Macrocycle-assembled membranes for high-salinity organic wastewater treatment

Domain: chemistry
Published: 2026-01-17
Editorial outcome: minor_revision

Abstract
Membrane processes offer a promising pathway for selectively separating organics and salts to enable water reuse and resource recovery. While polymeric membranes incorporating macrocyclic molecules that feature amphiphilic nature and tunable cavities are well suited for this purpose, traditional macrocycles with limited reactive sites and uncontrolled diffusion are challenging to be assembled into highly interconnected membranes. Here, we introduce tetra-aldehyde appended calixarene (TACA), a macrocyclic monomer featuring three-dimensional cavity and moderate reactivity, for creating loose-structured nanofilms via unidirectional diffusion assisted interfacial polymerization (UDIP). Precise positioning of the lipophilic TACA at the organic phase boundary allows it to polymerize with aqueous-phase diamines on the hydrogel surface, facilitating an undisturbed environment for controlled polymerization. The resultant thin macrocycle-assembled membranes featuring intrinsic water-facilitated through-cavity exhibited high water permeability of 63.8 L m-2 h-1 bar-1, and exceptional dye/salt selectivity and structural robustness, as evidenced by efficient diafiltration of binary dye/salt mixtures and superior operational stability. This work highlights the potential of macrocycle-assembled membranes for high-salinity organic wastewater treatment.

Introduction
The treatment and reuse of industrial wastewaters are central to addressing global water scarcity and enabling circular water economies1,2. In particular, saline organic wastewaters produced by industries such as textiles, petrochemicals, and pharmaceuticals pose a significant challenge to conventional treatment processes due to the co-existence of high concentrations of organic contaminants and inorganic salts3,4. Membrane-based separations provide promising solutions for precise separation of organics and salts, facilitating water reuse, resource recovery, and zero-liquid discharge5–7. Currently, the treatment of organic-laden saline wastewaters primarily relies on polyamide-based membranes, which exhibit limited selectivity for separating organic molecules from inorganic ions8,9. This limitation arises from the rapid interfacial polymerization of planar, highly reactive monomers, resulting in membranes with low microporosity and restricted free volume10,11. As a result, both organic compounds and salts are often rejected indiscriminately. To address this challenge, next-generation membranes must feature larger and more interconnected free-volume elements to achieve rapid and efficient molecule/ion separations.

Macrocyclic molecules with intrinsic through cavities emerge as promising building blocks for high-performance sieving membranes12,13. Notably, macrocycle-based membranes often demonstrate substantially improved water permeabilities or solvent fluxes compared to conventional polyamide-based membranes14,15. The three-dimensional stereochemical configurations and diverse chemical functionalities of macrocyclic molecules enable precise control over monomer diffusion kinetics in both bulk and interfacial environments16,17. This controlled monomeric diffusion facilitates the formation of thin polymeric nanofilms with tunable crosslinking density and a narrow pore size distribution18,19. Importantly, the well-defined intrinsic micropores of these macrocycles evolve into interconnected nanopores within the crosslinked membrane, thereby enhancing the membrane microporosity and improving solvent transport efficacy20,21. Functionalized macrocycles (e.g., amine-cyclodextrin22, pillararene23 and Noria24) have been utilized to fabricate microporous membranes exhibiting exceptional performance in gas separation, organic solvent nanofiltration, and reverse osmosis. However, the commonly used amide reaction during fabrication often produces an excessively dense crosslinked network with sub-nanoscale pores. This limits its ability to separate molecular/ion mixtures and hinders its effectiveness in treating saline organic-rich waters. In contrast, calixarenes maintain the structural characteristics of traditional macrocyclic molecules while offering tunable configurations and easy chemical modification. This provides a foundation for precise control over membrane architecture. By altering chemical bonding type, polymer membranes with adjustable network structures are fabricated.

Here, we identify tetra-aldehyde-functionalized calix[4]arene (TACA) as promising three-dimensional building blocks to construct high-porosity polyimine membranes for improved molecule/ion separation. TACA, with four aldehyde groups, enables moderate Schiff base reaction with diamines, facilitating the formation of loosely structured networks. Moreover, TACA contains four phenolic hydroxyl groups positioned para to the aldehydes, and four methylene that connects four benzene rings in a cone-shaped arrangement. This nonplanar, rigid framework possesses internally connected calix-shaped cavities, naturally forming a continuous pathway for water transport. In contrast to other contorted macromolecules, TACA offers several advantages for the synthesis of thin-film composite (TFC) membranes. First, the hydrophobicity and relatively large size of TACA confine it to the organic phase, while the aqueous-phase m-phenylenediamine (MPD) diffuses unidirectionally across the phase boundary, enabling precise spatial control over interfacial polymerization (Fig. 1a, b). Second, the less reactive aldehyde groups in TACA allow better control over the Schiff base reaction, enabling more flexible regulation of film compactness. Third, hydroxyl groups on the lower rim of the calix-shaped cavities promote the formation of hydrophilic channels that facilitate water transport25. Last, TACA exhibits low toxicity and biocompatibility, making it a highly attractive material for membrane fabrication26.

