain amount of NaAsO2, Na2HAsO4·7H2O, and Cd(NO3)2·4H2O were dissolved in deionized water to obtain corresponding AsIII, AsV, and Cd2+ solution. Then the LDO were added to the heavy metal ions solution and stirred until the adsorption equilibrium was reached. The supernatant was separated with a 0.22 μm membrane filter. The concentrations of heavy metals in solution were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). All experiments were carried out in duplicate, and the average data were used for analysis. The heavy metals adsorption capacity and removal rate were calculated by the following equations:

Q = (C0 ‒ Ce)×V / m (1)

R = (C0 ‒ Ce) / C0 × 100% (2)

where C0 (mg L−1) and Ce (mg L−1) are the initial and final concentrations of AsIII/V and Cd2+, respectively, V (L) is the volume of aqueous solution, m (g) is the adsorbent mass, and Q (mg g−1) is the adsorption amount for AsIII/V and Cd2+, R is the removal rate of AsIII/V and Cd2+.

AsIII oxidation and Cd2+ adsorption sequential experimental details
To investigate the sequence of AsIII oxidation and Cd2+ adsorption during their co-adsorption process, batch experiments were conducted with initial concentrations of 100 mg L−1 AsIII and 200 mg L⁻¹ Cd2+ in 100 mL solution with 0.10×g LDO adsorbent. Three independent experiments (AsIII-only, Cd2+-only, and AsIII/Cd2+ co-contamination) were started simultaneously. After 1 h adsorption with continuous mixing, suspensions were centrifuged (2100×g, 3 min) for solid-liquid separation. Parallel experiments involved sequential addition: the complementary heavy metal was introduced to respective monometallic systems after initial 1 h adsorption, followed by 1 h reaction prior to centrifugation. All obtained solids were characterized by XRD analysis.

In manuscript, condition 1: Cd2+ was added first at 0 min, followed by AsIII 1 h later; condition 2: AsIII was added first at 0 min, followed by Cd2+ 1 h later; condition 3: AsIII and Cd2+ were added simultaneously at 0 min.

The practical remediation details of contaminated soil
The experimental field was subdivided into three plots, each 3×3 m size. Remediation agents were surface-applied at a dosage of 0.67 kg per plot (750 kg per hectare) and subsequently tilled to a depth of 20 cm to ensure thorough integration with the soil. Soil sampling was conducted at 0, 15, 30, 60, and 120 days to assess the stabilization efficiency of As and Cd. Sampling procedures strictly followed China’s Technical Specification for Soil Environmental Monitoring (HJ/T 166-2004). Specifically, five subsites (0–20 cm depth) were arranged in a plum blossom pattern within each plot; samples from these points were homogenized, and a 1 kg composite sample was retained for analysis. Following removal of plant debris and gravel, soils were nature-dry and sieved through a 40‒mesh screen. As concentrations were determined by atomic fluorescence spectrometry, while Cd levels were quantified using graphite furnace atomic absorption spectrometry.

The practical remediation details of contaminated wastewater
First, insoluble solids were removed from nature wastewater through 0.45 μm membrane filtration prior to adsorption experiments. Then, 0.5×g of LDO was added into 500 mL of actual wastewater containing heavy metal ions. The adsorption time was 2 h under stirring, the supernatant was separated with a 0.22 μm membrane filter. The concentrations of heavy metals in actual wastewater were determined by ICP-MS.

The regenerative experiment details of MgMn-LDO
The regeneration performance of the MgMn-LDO was systematically evaluated via 10 consecutive laboratory cycling experiments. The experimental setup fixed the initial concentrations of As and Cd at 10 and 20 mg L‒1, respectively, while 50 mg L‒1 Na2CO3 solution was selected as the regeneration agent. The 1 g L‒1 as the dosage standard to proceed regeneration test. The adsorption time was 2 h under stirring, the supernatant was separated with a 0.22 μm membrane filter. The concentrations of heavy metals in actual wastewater were determined by ICP-MS.

Characterization of materials
The crystal structure of resulting sample was analyzed by a powder X-ray diffraction device (JDX-3530, Tokyo, Japan) using Cu Kα radiation (λ=1.5418 Å) with a 2θ value ranging from 5° to 70° with a scanning speed of 10° min‒1. The surface binding states and elemental speciation of the samples before and after AsIII/Cd2+ sorption was analyzed by XPS on a spectrometer (Thermo Scientific ESCALAB 250) with a focused monochromatic Al Ka X-ray source, in which all of the binding energies were calibrated with reference to the C 1s peak (284.8 eV). The data analysis was conducted using XPS peak software (version 2.3.12.8). The morphologies and microstructures of the samples were observed using field-emission scanning electron microscopy (Merlin VP Compact, 15 kV), and TEM (JEOL-2010, 200 kV, equipped with an EDX spectrometer). The concentrations of AsIII and Cd2+ in the solutions were measured by ICP-OES (PerkinElmer 8300) and ICP-MS (PerkinElmer NexION 300X). EPR spectra were recorded on a JEOL JES-FA200 EPR spectrometer to detect the presence of oxygen vacancies. The XAFS data were processed according to the standard procedures using the Athena module implemented in the IFEFFIT software packages. The EXAFS spectra were obtained by subtracting the post-edge background from the overall absorption and then normalizing with respect to the edge-jump step. Subsequently, the χ(k) data of were Fourier transformed to real (R) space using a Hanning windows (dk=1.0 Å−1) to separate the EXAFS contributions from different coordination shells. To obtain the quantitative structural parameters around central atoms, least-squares curve parameter fitting was performed using the ARTEMIS module of IFEFFIT software packages.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Some related issues should be addressed before acceptance for pubication.\n1) In Figure b, how to confirm the presentation for the four-level topological transformation.\n2) Mg can dissolute from the layered framework. Why can Mn not be leached from the layered framework?\n3) The isomorphous substitution of Mg2+ in LDO(H) by Cd2+ is thermodynamically unfavorable. Why can Mg be replaced by\nCd?\n4) How to calculate interlayering spacing layered framework?\n5) The comparative experiments fully demonstrate that AsIII undergoes oxidation by Mn4+ centers and occurs electron\ntransfer. The reduction of Mn4+ triggers LDO→Cd-LDH(AsIII/Cd2+) topological transformation via proton insertion. What role\ndo the Cd(II) adsorption play for As(III) redox and mineralization?\n6) As species was presence in the formation of binuclear AsO4 tetrahedron? How many is the valence state of As?\n7) How to confirm As(III) was oxidized in to As(V) and Mn4+ was reduced Mn3+? XPS is not entirely accurate for valence\nstate analysis. There should be relevant experiments and characterizations.", "reviewer_2": "General comment:\nLayered double hydroxides (LDHs) have been recognized to have great potential for the treatment of heavy metals in\nwastewater and soil through various mechanisms. Up to now, many research on the adsorption performance and\nremediation effect of As/Cd contaminated water and soil using various LDH such as CaAl-LDH, .FeMnCa-LDHs, .FeMnCa-\nLDHs, Fe3O4@Mg/Al/Fe-LDH etc. has been carried out widely. Some published literature has shown that the adsorption\ncapacity of LDH/LDO reached 612.0 mg/g for AsIII and 625.0 mg/g for Cd2+. If some of these materials are used to\nremediate the AsIII and Cd2+ coexisting polluted water and soil, the performance can be expected since the adsorption\ncapacity perhaps be enhanced obviously according to previous research.\nIn this article, the MgMn-LDO prepared by the authors has excellent adsorption properties for both Cd and As, and the\nfeasibility of the application of MgMn-LDO in the composite contamination of Cd2+ and AsIII has been comprehensively\ninvestigated in terms of material research and development, performance exploration, mechanism revelation, and production\nand application. The adsorption mechanism and adsorption pathway of LDO on Cd2+ and AsIII were revealed. Overall, the\nmanuscript is good in language organization, results statement and mechanism analysis. The authors, however, suggest\nthat the novelty of the study is not enough, and the experimental design is not so clear, and the key contents are not\nsufficiently discussed. Moreover, the remediation performance and function of materials are often affected by many factors\nrelated to physical, chemical and biological activities as well as material aging process itself. The human health risk of\nMgMn-LDO entering into crops through food chain should also be considered when it is applied into farmland.\nIntroduction\nThe authors have explored the structure and characteristics of MgMn-LDO in detail in their previous studies\n(https://doi.org/10.1016/j.jenvman.2019.06.002), and have clarified its performance and mechanism for remediation of Cd2+\npollution. In this study, the authors only changed the target pollutant (AsIII/Cd2+) and deeply analyzed its mechanism and\npathway in the synergistic remediation of AsIII and Cd2+. Therefore, it seems that the authors did not develop the innovative\nnew material and the innovation of this article needs to be developed.\nAnalysis and Discussion:\n1. The authors made LDOs calcined at different temperatures, but the authors did not provide the calcination temperature of\nwhich LDOs were applied in the subsequent experiments.\n2. Pilot experiment is the key to judge the performance of the material, while the authors mentioned the remediation of As\nand Cd pollution in actual water bodies and actual soil, and did not account for the amount of material, remediation time and\nother key information, and did not give the detailed test methods and steps in the materials and methods. We are eager to\nknow more about the impacts in actual water bodies and soils.\n3. What is the right amount of material to apply in real water applications? How is material recycling achieved after use? Is it\nreusable?\n4. For real soil applications, what is the long term stability of the material to immobilize soil As and Cd?\nMaterials and Methods:\nRegarding the setting of pollutant concentrations, although it is necessary to adjust different pollutant concentrations\naccording to the purposes of different experiments to explore different scientific issues, the author's setting of pollutant\nconcentrations throughout the entire experimental process was unclear and chaotic. Meanwhile, the author lacks the\nprovision of key experimental information.\n1. In section 1.5 adsorption kinetics experiments, what is the basis for selecting the initial concentration regarding co-\nadsorption of AsIII/Cd2+? Why was the initial concentration of AsIII only set to remain at 100 mg/L and the initial\nconcentration gradient of Cd2+ increased. Keeping the initial concentration of Cd2+ certain, is there any other conclusion\nwhen increasing the initial concentration of As?\n2. In the kinetic fitting section of section 1.6, the authors mention that the adsorption rate of AsIII/Cd2+ by LDO is extremely\nfast, so the initial concentration of the mixed solution was reduced. It is recommended that the authors add the initial\nconcentration of the reset co-adsorption kinetic test.\n3. In the adsorption of other coexistence systems, the authors generally set the initial concentration of Cd2+ solution to be\ntwice the initial concentration of AsIII solution. However, in section 1.13, the initial concentration of AsIII/Cd2+ mixed\nsolution, the authors set it to be the same or the initial concentration of AsIII solution is greater than the initial concentration of\nCd2+ solution, what is the basis for the selection of the concentration in this experiment?\n4. Why is the initial concentration of co-adsorbed AsV/Cd2+ in section 1.15 not consistent with the co-adsorbed AsIII/Cd2+\nconcentration gradient in the previous section 1.5?\n5. When exploring the effects of pH and salt ions on LDO coadsorption in Sections 1.16 and 1.17, the initial concentrations\nof AsIII/Cd2+ solutions did not remain consistent; what is the reason for the discrepancy? In Section 1.18, information on the\ninitial concentration of AsIII/Cd2+ solutions and the amount of LDO added is not given.\n6. The test in “Supplementary Fig. 2” is not given in the method? What is the initial As/Cd concentration and the amount of\nmaterial applied for this test?", "reviewer_3": "This manuscript provides a strategy for the simultaneous remediation of AsIII/Cd2+ co-contaminated systems under neutral\nconditions from the water matrix by layered double metal oxide (LDO) with the thermal topotactic transformation of LDH,\nachieving 821.7 and 1895.6 mg/g/g maximum adsorption capacities, respectively. This breakthrough addresses the\nlongstanding challenges of low adsorption capacity and sluggish kinetics in coexisting heavy metal systems. It is a\npromising material for the removal of coexisting heavy metals.\nIt is a topic of interest to researchers in the related areas, but there are some\nproblems that must be solved before it is considered for publication. My detailed\ncomments are as follows:\n1. In the Introduction, add a comparison between LDO and existing nanocomposites (e.g., iron-manganese oxides,\ngraphene nanotubes) between the third and fourth sentences. This addition can strengthen the logical coherence of the\nintroduction.\n2. In the AsⅢ and Cd2+ shifted from remediation targets to mutual adsorption enhancers section, it is necessary to increase\nthe pH changes of LDO in water and the quantitative leaching data of LDO under acidic/alkaline conditions at\nSupplementary Figs. 7–11.\n3. In the Prior oxidation of AsⅢ triggers topological transformation from LDO to LDH, changing Cd2+ adsorption pathway\nsection, please prove that the hydrated LDH here contains Cd2+ and how to prove that it is CdMgMn-LDH in the case of\ncondition 2. Also, in order to prove that the LDH after hydration of AsⅢ should be compared with the LDH after hydration of\npristine LDO, and that there is a lattice shift in order to prove the restoration of AsⅢ to the LDH.\n4. In the Prior oxidation of AsⅢ, triggers topological transformation from LDO to LDH, changing Cd2+ adsorption pathway\nsection, the data proved insufficient. Tables or graphs, supplementary data Qe on SI on the last sentence of the first\nparagraph and the fourth sentence of the third paragraph here\n5. In the Prior oxidation of AsⅢ triggers topological transformation from LDO to LDH, changing Cd2+ adsorption pathway\nsection, the textual description in the third paragraph should follow after the XPS isovalent state-related characterisation,\notherwise it would not be possible to account for the electron transfer of AsⅢ and Mn4+.\n6. Prior oxidation of AsⅢ triggers topological transformation from LDO to LDH, changing the Cd2+ adsorption pathway\nsection, which cannot account for proton insertion in the last sentence of the fifth paragraph.\n7. In the Prior oxidation of AsⅢ, the topological transformation from LDO to LDH, changing the Cd2+ adsorption pathway\nsection, is the arsenic species on the surface in the form of AsO4? Please labeled in the corresponding XRD (e.g. Fig. 4b, c\nand 5c) in the seventh sentence of the sixth paragraph.\n8. Prior oxidation of AsⅢ triggers topological transformation from LDO to LDH, changing the Cd2+ adsorption pathway\nsection. In what way is this ratio (Cd2+: Mg2+) obtained in the third sentence of the 12th paragraph?\n9. In Fig. 4d-4e, while TEM-EDS offers qualitative elemental analysis, it is recommended to complement this with\nquantitative techniques such as Inductively Coupled Plasma (ICP) analysis or thermogravimetric analysis to accurately\ndetermine elemental compositions and validate the material's consistency.\n10. Figures should be correctly labeled and clear. For example, ①In Fig. 2e and 7c, substances in the figure notes should be\nclearly labeled; ②In Fig. 3j, 4h and 4i， the meaning of the table is not clear, adding (a)\\Ⅰ\\① and other serial number\nexpression; ③In Fig. 4a-4c, the * and # characteristic peaks need to be clearly labeled in the graphs; ④In Fig. 5a， labelling\nerrors and correcting the corresponding illustrations.\n11. This is not sufficiently supported; please add the appropriate references. For example, ①on the fifth sentence of the first\nparagraph in the Bulk hydroxylation topology: water molecule-induced interlayer hydrolysis enables global activation of\nactive sites (non-surface dependent) section; ②on the fourth and fifth sentence of the eighth paragraph in the Prior\noxidation of AsⅢ triggers topological transformation from LDO to LDH, changing Cd2+ adsorption pathway section.\n12. The description needs to be modified. For example, ①in the Introduction, the formats of references and citation styles\nshould be unified; ②In the Prior oxidation of AsIII triggers topological transformation from LDO to LDH, changing Cd2+ adsorption\npathway section, the Fig. 4i should be indicated in the third sentence of the second paragraph.\nThe Submission is to be utter improved to make it worthy of publication.", "reviewer_4": "This study presents a MgMn-layered double oxide (LDO) achieving\nexceptional adsorption capacities for As(III) and Cd2+ in mixed systems. The\nremarkable performance stems from a four-step topological transformation that\neffectively decouples As-oxidation from Cd-uptake processes. While the research\noffers timely and potentially significant contributions to water and soil\nremediation technologies, several issues require attention before publication.\nSpecifically, the manuscript needs improvements in experimental validation\nprotocols, data presentation clarity, and overall structural organization. The\nabsence of page and line numbering in the manuscript made it difficult for me to\nmake more specific comments.\nThe following areas require particular attention from the authors.\nArsenic speciation analysis lacks quantitative solution data. While XPS identifies mixed AsIII/AsV states, HPLC-ICP-MS\nanalysis of both filtrates and solids is needed to properly track AsIII→AsV oxidation kinetics.\nRegeneration and stability testing is insufficient. Data provided only for Cd desorption/regeneration (Supp. Fig. 31) but\nmissing for the more toxic As(III). Testing should extend to at least 10 cycles with comprehensive evaluation of long-term\nstability and potential leaching of all components (Mn, Mg, As, Cd).\nMechanism validation relies solely on post-adsorption analysis. The study requires in-situ characterization during\ntransformation stages using TEM and spectroscopic techniques. No in-situ Raman/FTIR tracking of AsIII oxidation\nintermediates is presented, and TEM evidence of layer expansion during Cd2+ substitution is limited.\nReal-world application testing is inadequate with only one sewage sample tested. The study should include varied real-\nworld samples across different pH levels and competing ions. Testing with organic co-contaminants common in wastewater\nis limited, and As/Cd leaching evaluation under different environmental conditions is missing.\nScalability and economics analysis is missing. The study should address cost-effectiveness and economic feasibility,\nprovide specific details on synthesis costs and energy consumption during calcination, and include comprehensive cost\nanalysis for large-scale production.\nWriting and organization require enhancement. Complex, multi-clause sentences should be simplified, transitions between\nsections improved, and technical terms defined consistently. The conclusion needs strengthening to highlight broader\nimplications, and key methodologies from supplementary materials should be summarized in the main text."}, "author_response": "Responses to Reviewer\nResponses to Reviewer 1\nOverview: Some related issues should be addressed before acceptance for\npublication.\n1. In Figure b, how to confirm the presentation for the four-level topological\ntransformation.\nAuthor Response:\nThank you for your comments. This is a very good question, which has made us\nrealize that the original schematic description was insufficient, leading to reviewers\nbeing unable to understand the meaning of the figure. Therefore, we have added a\nprocess description of the topological transition schematic. In addition, we have also\nmodified and added the structural names during the topological process on the Fig. 1b.\nIt should be noted that these four-levels of topological transformation are exactly the\nkey contents of our research in the main text, so it is impossible to list them one by one\nhere. However, we have summarized the relevant paragraph contents as follows, with\nthe corresponding research paragraphs marked.\n⚫ Thermally driven primary topological transformation (Topology I) from MgMn-\nLDH to MgMn-LDO. This process involves high-density oxygen vacancies (V )\\nO\nand vacancy clusters, inducing local charge redistribution, resulting in a charge\ndensity gradient that enhances electrostatic interactions with polar water molecules.\nPage 5 Line 90\nIn this work, the framework structure of MgMn-LDO (LDO) is successfully\nconstructed through calcination of MgMn-LDH (LDH) precursor.\nPage 11 Line 198\nThe presence of Mg2+ defects can be confirmed by extended X-ray absorption fine\nstructure (EXAFS, Supplementary Fig. 29–30 and Fig. 3b). The peak intensity of Mn‒\nM bonds at 2.73 Å for LDO is weaker than that of LDH, revealing an increased\nunsaturated metal site. The decreased intensity for Mn‒O bond at 1.47 Å confirm the\n1\nexistence of oxygen vacancies50.\nPage 11 Line 196\nThe reason lies in the formation of metal defects and oxygen defects during the\ntransformation of LDH to LDO triggered by heat (Topology I) 48,49.\nPage 11 Line 204\nThe electron paramagnetic resonance (EPR) of LDO shows a stronger signal\nlocated at g = 2.003 than that in LDH, demonstrating the presence of much more oxygen\nvacancies (Fig. 3c) 51.\nPage 12 Line 212\nThese observations indicate high-density oxygen vacancies and vacancy clusters\ninduce localized charge redistribution, enhancing electrostatic interactions with polar\nwater 53.\n⚫ Water molecule-driven secondary topological transformation (Topology II) from\nMgMn-LDO to LDO(H) due to appearance of metal defects and oxygen defects\nduring the Topology I. During this process, spontaneous water-induced interlayer\nhydrolysis occurs, leading to the global activation of sites. This non-surface-\ndependent process provides a crucial prerequisite for achieving high adsorption\ncapacity.\nPage 10 Line 188‒Page 13 Line 236\nBulk hydroxylation topology. This part of the content all belongs to Topology\nII.\nPage 12 Line 226\nMoreover, metal sites (Mg, Mn) favor OH⁻ over H O (more negative binding\n2\nenergies), aiding H O dissociation and LDO hydroxylation. Mn binds OH⁻ stronger\n2\nthan Mg, making it optimal for H O dissociation.\nAfter that, the Gibbs free energy (ΔG) for the hydroxylation of LDO (with a\nchemical formula of Mg Mn O H ) to LDO(H) (with a chemical formula of\n12 3 22 8\nMg Mn O H ) is calculated to be −43.41 eV, which is far lower than that of MgO\n12 3 30 24\n2\n(with a chemical formula of Mg O ) to Mg(OH) (with a chemical formula of\n8 8 2\nMg (OH) ) (−16.10 eV) (Fig. 3i‒3j and Supplementary Fig. 39).\n8 16\nPage 12 Line 232\nThese results reveal that LDO hydroxylates more strongly than MgO. MgO only\nsurface-hydroxylates while LDO fully does so via rich sites/defects. Its 2D structure\nenables spontaneous bulk hydroxylation via H O-induced interlayer hydrolysis,\n2\nactivating sites globally. This is key for high adsorption.\n⚫ Preferential oxidation of heavy metal AsIII drives the tertiary topological\ntransformation (Topology III) from LDO to LDH(AsIII). During this process, the\nstrong binding ability facilitating the redox reaction between Mn4+ and AsIII, and\ndriving the reconstruction of the LDH layered structure.\nPage 14 Line 247‒Page 20 Line 367\nThis part of the content all belongs to Topology III.\nPrior oxidation of AsIII triggers Topology III transformation. This process\nconverts LDO back to LDH, thereby altering the adsorption pathway of Cd2+.\nPage 5 Line 104: “Through electron transfer between AsIII and Mn4+, the LDO\nundergoes a topological transformation into an LDH, enabling AsIII/AsV to be deeply\nfixed within the LDH interlayers.”\nPage 18 Line 317: “The reduction of Mn4+ triggers LDO→Cd-LDH(AsIII/Cd2+) \ntopological transformation via electron transfer.”\nPage 19 Line 341: “DFT calculations characterized adsorption-oxidation\nprocesses and active sites. As shown in Fig. 5f, AsIII binding energy on Mn sites in\nLDO(H) (−1.48 eV) was far more negative than on Mg sites (−0.36 eV), meaning AsIII\npreferentially adsorbs on Mn sites to drive Mn4+/AsIII redox (forming Mn3+/AsV),\nconverting LDO(H) to LDH (AsIII).”\n⚫ Isomorphous substitution of heavy metal Cd2+ promotes the quaternary topological\ntransformation (Topology IV) from LDH(AsIII) to Cd-LDH(AsIII/Cd2+). Cd2+\nsubstitution induces localized tensile strain within the layers, facilitating electron\n3\ntransfer from AsIII to Mn4+ and thereby promoting AsIII oxidation. Concurrently,\nthe local expansion effect accelerates the diffusion of AsIII, enhancing its\nadsorption rate.\nPage 21 Line 378‒Page 25 Line 441\nThe presence of Cd2+ triggers Topology IV transformation. This part of the\ncontent all belongs to Topology IV.\nPage 5 Line 106: “Meanwhile, the original adsorption pathway for Cd2+ is altered,\ncausing Cd2+ to enter the layer via isomorphic substitution, which induces lattice\nexpansion and significantly enlarges the bulk diffusion channels.”\nPage 22 Line 386: “Cd2+ substitution for Mg2+ changes the local tensile strain\nwithin the layers, promoting electron transfer of AsIII-Mn4+ and AsIII oxidation.”\nPage 25 Line 439: “Therefore, DFT calculations verify that Cd2+ substitution\nbenefits AsIII diffusion by local expansion effect.”\nFig. 1 (b) Schematic presentation for the four-level topological transformation.\n2. Mg can dissolute from the layered framework. Why can Mn not be leached from\nthe layered framework?\nAuthor Response:\nThis is an excellent question. It is precisely due to these inherent properties of\nLDH that mutual promotion can be achieved in co-adsorption. We will explain this issue\n4\nfrom two aspects respectively.\n2.1 Mg can dissolute from the layered framework\nAll solid substances in the aqueous phase essentially exist in a state of slight\ndissolution equilibrium, and LDH is no exception (ACS Appl. Mater. Interfaces 2022,\n14, 37823-37832; Chem. Eng. J. 2016, 303, 331-337). Therefore, in reality, the metal\nions (Mg and Mn) in the layers of LDH in the aqueous phase are subject to\na dissociation-crystallization equilibrium. When Cd2+ are introduced into the system,\nthe system will re-select the product formed according to the principle of\nthermodynamic stability (Adv. Funct. Mater. 