Dynamic stretching beyond electron transfer in a homointerpenetrated metal‒organic framework for enhanced Fenton-like reactions

Domain: neuroscience
Published: 2026-01-30
Editorial outcome: minor_revision

Abstract
While extensive efforts have been devoted to enhancing electron transfer efficiency through metal valence cycling in heterogeneous Fenton-like reactions, the potential catalytic improvement induced by dynamic structural stretching remain unexplored. Here, we introduce a homointerpenetrated Fe-based metal‒organic framework (BUC-95) featuring a dynamic stretchable structure that significantly boosts the heterogeneous Fenton-like catalytic performance. BUC-95’s unique stretchable structure achieved effective peroxydisulfate activation for degrading various micropollutants via Fe(IV)=O species, facilitated by a reduced energy barrier for Fe(IV)=O formation through modulation of the electron density at Fe sites. DFT calculations suggest that, compared with the isostructural analogue with hydrogen bond-restricted stretching, the flexible dynamic stretching in BUC-95 overcomes the inherent electron transfer limitations from Fe sites to peroxydisulfate, enhancing the ofloxacin degradation performance. Practically, BUC-95 demonstrated effective continuous-flow degradation and detoxification of micropollutants. This work establishes dynamic stretching as a crucial design principle for advancing environmental remediation materials and technologies.

Introduction
Fenton-like reactions have been extensively employed to degrade emerging refractory contaminants in wastewater. These reactions leverage the ability of oxidants such as hydrogen peroxide (H2O2), peroxydisulfate (PDS), and peroxymonosulfate (PMS) to form diverse reactive oxygen species (ROSs) through activation processes1–5. During the reaction process, the efficiency of electron transfer from catalytic sites to the oxidants plays a critical role, as it directly governs the productivity and speciation of ROSs6,7. Extensive research efforts have been devoted to designing heterogeneous catalysts from micron to atomic scales8,9 to increase electron transfer kinetics through strategically modulating the electronic microenvironment surrounding catalytically active sites10–13. Nevertheless, the inherent complexity of interfacial reaction dynamics frequently induces transient structural evolution in catalysts, a phenomenon often overlooked in conventional studies but capable of exerting profound implications on the overall catalytic oxidation mechanisms14–16.

A few recent research efforts have focused on elucidating the critical role of dynamic structural distortion in modulating the local coordination environment of metal sites during catalytic processes. For example, it was reported that the interaction between host and guest molecules might induce the stretching vibrations of O‒Sr‒O and Co/Ti‒O bonds within the Co/La-SrTiO3 catalyst to increase electron transfer efficiency from PMS to metal sites16. However, the current understanding remains constrained by two fundamental limitations: (1) the catalytic performance improvement achievable through stretching vibrations of metal‒oxygen bonds is inherently limited because of the insufficient structural adaptability of conventional catalysts; and (2) the development of synthetic strategies for engineering catalysts with programmable dynamic stretching architectures presents technical challenges, particularly in advanced oxidation processes. More importantly, the relationship between the structural dynamic stretching of catalysts and the resulting catalytic activity remains poorly defined.

Interpenetrated metal‒organic frameworks (MOFs) offer a promising paradigm for addressing these challenges. Characterized by mutually entangled yet noncovalently bonded identical networks17,18, these architectures might exhibit intrinsic structural flexibility derived from the tunable spatial separation between constituent frameworks. This unique structural feature enables reversible deformation of the entire framework in response to external stimuli like chemical activation. Unlike the localized pore breathing in conventional MOFs or the ligand-based flexibility in flexible MOFs (Supplementary Fig. 1), the large-scale dynamic adaptability of interpenetrated MOFs make them ideal model systems for studying whole-framework dynamics in Fenton-like reaction mechanisms.

In this work, a homointerpenetrated MOF (denoted BUC-95, CCDC:2352385) with a dynamically stretchable framework was synthesized, which exhibited exceptional degradation efficiency for diverse organic contaminants through a high-valent iron-oxo (Fe(IV)=O)-dominated oxidation pathway. Experimental characterizations and density functional theory (DFT) calculations revealed that the presence of hydroxylated BUC-95 not only regulated the d-orbitals electron density of Fe but also greatly reduced the activation energy barrier, promoting the formation of Fe(IV)=O in the BUC-95-OH/PDS system. Compared with the homointerpenetrated BUC-96 counterpart with restricted dynamic stretching, the flexible dynamic stretchability of the homointerpenetrated BUC-95 framework overcame the limitation of weak electron transfer performance in PDS activation processes to ultimately improve the catalytic ofloxacin (OFC) degradation performance. Furthermore, the construction of a fixed-bed continuous-flow catalytic reactor and tests with multiple toxicity assessment systems confirmed the stable long-term catalytic activity and exceptional detoxification capabilities of the BUC-95/PDS system. This work provides insight into the design and preparation of interpenetrated MOFs with dynamic stretching features for highly efficient water purification via Fenton-like reactions.

Results
Characterization and structural analysis
BUC-95 was synthesized from FeSO4·7H2O, 4,4′-bipyridine (bpy) and 1,4-benzenedicarboxylic acid (H2bdc) via a facile microwave-assisted method (Supplementary Fig. 2). According to scanning electron microscopy (SEM) (Supplementary Fig. 3) and high-resolution transmission electron microscopy (HR-TEM) (Fig. 1b) analysis, BUC-95 exhibited a rod-like morphology, with particles sized ~15.0μm×1.0μm×0.3μm. The small size of the particles rendered the conventional single-crystal X-ray technique unsuitable, so microcrystalline electron diffraction (microED) was employed to acquire single-crystal data19,20. The crystal structure was determined ab initio from the microED dataset using the SHELX software package21 (Supplementary Tables 1 and 2). The 3D reconstructed reciprocal lattice (Fig. 1a) obtained via microED revealed that BUC-95 (molecular formula Fe4(bpy)4(bdc)4) crystallizes in a triclinic unit cell with a = 11.490(2) Å, b = 16.460(3) Å and c = 21.183(4) Å and belongs to space group P1. BUC-95 features a homointerpenetrated structure consisting of a pair of identical 3D frameworks. The framework contains paddle-wheel-type binuclear Fe units, where each Fe atom is coordinated by four oxygen atoms from COO– groups of three deprotonated bdc2− ligands and two nitrogen atoms from two bpy ligands, forming a 3D framework (Fig. 1c and Supplementary Fig. 4).

The experimental powder X-ray diffraction (PXRD) patterns showed strong agreement with the simulated profiles derived from crystallographic data determined via microED, thereby confirming the phase purity of the as-synthesized BUC-95 (Fig. 1e). This finding was also confirmed through HR-TEM (Fig. 1d), elemental mapping (Supplementary Fig. 5), X-ray photoelectron spectroscopy (XPS) (Supplementary Fig. 6), Fourier transform infrared (FTIR) (Supplementary Fig. 7)22, thermogravimetric analysis (TGA) (Supplementary Fig. 8), and elemental analyses (Supplementary Table 3).

To elucidate the role of dynamic stretching in BUC-95, BUC-96 (CCDC: 2263764) (Supplementary Fig. 9) was synthesized as an isostructural analog for comparison23. In BUC-96, H2bdc was replaced with 2,5-dihydroxyterephthalic acid (H4dhtp). Single-crystal X-ray diffraction (SCXRD) data revealed that BUC-96 adopts a homointerpenetrated 3D framework, in which Fe sites are coordinated with four oxygen atoms from three partly deprotonated H2dhtp2− ligands and two nitrogen atoms from two bpy ligands (Supplementary Fig. 10). It was observed that N,N-dimethylformamide (DMF) molecules were encapsulated within the channels of BUC-96, where the O atoms from DMF form hydrogen bonds (2.509 Å) with hydrogen atoms from bpy ligand. These interactions almost completely restrict the dynamic stretching behavior inherent to the homointerpenetrated framework (Supplementary Fig. 11 and Supplementary Video 1). Additionally, the independent gradient model (IGM) visualization further demonstrated strong hydrogen-bonding interactions (represented by blue isosurfaces) between the DMF molecule and bpy ligands24 (Supplementary Fig. 12).

As depicted in Fig. 1f and Supplementary Fig. 13, the X-ray absorption near edge structure (XANES) data and corresponding fitted information indicated that the valence state of Fe ranged between +2 and +3 in BUC-95 and BUC-96. This observation aligns with the Fe 2p XPS spectra (Supplementary Fig. 14). Additionally, a distinct positive shift (ca. 0.35 eV) in the Fe K-edge and the increased intensity of the whole O K-edge (Supplementary Fig. 15) were observed for BUC-95 compared with BUC-96, indicating a lower electron density at the Fe and O centers in BUC-9525. Extended X-ray absorption fine structure (EXAFS) spectra confirmed that the Fe atoms in BUC-95 and BUC-96 were six-coordinated by four O atoms from bdc2− or H2dhtp2− and two N atoms from bpy ligands (Fig. 1g). In particular, the EXAFS results revealed that the average lengths of the Fe‒O and Fe‒N bonds in BUC-95 were 2.402 Å and 2.255 Å, respectively (Supplementary Table 4), which are comparable to those of the Fe‒O (1.98 Å ~ 2.402 Å) and Fe‒N (2.14 Å ~ 2.255 Å) bond obtained from microED. The wavelet transform (WT) (Fig. 1h and Supplementary Fig. 16) plots revealed a clear intensity feature at ca. 3.0 Å−1 corresponding to Fe‒O/N coordination shells in both BUC-95 and BUC-96, whereas the absence of characteristic Fe‒Fe scattering paths at ca. 7.0 Å−1 excluded Fe‒Fe bonds.

Catalytic performance and preliminary mechanism
To systematically assess the Fenton-like catalytic efficiency of BUC-95 across various oxidant systems, ofloxacin (OFC), a representative fluoroquinolone antibiotic, was selected as the model contaminant. BUC-95 demonstrated superior peroxydisulfate (PDS) activation capability, achieving >99.99% OFC removal within 10.0 min, accompanied by an exceptional pseudo-first-order rate constant (kobs) of 5.52 min−1 (Fig. 2a and Supplementary Fig. 17). This performance surpassed those in different systems like BUC-95/PMS (81.4% removal, 2.94 min−1), BUC-95/H2O2 (86.6% removal, 3.46 min−1), conventional homogeneous Fe(II)/PDS (13.0% removal, 0.37 min−1) (Supplementary Fig. 18). And it also exceeded other MIL-based systems like MIL-88A(Fe)/PDS (41.2% removal, 0.82 min−1), MIL-88B(Fe)/PDS (41.7% removal, 0.83 min−1), MIL-88C(Fe)/PDS (48.43% removal, 0.94 min−1), MIL-53(Fe)/PDS (46.23% removal, 0.90 min−1), MIL-100(Fe)/PDS (41.96% removal, 0.73 min−1) and MIL-101(Fe)/PDS (54.46% removal, 0.79 min−1) by 1.88-fold, 1.60-fold, 14.9-fold, 6.73-fold, 6.65-fold, 5.87-fold, 6.13-fold, 7.56-fold and 6.99-fold, respectively (Supplementary Figs. 19 and 20), which was further supported by the normalized results based on BET surface area and Fe content between MIL-based catalyst and BUC-95 (Supplementary Fig. 21 and Supplementary Table 5).

DFT calculations were applied to investigate the difference in the activation process of PDS, PMS and H2O2 on BUC-95. Computational modeling of the adsorption configurations revealed distinct binding energetics: PDS exhibited the most favorable adsorption energy (Eads = −6.95 eV) on BUC-95, followed by H2O2 (−4.94 eV) and PMS (−2.16 eV) (Fig. 2b and Supplementary Fig. 22). Bader charge analysis was applied to quantify the interfacial electron transfer, revealing that 1.6437 e⁻ were transferred from BUC-95 to PDS, which was greater than those to H2O2 (1.0452 e⁻), and PMS (1.0367 e⁻) (Supplementary Fig. 23). These results collectively confirmed that PDS is the thermodynamically preferred oxidant activated by BUC-95.