The porous substrate underlying the crosslinked nanofilm also substantially influences the microstructure and physicochemical properties of the nanofilm. During interfacial polymerization, the substrate functions as an “interfacial reactor”, providing both the reaction interface and a reservoir for aqueous-phase monomers27. However, relatively hydrophobic substrates often lead to uneven distribution of aqueous-phase monomers, resulting in non-uniform film thickness and a broad pore size distribution28–30. In contrast, Kevlar hydrogel, a highly hydrated three-dimensional nanofibrous network, stabilizes the interfacial polymerization interface by acting as the aqueous phase and simultaneously regulates monomer diffusion31,32. The controlled diffusion of diamine monomers during interfacial polymerization is attributed to its electrostatic and hydrogen-bonding interactions with the carboxyl-rich hydrogel. Moreover, the water-rich environment of the hydrogel effectively dissipates heat from the exothermic polymerization, maintaining a stable reaction environment conducive to a smooth and well-structured selective layer33. Leveraging these properties, we introduce a strategy that combines the moderately reactive, three-dimensional contorted TACA macrocycle to fabricate loosely structured TFC membranes with highly interconnected porous networks. Kevlar hydrogel was employed as the porous substrate to in situ fabricate polyimine-based TACA-MPD composite membranes via unidirectional diffusion-assisted interfacial polymerization (UDIP). In contrast to traditional interfacial polymerization, the UDIP process uses a Kevlar hydrogel to prevent direct contact between the two-phase solutions, thereby achieving superior control over the reaction. Furthermore, UDIP provides a sustained and stable monomer supply for film formation, which promotes structural self-healing conducive to the formation of defect-free thin films. A systematic exploration of critical synthesis conditions (e.g., monomeric molar concentration/ratio and reaction duration) was conducted to elucidate their role in morphological structure and physicochemical properties of the synthesized TACA-MPD membranes. Our macrocycle-assembled membranes exhibited impressive dye/salt selectivity, remarkable structural robustness, and operational stability, as demonstrated by the efficient separation of binary dye/salt mixtures. Combined experimental and molecular simulation results revealed that the exceptional water permeability and separation performance stem from the well-defined, rigid interconnected cavities formed within TACA-MPD nanofilms (Fig. 1c, d).

Results
Tetra-aldehyde appended calixarene (TACA) was synthesized to incorporate multiple reactive sites (i.e., formyl group, -CHO) based on Duff aldehyde synthesis. The introduction of the formyl group onto the aromatic rings and good solubility in the DCM solution are both essential for subsequent membrane fabrication via Schiff base reaction (reaction between aldehyde and amine; Supplementary Figs. 1, 2, Supplementary Note 1, 2 and Supplementary Table 1)34. Supplementary Fig. 3 depicts the chemical structure and internal pore information of TACA molecules, which feature a wide upper rim (10.94 Å), a narrow lower rim (3.45 Å), and a calix-shaped structure. The presence of hydrophilic hydroxyl groups within the calix-shaped structure is expected to promote rapid water transport35. The resultant powders shown in Supplementary Fig. 4 appear pale yellow and exhibit a nanoparticle morphology with sizes ranging from 50 to 150 nm. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectra further verified the formation of TACA molecules (Supplementary Figs. 4–6, Supplementary Note 3). Considering the tetra-aldehyde sites on the upper rim of TACA, its reaction with MPD is expected to form imine-linked polymers that possess three-dimensional, highly crosslinked, and intrinsically interconnected networks (Fig. 1d, Supplementary Fig. 7).

Figure 2a presents the chemical structure of the imine-linked TACA-MPD network formed via Schiff base condensation. The electrostatic potential maps of both TACA and polyimine structural units reveal the presence of negatively charged cavities, which can strengthen Donnan exclusion for rejecting anionic dye molecules (Fig. 2b, Supplementary Fig. 8)36. A free-standing interfacial polymerization approach was employed to explore the polymerizability of TACA and MPD. Upon introduction of the MPD/aqueous phase onto the surface of the TACA/dichloromethane (DCM) phase, a yellow thin film gradually formed at the interface within 30 min (Fig. 2c). The resulting free-standing film exhibited integrity and continuity, as shown in the cross-sectional scanning electron microscopy (SEM) image (Supplementary Fig. 9). High-magnification SEM reveals that the continuous nanofilm is primarily consisted of cohesive and densely packed nodules with size in the range of 10–15 nm (Fig. 2d, e). While nodular structures in traditional interfacial polymerization are driven by convective flow from exothermic reactions, the morphology of the TACA-MPD membrane is controlled by the dynamic assembly and fusion of imine-bonded polymer particles. Additionally, transmission electron microscopy (TEM) images confirmed the uniform distribution of the hollow and bubble-like nodules in three dimensions (Fig. 2f, g), a structure that is anticipated to facilitate rapid water transport37,38. The thickness of the TACA MPD -3 film (prepared using 0.5 mM of each monomer with a 3-h reaction time), as measured by AFM, is approximately 12 nm (Fig. 2h, i). Moreover, a linear relationship between reaction time and film thickness was observed, enabling precise control over film thickness ranging from 8 to 22 nm (Fig. 2j, Supplementary Fig. 10). This minor thickness increment of 14 nm over 6-h reaction duration differentiates our controlled growth behavior from traditional IP. Based on its strong hydrophobicity and stable intermolecular hydrogen bonding interactions, TACA preferentially adsorbs and self-assembles into a thin film at the oil-water interface formed when an aqueous phase is added. This assembly behavior aligns with established principles of interfacial self-organization, where sufficiently strong interactions such as hydrogen bonding, hydrophobic effects, electrostatic forces, or π–π stacking enable film formation39,40. During the growth of the TACA-MPD nanofilm, a TACA-rich layer forms initially. This interfacial layer serves a dual function in the subsequent interfacial polymerization: (i) it forms an effective physical barrier that restricts diamine diffusion and (ii) it enables confined growth of the polyimine nanofilm with nanoscale increments in thickness41.