2022, 32, 2106645; Chem. Eng. J. 2021,\n407, 127178). In our system, CdMgMn-LDH has a significantly lower Gibbs free\nenergy than that of MgMn-LDH (Fig. 1c, Fig. 4h). Consequently, the replacement of\nMg2+ by Cd2+ occurs. Similar phenomena have also been reported in the literature.\nSuch as the mechanism of Cd2+ isomorphously substituting for Ca2+ in LDH laminate to form\nCdAl-LDH, previous studies have demonstrated through similar ionic radii and DFT\ncalculations that CdAl-LDH is thermodynamically more stable. Likewise, the ionic\nradius of Cd2+ (0.95 Å) is relatively close to that of Mg2+ (0.72 Å), which makes it\npossible for Cd2+ to construct lamellae of LDHs by isomorphic substitution of Mg2+.\n(Chem. Eng. J. 2023, 451, 138500; Chemosphere, 2024, 352, 141399)\n2.2 Mn not be leached from the layered framework\nThe reason for the phenomenon that Cd2+ substitutes Mg2+, instead of Mn3+/4+ in\nLDH(AsIII), derives from their opposite free energy changes of these two processes.\nThe substitution of Mg2+ by Cd2+ is thermodynamically favorable with Gibbs free\nenergy changes (ΔGs) < 0 eV (Fig. 4h) while the substitution of Mn3+/4+ by Cd2+ is\nthermodynamically unfavorable with ΔGs > 0 eV. Inspired by this comment of reviewer,\nthe Gibbs free energy diagram of substituting Mn by Cd2+ in LDH(AsIII) has been\ncalculated and displayed below. The reaction formula of step 1 in Fig. A is\nMg Mn O H (AsO )(AsO ) + Cd2+ → Mg Mn CdO H (AsO )(AsO ) + Mn2+.\n24 6 56 48 2 4 24 5 56 48 2 4\nThe chemical formulae of the other five steps are similar. The ΔGs of steps 1, 2, 3, 4,\n5, and 6 are 4.34, 1.53, 4.35, 4.25, 4.80, and 4.17 eV, respectively. All ΔGs of\n5\nsubstituting Mn by Cd are all much larger than 0 eV. Therefore these steps are\nthermodynamically unfavorable and won’t happen. Thus Mn is not leached from\nLDH(AsIII).\nFig. 1 (c) The Gibbs free energy diagram of four-level topological transformation.\nFig. 4 (h) Gibbs free energy diagram for the isomorphous substitution of Mg by Cd in LDH(AsIII)\nwith geometries of representative intermediates displayed (I represent the number of Mg of the\nMgMn-LDH(As) laminates replaced by Cd).\nFig. A Gibbs free energy diagram of substituting Mn by Cd in LDH(AsIII). The optimized\ngeometries of intermediates are also shown. The color code is the same with that in Fig. 1 in original\nmanuscript.\nenergies successfully reversed the usual sequence in AsIII/Cd2+ co-adsorption, causing\nAsIII oxidation to precede Cd2+ adsorption (Fig. 1c).”\nPage 15 Line 275 in manuscript: “As shown in Fig. 4h, after oxidation of AsIII\non LDH (AsIII), the ΔGs for the isomorphous substitution of each Mg2+ cation by each\nCd2+ cation are all smaller than 0 eV, indicating this process is spontaneous.”\n3. The isomorphous substitution of Mg2+ in LDO(H) by Cd2+ is thermodynamically\nunfavorable. Why can Mg be replaced by Cd?\nAuthor Response:\nThank you for your comments. We apologize that the calculations presented in the\nmanuscript did not provide you with a clear understanding of the isomorphous\nsubstitution of Cd2+. Here, the LDO(H) represent LDO after hydration (MgMn-LDO-H O),\n2\nand the LDH(As) represent LDO after AsIII adsorption. Thus, the\nthermodynamics of Mg2+ being substituted by Cd2+ in the two structures are different.\n3.1 The isomorphous substitution of Mg2+ in LDO(H) by Cd2+ is thermodynamically\nunfavorable.\nAs shown in Fig. 4i, when Cd2+ undergoes isomorphous substitution for Mg2+ in\nthe laminate of LDO(H) (a hydroxyl-rich 2D layered structure formed by hydration of\nLDO), the Gibbs free energy change (ΔG) of this process is consistently greater than 0,\ndemonstrating its thermodynamically unfavorable. This is because when Cd2+ contacts\nLDO(H), it rapidly combines with OH⁻ to form thermodynamically more stable\nCd(OH) .\n2\n3.2 The isomorphous substitution of Mg2+ in LDH(As) by Cd2+ is thermodynamically\nfavorable.\nPrior oxidation of AsIII triggers a three-stage topological transformation (LDO →\nLDH(As)). As shown in Fig. 4h, after the oxidative adsorption of AsIII on LDH(As), the\nGibbs free energy change for each Cd2+ undergoing isomorphous substitution of Mg2+\ncations in the layers are consistently negative (<0 eV), demonstrating the spontaneous\nnature of Cd2+ replacing Mg2+ in LDH(As) laminate. This is because stable structure of\nLDH accommodates Cd2+ within octahedral vacancies of the laminate, while interlayer\nanions electrostatically stabilize the laminate and compensate for local distortions\ninduced by isomorphous substitution.\nFig. 4 (h) Gibbs free energy diagram for the isomorphous substitution of Mg by Cd in LDH(AsIII)\nwith geometries of representative intermediates displayed (I represent the number of Mg of the\nMgMn-LDH(As) laminates replaced by Cd). (i) Gibbs free energy diagram for the isomorphous\nsubstitution of Mg by Cd in LDO(H) with geometries of intermediates displayed (I represent the\nnumber of Cd replacing Mg in MgMn-LDO(H)).\nPage 15 Line 275 in manuscript in manuscript: “As shown in Fig. 4h, after oxidation of AsIII\non LDH (AsIII), the ΔGs for the isomorphous substitution of each Mg2+ cation by each\nCd2+ cation are all smaller than 0 eV, indicating this process is spontaneous.”\nPage 15 Line 277 in manuscript in manuscript: “In contrast, the ΔGs of isomorphous\nsubstituting Mg2+ in LDO(H) by Cd2+ is larger than 0 eV, demonstrating is\nthermodynamically unfavorable (Fig. 4i).”\n4. How to calculate interlayering spacing layered framework?\nAuthor Response:\nWe have explained in detail the calculate method in Supplementary Information.\nPage S12 Line 223 in Supplementary Information: In the XRD patterns,\n8\ndiffraction peaks near 10° were selected, and Bragg's law was applied to calculate the\ninterlayer spacing using the following formula:\n𝑛𝜆 = 2𝑑sin𝜃\nHere, n: order of diffraction (positive integer, typically n = 1 for the principal peak); λ:\nwavelength of incident X-rays (commonly λ = 1.5418 Å for Cu Kα radiation); d:\ninterplanar spacing; θ: diffraction angle (Bragg angle, equal to half the angle of the\ndiffraction peak position).\n5. The comparative experiments fully demonstrate that AsIII undergoes oxidation by\nMn4+ centers and occurs electron transfer. The reduction of Mn4+ triggers\nLDO→Cd-LDH(AsIII/Cd2+) topological transformation via proton insertion.\nWhat role do the Cd(II) adsorption play for As(III) redox and mineralization?\nAuthor Response:\nThis is a rather good question and exactly the focus of our attention. We will\nanswer this question in two parts.\n5.1 The Cd2+ adsorption promotes the oxidation of AsIII\nCd2+ adsorption induces isomorphous substitution of Mg2+ in the laminate,\nmodifying local tensile strain and promoting AsIII oxidation. The AsIII→AsV oxidation\nprocess is conclusively demonstrated by the blue shift of the AsIII-O peak in time-\nresolved semi-in situ FTIR spectra (Supplementary Fig. 50), along with the red shift of\nAsIII-O and concurrent blue shift of Mn4+-O peaks in in-situ Raman measurements (Fig.\n6b). DFT calculated analyses further validate this mechanism: Mulliken charge analysis\nconfirms enhanced electron transfer from Mn to O upon Cd substitution (Fig. 6d),\nelectron density isosurface calculations reveal strain-induced electron delocalization\n(Fig. 6e), and ICOHP analysis identifies destabilization of the Mn‒O bond (Fig. 6f).\nCollectively, these results establish that Cd2+-induced tensile strain promotes charge\ndelocalization and weakens the Mn‒O bond, ultimately driving electron transfer from\nAsIII to Mn and thereby accelerating AsIII oxidation.\n5.2 The Cd2+ adsorption accelerates the mineralization rate, which is conducive to the\n9\nformation of ultra-stable mineralized structures\nFirstly, in terms of mineralization rate, the introduction of Cd2+ remarkably\nenhances the AsIII mineralization rate by 181‒fold in MgMn-LDO. This enhancement\nis attributed to lattice expansion and interlayer spacing increase by the larger ionic\nradius of Cd2+, as confirmed by the low-angle shift of the (003) XRD peak (Fig. 7a).\nMeanwhile, DFT calculations with varying Cd2+ ratios demonstrate progressively\nreduced diffusion energy barriers for AsIII (Fig. 7d). These analyses indicating that\nisomorphous substitution of Cd2+ enhance AsIII diffusion through localized lattice\nexpansion effects, and accelerates the mineralization rate of AsIII.\nSecondly, in terms of ultra-stable mineralized structures, all solid materials in\naqueous systems inherently establish micro-dissolution equilibria, and LDHs are no\nexception. Consequently, Mg2+ and Mn3+/4+ ions within LDH layers maintain\ndissociation-recrystallization equilibria in aqueous environments. Upon introduction of\nCd2+, the system preferentially forms thermodynamically stabilized phases. In our\nsystem, the Gibbs free energy of the resulting Cd-LDH (As/Cd) phase is significantly\nlower than that of pristine MgMn-LDH (Fig. 1c). This energy disparity drives the\nsubstitution of Mg2+ by Cd2+, ultimately forming an ultrastable mineralized structure\n(Fig. 4h).\nSupplementary Fig. 50 The semi in-situ FT-IR of Cd-MgMn-LDH(As/Cd) in various adsorption\ntime.\nvarious adsorption time. (c) Magnitude of k4-weighted Fourier transforms of R-space EXAFS\nspectra of Mn. (d) Mulliken charges of Mn−O−Mg structure in LDO(H) and Mn−O−Cd structure\nin Cd-LDO(H). (e) lattice expansion of Cd-LDH(As/Cd) compared to LDH(As) and corresponding\nelectron density isosurface, with Mg−Mg and Mg−Mn distances labeled. (f) ICOHP of Mn‒O bond\nin LDH(As) and Cd-LDH(As/Cd).\nFig. 7 (a) XRD patterns in different Cd/Mg molar rate. (b) High-resolution TEM of Cd-LDH(As/Cd)\nin different Cd/Mg molar rate. (c) The schematic diagram of As migration path after Cd replacement.\n(d) Relationships between energy barriers of As migration along two pathways versus atomic ratios\n11\nof Mg to Cd. As represents AsIII, Cd represents Cd2+ and Mg represents Mg2+ in figures.\nFig. 1 (c) The Gibbs free energy diagram of four-level topological transformation. As represents\nAsIII and Cd represents Cd2+ in figures.\nFig 4 (h) Gibbs free energy diagram for the isomorphous substitution of Mg by Cd in LDH(AsIII)\nwith geometries of representative intermediates displayed (I represent the number of Mg of the\nMgMn-LDH(As) laminates replaced by Cd).\nPage 21 Line 378‒Page 25 Line 441\nThe presence of Cd2+ triggers Topology IV transformation. This part of the\ncontent all belongs to the role of Cd2+ adsorption.\nPage 5 Line 106: “Meanwhile, the original adsorption pathway for Cd2+ is altered,\ncausing Cd2+ to enter the layer via isomorphic substitution, which induces lattice\nexpansion and significantly enlarges the bulk diffusion channels.\nPage 22 Line 386 in manuscript: “Cd2+ substitution for Mg2+ changes the local\n12\ntensile strain within the layers, promoting electron transfer of AsIII-Mn4+ and AsIII\noxidation. The variation in tensile strain can be observed in Raman spectroscopy, where\nthe Mn4+‒O peak progressively shifts to lower wavenumbers from 626.8 to 606.7 cm‒1\nas increasing Cd2+ (Fig. 6b), indicating a longer Mn‒O bond is easier to break. The\nsame conclusion can also be drawn from EXAFS, where Mn‒M of Cd-LDH(AsIII/Cd2+) \nlocated at 2.64 Å is longer than that of LDH(AsIII) (2.61 Å) in Fig. 6c.”\nPage 22 Line 392 in manuscript: “The correlation between localized tensile\nstrain and electron transfer was systematically investigated through DFT calculations.\nFirstly, the Mulliken charge analysis shows that the partial charges of Mn and O are\n1.82 e and ‒1.00 e in Mg‒O‒Mn (Fig. 6d), the more electrons are transferred from Mn\nto O due to the local tensile strain in the structure by Cd substitution, resulting in a\ncharge of Mn and O are 1.86 e and ‒1.02 e, respectively, which demonstrates that Cd\nsubstitution promotes the electron transfer of Mn.”\nPage 22 Line 398 in manuscript: “This charge redistribution is further\ncorroborated by the electron density isosurface calculations (Fig. 6e), which\ndemonstrate that the Mg–Cd distance elongation (3.54 Å vs. Mg–Mg: 3.21 Å) promotes\nelectron delocalization under tensile strain.”\nPage 23 Line 401 in manuscript: “The integrated crystal orbital Hamilton\npopulation (ICOHP) analysis provides additional insight (Fig. 6f) 61, showing a\nreduction in the covalent character of the Mn–O bond (ICOHP: −1.33 to −1.11), which\nindicates an increased ability of Mn to accept electrons.”\nPage 23 Line 403 in manuscript: “Together, these results establish a coherent\nmechanism: Cd2+ induced strain promotes charge delocalization, destabilizes the Mn–\nO bond, and ultimately facilitates electron transfer from AsIII to transfer to Mn, thereby\nenhancing the oxidation of AsIII.”\nPage 5 Line 96 in manuscript: “Unexpectedly, compare the adsorption of AsIII\nor Cd2+ alone, not only was adsorption capacity improved, but rate also increased by\n181 times.”\nPage 24 Line 417 in manuscript: “The isomorphous substitution of Cd2+ in LDH\n13\nlayers resembles natural mineral isostructural substitution 62. Specifically, larger radius\ninduces structural relaxation, lattice expansion, and interlayer spacing variation, as\nconfirmed by XRD patterns (Fig. 7a) 63. In 100 mg L–1 AsIII solution, as Cd2+: Mg2+\nrises from 1:28 to 1:7, (003) peak of Cd-LDH(AsIII/Cd2+) shifts from 11.6° to\n11.2°; HRTEM shows lattice expansion (from 0.21 to 0.27 nm, Fig. 7b) and time-dependent\ngrowth (from 0.205 to 0.211 nm, Supplementary Fig. 63) 64. Increased spacing reduces\nAsIII diffusion resistance, boosting its rate.”\nPage 24 Line 429 in manuscript: “To verify this mechanism, the diffusion energy\nbarriers of AsIII in Cd-LDH(AsIII/Cd2+) with Cd2+/Mg2+ molar ratio of approximately 1 :\n28, 1 : 14, and 1 : 7 following path I (away from Cd2+) and path II (close to Cd2+) are\ncalculated and displayed in Fig. 7d. The optimized geometries of diffusion\nintermediates are shown in Supplementary Fig. 64. For Cd2+/Mg2+ = 1 : 28, the diffusion\nenergy barriers are calculated to be 0.27 eV in path I and 0.42 eV in path II. The\ndiffusion of AsIII along the path away from Cd2+ is significantly easier than that close\nto Cd2+. With the increasing amount of Cd2+, the diffusion energy barriers of AsIII along\npath I decreases progressively, reaching 0.24 eV for Cd2+/Mg2+ = 1 : 14 and 0.20 eV for\na ratio of 1 : 7. On the other hand, the diffusion energy barriers of AsIII along path II is\nfurther increased to 0.45 eV for Cd2+/Mg2+ = 1 : 14 and 0.46 eV for a ratio of 1 : 7.\nTherefore, DFT calculations verify that Cd2+ substitution benefits AsIII diffusion by\nlocal expansion effect.”\nPage 5 Line 102 in manuscript: “The distinct AsIII oxidation and Cd2+ adsorption\nenergies successfully reversed the usual sequence in AsIII/Cd2+ co-adsorption, causing\nAsIII oxidation to precede Cd2+ adsorption (Fig. 1c).”\nPage 15 Line 275 in manuscript: “As shown in Fig. 4h, after oxidation of AsIII\non LDH (AsIII), the ΔGs for the isomorphous substitution of each Mg2+ cation by each\nCd2+ cation are all smaller than 0 eV, indicating this process is spontaneous.”\n6. As species was presence in the formation of binuclear AsO tetrahedron? How\n4\nmany is the valence state of As?\nThank you for your comments. AsIII as the target pollutant, is essential for us to\nunderstand the speciation and oxidation states. We will answer question in two parts.\n6.1 The presence formation of As\nIn Fig. 5a, the results of As 3d XPS verified AsIII of 53.8% have transformed AsV，\ntherefore, the presence formation of AsV that have oxidized is binuclear AsO\n4\ntetrahedron, and the unoxidized AsIII retains its original trigonal pyramidal molecular\ngeometry. The existence of AsO as confirmed by XAFS results (Fig. 5d,\nlength is 1.68 Å after adsorption of AsIII/Cd2+ by LDO, closely consistent with those of\nthe AsV/Cd2+ adsorption product (CN = 3.9, R = 1.68 Å) and approach the standard\nNa HAsO reference data (CN = 4.0, R = 1.68 Å). The consistency in CN and R values\n2 4\nof As-O demonstrates tetrahedral coordination of As, providing structural evidence for\nAsIII oxidation during adsorption. (Environ. Sci. Technol. 2012, 46, 986-994; Environ.\nSci. Technol. 2013, 47, 1009−1016; J. Phys. Chem. B 2005, 109, 3227-3232; Appl.\nGeochem. 2013, 38, 110–120.)\n6.2 The valence state of As\nAs in AsO units exists in the pentavalent state (AsV).\nSupplementary Table 11. Local structure parameters around As estimated by EXAFS analysis.\nSample Shell CN R (Å) σ2 (Å2)\nNa2HAsO4 As-O 4.0 1.68 0.0038\nAs-O 4.2 1.68 0.0056\nLDH(AsIII)\nAs-M 1.1 3.23 0.0168\nAs-O 3.9 1.68 0.0022\nLDO(H)(AsV)\nAs-M 1.5 3.24 0.0087\nPage 17 Line 297: “The electron transfer from AsIII to Mn4+ during adsorption,\nforming AsV and Mn3+, as confirmed by XPS and XANES. For As, post-adsorption Cd-\nLDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9 eV (AsV, Fig. 5a);\nLDO raised AsV to 53.8% (vs. LDH’s 18.0%), showing stronger oxidation 54,\nwhich also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR and in-situ Raman\n(Supplementary Fig. 49‒51).”\nPage 18 Line 324 in manuscript: “EXAFS probed As coordination: Cd-\nLDH(AsIII/Cd2+) had As−O (1.23 Å, first shell) and As−M (2.80 Å, second shell) bonds\n(Fig. 5d). Its As–O coordination number (4.2) and distance (1.68 Å) matched\nNa HAsO (4.0, 1.68 Å) (Supplementary Table 11), indicating binuclear AsO\n2 4 4\ntetrahedra is thermodynamically favored. These tetrahedra bridge MO octahedra via\n6\n16\ncorner/edge-sharing, boosting stability and electron transfer between AsIII and Mn4+ 57,58.\nThis allows As incorporation into layers (not just surface), increasing sorption capacity\npost-transformation.”\n7. How to confirm As(III) was oxidized in to As(V) and Mn4+ was reduced Mn3+?\nXPS is not entirely accurate for valence state analysis. There should be relevant\nexperiments and characterizations.\nAuthor Response:\nThank you for your guiding comments. To address this concern, we acknowledge\nthat while XPS provides valuable surface information, its accuracy for valence state\nanalysis can be limited by spectral overlaps and surface sensitivity. To conclusively\nconfirm the oxidation of AsIII to AsV and reduction of Mn4+ to Mn3+, we employed\ncomplementary characterizations. For example, in-situ X-ray Absorption Near-Edge\nStructure (XANES) directly probes the local electronic environment of As and Mn via\ntheir K-edge absorption spectra, enabling precise valence state determination\n(Supplementary Fig. 52–53). The shift in absorption edge energy for As (e.g., from\n11870 eV for AsIII to 11874 eV for AsV) (Environ. Sci. Technol. 2005, 39, 9147-9155;\nEnviron. Sci. Technol. 2013, 47, 1009-1016) and Mn (e.g., Mn3+/Mn4+ ratio analysis via\npre-edge features) (Ind. Eng. Chem. Res. 2023, 62, 15600–15612; Nat. Commun. 2025,\n16, 3900) provides quantitative evidence of redox transitions. Thus, these techniques,\ncombined with XPS and XANES, provide a multi-faceted validation of the redox\nprocesses, mitigating the limitations of XPS alone.\nSupplementary Fig. 53 K-edge XANES spectra of As of Cd-LDH(As/Cd) and reference samples.\nPage 17 line 301 in manuscript: “For Mn, XPS shows Mn 2p peaks at 643.1 and\n653.8 eV (Mn3+) (Fig. 5b); its proportion in Cd-LDH(AsIII/Cd2+) (84.0%) exceeds\nLDO’s 35.9%, confirming Mn4+ reduction with AsIII oxidation, as confirmed by\nXANES. Cd-LDH(AsIII/Cd2+) has a 1.02 eV lower Mn K-edge (lower oxidation state)\nand an As K-edge 11874 eV peak (AsV, Supplementary Fig. 52‒53), verifying electron\ntransfer 55.”\nGeneral comment:\n1. Layered double hydroxides (LDHs) have been recognized to have great potential\nfor the treatment of heavy metals in wastewater and soil through various\nmechanisms. Up to now, many research on the adsorption performance and\nremediation effect of As/Cd contaminated water and soil using various LDH such\nas CaAl-LDH, FeMnCa-LDHs, FeMnCa-LDHs, Fe O @Mg/Al/Fe-LDH etc. has\n3 4\nbeen carried out widely. Some published literature has shown that the adsorption\ncapacity of LDH/LDO reached 612.0 mg/g for AsIII and 625.0 mg/g for Cd2+. If\nsome of these materials are used to remediate the AsIII and Cd2+ coexisting polluted\nwater and soil, the performance can be expected since the adsorption capacity\nperhaps be enhanced obviously according to previous research.\nAuthor Response:\nThank you for carefully reading and providing the literature comparison. This is\nvery helpful for us to conduct the material comparison. According to your suggestion,\nwe synthesized all the materials mentioned in the literature and applied them to the co-\ncontamination system of AsIII and Cd2+ with initial AsIII/Cd2+ concentrations of 100/200\nmg/L‒1, and the results has been listed in Table A. As expected, compared with the\ntreatment of single pollutants, the adsorption capacity was improved in all cases.\nThis precisely confirms the universality of the principle and method we proposed.\nSpecifically, for AsIII single system, the adsorption capacity of MgMn-LDO for\nAsIII arrived at about 60.9 mg g‒1 (≈ 61.0%) within 10 min, is significantly superior to\nother materials (< 36 mg g‒1). For AsIII/Cd2+ co-contaminated system, the adsorption\ncapacity of MgMn-LDO for AsIII arrived at about 100 mg g‒1 (≈ 100%) within 10 min,\nexhibiting exceptionally fast adsorption kinetics and superior performance, while the\nadsorption capacity of other materials is less than 70.4 mg g‒1 (70%). This could due to\nthe abundant defect sites of MgMn-LDO accelerate hydration, thereby promoting\noverall material hydroxylation and increasing active sites. In addition, the strong\n19\noxidative capacity of Mn4+ rapidly oxidizes AsIII to AsV, facilitating both topotactic\nstructural transformation and accelerated AsIII immobilization. For Cd2+ single system,\nthe adsorption capacity arrived at 200 mg g‒1 (100%) within 10 min, except for\nFeMnCa-LDHs and Fe O @Mg/Al/Fe-LDH; for AsIII/Cd2+ co-contaminated system,\n3 4\nthere are no enhance of other materials for Cd2+ adsorption capacity due to have\nachieved adsorption fully, FeMnCa-LDHs and Fe O @Mg/Al/Fe-LDH exhibited poor\n3 4\nadsorption capacity compared to MgMn-LDO even if there is an improvement.\nTable A Data on the adsorption performance of AsIII and Cd2+ in AsIII/Cd2+ single and co-\ncontaminated system under 10 min for different materials.\nQ (mg g‒1) Q (mg g‒1)\nMaterials Ions t (min) Ref\nsingle system co-contaminated system\nAsIII 25.6 70.4\nCaAl-LDH 10 [1]\nCd2+ 200 200\nAsIII 35.8 46.2\nFeMnCa-LDHs 10 [2]\nCd2+ 20.9 38.9\nFe O @Mg/Al/Fe- AsIII 29.9 31.4\n3 4\n10 [3]\nLDH Cd2+ 10.1 18.5\nAsIII 15.5 60.3\nCaAl-900 10 [4]\nCd2+ 200 200\nAsIII 25.9 65.3\nCa AlCl-LDH 10 [5]\nAsIII 60.9 99.9 This\nMgMn-LDO 10\nCd2+ 200 200 work\nRef:\n[1] J. Cent. South. Univ. 2024, 31, 1292-1305.\n[2] Inorg. Chem. Commun. 2024, 163, 112312.\n[3] J. Water Process Eng. 2024, 68, 106444.\n[4] Chem. Eng. J. 2024, 300, 120553.\n20\n[5] Chemosphere 2024, 352, 141399.\n2. In this article, the MgMn-LDO prepared by the authors has excellent adsorption\nproperties for both Cd and As, and the feasibility of the application of MgMn-\nLDO in the composite contamination of Cd2+ and AsIII has been comprehensively\ninvestigated in terms of material research and development, performance\nexploration, mechanism revelation, and production and application. The\nadsorption mechanism and adsorption pathway of LDO on Cd2+ and AsIII were\nrevealed. Overall, the manuscript is good in language organization, results\nstatement and mechanism analysis. The authors, however, suggest that the novelty\nof the study is not enough, and the experimental design is not so clear, and the key\ncontents are not sufficiently discussed.\nAuthor Response:\nWe sincerely appreciate the reviewer’s constructive comments and positive\ncomments on our work. Regarding the concerns about insufficient novelty, unclear\nexperimental design, and inadequate discussion of key points, we have made a point-\nto-point revision of the proposed question, and all of the changes in the revised\nmanuscript are highlighted in yellow.\n3. Moreover, the remediation performance and function of materials are often\naffected by many factors related to physical, chemical and biological activities as\nwell as material aging process itself.\nAuthor Response:\nThank you for your valuable suggestions, this is indeed an insightful perspective.\nAs you suggested, we collected actual soil samples before and after-remediation\nthrough different remediation condition for analysis.\n3.1 The impact of physical activities\nWe investigated the remediation effects of MgMn-LDO on soil under different\ntemperature conditions. The results are shown in the Supplementary Table 4. When the\n21\nremediation temperature was set at the lower level of 10 ℃, the total concentrations of\nboth As and Cd in the soil decreased (As: from 0.159 to 0.107 mg/kg; Cd: from 0.054\nto 0.011 mg/kg). At 30 ℃, the post-remediation concentrations of total As/Cd also\ndecreased significantly, showing no substantial difference from those observed at 10 ℃.\nThis demonstrates that the remediation performance of MgMn-LDO remains\nunaffected by external physical conditions.\nSupplementary Table 4. The As/Cd concentration in field soil before and after\nremediation in different temperature\nBefore (mg/kg) After (mg/kg)\n10 ℃ 30 ℃\nAs Cd As Cd As Cd\nsample 0.159 0.054 0.107 0.011 0.102 0.010\n3.2 The impact of nature heavy metal-contaminated farmland\nWe selected three nature heavy metal-contaminated farmland to investigate the\nremediation effects of MgMn-LDO. The results are presented in Supplementary Table\n5. After remediation across three distinct pH conditions, the total concentrations of both\nAs and Cd in the soil decreased (For example, As: from 0.187 to 0.110; Cd: from 0.057\nto 0.019). This indicates that the remediation performance of MgMn-LDO remains\nunaffected under nature condition.\nSupplementary Table 5. The As/Cd concentration in field soil before and after\nremediation in different pH\nBefore (mg/kg) After (mg/kg)\npH As Cd As Cd\nSoil 1 5.21 0.187 0.057 0.110 0.019\nSoil 2 5.56 0.162 0.049 0.108 0.010\nSoil 3 5.87 0.170 0.051 0.098 0.011\n3.3 The aging process of MgMn-LDO\nConsidering material aging concerns, the XRD analyses are conducted on\n22\nkilogram-scale synthesized MgMn-LDO over time. The results shown in\nSupplementary Fig. 14, the characteristic peaks of LDO remained virtually unchanged\nafter half a year ambient storage in package, demonstrating negligible environmental\nimpact on material structural integrity as a remediation agent.\nSupplementary Fig. 14 The XRD patterns of MgMn-LDO.