The BUC-95/PDS system exhibited a 2.3-order-of-magnitude increase in reaction rate (kobs = 5.52 min−1) compared with that of its structural analog BUC-96 (kobs = 0.03 min−1, Fig. 2c), suggesting that the flexible dynamic stretching of the homointerpenetrated BUC-95 framework may substantially enhance the catalytic performance compared with the BUC-96 with restricted stretching induced by hydrogen bonding interactions.

Additionally, broad-spectrum degradation capability was validated for diverse contaminants, like enrofloxacin (ENR, kobs = 6.50 min−1), norfloxacin (NOR, 8.61 min−1), ciprofloxacin (CIP, 9.96 min−1), tetracycline (TC, 9.98 min−1), and diclofenac (DCF, 9.95 min−1), with performance exceeding that of other catalysts by 1~3 orders of magnitude (Fig. 2d, e, Supplementary Fig. 24 and Supplementary Table 6), which were consistent with the electrostatic potential (ESP) results. Nearly 100% OFC degradation efficiency and minimal Fe leaching (<1.5 mg L−1) after ten operational cycles demonstrated the robust reusability and stability of BUC-95 (Fig. 2f and Supplementary Fig. 25), which were confirmed by the SEM images and PXRD patterns of the BUC-95 after five and ten cycles (Supplementary Fig. 26). BUC-95 maintained robust catalytic performance under a low PDS dosage (0.35 mM) across a wide pH range (2.5~8.5) (Supplementary Fig. 27), demonstrated strong resistance to multiple anions (Cl−, SO42−, NO3−, HCO3−) and humic acid (HA) (Supplementary Fig. 28), and performed effectively in complicated aqueous matrices like tap water, lake water, and rainwater (Supplementary Fig. 29). These results collectively suggest that nonradical oxidation pathways might dominate the degradation process. The addition of Cl− resulted in only minor inhibition of OFC degradation (<13.0% decline), which could be attributed to the competitive consumption of a few active species to form less reactive chlorine radicals3. Similarly, the slight decline in catalytic performance (ca. 20.0%) observed in simulated aqueous samples formulated from tap water was ascribed to the relatively high Cl− content, as quantified by ion chromatography (CIC-D160+, Qingdao Shenghan Chromatograph Technology Co., Ltd.) (Supplementary Table 7).

To identify the ROSs involved in the BUC-95/PDS/OFC system, quenching experiments were conducted using methanol (MeOH, for SO4•−), tert-butanol (TBA, for •OH), benzoquinone (BQ, for O2•−), nitrogen (N2, for O2•−), and L-histidine (L-his, for 1O2) as trapping agents11,26,27. The presence of these trapping agents led to slight inhibition (MeOH: 4.8% inhibition; TBA: 4.4% inhibition; L-his: 2.7% inhibition; BQ: 5.9% inhibition) of OFC degradation (Fig. 2g and Supplementary Fig. 30), demonstrating the negligible role of SO4•−, •OH, O2•−, and 1O2. Moreover, the electron spin resonance (ESR) results (Supplementary Fig. 31) revealed the presence of DMPO-SO4•−, DMPO-•OH, DMPO-O2•−, and TEMP-1O2 signals, indicating the formation of SO4•−, •OH, O2•−, and 1O2. Upon the addition of D2O, the TEMP-1O2 signal showed an obvious decrease (Supplementary Fig. 32a), a phenomenon attributable to solvent isotope and exchange effects between D2O and H2O28. To further evaluate the contribution of 1O2 in the BUC-95/PDS system, the OFC degradation experiment was conducted in D2O. Only slight declines in both OFC degradation efficiency (ca. 7.0%) and reaction rate (1.9 min−1) were observed (Supplementary Fig. 32b), indicating that 1O2 did not play a substantive role in OFC removal.

As probes of radicals, benzoic acid (BA) and 4-nitrobenzoic acid (NBA), which have low ESP values (Supplementary Fig. 33), slightly inhibited OFC removal. The degradation efficiencies of BA and NBA were only approximately 12.0% and 22.0%, respectively, further indicating the minor roles of SO4•− and •OH (Supplementary Fig. 34). While, the use of dimethyl sulfoxide (DMSO), a high-valent iron-oxo (HVIO) scavenger, resulted in obvious inhibition (with a 23.57% decrease in removal efficiency) (Fig. 2g). This observation, coupled with the maintained catalytic activity under radical-suppressing conditions, strongly suggests that HVIO serves as the primary oxidative species rather than conventional ROSs.

Mechanistic insights into Fe(IV)=O formation
To investigate HVIO species formation, chemical trapping, Mössbauer spectroscopy and first-principles modeling were employed. HVIO species can oxidize methyl phenyl sulfoxide (PMSO) into methyl phenyl sulfone (PMSO2)29,30. PMSO oxidation tests revealed the production of 35.21 µM PMSO2 (6.4-fold increase compared to that of the individual PDS system), with a kobs of 0.31 min−1 (103-fold increase over that of the individual PDS system) using the BUC-95/PDS system (Fig. 3a and Supplementary Fig. 35). The 57Fe Mössbauer spectra of BUC-95 revealed a characteristic quadrupole splitting shift of −0.17 mm s−131,32, which is characteristic of the formation of HVIO species (Fig. 3b, c and Supplementary Table 8).

Typically, the formation of HVIO species can be attributed to both Fe(II) and Fe(III)33. Site masking experiments using 1,10-phenanthroline (phen, for Fe(II)) and KSCN (for Fe(III)) demonstrated that Fe(II) is the predominant precursor for HVIO formation, with OFC degradation inhibition rates of 29.03% and 86.03% following the addition of phen and KSCN, respectively (Supplementary Fig. 36). XPS quantification revealed a 15.78% decrease in the Fe(II) content after the reaction (Supplementary Fig. 37), which is generally consistent with the HVIO concentration (16.4%) determined via Mössbauer spectroscopy (Fig. 3d). Fluorobenzene (FB) was selected as the specific probe to determine the contribution of SO4•− to the HVIO formation because of its strong ability to coordinate with radicals. PMSO consumption (71.35 µM) significantly increased, whereas PMSO2 production (32.21 µM) did not obviously change in the BUC-95/PDS/FB system (Fig. 3a). These findings suggest that it is not the primary pathway for HVIO formation, highlighting a distinct pathway from conventional SO4•−-mediated ones34.

Previous literature reported that Fe sites, acting as the Lewis acid sites, can capture -OH from H2O to form Fe-OH species, which subsequently convert into HVIO species33,35. In BUC-95, electron paramagnetic resonance (EPR) spectroscopy revealed signals of oxygen vacancies at g = 2.003 (Supplementary Fig. 38), suggesting that oxygen vacancies may serve as favorable sites for Fe-OH formation. Further evidence comes from the O 1s XPS spectra, where a new peak emerges at 533.2 eV after reaction (Fig. 3e), consistent with the formation of Fe-OH species. These findings support a reaction mechanism in which HVIO generation is initiated by the adsorption of -OH from H2O onto Lewis acidic Fe(II) sites in BUC-95, forming Fe-OH intermediates that undergo a two-step oxygen atom transfer pathway to ultimately generate HVIO and SO42−.

Considering that HVIO species may exist as either Fe(IV)=O or Fe(V)=O, DFT calculations were conducted to identify the dominant HVIO species in the BUC-95-OH/PDS system36,37. A DFT model of BUC-95-OH/PDS was constructed, and the corresponding total adsorption energy for -OH and PDS was calculated as −9.61 eV, indicating that the HVIO formation spontaneous despite the presence of -OH groups (Fig. 3f). Bader charges from the two Fe sites to PDS and -OH were 1.6690 and 0.4823 (Fig. 3g), respectively, indicating that the -OH group in BUC-95 may facilitate partial charge transfer to support HVIO formation. This interpretation aligns with the observed reduction in electron density at the Fe site from 7.06 to 6.29 in the BUC-95-OH/PDS system (Supplementary Fig. 39). To assess the interaction between BUC-95-OH and PDS, the projected crystal orbital Hamilton population (pCOHP) was used. The calculated bond energies for Fe‒O (O from -OH) and Fe‒O (O from PDS) in the BUC-95-OH/PDS system were 1.82 eV and 2.00 eV, respectively, which are slightly lower than that of the Fe‒O bond in the BUC-95/PDS system (2.03 eV). This finding suggests that PDS is more readily desorbed during HVIO formation in the BUC-95-OH/PDS system (Fig. 3h).

More importantly, the critical roles of Fe and O orbitals and spin electrons in regulating Fe(IV)=O formation was strongly supported by projected density of states (PDOS) analysis (Supplementary Figs. 40–44). The splitting pattern of the Fe d orbitals undergoes significant changes upon adsorption of PDS and surficial -OH. This co-adsorption induces a transition in the crystal field splitting of Fe sites from tetrahedral to octahedral configuration, accompanied by a redistribution of electron density (Supplementary Fig. 45). Hybridization between the p orbitals of O atoms from PDS as well as -OH groups and the d orbitals of the Fe centers in BUC-95 lead to the formation of antibonding orbitals cross the Fermi level. As a result, two electrons from Fe dz2 orbitals are transferred to promote the formation of Fe(IV)=O species (Fig. 3i). The doublet peaks at pre-edge (ca. 528.0~535.0 eV) in O K-edge XAFS spectra revealed the feature of Fe 3d-O 2p hybridization (Fig. 3j). The reduced shaded area percentage (from 14.21% to 9.14%) and the decreased intensity of doublet peaks after reaction, verifying the intense hybridization between Fe 3d and O 2p orbitals, which supported the above results38,39. Thermodynamic profiling on the basis of the Gibbs free energy of the Fe(IV)=O formation process with and without -OH groups in BUC-95 demonstrated that BUC-95-OH exhibited a lower energy (−3.55 eV) than did BUC-95 (1.71 eV) in the rate-limiting step. This finding suggests that the energy barrier for Fe(IV)=O formation was markedly reduced in the presence of -OH groups (Fig. 3k).

Fe(IV)=O is recognized as a nonradical ROS with strong electrophilic properties and preferentially oxidizes electron-rich pollutants, as observed in highest occupied molecular orbital (HOMO) energy correlations40. The selective oxidation behavior of Fe(IV)=O in degrading the above mentioned electron-rich pollutants, such as ENR, NOR, CIP, TC, DCF, and electron-deficient pollutants, such as BA and NBA, was assessed by calculating their HOMO energy levels41. The HOMO values of ENR (−5.79 eV), NOR (−6.05 eV), CIP (−6.00 eV), TC (−6.16 eV), DCF (−6.14 eV) and OFC (−5.66 eV) were much higher than those of BA (−7.62 eV) and NBA (−8.23 eV) (Supplementary Fig. 46)42,43. These findings suggest that it is difficult for Fe(IV)=O to degrade electron-deficient pollutants, which is consistent with the results of the probing experiments.

Premixing experiments for BUC-95 and PDS at various time intervals (Supplementary Fig. 47), the open-circuit potential curves (Supplementary Fig. 48) and the i-t curve (Supplementary Fig. 49) excluded the contribution of the electron transfer process (ETP)44. The contributions of ROSs to OFC degradation were also assessed via probing experiments45,46. The contribution of Fe(IV)=O species to OFC degradation reached 85.6%, which was greater than those of SO4•− (8.0%) and •OH (6.4%) (Supplementary Fig. 50). Overall, based on the mechanism exploration of HVIO formation and OFC degradation, Fe(IV)=O species, rather than radicals, were recognized as the dominant ROSs in the BUC-95/PDS/OFC system (Fig. 3l), which aligned with the anion resistance and pH robustness results.