To fabricate polyimine-based TFC membranes, UDIP was employed using a polyamide-based Kevlar hydrogel as the porous support. The Kevlar support was positioned between the aqueous and organic phases containing the respective monomers. Owing to its hydrophobicity and large molecular size, TACA remained evenly distributed at the organic/support interface. As MPD molecules diffused towards this interface, they polymerized with TACA to form a polyimine nanofilm on the Kevlar support (Supplementary Fig. 11). The Kevlar support exhibited a smooth surface with a roughness of 20.7 nm (Fig. 3a, Supplementary Fig. 12). The TACA MPD -3 membrane showed a denser, homogeneous morphology with a similar roughness (Ra = 20.3 nm, Fig. 3b). The smooth and dense surface structure is attributed to the confinement effect of the Kevlar hydrogel, which slows down the diffusion of MPD molecules via hydrogen bonding and electrostatic interactions42,43, thereby enabling enhanced control over the interfacial polymerization reaction.

Cross-sectional TEM imaging shows that the thickness of TACA MPD -3 nanofilm is 90 ± 5 nm, consistent with the result of cross-sectional SEM observations (Fig. 3c, Supplementary Fig. 13). The nanofilm formed on Kevlar hydrogel shows distinctly greater thickness compared to the free-standing film (Fig. 2j). The mechanism of film thickness enhancement during the UDIP process closely relates to the Kevlar hydrogel, which mitigates the TACA self-assembly by establishing electrostatic and hydrogen-bonding interactions with the TACA molecules. This results in a less compact TACA-assembled film structure compared to that formed at a free water- interface. This loose structure sustains diamine transport, which in turn facilitates the continuous polymerization with TACA at the interface, ultimately leading to thicker film formation.

Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectra of the Kevlar support and the as-fabricated TFC membranes confirm the successful formation of the imine (C=N) bond via Schiff base condensation44, as evidenced by the disappearance of the characteristic N-H peaks from MPD and –CHO peaks from TACA (Fig. 3d, Supplementary Fig. 14). The formation of the polyimine layer was further verified by X-ray photoelectron spectroscopy (XPS), with the C 1s and N 1s spectra revealing the presence of C–O/H-C=O, C–N=C and C–NH2 functional groups (Supplementary Figs. 15–16)45. XPS analysis also showed a substantial increase in oxygen content, reaching 19.8% in the TACA-MPD-TFC membrane (Fig. 3e, Supplementary Table 2). This increase is attributed to the abundant oxygen-containing moieties (–OH, –CHO) within TACA, which can potentially enhance water transport by increasing the affinity of the membrane for water molecules. X-ray diffraction (XRD) characterization indicates that the polyimine layer exhibits an amorphous structure (Supplementary Fig. 17)32.

The formation of the TACA-MPD layer resulted in increased hydrophobicity compared to Kevlar support, as evidenced by water contact angle (WCA, Fig. 3f). The high WCA indicates that hydrophobic benzene rings are oriented toward the surface14. Extending the reaction time further increased the hydrophobicity of the TACA-MPD layer, with the WCA increased from 82.4° to 91.4° as the reaction time increased from 1 to 7 h (Fig. 3f, Supplementary Fig. 18). While the membrane surface maintains hydrophobic, the presence of internal polar hydrophilic functional groups (as evidenced by XPS results) augment interactions with water molecules through hydrogen bonding. This, in turn, facilitates the enhanced water transport across the TACA-assembled layer. Thermogravimetric analysis showed that the TACA-MPD selective layer maintained an overall high thermal stability (Supplementary Fig. 19). The high stability of the polymer network is ascribed to the rigid benzene ring structure and the non-planar methylene bridges in calixarene that allow rotational freedom of phenolic hydroxyls, enabling various spatial arrangements.

A negative surface charge is observed across a wide pH range for the TACA-MPD membrane (Fig. 3g), attributed to the electron-rich cavity of TACA and its phenolic hydroxyl groups. This negative charge can promote strong electrostatic repulsion against negatively charged organic molecules, such as organic dyes, and enhance their rejection. Moreover, the synergistic effect of the multi-pathway dye rejection mechanism in the TACA-MPD membrane enables it to achieve highly efficient rejection of dye molecules, even close to their isoelectric point: (i) dye molecules aggregate through hydrophobic interactions, reducing their diffusivity; (ii) enhanced size exclusion effects from the densely cross-linked network; and (iii) strong electrostatic repulsion provided by the electron-rich cavities in TACA. The rejection of polyethyleneglycol (PEG) with different molecular weights was tested to evaluate the molecular weight cut-off (MWCO) and pore size distribution of the TFC membrane. The MWCO of the TACA MPD -3 membrane was 11480 g/mol, and the average pore diameter was 3.4 nm (see Supplementary Fig. 20). This result indicates that the rigid-flexible conformation of TACA facilitates the formation of a stable and loose polymer network structure with diamine monomers, which effectively reduces the transport resistance of water molecules and ions within the membrane pores46.