\nPage 7 Line 133 in manuscript inset: “In addition, the structure of LDO is stable,\nand its removal efficiency for AsIII/Cd2+ is independent of pH value, coexisting salts,\nand metal ions (Supplementary Fig. 9–18 and Supplementary Table 4‒5).”\n4. The human health risk of MgMn-LDO entering into crops through food chain\nshould also be considered when it is applied into farmland.\nAuthor response:\nThe safety of the mineralizer is an issue we must consider. Your question prompted\nus to consider the impact of mineralization on food safety.\nFirstly, Mg and Mn are ubiquitous soil elements and essential micronutrients for\nplants. Furthermore, China's agricultural soil contamination control standard (GB\n15618-2018, Soil Environmental Quality Risk Control Standard) specifies no\n23\nmaximum permissible limits for these elements. Secondly, the Mn content in MgMn-\nLDO was about 12%, according to the dosage of 750 kg MgMn-LDO per hectare, the\nMn content in the soil sample was about 26 mg/kg (the mass of soil was about 3000\nt/ha), was substantially lower than the background manganese level in soil (400-600\nmg/kg). For Mg, the Mg balances were negative in most crop soil in China, indicating\nthat the input of Mg fertilizer has been seriously neglected and is insufficient. Thirdly,\nwe sampled rice plants three agricultural plots. For each plot, rice plants were collected\nboth before and after land remediation, and measured changes in metal content. The\nresults are shown in the Supplementary Table 10.\nDetection of rice grown in remediated versus unremediated farmland demonstrates\na significant decrease in As/Cd content post-remediation. Concurrently, analysis of\nMg/Mn levels in rice plants revealed increased Mg accumulation, attributed to Mg\nleaching from MgMn-LDO during the remediation. As a key chlorophyll component,\nmagnesium supports photosynthesis and metabolic enzyme activation, while Mn did\nnot accumulate to inhibitory levels. These findings confirm that MgMn-LDO\nremediation reduces heavy metals in farmland-grown rice without plant contamination\nor food chain risks, as it avoids toxic bioaccumulation while supplying beneficial\nnutrients.\nSupplementary Table 10 The metal ions concentration in rice before and after remediation\nBefore (mg/kg) After (mg/kg)\nUnit: (mg/kg)\nMg Mn As Cd Mg Mn As Cd\n1 598.32 35.31 0.321 0.355 849.65 89.91 0.035 0.165\n2 600.89 51.22 0.257 0.320 921.00 126.54 0.032 0.160\n3 615.62 40.98 0.135 0.294 959.64 100.20 0.028 0.135\nPage 9 Line 174 in manuscript insert: “MgMn-LDO remediation reduces heavy\nmetals in farmland-grown rice without plant contamination or food chain risks, as it\navoids toxic bioaccumulation while supplying beneficial nutrients (Supplementary\nIntroduction\n1. The authors have explored the structure and characteristics of MgMn-LDO in\ndetail in their previous studies (https://doi.org/10.1016/j.jenvman.2019.06.002),\nand have clarified its performance and mechanism for remediation of Cd2+\npollution. In this study, the authors only changed the target pollutant (AsIII/Cd2+)\nand deeply analyzed its mechanism and pathway in the synergistic remediation of\nAsIII and Cd2+. Therefore, it seems that the authors did not develop the innovative\nnew material and the innovation of this article needs to be developed.\nAuthor Response:\nThank you for your thorough review and literature curation. Your questions will\nsignificantly advance our understanding of the novelty of materials. We will address\nthe concern regarding the novelty of our study from two aspects:\n1.1 Novelty of the research target\nThe shift from single-pollutant treatment to the co-contamination system of\nAsIII/Cd2+ is not a simple addition of pollutants. In a co-contamination scenario, Cd2+\nand AsIII compete for adsorption sites on the material surface due to their distinct\nchemical forms and transformation mechanisms (Water Res. 2022, 221, 118804; Sci.\nTotal Environ. 2021, 750, 141672). Moreover, their co-existence may trigger complex\nchemical interactions, such as redox reactions and the formation of new chemical\nspecies, which pose significant challenges to traditional remediation methods. Most\nexisting materials suffer from performance degradation when dealing with co-\ncontaminants (J. Environ. Manage. 2022, 319, 115658). Our research, however,\ndemonstrates a significant breakthrough: MgMn-LDO not only overcomes this\ncompetitive challenge but also enhances the simultaneous removal efficiency of both\nCd2+ and AsIII, achieving 10.0% and 18.8% increases in adsorption capacity compared\nto single-pollutant treatments (Fig. 2c), respectively, and 181‒fold accelerate in AsIII\n25\nadsorption rate (Fig. 6a). This is enabled by the material strong bulk hydroxylation\ncapability and structural topological transformation properties, which optimize binding\nsites and promote dual-pollutant removal. This innovation offers a novel solution to a\nlongstanding limitation in co-contamination remediation, marking a substantial\nadvancement beyond previous studies.\nFig.2 (c) The removal capacity of LDO for As and Cd in single and co-contaminated system.\nFig. 6 (a) The adsorption kinetic of LDO in As and As/Cd = 100/200 mg L‒1.\nPage 3 Line 42 in manuscript: “Arsenite and cadmium co-contamination\n(AsIII/Cd2+) poses a significant global environmental challenge. However, remediation\nefforts are hindered primarily by the distinct chemical forms and transformation\nmechanisms of these two pollutants 1‒6.\nPage 3 Line 51 in manuscript: “However, in AsIII/Cd2+ co-contaminated\n26\nenvironments, the oxidation capacity of such materials often fails to function fully. The\nprimary reason is that the strong coordination ability of Cd2+ preferentially occupies all\nof adsorption sites formed by surface hydroxyl (‒OH) groups generated through oxide\nhydration, including oxidation sites 13‒15.”\nPage 4 Line 81 in manuscript: “However, the challenge lies in the synchronous\nimmobilization of AsIII/Cd2+, where competitive inhibition during interfacial adsorption\nsignificantly diminishes their effectiveness.”\nPage 4 Line 83 in manuscript: “Fortunately, LDOs possess a unique property:\ntopological transformation, allowing them to revert to the LDH structure 25‒29. By\nharnessing this transformation, it becomes possible to spatially and temporally\ndecouple the oxidation process of AsIII from the adsorption process of Cd2+, effectively\nmitigating the competitive inhibition effect. This innovative strategy can pave the way\nfor overcoming current limitations and achieving efficient synchronous immobilization\nof AsIII/Cd2+.”\nPage 7 Line 125 in manuscript: “Unexpectedly, although the pH value increased\nonce added the LDO into solution (Supplementary Fig. 1), when using as-prepared\nLDO by calcining LDH at 350 ℃(Supplementary Fig. 2‒4) to adsorb AsIII/Cd2+ co-\ncontaminants, the maximum adsorption capacity for AsIII can reach 821.7 mg g⁻1,\nwhich is five times the current highest value (Starch‒FeMnO , 161.29 mg g⁻1) 30; and for Cd2+\nreach 1895.6 mg g⁻1, which is three times the current highest value (graphene/δ‒MnO ,\n2\n644 mg g⁻1) (Fig. 2a‒2b, Supplementary Fig. 5‒8 and Supplementary Table 2‒3) 39.\nMore importantly, these values are higher than the adsorption capacities of LDO for\ntreating AsIII (691.6 mg g⁻1) and Cd2+ (1723.1 mg g⁻1) individually (Fig. 2c).”\nPage 5 Line 96 in manuscript: “Unexpectedly, compare the adsorption of AsIII\nor Cd2+ alone, not only was adsorption capacity improved, but rate also increased by\n181 times.”\nPage 21 Line 378 in manuscript: “The presence of Cd2+ significantly enhances\nthe adsorption rate of LDO for AsIII (Fig. 6a). When LDO is used alone for AsIII\nadsorption (C = 100 mg L⁻¹), it takes 7 h to reach adsorption equilibrium. Surprisingly,\n0\nwhen the introduction of Cd2+ (200 mg L‒1), the adsorption of AsIII by LDO reaches\nequilibrium in just 10 min. The adsorption rate constant (k) increases from 0.0183 to\n3.3200 g h‒1 mg‒1 (Supplementary Fig. 61‒62 and Supplementary Table 13),\nrepresenting an approximately 181‒fold enhancement. This phenomenon can be\nattributed to increased oxidation rate and diffusion rate.”\nPage 6 Line 108 in manuscript: “This multi-level topological transformation\nplays a central role by not only safeguarding the high reactivity of the adsorbent during\nthe process but also conferring an ultra-stable mineralized encapsulation in the final\nadsorption structure.”\n1.2 Material innovation\nThis is an excellent question, which makes us realize that the reviewer’s\nmisunderstanding arises from our insufficiently clear expression. In fact, the materials\nwe prepared are innovative in two aspects, including the ratio of layered metal element,\nand the calcination environment. Specifically:\n1) Synthetic layered metal element ratio. In our work, we employed MgMn-LDH\n(Mg:Mn = 5:1) as the precursor. In contrast, conventional LDHs typically form at ratios\nof 2:1–4:1 due to Paulingˈs rule. (Catal. Today 1991, 11, 173-301; The Periodic Table\nII. 2019, 182, 89-120), including the literature you proposed, the composition rate is\n2:1. The unique capability of synthesizing MgMn-LDH with Mg:Mn = 5:1 arises\nfrom structural adaptability and redox versatility of Mn. Firstly, the ionic radius of Mn3+\nand Mn4+ are 0.65 Å and 0.53 Å, respectively, which are close to the ionic radii of\ncommon LDH layer-metal ions, such as Al3+ (0.54 Å) and Fe3+ (0.65 Å). The matching\nof ionic radius result in Mn3+/Mn4+ to enter the laminate and form a stable LDH\nstructure. Furthermore, the laminate of LDHs is formed by the substitution of a portion\nof divalent metal cations with trivalent metal cations, resulting in positively charged\nlaminate. In terms of MgMn-LDH synthesis, the highly alkaline environment during\npreparation oxidizes part of Mn3+ to Mn4+ (Mn-XPS analysis indicates approximately\n41.9% of Mn3+ is oxidized to Mn4+) (Fig. A). When high-valence Mn4+ replaces Mg2+\nin the laminate, it causes a dramatic increase in positive charge within the laminate,\n28\nleading to structural destabilization. Therefore, in order to maintain structural stability,\nit is necessary to increase the proportion of Mg2+ to dilute the high charge density\nwithout altering the total Mn content. Consequently, for the special element Mn\nentering the laminate of LDHs, the synthesis of high-ratio LDH of Mg/Mn is feasible.\nAnd to some extent, it increases the active sites for AsIII adsorption, promoting the\nadsorption process (Supplementary Information 58). Additionally, the synthesis process\nof LDH with a high Mg/Mn ratio is simple, requiring only the adjustment of metal salt\nmolar ratios, and ensuring operational simplicity.\nFig. A The Mn 2p XPS spectra of MgMn-LDH.\nSupplementary Fig. 58 The As removal rate of LDO in different molar rate of Mg and Mn (5:1,\n4:1, 3:1, and 2:1) under 350 ℃ calcine.\nPage 18 Line 334 in manuscript: “Due to the inherently low affinity between As\nand MnO in binary oxides compared to magnesium oxides, a higher proportion of Mn\n2\n29\nin the LDO leads to a reduction in adsorption efficiency, as confirmed by that the\nadsorption capacity decreases with increasing Mn content from Mg:Mn = 5:1, 4:1, 3:1,\n2:1 (Supplementary Fig. 56–58). Therefore, to balance sufficient oxidation sites (Mn‒\nOH) and maximize adsorption sites (Mg‒OH), the optimal Mg:Mn = 5:1 in the LDO\nwas chosen.”\n2) Calcination environment. The referenced study employs N -atmosphere\n2\ncalcination, which inhibits oxidation of multivalent Mn3+, preserving its trivalent state\nin the layered structure and stabilizing the 2D framework. In contrast, our material\nutilizes direct air calcination in a muffle furnace. Crucially, our approach can achieve\nequivalent Mn4+ dominance in MgMn-LDO, which effectively oxide AsIII to AsV and\nimmobilization in situ (Fig. 5a). This method simplifies preparation process and reduces\nproduction costs.\nFig. 5 (a) The As 3d XPS spectra of Cd-LDH(As/Cd) and LDH(As/Cd).\nPage S4 Line 58 in Supplementary Information: “1.3 Synthesis of MgMn-LDO\nMgMn-LDO was obtained by calcined the MgMn-LDH at different temperatures\n(200, 250, 350, 450, 550, and 650 ℃) for 3 h in air, with a heating rate of 5 ℃·min‒1.”\nPage 17 Line 297 in manuscript: “The electron transfer from AsIII to Mn4+ during\nadsorption, forming AsV and Mn3+, as confirmed by XPS and XANES. For As, post-\nadsorption Cd-LDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9 eV (AsV,\nwhich also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR and in-situ Raman\n(Supplementary Fig. 49‒51).”\nAnalysis and Discussion:\n1. The authors made LDOs calcined at different temperatures, but the authors did\nnot provide the calcination temperature of which LDOs were applied in the\nsubsequent experiments.\nAuthor Response:\nThank you for your advice. It’s helpful for us to complete the material detail.\nThrough comparing the structural characteristics and adsorption performance\n(Supplementary Fig. 2‒3) of materials at different calcination temperatures, 350 ℃ was\nultimately selected as the optimal calcination temperature for MgMn-LDH. All\nsubsequent experiments in the manuscript were conducted using MgMn-LDO calcined\nat 350 ℃. The calcination temperature details are added to Supplemental Information\n1.19 section. The reasons lie in that the maximum specific surface area. As shown in\nSupplementary Fig. 4, when the calcination temperature arrived at 200 ℃, the BET\nspecific surface area is relatively low (53.5479 m2 g‒1), as the calcination temperature\nincreases, the specific surface area progressively increases. At 350°C, our material\nachieved its highest specific surface area of 146.9733 m2 g‒1. Further increasing the\ncalcination temperature led to the specific surface area decreased, which is mainly\nattributed to the sintering phenomenon. Meanwhile, the adsorption rate for AsIII reach\nup to 99.0% at a calcination temperature of 350 ℃.\n(200, 250, 350, 450, 550, and 650℃).\nSupplementary Fig. 3 The As removal rate of calcine production in different temperature (200,\n250, 350, 450, 550, and 650℃) in As/Cd solution.\ntemperature. (200, 250, 350, 450, 550, and 650℃).\nPage 7 Line 125 in manuscript revise: “Unexpectedly, although the solution pH\nvalue increased with adding LDO calcined at 350 ℃ (Supplementary Fig. 1‒4), the\nmaximum adsorption capacity for AsIII can reach 821.7 mg g⁻1, which is five times the\ncurrent highest value (Starch‒FeMnO , 161.29 mg g⁻1) 30; and for Cd2+ reach 1895.6\nx\nmg g⁻1, which is three times the current highest value (graphene/δ‒MnO , 644 mg g⁻1)\n2\n(Fig. 2a‒2b, Supplementary Fig. 5‒8 and Supplementary Table 2‒3) 39.”\nPage S14 Line 275 in Supplementary Information insert: “1.19 The adsorption\ndetails of LDO under different calcined temperature in AsIII/Cd2+.”\nTo investigate the effect of calcination temperature on adsorption performance,\n0.1\ng of LDO was added to 100 mL of a co-contaminated aqueous solution (AsIII/Cd2+ =\n100/200 mg L‒1). The mixture was agitated for 2 h to attain adsorption equilibrium.\nSubsequently, the supernatant was filtered through a 0.22 μm membrane filter. The\nresidual ion concentrations in the filtrate were quantified by ICP-OES, enabling the\n33\ncalculation of adsorption efficiency.”\n2. Pilot experiment is the key to judge the performance of the material, while the\nauthors mentioned the remediation of As and Cd pollution in actual water bodies\nand actual soil, and did not account for the amount of material, remediation time\nand other key information, and did not give the detailed test methods and steps in\nthe materials and methods. We are eager to\nknow more about the impacts in actual water bodies and soils.\nAuthor Response:\nThank you for your comments. As you suggested, we added the details of actual\nwater bodies and soils experiment in the Supplementary Information.\n2.1 The practical remediation of contaminated soil.\nPage S15 Line 293 in Supplementary Information insert:\n“The experimental field was subdivided into three plots, each 3 m × 3 m in size.\nRemediation agents were surface-applied at a dosage of 0.67 kg per plot (750 kg per\nhectare) and subsequently tilled to a depth of 20 cm to ensure thorough integration with\nthe soil. Soil sampling was conducted at 0, 15, 30, 60, and 120 days to assess the\nstabilization efficiency of As and Cd. Sampling procedures strictly followed\nChina’s Technical Specification for Soil Environmental Monitoring (HJ/T 166-2004).\nSpecifically, five subsites (0–20 cm depth) were arranged in a plum blossom pattern\nwithin each plot; samples from these points were homogenized, and a 1 kg composite\nsample was retained for analysis. Following removal of plant debris and gravel, soils\nwere nature-dry and sieved through a 40‒mesh screen. As concentrations were\ndetermined by atomic fluorescence spectrometry, while Cd levels were quantified using\ngraphite furnace atomic absorption spectrometry.”\n2.2 The practical water remediation.\nFor actual wastewater treatment performance, owing to multiple reasons, we\ncollected complex wastewater sample and treated in the lab with 1 g/L MgMn-LDO.\nSubsequently, we will coordinate with local authorities to conduct pilot-scale\nexperiments on site. As/Cd in wastewater were quantified via ICP-MS.\nPage S16 Line 307 in Supplementary Information insert:\n“First, insoluble solids were removed from nature wastewater through 0.45 μm\nmembrane filtration prior to adsorption experiments. Then, 0.5 g of LDO was added\ninto 500 mL of actual wastewater containing heavy metal ions. The adsorption time was\n2 h under stirring, the supernatant was separated with a 0.22 μm membrane filter. The\nconcentrations of heavy metals in actual wastewater were determined by ICP-MS.”\n3. What is the right amount of material to apply in real water applications? How\nis material recycling achieved after use? Is it reusable?\nAuthor Response:\n3.1 In actual wastewater treatment, we employed a standard dosage of 1 g/L for\nthe remediation agent.\n3.2 To realize the material recycling, MgMn-LDO remediation material was high-\nspeed centrifugated in the lab to achieve reuse.\n3.3 The regeneration performance of the MgMn-LDO was systematically\nevaluated via 10 consecutive laboratory cycling experiments. The experimental setup\nfixed the initial concentrations of As and Cd at 10 and 20 mg L‒1, respectively, while\n50 mg L‒1 Na CO solution was selected as the regeneration agent. As demonstrated in\n2 3\nSupplementary Fig. 16, after 10 regeneration cycles, the removal efficiency remained\nat 90.2% for As and 100% for Cd, showcasing remarkable recyclability. The reason lies\nin that high-concentration CO 2‒ in the regeneration solution displaces intercalated As\n3\nanions through anion exchange, reforming CO 2‒-intercalated LDH. This structural\n3\nreconstruction allows the MgMn-LDO to reactivate its adsorption capacity for As upon\nsubsequent use. In addition, the high Mg content in MgMn-LDO (Mg:Mn = 5:1)\nenables sufficient isomorphic substitution of Cd within the lattice, while bulk\nhydroxylation reactions generate abundant surface hydroxyl groups. These hydroxyl\nmoieties persist as active adsorption sites for both As and Cd across multiple cycles,\nmaintaining consistent removal efficiency.\nPage 7 Line 133 in manuscript insert: “In addition, the structure of LDO is stable,\nand its removal efficiency for AsIII/Cd2+ is independent of pH value, coexisting salts,\nand metal ions (Supplementary Fig. 9–18 and Supplementary Table 4‒5).”\nPage S16 Line 315 in Supplementary Information insert: “\n1.23 The regenerative experiment details of MgMn-LDO.\nThe regeneration performance of the MgMn-LDO was systematically evaluated\nvia 10 consecutive laboratory cycling experiments. The experimental setup fixed the\ninitial concentrations of As and Cd at 10 and 20 mg L‒1, respectively, while 50 mg L‒1\nNa CO solution was selected as the regeneration agent. The 1g/L as the dosage\n2 3\nstandard to proceed regeneration test. The adsorption time was 2 h under stirring, the\nsupernatant was separated with a 0.22 μm membrane filter. The concentrations of heavy\nmetals in actual wastewater were determined by ICP-MS.”\n4. For real soil applications, what is the long term stability of the material to\nimmobilize soil As and Cd?\nAuthor Response:\nThe as-prepared MgMn-LDO, used in real soil remediation via an in-situ\n36\nimmobilization technique, has effectively stabilized As/Cd for up to 5 years (Fig. 2h).\nThe actual data is still being updated.\nFig.2 (h) The concentration of before and after remediation of As/Cd co-contaminated soil and rice.\nPage 9 Line 167 in manuscript: “Secondly, when LDO was added the\ncontaminated soil located at Liling in Hunan province, the exchangeable total As and\nCd decreases 66.9% and 91.1%, respectively compared with the control sample (Fig.\n2h). Although it is an in-situ immobilization technology, it can effectively stabilize\nAsIII/Cd2+ over the long term, having already reached 5 years (with ongoing updates to\nthe actual data). Importantly, the concentrations of total As and Cd in rice was 0.239\nand 0.141 mg/kg, which is safety level according to the China Standard of GB2762-\n2022 (As ≤ 0.5 mg/kg, Cd ≤ 0.2 mg/kg).”\nMaterials and Methods:\nRegarding the setting of pollutant concentrations, although it is necessary to\nadjust different pollutant concentrations according to the purposes of different\nexperiments to explore different scientific issues, the author's setting of pollutant\nconcentrations throughout the entire experimental process was unclear and\nchaotic. Meanwhile, the author lacks the provision of key experimental\ninformation.\nAuthor Response:\npollutant concentration settings. This issue has prompted us to systematically\nrationalize the experimental design. As you suggested, the reasons for our choice of\nexperimental conditions have been listed, and the concentration range has been\nexpanded to demonstrate the existing trends. The missing relevant experimental details\nhave also been added to the Supplementary Information. In addition, to maximize the\nuniformity of concentrations, we have made corresponding adjustments.\n1. In section 1.5 adsorption kinetics experiments, what is the basis for selecting the\ninitial concentration regarding co-adsorption of AsIII/Cd2+? Why was the initial\nconcentration of AsIII only set to remain at 100 mg/L and the initial concentration\ngradient of Cd2+ increased. Keeping the initial concentration of Cd2+ certain, is\nthere any other conclusion when increasing the initial concentration of As?\nAuthor Response:\nThank you for your comments. The selection of initial concentration of kinetics is\nvital for determining the adsorption rate trend. It is necessary to expand the initial\nconcentration range to prove the existing trend.\n1.1 The reason for selecting an initial AsIII concentration of 100 mg L‒1 in the kinetics\nstudy is as follows.\nDue to the unique properties of AsIII, which exists as molecular species across a\nwide pH range, many adsorbents face inherent limitations in achieving complete\nremoval for high concentrations AsIII. Specifically, materials with restricted surface\nactive sites (e.g., CeO , MnO ) (Environ. Sci. Technol, 2022, 56, 10412-10422;\n2 2\nLangmuir 2024, 40, 26387-26395; J. Mater. Chem. A 2014, 2, 2374-2382) have been\nshown to only enable thorough AsIII elimination at lower concentrations (10–20 mg L‒\n1).\nInterestingly, our as-prepared MgMn-LDO is also effective for the deep treatment\nof high-concentration AsIII (Fig. 2c), in addition to low-concentration cases (Fig. 2f).\nTo ensure direct comparability with established literature, we intentionally selected an\n38\ninitial AsIII concentration of 100 mg L‒1. This benchmark aligns with the concentration\nranges commonly used in studies of analogous adsorbents, allowing for rigorous\nperformance validation and highlighting the superior adsorption capacity of our\nmaterial relative to state-of-the-art systems (Environ. Sci.: Nano, 2016, 3, 94).\nFig. 2 (c) The removal capacity of LDO for As and Cd in single and co-contaminated system.\nFig.2 (f) The residual concentrations of As and Cd at varying adsorbent dosages across different\ninitial concentrations.\nPage 7 Line 125 in manuscript: “Unexpectedly, although the solution pH value\nincreased with adding LDO calcined at 350 ℃ (Supplementary Fig. 1‒4), the maximum\nadsorption capacity for AsIII can reach 821.7 mg g⁻1, which is five times the current\nhighest value (Starch‒FeMnO , 161.29 mg g⁻1) 30; and for Cd2+ reach 1895.6 mg g⁻1,\nx\n39\nwhich is three times the current highest value (graphene/δ‒MnO , 644 mg g⁻1) (Fig.\n2\n2a‒2b, Supplementary Fig. 5‒8 and Supplementary Table 2‒3) 39. More importantly,\nthese values are higher than the adsorption capacities of LDO for treating AsIII (691.6\nmg g⁻1) and Cd2+ (1723.1 mg g⁻1) individually (Fig. 2c). This anomaly indicates that\nAsIII and Cd2+ become triggers for mutually enhancing adsorption performance.”\nPage 8 Line 149 in manuscript: “The deep-remove of AsIII/ Cd2+ co-\ncontaminates remains an unresolved challenge in practical applications 41,42.\nRemarkably, LDO demonstrates unprecedented deep-remove capabilities in AsIII/Cd2+\nco-contaminated systems. As evidenced in Fig. 2f, when the initial concentrations of\nAsIII/Cd2+ are 0.1/0.1 and 1.5/1.5 mg L‒1, 0.5 g L‒1 of the adsorbent LDO achieves\nextremely low residual concentrations of AsIII/Cd2+ (AsIII ≤ 4 μg L‒1; Cd2+ ≤ 2 μg L‒1),\nwhich meet WHO drinking water standards 43,44. Especially, even when the initial\nconcentrations of AsIII/Cd2+ rise to 12.0 mg L‒1, 1.0 g L‒1 of the adsorbent still achieves\nlow residual concentrations with AsIII = 5 μg L‒1 and Cd2+ = 1.8 μg L‒1, which is\ncurrently unattainable by other materials.”\n1.2 The fixing the AsIII concentration while incrementally increasing Cd2+\nconcentrations.\nFor the initial selection of concentrations, our focus was on adsorption\nperformance, namely deep removal of high concentrations, adsorption capacity, and\nrate. Therefore, AsIII (100 mg L‒1) and Cd2+ (200 mg L‒1) was initially chosen. However,\nkinetic tests revealed that this combination caused adsorption equilibrium to occur\nwithin 10 min, which was too rapid for precise kinetic modeling (Fig. 6a). To resolve\nthis, we reduced Cd2+ concentrations to 50–100 mg L‒1, slowing the AsIII adsorption\nrate to enable detailed monitoring of the kinetic process. Similarly, for Cd2+ adsorption,\nequilibrium was achieved within 10 min at an initial of 200 mg L‒1. Therefore, we\nslowed down the adsorption rate by increasing the initial concentration of Cd2+ (C\n0(Cd2+)\n= 300, 500 and 600 mg L‒1).\nFig. 2 (d) The sorption kinetics of As and Cd in different As/Cd initial concentration.