Significance of dynamic stretching on PDS activation
In contrast to conventional PDS activation paradigms that are governed primarily by electron transfer processes, electrochemical measurements revealed a distinct structure-activity difference of PDS activation between BUC-95 and BUC-96. The cyclic voltammetry (CV) profiles obtained for BUC-95 and BUC-96 after 20 cycles were recorded (Supplementary Fig. 51), and their corresponding double-layer capacitance (Cdl) values were calculated47. The Cdl of BUC-95 (9.05 mF cm−2) was lower than that of BUC-96 (9.10 mF cm−2), indicating that BUC-96 has a larger electrochemically active area for highly efficient PDS activation than does BUC-95 (Fig. 4a, b)48. The influence of the specific surface area of the as-synthesized samples on the above results was excluded (Supplementary Figs. 52 and 53 and Supplementary Table 9). Compared with that of BUC-95, a smaller electrochemical impedance spectroscopy (EIS) semicircle diameter was distinctly observed in BUC-96. This finding suggests that BUC-96 exhibits faster electron transfer efficiency (Fig. 4c). Meanwhile, post-reaction analysis revealed a more pronounced reduction in the Fe(Ⅱ) content was observed in BUC-96 (~17.54%) compared to BUC-95 (~15.78%), suggesting that BUC-96 exhibits stronger electron transfer and donating capabilities during PDS activation (Supplementary Fig. 54). However, BUC-96 did not exhibit satisfactory OFC degradation performance for PDS activation even with its superior electron transfer ability. This inverse correlation between electronic conductivity and reactivity underscores the critical role of flexible dynamic stretching, which influences more than just electron transfer in BUC-95.

To explore the significance of flexible dynamic stretching in the BUC-95/PDS system, comparative in situ PXRD tests of BUC-95 and BUC-96 under various environments were conducted. As shown in Fig. 4d, BUC-95 exhibited noticeable peak shifts in its PXRD patterns upon exposure to H2O and PDS, whereas BUC-96 maintained consistent diffraction peak positions under identical conditions. This contrast serves as direct evidence for the presence of flexible dynamic stretching in BUC-95. Additional confirmation was provided through in situ XPS, XAFS, FTIR and Raman characterizations. The Fe 2p3/2 peak in BUC-95 exhibited a clear binding energy shift (ca. 0.4 eV) with the addition of H2O and PDS (Supplementary Fig. 55a), in stark contrast to the minimal spectral variation (ca. 0.07 eV) observed in BUC-96 (Supplementary Fig. 55b). Meanwhile, in situ XANES analysis revealed that the absorption edge of pristine BUC-95 shifted toward higher energy upon water addition, with ΔE values of 0.14 eV and 0.28 eV after 1.0 min and 5.0 min, respectively. More obvious shifts (ΔE = 0.87 eV and 1.29 eV, respectively) were observed with the addition of PDS over the same time intervals. These energy shifts reflect structural changes induced by flexible dynamic stretching and an elevated oxidation state of Fe in BUC-95, consistent with the formation of Fe(IV)=O species (Fig. 4e and Supplementary Fig. 56).

Moreover, the in situ FTIR spectra of BUC-95 exhibited a red shift from 1395.94 cm−1 to 1392.41 cm−1 following the addition of PDS after 5.0 min of reaction (Fig. 4f). The Raman peaks at 708.6 cm−1 and 769.9 cm−1 for BUC-95 were attributed to Fe‒O and Fe‒N bonds. Upon introducing PDS into this reaction system, clear red shifts of the Fe‒O bond (from 708.6 cm−1 to 702.4 cm−1) and Fe‒N bond (from 769.9 cm−1 to 765.7 cm−1) were observed, indicating that the occurrence of large-scale and flexible dynamic change in BUC-95 may contribute to PDS activation (Fig. 4g). Moreover, PDS was consumed, with its initial concentration decreasing from 0.35 mM to 0.013 mM after the reaction, demonstrating successful PDS activation on the BUC-95 surface (Supplementary Fig. 57). After OFC was added to the above solution, all the Raman peaks returned to their original positions, and no new peaks were observed. Overall, the synergistic evidence from both crystallographic and electronic structure analyses conclusively indicates the presence of reversible and flexible dynamic stretching in BUC-95.

The homointerpenetrated framework of BUC-95 resulted in two geometrically distinct Fe coordination environments: (1) Dynamic dual-Fe sites (denoted Fe-Fe’), formed between two identically interpenetrated frameworks, exhibited interatomic distances ranging from 6.96 Å to 8.40 Å, as determined by microED (Supplementary Fig. 58); (2) Static and rigid dual-Fe sites (denoted Fe-Fe) confined within individual frameworks, displayed significantly shorter distances (3.82 Å) than did the Fe-Fe’ sites (Supplementary Fig. 59). Comparative analysis with the isostructural analog BUC-96 revealed structural convergence in both dynamic dual-Fe sites (denoted Fe-Fe”, ranging from 6.96 Å to 8.25 Å, Supplementary Fig. 60) and static sites (Fe-Fe in BUC-96 being 3.96 Å, static site Fe-Fe in BUC-95 being 3.82 Å; Supplementary Fig. 61). However, the flexible dynamic Fe-Fe’ configuration remained unique to BUC-95, as hydrogen bond in BUC-96 restricts such stretching within its interpenetrated framework. Importantly, the local coordination environments of Fe sites are identical in both MOFs (Supplementary Fig. 62), indicating that the enhanced PDS activation and OFC degradation in BUC-95 originate from its flexible dynamic stretching rather than differences in local metal coordination.

To investigate the role of structural dynamics on catalytic enhancement, comparative DFT calculations for BUC-95 and its analog BUC-96 were performed (Supplementary Fig. 63). Owing to their structural similarity, the adsorption energy of PDS on the Fe-Fe’ site in BUC-95 (−6.95 eV) and the corresponding O–O bond length (1.51 Å) closely match those in BUC-96 (−6.96 eV and 1.50 Å, respectively). This similarity indicates that PDS adsorption is not the primary factor driving the enhanced activation in BUC-95. Furthermore, Bader charge analysis reveals that electron transfer from the dynamic Fe-Fe’ sites to PDS is lower in BUC-95 (1.6437 e⁻) than that from the Fe-Fe” site in BUC-96 (1.6870 e⁻, Fig. 4h), suggesting that BUC-96 facilitates more efficient electron transfer, a conclusion consistent with electrochemical characterization.

Furthermore, PDOS analysis further reveals that the electron-occupied orbitals near the Fermi level (EF) in both BUC-95 and BUC-96 are governed primarily by Fe 3d, O 2p, and N 2p orbitals (Supplementary Figs. 64 and 65), consistent with Fe sites serving as the optimal PDS adsorption loci in both frameworks. To elucidate the role of dynamic structural flexibility, the electron distributions of the Fe 3d orbitals of BUC-95 and BUC-96 before and after PDS adsorption were compared (Fig. 4i). Upon PDS adsorption, the Fe 3d orbital area in BUC-96 undergoes a greater variation (Δarea = 0.74) than that in BUC-95 (Δarea = 0.04), indicating stronger electron transfer from BUC-96 to PDS and more effective electronic interaction at its Fe sites. These results were consistent with the Bader charge analysis, XAFS, and multiple electrochemical analyses.

Additionally, in situ molecular dynamics simulations under varied chemical environments and time resolutions (5.0, 10.0, 15.0, and 20.0 ps) confirm that BUC-95 exhibits clear reversible dynamic stretching in the presence of H2O and PDS (Fig. 4j and Supplementary Videos 2 and 3). In contrast, BUC-96 shows no significant structural change under the same condition (Supplementary Fig. 66 and Supplementary Videos 4-5). These findings further provide solid evidence for the unique, flexible dynamic stretching in the homointerpenetrated framework of BUC-95.

In summary, BUC-95 exhibited a weaker electron transfer ability in terms of PDS activation than BUC-96; however, its flexible dynamic stretching minimized the reliance on electron transfer efficiency, this mechanism significantly increased the Fenton-like catalytic efficiency, as evidenced by the excellent degradation performance (Supplementary Video 6).

Continuous-flow tests and toxicity assessment
To evaluate the practical applicability of the BUC-95/PDS system, a continuous-flow reactor was developed for the continuous and long-term removal of pollutants from pure water (Fig. 5a-b). BUC-95 was immobilized on a three-dimensional macroporous polyurethane sponge (2.0 cm × 2.0 cm × 1.0 cm) to construct a supported BUC-95@sponge (BS) catalyst. Polyvinyl butyral (PVB) was employed as a binder, providing satisfactory stability and flexibility (Fig. 5b and Supplementary Fig. 67). SEM images revealed that the rod-like BUC-95 was immobilized and uniformly distributed across the sponge. This finding was supported by EDS mapping, which verified the presence of Fe, N, O, and C (Fig. 5d). Compared with that of the blank sponge, the BS catalyst exhibited increased hydrophilicity, with a water contact angle of 54.85° (versus 113.97°) (Fig. 5b), facilitating interfacial contact between the catalyst, PDS, and pollutants. The hydraulic residence time was calculated to be 62.5 min. The BS/PDS system achieved >99.99% OFC (10.0 mg L−1) degradation efficiency within 110.0 h and maintained a high efficiency of >85% after 192.0 h in the simulated wastewater formulated by ultrapure water. In contrast, the individual PDS and PDS/sponge systems demonstrated negligible catalytic activity (~1.5% and ~1.9% degradation, respectively, Fig. 5e). Throughout the reaction, the BS catalyst exhibited high stability, with iron leaching concentrations remaining below <1.50 mg L−1, well under the limit specified by the Chinese National Standard (DB11/307–2013). SEM image (Supplementary Fig. 68) of the used BS after the reaction was identical to that of fresh BS, confirming its structural robustness and reusability. These results highlight the potential of the BUC-95 catalyst for scalable water treatment applications.

The degradation pathways of OFC in the BUC-95/PDS system were proposed on the basis of the Fukui index of OFC49 and ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) analysis results (Supplementary Figs. 69–72). The toxicity of OFC and its degradation intermediates was initially assessed via the Toxicity Estimation Software Tool (TEST) (Supplementary Fig. 73), along with plant and microorganism experiments. In the plant growth experiments, the root length, stem length, and growth status of mung beans in the degraded OFC solution obviously exceeded those in the undegraded OFC solution (Fig. 5f and Supplementary Fig. 74) because the BUC-95/PDS system not only effectively degrades organic pollutants but also ensures the generation of nontoxic intermediate products50,51. As depicted in Fig. 5g, the inhibition zone diameters measured in the blank solution (PBS), undegraded OFC solution, and degraded OFC solution at 10.0 min against E. coli were 8.0 mm, 22.0 mm and 10.0 mm, respectively, demonstrating the low/free toxicity of the OFC degradation products in the BUC-95/PDS system. These findings were confirmed by antibacterial experiments with multiple bacteria (Fig. 5h). By integrating high pollutant removal efficiency with effective detoxification and crop cultivation, the BUC-95/PDS system exhibited strong potential for practical applications in wastewater purification.

Methods
Synthesis of BUC-95 and BUC-96
BUC-95 was prepared using FeSO4·7H2O (3.0 mmol), 4,4′-bipyridine (bpy, 3.0 mmol), and 1,4-benzenedicarboxylic acid (H2bdc, 3.0 mmol) dissolved in 45.0 mL of DMF and 20.0 mL of deionized water. The mixture was placed in a 250.0 mL reaction vessel and subjected to a microwave-assisted process (XH-100B, Xianghu Co., Beijing). The temperature of the mixture was raised to 106.0 °C within 2.0 min and held for 90.0 min, using a heating power of 700 W and a heating rate of 53.0 °C min−1. After the mixture had cooled to room temperature, the resulting crystals were collected through filtration and washed with deionized water. BUC-96 was synthesized following the same procedure, with the only difference being the replacement of H2bdc with 2,5-dihydroxyterephthalic acid (H4dhtp).

Detailed synthesis methods for other catalysts and the characterization techniques used are provided in Supplementary Notes 2–4.