To elucidate the influence of diffusion kinetics and interfacial polymerization mechanisms on membrane formation, we examined monomer partitioning and polymer growth behavior at the molecular level. The partition coefficient (log P) is a measure of the relative distribution of a compound between an organic phase and an aqueous phase. A higher log P value corresponds to an increased lipophilicity and preferential partitioning into the organic medium, while a lower value denotes enhanced aqueous solubility and a dominant affinity for the aqueous phase. Partition coefficient measurements revealed that MPD, with a log P of -0.45, is hydrophilic but still moderately soluble in DCM, while TACA, with a log P > 3, is highly hydrophobic and insoluble in water (Fig. 3h, Supplementary Fig. 21 and Supplementary Note 4)47. These properties suggest that TACA concentrates at the organic (DCM) interface, where MPD diffuses from the aqueous phase to initiate interfacial polymerization.

To confirm this directional polymer growth, MPD and TACA were placed on opposite sides of the Kevlar support, composed of a hydrogel layer and a non-woven fabric. When the TACA/DCM phase contacted the hydrogel side, nodular structures emerged on its surface, while the non-woven fabric remained smooth (Supplementary Fig. 22a, b). In the reversed configuration, with the MPD/aqueous phase facing the hydrogel, nodule formation was observed on the non-woven fabric (Supplementary Fig. 22c, d). These observations confirm the directional growth of imine-linked polymers at the DCM interface.

UV-Vis spectroscopy further verified the partitioning of MPD molecules into the DCM phase (Supplementary Fig. 23). Increasing the initial MPD concentration enhanced its interfacial accumulation and diffusion rate (Fig. 3i, Supplementary Fig. 24). These findings suggest that extending the reaction time or increasing the monomer concentration could enhance polymerization degree and consequently affect the surface properties of the polyimine membrane48.

To further investigate the influence of fabrication conditions on UDIP, the morphology of the membrane was characterized under varying TACA concentrations (Supplementary Figs. 25–28). At low TACA concentrations, the reaction proceeded mildly, yielding smooth, particle-free surfaces. Increasing TACA concentration led to an intensified interfacial polymerization process, leading to the gradual formation of surface particles and wrinkles. At excessively high TACA concentrations, the vigorous reaction combined with the rigid benzene ring structure led to the formation of wrinkles and cracks on the membrane surface.

Based on the experimental observations, a mechanistic pathway for TACA-MPD membrane formation is proposed (Fig. 3j). The process begins with the confined diffusion of MPD toward the organic interface, where it undergoes a Schiff base reaction with TACA, initiating the nucleation and growth of polymer nodules. These particles aggregate and coalesce on the Kevlar support, forming a continuous nanofilm through the dynamic breaking and reforming of imine bonds49. As the reaction progresses, continued particle growth and accumulation lead to an increased nanofilm thickness50. The diffusion rate of MPD and the concentrations of both monomers govern the polymerization kinetics and resulting membrane morphology. Higher monomer concentrations and longer reaction times promote film growth but may also induce defects such as wrinkles and cracks due to excessive particle formation.

The separation performance (water permeance and dye rejection) of various TACA-MPD membranes was evaluated using a crossflow apparatus with feed solutions containing organic dyes and/or inorganic salts. As depicted in Supplementary Fig. 29, extending the reaction time from 1 to 7 h led to a gradual decrease in the water permeance but significantly improved dye rejection, reaching 99.8% for Congo red and 99.1% for Methyl blue. This enhancement is attributed to increased membrane thickness and crosslinking degree51. Notably, the TACA MPD -3 membrane (prepared with 0.5 mM of each monomer and 3 h of reaction time) exhibited a high water permeability of 63.8 L m-2 h-1 bar-1 and an ultra-high Congo red rejection of 99.8% (Supplementary Fig. 29b). To further assess the impact of monomer concentration, membranes were prepared under a fixed 3-h reaction time. Increasing TACA concentration from 0.4 to 0.7 mM led to the formation of a thicker and denser selective layer, improving dye rejection but reducing water permeance (Supplementary Fig. 30). Similarly, increasing MPD concentration from 0.25 to 1.0 mM yielded improved dye retention and decreased water permeance (Fig. 4a), as higher MPD levels enhance its diffusion to the DCM interface, promoting the formation of a more compact and highly crosslinked nanofilm.

As illustrated in Fig. 4b, the TACA MPD -3 exhibited high rejections for a wider range of organic dyes (Congo red: 99.6%, Direct red 23: 99.4%, Methyl blue: 98.9%, Direct yellow 12: 99.0%, Acid fuchsin: 90.9%, Methyl orange: 77.5%). More importantly, this TFC membrane featured low rejections toward inorganic salt ions (Na2SO4: 27.7%, NaCl: 1.1%), demonstrating its high potential for efficient fractionation of dye/salt mixtures. Dye molecules exhibit a strong tendency to agglomerate into larger, less diffusive clusters in aqueous media, a phenomenon resulting from hydrophobic and π–π stacking interactions within their aromatic moieties52,53. These inherent characteristics make loose-structured membranes (e.g., TACA-MPD) particularly well-suited for dye purification. This is because dense-structured membranes inevitably reject both dyes and salts and lead to an undesirable elevation of osmotic pressure that compromises separation efficiency. Additionally, the TACA-MPD nanofilm features electron-rich cavities and a negatively charged surface, which establishes significant electrostatic repulsion against anionic dyes, substantially contributing to the observed high rejections41. Furthermore, the TACA-MPD nanofilm features an interconnected network of calix-shaped cavities and crosslinked voids, forming low-resistance nanochannels that facilitate rapid transport of both water molecules and hydrated ions.