\nPage S31 in Supplementary Information: “LDO can achieve removal efficiency\nof 90% for AsIII within 3 h and 100% for Cd2+ within just 1 h, as illustrated in Fig. 2d.\nSince the fastest adsorption can reach equilibrium within 10 min for AsIII/Cd2+ (C\n0(As(III))\n= 100 mg L‒1, C = 200 mg L‒1), it is not conducive to monitoring the kinetic\n0(Cd2+)\nprocess. In terms of AsIII adsorption, the addition of Cd2+ enhanced the adsorption rate.\nTherefore, we slowed down the adsorption rate by reducing the initial concentration of\nCd2+ (C = 50 and 100 mg L‒1) to fit the kinetic process. In terms of Cd2+ adsorption,\n0(Cd2+)\nequilibrium was achieved within 10 min at a low concentration of 200 mg L‒1.\nTherefore, we slowed down the adsorption rate by increasing the initial concentration\nof Cd2+ (C = 300, 500 and 600 mg L‒1) to fit the kinetic process.”\n0\n41\n1.3 The fixing initial Cd2+ concentration and varying AsIII concentrations.\nAs you suggested, we unified the initial concentration of Cd2+ to 300 mg L‒1 and\ngradually increased the concentration of AsIII, with the results shown in Fig. B. In terms\nof AsIII, the equilibrium was reached in 7 h under the condition of an initial concentration\nof 100 mg L‒1 AsIII in a single system (Fig. 6a), whereas the addition of 300 mg L‒1 Cd2+\naccelerated the adsorption rate to just 10 min, indicating the addition of Cd2+ markedly\nenhanced the adsorption rate. In terms of Cd2+, it is difficult to observe minor\nenhancement due to the excessively rapid adsorption rate (< 10 min). Then, we fitted the\nkinetic curves of the newly added initial concentrations using both the pseudo-first-order\nand pseudo-second-order kinetic models. The results as shown in Fig. C and Table B,\nindicate that all curves exhibit excellent fits with the pseudo-second-order kinetic model\n(R2 ≈ 1), demonstrating that the adsorption processes follow chemical adsorption\nmechanisms. These results are consistent with kinetics in manuscript (Fig. 2d,\nSupplementary Fig. 20‒23, and Supplementary Table 6).\nFig. 6 (a) The adsorption kinetic of LDO in As and As/Cd = 100/200 mg L‒1.\nFig. C The Pseudo-first-order and Pseudo-second-order kinetic fitting plots of As/Cd in different\ninitial concentration As/Cd solution on LDO (As/Cd = 50/300, 100/300 and 200/300 mg L‒1).\nTable B Kinetics model parameters of AsIII and Cd2+ adsorbed onto LDO (AsIII/Cd2+ = 50/300,\n100/300, and 200/300 mg L‒1).\nPseudo-first-order model Pseudo-second-order model\nQ (mg g‒1) k (h‒1) R2 Q (mg g‒1) k (g h‒1 mg‒1) R2\ne,cal 1 e,cal 2\nAs (As/Cd = 50/300) 2.4866 0.32 0.0926 110.01 2.38×1013 1\nAs (As/Cd = 100/300) 2.5835 0.34 0.1014 110.01 1.12×103 1\nAs (As/Cd = 200/300) 26.1134 1.03 0.8045 110.86 0.30 0.9999\nCd (As/Cd = 50/300) 23.5226 1.09 0.4878 310.56 0.47 0.9999\nCd (As/Cd = 200/300) 19.8426 1.04 0.4593 310.56 0.64 0.9999\nFig. 2 (d) The sorption kinetics of As and Cd in different As/Cd initial concentration.\nSupplementary Fig. 20 The Pseudo-first-order kinetic fitting plots of As in different initial\nconcentration As/Cd solution on LDO (As/Cd = 100/50 and 100/100 mg L‒1).\nconcentration As/Cd solution on LDO (As/Cd = 100/500 and 100/600 mg L‒1).\nSupplementary Fig. 22 The Pseudo-second-order kinetic fitting plots of As in different initial\nconcentration As/Cd solution on LDO (As/Cd = 100/50 and 100/100 mg L‒1).\nSupplementary Fig. 23 The Pseudo-second-order kinetic fitting plots of Cd in different initial\nconcentration As/Cd solution on LDO (As/Cd = 100/500 and 100/600 mg L‒1).\n(AsIII/Cd2+ = 100/50, 100/100, 100/500, and 100/600 mg L‒1).\nPseudo-first-order model Pseudo-second-order model\nQe,cal (mg g‒1) k1 (h‒1) R2 Qe,cal (mg g‒1) k2 (g h‒1 mg‒1) R2\nAsIII (AsIII/Cd2+ = 100/50) 51.66 0.5891 0.9514 100.91 0.0618 0.9978\nAsIII (AsIII/Cd2+ = 100/100) 28.53 0.5621 0.8450 100.60 0.1690 0.9998\nCd2+ (AsIII/Cd2+ = 100/500) 130.72 1.0164 0.7385 507.61 0.0285 0.9998\nCd2+ (AsIII/Cd2+ = 100/600) 507.11 0.8668 0.9348 636.94 0.0048 0.9941\nPage 21 Line 378 in manuscript: “The presence of Cd2+ significantly enhances\nthe adsorption rate of LDO for AsIII (Fig. 6a). When LDO is used alone for AsIII\nadsorption (C = 100 mg L⁻¹), it takes 7 h to reach adsorption equilibrium. Surprisingly,\n0\nwhen the introduction of Cd2+ (200 mg L‒1), the adsorption of AsIII by LDO reaches\nequilibrium in just 10 min. The adsorption rate constant (k) increases from 0.0183 to\n3.3200 g h‒1 mg‒1 (Supplementary Fig. 61‒62 and Supplementary Table 13),\nrepresenting an approximately 181‒fold enhancement. This phenomenon can be\nattributed to increased oxidation rate and diffusion rate.”\nPage 7 Line 137 in manuscript: “The adsorption of both AsIII and Cd2+ are\nchemical, with intraparticle diffusion controlling rate, supported by kinetics and fittings.\nA series of concentrations were used to fit the adsorption process. Specifically, the\ninitial concentration of AsIII remain unchanged and the initial concentration of Cd2+ is\n= 50, 100, 200, 300, 400, 500 and 600 mg L‒1.”\nPage 7 Line 141 in manuscript: “All adsorption process follows pseudo-second-\norder kinetics, with an excellent fit indicated by an R2 value (> 0.99) (Fig. 2d and\nSupplementary Fig. 19‒23 and Supplementary Table 6).”\n2. In the kinetic fitting section of section 1.6, the authors mention that the\nadsorption rate of AsIII/Cd2+ by LDO is extremely fast, so the initial concentration\n46\nof the mixed solution was reduced. It is recommended that the authors add the\ninitial concentration of the reset co-adsorption kinetic test.\nAuthor Response:\nThank you for your good suggestions. As you suggested, we added a series of\ninitial concentrations (AsIII/Cd2+ = 50/300, 100/300 and 200/300 mg L‒1) in the kinetic\nsection to verify the adsorption trend. Additionally, we fitted the kinetic curves of the\nnewly added initial concentrations using both the pseudo-first-order and pseudo-\nsecond-order kinetic models. The results, as shown in Fig. C and Table B, indicate that\nall curves exhibit excellent fits with the pseudo-second-order kinetic model (R2 ≈ 1),\ndemonstrating that the adsorption processes follow chemical adsorption mechanisms.\nThese findings align with the results for other initial concentrations presented in\nmanuscript, confirming that varying the initial concentrations of AsIII/Cd2+ does not\nalter the adsorption trend or mechanism (Fig. 2d, Supplementary Fig. 20‒23, and\nSupplementary Table 7).\nFig. 2 (d) The sorption kinetics of As and Cd in different As/Cd initial concentration.\ninitial concentration As/Cd solution on LDO (As/Cd = 50/300, 100/300 and 200/300 mg L‒1).\nTable B. Kinetics model parameters of AsIII and Cd2+ adsorbed onto LDO (AsIII/Cd2+ = 50/300,\n100/300, and 200/300 mg L‒1).\nPseudo-first-order model Pseudo-second-order model\nQ (mg g‒1) k (h‒1) R2 Q (mg g‒1) k (g h‒1 mg‒1) R2\ne,cal 1 e,cal 2\nAs (As/Cd = 50/300) 2.4866 0.32 0.0926 110.01 2.38×1013 1\nAs (As/Cd = 100/300) 2.5835 0.34 0.1014 110.01 1.12×103 1\nAs (As/Cd = 200/300) 26.1134 1.03 0.8045 110.86 0.30 0.9999\nCd (As/Cd = 50/300) 23.5226 1.09 0.4878 310.56 0.47 0.9999\nCd (As/Cd = 100/300) 21.8356 1.07 0.4758 310.56 0.54 0.9999\nCd (As/Cd = 200/300) 19.8426 1.04 0.4593 310.56 0.64 0.9999\nPage 7 Line 137 in manuscript: “The adsorption of both AsIII and Cd2+ are\nchemical, with intraparticle diffusion controlling rate, supported by kinetics and fittings.\nA series of concentrations were used to fit the adsorption process. Specifically, the\ninitial concentration of AsIII remain unchanged and the initial concentration of Cd2+ is\n= 50, 100, 200, 300, 400, 500 and 600 mg L‒1.”\nPage 7 Line 141 in manuscript: “All adsorption process follows pseudo-second-\norder kinetics, with an excellent fit indicated by an R2 value (> 0.99) (Fig. 2d and\nSupplementary Fig. 19‒23 and Supplementary Table 7).”\n3. In the adsorption of other coexistence systems, the authors generally set the\ninitial concentration of Cd2+ solution to be twice the initial concentration of AsIII\nsolution. However, in section 1.13, the initial concentration of AsIII/Cd2+ mixed\nsolution, the authors set it to be the same or the initial concentration of AsIII\nsolution is greater than the initial concentration of Cd2+ solution, what is the basis\nfor the selection of the concentration in this experiment?\n3.1 Cd2+ concentration is higher than AsIII, which is twice the initial concentration of\nAsIII.\nAs shown in the adsorption isotherm experiment (Fig. 2c), the four-level\ntopological transition resulted in an exceptionally high Cd2+ adsorption capacity of\n1895.6 mg g‒1, approximately twice that of AsIII (821.7 mg g‒1). Consequently, the\ninitial concentrations of AsIII/Cd2+ were standardized to 100/200 mg L‒1 in subsequent\nexperimental conditions.\nFig.2 (c) The removal capacity of LDO for As and Cd in single and co-contaminated system.\nPage 7 Line 125 in manuscript: “Unexpectedly, although the solution pH value\nincreased with adding LDO calcined at 350 ℃ (Supplementary Fig. 1‒4), the maximum\nadsorption capacity for AsIII can reach 821.7 mg g⁻1, which is five times the current\nhighest value (Starch‒FeMnO , 161.29 mg g⁻1) 30; and for Cd2+ reach 1895.6 mg g⁻1,\nx\nwhich is three times the current highest value (graphene/δ‒MnO , 644 mg g⁻1) (Fig.\n2\n2a‒2b, Supplementary Fig. 5‒8 and Supplementary Table 2‒3) 39. More importantly,\nthese values are higher than the adsorption capacities of LDO for treating AsIII (691.6\nmg g⁻1) and Cd2+ (1723.1 mg g⁻1) individually (Fig. 2c). This anomaly indicates that\nAsIII and Cd2+ become triggers for mutually enhancing adsorption performance.”\n49\n3.2 AsIII concentration is same or the greater than the Cd2+.\nTo standardize the initial concentrations of AsIII/Cd2+, several additional\nconcentration levels (10/20, 20/40, 50/100, 100/200, 200/400, and 500/1000) were\nadded for investigation, and it was found that they had no impact on the experimental\nresults. The results are shown in Supplementary Fig. 48, the characteristic (003) peak\ngradually shifted toward lower angles with increasing initial concentration of AsIII.\nAccording to Braggˈs law, we calculated the interlayer spacing, as the initial AsIII\nconcentration increased from 10 to 200 mg L‒1, the interlayer spacing progressively\nexpanded from 0.7271 to 0.7650 nm. This tendency is consistent with the results of\nmanuscript. Therefore, to maintain consistency in concentration selection throughout\nthe paper, the original concentrations and data were revised, as shown in Fig. 4g.\nSupplementary Fig. 48 The XRD patterns in different initial As/Cd concentration (C =\n0(AsIII/Cd2+)\n10/20, 20/40, 50/100, 100/200, 200/400, and 500/1000).\nconcentration in co-contamination system.\nPage 14 Line 267 in manuscript revised: “As locates in LDH interlayers, shown\nby increased interlayer spacing with higher adsorption capacity. Fig. 4g shows Cd-\nLDH(AsIII/Cd2+) interlayer spacing increased from 0.74 to 0.78 nm as time extended 0‒\n12 h, with adsorption capacity rising from 0 to 99.7 mg g‒1 (Supplementary Fig. 46);\nsimultaneously, spacing increased from 0.73 to 0.77 nm as AsIII concentration rose 10‒\n500 mg L‒1, with capacity up to 389 mg g‒1 (Supplementary Fig. 47‒48).”\n4. Why is the initial concentration of co-adsorbed AsV/Cd2+ in section 1.15 not\nconsistent with the co-adsorbed AsIII/Cd2+ concentration gradient in the previous\nsection 1.5?\nAuthor Response:\nThe concentration disparity between AsV/Cd2+ and AsIII/Cd2+ systems is rooted in\npreventing premature AsV-Cd2+ precipitation, which is critical for enabling LDO to\ndrive ultra-stable mineralization rather than spontaneous precipitation. The rationale is\nstructured as follows:\nAsIII is neutral form and exists as H AsO , showing weak interaction with Cd2+,\n3 3\n51\nallowing higher Cd2+ (200 mg/L) without precipitation. In contrast, AsV is anionic form\nand dissociates into H AsO ⁻/HAsO 2⁻ (pK ≈ 2.3, pK ≈ 6.8, pK ≈ 11.6) (Int. J.\n2 4 4 a1 a2 a3\nAnal. Chem. 2019, 1, 3280840), forming insoluble Cd (AsO ) or related\n3 4 2\nhydroxy/hydrated compounds (Chem. Eng. J., 2021, 424, 130410; Sci. Total Environ.,\n2019, 666, 956-963) with Cd2+. This precipitation occurs rapidly at high Cd2+, which\ninterferes with LDO’s adsorption-driven mineralization. Thus, during AsV/Cd2+\nsolution preparation, these compounds are difficult to dissolve, it is necessary to adjust\nCd2+ initial concentration.\nPage 18 Line 319 in manuscript insert: “The topological transformation from\nLDO to Cd-LDH(AsIII/Cd2+) is accompanied by the intercalation of AsIII and/or AsV\nand multi-site coordination, which is key to enhancing the removal capacity of AsIII.\nThe adsorption capacities of 821.8 mg g‒1 for AsIII/Cd2+ and 240.0 mg g‒1 for AsV/Cd2+,\nrespectively (Supplementary Fig. 55). Note that AsV/Cd2+ solution need Cd2+\nconcentration adjustment due to poor solubility.”\n5. When exploring the effects of pH and salt ions on LDO coadsorption in Sections\n1.16 and 1.17, the initial concentrations of AsIII/Cd2+ solutions did not remain\nconsistent; what is the reason for the discrepancy? In Section 1.18, information on\nthe initial concentration of AsIII/Cd2+ solutions and the amount of LDO added is\nnot given.\nAuthor Response:\n5.1 To standardize the initial concentrations of AsIII/Cd2+, several additional\nconcentration levels (100/50, 100/100, and 100/200) were added for investigation, and\nit was found that they had no impact on the AsIII/Cd2+ adsorption capacity. All\nexperimental data demonstrate AsIII removal efficiencies exceeding 98%, while\ncomplete (100%) Cd2+ removal is consistently achieved. Therefore, to maintain\nconsistency in concentration selection throughout the paper, the original concentrations\nand data were revised, as shown in Supplementary Fig. 9‒12.\nand 7.44) environment in As/Cd co-contaminated system.\nSupplementary Fig. 10 The metal ions Cd removal rate of different pH (2.63, 3.91, 4.98, 5.86, 6.68,\nand 7.44) environment in As/Cd co-contaminated system.\nSupplementary Fig. 12 The Cd removal rate in different salts.\nPage 7 Line 133 in manuscript revise: “In addition, the structure of LDO is stable,\nand its removal efficiency for AsIII/Cd2+ is independent of pH value, coexisting salts,\nand metal ions (Supplementary Fig. 9–18 and Supplementary Table 4‒5).”\nPage S13 Line 251 in Supplementary Information revise: “To simulate the\nadsorption performance of heavy metals AsIII/Cd2+ in acidic wastewater, 0.10 g of LDO\nadsorbent was added to 100 mL of an AsIII/Cd2+ composite solution (initial\nconcentration: 100/200 mg L‒1) under varying pH conditions (2.63, 3.91, 4.98, 5.96,\n6.68, and 7.44).”\nindustrial wastewater matrices, competitive adsorption experiments were conducted\nwith 0.10 g LDO in 100 mL co-contaminated solution (AsIII/Cd2+ = 100/200 mg L‒1)\ncontaining 100 mg L‒1 of representative salts: sulfate (SO 2‒), silicate (SiO 2‒), chloride\n4 3\n(Cl‒), and carbonate (CO 2‒).”\n3\n5.2 In Section 1.18, the initial concentration of AsIII/Cd2+ solutions and the amount of\nLDO added is 100/200 mg L‒1 and 0.10 g.\nPage S14 Line 268 in Supplementary Information revise: “1.18 Effect of metal\nions on AsIII/Cd2+ adsorption experiment details.\nThe solution of Cu2+, Ni2+, and Zn2+ used in this experiment was prepared from\nCu(NO ) , Ni(NO ) , and Zn(NO ) , respectively. The initial concentration for Cu2+,\n3 2 3 2 3 2\nNi2+, and Zn2+ was 100 mg L‒1. 0.10 g of LDO adsorbent was added to 100 mL of an\nAsIII/Cd2+ composite and other ions solution (initial concentration: 100/200 mg L‒1).\nAll the concentrations in aqueous solution were determined by ICP-OES.”\n6. The test in “Supplementary Fig. 2” is not given in the method? What is the initial\nAs/Cd concentration and the amount of material applied for this test?\nAuthor Response:\nThank you for identifying the omissions, which significantly contributes to perfect\nour experimental detail.\n6.1 We have added the missing experimental methods into the Supplemental\nInformation.\nPage S14 Line 275 in Supplementary Information inset: “The adsorption\ndetails of LDO under different calcined temperature in AsIII/Cd2+.\nTo investigate the effect of calcination temperature on adsorption performance, 0.1\ng of LDO was added to 100 mL of a co-contaminated aqueous solution (AsIII/Cd2+ =\n100/200 mg L‒1). The mixture was agitated for 2 h to attain adsorption equilibrium.\nSubsequently, the supernatant was filtered through a 0.22 μm membrane filter. The\nresidual ion concentrations in the filtrate were quantified by ICP-OES, enabling the\n55\ncalculation of adsorption efficiency.”\n6.2 the initial AsIII/Cd2+ concentration is 100/200 mg L‒1, and the amount of LDO is 1g\nL‒1. The corresponding content is inserted Page S14 Line 275 in Supplementary\nInformation.\nSupplementary Fig. 3 The As removal rate of calcine production in different temperature (200,\n250, 350, 450, 550, and 650℃) in As/Cd solution.\nResponses to Reviewer 3\nOverview: This manuscript provides a strategy for the simultaneous remediation\nof AsIII/Cd2+ co-contaminated systems under neutral conditions from the water\nmatrix by layered double metal oxide (LDO) with the thermal topotactic\ntransformation of LDH, achieving 821.7 and 1895.6 mg/g maximum adsorption\ncapacities, respectively. This breakthrough addresses the longstanding challenges\nof low adsorption capacity and sluggish kinetics in coexisting heavy metal systems.\nIt is a promising material for the removal of coexisting heavy metals.\nIt is a topic of interest to researchers in the related areas, but there are some\nproblems that must be solved before it is considered for publication. My detailed\ncomments are as follows:\nAuthor Response:\nwith our material of MgMn-LDO is a promising material for coexisting heavy metal\nchallenges. Your comments are greatly helpful for improving the quality of our\nmanuscript. Therefore, we will reply to your questions one by one.\n1. In the Introduction, add a comparison between LDO and existing\nnanocomposites (e.g., iron-manganese oxides, graphene nanotubes) between the\nthird and fourth sentences. This addition can strengthen the logical coherence of\nthe introduction.\nAuthor Response:\nThank you very much for your good comments. As you suggested, we have added\nsome related content and reference. For example, a demonstrated by Zhang et al.\n(Environ. Sci. Technol. 2014, 48, 10316−10322), their bimetallic oxide system revealed\ndistinct functional partitioning: FeOOH exclusively served as an adsorbent, forming\nbidentate binuclear corner-sharing complexes with AsIII, while MnO primarily acted\nx\nas an oxidant that catalytically converted AsIII to AsV, with resultant MnOOH further\npropagating oxidative transformation. In parallel, graphene nanotube architectures have\nemerged as advanced arsenic remediation platforms. Notably, Luan et al. (ACS Appl.\nMater. Interfaces 2018, 10, 20467−20477) sputtered Cu onto carbon nanotube films,\nforming ultra-stable and highly permeable composite materials. Within this system,\ncatalytically active Cu nanoparticles mediate AsIII oxidation, enabling subsequent\nchemisorption of AsV onto copper hydroxide surfaces.\nPage 5 Line 94 in manuscript insert: “Conventional materials such as iron-\nmanganese oxides and graphene nanotubes exhibit adsorption capacities for AsIII rarely\nexceeding 100 mg g‒1 due to their limited active sites 32,33.”\nThe order of references has been revised.\n32. Zhang, G. S. et al. Respective Role of Fe and Mn Oxide Contents for Arsenic\nSorption in Iron and Manganese Binary Oxide: An X‑ray Absorption Spectroscopy\n33. Luan, H. Y. et al. As(III) Removal from Drinking Water by Carbon Nanotube\nMembranes with Magnetron-Sputtered Copper: Performance and Mechanisms. ACS\nAppl. Mater. Interfaces 10, 20467−20477 (2018).\n2. In the AsⅢ and Cd2+ shifted from remediation targets to mutual adsorption\nenhancers section, it is necessary to increase the pH changes of LDO in water and\nthe quantitative leaching data of LDO under acidic/alkaline conditions at\nSupplementary Figs. 7–11.\nAuthor Response:\nThank you for your comments. The environmental release of toxic metals from\nadsorbents may cause secondary pollution; therefore, your suggestion is crucial for\nevaluating the environmental safety profile of our material. As you suggested, we have\nsupplemented relevant experimental data as detailed below:\n2.1 The pH changes of LDO in water\nAs suggested, we have supplemented pH value for LDO aqueous suspensions over\ntime. The results are shown in Supplementary Fig. 1, the initial pH value of deionized\nwater is 6.29. As LDO is a complex bimetallic oxide, the hydrolysis process releasing\na large amount of OH‒. Therefore, the strong alkalinity (pH = 10.73) was exhibited\nwhen LDO was initially put into water. However, the pH decreased to 10.44 when the\nreaction time extended to 8 h. This phenomenon is likely attributed to the dissolution\nof atmospheric CO , which forms carbonic acid that progressively neutralizes OH⁻ ions.\npH decline.\nPage S21 in Supplementary Information insert:\nPage 7 Line 125 in manuscript revise: “Unexpectedly, although the solution pH\nvalue increased with adding LDO calcined at 350 ℃ (Supplementary Fig. 1‒4), the\nmaximum adsorption capacity for AsIII can reach 821.7 mg g⁻1, which is five times the\ncurrent highest value (Starch‒FeMnO , 161.29 mg g⁻1) 30; and for Cd2+ reach 1895.6\nx\nmg g⁻1, which is three times the current highest value (graphene/δ‒MnO , 644 mg g⁻1)\n2\n(Fig. 2a‒2b, Supplementary Fig. 5‒8 and Supplementary Table 2‒3) 39.”\n2.2 The ions leaching from LDO layer\nAccording to your recommendation, we have further quantified the leaching\nexperimental of Mg2+/Mn3+/4+ ions under different pH, salts, and co-existing metal ions.\nThe results as following:\nIn the pH-dependent adsorption experiment, when the pH is 2.65, Mg2+ leaching\nincreased significantly, attributed to partial neutralization between the alkaline LDO\nframework and strong acidity, when the pH increased, the concentration of Mg2+\nleaching remained 50‒70 mg L‒1 (Supplementary Fig. 15a). In contrast, the Mn3+/4+\ncontent in solution remained consistently very low constant value (approximately zero),\nindicating negligible Mn leaching from the layered framework.\nIn the salt (Na SO , NaSiO , NaCl, and NaCO ) and co-existing metal ions (Ni2+,\n2 4 3 3\nCu2+, and Zn2+) adsorption experiments, Mg2+ leaching consistently ranged between\n50‒70 mg L‒1 (Supplementary Fig. 15b‒c) due to the isomorphous substitution of Cd2+.\nCrucially, Mn3+/4+ leaching remained negligible across all conditions (approximately\n59\nzero). These findings collectively demonstrate the applicability of our material in actual\nwastewater matrices and soil environments without secondary contamination risks.\nPage S28 in Supplementary Information insert:\nSupplementary Fig. 15 The leaching amount of Mg/Mn ions in As/Cd adsorption: (a) different pH;\n(b) different salt species; (c) different metal ions (C = 100/200 mg L‒1).\n0(As/Cd)\nPage 7 Line 133 in manuscript revise: “In addition, the structure of LDO is stable,\nand its removal efficiency for AsIII/Cd2+ is independent of pH value, coexisting salts,\nand metal ions (Supplementary Fig. 9–18 and Supplementary Table 4‒5).”\n3. In the Prior oxidation of AsⅢ triggers topological transformation from LDO to\nLDH, changing Cd2+ adsorption pathway section, please prove that the hydrated\nLDH here contains Cd2+ and how to prove that it is CdMgMn-LDH in the case of\ncondition 2. Also, in order to prove that the LDH after hydration of AsⅢ should be\ncompared with the LDH after hydration of pristine LDO, and that there is a lattice\nshift in order to prove the restoration of AsⅢ to the LDH.\nAuthor Response:\nThank you for your good comments. Your insightful suggestion has significantly\nenhanced our mechanistic understanding of Cd2+ isomorphous substitution for Mg2+\nwithin the layered structure.\n3.1 The evidence of Cd element existing in hydrated LDH\nHR-TEM/ICP analyses confirmed Cd element existing in the adsorbent, where at\n10 min adsorption, solid-phase Mg2+ and Cd2+ concentrations measured 188.76 and\n98.68 mg L‒1 respectively, when the adsorption time reached 30 min, the content of\nMg2+ decreased to 165.56 mg L‒1 and the content of Cd2+ increased to 164.68 mg L‒1\n(Supplementary Fig. 45), demonstrating progressive Mg2+ leaching coupled with Cd2+\nsubstitution into the layered lattice. Concurrent HR-TEM elemental mapping also\nverified the existing of Cd element (Fig. 4d‒e).\nPage S40 in Supplementary Information insert:\ntime.\nFig. 4 (d‒e) TEM-EDS elemental mapping and HRTEM results of Mg/Cd ions mass fraction in\ndifferent As/Cd adsorption time (10 and 30 min).\nPage 14 Line 260 in manuscript revise: “This topological shift alters Cd2+\nadsorption from surface ligand exchange to LDH lattice substitution, as confirmed by\ntime-resolved TEM mapping (Fig. 4d‒4e) and ICP (Supplementary Fig. 45). Mg2+ in\nCd-LDH(AsIII/Cd2+) decreased from 23.29% to 8.97%, whereas Cd2+ increased from\n15.71% to 31.04%, indicating Cd2+ replaces the Mg2+ via isomorphous substitution with\nMg2+ leaching.”\n61\n3.2 The evidence for CdMgMn-LDH formation in the case of condition 2\nFirstly, the formation of LDH can be confirmed by XRD. As shown in Fig. 4b,\nafter AsIII/Cd2+ adsorption, the peaks at 11.6°, 22.9°, 34.4°, and 59.5° exclusively\ncorrespond to (003), (006), (009), and (110) planes of LDH, with no impurity phases,\nverified the formation of LDH purity phase. Subsequent ICP analyses confirmed Cd2+\nexisting in the adsorbent, and progressive Mg2+ leaching coupled with Cd2+ substitution\ninto the layered lattice (Supplementary Fig. 45). Concurrent HR-TEM elemental\nmapping verified homogeneous Mg2+/Cd2+ distribution throughout the lamellar\nstructure, with atomic percentages shifting from 23.29% Mg2+ and 15.71% Cd2+ at 10\nmin to 8.97% Mg2+ and 31.04% Cd2+ at 30 min (Fig. 4d‒e), collectively confirming\nphase-pure CdMgMn-LDH formation. At the same time, after oxidative adsorption of\nAsIII on LDH (AsIII), the Gibbs free energy changes (ΔGs) for the isomorphous\nsubstitution of each Mg2+ cation by each Cd2+ cation are all smaller than 0 eV (Fig. 4h),\nindicating that the isomorphous substitution of Mg2+ in LDH(AsIII) to Cd2+ can happen\nspontaneously.\nFig. 4 (b) adsorption of As first, followed by adsorption of Cd; and (c) simultaneous adsorption (#\nrepresent Cd(OH) ; * represent (003) characteristic peak of LDH).\n2\ntime.\nFig. 4 (d‒e) TEM-EDS elemental mapping and HRTEM results of Mg/Cd ions mass fraction in\ndifferent As/Cd adsorption time (10 and 30 min).\nFig. 4 (h) Gibbs free energy diagram for the isomorphous substitution of Mg by Cd in LDH(AsIII)\nwith geometries of representative intermediates displayed.