Catalytic performance experiments
The degradation performance of different catalysis systems for OFC was evaluated using a PCX-50C reactor (Beijing Perfectlight Technology Co., Ltd.) with a stirring speed of 200.0 rpm operated at room temperature. In a typical setup, 0.2 g L−1 of catalyst was dispersed in 50.0 mL of OFC solution (10.0 mg L−1), and 0.35 mM of PDS was added to initiate the reaction. At specific intervals, 1.0 mL of reaction mixture was retrieved through a 0.22 µm membrane and injected into a vial containing 10.0 µL of methanol to terminate the catalytic reaction. The degradation kinetics were evaluated using a first-order rate equation: ln(Ct/C0) = −kt, where Ct, C0 and k are the residual concentration of pollutant at t min (mg L−1), initial concentration of pollutants (mg L−1) and degradation rate constant (min−1), respectively. The pH values were adjusted with H2SO4 or NaOH solutions. The methods used to analyze the residual concentrations of different pollutants are provided in Supplementary Note 5. All the experiments were carried out at least three times.

DFT calculation details
First-principles calculations based on DFT were performed using the Vienna Ab initio Simulation Package (VASP) in this work52. The exchange-correlation energy was treated using the Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA)53. The BUC-95 model included a total of 260 atoms. Following tests for energy cut-off and k-point spacing tests, the energy was set to 300 eV, and a k-point spacing of 1×1×1 was used. The spin state was opened because of the presence of Fe, and the DFT+U approach was applied with a U value of 4.0 (d orbitals)54. The convergence standards for optimizing the crystal structure were <5.0×10−5 eV atom−1 (energy tolerance) and 0.05 eV Å−1 (maximum force tolerance). The specific calculation details are presented in Supplementary Note 10.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors reported significant and interesting work on performance and mechanism of PDS activation over a homointerpenetrated Fe-based metal-organic framework (BUC-95) with dynamic stretching structure, which is affirmed by MicroED, in situ characterization techniques (XRD, Raman, FT-IR and XPS) and DFT calculations. Compared with the noninterpenetrated BUC-96, the dynamic stretchable structure of BUC-95 overcomes the limitation of weak electron transfer ability in peroxydisulfate (PDS) activation, thus achieving excellent degradation performance of multiple pollutants. Moreover, BUC-95 exhibits long-term water purification and detoxification capabilities. Therefore, this work can be accepted for publication to some minor revisions.\n1. The authors mentioned the 3D printing in the Supplementary Figure 3b, however they did not mention it in the main text. They should describe briefly the 3D printing method and parameters to illustrate how to obtain the molecular model with homointerpenetrated structure.\n2. The authors are suggested to explain the slight inhibition with addition of Cl−. Also, to further determine the nonradical Fe(IV)=O is as the major oxidation pathway, the influence of humic acid on OFC degradation should be supplemented.\n3. Fe-OH group in BUC-95 is an important precursor for generating the Fe(IV)=O species, so the formation process of Fe-OH should be further explained.\n4. The authors mentioned that “However, the TEMP-1O2 signal showed a notable decrease upon the addition of D2O, indicating that 1O2 did not contribute to OFC removal”. The reason of signal decrease should be provided. In addition, The OFC degradation experiment in D2O should be supplemented to further confirm the contribution of 1O2.\n5. The continuous flow degradation experiment of OFC in the individual PDS system should be supplemented to exclude the self-degradation from PDS decomposition.\n6. The authors should ensure that all supplementary figures and tables are properly referenced in the main text, with adequate contextual information provided either in the main text or supplementary materials to facilitate interpretation.", "reviewer_2": "Ths work present a homointerpenetrated Fe-MOF, BUC-95, designed for the degradation of organic pollutants through Fenton-like reactions mediated by dynamic stretching effects. The study provides a comprehensive investigation into the dynamic stretching mechanism and the formation of Fe(IV)=O species, supported by extensive experimental and theoretical analyses. Additionally, the practical application of continuous-flow degradation demonstrates the material's potential for real-world environmental remediation. The findings highlight the critical role of dynamic structural flexibility in enhancing catalytic efficiency, offering a novel design strategy for next-generation environmental catalysts. Some minor revisions should be further addressed:\n1.The formation of Fe(IV)=O results in electron depletion from Fe sites, primarily altering electron density and valence states rather than directly influencing spin states. The authors should revise the abstract to clarify this distinction, emphasizing changes in electron distribution rather than spin state modulation.\n2.The observed decrease in 1O2 ESR signal intensity in D2O (Supplementary Figure S27) contradicts the expected prolonged lifetime effect. Either a mechanistic explanation or experimental verification should be added.\n3.The continuous-flow experiment demonstrated 100% OFC (10 mg L-1) degradation over 50 hours, suggesting that the cycling test’s five cycles (showing no decline) should be extended to at least ten cycles for more robust stability assessment.\n4.For the simulated wastewater from tap water, the OFC degradation efficiency was inhibited. The authors should provide explanations.\n5.The d-orbital electron arrangement of Fe sites in pristine BUC-95 should be included (Figure 3i) to properly compare with the PDS-OH co-adsorption system, as the coordination number difference significantly affects the d-orbital configuration.\n6.The authors should describe the detailed procedure concerning how to immobilize the catalyst on the blank sponge. And the authors should provide the hydraulic residence time of the continuous process in the fixed-bed reactor.", "reviewer_3": "This paper describes the development of homointerpenetrated BUC-95 MOF which exhibited a dynamically stretchable structure and highlighted that this particular MOF is superior to BUC-96, an isostructural analogue of BUC-95 with noninterpenetrated 3D framework, for heterogeneous Fenton-like reactions. The DFT simulation results provided new insights into the role of this dynamically stretchable structure in facilitating the adsorption of peroxydisulfate, increasing the O‒O bond length, thereby overcoming electron transfer issues. To demonstrate the practicality, the authors have also assembled a continuous fixed bed reactor with good stability and high detoxification capability. Overall, the work is original and significant and revealed the advantages of dynamically stretchable structure in homointerpenetrated MOF for Fenton-like reactions and the simulation results also provided the possible mechanisms behind the observed improvements in catalytic performance for Fenton-like reactions. Therefore, I recommend the publication of this paper after addressing the following comments:\n1. In Characterization, the authors should specify the degassing conditions used prior to the BET tests to allow for reproduction by others.\n2. In Supplementary Figure 7, please indicate clearly the different stages of decomposition and the weight loss for each stage.\n3. In Supplementary Figure 21, the SEM image of the used BUC-95 is after only one cycle or after 5 cycles. This needs to be clarified more clearly.\n4. In Supplementary Figure 46, some adsorption and desorption points in the N2 sorption isotherms appear to be missing. I recommend the authors to repeat the measurements until fully connected adsorption and desorption curves are obtained.\n5. In relation to Comment 4, please also supply the corresponding pore size distribution plots for BUC-95 and BUC-96.\n6. MOFs are known for their high surface areas. However, the prepared BUC-95 and BUC-96 seem to have low specific surface areas. What are the reasons behind this?\n7. Did the authors calibrate the XPS with reference to C 1s before deconvoluting the high-resolution spectra? If they did, this should be specified in the Characterization section.\n8. The authors should provide SEM images of the control MOF, BUC-96, as well in the SI.\n9. The Fe 2p XPS of BUC-96 before and after the reaction can also be supplied and compared with those of BUC-95.\n10. How much are the C, Fe, N, and O contents in the prepared BUC-95?\n11. The authors proposed that \"dynamic stretching\" in a homointerpenetrated MOF (BUC-95) improved the Fenton-like catalysis beyond traditional electron transfer mechanisms. Can the authors better clarify how this dynamic stretching is fundamentally different from known flexible MOF behaviours or ligand breathing effects in other systems?\n12. The authors infer dynamic flexibility from PXRD, Raman, and XPS shifts. Can the authors provide more quantitative data (e.g., peak shifts, time-resolved measurements) or in situ structural dynamics simulations to more rigorously define and support the claim of “dynamic stretching”?\n13. What is the expected lifetime of the BUC-95@sponge material? Can the catalyst be regenerated?\n14. On Pages 7-8, the authors showed the BUC-95 demonstrated superior peroxydisulfate (PDS) activation capability than the MIL-based systems. Were the loading amounts, surface areas, and Fe content normalized across all comparative systems to ensure a fair benchmark?\n15. On Page 12, the authors mentioned that BUC-96 has better conductivity, yet BUC-95 shows better performance due to the dynamic stretching. How do the authors rule out contributions from differences in Fe oxidation state distributions or local Fe site environments rather than dynamic behavior?\n16. The authors highlighted that the catalytic enhancement for Fenton-like reactions is due to dynamic stretching of BUC-95. How do the authors ensure that other factors, such as pore size, Fe dispersion, morphology, surface area, did not contribute to the catalytic enhancement?\n17. Minor inconsistencies: In the manuscript and SI, the authors sometimes italicized symbols in texts and plots but in other parts, the symbols are not italicized. They need to ensure all symbols are italicized in the text and figures in both the manuscript and SI.\n18. I recommend the authors to add a schematic figure of the proposed Fe(IV)=O generation and pollutant degradation mechanism to clarify the reaction sequence.\n19. In some OFC degradation figures in the main manuscript and SI, error bars and replicate measurements seem to be missing."}, "author_response": "Dear reviewers,\nThank you for your comments and directions on our manuscript. In this revision, we solved all the problems required by all reviewers one by one.\nWe confirmed that we had provided all the requested items in this submission.\nThank you again for your useful comments on this submission.\nNote:\nOur responses to the reviewers’ comments are shown in color red. The Table RX or Fig. RX are used to clearly explain reviewer questions without appearing in the revised manuscript or supplementary information.\nAll actions of editing taken are shown in color blue.\nThe figure and table numbers referred correspond to those in the revised manuscript.\nReviewer #1 (Remarks to the Author):\nThe authors reported significant and interesting work on performance and mechanism of PDS activation over a homointerpenetrated Fe-based metal‒organic framework (BUC-95) with dynamic stretching structure, which is affirmed by MicroED, in situ characterization techniques (XRD, Raman, FT-IR and XPS) and DFT calculations. Compared with the noninterpenetrated BUC-96, the dynamic stretchable structure of BUC-95 overcome the limitation of weak electron transfer ability in PDS activation, thus achieving excellent degradation performance of multiple pollutants. Also, BUC-95 exhibits long-term water purification and detoxification capabilities. Therefore, this work can be accepted for publication to some minor revisions.\nResponse: We were greatly honored to receive your positive comments. Your useful suggestions will greatly help to improve the quality of this work, and we had responded your issues one by one as the following:\nQ 1-1. The authors mentioned the 3D printing in the Supplementary Figure 3(b), however they did not mention it in the main text. They should describe briefly the 3D printing method and parameters to illustrate how to obtain the molecular model with homointerpenetrated structure.