The separation performance of the TACA MPD -3 membrane was evaluated for Congo red/NaCl mixtures across a range of NaCl concentrations (1–30 g/L, Supplementary Fig. 31). As NaCl concentration increased, NaCl rejection decreased from 12.1% to 0.5%, while Congo red rejection remained consistently high (>98%), with only a slight decrease (less than 1%). The slight decrease in dye rejection was likely ascribed to the enhanced dye dispersion and diminished membrane surface charge under high salt concentrations54. The high separation factor, even under high salinity, highlight the potential of TACA-MPD membranes for effective dye/salt separation for high salinity organic wastewaters.

To further demonstrate its feasibility, a diafiltration process was conducted using a 500 mL feed solution containing 200 ppm Congo red and 30 g/L NaCl (Fig. 4c, experimental procedure detailed in “Methods”). During the process, 250 mL of deionized water was added to the feed once the water recovery reached 50%. As deionized water was introduced, NaCl concentrations decreased notably in both the permeate and feed solutions. Throughout the diafiltration process, the TACA-MPD membrane maintained high Congo red rejection (98%), indicating minimal dye loss. In the initial stage, the high osmotic pressure of the feed solution led to reduced permeate flux and prolonged time to reach 50% water recovery. To reduce the NaCl concentration in the feed to below 0.5 g/L, the total water consumption using the TACA-MPD membrane was 1750 mL, distinctly lower than that required by commercial nanofiltration (NF) membranes. Furthermore, the energy consumption of the TACA-MPD diafiltration process was only 131 kWh m-3, substantially lower than that of the NF 270 membrane (228 kWh m-3), demonstrating a significant advantage of the TACA-MPD membrane in enhancing process efficiency (Supplementary Table 4)52.

The long-term filtration performance of the TACA-MPD membranes was tested under 2 bar (Fig. 4d). The permeance and rejection of a mixed solution containing 100 ppm Congo red and 1 g/L NaCl experienced negligible changes during 48 h of continuous operation, which demonstrates exceptional long-term operational stability. SEM and FTIR characterizations further reveal the superior stability of the TACA-MPD membranes. The SEM images (Supplementary Fig. 32a, b) showed minimal dye accumulation on the surface following prolonged testing, directly indicating remarkable antifouling capabilities. Moreover, the near-perfect overlap between the FTIR spectra obtained before and after operation (Supplementary Fig. 32c) serves as compelling evidence for their structural integrity and resilience under prolonged operational conditions. The synergy between dynamic imine bonds and the UDIP self-healing process enables the TACA-MPD membrane to reach a state of thermodynamic stability. Furthermore, the rigid three-dimensional structure of TACA enhances its microporosity and structural stability, which holds considerable potential for practical application. UV-Vis spectral analysis (Supplementary Fig. 33, Supplementary Note 5) was conducted to evaluate potential monomer leaching from the TACA-MPD membranes, which may lead to safety concerns. No detectable leaching of either MPD or TACA was observed under static (prolonged immersion) or dynamic (filtration) conditions. This finding strongly confirms the exceptional stability of the polyimine membrane, supporting both the chemical robustness and environmental safety of the membrane.

A comparison of dye retention and permeability of TACA-MPD membranes with literature values is presented in Fig. 4e55–72. Results reveal that macrocycle-assembled membranes exhibit both high water permeance and dye rejection, outperforming many state-of-the-art membranes (Supplementary Table 5). By preparing TFC membranes using either conventional monomers or in situ IP strategies, we further demonstrate the potential of TACA macrocyclic molecules for constructing polyimine membranes. The resulting performance demonstrates the superior advantages of both the UDIP approach and TACA monomers for fabricating high-flux and high-selective polyimine-TFC membranes (Supplementary Fig. 34, Supplementary Note 6). To verify the scalable application of TACA, various configurations of diamine monomers were utilized to fabricate polyimine membranes. As shown in Fig. 4f, Supplementary Figs. 35, 36, the TACA-based polyimine membranes exhibit high rejection of small organic pollutants, demonstrating the potential of TACA as the monomer for membrane separation. More importantly, TACA-MPD membranes offer multiple water transport pathways while maintaining a superior rejection of various dyes via sieving and Donnan effects, enabling efficient dye/salt separation for saline organic wastewaters.