\nPage 14 Line 252 in manuscript: “Adsorption solids at 1 and 2 h (Fig. 4a‒4c):\nCondition 1 showed only Cd(OH) peaks at 2θ = 18.8, 29.7, 35.5, 38.1, 49.3, 56.2, 59.1°\n2\n63\n(Supplementary Fig. 40). Conition 2 showed LDH peaks 2θ = 11.3, 22.3, 34.7, 38.2,\n59.3, 60.1°: AsIII restores LDO to LDH (Supplementary Fig. 41‒42), with Cd2+\nincorporating into LDH lattice without altering its layered structure. Condition 3 solids\nmatched 2, meaning simultaneous AsIII/Cd2+ generates stable LDH. Cd2+ did not affect\nAsIII adsorption (Supplementary Fig. 43‒44). Results confirm co-adsorption: AsIII\noxidation precedes Cd2+ adsorption, triggering LDO-to-LDH transformation.”\nPage 14 Line 260 in manuscript revise: “This topological shift alters Cd2+\nadsorption from surface ligand exchange to LDH lattice substitution, as confirmed by\ntime-resolved TEM mapping (Fig. 4d‒4e) and ICP (Supplementary Fig. 45). Mg2+ in\nCd-LDH(AsIII/Cd2+) decreased from 23.29% to 8.97%, whereas Cd2+ increased from\n15.71% to 31.04%, indicating Cd2+ replaces the Mg2+ via isomorphous substitution with\nMg2+ leaching.”\nPage 15 Line 275 in manuscript: “As shown in Fig. 4h, after oxidation of AsIII\non LDH (AsIII), the ΔGs for the isomorphous substitution of each Mg2+ cation by each\nCd2+ cation are all smaller than 0 eV, indicating this process is spontaneous.”\n3.3 The lattice shift from the LDH after hydration of pristine LDO to LDH after\nhydration of AsⅢ.\nLattice resolution images of hydrated LDO (LDO(H)) versus post-adsorption Cd-\nLDH(As/Cd), revealing distinct lattice expansions from 0.21 nm in LDO(H) to 0.27 nm\n(Fig. 3f) in Cd-LDH(As/Cd) (Fig. 7b). This might attribute to Mn-As interactions\nredirecting Cd2+ adsorption toward isomorphous substitution within LDH layers, where\nlarger ionic radius Cd2+ displaces Mg2+ lead to lattice expansion.\nFig. 3 (f) HR‒TEM images and of LDO(H).\nPage 11 Line 206 in manuscript revise: “In addition, microscopic changes show\noxygen vacancies/clusters (Fig. 3d–3f and Supplementary Fig. 31–33). LDH has\nirregular hexagonal nanosheets (40‒80 nm radial, ~20 nm thick). Calcination preserved\nmorphology; hydrolysis distorted LDO(H) into thinner flakes. LDO’s 0.15 nm smaller\nlattice spacing (vs. LDH) indicates topological rearrangement, exposing defects to\naffect hydrolysis 52.”\nPage 24 Line 421 in manuscript insert: “HRTEM shows lattice expansion (from\n0.21 to 0.27 nm, Fig. 7b) and time-dependent growth (from 0.205 to 0.211 nm,\nSupplementary Fig. 63) 64. Increased spacing reduces AsIII diffusion resistance,\nboosting its rate.”\n4. In the Prior oxidation of AsⅢ, triggers topological transformation from LDO to\nLDH, changing Cd2+ adsorption pathway section, the data proved insufficient.\nTables or graphs, supplementary data Q on SI on the last sentence of the first\ne\nparagraph and the fourth sentence of the third paragraph here\nAuthor Response:\nThank you for your comments. As you suggested, the relevant Q data have been\ne\nadded to the Supplementary Information.\n4.1 The last sentence of the first paragraph in manuscript\nAs you suggested, we added the AsIII adsorption capacity in AsIII/Cd2+ co-\ncontaminate under different initial concentration and adsorption time.\nFig. 46. When the adsorption time reach at 10 min, the adsorption capacity achieves\n99.1 mg L‒1 (99.1%) in the AsIII/Cd2+ initial concentration is 100/200 mg L‒1. At this\nstage, the interlayer spacing gradually expands due to AsIII intercalation, which are\nconsistent with experimental data of interlayer expansion in the Fig. 4g.\nSecondly, the AsIII adsorption capacity of different initial concentration as shown\nin Supplementary Fig. 47. When the initial concentration of AsIII increased from 10 to\n500 mg L‒1, the adsorption capacity from 9.99 to 389 mg g‒1. At this stage, the interlayer\nspacing gradually expands due to AsIII intercalation, which are consistent with\nexperimental data of interlayer expansion in the Fig. 4g.\nSupplementary Fig. 46 The adsorption capacity of AsIII in different adsorption time under\nAsIII/Cd2+ co-contaminated system.\nFig. 4 (g) The interlayer spacing of Cd-LDH (As/Cd) in different adsorption time and initial As\nconcentration in co-contamination system.\nPage 14 Line 267 in manuscript revise: “As locates in LDH interlayers, shown\nby increased interlayer spacing with higher adsorption capacity. Fig. 4g shows Cd-\nLDH(AsIII/Cd2+) interlayer spacing increased from 0.74 to 0.78 nm as time extended 0‒\n12 h, with adsorption capacity rising from 0 to 99.7 mg g‒1 (Supplementary Fig. 46);\nsimultaneously, spacing increased from 0.73 to 0.77 nm as AsIII concentration rose 10‒\n500 mg L‒1, with capacity up to 389 mg g‒1 (Supplementary Fig. 47‒48).”\n4.2 The fourth sentence of the third paragraph in manuscript\nenhances adsorption capacity of AsIII. As shown in Fig. 2c, the maximum adsorption\ncapacity for AsIII can reach 821.7 mg g‒1, and for Cd2+ reach 1895.6 mg g‒1, which is\nsignificantly higher than the highest value reported in the current literature. The high\nadsorption capacity is contributed to the four-level topological transformation of LDH\n→ Cd-LDH(As/Cd). \nFig.2 (c) The removal capacity of LDO for As and Cd in single and co-contaminated system.\nPage 7 Line 125 in manuscript: “Unexpectedly, although the solution pH value\nincreased with adding LDO calcined at 350 ℃ (Supplementary Fig. 1‒4), the maximum\nadsorption capacity for AsIII can reach 821.7 mg g⁻1, which is five times the current\nhighest value (Starch‒FeMnO , 161.29 mg g⁻1) 30; and for Cd2+ reach 1895.6 mg g⁻1,\nx\nwhich is three times the current highest value (graphene/δ‒MnO , 644 mg g⁻1) (Fig.\n2\n2a‒2b, Supplementary Fig. 5‒8 and Supplementary Table 2‒3) 39. More importantly,\nthese values are higher than the adsorption capacities of LDO for treating AsIII (691.6\nmg g⁻1) and Cd2+ (1723.1 mg g⁻1) individually (Fig. 2c). This anomaly indicates that\nAsIII and Cd2+ become triggers for mutually enhancing adsorption performance.”\n5. In the Prior oxidation of AsⅢ triggers topological transformation from LDO to\nLDH, changing Cd2+ adsorption pathway section, the textual description in the\nthird paragraph should follow after the XPS isovalent state-related\ncharacterisation, otherwise it would not be possible to account for the electron\ntransfer of AsⅢ and Mn4+.\nAuthor Response:\nThank you for your comments. Your insightful suggestions have better delineated\nthe AsIII-Mn4+ electron transfer in the manuscript, enhancing the structural coherence.\nDue to space constraints, we have combined the content from two sections to make the\ndescription of electron transfer more concise.\nPage 17 Line 297 in manuscript revise: “The electron transfer from AsIII to Mn4+\nduring adsorption, forming AsV and Mn3+, as confirmed by XPS and XANES. For As,\npost-adsorption Cd-LDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9\neV (AsV, Fig. 5a); LDO raised AsV to 53.8% (vs. LDH’s 18.0%), showing stronger\noxidation 54, which also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR and\nin-situ Raman (Supplementary Fig. 49‒51). For Mn, XPS shows Mn 2p peaks at 643.1\nand 653.8 eV (Mn3+) (Fig. 5b); its proportion in Cd-LDH(AsIII/Cd2+) (84.0%) exceeds\nLDO’s 35.9%, confirming Mn4+ reduction with AsIII oxidation, as confirmed by\nXANES. Cd-LDH(AsIII/Cd2+) has a 1.02 eV lower Mn K-edge (lower oxidation state)\nand an As K-edge 11874 eV peak (AsV, Supplementary Fig. 52‒53), verifying electron\ntransfer 55.”\n6. Prior oxidation of AsⅢ triggers topological transformation from LDO to LDH,\nchanging the Cd2+ adsorption pathway section, which cannot account for proton\ninsertion in the last sentence of the fifth paragraph.\nAuthor Response:\nThank you for your comment. We apologize for the inaccuracy in describing\nproton insertion, this has been corrected in the manuscript:\nPage 18 Line 317 in manuscript revised: “The reduction of Mn4+ triggers\n7. In the Prior oxidation of AsⅢ, the topological transformation from LDO to LDH,\nchanging the Cd2+ adsorption pathway section, is the arsenic species on the surface\nin the form of AsO ? Please labeled in the corresponding XRD (e.g. Fig. 4b, c\n4\nand 5c) in the seventh sentence of the sixth paragraph.\nAuthor Response:\nThank you for your comments. AsIII as the target pollutant, is essential for us to\nunderstand the speciation and oxidation states. We will answer question in two parts.\n7.1 The presence formation of AsV that have oxidized is binuclear AsO tetrahedron as\n4\nconfirmed by XAFS results.\nIn Fig. 5a, the results of As 3d XPS verified AsIII of 53.8% have transformed AsV，\ntherefore, the presence formation of AsV that have oxidized is binuclear AsO\n4\ntetrahedron, and the unoxidized AsIII retains its original trigonal pyramidal molecular\ngeometry. The existence of AsO can be verified by XAFS results. As shown in\n1.68 Å after adsorption of AsIII/Cd2+ by LDO, closely consistent with those of the\nAsV/Cd2+ adsorption product (CN = 3.9, R = 1.68 Å) and approach the standard\nNa HAsO reference data (CN = 4.0, R = 1.68 Å). The consistency in CN and R values\n2 4\nof As-O demonstrates tetrahedral coordination of As, providing structural evidence for\nAsIII oxidation during adsorption. (Environ. Sci. Technol. 2012, 46, 986-994; Environ.\nSci. Technol. 2013, 47, 1009−1016; J. Phys. Chem. B 2005, 109, 3227-3232; Appl.\nGeochem. 2013, 38, 110–120.)\nSupplementary Table 11. Local structure parameters around As estimated by EXAFS analysis.\nSample Shell CN R (Å) σ2 (Å2)\nNa2HAsO4 As-O 4.0 1.68 0.0038\nAs-O 4.2 1.68 0.0056\nLDH(AsIII)\nAs-M 1.1 3.23 0.0168\nAs-O 3.9 1.68 0.0022\nLDO(H)(AsV)\nAs-M 1.5 3.24 0.0087\nPage 17 Line 297 in manuscript: “The electron transfer from AsIII to Mn4+ during\nadsorption, forming AsV and Mn3+, as confirmed by XPS and XANES. For As, post-\nadsorption Cd-LDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9 eV (AsV,\nFig. 5a); LDO raised AsV to 53.8% (vs. LDH’s 18.0%), showing stronger oxidation 54,\nwhich also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR and in-situ Raman\n(Supplementary Fig. 49‒51).”\nPage 18 Line 324 in manuscript: “EXAFS probed As coordination: Cd-\nLDH(AsIII/Cd2+) had As−O (1.23 Å, first shell) and As−M (2.80 Å, second shell) bonds\n(Fig. 5d). Its As–O coordination number (4.2) and distance (1.68 Å) matched\nNa HAsO (4.0, 1.68 Å) (Supplementary Table 11), indicating binuclear AsO\n2 4 4\ntetrahedra is thermodynamically favored. These tetrahedra bridge MO octahedra via\n6\n16\ncorner/edge-sharing, boosting stability and electron transfer between AsIII and Mn4+ 57,58.\nThis allows As incorporation into layers (not just surface), increasing sorption capacity\npost-transformation.”\n7.2 The relevant labeled have marked at Fig. 4b‒c and Fig. 5c.\nFig. 4b‒c have been revised according to you suggestion in manuscript:\nFig. 4 XRD patterns of different adsorption process: (b) adsorption of As first, followed by\nadsorption of Cd; and (c) simultaneous adsorption (* represent (003) characteristic peak of LDH).\nFig. 5 (c) XRD patterns of LDO after adsorbing different anions.\n8. Prior oxidation of AsⅢ triggers topological transformation from LDO to LDH,\nchanging the Cd2+ adsorption pathway section. In what way is this ratio (Cd2+:\nMg2+) obtained in the third sentence of the 12th paragraph?\nAuthor Response:\nThank you for your comment. The Cd2+: Mg2+ ratio in the manuscript was\ndetermined via concentration measurements. Specifically, MgMn-LDO solids were\ndigested with HCl and a trace amount of H O (The dissolution kinetics of structural\n2 2\nMn4+ to soluble Mn2+ under acidic conditions are extremely sluggish, necessitating\nH O to rapidly catalyze its reduction to readily soluble Mn2+), followed by\n2 2\n72\nquantification of Mg2+ concentration using ICP analysis. Since Cd2+ was fully adsorbed\neven at elevated concentrations, its concentration was calculated based on the initial\nconcentration of the prepared solution. All relative experimental processes have added\nto Supplementary Information.\nPage S15 Line 284 in Supplementary Information insert:\n1.20 The calculate way of Cd2+: Mg2+ ratio\nThe Cd2+: Mg2+ is the ratio of element concentration. MgMn-LDO solids were\ndigested with HCl and a trace amount of H O (The dissolution kinetics of structural\n2 2\nMn4+ to soluble Mn2+ under acidic conditions are extremely sluggish, necessitating\nH O to rapidly catalyze its reduction to readily soluble Mn2+), followed by\n2 2\nquantification of Mg2+ concentration using ICP analysis. Since Cd2+ was fully adsorbed\neven at elevated concentrations, its concentration was calculated based on the initial\nconcentration of the prepared solution.\n9. In Fig. 4d-4e, while TEM-EDS offers qualitative elemental analysis, it is\nrecommended to complement this with quantitative techniques such as\nInductively Coupled Plasma (ICP) analysis or thermogravimetric analysis to\naccurately determine elemental compositions and validate the material's\nconsistency.\nAuthor Response:\nThank you for your comment. According to your suggestion, ICP data have been\nsupplemented and shown in Supplementary Fig. 45. Cd-LDH(As/Cd) solids obtained\nat different adsorption time (10 and 30 min) were digested with HCl and subjected to\nICP analysis. The results indicated when adsorption time increased from 10 min to 30\nmin, Mg2+ content decreased from 188.76 to 165.56 mg L‒1 while Cd2+ content\nincreased from 98.68 to 164.68 mg L‒1. This trend is consistent with Fig. 4d‒e in\nmanuscript, thereby confirming the isomorphous substitution process of Cd2+.\nPage S40 in Supplementary Information insert:\ntime.\nFig. 4 (d‒e) TEM-EDS elemental mapping and HRTEM results of Mg/Cd ions mass fraction in\ndifferent As/Cd adsorption time (10 and 30 min).\nPage 14 Line 260 in manuscript revise: “This topological shift alters Cd2+\nadsorption from surface ligand exchange to LDH lattice substitution, as confirmed by\ntime-resolved TEM mapping (Fig. 4d‒4e) and ICP (Supplementary Fig. 45). Mg2+ in\nCd-LDH(AsIII/Cd2+) decreased from 23.29% to 8.97%, whereas Cd2+ increased from\n15.71% to 31.04%, indicating Cd2+ replaces the Mg2+ via isomorphous substitution with\nMg2+ leaching.”\n10. Figures should be correctly labeled and clear. For example, ①In Fig. 2e and\n7c, substances in the figure notes should be clearly labeled; ②In Fig. 3j, 4h and\n4i， the meaning of the table is not clear, adding (a)\\Ⅰ\\① and other serial number\nexpression; ③In Fig. 4a-4c, the * and # characteristic peaks need to be clearly\nlabeled in the graphs; ④In Fig. 5a，labelling errors and correcting the\n74\ncorresponding illustrations.\nAuthor Response:\nYour suggestions have been highly valuable for enhancing the quality of our\nfigures. As you suggested, we have implemented corresponding revisions in the figures,\nas detailed below:\n① In Fig. 2e and Fig. 7c, substances in the figure notes have been clearly labeled.\nFig. 2 (e) Weber‒Morris intraparticle diffusion plots of LDO for As/Cd co-contaminated system.\nFig. 7 (c) The schematic diagram of As migration path after Cd replacement.\n② In Fig. 3j, 4h and 4i, serial number expression (I) has been added.\nintermediates displayed (I represent each hydration).\nFig. 4 (h) Gibbs free energy diagram for the isomorphous substitution of Mg by Cd in LDH(AsIII)\nwith geometries of representative intermediates displayed (I represent the number of Mg of the\nMgMn-LDH(As) laminates replaced by Cd). (i) Gibbs free energy diagram for the isomorphous\nsubstitution of Mg by Cd in LDO(H) with geometries of intermediates displayed. As represents AsIII\nand Cd represents Cd2+ in figures (I represent the number of Cd replacing Mg in MgMn-LDO(H)).\n③ In Fig. 4a-4c, the * and # characteristic peaks have been clearly labeled in the graphs.\nFig. 4 XRD patterns of different adsorption process: (a) adsorption of Cd first, followed by\nadsorption of As; (b) adsorption of As first, followed by adsorption of Cd; and (c) simultaneous\nadsorption (# represent Cd(OH) ; * represent (003) characteristic peak of LDH).\n2\n76\n④ In Fig. 5a, the Cd-LDH(As/Cd) was wrongly marked as LDO(As/Cd), the figures\nin the manuscript have been revised.\nFig. 5 (a) The As 3d XPS spectra of Cd-LDH(As/Cd) and LDH(As/Cd).\n11. This is not sufficiently supported; please add the appropriate references. For\nexample, ①on the fifth sentence of the first paragraph in the Bulk hydroxylation\ntopology: water molecule-induced interlayer hydrolysis enables global activation\nof active sites (non-surface dependent) section; ②on the fourth and fifth sentence\nof the eighth paragraph in the Prior oxidation of AsⅢ triggers topological\ntransformation from LDO to LDH, changing Cd2+ adsorption pathway section.\nAuthor Response:\nThank you for your comments. As you suggested, we have incorporated relevant\nreferences into the appropriate sections of the manuscript.\n① To meet the word count requirement for subheadings, we have revised the\nsubheadings to “Bulk hydroxylation topology”. Consequently, the corresponding\nreferences have been added to the main text.\nPage 10 Line 188 in manuscript: “Bulk hydroxylation topology (Topology I\nand II). In the treatment of AsIII/Cd2+ using metal oxides, whether at oxidation sites or\nadsorption sites, the initial chemical reaction involves ligand exchange between\nAsIII/Cd2+ and the ‒OH groups on the surface of the adsorbent 45,46. Thus, the variations\nin the ‒OH groups of LDO was monitored by X-ray photoelectron spectroscopy (XPS,\nOH\n71.8%, far exceeding that of LDH (50.4%) and LDO (36.8%). Meanwhile, the content\nof lattice oxygen (O ) in LDO(H) significantly reduced to 4.8% compared with that of\nL\nconventional LDH (18.7%) and LDO (47.6%) 47. The reason lies in the formation of\nmetal defects and oxygen defects during the transformation of LDH to LDO triggered\nby heat (Topology I) 48,49.”\n48. Ou, G. et al. Tuning defects in oxides at room temperature by lithium reduction.\nNat. Commun. 9, 1302 (2018).\n49. Zheng, J. X. et al. Cationic defect engineering in spinel NiCo O for enhanced\n2 4\nelectrocatalytic oxygen evolution. ACS Catal. 12, 10245-10254 (2022).\n② Page 19 Line 349 in manuscript: “Fig. 5g shows calculated M‒O bond energies:\nAsIII (AsO −) oxidation to AsV (AsO 3−) requires O transfer from LDO, necessitating\n2 4\nM‒O cleavage. Mn‒O (2.49 eV) is weaker than Mg‒O (2.63 eV), so Mn sites favor O\ntransfer and oxidation 59,60.”\n59. Wang, X. Y. et al. Exploring the dynamic evolution of lattice oxygen on exsolved-\nMn O @SmMn O interfaces for NO Oxidation. Nat. Commun. 15, 7613 (2024).\n2 3 2 5\n60. Song, S. N. et al. Modulation mechanism of Mn-O strength in α-MnO catalyst for\n2\nhigh-efficiency catalytic combustion of propane. Appl. Catal. B-Environ. Energy 354,\n124120 (2024).\n12. The description needs to be modified. For example, ①in the Introduction, the\nformats of references and citation styles should be unified; ②In the Prior\noxidation of AsIII triggers topological transformation from LDO to LDH, changing\nCd2+ adsorption pathway section, the Fig. 4i should be indicated in the third\nsentence of the second paragraph.\nAuthor Response:\nThank you for your comments. The corresponding modifications have been\nreflected in the manuscript.\n① The reference format has been revised to the requirements of Nature\n②Page 15 Line 277 in manuscript revise: “In contrast, the ΔGs of isomorphous\nsubstituting Mg2+ in LDO(H) by Cd2+ is larger than 0 eV, demonstrating is\nthermodynamically unfavorable (Fig. 4i).”\n13. The Submission is to be utter improved to make it worthy of publication.\nAuthor Response:\nWe sincerely appreciate your comprehensive feedback, which has significantly\nguided the improvement of our manuscript. In response to your suggestion, we have\nundertaken a thorough revision to enhance the manuscript’s quality for publication.\nResponses to Reviewer 4\nOverview: This study presents a MgMn-layered double oxide (LDO) achieving\nexceptional adsorption capacities for As(III) and Cd2+ in mixed systems. The\nremarkable performance stems from a four-step topological transformation that\neffectively decouples As-oxidation from Cd-uptake processes. While the research\noffers timely and potentially significant contributions to water and soil\nremediation technologies, several issues require attention before publication.\nSpecifically, the manuscript needs improvements in experimental validation\nprotocols, data presentation clarity, and overall structural organization. The\nabsence of page and line numbering in the manuscript made it difficult for me to\nmake more specific comments.\nThe following areas require particular attention from the authors.\nAuthor Response:\nThank you for your comments. We appreciate your positive for our work. As you\nsuggested, the page and line numbering in the manuscript have added. Your comments\nare greatly helpful. As you suggested, all of the changes in the revised manuscript are\nhighlighted in yellow.\n1. Arsenic speciation analysis lacks quantitative solution data. While XPS\nidentifies mixed AsIII/AsV states, HPLC-ICP-MS analysis of both filtrates and\nsolids is needed to properly track AsIII→AsV oxidation kinetics.\nAuthor Response:\nThank you for your comment. As you suggested, we conducted kinetic\nexperiments for AsIII/Cd2+ adsorption by sampling both liquid and solid phases at\ndesignated time intervals for HPLC-ICP-MS detection. Given that adsorption\nequilibrium was reached within 10 min, samples were collected at 1, 3, 5, 7, and 10 min.\nLiquid samples were filtered and diluted prior to analysis. Solid samples (0.005 g) were\ndissolved in 5 mL of dilute hydrochloric acid, diluted, and subsequently analyzed. The\nanalytical results are presented in the Supplementary Fig. 49, where in the initial 100%\nAsIII solution, 35.2% of AsIII is oxidized to AsV within 1 min of adsorption, while 34.5%\nof AsIII remains in the solution. As adsorption progresses, the oxidation of AsIII\ncontinues to increase. Upon reaching adsorption equilibrium at 10 min, the proportion\nof AsV in the solid phase reaches 51.0%, which consistent with the As in XPS data in\nFig. 5a, while almost no AsV remains in the solution. This demonstrates that the\noxidized AsV directly binds to Mn sites in LDH laminate, forming AsV-Mn3+ complexes\nto achieve adsorption.\nSupplementary Fig. 49 HPLC-ICP-MS analysis of (a) Cd-LDH(As/Cd) solid and (b) filtrates in\ndifferent adsorption time.\nPage 17 Line 297 in manuscript insert: “The electron transfer from AsIII to Mn4+\nduring adsorption, forming AsV and Mn3+, as confirmed by XPS and XANES. For As,\npost-adsorption Cd-LDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9\neV (AsV, Fig. 5a); LDO raised AsV to 53.8% (vs. LDH’s 18.0%), showing stronger\noxidation 54, which also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR and\nin-situ Raman (Supplementary Fig. 49‒51).”\n2. Regeneration and stability testing is insufficient. Data provided only for Cd\ndesorption/regeneration (Supp. Fig. 31) but missing for the more toxic As(III).\nTesting should extend to at least 10 cycles with comprehensive evaluation of long-\nterm stability and potential leaching of all components (Mn, Mg, As, Cd).\nAuthor Response:\nThank you for your comments. As you suggested, we have supplemented the\nexperiments on the relevant regenerative performance as follows:\n2.1 Desorption/regeneration of AsIII\nThe regeneration experimental detail as following: the initial concentration of\nAsIII/Cd2+ fixed at 10/20 mg L‒1, and choose the 50 mg L‒1 of Na CO as the\n2 3\nregeneration solution. After 10 regeneration cycles, as the Supplementary Fig. 16, the\nremoval rate of regenerated LDO still reached at 90.2% for AsIII and 100% for Cd2+.\n3\nanion exchange to reforming CO 2‒-intercalated LDH. After calcination, the\n3\nintercalation mechanism can continue to be utilized for the adsorption of AsIII.\nSupplementary Fig. 16 The regenerative capacity of LDO in As/Cd adsorption.\nPage S16 Line 315 in Supplementary Information insert: “\n1.23 The regenerative experiment details of MgMn-LDO.\nThe regeneration performance of the MgMn-LDO was systematically evaluated\nvia 10 consecutive laboratory cycling experiments. The experimental setup fixed the\ninitial concentrations of As and Cd at 10 and 20 mg L‒1, respectively, while 50 mg L‒1\nNa CO solution was selected as the regeneration agent. The 1g/L as the dosage\n2 3\nstandard to proceed regeneration test. The adsorption time was 2 h under stirring, the\nsupernatant was separated with a 0.22 μm membrane filter. The concentrations of heavy\nmetals in actual wastewater were determined by ICP-MS.”\n2.2 Long-term stability and potential leaching of all components\nLeaching tests of Mg2+/Mn3+/4+ ions were performed on solutions from 10\nadsorption-desorption cycles, with results presented in Supplementary Fig. 17. Due to\nisomorphous substitution triggered by Cd2+ introduction during each cycle, a fraction\nof Mg2+ leached out progressively. In contrast, negligible Mn3+/4+ leaching was\n82\nobserved, demonstrating the long-term structural stability of LDO.\nAt the same time, we have test AsIII/Cd2+ ions leaching of Cd-LDH(As/Cd) at 10\ncycles. The results are shown in Supplementary Fig. 18. The AsIII/Cd2+ content in Cd-\nLDH(As/Cd) remained consistently very low constant value (approximately zero),\nindicating form the Cd-LDH(As/Cd) superstable mineralized state.\nSupplementary Fig. 17 The leaching amount of Mg/Mn in process of regenerative experiments.\nSupplementary Fig. 18 The leaching amount of As/Cd in Cd-LDH(As/Cd).\nPage 7 Line 133 in manuscript insert“In addition, the structure of LDO is stable,\nand its removal efficiency for AsIII/Cd2+ is independent of pH value, coexisting salts,\nand metal ions (Supplementary Fig. 9–18 and Supplementary Table 4‒5).”\n3. Mechanism validation relies solely on post-adsorption analysis. The study\nrequires in-situ characterization during transformation stages using TEM and\nspectroscopic techniques. No in-situ Raman/FTIR tracking of AsIII oxidation\nintermediates is presented, and TEM evidence of layer expansion during Cd2+\nsubstitution is limited.\nAuthor Response:\nThank you for your comments. In-situ monitoring is more advantageous for\ntracking the reaction process. As you suggested, we added various in-situ\ncharacterization to verify relevant mechanism. The detail analysis as follows:\n3.1 The experimental detail of in-situ characterization\nIn our co-contaminated system, we proceed in-situ characterization by sampling\nin different adsorption time. The specific testing procedure and results are illustrated\nbelow: MgMn-LDO adsorbent was placed in AsIII/Cd2+ solutions with initial\nconcentrations of 100/200 mg L‒1. Upon reaching predetermined adsorption times, the\nmixtures were immediately centrifuged, and the collected solids were dried for\nsubsequent characterization. Given that adsorption equilibrium was achieved at 10 min,\nthe adsorption times were set at: 0.5, 1, 5, 7, and 10 min.