\nResponse 1-1: To better understand the homointerpenetrated structure obtained from 3D printing method for readers, we have provided the details of 3D printing method and parameters in the revised supplementary information.\nSupplementary information revision:\nSupplementary Note 11: 3D printing method\nThe method employs Mercury 3.7, Fusion360, and Bambu Studio, with each software respectively responsible for the conversion, dissection, and slicing of crystal structure files respectively. Mercury 3.7 and its subsequent versions are a equipped with a \"3D Print\" function that facilitates the conversion of CIF files to STL files. To carry out this conversion, navigate to File >> 3D Print and configure the parameters as 2 follows: select STL (monochrome) as the File Format, set the Scale (mm Å-1) to 10, and turn off the Generate Support Framework option. After applying these settings click Generate to create the STL file for subsequent slicing and modeling. Autodesk Fusion 360 serves as the software for dissecting the crystal, enabling accurate cutting of the crystal structure within the STL file. Slicing is accomplished using Bambu Studio in conjunction with the Bambu Lab X1C Combo 3D printer. This program processes the STL file to generate a CTB file, which is then transmitted to the 3D printer to complete the 3D printing process.\nQ 1-2. The authors are suggested to explain the slight inhibition with addition of Cl−. Also, to further determine the nonradical Fe(IV)=O is as the major oxidation pathway, the influence of humic acid on OFC degradation should be supplemented.\nResponse 1-2: To improve clarity and facilitate comprehension for readers, we have supplemented the detailed explanations of the slight inhibition with addition of Cl−. In addition, the OFC degradation experiment in the presence of humic acid (HA) is conducted. As shown in supplementary Fig. 27, no obvious inhibition is observed with addition of HA, further demonstrating the dominant role of Fe(IV)=O species for OFC degradation.\nManuscript revision:\nNotably, BUC-95 maintained robust catalytic performance under a low PDS dosage (0.35 mM) across a wide pH range (2.5 ~ 8.5) (Supplementary Fig. 26), demonstrated strong resistance to multiple anions (Cl−, SO 2−, NO −, HCO −) and humic acid (HA) 4 3 3 (Supplementary Fig. 27), and performed effectively in complicated aqueous matrices like tap water, lake water, and rainwater (Supplementary Fig. 28). These results collectively suggest that nonradical oxidation pathways might dominate the degradation process. The addition of Cl− resulted in only minor inhibition of OFC degradation (<13.0% decline), which could be attributed to the competitive consumption of a few active species to form less reactive chlorine radicals 3. Similarly, the slight decline in catalytic performance (~20.0%) observed in simulated aqueous 3 samples formulated from tap water was ascribed to the relatively high Cl− content, as quantified by ion chromatography (CIC-D160+, Qingdao Shenghan Chromatograph Technology Co., Ltd.) (Supplementary Table 7).\nSupplementary Fig. 27 (a) The OFC degradation efficiencies and (b) the corresponding k values with presence of different inorganic ions and humic acid in the BUC-95/PDS system.\nSupplementary Table 7. The Cl− concentration in different real water samples.\nTap Water Lake Water Rain Water\nCl− (mg L-1) 22.57 9.32 0.45\nNote:\nThe real water samples (Tap Water, Rain Water, and Lake Water (Minghu lake)) are obtained on August 20, 2025, from the Daxing campus, Beijing University of Civil Engineering and Architecture.\nReference:\n3. Wang F, et al. The Pivotal Role of Selenium Vacancies in Defective FeSe @MoO 2 3 for Efficient Peroxymonosulfate Activation: Experimental and DFT Calculation. ACS ES&T Engg 4, 153-165 (2024).\nResponse 1-3: We have explained the Fe-OH group formation process in the BUC-95/PDS system for the better comprehension of readers in the revised manuscript.\nManuscript revision:\nPrevious literatures reported Fe sites, acting as the Lewis acid sites, can capture -OH from H O to form Fe-OH species, which subsequently converted into HVIO species 33, 2 35. In BUC-95, electron paramagnetic resonance (EPR) spectroscopy revealed signals of oxygen vacancies at g = 2.003 (Supplementary Fig. 37), suggesting that oxygen vacancies may serve as favourable sites for Fe-OH formation. Further evidence comes from the O 1s XPS spectra, where a new peak emerges at 533.2 eV after reaction (Fig. 3e), consistent with the formation of Fe-OH species. These findings support a reaction mechanism in which HVIO generation is initiated by the adsorption of -OH from H O 2 onto Lewis acidic Fe(II) sites in BUC-95, forming Fe-OH intermediates that undergo a two-step oxygen atom transfer pathway to ultimately generate HVIO and SO 2−. 4\nReferences:\n33. Bao Y, et al. Generating High-valent Iron-oxo ≡FeIV=O Complexes in Neutral Microenvironments through Peroxymonosulfate Activation by Zn−Fe Layered Double Hydroxides. Angew Chem, Int Ed61, e202209542 (2022).\n35. Park EJ, Kim MS, Lee C. Aqueous Fe(IV) and Cu(III) species from Fenton (-like) reactions: Chemistry and environmental applications. Water Res287, 124169 (2025).\nQ 1-4. The authors mentioned that “However, the TEMP-1O signal showed a notable 2 decrease upon the addition of D O, indicating that 1O did not contribute to OFC 2 2 removal”. The reason of signal decrease should be provided. In addition, The OFC degradation experiment in D O should be supplemented to further confirm the 2 contribution of 1O . 2\nManuscript revision:\nUpon the addition of D O, the TEMP-1O signal showed a notable decrease 2 2 (Supplementary Fig. 31a), a phenomenon attributable to solvent isotope and exchange effects between D O and H O 28. To further evaluate the contribution of 1O in the BUC- 2 2 2 95/PDS system, the OFC degradation experiment was conducted in D O. Only slight 2 declines in both OFC degradation efficiency (ca. 7.0%) and reaction rate (1.9 min-1) were observed (Supplementary Fig. 31b), indicating that 1O did not play a substantive 2 role in OFC removal.\nSupplementary Fig. 31 (a) The ESR spectrum of TEMP-1O and (b) the OFC 2 degradation efficiencies upon the addition of D O. 2\nReference:\n28. Shao P, et al. Revisiting the Graphitized Nanodiamond-Mediated Activation of Peroxymonosulfate: Singlet Oxygenation versus Electron Transfer. Environ Sci Technol 55, 16078-16087 (2021).\nResponse 1-5: We redesigned the fixed-bed reactor and performed renewed continuous flow degradation experiments for OFC in the individual PDS, blank sponge/PDS, and BS/PDS systems. The column volume of current fixed-bed reactor is 2.5 L, which is 5-fold larger than the previous reactor (0.5 L). However, the current hydraulic retention time (62.5 min) is comparable to that of the previous reactor (50.0 min). The BS/PDS system achieved >99.99% OFC (10.0 mg L-1) degradation over 110 h of continuous operation, more than doubling the duration of previously attained, thereby demonstrating the long-term stability and practical viability of the BS catalyst.\nManuscript revision:\nThe hydraulic residence time was calculated to be 62.5 min. Remarkably, the BS/PDS system achieved >99.99% OFC (10.0 mg L-1) degradation efficiency within 110.0 h and maintained a high efficiency of >85% after 192.0 h in the simulated wastewater formulated by ultrapure water. In contrast, the individual PDS and PDS/sponge systems demonstrated negligible catalytic activity (~1.5% and ~1.9% degradation, respectively, Fig. 5e). Throughout the reaction, the BS catalyst exhibited high stability, with iron leaching concentrations remaining below <1.50 mg L-1, well under the limit specified by the Chinese National Standard (DB11/307–2013).\nFig. 5 (e) Continuous degradation of the OFC in the BS/PDS system.\nResponse 1-6: We have verified that all supplementary figures and tables are appropriately cited in the main manuscript. In addition, essential explanations have been added to the revised supplementary information to enhance clarity and provide necessary context.\nSupplementary information revision:\nSupplementary Fig. 6 The FTIR spectrum of H bdc and BUC-95. 2\nNote:\nThe Fourier transform infrared (FTIR) spectra revealed a significant decrease in the intensity of the peak at approximately 1279 cm-1, corresponding to the C-O stretching vibration, in BUC-95 compared to individual H bdc ligand. This result verifies the 2 strong coordination between Fe(II) and -COOH groups (Supplementary Fig. 6) 5.\nReference:\n5. Liu S, et al. Engineered Metal–Organic Framework with Stereotactic Anchoring and Spatial Separation of Porphyrins for Amplified Ultrasound-Mediated Pyroptosis and Cancer Immunotherapy. Angew Chem, Int Ed 64, e202421402 (2025).\nNote:\nAs shown in BUC-95 TGA curve (Supplementary Fig. 7), three stages of weight loss were observed. The first weight-loss stage at ca. 30.0 ~ 200.0 oC, with weight reduction of ~10%, is attributed to the dehydration. The second weight loss (~10.0%) stage occurred at 200.0 ~ 360.0 oC, corresponding to the partial decomposition of organic ligand of BUC-95. The final weight loss (~52.0%) stage was observed at 360.0 ~ 390.0 oC, which could be ascribed to the complete decomposition of organic ligand of BUC-95. Overall, TGA result showed that BUC-95 processed a good thermal stability up to ca. 360.0 oC.\nNote:\nThe XPS survey spectrum of fresh BUC-95 exhibited the characteristic peaks of Fe, O, N, and C, initially proving the successful preparation of BUC-95 (Supplementary Fig. 5).\nSupplementary Fig. 13 The Fe 2p XPS spectrum of (a) BUC-95 and (b) BUC-96 before reaction.\nNote:\nReviewer #2 (Remarks to the Author):\nThe authors present a homointerpenetrated Fe-MOF, BUC-95, designed for the degradation of organic pollutants through Fenton-like reactions mediated by dynamic stretching effects. The study provides a comprehensive investigation into the dynamic stretching mechanism and the formation of Fe(IV)=O species, supported by extensive experimental and theoretical analyses. Additionally, the practical application of continuous-flow degradation demonstrates the material's potential for real-world environmental remediation. The findings highlight the critical role of dynamic structural flexibility in enhancing catalytic efficiency, offering a novel design strategy for next-generation environmental catalysts. I suggest that this work can be accepted for publication in Nature Communications subject to some minor revisions.\nResponse: We were greatly honored to receive your positive comments. Your useful suggestions will greatly help to improve the quality of this work, and we had responded your issues one by one as the following.\nQ 2-1. The formation of Fe(IV)=O results in electron depletion from Fe sites, primarily altering electron density and valence states rather than directly influencing spin states. The authors should revise the abstract to clarify this distinction, emphasizing changes in electron distribution rather than spin state modulation.\nResponse 2-1: We have revised the abstract to clarify this distinction, emphasizing changes in electron distribution rather than spin state modulation in the revised manuscript.\nAbstract:\nWhile extensive efforts have been devoted to enhancing electron transfer efficiency through metal valence cycling in heterogeneous Fenton-like reactions, the potential catalytic improvement induced by dynamic structural stretching remain unexplored. Here, we introduce a homointerpenetrated Fe-based metal‒organic framework (BUC-95) featuring a dynamic stretchable structure that significantly boosts the heterogeneous Fenton-like catalytic performance. BUC-95's unique stretchable structure achieved effective peroxydisulfate activation for degrading various micropollutants via Fe(IV)=O species, facilitated by a reduced energy barrier for Fe(IV)=O formation through modulation of the electron density at Fe sites. DFT calculations suggest that, compared with the isostructural analogue with hydrogen bond-restricted stretching, the flexible dynamic stretching in BUC-95 overcomes the inherent electron transfer limitations from Fe sites to peroxydisulfate, enhancing the ofloxacin degradation performance. Practically, BUC-95 demonstrated effective continuous-flow degradation and detoxification of micropollutants. This work establishes dynamic stretching as a crucial design principle for advancing environmental remediation materials and technologies.