Macrocyclic compound-based membranes typically offer two types of transport pathways: hydrophilic channels (path 1) and hydrophobic inner cavities (path 2)35. The hydroxyl groups on the exterior of TACA and imine linkage promote water molecule partition on the surface pore, while hydrophobic nanochannels of TACA molecules favor rapid water transport due to low friction with the hydrophobic pore wall73. The abundant hydroxyl groups at the bottom of TACA act as artificial water channels, actively drawing water molecules from the cavity via hydrogen bonding interactions to create a high-speed water transport pathway. The transport of water molecules through the hydrophobic inner cavity was simulated using Density functional theory (DFT) calculations. As illustrated in Fig. 5a, the transfer of water molecules from the intrinsic through cavity to the hydroxyl group (path 2) of the TACA was energetically favorable (Supplementary Figs 37, 38, Supplementary Note 7). For path 2, the transfer along the upper rim to the lower rim of the cavity was feasible, with the potential energy for interaction between the water molecule and the structural unit ranging from -0.024 to -0.562 eV. The electrostatic force between the water molecule and the structural unit diminished as the water molecule moved farther from the cavity (from -0.162 to -0.123 eV), aligning with the Coulomb force rule74,75. Despite increased surface hydrophobicity of the polymer membrane, the weak interaction between water molecules and the hydrophobic wall of the cavity contributes to rapid water transport76. Overall, the TACA structure provides rich reactive sites for the Schiff base reaction and establishes an adaptable channel for efficient water transport. Investigating the proportion of transport pathways of water molecules within macrocyclic membranes is crucial for elucidating the transmembrane mechanism. Although this mechanism falls beyond the scope of the present study, it constitutes a key direction for future research and will focus on clarifying the specific transport processes and the contribution of macrocyclic cavities.

To elucidate the relationship between the three-dimensional interconnected microstructure of the TACA-MPD network and its rapid transport properties, a realistic polymer structure model was constructed using molecular dynamics (MD) simulations to visualize membrane microstructures (Fig. 5b, Supplementary Figs. 39, 40). The TACA MPD -3 membrane exhibited high porosity with continuous voids under different probe sizes. As the probe size increased, the volume of interconnected micropores decreased. These results demonstrate that the TACA-MPD membrane possesses a high microporosity and interconnectivity, which facilitate the transport of small molecules such as water molecules and inorganic salt ions. They further highlight the advantage of cavity-containing TACA as building blocks for a separation membrane.

MD simulations were employed to further explore the transport behavior of dye molecules (Congo red and Methyl blue) and salt ions (Na+, Cl− and SO42−) across the TACA MPD -3. As presented in Fig. 5c, Supplementary Figs. 41, 42, Congo red and Methyl blue molecules were trapped on the membrane surface, whereas inorganic salt ions readily transported across the membrane to the permeate chamber within 50 ns. As expected, the number of dye molecules and ions permeating the membrane and their diffusion coefficients (Fig. 5d, e) revealed that TACA MPD -3 has an impressively high ionic permeability relative to Congo red and Methyl blue. Furthermore, high dye rejections were validated by comparing the density distribution of dye molecules and salt ions in the z-direction (Fig. 5f). In summary, MD simulations, together with experimental results, revealed that TACA MPD -3 network structure facilitates salt ion passage while effectively impeding dye molecule transport.

Methods
Fabrication of Kevlar hydrogel support membrane
Kevlar hydrogel support membranes were fabricated via a wet phase inversion method42,77. A mixture of 1.2 g Kevlar fibers, 1.2 g KOH, 1.2 mL water, and 60 mL DMSO was magnetically stirred at room temperature for 24 h to obtain a homogeneous and transparent dark red solution. The solution was subsequently centrifuged at 6578 xg to remove air bubbles and KOH precipitates. The non-woven fabric was fixed onto a clean glass plate, and then the treated solution was cast onto it with a casting knife set to 250 μm thickness. The coated glass plate was immediately immersed in a deionized water bath (26 °C). The Kevlar hydrogel support membrane was formed by phase inversion for 6 min.

Preparation of free-standing TACA-MPD films
Freestanding films were fabricated by interfacial polymerization at the free water-DCM interface. TACA was dissolved in 50 mL of DCM to prepare a 0.5 mM organic phase solution. MPD was dissolved in 50 mL of deionized water to form a 0.5 mM aqueous solution. The organic phase solution was poured into a glass petri dish, followed by the slow addition of the aqueous phase onto its surface to form a stable water/DCM interface. The petri dish was then covered to prevent disturbance from airflow. After a 3-h interfacial polymerization reaction at room temperature, the film at the interface was carefully transferred using a silicon wafer or anodized aluminum for subsequent characterization.

Preparation of TACA-MPD macrocyclic-based membranes
The TACA-MPD membrane was fabricated by UDIP using the Kevlar hydrogel as substrate. The Kevlar hydrogel membrane was secured between the two chambers of a diffusion cell. 30 mL of 0.5 mM MPD/aqueous solution was added to one chamber, followed immediately by adding 30 mL of 0.5 mM TACA/DCM solution to the chamber on the opposite side. The TACA MPD -3 membrane was synthesized with a 3-h reaction under undisturbed conditions. A series of TACA-MPD membranes was fabricated by adjusting the monomer concentrations in the organic and aqueous phases, as well as the reaction time. The prepared membranes were designated as TACA MPD -Z, where X represents the TACA concentration (0.4, 0.5, 0.6, and 0.7 mM), Y represents the MPD concentration (0.25, 0.50, 0.75, and 1.0 mM), and Z represents the reaction time (1, 3, 5, and 7 h). By balancing dye rejection and water permeance, we identified the optimal membrane, which was fabricated using 0.5 mM TACA and 0.5 mM MPD under a 3 h reaction condition (referred to as TACA MPD -3), and used it for subsequent dye/salt separation tests.