\nThe corresponding content add to Supplementary Information Page S17 Line\n323\n3.2 Analysis results\nAs shown in Supplementary Fig. 50, the characteristic peak at 851.4 cm‒1\ncorresponds to AsIII‒O. This peak gradually blue-shifts to 860.1 cm‒1 as adsorption\nprogresses to 10 min, indicating the oxidation of AsIII to AsV. As confirmed by the red-\nshift of the characteristic peak at 451.3 cm‒1 in the in-situ Raman spectrum\n(Supplementary Fig. 51). Additionally, the blue-shift of the peak at 626.8 cm‒1\ndemonstrates the concurrent reduction of Mn4+ during AsIII oxidation.\nIn Supplementary Fig. 63, the lattice parameter progressively expands from 0.205\nnm to 0.211 nm with increasing adsorption time, demonstrating the isomorphous\nsubstitution of Cd2+. This lattice expansion promotes the diffusion of AsIII.\nSupplementary Fig. 50 The semi in-situ FT-IR of Cd-MgMn-LDH(As/Cd) in various adsorption\ntime.\nSupplementary Fig. 51 The in-situ Raman of Cd-MgMn-LDH(As/Cd) in various adsorption time.\nSupplementary Fig. 63 The HRTEM results of Cd-MgMn-LDH(As/Cd) in various adsorption time.\nPage 17 Line 297 in manuscript insert: “The electron transfer from AsIII to Mn4+\nduring adsorption, forming AsV and Mn3+, as confirmed by XPS and XANES. For As,\npost-adsorption Cd-LDH(AsIII/Cd2+) shows As 3d signals at 44.9 eV (AsIII) and 45.9\neV (AsV, Fig. 5a); LDO raised AsV to 53.8% (vs. LDH’s 18.0%), showing stronger\noxidation 54, which also can be confirmed by HPLC-ICP-MS, semi-in-situ FT-IR and\nin-situ Raman (Supplementary Fig. 49‒51).”\nPage 24 Line 420 in manuscript revise: “In 100 mg L–1 AsIII solution, as Cd2+:\n11.2°; HRTEM shows lattice expansion (from 0.21 to 0.27 nm, Fig. 7b) and time-\ndependent growth (from 0.205 to 0.211 nm, Supplementary Fig. 63) 64. Increased\nspacing reduces AsIII diffusion resistance, boosting its rate.”\n4. Real-world application testing is inadequate with only one sewage sample tested.\nThe study should include varied real-world samples across different pH levels and\ncompeting ions. Testing with organic co-contaminants common in wastewater\nis limited, and As/Cd leaching evaluation under different environmental conditions\nis missing.\nAuthor Response:\nWe appreciate the reviewer’s insight into the limitations of real-world application\ntesting. We acknowledge the insufficiency of single-sample testing and environmental\ncondition simulations, and will address these via multi-dimensional experimental\ndesigns.\n4.1 Add the sewage samples\nAs you suggested, we have added 3 typical wastewater samples (industrial,\ndomestic, agricultural renoff) with diverse water quality. And design pH gradient tests\n(e.g., pH 3, 5, 7) for each sample, introduce common competing ions (Ca2+, Mg2+, Cl⁻,\nSO 2⁻) at different initial concentrations to analyze interference effects on As/Cd\n4\nadsorption. The results as shown in Supplementary Fig. 26, confirm all the removal\nefficiency of As/Cd can arrive at above 95%, is independent of pH value, coexisting\nions in real-world wastewater.\n4.2 Testing of organic co-contaminants\nIn order to verify the effect of organic co-contaminants, we have chosen several\nkinds of representative organic pollutants (humic acid, phenol, surfactants) to evaluate\nthe effects As/Cd adsorption. As shown in Supplementary Fig. 27, the removal\nefficiency of As/Cd can arrive at above 95%, indicating the adsorption process is\nindependent of organic co-contaminants. Meanwhile, the TOC value decreased from\n86\n10.91 to 8.53 before and after remediation, demonstrating that LDO not only removed\nheavy metals from the water but also decomposed or eliminated some organic\npollutants, thereby reducing the pollution load on the water body.\n4.3 As/Cd leaching evaluation under different environmental conditions\nWe have simulated several environmental factors: experimental temperature (25°C,\n35°C, 45 °C), wet-dry environmental condition, light-dark environmental condition. As\nshown in Supplementary Fig. 28, the removal efficiency of As/Cd can arrive at above\n95%, indicating the adsorption process is independent of environmental conditions.\nSupplementary Fig. 26 The removal rate of (a) As and (b) Cd in co-contaminated system. (pH = 3,\n5, and 7; ions: Ca2+, Mg2+, Cl⁻, SO 2⁻).\norganic pollution: humic, phenol, and surfactant).\nenvironmental condition: (a) adsorption temperature, (b) wet-dry environmental condition, and (c)\nlight-dark environmental condition).\nPage 9 Line 165 in manuscript insert: “Additionally, LDO has demonstrated\nexcellent adsorption capacity for AsIII/Cd2+ in various wastewater environments\n(Supplementary Fig. 26‒28).”\n5. Scalability and economics analysis is missing. The study should address cost-effectiveness and economic feasibility,\nprovide specific details on synthesis costs and energy consumption during calcination, and include comprehensive cost\nanalysis for large-scale production.\nAuthor Response:\nCost analysis constitutes an indispensable consideration in industrial-scale\nmaterial production. By reducing energy expenditures and mitigating carbon emissions,\nenterprises can better fulfill societal demands for environmental protection while\nenhancing their sustainable development credentials. For materials, improved\neconomic viability facilitates wider implementation in practical applications and\nindustrial processes. As you suggested, we have calculated the cost of our materials.\nSupplementary Table 8. Cost table for the preparation of MgMn-LDH.\nChemical Unit Price (¥/t) Amount Used (t) Total Cost (¥)\nMg(NO ) ·6H O 2200 3.1 6820\n3 2 2\n3 2 2\nNaOH 2100 0.92 1932\nTotal Cost Breakdown:\n1. raw cost of MgMn-LDH:\n6820+5160+1932=13912 ¥/t\n2. Energy consumption:\nelectric energy:1920 kWh×0.95 ¥/kWh=1824 ¥\nNatural Gas (including dry and calcined): 410 Nm3×3.5 ¥/Nm3=1435 ¥\n3. Total cost MgMn-LDO:\n13912 +1824 +1435=17171¥\nThe yield of MgMn-LDO: 1t×74.5%=745kg\nNamly: the direct cost of MgMn-LDO was 17171÷745×1000=23048 ¥/t\nAccording to the optimal dosage of 750 kg⋅ha−1, the cost of remediation with MgMn-\nLDO is about 1725 ¥ per hectare.\nFurthermore, if we chose MgSO and MnSO as raw materials, and with the future\n4 4\nbreakthroughs in key technologies for large-scale production, the production cost will\nfurther significantly reduce. Moreover, based on the experiment dates, the effect can\nlast for many years with once remediation, exhibiting cost-effective for practical\napplications.\nPage 8 Line 158 in manuscript insert: “Owing to the convenient and economical\nsynthesis method (Supplementary Table 8), the LDO can be scaled up for kilogram-\nscale production, verifying the high feasibility for practical applications in remediation\nof wastewater and contaminated soil (Supplementary Fig. 24‒25).”\n6. Writing and organization require enhancement. Complex, multi-clause\nsentences should be simplified, transitions between sections improved, and\n89\ntechnical terms defined consistently. The conclusion needs strengthening to\nhighlight broader implications, and key methodologies from supplementary\nmaterials should be summarized in the main text.\nAuthor Response:\nWe deeply appreciate your constructive feedback on enhancing the manuscript’s\nwriting and organizational structure. To address your concerns, we have undertaken a\nsystematic revision.\nReviewer 1\nAuthor Response:\nThank you for agreeing with the acceptance of this manuscript.\nReviewer 2\nOverview: This study prepared MgMn LDO material with high adsorption\nperformance for arsenic and cadmium, which has a certain positive effect on the\ntreatment of arsenic cadmium composite pollution environment, especially for site\npollution remediation. It is worth mentioning that from published literature,\nMgMn-LDO in detail (https://doi.org/10.1016/j.jenvman.2019.06.002) has been\ndeveloped and research on the adsorption performance of Cd has also conducted.\nIn this MS, MgMn LDO material has excellent adsorption capacity of AsIII and\nCd, and its application prospects are worth looking forward to. However, the\nfollowing issues still exist.\nAuthor Response:\nThank you for the reviewer’s recognition of our work and the valuable comments\nprovided. These suggestions have helped us gain a deeper understanding of relevant\nissues, not only improving the quality of our manuscript but also providing important\ninsights for our future research.\nWe greatly appreciate the reference provided by the reviewer. The cited literature\n(https://doi.org/10.1016/j.jenvman.2019.06.002) has provided excellent guidance for\nour work. The study’s findings on the co-removal of organic tetracycline and Cd, the\nenrichment of M-OH active sites as the basis for surface cadmium precipitate formation,\nand the synergistic promotion mechanisms have offered valuable inspiration and\nreference for our research. Building upon this foundation, our study focuses on the\nsynergistic adsorption performance of MgMn-LDO in AsIII and Cd2+ composite\npollution systems. The main distinction from the referenced literature lies in the\ndifferent adsorption pathways and mechanisms for Cd2+ removal. Additionally, we\nexplored the application potential of MgMn-LDO for remediation of actual AsIII and\nCd2+ contaminated sites, thereby expanding the application scope of this material.\nBased on these considerations, we have made corresponding modifications and\nemphasis in the relevant sections of our manuscript, and have included this valuable\nreference in our citation list. We sincerely appreciate the reviewer’s constructive\nfeedback.\nPage 4 Line 79 in manuscript insert: Among various materials, layered double oxides\n(LDOs) offer promising structural advantages and have demonstrated exceptional\nperformance in immobilizing single heavy metals, such as As, Pb, and Cd21‒24 For\ninstance, MgMn-LDO (Mg:Mn = 2:1) has previously been reported to exhibit excellent\nCd removal efficiency due to the formation of CdCO and Cd(OH) 25.\n3 2\nPage 29 insert: [25] Chen, M. Q. et al. Environmental application of MgMn-layered\ndouble oxide for simultaneous efficient removal of tetracycline and Cd pollution:\nPerformance and mechanism. J. Environ. Manage. 246, 164-173 (2019).\nFurther Comments\n1. In terms of the influence of competitive ions on the adsorption of arsenic and\ncadmium by materials, this article only explores the effects of sulfate ions, Cl-,\nCO 2-, and SiO 2-, and does not consider the effects on PO 3-, NO -, and DOM\n3 3 4 3\n(dissolved organic matter). It is precisely that these factors should not be ignored\nin terms of their impact on the adsorption performance of materials.\nAuthor Response:\nThank you for pointing out this important aspect that we overlooked in our initial\nstudy. We acknowledge that the influence of competitive ions on adsorption\nperformance is a crucial factor that requires comprehensive evaluation.\nIn response to your valuable comment, we have supplemented our investigation\nby examining the effects of additional anions, specifically PO 3– and NO –, on the\n4 3\nadsorption performance of MgMn-LDO for AsIII and Cd2+ removal. Furthermore,\nregarding dissolved organic matter (DOM), while there are numerous types of organic\ncompounds present in natural water systems, humic acid, phenol, and linear\nalkylbenzene sulfonate (LAS) are among the most representative organic substances\ncommonly found in contaminated environments. Therefore, we have conducted\nadditional experiments to evaluate the influence of humic acid, phenol, and LAS on the\nadsorption performance of our material.\nThe supplementary results have been added in Supplementary Fig. 16‒17 and\nSupplementary Fig. 27, and the removal efficiency of As/Cd can arrive at above 90%,\nindicating the adsorption process is independent of environmental conditions. These\nfindings provide a more comprehensive understanding of the material’s performance\nunder realistic environmental conditions and enhance the practical applicability of our\nresearch. We have incorporated these results and discussions into the revised\nmanuscript to address this important consideration raised by the reviewer.\nSupplementary Fig. 16 The As removal rate in different salts.\nSupplementary Fig. 17 The Cd removal rate in different salts.\nSupplementary Fig. 27 The removal rate of As and Cd in co-contaminated system.\n(different organic pollution: humic, phenol, and LAS).\nPage 7 Line 136 in manuscript: In addition, the structure of LDO is stable\n(Supplementary Fig. 9‒13), and its removal efficiency for AsIII/Cd2+ is independent of\npH value, coexisting salts, and metal ions (Supplementary Fig. 14–18).\nPage 9 Line 169 in manuscript revise: Additionally, LDO has demonstrated excellent\nadsorption capacity for AsIII/Cd2+ in domestic wastewater environments\n(Supplementary Fig. 26‒28).\nPage s34 in Supplementary Information: Regarding dissolved organic matter (DOM),\nwhile there are numerous types of organic compounds present in natural water systems,\nhumic acid, phenol, and linear alkylbenzene sulfonate (LAS) are among the most\nrepresentative organic substances commonly found in contaminated environments.\nTherefore, we have evaluated the influence of humic acid, phenol, and LAS on the\nadsorption performance of our material. As shown in Supplementary Fig. 27, the\nremoval efficiency of As/Cd can arrive at above 95%, indicating the adsorption process\nis independent of DOM.\n2. In this study, the experimental soil used by the author was not arsenic\ncadmium compound contaminated soil, but uncontaminated soil (Seen from\nSupplementary Table 5. The As/Cd concentration in field soil before and after\nremediation in different pH was very limited). As immobilization technology was\nconcerned, available heavy metal content was paid more attention rather than\ntotal content. Thus, such a research case does not have representativeness and\ntypicality. For clean soil, it is impossible to carry out remediation of arsenic\ncadmium contaminated soil.\nAuthor Response:\nWe sincerely thank the reviewer for this valuable comment. Your comment on soil\nselection is highly instructive for evaluating the performance of our material and\nprovides valuable guidance for our future studies. As you correctly note,\nuncontaminated soil cannot be used to study remediation of soils polluted with As and\nCd. We recognized that unclear data labeling and insufficient data quantity led to this\nmisunderstanding, and accordingly we revised the labeling and supplemented the data.\nThe data now include the total amounts of As and Cd for pre-remediation, their\ncorresponding bioavailable fractions, and the bioavailable fractions of post-remediation\nby MgMn-LDO. Especially, we have supplemented highly contaminated farmland soil\nand industrial soil.\n2.1 Remediation of low-available heavy metal contaminated farmland\nFrom the Supplementary Table 8, the total As/Cd of pre-remediation is 31.21 and\n0.44 mg kg‒1 for the soli 1, 32.52 and 0.40 mg kg‒1 for soil 2, and 35.11 and 0.40 mg\nkg‒1 for soil 3, 33.43 and 0.59 mg kg‒1 for soil 4, indicating contamination according to\nthe Soil environmental quality‒Risk control standard for soil contamination of\nagricultural land (GB 15618‒2018) (As: pH≤6.5, total As≤30; pH>7.5, total As≤20; Cd:\npH≤5.5, total Cd≤0.3, 5.5<pH≤6.5, total Cd≤0.4; pH>7.5, total Cd≤0.8 unit: mg kg‒1).\nIt should be noted that although the available fractions of As/Cd in the soil 1–4 were\nrelatively low (about 0.166/0.055 mg kg‒1), the concentrations of As/Cd in rice grains\ngrown in this soil reached 0.472/0.563 mg kg‒1 (Supplementary Fig. 29). This is close\nto the limit of As and exceeded the limit of Cd according to the National Food Safety\nStandard (GB 2762-2022), where the threshold values are: As < 0.5 mg kg‒1; Cd < 0.1\nmg kg‒1. In contrast, after remediation, the concentrations of As/Cd in rice reached\n0.239/0.141 mg kg‒1, meeting the national standard.\nIn summary, although the bioavailable fractions before remediation were not high,\nthey were sufficient to cause the rice to exceed regulatory limits; remediation\neffectively suppressed As/Cd accumulation in rice, achieving national standard.\n2.2 Remediation of high-available heavy metal contaminated farmland\nTo better address your concern regarding remediation of highly contaminated soils,\nwe further selected polluted soil samples from Yiyang County (28.41 °N, 117.39 °E),\nShangrao, jiangxi Province for analysis of available heavy metals. As shown in updated\nSupplementary Table 8 (Soil 5), the total As/Cd concentrations in the soil before\nremediation were 33.10/0.51 mg kg‒1, respectively, indicating a typical heavy metal-\ncontaminated site. After MgMn-LDO treatment, the available As/Cd concentrations in\nsoil from 1.419/0.289 mg kg‒1 decreased to 0.550/0.021 mg kg‒1, respectively. The\npercentage reduction in concentration reached values 61.2% and 92.7%, respectively.\nSuch a reduction degree is significantly greater than that of low-concentration pollution\nsoils 1–4, where the percentage reduction in concentration of As/Cd is range from 32%–\n43%/66%–82%, respectively, proving the effectiveness of the in-situ mineralization\ntechnology. It should also be noted that the bioavailable fractions of As in the post-\nremediated soil remain at a relatively high level, attributed to the severe As\ncontamination of the soil pre-remediation. Nevertheless, by optimizing the remediation\nstrategy, such as adopting a batch-wise and time-phased (e.g., annual) treatment\napproach, it is expected to be further reduced. As the remediation cycle is measured in\nyears, the data is being continuously updated.\n2.3 Remediation of highly contaminated industrial soils\nTo investigate soils with higher levels of contamination, we selected heavy metal\ncontaminated soils from the Dongfang mining site (18.87 °N, 108.72 °E), Hainan\nProvince. The concentration of heavy metals As/Cd in solution leached were\ndetermined using the TCLP (Toxicity Characteristic Leaching Procedure) method\n(United States Environmental Protection Agency (EPA) Method 1311), and the detailed\nprocedure has been added to the Supplementary Information. As shown in updated Fig.\n2h, the concentration of As and Cd in solution leached were 87.1/42.3 μg L‒1. After\nremediation with MgMn-LDO, the concentration of As and Cd in solution leached\ndecreased to 16.7 and 3.5 μg L‒1, respectively. The percentage reduction in\nconcentration reached values 80.8% and 91.7%, demonstrating that MgMn-LDO is\neffective in treating highly contaminated real-world industrial soils.\nSupplementary Table 8. The As/Cd concentration in field soil before and after\nremediation in different pH.\nBefore (mg kg‒1) After (mg kg‒1)\ntotal total available available reduced percentage available reduced percentage\npH available As\nAs Cd Cd As (As, %) Cd (Cd, %)\nSoil 1 5.21 31.21 0.187 0.44 0.057 0.110 41.2% 0.019 66.7%\nSoil 2 5.56 32.52 0.162 0.40 0.049 0.108 33.3% 0.010 79.6%\nSoil 3 5.87 35.11 0.170 0.40 0.051 0.098 42.4% 0.011 78.4%\nSoil 4 5.77 33.43 0.166 0.59 0.055 0.112 32.5% 0.010 81.8%\nSoil 5 5.44 33.10 1.419 0.51 0.289 0.550 61.2% 0.021 92.7%\nSoil 6 8.15 28.87 0.338 24.82 0.205 0.132 61.0% 0.023 88.8%\nFig. 2h The concentration of before and after remediation of mining site soil in solution\nleached.\nSupplementary Fig. 29 The concentration of before and after remediation of As/Cd\nco-contaminated soil and rice.\nPage 9 Line 173 in manuscript revise: In addition, this in‒situ immobilization\ntechnology had applied to heavy metal–contaminated farmland. The remediation\nexperiments demonstrated that MgMn-LDO obviously reduces available heavy metals\nin farmland, with good applicability in both acidic and alkaline soils (see for detailed\ndiscussion, Supplementary Fig. 29 and Supplementary Table 8‒10).\nPage 9 Line 170 in manuscript revise: Secondly, when LDO was added the highly\ncontaminated natural industrial soils located at the Dongfang mining site (18.87 °N,\n108.72 °E), Hainan Province, the concentration of As and Cd in solution leached\ndecreases 80.8% and 91.7%, respectively after remediation (Fig. 2h).\nPage s35 in Supplementary Information: By in-situ immobilization technology, LDO\nwas added the contaminated soil located at Liling in Hunan province. The available As\nand Cd decreases 66.9% and 91.1%, respectively compared with the control sample.\nImportantly, the concentrations of available As and Cd in rice was 0.239 and 0.141 mg\nkg‒1, which is safety level according to the China Standard of GB2762-2022 (As ≤\n0.5 mg kg‒1, Cd ≤ 0.2 mg kg‒1). MgMn-LDO remediation reduces heavy metals in\nfarmland-grown rice without plant contamination or food chain risks, as it avoids toxic\nbioaccumulation while supplying beneficial nutrients.\nPage s57 in Supplementary Information: Here are some real data on the remediation\nof heavy metals in contaminated farmland soils. As shown in Supplementary Table 8,\nin acidic soils (Soils 1–5), the total concentrations of As and Cd ranged from 31.21–\n35.11 mg kg‒1 and 0.40–0.59 mg kg‒1, respectively, indicating contamination according\nto the Soil Environmental Quality – Risk Control Standard for Soil Contamination of\nAgricultural Land (GB 15618-2018), where the threshold values are: As, pH ≤ 6.5, ≤30\nmg kg‒1; pH > 7.5, ≤20 mg kg‒1; Cd, pH ≤ 5.5, ≤0.3 mg kg‒1; 5.5 < pH ≤ 6.5, ≤0.4 mg\nkg‒1; pH > 7.5, ≤0.8 mg kg‒1. It should be noted that although the available fractions of\nAs/Cd in the soil 1–4 were relatively low (about 0.166/0.055 mg kg‒1), the\nconcentrations of As/Cd in rice grains grown in this soil reached 0.472/0.563 mg kg‒1\nfor (Supplementary Fig. 29). This is close to the limit of As and exceeded the limit of\nCd according to the National Food Safety Standard (GB 2762-2022), where the\nthreshold values are: As < 0.5 mg kg‒1; Cd < 0.1 mg kg‒1. In contrast, after remediation,\nthe concentrations of As/Cd in rice reached 0.239/0.141 mg kg‒1, meeting the national\nstandard.\nThe highly contaminated soil 5 located at Yiyang County (28.41 °N, 117.39 °E),\nShangrao, jiangxi Province, has also been carried out the remediation. As shown in\nupdated Supplementary Table 8, the total As/Cd concentrations in the soil before\nremediation were 33.10/0.51 mg kg‒1, respectively, indicating a typical heavy metal-\ncontaminated site. After MgMn-LDO treatment, the available As/Cd concentrations in\nsoil from 1.419/0.289 mg kg‒1 decreased to 0.550/0.021 mg kg‒1, respectively. The\npercentage reduction in concentration reached values 61.2% and 92.7%, respectively.\nSuch a reduction degree is significantly greater than that of low-concentration pollution\nsoils 1–4, where the percentage reduction in concentration of As/Cd is range from 32%–\n43%/66%–82%, respectively, proving the effectiveness of the in-situ mineralization\ntechnology. It should also be noted that the bioavailable fractions of As in the post-\nremediated soil remain at a relatively high level, attributed to the severe As\ncontamination of the soil pre-remediation. Nevertheless, by optimizing the remediation\nstrategy, such as adopting a batch-wise and time-phased (e.g., annual) treatment\napproach, it is expected to be further reduced. As the remediation cycle is measured in\nyears, the data is being continuously updated.\nIn practice, LDO materials also demonstrate good remediation effects in more\nhigher pH soil environments. For example, we have conducted remediation using\nalkaline contaminated soil (pH = 8.15) collected from Baiyin City, Gansu Province\n(36.60 °N, 104.18 °E) (Soil 6). This area has suffered from long-term mining, smelting,\nand industrial activities, where heavy metal pollution is transported through the\nDongdagou stream into the Yellow River, causing severe contamination of the\nsurrounding farmland (Zhang et al. Sustainability, 2024; He et al. Eco-Environment &\nHealth, 2021). After remediation with MgMn-LDO, the available As/Cd contents in the\nsoil decreased from 0.338/0.205 mg kg‒1 to 0.132/0.023 mg kg‒1. The reduced\npercentage in concentration reached 61.0% and 88.8%, demonstrating MgMn-LDO\nmaterial can effectively remediate heavy metal–contaminated soils under different pH\nconditions.\nPage s59 in Supplementary Information: This in‒situ immobilization technology had\napplied to heavy metal–contaminated farmland. The remediation experiments\ndemonstrated that MgMn-LDO effectively reduces heavy metals in farmland and\ngrown rice without plant contamination or food chain risks, as it avoids toxic\nbioaccumulation while supplying beneficial nutrients. It should also be noted that the\nMn content in rice reaches 89‒127 mg kg‒1. Although there is currently no established\nlimit standard for it, considering the potential impacts of long-term and large-scale\napplication, efforts should be made to optimize material formulations—for instance,\nadjusting the Mg/Mn ratio to reduce the bioavailability of manganese. Since the rice\ncultivation cycle is measured in years, the data is continuously being updated.\nPage s17 Line 331 in Supplementary Information insert:\n1.25 The detailed information of TCLP (Toxicity Characteristic Leaching\nProcedure) method\nThe leachability of As and Cd in soils was determined using the U.S. EPA Toxicity\nCharacteristic Leaching Procedure (TCLP, 1311). The appropriate extraction fluid is\nextraction fluid #1 of the TCLP due to the pH of mining site soil is 4.87. This is prepared\nby adding 5.7 mL of glacial CH CH OOH to 500 mL of deionized water, adding 64.3\n3 2\nmL of 1N NaOH and dilute to a volume of 1 liter. When correctly prepared, the pH is\n4.93±0.05. The soils were extracted at a liquid-to-solid ratio of 20:1 (v/w) by mechanic\nshaker for 18 h at room temperature (22 °C). After this shaking period, the samples\nwere filtrated and the concentrations of As and Cd were determined by an ICP-OES.\n3. The results of crop planting experiments indicate that the manganese content\nin rice grains has exceeded relevant standards (Supplementary Table 10, the Mn\ncontent was 89.91~126.54 mg/kg after remediation, much higher than those\n35.31~51.22 mg/kg before remediation), which poses a significant impact on food\nsafety. According to the National Food Safety Standard-Food Medium Limit\nStandards (GB 2760-2014), the limit of manganese in colored foods is 50mg/kg,\nand that in dietary supplements is 30mg/kg (calculated as elemental manganese),\nthe data of Mn in rice exceeded seriously this standard according to this MS.\nWhat’s more, in the case of long-term and large-scale application, the risks are\nmore obvious, making it unsuitable for use in farmland.