\nQ 2-2. The observed decrease in 1O ESR signal intensity in D O (Supplementary 2 2 Figure S27) contradicts the expected prolonged lifetime effect. Either a mechanistic explanation or experimental verification should be added.\nResponse 2-2: The decrease of the TEMP-1O signal upon D O addition has been 2 2 thoroughly explained in the revised manuscript to improve reader understanding. Furthermore, OFC degradation experiments conducted in a D O medium confirm that 2 1O plays a negligible role in the BUC-95/PDS system. 2\nManuscript revision:\nUpon the addition of D O, the TEMP-1O signal showed a notable decrease 2 2 (Supplementary Fig. 31a), a phenomenon attributable to solvent isotope and exchange 12 effects between D O and H O 28. To further evaluate the contribution of 1O in the BUC- 2 2 2 95/PDS system, the OFC degradation experiment was conducted in D O. Only slight 2 declines in both OFC degradation efficiency (ca. 7.0%) and reaction rate (1.9 min-1) were observed (Supplementary Fig. 31b), indicating that 1O did not play a substantive 2 role in OFC removal.\nSupplementary Fig. 31 (a) The ESR spectrum of TEMP-1O and (b) the OFC 2 degradation efficiencies upon the addition of D O. 2\nReference:\n28. Shao P, et al. Revisiting the Graphitized Nanodiamond-Mediated Activation of Peroxymonosulfate: Singlet Oxygenation versus Electron Transfer. Environ Sci Technol 55, 16078-16087 (2021).\nQ 2-3. The continuous-flow experiment demonstrated 100% OFC (10 mg L-1) degradation over 50 hours, suggesting that the cycling test’s five cycles (showing no decline) should be extended to at least ten cycles for more robust stability assessment.\nResponse 2-3: We have supplemented the OFC cycling degradation experiment to ten cycles for more robust stability assessment in the revised manuscript.\nManuscript revision:\nNearly 100% OFC degradation efficiency and minimal Fe leaching (<1.5 mg L-1) after ten operational cycles demonstrated the robust reusability and stability of BUC- 13 95 (Fig. 2f and Supplementary Fig. 24), which were confirmed by the SEM images and PXRD patterns of the BUC-95 after five and ten cycles (Supplementary Fig. 25).\nFig. 2 (f) Cyclic performance of BUC-95 over multiple reaction cycles.\nQ 2-4. For the simulated wastewater from tap water, the OFC degradation efficiency was inhibited. The authors should provide explanations.\nResponse 2-4: In the revised manuscript, we have provided an explanation for the inhibition of OFC degradation observed in the simulated wastewater formulated from tap water. Considering that tap water contains a considerable amount of Cl− and the OFC degradation performance is slightly inhibited with addition of Cl−, we quantified the contents of Cl− in three real water matrices to clarify the role in the minor decline of OFC removal. As shown in supplementary Table 7, tap water exhibited the highest Cl− concentration (22.57 mg L-1), followed by lake water (9.32 mg L-1), and rain water (0.45 mg L-1), which aligns with the OFC degradation trend in these three real water bodies. Therefore, the inhibition of OFC removal in tap water can be contributed to the 14 elevated Cl− content, which consumes some reactive species to form less oxidizable chlorine radicals.\nManuscript revision:\nNotably, BUC-95 maintained robust catalytic performance under a low PDS dosage (0.35 mM) across a wide pH range (2.5 ~ 8.5) (Supplementary Fig. 26), demonstrated strong resistance to multiple anions (Cl−, SO 2−, NO −, HCO −) and humic acid (HA) 4 3 3 (Supplementary Fig. 27), and performed effectively in complicated aqueous matrices like tap water, lake water, and rainwater (Supplementary Fig. 28). These results collectively suggest that nonradical oxidation pathways might dominate the degradation process. The addition of Cl− resulted in only minor inhibition of OFC degradation (<13.0% decline), which could be attributed to the competitive consumption of a few active species to form less reactive chlorine radicals 3. Similarly, the slight decline in catalytic performance (~20.0%) observed in simulated aqueous samples formulated from tap water was ascribed to the relatively high Cl− content, as quantified by ion chromatography (CIC-D160+, Qingdao Shenghan Chromatograph Technology Co., Ltd.) (Supplementary Table 7).\nSupplementary Fig. 27 (a) The OFC degradation efficiencies and (b) the corresponding k values with presence of different inorganic ions and humic acid in the BUC-95/PDS system.\nSupplementary Table 7. The Cl− concentration in different real water samples.\nCl− (mg L-1) 22.57 9.32 0.45\nNote:\nThe real water samples (Tap Water, Rain Water, and Lake Water (Minghu lake)) are obtained on August 20, 2025, from the Daxing campus, Beijing University of Civil Engineering and Architecture.\nReference:\n3. Wang F, et al. The Pivotal Role of Selenium Vacancies in Defective FeSe @MoO 2 3 for Efficient Peroxymonosulfate Activation: Experimental and DFT Calculation. ACS ES&T Engg 4, 153-165 (2024).\nQ 2-5. The d-orbital electron arrangement of Fe sites in pristine BUC-95 should be included (Figure 3i) to properly compare with the PDS-OH co-adsorption system, as the coordination number difference significantly affects the d-orbital configuration.\nResponse 2-5: We have supplemented the analysis of the d-orbital electron arrangement of Fe sites in pristine BUC-95 in the revised manuscript to facilitate comparison with the PDS-OH co-adsorption system.\nManuscript revision:\nThe splitting pattern of the Fe d orbitals undergoes significant changes upon adsorption of PDS and surficial -OH. This co-adsorption induces a transition in the crystal field splitting of Fe sites from tetrahedral to octahedral configuration, accompanied by a redistribution of electron density (Supplementary Fig. 44). Hybridization between the p orbitals of O atoms from PDS as well as -OH groups and the d orbitals of the Fe centres in BUC-95 leads to the formation of antibonding orbitals cross the Fermi level. As a result, two electrons from Fe dz2 orbitals are transferred to promote the formation of Fe(IV)=O species (Fig. 3i).\nQ 2-6. The authors should describe the detailed procedure concerning how to immobilize the catalyst on the blank sponge. And the authors should provide the hydraulic residence time of the continuous process in the fixed-bed reactor.\nResponse 2-6: We have supplemented the detailed method of immobilizing the BUC-95 catalyst on the blank sponge in the revised supplementary information. Furthermore, the hydraulic residence time of the continuous-flow process in the fixed-bed reactor is calculated to be 62.5 min.\nSupplementary information revision:\nSupplementary Note 12: The preparation method of BUC-95@Sponge\n5.0 g of BUC-95 and 400.0 mg of polyvinyl butyral was ultrasonically dispersed in ethanol (400.0 mL) for 30.0 min and then the blank sponge (5.0 g) was added to the above suspension. Subsequently, the sponge absorbed BUC-95 (BUC-95@sponge, BS) was dried at 60 °C.\nManuscript revision:\nThe hydraulic residence time was calculated to be 62.5 min.\nReviewer #3 (Remarks to the Author):\nResponse: We were greatly honored to receive your positive comments. Your useful suggestions will greatly help to improve the quality of this work, and we responded your issues one by one as the following.\nQ 3-1. In Characterization, the authors should specify the degassing conditions used prior to the BET tests to allow for reproduction by others.\nResponse 3-1: We have specified the degassing conditions in the BET tests process to allow for reproduction by others in the revised supplementary information.\nSupplementary information revision:\nThe surface area and pore size distribution were obtained on a TriStar Ⅱ 3020 (Micromeritics, USA) at 77.0 K adopting the Brunauer-Emmett-Teller (BET) method and Barrett-Joyner-Halenda (BJH) pore analysis method. The degassing condition was described as follow: initially, the samples were degassed at 120.0 °C for 6.0 h under vacuum. Once the required vacuum level was reached, the samples were transferred to the analysis station for adsorption-desorption tests. The physical adsorption isotherm 18 was recorded at 77.0 K. The BET method was used to calculate the specific surface area, while the BJH pore analysis method was applied to derive the total pore volume and average pore diameter.\nQ 3-2. In Supplementary Figure 7, please indicate clearly the different stages of decomposition and the weight loss for each stage.\nResponse 3-2: We have indicated clearly the different stages of decomposition and the weight loss for each stage in Supplementary Fig. 7 in the revised supplementary information.\nSupplementary information revision:\nSupplementary Fig. 7 The TGA curve of fresh BUC-95.\nNote:\nAs shown in BUC-95 TGA curve (Supplementary Fig. 7), three stages of weight loss were observed. The first weight-loss stage at ca. 30.0 ~ 200.0 oC, with weight reduction of ~10%, is attributed to the dehydration. The second weight loss (~10.0%) stage occurred at 200.0 ~ 360.0 oC, corresponding to the partial decomposition of organic ligand of BUC-95. The final weight loss (~52.0%) stage was observed at 360.0 ~ 390.0 oC, which could be ascribed to the complete decomposition of organic ligand 19 of BUC-95. Overall, TGA result showed that BUC-95 processed a good thermal stability up to ca. 360.0 oC.\nQ 3-3. In Supplementary Figure 21, the SEM image of the used BUC-95 is after only one cycle or after 5 cycles. This needs to be clarified more clearly.\nResponse 3-3: The SEM image of used BUC-95 in the initially submitted version is after five cycles. In this revision, the cycling experiments have been extended to ten cycles, and accordingly, the SEM image has been updated to show the used BUC-95 after ten reaction cycles.\nSupplementary information revision:\nSupplementary Fig. 25 (a) PXRD patterns and (b-c) SEM images of used BUC-95 after five and ten cycles reaction, respectively.\nResponse 3-4: The N adsorption-desorption isotherms obtained using a mini BET 2 analyses device (BELSORP-mini II, BEL JAPAN, INC.), resulting in inconsistencies in certain data points. To ensure high data reliability, we re-measured the N₂ adsorption– desorption isotherms and pore size distributions using a high-precision analyzer (TriStar II 3020, Micromeritics, USA), and the updated results are provided in the revised supplementary information.\nSupplementary information revision:\nSupplementary Fig. 51 (a) The N adsorption-desorption isotherms and (b) pore size 2 distribution plots of BUC-95 and BUC-96.\nSupplementary Fig. 52 The calculated pore size distribution plots of (a) BUC-95 and (b) BUC-96 from crystallographic data.\nDue to the relatively low BET surface area of BUC-96 and BUC-95, the corresponding average pore size distribution plots derived therefrom exhibit reduced accuracy. The average pore size obtained is likely a result of pore channel accumulation rather than a faithful representation of the true pore size distribution. Consequently, DFT calculations are employed to determine the pore size distributions of BUC-95 and BUC-96 using their crystallographic data (CIF files). As depicted in Supplementary Fig. 52, the stimulated pore size of BUC-95 and BUC-96 is calculated to be 4.4 Å and 2.02 Å, respectively. These diminutive pore dimensions are insufficient to permit the entry of OFC molecules (13.8 Å) into the pore channels and their subsequent interaction with Fe sites and PDS. In all, these findings indicate that neither the BET surface area nor the pore size contributes to the degradation of OFC.\nSupplementary Table 9. The BET surface area and pore size distribution of BUC-95 and BUC-96.\nSamples BET surface area (m2 g-1) Average pore size (nm)\nBUC-95 92.0 7.1\nBUC-96 4.0 15.5\nQ 3-5. In relation to Comment 4, please also supply the corresponding pore size distribution plots for BUC-95 and BUC-96.\nResponse 3-5: We also supplemented the corresponding pore size distribution plots of BUC-95 and BUC-96 detected via the high-precision instrument (TriStar Ⅱ 3020, Micromeritics, USA) in the revised supplementary information.\nSupplementary information revision:\nSupplementary Fig. 52 The calculated pore size distribution plots of (a) BUC-95 and (b) BUC-96 from crystallographic data.