Membrane performance tests
The performance of membranes was evaluated using a crossflow test apparatus with a membrane area of 7.1 cm2. The membrane was first compacted with deionized water at 2 bar for 30 min to reach a steady state. The compacted membrane was then tested with the test solutions at 1 bar. The water permeability (P, L m-2 h-1 bar-1) was calculated as follows:

P = V / (A × Δt × ΔP)

where V (L) is the permeate volume over operational time Δt (h), A (m2) represents the effective membrane area, and ΔP (bar) is the applied pressure.

The separation performance of dyes and salts (100 ppm for Congo red, 1–30 g/L for NaCl) was measured by filtering different single and mixed solutions. The concentration of dyes was determined by a UV–Vis spectrophotometer (UV-1800, Shimadzu) and the concentration of salts was analyzed by a conductivity meter (DDS-307A, INESA). Rejections of dyes and salts were calculated using Eq. (2):

R = (1 - CP / CF) × 100%

where CP and CF are the concentration of the permeate and feed solution, respectively.

Dye/salt separation was performed in diafiltration mode using a simulated textile wastewater containing 200 ppm Congo red and 30 g/L NaCl. The dye/salt separation performance of the membranes was evaluated at an operating pressure of 2 bar. The initial volume of the feed solution was 500 mL. Once reduced to 250 mL, concentrations of dyes and salts in both feed and permeate solutions were measured. Then, 250 mL of deionized water was added to the feed solution. This process of measurement and dilution was repeated until the concentration of NaCl in the feed solution decreased to below 0.5 g/L.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In the manuscript titled Macrocycle-assembled membranes for high-salinity organic wastewater treatment, Li et al. used macrocyclic molecules as building blocks to prepare polymeric membranes that can selectively fractionate organics and salts. The authors adopted unidirectional diffusion assisted interfacial polymerization to fabricate macrocycle-assembled, loose-structured polyimine membranes. Also, the utilization of water-rich Kevlar hydrogel could form a stable and undisturbed reaction interface, thereby yielding a smooth and moderately crosslinked nanofilm. The novelty of this work is high, and the results are very interesting. For example, the TACA-MPD membrane exhibits exceptional dye/salt selectivity and structural stability, showing great potential for treating complex water bodies, such as textile wastewater. Considering the overall high quality of this work, I recommend its acceptance by Nature Communications after some minor revisions. The specific comments are as follows.\n\n- The abstract section is slightly wordy and it is recommended that a more concise and emphasized abstract be provided.\n- What are the characteristics and advantages of TACA macrocyclic molecules compared to typical ones, like cyclodextrins and cucurbiturils? Why are they suited as building blocks for separation membranes?\n- Is the ability to self-assemble at the interface a property common to macrocyclic molecules? Does this self-assembly occur in the UDIP process? Why are TFC membranes thicker than free-standing films?\n- XPS confirms that the oxygen-rich functional groups of TACA increase the oxygen content on the membrane surface, which is proposed to enhance the membrane-water affinity. However, the water contact angles indicate surface hydrophobicity. This seems to present two contradictory results. Please explain how a hydrophobic surface can exhibit high hydrophilicity.\n- The pore size of the TFC membrane is 3.4 nm. Please explain how such a large pore size can achieve high rejection of dye molecules.\n- Please provide more details on the relationship between partition coefficients, hydrophilicity, and monomer diffusion or reaction regions.", "reviewer_2": "This study presents the fabrication of loosely structured macrocycle-assembled membranes as a promising approach for effective dye/salt separation in high-salinity organic wastewater treatment. The authors systematically evaluate the optimal concentrations of MPD and TACA, along with reaction time, to optimize membrane formation. The separation performance of the fabricated membranes is subsequently assessed, revealing high rejection rates for a broad range of organic dyes (most exceeding 99%). Furthermore, molecular-level mechanisms are provided to substantiate the observed separation behavior. Overall, the research strategy is well-conceived, and the methodology is clearly described. The results are thoroughly presented and interpreted, offering strong support for the conclusions. I recommend this article for publication after revisions. Detailed comments are as follows:\n1. In lines 216-219, it is mentioned that “A negative surface charge is observed across a wide pH range for the TACA-MPD membrane (Fig. 3g), attributed to the electron-rich cavity of TACA and its phenolic hydroxyl groups. This negative charge can promote strong electrostatic repulsion against negatively charged organic molecules, such as organic dyes, and enhance their rejection.” Given that the surface charge becomes positive below pH 5, does this imply that the TACA-MPD membrane should be operated at pH ≥ 5 to maintain a negatively charged surface and thus achieve effective electrostatic exclusion of anionic organic dyes?\n2. In Fig. 3h and 3j, the effects of varying MPD and TACA concentrations on membrane performance are examined. To improve clarity and practical applicability, it is recommended that the authors specify the optimal concentration ranges of MPD and TACA identified in this study. Providing these ranges would help readers better understand the design window for achieving favorable membrane performance.\n3. In Fig. 4d, the long-term filtration performance of the membrane is evaluated. Although the permeance and rejection of the mixed solution demonstrate exceptional long-term operational stability, could the authors clarify whether any physicochemical or structural changes occurred in the membrane material after prolonged operation? Specifically, were there any post-filtration characterizations (e.g., SEM, FTIR) conducted to assess potential fouling, degradation, or structural integrity loss?