\nAuthor Response:\nThank you for your important concern regarding food safety. Following your\nvaluable suggestions, we have made the following significant revisions: 1)\nsupplemented the main text with industrial contaminated site remediation experiments\nusing real As/Cd co-contaminated soils, validating the effectiveness and safety of\nMgMn-LDO in industrial environments (Fig. 2h); 2) refocused the main text\napplications on industrial site remediation, emphasizing the technology’s advantages in\nnon-agricultural settings. Please refer to the answer in 2.3 of Question 2 for details.\nMeanwhile, we have chosen to retain the agricultural soil remediation data by\nmoving it to supplementary materials, based on the following scientific considerations:\nUpon careful verification, the GB 2760-2014 standard cited refers to the “National\nStandard for Food Additive Use,” where manganese limits pertain to food additive\nusage restrictions rather than contaminant limits in food products. Currently, no specific\nfood safety limits for manganese content in rice have been established either\ndomestically or internationally (Codex Alimentarius Commission. General Standard for\nContaminants and Toxins in Food and Feed (CXS 193-1995, Rev.2023); National Food\nSafety Standard—Maximum Levels of Contaminants in Foods (GB 2762‒2022)), as\nmanganese is an essential micronutrient naturally present in soil-plant systems. Given\nthe absence of clear food safety standards, we believe it would be inappropriate to\ncompletely dismiss the excellent simultaneous As/Cd removal performance\ndemonstrated by MgMn-LDO in agricultural remediation.\nYour valuable suggestions have provided us with important insights. In our future\nresearch, we will focus on optimizing material formulations, such as adjusting the\nMg/Mn ratio to reduce manganese bioavailability, ensuring absolute safety for\nagricultural applications and achieving dual protection for both environmental\nremediation and food safety.\nFig. 2h The concentration of before and after remediation of mining area soil in solution\nleached.\nSupplementary Table 10. The metal ions concentration in rice before and after\nremediation.\nBefore (mg kg‒1) After (mg kg‒1)\nUnit: (mg kg‒1)\nMg Mn As Cd Mg Mn As Cd\n1 598.32 35.31 0.321 0.355 849.65 89.91 0.035 0.165\n2 600.89 51.22 0.257 0.320 921.00 126.54 0.032 0.160\n3 615.62 40.98 0.135 0.294 959.64 100.20 0.028 0.135\nPage 9 Line 170 in manuscript revise: Secondly, when LDO was added the highly\ncontaminated natural industrial soils located at the Dongfang mining site (18.87 °N,\n108.72 °E), Hainan Province, the concentration of As and Cd in solution leached\ndecreases 80.8% and 91.7%, respectively after remediation (Fig. 2h).\nPage s59 in Supplementary Information: This in‒situ immobilization technology had\napplied to heavy metal–contaminated farmland. The remediation experiments\ndemonstrated that MgMn-LDO effectively reduces heavy metals in farmland and\ngrown rice without plant contamination or food chain risks, as it avoids toxic\nbioaccumulation while supplying beneficial nutrients. It should also be noted that the\nMn content in rice reaches 89‒127 mg kg‒1. Although there is currently no established\nlimit standard for it, considering the potential impacts of long-term and large-scale\napplication, efforts should be made to optimize material formulations—for instance,\nadjusting the Mg/Mn ratio to reduce the bioavailability of manganese. Since the rice\ncultivation cycle is measured in years, the data is continuously being updated.\nPage s17 Line 331 in Supplementary Information insert:\n1.25 The detailed information of TCLP (Toxicity Characteristic Leaching\nProcedure) method.\nThe leachability of As and Cd in soils was determined using the U.S. EPA Toxicity\nCharacteristic Leaching Procedure (TCLP, 1311). The appropriate extraction fluid is\nextraction fluid #1 of the TCLP due to the pH of mining site soil is 4.87. This is prepared\nby adding 5.7 mL of glacial CH CH OOH to 500 mL of deionized water, adding 64.3\n3 2\nmL of 1N NaOH and dilute to a volume of 1 liter. When correctly prepared, the pH is\n4.93±0.05. The soils were extracted at a liquid-to-solid ratio of 20:1 (v/w) by mechanic\nshaker for 18 h at room temperature (22 °C). After this shaking period, the samples\nwere filtrated and the concentrations of As and Cd were determined by an ICP-OES.\n4. The experiment on the influence of materials on the stability of arsenic\ncadmium adsorption should choose different soil types with different pH values\n(considering various acidic and alkaline conditions), but this study chose acidic\nsoils.\nAuthor Response:\nThank you for this important question regarding soil type selection. We\nacknowledge that testing the material’s stability across different soil pH conditions is\ncrucial for comprehensive evaluation.\nActually, the selection of acidic soils represents a very important aspect of our\npractical soil remediation work. Because under acidic conditions, the solubility and\nmobility of metals such as Cd and As are enhanced in soils, posing higher ecological\nand food safety risks (China national soil contamination survey report. CWR 2014; Mi\net al. Agronomy, 2025; Ning et al. Sustainability, 2019). Therefore, when selecting soil\nenvironments for testing, we specifically focused on acidic soils to explore the\nremediation effectiveness of our LDO material under challenging acidic soil conditions.\nIn practice, LDO materials also demonstrate good remediation effects in more\nhigher pH soil environments. For example, we have conducted remediation using\nalkaline contaminated soil (pH = 8.15) collected from Baiyin City, Gansu Province\n(36.60 °N, 104.18 °E) (Soil 6 in Supplementary Table 8). This area has suffered from\nlong-term mining, smelting, and industrial activities, where heavy metal pollution is\ntransported through the Dongdagou stream into the Yellow River, causing severe\ncontamination of the surrounding farmland (Zhang et al. Sustainability, 2024; He et al.\nEco-Environment & Health, 2021). After remediation with MgMn-LDO, the available\nAs/Cd contents in the soil decreased from 0.338/0.205 mg kg‒1 to 0.132/0.023 mg kg‒\n1. The reduced percentage in concentration reached 61.0% and 88.8%, demonstrating\nMgMn-LDO material can effectively remediate heavy metal–contaminated soils under\ndifferent pH conditions.\nIn summary, although some data for different soil types remain incomplete due to\nthe long remediation cycles, preliminary results support our conclusion that MgMn-\nLDO can simultaneously immobilize As and Cd, though the mechanisms and efficiency\nmay vary depending on the soil chemistry.\nSupplementary Table 8. The As/Cd concentration in field soil before and after\nremediation in different pH.\nBefore (mg kg‒1) After (mg kg‒1)\ntotal total available available reduced percentage available reduced percentage\npH available As\nAs Cd Cd As (As, %) Cd (Cd, %)\nSoil 1 5.21 31.21 0.187 0.44 0.057 0.110 41.2% 0.019 66.7%\nSoil 2 5.56 32.52 0.162 0.40 0.049 0.108 33.3% 0.010 79.6%\nSoil 3 5.87 35.11 0.170 0.40 0.051 0.098 42.4% 0.011 78.4%\nSoil 4 5.77 33.43 0.166 0.59 0.055 0.112 32.5% 0.010 81.8%\nSoil 5 5.44 33.10 1.419 0.51 0.289 0.550 61.2% 0.021 92.7%\nSoil 6 8.15 28.87 0.338 24.82 0.205 0.132 61.0% 0.023 88.8%\nPage 9 Line 173 in manuscript revise: In addition, this in‒situ immobilization\ntechnology had applied to heavy metal–contaminated farmland. The remediation\nexperiments demonstrated that MgMn-LDO obviously reduces available heavy metals\nin farmland, with good applicability in both acidic and alkaline soils (see for detailed\ndiscussion, Supplementary Fig. 29 and Supplementary Table 8‒10).\nPage s58 in Supplementary Information: In practice, LDO materials also\ndemonstrate good remediation effects in more higher pH soil environments. For\nexample, we have conducted remediation using alkaline contaminated soil (pH = 8.15)\ncollected from Baiyin City, Gansu Province (36.60 °N, 104.18 °E) (Soil 6). This area\nhas suffered from long-term mining, smelting, and industrial activities, where heavy\nmetal pollution is transported through the Dongdagou stream into the Yellow River,\ncausing severe contamination of the surrounding farmland (Zhang et al. Sustainability,\n2024; He et al. Eco-Environment & Health, 2021). After remediation with MgMn-LDO,\nthe available As/Cd contents in the soil decreased from 0.338/0.205 mg kg‒1 to\n0.132/0.023 mg kg‒1. The reduced percentage in concentration reached 61.0% and\n88.8%, demonstrating MgMn-LDO material can effectively remediate heavy metal–\ncontaminated soils under different pH conditions.\n5. Therefore, overall, the experimental design of this paper is not complete and\nscientifically sound, and there are certain technical risks. It is recommended to\nchoose arsenic cadmium composite contaminated soil in industrial sites for the\nexperiment, preferably not for farmland soil. Delete the relevant results related to\nfarmland and supplement relevant experiments based on the above opinions.\nAuthor Response:\nThank you for your valuable suggestions. Following your recommendations, we\nhave supplemented our study with experiments conducted on industrial sites using\nactual As/Cd co-contaminated soils, which from the Dongfang mining site (18.87 °N,\n108.72 °E), Hainan Province. The concentration of heavy metals As and Cd in solution\nleached were determined using the TCLP (Toxicity Characteristic Leaching Procedure)\nmethod, and the detailed procedure has been added to the Supplementary Information.\nAs shown in Fig. 2h, the concentration As and Cd contents in solution leached of\noriginal mining site soil were 87.1 and 42.3 μg L‒1, respectively. After remediation with\nMgMn-LDO, the concentration As and Cd in solution leached decreased to 16.7 and\n3.5 μg L‒1, respectively. The percentage reduction in concentration reached values 80.8%\nand 91.7%, demonstrating that MgMn-LDO is effective in treating highly contaminated\nreal-world industrial soils.\nWe would like to express our special thanks to you for pointing out the certain\ntechnical risks associated with the application of LDO remediation materials in\nfarmland soil, as well as for suggesting that we delete the relevant content. In fact, our\nresearch findings on farmland soils with different levels of pollution, including those\nwith low bioavailable heavy metal content, high bioavailable heavy metal content, and\nunder different soil pH conditions, demonstrate that the MgMn-LDO can\nsimultaneously immobilize As and Cd. More importantly, considering the severe global\nchallenge of heavy metal contamination in farmland soils and its impact on food\nsecurity, as well as sustainable development goals, we are committed to providing safe\nand feasible technical solutions for agricultural soil remediation. Therefore, following\nthe reviewer’s friendly suggestion, we have emphasized industrial site applications in\nthe main text while moving farmland soil data to the supplementary materials\n(Supplementary Fig. 29, Supplementary Table 8‒10), balancing scientific rigor with\npractical application value.\nFig. 2h The concentration of before and after remediation of mining area soil in solution\nleached.\nSupplementary Fig. 29 The concentration of before and after remediation of As/Cd\nco-contaminated soil and rice.\nSupplementary Table 8. The As/Cd concentration in field soil before and after\nremediation in different pH.\nBefore (mg kg‒1) After (mg kg‒1)\ntotal total available available reduced percentage available reduced percentage\npH available As\nAs Cd Cd As (As, %) Cd (Cd, %)\nSoil 1 5.21 31.21 0.187 0.44 0.057 0.110 41.2% 0.019 66.7%\nSoil 2 5.56 32.52 0.162 0.40 0.049 0.108 33.3% 0.010 79.6%\nSoil 3 5.87 35.11 0.170 0.40 0.051 0.098 42.4% 0.011 78.4%\nSoil 4 5.77 33.43 0.166 0.59 0.055 0.112 32.5% 0.010 81.8%\nSoil 5 5.44 33.10 1.419 0.51 0.289 0.550 61.2% 0.021 92.7%\nSoil 6 8.15 28.87 0.338 24.82 0.205 0.132 61.0% 0.023 88.8%\nSupplementary Table 9. The As/Cd concentration in field soil before and after\nremediation in different temperature\nBefore (mg kg‒1) After (mg kg‒1)\n10 ℃ 30 ℃\nAs Cd As Cd As Cd\nsample 0.159 0.054 0.107 0.011 0.102 0.010\nSupplementary Table 10. The metal ions concentration in rice before and after\nremediation.\nBefore (mg kg‒1) After (mg kg‒1)\nUnit: (mg kg‒1)\nMg Mn As Cd Mg Mn As Cd\n1 598.32 35.31 0.321 0.355 849.65 89.91 0.035 0.165\n2 600.89 51.22 0.257 0.320 921.00 126.54 0.032 0.160\n3 615.62 40.98 0.135 0.294 959.64 100.20 0.028 0.135\nPage 9 Line 173 in manuscript revise: In addition, this in‒situ immobilization\ntechnology had applied to heavy metal–contaminated farmland. The remediation\nexperiments demonstrated that MgMn-LDO obviously reduces available heavy metals\nin farmland, with good applicability in both acidic and alkaline soils (see for detailed\ndiscussion, Supplementary Fig. 29 and Supplementary Table 8‒10).\nPage 9 Line 170 in manuscript revise: Secondly, when LDO was added the highly\ncontaminated natural industrial soils located at the Dongfang mining site (18.87 °N,\n108.72 °E), Hainan Province, the concentration of As and Cd in solution leached\ndecreases 80.8% and 91.7%, respectively after remediation (Fig. 2h).\nPage s35 in Supplementary Information: By in-situ immobilization technology, LDO\nwas added the contaminated soil located at Liling in Hunan province. The available As\nand Cd decreases 66.9% and 91.1%, respectively compared with the control sample.\nImportantly, the concentrations of available As and Cd in rice was 0.239 and 0.141 mg\nkg‒1, which is safety level according to the China Standard of GB2762-2022 (As ≤\n0.5 mg kg‒1, Cd ≤ 0.2 mg kg‒1). MgMn-LDO remediation reduces heavy metals in\nfarmland-grown rice without plant contamination or food chain risks, as it avoids toxic\nbioaccumulation while supplying beneficial nutrients.\nPage s57 in Supplementary Information: Here are some real data on the remediation\nof heavy metals in contaminated farmland soils. As shown in Supplementary Table 8,\nin acidic soils (Soils 1–5), the total concentrations of As and Cd ranged from 31.21–\n35.11 mg kg‒1 and 0.40–0.59 mg kg‒1, respectively, indicating contamination according\nto the Soil Environmental Quality – Risk Control Standard for Soil Contamination of\nAgricultural Land (GB 15618-2018), where the threshold values are: As, pH ≤ 6.5, ≤30\nmg kg‒1; pH > 7.5, ≤20 mg kg‒1; Cd, pH ≤ 5.5, ≤0.3 mg kg‒1; 5.5 < pH ≤ 6.5, ≤0.4 mg\nkg‒1; pH > 7.5, ≤0.8 mg kg‒1. It should be noted that although the available fractions of\nAs/Cd in the soil 1–4 were relatively low (about 0.166/0.055 mg kg‒1), the\nconcentrations of As/Cd in rice grains grown in this soil reached 0.472/0.563 mg kg‒1\nfor (Supplementary Fig. 29). This is close to the limit of As and exceeded the limit of\nCd according to the National Food Safety Standard (GB 2762-2022), where the\nthreshold values are: As < 0.5 mg kg‒1; Cd < 0.1 mg kg‒1. In contrast, after remediation,\nthe concentrations of As/Cd in rice reached 0.239/0.141 mg kg‒1, meeting the national\nstandard.\nThe highly contaminated soil 5 located at Yiyang County (28.41 °N, 117.39 °E),\nShangrao, jiangxi Province, has also been carried out the remediation. As shown in\nupdated Supplementary Table 8, the total As/Cd concentrations in the soil before\nremediation were 33.10/0.51 mg kg‒1, respectively, indicating a typical heavy metal-\ncontaminated site. After MgMn-LDO treatment, the available As/Cd concentrations in\nsoil from 1.419/0.289 mg kg‒1 decreased to 0.550/0.021 mg kg‒1, respectively. The\npercentage reduction in concentration reached values 61.2% and 92.7%, respectively.\nSuch a reduction degree is significantly greater than that of low-concentration pollution\nsoils 1–4, where the percentage reduction in concentration of As/Cd is range from 32%–\n43%/66%–82%, respectively, proving the effectiveness of the in-situ mineralization\ntechnology. It should also be noted that the bioavailable fractions of As in the post-\nremediated soil remain at a relatively high level, attributed to the severe As\ncontamination of the soil pre-remediation. Nevertheless, by optimizing the remediation\nstrategy, such as adopting a batch-wise and time-phased (e.g., annual) treatment\napproach, it is expected to be further reduced. As the remediation cycle is measured in\nyears, the data is being continuously updated.\nIn practice, LDO materials also demonstrate good remediation effects in more\nhigher pH soil environments. For example, we have conducted remediation using\nalkaline contaminated soil (pH = 8.15) collected from Baiyin City, Gansu Province\n(36.60 °N, 104.18 °E) (Soil 6). This area has suffered from long-term mining, smelting,\nand industrial activities, where heavy metal pollution is transported through the\nDongdagou stream into the Yellow River, causing severe contamination of the\nsurrounding farmland (Zhang et al. Sustainability, 2024; He et al. Eco-Environment &\nHealth, 2021). After remediation with MgMn-LDO, the available As/Cd contents in the\nsoil decreased from 0.338/0.205 mg kg‒1 to 0.132/0.023 mg kg‒1. The reduced\npercentage in concentration reached 61.0% and 88.8%, demonstrating MgMn-LDO\nmaterial can effectively remediate heavy metal–contaminated soils under different pH\nconditions.\nPage s59 in Supplementary Information: This in‒situ immobilization technology had\napplied to heavy metal–contaminated farmland. The remediation experiments\ndemonstrated that MgMn-LDO effectively reduces heavy metals in farmland and\ngrown rice without plant contamination or food chain risks, as it avoids toxic\nbioaccumulation while supplying beneficial nutrients. It should also be noted that the\nMn content in rice reaches 89‒127 mg kg‒1. Although there is currently no established\nlimit standard for it, considering the potential impacts of long-term and large-scale\napplication, efforts should be made to optimize material formulations—for instance,\nadjusting the Mg/Mn ratio to reduce the bioavailability of manganese. Since the rice\ncultivation cycle is measured in years, the data is continuously being updated.\nPage s17 Line 331 in Supplementary Information insert:\n1.25 The detailed information of TCLP (Toxicity Characteristic Leaching\nProcedure) method\nThe leachability of As and Cd in soils was determined using the U.S. EPA Toxicity\nCharacteristic Leaching Procedure (TCLP, 1311). The appropriate extraction fluid is\nextraction fluid #1 of the TCLP due to the pH of mining site soil is 4.87. This is prepared\nby adding 5.7 mL of glacial CH CH OOH to 500 mL of deionized water, adding 64.3\n3 2\nmL of 1N NaOH and dilute to a volume of 1 liter. When correctly prepared, the pH is\n4.93±0.05. The soils were extracted at a liquid-to-solid ratio of 20:1 (v/w) by mechanic\nshaker for 18 h at room temperature (22 °C). After this shaking period, the samples\nwere filtrated and the concentrations of As and Cd were determined by an ICP-OES.\nResponses to Reviewer 4\nOverview: I am happy with the revision.\nAuthor Response:\nThank you for your recommending for publication without any revision.\nResponse to Reviewers\nReviewer 2\nOverview: Although the author has made certain revisions and improvements to\nthis paper, there are still many issues that remain to be determined:\nAuthor Response:\nWe would like to express our sincere gratitude for the comprehensive review and\nvaluable feedback. Especially, the reviewer’s detailed comments have not only\npinpointed several areas that needed improvement but have also provided insightful\nsuggestions on how to address them. These constructive remarks have significantly\ncontributed to the enhancement of our manuscript, and we are committed to revising\nour work accordingly. Thank you for your continued efforts and support in refining our\nmanuscript.\n(1) The results of this study have certain application value for the remediation of\nindustrial site pollution. However, the five types of soil used in this study all belong\nto slightly polluted farmland soil. If evaluated by the standard for construction\nland (GB36600-2018), they may not be considered polluted. Therefore, using the\nresults of slightly polluted farmland to indicate the remediation effect of industrial\npolluted sites inherently has limitations and uncertainties.\nAuthor Response:\nThank you for your suggestions. This issue was also mentioned in your previous\nreview comments, and our revisions were insufficient due to our incomplete\nconsiderations. We greatly appreciate the highly valuable information you have\nprovided on several occasions, including standards, literature, and other references,\nwhich have significantly helped improve the quality of our paper.\nBased on your advice and the requirements of the “Standard for Construction Land”\n(GB 36600-2018), we have supplemented the remediation results for highly\ncontaminated soils, showing that the concentrations levels of As (22.8–82.1 mg kg–1)\nand Cd contamination (21.1–100.5 mg kg–1). Additionally, in the remediation of heavily\ncontaminated soils, a systematic study was conducted on the effects of different\npollution levels (high, medium, low), pH values, and soil types on remediation efficacy.\nThe related results are presented in Figure 2h and Tables 9–11.\n1.1 Different pollution levels\nBased on your advice, we have supplemented the remediation results for soils\ncontaminated with different gradient concentrations, as shown in Supplementary Table\n9. We used Soil 2 as the baseline and created controlled concentration gradients by\nadding standard samples to Soil 2 to prepare soils with higher contamination levels,\nresulting in the obtained soils labeled as Soil 2-1, Soil 2-2, Soil 2-3, Soil 2-4, Soil 2-5,\nand Soil 2-6. Similar treatment methods have been widely used in previous studies (J.\nHazard. Mater., 2022, 423, 127104; J. Clean. Prod., 2021, 297, 126506). We would\nlike to note that we did not choose six field-collected soils with varying levels of\ncontamination. This controlled approach eliminates confounding factors that would\narise from the inherent heterogeneity of naturally contaminated soils, such as\ndifferences in organic matter, mineralogy, and other soil properties, thereby allowing\nfor a precise evaluation of single-variable effects that would be impossible with\nmultiple field-collected samples.\nIn our concentration gradient experiments, soil samples were categorized into three\ncontamination levels. For the low-contamination group (Soil 2 and Soil 2-1), As\nconcentrations ranged from 22.8 to 23.5 mg kg–1 and Cd from 21.1 to 25.3 mg kg–1,\nwith removal efficiencies of 87.8%–93.8% for As and 90.5%–91.4% for Cd. For the\nmedium-contamination group (Soil 2-2 and Soil 2-3), As concentrations ranged from\n31.2 to 50.5 mg kg–1 and Cd from 30.5 to 69.9 mg kg–1, achieving removal efficiencies\nof 88.4%–90.8% for As and 89.0%–90.1% for Cd. For the high-contamination group\n(Soil 2-4, Soil 2-5, and Soil 2-6), As concentrations were in the range of 72.1–82.1 mg\nkg–1 and Cd ranged from 79.8 to 100.5 mg kg–1, with removal efficiencies remaining\nhigh at 91.9%–92.1% for As and 88.2%–90.7% for Cd. Although the percentage\nremoval rates remain relatively stable across the concentration gradient, the absolute\namount of contaminants removed increases significantly with higher pollution levels,\ndemonstrating outstanding robustness of the remediation approach.\nEffective remediation across a wide range of contamination levels (As: 22.8–82.1\nmg kg–1; Cd: 21.1–100.5 mg kg–1) demonstrates the method’s capability to handle\nvarying degrees of industrial contamination.\n1.2 Different pH values\nBased on the data from Supplementary Table 10, the influence of pH on the\nremediation efficacy of LDO was systematically examined using Soil 1-4 as the\nbaseline. The initial pH of Soil 1-4 was 4.21. When adjusted to pH 3.89 (Soil 1-4-1),\nthe As concentration in solution decreased from 303 μg L–1 to 21 μg L–1 after\nremediation, resulting in a removal efficiency of 93.1%. Similarly, the Cd level was\nreduced from 303 μg L–1 to 20 μg L–1, achieving a removal rate of 93.4%. At a neutral\npH of 6.52 (Soil 1-4-2), initial As and Cd concentrations were 661 μg L–1 and 605 μg\nL–1, respectively. After remediation, As dropped to 47 μg L–1 and cadmium to 39 μg L–\n1, with removal efficiencies reaching 92.9% for As and 93.6% for Cd. When the pH was\nfurther adjusted to a more alkaline value of 8.05 (Soil 1-4-3), the initial As and Cd\nconcentrations were 713 μg L–1 and 621 μg L–1. Post-treatment, the concentrations\ndecreased to 54 μg L–1 and 40 μg L–1, translating to removal efficiencies of 92.4% for\nAs and 93.6% for Cd.\nNo matter the pH variation within the tested range (3.89–8.05), the LDO\nmaintained high removal efficiencies (around 90%), demonstrating excellent pH\nadaptability. This broad pH tolerance indicates that the remediation process is highly\nrobust, capable of effectively remediating high-concentration contaminated soils across\ndiverse pH conditions with minimal operational adjustments.\n1.3 Different soil types\nBased on the data from Supplementary Table 11, three soil types, including loamy\nsoil (Soil 1-4), sandy soil (Soil 3), and clayey soil (Soil 4), were tested. In loamy soil,\ninitial As and Cd concentrations were 316 μg L–1 and 331 μg L–1, respectively. After\ntreatment, the concentrations decreased to 32 μg L–1 for As and 28 μg L–1 for Cd,\nachieving removal efficiencies of 89.9% for As and 91.5% for Cd. In sandy soil, the\ninitial levels As and Cd concentrations were 289 μg L–1 and 299 μg L–1, respectively.\nPost-remediation concentrations were reduced to 30 μg L–1 for As and 27 μg L–1 for Cd,\ncorresponding to removal rates of 89.6% for As and 91.0% for Cd. For clayey soil,\ninitial As and Cd concentrations were 318 μg L–1 and 342 μg L–1, respectively, the\ntreatment lowered these concentrations to 28 μg L–1 and 26 μg L–1. This resulted in\nremoval efficiencies of 91.2% for As and 92.4% for Cd.\nThe LDO exhibits high versatility and consistent performance across different soil\ntextures, effectively removing high concentrations of pollutants in various soil matrices.\nFig. 2h The concentration of before and after remediation of mining site soil in solution\nleached.\nSupplementary Table 9. Effects of different As/Cd concentrations on MgMn-LDO\nremediation of mining site soils (dose: 3%).\nBefore (μg L–1) After (μg L–1)\nTotal reduced\nAs/Cd\nSoil reduced percentage\n(mg kg–1) As Cd As Cd\npercentage\n(As, %) (Cd, %)\nSoil 2 22.8/21.1 107 186 13 87.8% 16 91.4%\nSoil 2-1 23.5/25.3 129 211 8 93.8% 20 90.5%\nSoil 2-2 31.2/30.5 155 283 18 88.4% 28 90.1%\nSoil 2-3 50.5/69.9 314 684 29 90.8% 75 89.0%\nSoil 2-4 72.1/80.4 382 755 30 92.1% 89 88.2%\nSoil 2-5 81.5/79.8 416 739 33 92.1% 81 89.0%\nSoil 2-6 82.1/100.5 422 1001 34 91.9% 93 90.7%\nNote: The As/Cd concentrations in the table were measured using the TCLP method (extraction fluid\n#1).