\nNote:\nDue to the relatively low BET surface area of BUC-96 and BUC-95, the corresponding average pore size distribution plots derived therefrom exhibit reduced accuracy. The average pore size obtained is likely a result of pore channel accumulation rather than a faithful representation of the true pore size distribution. Consequently, DFT calculations are employed to determine the pore size distributions of BUC-95 and BUC-96 using their crystallographic data (CIF files). As depicted in Supplementary Fig. 52, the stimulated pore size of BUC-95 and BUC-96 is calculated to be 4.4 Å and 2.02 Å, respectively. These diminutive pore dimensions are insufficient to permit the entry of OFC molecules (13.8 Å) into the pore channels and their subsequent interaction 23 with Fe sites and PDS. In all, these findings indicate that neither the BET surface area nor the pore size contributes to the degradation of OFC.\nSupplementary Table 9. The BET surface area and pore size distribution of BUC-95 and BUC-96.\nSamples BET surface area (m2 g-1) Average pore size (nm)\nBUC-95 92.0 7.1\nBUC-96 4.0 15.5\nQ 3-6. MOFs are known for their high surface areas. However, the prepared BUC-95 and BUC-96 seem to have low specific surface areas. What are the reasons behind this?\nResponse 3-6: While high surface area is a hallmark feature of many metal–organic frameworks (MOFs), not all MOFs process a ultra-high specific surface area. The specific surface area of MOFs is influenced by some key factors like synthesis method, solvent selection, pore accessibility, and particle size.\nFirst, MOFs synthesized by solvent/hydrothermal method generally exhibit high surface area. This is attributed to the extended synthesis time, which allows sufficient nucleation and growth periods, resulting in small pore sizes and a homogeneous distribution, thereby leading large specific surface areas. While, certain rapid MOF synthesis methods (microwave synthesis) involve short reaction times, which restrict adequate crystal growth. This causes structural defects in the framework that block the pores, preventing N (the probe for BET specific surface area testing) from entering and 2 thus resulting in a low specific surface area.\nAdditionally, if organic solvents (such as DMF or methanol) are used during MOF synthesis, these solvents may occupy the MOF's pores, resulting in the formation of small pore sizes and consequently reducing the specific surface area.\nLast but not least, the size of MOF particles also significantly affects the specific surface area. In general, The specific surface area of MOF is related inversely to particle size. The smaller the particle size of MOF, the higher the specific surface area.\nQ 3-7. Did the authors calibrate the XPS with reference to C 1s before deconvoluting the high-resolution spectra? If they did, this should be specified in the Characterization section.\nResponse 3-7: We have ensured that all XPS analyses are calibrated with reference to C 1s before fitting the high-resolution spectra and specified in the characterization section in the supplementary information.\nSupplementary information revision:\nX-ray photoelectron spectroscopy (XPS) measurements, both ex situ and in situ, were performed using a Thermo ESCALAB 250XI system. All XPS spectra were calibrated with reference to the C 1s peak prior to high-resolution spectral fitting.\nQ 3-8. The authors should provide SEM images of the control MOF, BUC-96, as well in the SI.\nResponse 3-8: We have supplemented the SEM image of BUC-96 in the revised supplementary information.\nSupplementary information revision:\nNote:\nBUC-96 exhibited a rod-like morphology similar with BUC-95, with particles sized approximately 10.0 μm × 2.0 μm × 1.0 μm (Supplementary Fig. 8).\nQ 3-9. The Fe 2p XPS of BUC-96 before and after the reaction can also be supplied and compared with those of BUC-95.\nResponse 3-9: We have supplemented the Fe 2p XPS of BUC-96 before and after the reaction, and compared with those of BUC-95 in the revised manuscript and supplementary information.\nManuscript revision:\nMeanwhile, post-reaction analysis revealed a more pronounced reduction in the Fe(Ⅱ) content was observed in BUC-96 (~17.54%) compared to BUC-95 (~15.78%), suggesting that BUC-96 exhibits stronger electron transfer and donating capabilities during PDS activation (Supplementary Fig. 53).\nSupplementary Fig. 53 The Fe 2p XPS spectrum of BUC-96 before and after reaction.\nQ 3-10. How much are the C, Fe, N, and O contents in the prepared BUC-95?\nResponse 3-10: We have supplemented the contents of Fe, O, C, and N in the fresh BUC-95. The Fe content is detected by inductively coupled plasma optical emission spectrometer (ICP-OES, ICP-5000, Focused Photonics (Hangzhou) Inc.). C, O, and N contents are determined by the elemental analyses (EA, Elementar Vario EL cube).\nSupplementary information revision:\nElements Actual content (%)\nFe 14.25%\nO 20.47%\nN 6.65%\nC 46.08%\nNote:\nFe content was detected to be 14.25% via inductively coupled plasma optical emission spectrometer (ICP-OES, ICP-5000, Focused Photonics (Hangzhou) Inc.). The contents of C, O, and N were determined to be 46.08%, 20.47%, and 6.65%, respectively, via the elemental analyses (EA, Elementar Vario EL cube).\nThe formula of BUC-95 was C H Fe N O . According to this formula, the 72 48 4 8 16 simulated percentage contents of Fe, O, C, and N were calculated as follow: 14.86%, 17.0%, 57.5%, and 7.5%.\nThe experimentally determined contents of Fe, O, and N were in good agreement with the simulated values. However, the measured C content was slightly lower than theoretically predicted. This discrepancy may be attributed to the adsorption of atmospheric moisture by BUC-95, which could increase the overall sample mass and thereby reduce the relative percentage of carbon. Overall, these results confirm the successful synthesis of BUC-95.\nQ 3-11. The authors proposed that \"dynamic stretching\" in a homointerpenetrated MOF (BUC-95) improved the Fenton-like catalysis beyond traditional electron transfer mechanisms. Can the authors better clarify how this dynamic stretching is fundamentally different from known flexible MOF behaviours or ligand breathing effects in other systems?\nResponse 3-11: We have thoroughly clarified the fundamental differences between the dynamic stretching of homointerpenetrated MOF, flexible MOF and ligand breathing effects of MOFs in the revised manuscript and supplementary information.\nThis unique structural feature enables reversible deformation of the entire framework in response to external stimuli like chemical activation. Unlike the localized pore breathing in conventional MOFs or the ligand-based flexibility in flexible MOFs (Supplementary Scheme 1), the large-scale dynamic adaptability of interpenetrated MOFs makes them ideal model systems for studying whole-framework dynamics in Fenton-like reaction mechanisms.\nSupplementary information revision:\nSupplementary Scheme 1. The fundamentally difference of dynamic stretching in flexible MOF behaviours, ligand breathing effects of MOFs, and interpenetrated MOFs systems.\nNote:\nInterpenetrated MOFs are divided into two types: homointerpenetrated and heterointerpenetrated, which are formed by two independent MOF sub-frameworks interpenetrating each other to form an \"interpenetrated structure\" 1. Under external stimulation, reversible relative sliding/shifting occurs between the sub-frameworks, thereby achieving large-scale dynamic stretching of the whole framework 2. However, 29 it should be noted that after dynamic stretching, the topological structure of the sub- framework itself remains unchanged, and only its spatial position changes.\nFlexible MOFs behavior refers to the reversible deformation (such as bending and compression) of a single MOF framework under external stimulation 3. However, it should be noted that its dynamic behavior originates from the adjustment of ligand conformation within a single framework, without synergy between multiple frameworks.\nThe ligand breathing effect of MOFs refers to the reversible contraction/expansion of pore size due to the local conformation of the ligand itself under external stimulation 4. However, the overall topological structure of the framework remains unchanged, and there is no collaboration between multiple frameworks.\nIn all, homointerpenetrated MOF is the \"dynamic of multiple frameworks\", flexible MOF is the \"dynamic of a single framework\", and ligand breathing effect of MOF is the \"dynamic of pore\" (Supplementary Scheme 1).\nReferences:\n1. Perl D, Lee SJ, Ferguson A, Jameson GB, Telfer SG. Hetero-interpenetrated metal– organic frameworks. Nat Chem15, 1358-1364 (2023).\n2. Cao J, Ma W, Lyu K, Zhuang L, Cong H, Deng H. Twist and sliding dynamics between interpenetrated frames in Ti-MOF revealing high proton conductivity. Chem Sci 11, 3978-3985 (2020).\n3. Li N, Pang J, Lang F, Bu X-H. Flexible Metal–Organic Frameworks: From Local Structural Design to Functional Realization. Acc Chem Res 57, 2279-2292 (2024).\n4. Alhamami M, Doan H, Cheng C-H. A Review on Breathing Behaviors of Metal- Organic-Frameworks (MOFs) for Gas Adsorption. Materials7, 3198-3250 (2014).\nQ 3-12. The authors infer dynamic flexibility from PXRD, Raman, and XPS shifts. Can the authors provide more quantitative data (e.g., peak shifts, time-resolved measurements) or in situ structural dynamics simulations to more rigorously define and support the claim of “dynamic stretching”?\nResponse 3-12: We have provided some peak shifts quantitative data of in situ XPS, in situ FTIR, and in situ Raman, as summarized below:\nThe Fe 2p peak in BUC-95 exhibited a clear binding energy shift (ca. 0.4 eV) with 3/2 the addition of H O and PDS (Supplementary Fig. 54a), in stark contrast to the 2 minimal spectral variation (ca. 0.07 eV) observed in BUC-96 (Supplementary Fig. 54b).\nMoreover, the in situ FTIR spectra of BUC-95 exhibited a redshift from 1395.94 cm- 1 to 1392.41 cm-1 following the addition of PDS after 5.0 min of reaction (Fig. 4f). Notably, the Raman peaks at 708.6 cm-1 and 769.9 cm-1 for BUC-95 were attributed to Fe‒O and Fe‒N bonds. Upon introducing PDS into this reaction system, clear redshifts of the Fe‒O bond (from 708.6 cm-1 to 702.4 cm-1) and Fe‒N bond (from 769.9 cm-1 to 765.7 cm-1) were observed, indicating that the occurrence of large-scale and flexible dynamic change in BUC-95 may contribute to PDS activation (Fig. 4g). After OFC was added to the above solution, all the Raman peaks returned to their original positions, and no new peaks were observed. Overall, the synergistic evidence from both crystallographic and electronic structure analyses conclusively indicates the presence of reversible and flexible dynamic stretching in BUC-95.\nAdditionally, to further verify the existence of flexible dynamic stretching in BUC- 95, we have supplemented the in situ XAFS measurement under different environments in the revised manuscript.\nManuscript revision:\nMeanwhile, in situ XANES analysis revealed that the absorption edge of pristine BUC-95 shifted toward higher energy upon water addition, with ∆E values of 0.14 eV and 0.28 eV after 1.0 min and 5.0 min, respectively. More obvious shifts (∆E = 0.87 eV and 1.29 eV, respectively) were observed with addition of PDS over the same time 31 intervals. These energy shifts reflect structural changes induced by flexible dynamic stretching and an elevated oxidation state of Fe in BUC-95, consistent with the formation of Fe(IV)=O species (Fig. 4e and Supplementary Fig. 55).\nFig. 4 (e) in situ XANES spectra of BUC-95 under different environments.\nSupplementary Fig. 55 (a) Photograph of the XAFS spectrometer, and (b) in situ flow reaction cell.\nImportantly, in situ structural dynamics simulations have been incorporated into the revised manuscript to rigorously characterize and substantiate the proposed “flexible dynamic stretching” behavior.\nManuscript revision:\nAdditionally, in situ molecular dynamics simulations under varied chemical environments and time resolutions (5.0, 10.0, 15.0, and 20.0 ps) confirm that BUC-95 exhibits clear reversible dynamic stretching in the presence of H O and PDS (Fig. 4i 2 and Supplementary Videos 2-3). In contrast, BUC-96 shows no significant structural change under the same condition (Supplementary Fig. 65 and Videos 4-5). These 32 findings further provide solid evidence for the unique flexible dynamic stretching in the homointerpenetrated framework of BUC-95.\nFig. 4 (j) In situ molecular dynamics simulation of BUC-95 under varying environments and time resolutions.