\nHere, we used Soil 2 as the baseline and created controlled concentration gradients\nby adding standard samples to Soil 2 to prepare soils with higher contamination levels,\nresulting in the obtained soils labeled as Soil 2-1, Soil 2-2, Soil 2-3, Soil 2-4, Soil 2-5,\nand Soil 2-6. Similar treatment methods have been widely used in previous studies (J.\nHazard. Mater., 2022, 423, 127104; J. Clean. Prod., 2021, 297, 126506). We would\nlike to note that we did not choose six field-collected soils with varying levels of\ncontamination. This controlled approach eliminates confounding factors that would\narise from the inherent heterogeneity of naturally contaminated soils, such as\ndifferences in organic matter, mineralogy, and other soil properties, thereby allowing\nfor a precise evaluation of single-variable effects that would be impossible with\nmultiple field-collected samples.\nIn our concentration gradient experiments, soil samples were categorized into\nthree contamination levels. For the low-contamination group (Soil 2 and Soil 2-1), As\nconcentrations ranged from 22.8 to 23.5 mg kg–1 and Cd from 21.1 to 25.3 mg kg–1,\nwith removal efficiencies of 87.8%–93.8% for As and 90.5%–91.4% for Cd. For the\nmedium-contamination group (Soil 2-2 and Soil 2-3), As concentrations ranged from\n31.2 to 50.5 mg kg–1 and Cd from 30.5 to 69.9 mg kg–1, achieving removal efficiencies\nof 88.4%–90.8% for As and 89.0%–90.1% for Cd. For the high-contamination group\n(Soil 2-4, Soil 2-5, and Soil 2-6), As concentrations were in the range of 72.1–82.1 mg\nkg–1 and Cd ranged from 79.8 to 100.5 mg kg–1, with removal efficiencies remaining\nhigh at 91.9%–92.1% for As and 88.2%–90.7% for Cd. Although the percentage\nremoval rates remain relatively stable across the concentration gradient, the absolute\namount of contaminants removed increases significantly with higher pollution levels,\ndemonstrating outstanding robustness and strong ecological economic advantages of\nthe treatment approach.\nEffective treatment across a wide range of contamination levels (As: 22.8–82.1\nmg kg–1; Cd: 21.1–100.5 mg kg–1) demonstrates the method’s capability to handle\nvarying degrees of industrial contamination.\nSupplementary Table 10. Effects of pH on the MgMn-LDO remediation of mining\nsite soils (dose: 3%).\nBefore (μg L–1) After (μg L–1)\nTotalAs/Cd\nSoil pH reduced percentage reduced percentage\n(mg kg–1) As Cd As Cd\n(As, %) (Cd, %)\nSoil 1-4 4.21 316 a 331 a 32 a 89.9% 28 a 91.5%\nSoil 1-4-1 3.89 303a 303 a 21 a 93.1% 20 a 93.4%\n56.7/31.5\nSoil 1-4-2 6.52 661 b 605 b 47 b 92.9% 39 b 93.6%\nSoil 1-4-3 8.05 713 b 621 b 54 b 92.4% 40 b 93.6%\nNote: a The As/Cd concentrations were measured using the TCLP method (extraction fluid #1).\nb The As/Cd concentrations were measured using the TCLP method (extraction fluid #2).\nHere, the influence of pH on the remediation efficacy of LDO was systematically\nexamined using Soil 1-4 as the baseline. The initial pH of Soil 1-4 was 4.21. When\nadjusted to pH 3.89 (Soil 1-4-1), the As concentration in solution decreased from 303\nμg L–1 to 21 μg L–1 after treatment, resulting in a removal efficiency of 93.1%. Similarly,\nthe Cd level was reduced from 303 μg L–1 to 20 μg L–1, achieving a removal rate of\n93.4%. At a neutral pH of 6.52 (Soil 1-4-2), initial As and Cd concentrations were 661\nμg L–1 and 605 μg L–1, respectively. After remediation, As dropped to 47 μg L–1 and\ncadmium to 39 μg L–1, with removal efficiencies reaching 92.9% for As and 93.6% for\nCd. When the pH was further adjusted to a more alkaline value of 8.05 (Soil 1-4-3), the\ninitial As and Cd concentrations were 713 μg L–1 and 621 μg L–1. Post-treatment, the\nconcentrations decreased to 54 μg L–1 and 40 μg L–1, translating to removal efficiencies\nof 92.4% for As and 93.6% for Cd.\nNo matter the pH variation within the tested range (3.89–8.05), the LDO\nmaintained high removal efficiencies (around 90%), demonstrating excellent pH\nadaptability. This broad pH tolerance indicates that the treatment process is highly\nrobust, capable of effectively remediating high-concentration contaminated soils across\ndiverse pH conditions with minimal operational adjustments.\nSupplementary Table 11. Effects of different soil types on MgMn-LDO remediation\nof mining site soils (dose: 3%).\nBefore (μg L–1) After (μg L–1)\nTotal reduced reduced\nAs/Cd\nSoil Soil Type\n(mg kg–1) As Cd As percentage Cd percentage\n(As, %) (Cd, %)\nSoil 1-4 loamy soil 56.7/31.5 316 331 32 89.9% 28 91.5%\nSoil 3 sandy soil 45.2/31.3 289 299 30 89.6% 27 91.0%\nSoil 4 clayey soil 51.5/37.6 318 342 28 91.2% 26 92.4%\nNote: The As/Cd concentrations were measured using the TCLP method (extraction fluid #1).\nHere, three soil types, including loamy soil (Soil 1-4), sandy soil (Soil 3), and\nclayey soil (Soil 4), were tested. In loamy soil, initial As and Cd concentrations were\n316 μg L–1 and 331 μg L–1, respectively. After treatment, the concentrations decreased\nto 32 μg L–1 for As and 28 μg L–1 for Cd, achieving removal efficiencies of 89.9% for\nAs and 91.5% for Cd. In sandy soil, the initial levels As and Cd concentrations were\n289 μg L–1 and 299 μg L–1, respectively. Post-remediation concentrations were reduced\nto 30 μg L–1 for As and 27 μg L–1 for Cd, corresponding to removal rates of 89.6% for\nAs and 91.0% for Cd. For clayey soil, initial As and Cd concentrations were 318 μg L–\n1 and 342 μg L–1, respectively, the treatment lowered these concentrations to 28 μg L–1\nand 26 μg L–1. This resulted in removal efficiencies of 91.2% for As and 92.4% for Cd.\nThe LDO exhibits high versatility and consistent performance across different soil\ntextures, effectively removing high concentrations of pollutants in various soil matrices.\nPage 9 Line 170 in manuscript revise: Secondly, when LDO was added the highly\ncontaminated industrial soils located at Changde City, Hunan Province, the\nconcentration of As and Cd in solution leached decreases 89.9% and 91.5%,\nrespectively after remediation (Fig. 2h).\nPage 9 Line 173 in manuscript revise: Based on the dose-effect relationship, an\noptimal LDO dosage of 2–3% was identified, offering the best balance between\ntreatment efficacy and LDO consumption (Supplementary Table 8 and detailed\ndiscussion). Moreover, the remediation efficiency for heavily contaminated soils\nremained high across various parameters, including different contamination levels, pH\nvalues, and soil types, with removal efficiencies consistently exceeding 87%\n(Supplementary Table 9‒11 and detailed discussion). These findings demonstrate the\nsubstantial practical potential of in-situ immobilization technique using LDO for the\nremediation of environments contaminated with heavy metals.\n(2) From an agricultural perspective, although the materials have a certain effect\non the remediation of slightly arsenic and cadmium polluted farmland,\nconsidering the factor of food safety, the author did not consider the impact of\nmaterial application on crop yield, soil enzyme activity, and soil physical and\nchemical properties such as pH and salinity. This is insufficient to support the safe\nutilization of arsenic and cadmium polluted farmland. Moreover, from the results\nof this study, the manganese content in crops is too high, posing a risk to food\nsafety. Although there are no relevant limit values in food safety standards, it can\nbe referred to other standards such as (BG4806.9-2023), which stipulates that the\nstandard for metal in food contact is ≤2.0mg/kg. According to the results of this\nstudy, the relevant indicators of rice far exceed this limit value, thus the potential\necological and food safety risks cannot be ignored.\nAuthor Response:\nWe sincerely appreciate the reviewer’s persistent and patient attention to this\ncritical issue, and we are grateful for the valuable reference standard (GB4806.9-2023)\nprovided, which has significantly enhanced our understanding of food safety\nconsiderations. We acknowledge that our previous grasp of various standards was\nincomplete, leading to insufficient depth in addressing this important concern.\nIn response to the reviewer’s constructive feedback regarding the potential risks\nassociated with farmland remediation, we have made substantial revisions to our\nmanuscript. Following the reviewer’s recommendation from the previous review, we\nhave completely removed all content related to farmland contamination remediation\nfrom our supplementary information (original Supplementary Table 10 and\ncorresponding details). Our study now focuses exclusively on the remediation of\nindustrial contaminated sites with varying degrees of pollution levels (Fig. 2h,\nSupplementary Table 8‒11 and detailed discussion), where food safety concerns are not\napplicable.\nImportantly, the reviewer’s comprehensive suggestions regarding farmland\nresearch, including the evaluation of crop yield impacts, soil enzyme activity, and soil\nphysicochemical property changes, provide invaluable guidance for our future research\nendeavors in agricultural soil remediation. We recognize that agricultural applications\nrequire a fundamentally different risk assessment framework that must prioritize food\nsafety, bioaccumulation potential, and comprehensive soil health indicators. These\ninsights will be instrumental in designing future studies specifically targeting farmland\nremediation, should we pursue this research direction with appropriate safety protocols\nand comprehensive risk assessments.\nBy refocusing our current work on industrial site remediation, we can better\ndemonstrate the technical efficacy and economic viability of our approach in contexts\nwhere the stringent food safety requirements do not apply, while laying the groundwork\nfor more comprehensive agricultural applications in future research.\nDetails of the changes to the main text and SI are provided under Question 1.\n(3) If we merely discuss the application of this research in industrial contaminated\nsites, its value is certainly worth looking forward to. However, in the experimental\ndesign of this paper, the representativeness of the contaminated site soil is not\nstrong, mainly due to the low content of arsenic and cadmium. The sixth type of\nsoil is acceptable, but it is necessary to focus on more different pH values, different\ngradients of cadmium and arsenic concentrations, and different dosages of\nmaterials to explore the corresponding dose-effect relationship, ecological\neconomy and feasibility. It is suggested to re-arrange representative soils for\nsupplementary experiments.\nAuthor Response:\nThank you very much for your valuable comments and constructive suggestions,\nwhich have significantly deepened our understanding of this work and provided\nprecious reference value for our subsequent related research. Your insightful feedback\nregarding the representativeness of contaminated site soil has led us to conduct\ncomprehensive supplementary experiments that greatly strengthen our study.\nIn response to your specific concerns, we have systematically investigated various\ngradients of As and Cd concentrations, different material dosages, different pH values,\nand multiple soil types. To ensure rigorous experimental control and isolate individual\nvariables, we employed a carefully designed experimental approach: for dosage effects\n(Supplementary Table 8), we used Soil 1 as the baseline and applied different MgMn-\nLDO dosages to create Soil 1-1, Soil 1-2, Soil 1-3, Soil 1-4, and Soil 1-5. For\nexamining different As/Cd concentrations (Supplementary Table 9), we used Soil 2\nas the baseline and created controlled concentration gradients by adding standard\nsamples to Soil 2 to prepare soils with higher contamination levels, resulting in the\nobtained soils labeled as Soil 2-1, Soil 2-2, Soil 2-3, Soil 2-4, Soil 2-5, and Soil 2-6. For\npH variations (Supplementary Table 10), we used Soil 1-4 as the baseline and\nadjusted pH levels to create Soil 1-4-1, Soil 1-4-2 and Soil 1-4-3. This controlled\napproach eliminates confounding factors that would arise from using naturally\ncontaminated soils with varying organic matter, mineralogy, and other soil properties,\nallowing for precise evaluation of single-variable effects, which would be impossible\nwith multiple field-collected soils due to their inherent heterogeneity. For soil type\neffects (Supplementary Table 11), we deliberately used three distinct soil types: Soil 1-\n4 (loamy soil), Soil 3 (sandy soil), and Soil 4 (clayey soil) to validate the universal\napplicability of our remediation approach across different soil matrices. Based on these\nsupplementary data, we would like to address the three key aspects you highlighted:\n3.1 Dose-effect relationship\nOur supplementary experiments establish clear quantitative dose-response patterns\nacross the Soil 1 series ranging from Soil 1-1 through Soil 1-5 (Supplementary Table\n8). The mathematical relationship shows that As removal efficiency progressively\nincreases from 86.7% at 1% dosage (Soil 1-1) to 91.1% at 5% dosage (Soil 1-5), while\nCd removal efficiency improves from 86.1% to 94.6% across the same dosage range.\nThe dose-response characteristics reveal a linear response phase within the 1–2%\ndosage range showing steady improvement, followed by a saturation phase beyond 3%\ndosage where marginal improvement diminishes significantly. This establishes the\noptimal dose range of 2–3% that provides the best balance between effectiveness\nand material consumption.\nFurthermore, as shown in Supplementary Table 9, our concentration-dependent\nresponse study using the Soil 2 series (Soil 2 through Soil 2-6) demonstrates that 3%\ndose-effect relationships remain consistent across different contamination levels\nspanning 22.8–82.1 mg kg–1 As and 21.1–100.5 mg kg–1 Cd, with removal efficiency\nmaintained above 88% for all scenarios, confirming the robustness and predictability\nof the treatment approach.\n3.2 Ecological economics\n3.2.1 Dose-effect economics\nBuilding upon the established dose-effect relationships, we conducted\ncomprehensive ecological-economic analysis that reveals optimal cost-benefit\nintegration. The cost for the preparation of LDO has been listed in Supplementary Table\n6. The cost-effectiveness analysis reveals that the 1–2% dosage range (Soil 1-1 to Soil\n1-3) provides the most significant benefit improvement. Because As removal rate\nincreased by 2.2% and Cd removal rate by 4.5% per $48.5 cost increase. However, the\n2–3% range (Soil 1-3 to Soil 1-4) shows diminishing marginal returns, with an\nadditional cost of $48.5, the As removal rate only increased by 1%, while the Cd\nremoval rate rose by 0.9%. Thus, cost-effectiveness maximization occurs at the 2%\ndosage level (Soil 1-3), where $97 m–3 investment achieves 88.9% As removal and 90.6%\nCd removal while maintaining soil biological integrity and achieving greater than 88%\ncontaminant immobilization.\n3.2.2 Environmental benefit economics\nHigher contamination levels demonstrate superior environmental benefit\neconomics. Specially, for low contamination Soil-2 (As: 22.8 mg kg–1, Cd: 21.1 mg kg–\n1) (Supplementary Table 9), the removal efficiencies achieved were 87.8% for As and\n91.4% for Cd, while for high contamination Soil 2-6 (As: 82.1 mg kg–1, Cd: 100.5 mg\nkg–1), the removal efficiencies were 91.9% for As and 90.7% for Cd. Although\npercentage removal rates show slight decreases at higher contamination levels, the\nabsolute environmental benefits per unit investment increase significantly due to the\nsubstantially larger quantities of contaminants removed. This demonstrates the\necological economic advantage where heavily contaminated soils generate greater\nenvironmental restoration value per dollar invested, as the same treatment cost achieves\nremoval of considerably more pollutant mass, thereby optimizing the balance between\necological remediation and economic input. This pattern exemplifies the ecological\neconomics principle of “environmental benefit maximization,” where economic\nefficiency is measured not merely by percentage improvements but by the total\nenvironmental restoration achieved per unit cost.\n3.3 Feasibility\nOur supplementary data demonstrate excellent technical, operational and economic\nrobustness across diverse environmental conditions:\n3.3.1 Technical feasibility\nConcentration robustness: The controlled concentration gradients study across\nthe Soil 2 series (Soil 2 through Soil 2-6) demonstrates superior economic adaptability\nacross pollution gradients, with removal rates remaining stable (87.8–93.8% for As,\n88.2–91.4% for Cd) across the entire tested range (Supplementary Table 9). Higher\ncontamination levels show consistent treatment effectiveness, validating the\ntreatment’s reliability under varying pollution scenarios.\npH adaptability: Using Soil 1-4 as the baseline and adjusting pH to create Soil 1-\n4-1 (pH 3.89), Soil 1-4-2 (pH 6.52) and Soil 1-4-3 (pH 8.05) (Supplementary Table 10),\nthe material maintains consistently high efficiency (89.9–93.6% removal rates) across\na wide pH range, demonstrating exceptional technical feasibility without requiring\nextensive pH adjustment. This broad pH tolerance significantly reduces operational\ncomplexity and costs.\nSoil type versatility: Our comparative study across three distinct soil types shows\nconsistent performance: Soil 1-4 loamy soil (As 89.9%, Cd 91.5%), Soil 3 sandy soil\n(As 89.6%, Cd 91.0%), and Soil 4 clayey soil (As 91.2%, Cd 92.4%) (Supplementary\nTable 11). This indicates universal applicability across diverse soil ecosystems without\ndisrupting soil structure or biological functions.\n3.3.2 Operational feasibility\nImplementation simplicity: Direct soil application without complex equipment\nrequirements\nQuality control: Predictable performance across all tested conditions ensures\nreliable outcomes\nMaintenance requirements: Minimal post-application monitoring needed based\non stability data\n3.3.3 Economic feasibility:\nCapital requirements: $48.5–145.5 m–3 represents competitive pricing compared\nto alternative technologies (ACS EST Engg., 2023, 3, 5, 714–724; Nature Environment\nand Pollution Technology, 2020, 19, 5, 1899-1904; Environ. Earth Sci., 2025, 84, 401)\nSupplementary Table 6. Cost table for the preparation of MgMn-LDH.\nChemical Unit Price (¥ t‒1) Amount Used (t) Total Cost (¥)\nMg(NO3)2·6H2O 2200 3.1 6820\nMn(NO3)2·4H2O 4300 (solution, 50%) 1.2 5160\nNaOH 2100 0.92 1932\nTotal Cost Breakdown:\n1. raw cost of MgMn-LDH: 6820 + 5160 + 1932 = 13912 ¥ t–1\n2. Energy consumption:\nelectric energy:1920 kWh × 0.95 ¥ kWh–1 = 1824 ¥\nNatural Gas (including dry and calcined): 410 Nm3×3.5 ¥ (Nm3) –1 = 1435 ¥\n3. Total cost MgMn-LDO:\n13912 +1824 +1435 = 17171 ¥\nThe yield of MgMn-LDO: 1 t×74.5% = 745 kg\nNamly: the direct cost of MgMn-LDO was 17171 ÷ 745 × 1000 = 23048 ¥ t–1 = 3230.3\n$ t–1\nAccording to the optimal dosage of 750 kg⋅ha−1, the cost of remediation with MgMn-\nLDO is about 1725 ¥ per hectare.\n4. Total cost MgMn-LDO (1 m3 of soil, Dose = 1%):\n1 m3 = 1.5 t; 1.5 t ×1%×3230.3 $ t–1 = 48.5 $\nNamly: According to the 1% dosage of MgMn-LDO, the cost per m3 of contaminated\nsoil is 48.5 $.\nFurthermore, if we chose MgSO and MnSO as raw materials, and with the future\n4 4\nbreakthroughs in key technologies for large-scale production, the production cost will\nfurther significantly reduce. Moreover, based on the experiment dates, the effect can\nlast for many years with once remediation, exhibiting cost-effective for practical\napplications.\nSupplementary Table 8. Effects of different MgMn-LDO dosages on the remediation\nof mining site soils.\nBefore (μg L–1) After (μg L–1)\nTotalAs/Cd\nSoil Soil Dose reduced percentage reduced percentage\n(mg kg–1) As Cd As Cd\n(As, %) (Cd, %)\nSoil 1-1 1% 42 86.7% 46 86.1%\nSoil 1-2 1.5% 40 87.3% 40 87.9%\nSoil 1 56.7/31.5 316 331 Soil 1-3 2% 35 88.9% 31 90.6%\nSoil 1-4 3% 32 89.9% 28 91.5%\nSoil 1-5 5% 28 91.1% 18 94.6%\nNote: The As/Cd concentrations in the table were measured using the TCLP method (extraction fluid\n#1).\nHere, the supplementary experiments establish clear quantitative dose-response\npatterns across the Soil 1 series ranging from Soil 1-1 through Soil 1-5. The\nmathematical relationship shows that As removal efficiency progressively increases\nfrom 86.7% at 1% dosage (Soil 1-1) to 91.1% at 5% dosage (Soil 1-5), while Cd\nremoval efficiency improves from 86.1% to 94.6% across the same dosage range. The\ndose-response characteristics reveal a linear response phase within the 1–2% dosage\nrange showing steady improvement, followed by a saturation phase beyond 3% dosage\nwhere marginal improvement diminishes significantly. This establishes the optimal\ndose range of 2–3% that provides the best balance between effectiveness and material\nconsumption.\nBuilding upon the established dose-effect relationships, we conducted\ncomprehensive ecological-economic analysis that reveals optimal cost-benefit\nintegration. The cost-effectiveness analysis reveals that the 1–2% dosage range (Soil 1-\n1 to Soil 1-3) provides the most significant benefit improvement. Because As removal\nrate increased by 2.2% and Cd removal rate by 4.5% per $48.5 cost increase. However,\nthe 2–3% range (Soil 1-3 to Soil 1-4) shows diminishing marginal returns, with an\nadditional cost of $48.5, the As removal rate only increased by 1%, while the Cd\nremoval rate rose by 0.9%. Thus, cost-effectiveness maximization occurs at the 2%\ndosage level (Soil 1-3), where $97 m–3 investment achieves 88.9% As removal and 90.6%\nCd removal while maintaining soil biological integrity and achieving greater than 88%\ncontaminant immobilization.\nPage 9 Line 173 in manuscript revise: Based on the dose-effect relationship, an\noptimal LDO dosage of 2–3% was identified, offering the best balance between\ntreatment efficacy and LDO consumption (Supplementary Table 8 and detailed\ndiscussion). Moreover, the remediation efficiency for heavily contaminated soils\nremained high across various parameters, including different contamination levels, pH\nvalues, and soil types, with removal efficiencies consistently exceeding 87%\n(Supplementary Table 9‒11 and detailed discussion). These findings demonstrate the\nsubstantial practical potential of in-situ immobilization technique using LDO for the\nremediation of environments contaminated with heavy metals.\nOther Details of the changes to the main text and SI are provided under Question\n1.\nResponse to Reviewer #2\nComments:\n1. This article has undergone multiple rounds of revisions and improvements, resulting in\na qualitative improvement in the quality of the paper. Although the material used in this\nstudy has a relatively low fixation efficiency for arsenic and cadmium at a dosage of 3%,\nthe passivation efficiency steadily increases with the increase of the dosage. Especially for\nthe remediation of soil in arsenic cadmium composite contaminated sites, it has a good\nremediation effect and certain application value. However, it should be discussed whether\nthere is an economic cost advantage when the dosage is increased. From the current quality\nof argumentation, it now basically meets the publication requirements of your journal.\nAuthor Response:\nWe sincerely appreciate your contributions to improving the quality of the manuscript,\nas well as your recognition of its enhanced quality and application value. For actual heavy metal\nremediation sites, economic efficiency is one of the indispensable considerations. According to\nyour suggestion, we have conducted a comprehensive eco-economic assessment for higher\ndosage of 6% and 10%.\n1. Cost Analysis:\nTotal cost MgMn-LDO (1 m3 of soil, Dose = 1%):\n1 m3 = 1.5 t; 1.5 t ×1%×3230.3 $ t–1 = 48.5 $\nSimilarly, the costs for different dosages are calculated as follows:\n1% dosage: 48.5 $ m–3 of contaminated soil\n6% dosage: 1.5 t × 6% × 3230.3 $ t⁻¹ = 291 $ m–3 of contaminated soil\n3\n10% dosage: 1.5 t × 10% × 3230.3 $ t⁻¹ = 484.5 $ m–3 of contaminated soil\n1.2 Economic Feasibility Assessment:\nThe cost analysis reveals a significant escalation pattern: from 1% to 6% dosage,\ncosts increase 6-fold, while from 6% to 10%, costs increase 1.67-fold. Although the 10%\ndosage demonstrates superior remediation efficiency, the cost reaches 484.5 $ m–3, which may be\neconomically prohibitive for large-scale remediation projects.\n1.3 Optimal Dosage Recommendation:\nConsidering both remediation effectiveness and economic viability, the 6% dosage (291\n$ m–3) represents the most advantageous option for practical applications. This dosage achieves\nan optimal balance between satisfactory remediation performance and reasonable cost control.\nThe 10% dosage could serve as an alternative for severely contaminated sites, but should be\nevaluated based on specific contamination levels and project budgets.\nAs the degree of heavy metal pollution and the area of remediation sites increase, the dosage\nof MgMn-LDO will rise accordingly, inevitably leading to increased costs. However, if we\nchoose MgSO and MnSO as raw materials, and with future breakthroughs in key technologies\n4 4\nfor large-scale production, the production cost will be further significantly reduced. Moreover,\nbased on our experimental data, the remediation effect can last for many years with a single\ntreatment, demonstrating long-term cost-effectiveness for practical applications.\nThis comprehensive cost-benefit analysis supports the practical applicability of our material\nwhile providing clear guidance for dosage selection in real-world remediation scenarios.\nPage s53 in Supplementary Information:\nSupplementary Table 7. Cost table for the preparation of MgMn-LDH.\nMg(NO3)2·6H2O 2200 3.1 6820\nMn(NO3)2·4H2O 4300 (solution, 50%) 1.2 5160\nNaOH 2100 0.92 1932\nTotal Cost Breakdown:\n1. raw cost of MgMn-LDH: 6820 + 5160 + 1932 = 13912 ¥ t–1\n2. Energy consumption:\nelectric energy:1920 kWh × 0.95 ¥ kWh–1 = 1824 ¥\nNatural Gas (including dry and calcined): 410 Nm3×3.5 ¥ (Nm3) –1 = 1435 ¥\n3. Total cost MgMn-LDO: 13912 +1824 +1435 = 17171 ¥\nThe yield of MgMn-LDO: 1 t×74.5% = 745 kg\nNamly: the direct cost of MgMn-LDO was 17171 ÷ 745 × 1000 = 23048 ¥ t–1 = 3230.3 $ t–\nabout 1725 ¥ per hectare.\n4. Total cost MgMn-LDO (1 m3 of soil, Dose = 1%):\n1 m3 = 1.5 t; 1.5 t ×1%×3230.3 $ t–1 = 48.5 $\nNamly: According to the 1% dosage of MgMn-LDO, the cost per m3 of contaminated soil is 48.5\n$.\nFurthermore, if we chose MgSO and MnSO as raw materials, and with the future\n4 4\nbreakthroughs in key technologies for large-scale production, the production cost will further\nsignificantly reduce. Moreover, based on the experiment dates, the effect can last for many years\nwith once remediation, exhibiting cost-effective for practical applications.\n5"}]

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