\nSupplementary Fig. 65 In situ molecular dynamics simulation of BUC-96 with addition of (a) H O and (b) PDS under varying environments and time resolutions. 2\nQ 3-13. What is the expected lifetime of the BUC-95@sponge material? Can the catalyst be regenerated?\nManuscript revision:\nThe hydraulic residence time was calculated to be 62.5 min. Remarkably, the BS/PDS system achieved >99.99% OFC (10.0 mg L-1) degradation efficiency within 110.0 h and maintained a high efficiency of >85% after 192.0 h in the simulated wastewater formulated by ultrapure water. In contrast, the individual PDS and PDS/sponge systems demonstrated negligible catalytic activity (~1.5% and ~1.9% degradation, respectively, Fig. 5e). Throughout the reaction, the BS catalyst exhibited high stability, with iron leaching concentrations remaining below <1.50 mg L-1, well under the limit specified by the Chinese National Standard (DB11/307–2013).\nQ 3-14. On Pages 7-8, the authors showed the BUC-95 demonstrated superior peroxydisulfate (PDS) activation capability than the MIL-based systems. Were the loading amounts, surface areas, and Fe content normalized across all comparative systems to ensure a fair benchmark?\nResponse 3-14: We need to clarity that except for the continuous-flow degradation section, which used the immobilized catalyst. Other experiments are conducted using powder catalysts, including the MIL-based comparison experiments. Therefore, in the comparison processes of OFC degradation by activating PDS between different MIL-based systems and BUC-95 system, the loading amounts normalization is not involved.\nIn addition, to normalize the BET surface and Fe content of different MIL-based systems and BUC-95 system for a fair benchmark, the BET surface (detected by TriStar Ⅱ 3020, Micromeritics, USA) and Fe contents (detected by ICP-OES) are measured as the following figures and tables in the revised manuscript and supplementary information.\nManuscript revision:\nAnd it also exceeded other MIL-based systems like MIL-88A(Fe)/PDS (41.2% removal, 0.82 min-1), MIL-88B(Fe)/PDS (41.7% removal, 0.83 min-1), MIL- 88C(Fe)/PDS (48.43% removal, 0.94 min-1), MIL-53(Fe)/PDS (46.23% removal, 0.90 min-1), MIL-100(Fe)/PDS (41.96% removal, 0.73 min-1) and MIL-101(Fe)/PDS (54.46% 35 removal, 0.79 min-1) by 1.88-fold, 1.60-fold, 14.9-fold, 6.73-fold, 6.65-fold, 5.87-fold, 6.13-fold, 7.56-fold and 6.99-fold, respectively (Supplementary Figs. 18-19), which was further supported by the normalized results based on BET surface area and Fe content between MIL-based catalyst and BUC-95 (Supplementary Fig. 20 and Table 5).\nSupplementary Fig. 20 The N adsorption-desorption isotherms of different MIL- 2 based catalysts and BUC-95.\nSupplementary Table 5. The BET surface areas and Fe contents of different MIL- based catalysts and BUC-95.\nSamples BET surface area (m2 g-1) Fe content (%)\nMIL-88A(Fe) 175.0 18.36\nMIL-88B(Fe) 67.0 15.48\nMIL-88C(Fe) 71.0 12.89\nMIL-53(Fe) 132.0 16.02\nMIL-100(Fe) 1264.0 16.50\nMIL-101(Fe) 44.0 17.96\nBUC-95 92.0 14.25\nSupplementary information revision:\nAccording to the previous literature 6, we conducted the normalization of surface area and Fe content and introduced an evaluation index for a fair benchmark, k = S,Fe k/(S × n ), where k represents the catalytic degradation rate for each molar Fe atom Fe S,Fe in each unit of adsorption area, k represents the OFC degradation rate constant, S represents the BET surface area, n = m × ω /M , represents the total molar Fe MOF Fe Fe amount of Fe, m represents the dosage of different Fe-based MOFs, ω represents MOF Fe the mass percentage of Fe, M represents the molar mass of Fe (55.85 g mol-1). Based Fe on above mentioned formula, the corresponding k values of different MIL-based S,Fe MOFs are calculated as the following: MIL-88A(Fe) (14.24 min-1 m-2 mol-1), MIL- 88B(Fe) (44.72 min-1 m-2 mol-1), MIL-88C(Fe) (57.31 min-1 m-2 mol-1), MIL-53(Fe) (23.76 min-1 m-2 mol-1), MIL-100(Fe) (1.96 min-1 m-2 mol-1), MIL-101(Fe) (55.76 min- 1 m-2 mol-1) (Supplementary Fig. 20 and Table 5). While, the k of BUC-95 is S,Fe calculated to be 235.29 min-1 m-2 mol-1, which is far higher than those of MIL-based systems. In addition, most MIL-based MOFs exhibited higher BET surface area and Fe content than BUC-95. Taking MIL-100(Fe) and BUC-95 as typical examples, MIL- 100(Fe) exhibited larger BET surface area (1264.0 m2 g-1) and higher Fe content (16.50 %) compared with those of BUC-95 (92.0 m2 g-1, 14.25%), however, the OFC degradation performance in the MIL-100(Fe)/PDS system (41.96% removal, 0.73 min- 1) is lower than that in the BUC-95/PDS system (>99.99% removal, 5.52 min-1), further strongly demonstrating the negligible effect of BET surface area and Fe content and pivotal role of the flexible dynamic stretching in BUC-95.\nReference:\n6. Zhou H, Ren W, Wang S, Duan X. Best practices for advanced oxidation processes. Nat Sustain, 10.1038/s41893-025-01655-0, (2025).\nQ 3-15. On Page 12, the authors mentioned that BUC-96 has better conductivity, yet BUC-95 shows better performance due to the dynamic stretching. How do the authors rule out contributions from differences in Fe oxidation state distributions or local Fe site environments rather than dynamic behavior?\nResponse 3-15: We used XPS quantitative technology to determine the content distributions of different Fe oxidation state in BUC-95 and BUC-96, as shown in the following Table R1. It can be obviously observed that the content of Fe(II) and Fe(III) in BUC-95 and BUC-96 is extremely similar. Therefore, the influence of Fe oxidation state distribution for the excellent OFC degradation performance is ruled out.\nTable R1. The relatively content of Fe oxidation state in BUC-95 and BUC-96.\nFe oxidation state content (%) BUC-95 BUC-96\nFe(II) 46.23 45.99\nFe(III) 53.77 54.01\nSupplementary Fig. 13 The Fe 2p XPS spectrum of (a) BUC-95 and (b) BUC-96 before reaction.\nIn addition, BUC-95 is synthesized from FeSO ·7H O, 4,4′-bipyridine (bpy) and 1,4- 4 2 benzenedicarboxylic acid (H bdc) via a facile microwave-assisted method. While, 2 BUC-96 is synthesized following the same procedure, with the only difference being the replacement of H bdc with 2,5-dihydroxyterephthalic acid (H dhtp). Combined 2 4 with the 3D printing schematic diagram of BUC-95 and BUC-96 and the local coordination environments obtained from MicroED result (Supplementary Figs. 58 38 and 60), we can observe directly that the local Fe site coordination environment in BUC-95 and BUC-96 is identical. Therefore, the influence of local Fe site environment for the excellent OFC degradation performance is ruled out in the revised manuscript.\nSupplementary Fig. 58 (a) The Fe(bdc) network in a single framework and (b) the 2 coordination environment of Fe atom in BUC-95.\nSupplementary Fig. 60 (a) The Fe(H dhtp) network in a single framework and (b) the 2 2 coordination environment of Fe atom in BUC-96.\nManuscript revision:\nImportantly, the local coordination environments of Fe sites are identical in both MOFs (Supplementary Fig. 61), indicating that the enhanced PDS activation and OFC degradation in BUC-95 originate from its flexible dynamic stretching rather than differences in local metal coordination.\nQ 3-16. The authors highlighted that the catalytic enhancement for Fenton-like reactions is due to dynamic stretching of BUC-95. How do the authors ensure that other factors, such as pore size, Fe dispersion, morphology, surface area, did not contribute to the catalytic enhancement?\nResponse 3-16: As noted in Response 3-5, the experimentally derived average pore size likely reflects interparticle textural porosity rather than the intrinsic pore structure of the crystalline frameworks. To accurately assess the accessible pore dimensions, we performed DFT-based pore size distribution calculations using the crystallographic data (CIF files) of BUC-95 and BUC-96. The results (Supplementary Fig. 52) reveal pore limiting diameters of 4.4 Å for BUC-95 and 2.02 Å for BUC-96, dimensions too narrow to accommodate OFC molecules (13.8 Å in kinetic diameter) or facilitate their interaction with embedded Fe sites and co-adsorbed PDS. We therefore conclude that pore size effects do not contribute significantly to the observed catalytic performance.\nThen, the Fe 2p XPS (Table R1) and ICP-OES (Table R2) results demonstrate that the Fe oxidation state and content in BUC-95 and BUC-96 are essentially identical. Additionally, as discussed in Response 3-14, we conducted the normalization of surface area and Fe content of BUC-95 and BUC-96 to exclude the contribution of Fe content and BET surface area. By calculation, the k of BUC-95 is calculated to be 235.29 S,Fe min-1 m-2 mol-1, which is far higher than that of BUC-96 (27.88 min-1 m-2 mol-1), further exclude the contribution of Fe content and BET surface area.\nTable R1. The relatively content of Fe oxidation state in BUC-95 and BUC-96.\nFe oxidation state content (%) BUC-95 BUC-96\nFe(II) 46.23 45.99\nFe(III) 53.77 54.01\nTable R2. The actual Fe content in BUC-95 and BUC-96 detected by ICP-OES.\nSamples Actual Fe content (%)\nBUC-95 14.25\nBUC-96 13.50\nQ 3-17. Minor inconsistencies: In the manuscript and SI, the authors sometimes italicized symbols in texts and plots but in other parts, the symbols are not italicized. They need to ensure all symbols are italicized in the text and figures in both the manuscript and SI.\nResponse 3-17: Thanks for your suggestion. We have formatted uniformly whole text and figures requiring italics in both the revised manuscript and supplementary information.\nSupplementary information revision:\nSupplementary Fig. 11 The Fe 2p XPS spectrum of (a) BUC-95 and (b) BUC-96 before reaction.\nSupplementary Fig. 37 The EPR signal of oxygen vacancy in the homointerpenetrated BUC-95.\nQ 3-18. I recommend the authors to add a schematic figure of the proposed Fe(IV)=O generation and pollutant degradation mechanism to clarify the reaction sequence.\nResponse 3-18: We have supplemented a schematic figure of Fe(IV)=O formation and OFC degradation to better clarify the reaction sequence in the revised manuscript.\nManuscript revision:\nOverall, based on the mechanism exploration of HVIO formation and OFC degradation, Fe(IV)=O species, rather than radicals, were recognized as the dominant ROSs in the BUC-95/PDS/OFC system (Fig. 3l), which aligned with the anion resistance and pH robustness results.\nFig. 3 (l) The schematic diagram of Fe(IV)=O generation and OFC degradation mechanisms in BUC-95/PDS system.\nQ 3-19. In some OFC degradation figures in the main manuscript and SI, error bars and replicate measurements seem to be missing.\nManuscript and Supplementary information revisions:\nFig. 2 (f) Lengths of roots and stems in different reaction solutions (inset: mung beans in different growth environments).\nSupplementary Fig. 56 (a) The PDS consumption and (b) the corresponding standard curve in the BUC-95/PDS system.\nReviewer #1 (Remarks to the Author):\nThe authors have made great effort to revise this manuscript and all of my comments have been addressed properly. Additionally, they also provided serious and reasonable responses to the comments of other reviewers. From the novelty of the manuscript and their attitude towards the revision, I recommend this work for publication.\nResponse: We sincerely appreciate your constructive feedback, affirmation of our revisions, and valuable recommendation for our manuscript’s publication.\nReviewer #2 (Remarks to the Author):\nThere is no further revision to be addressed, which can be accepted in nature communication.\nResponse: Thank for your confirmation of no further revisions and support for our manuscript’s acceptance in Nature Communications."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have made great effort to revise this manuscript and all of my comments have been addressed properly. Additionally, they also provided serious and reasonable responses to the comments of other reviewers. From the novelty of the manuscript and their attitude towards the revision, I recommend this work for publication.", "reviewer_2": "There is no further revision to be addressed, which can be accepted in nature communication."}, "author_response": "Response: We sincerely appreciate your constructive feedback, affirmation of our revisions, and valuable recommendation for our manuscript’s publication.\nResponse: Thank for your confirmation of no further revisions and support for our manuscript’s acceptance in Nature Communications."}]

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