\n4. While the fabrication of TACA–MPD membranes demonstrates excellent dye/salt separation performance, both MPD and TACA (or their precursors) may pose potential risks to human health and the environment due to their chemical toxicity and reactivity. Have the authors considered the environmental and occupational safety aspects associated with the use of these monomers, particularly in terms of residuals, disposal, and potential leaching from the membrane?\n5. In lines 404–406, the conclusion states that “This combination enables energy-efficient diafiltration without the need for high hydraulic pressures commonly required in traditional processes.” However, the manuscript does not present any quantitative or statistical data on energy consumption to support this claim. Could the authors clarify or provide relevant data to substantiate this conclusion?", "reviewer_3": "This article reports development of macrocyclic water treatment membranes via a new diffusion-assisted interfacial polymerization (IP) method. Nanoporous films containing calixarene macrocycles with intrinsic internal cavities exhibited a noteworthy combination of high dye rejection and high permeances for separation of aqueous salt and dye mixtures (Fig 4E). While incorporation of aligned macrocycles into polymer membranes has been previously reported for similar small molecule separations, this work establishes new methods of controlled film formation with enhanced control over membrane microstructure and increased separation performance. The use of a Kevlar hydrogel as a substrate for interfacial polymerization is innovative, and the authors clearly demonstrated how directional polymer growth can be controlled at the organic solvent interface. These materials could have potential for use as high performance sieving membranes for current and emerging water treatment applications.\nExperimental and simulation methods are sufficiently detailed to aid reproducibility.\nThe conclusions that these materials exhibit high separation performance are supported by evidence provided. Conclusions about how macrocycle incorporation and diffusion-assisted IP affect molecular diffusion pathways and how those in turn affect macroscopic transport still require additional supporting evidence.\nRecommended revisions or clarifications:\n1. It would help the reader to clarify the difference between “unidirectional” diffusion for interfacial polymerization (IP) and the conventional method of IP which also primarily occurs via growth in one dimension perpendicular to the membrane’s surface. The authors observed nodular structures on TACA membranes – how do these compare with nodular structures of other IP membranes?\n2. Does TACA remain as nanoparticles during IP or is it fully soluble at the concentrations used? If so, is there a solubility limit?\n3. Can the authors comment on the reversibility of dynamic imine linkages and the impact on mechanical and chemical stability in harsh operating conditions (e.g., acidic or basic solutions, exposure to bleach during washing and regeneration)? Why are these linkages expected to be stable under practical operating conditions based on previous literature or new observations?\n4. The study would benefit from more clear comparisons with control materials to better establish the mechanism of separation improvement. How do the permeances and rejections of membranes formed by “unidirectional diffusion-assisted IP” differ from those formed either (A) from the same monomers by conventional IP using other substrates like PES or (B) from conventional monomers such as TMC+MPD using the diffusion-assisted Kevlar hydrogel substrates (refs 32 and 33)? Can the authors quantify any flux enhancement for macrocycle membranes formed by diffusion-assisted IP compared to similar membranes without macrocycles or using conventional IP? This would provide strong evidence that the resulting structures are distinctly unique.\n5. Additional support is needed for the existence of “high-speed water transport pathway”s through the macrocycle internal cavities which was mostly speculated. Simulations showed network interconnectivity and porosity affected small molecule transport (around the macrocycles), but that is a distinctly different diffusion pathway from transport through the macrocycles. How many of the molecular trajectories in MD passed through the TACA macrocycles and how many went around them? Is this consistent with any observed flux enhancement compared to a control material without internal macrocyclic cavities?\n6. Please add citations for the structures shown in Figure 4E.\n7. Please clarify if “permeances” in Figure 4 subplots are solute or water permeances."}, "author_response": "Response to Reviewers: NCOMMS-25-49804\nReviewer #1:\nIn response to the insightful comments provided by the reviewers, we have revised the\nmanuscript accordingly and provided a point-by-point response to each comment. The\nmajor revisions include:\n1. Elucidated the distinctions between the UDIP process and conventional interfacial\npolymerization, as well as their impact on polymer structure. Analyzed the\nnanofilm growth mechanisms of the UDIP process versus those of free-standing\nfilms.\n2. Determined the feasible concentration range for fabricating TACA membranes via\nsolubility tests (new Figure S1-2 and Table S1), characterized the membranes after\ntest by SEM and FTIR (new Figure S32), and added a monomer leaching test (new\nFigure S33) to confirm the safety and long-term stability of the TACA-MPD\nmembrane.\n3. Provided a comparison of membrane performance fabricated by various methods\nacross different substrates, interfacial polymerization strategies, and reactive\nmonomers (new Figure S34) to validate the superiority of the TACA-MPD\nmembrane fabrication process.\n4. Clarified unclear aspects (such as the research background, rejection mechanisms\nand physical and chemical properties), and highlighted the innovations of this study.\nIn the manuscript titled Macrocycle-assembled membranes for high-salinity organic\nwastewater treatment, Li et al. used macrocyclic molecules as building blocks to prepare\npolymeric membranes that can selectively fractionate organics and salts. The authors\nadopted unidirectional diffusion assisted interfacial polymerization to fabricate\nmacrocycle-assembled, loose-structured polyimine membranes. Also, the utilization of\nwater-rich Kevlar hydrogel could form a stable and undisturbed reaction interface, thereby\nyielding a smooth and moderately crosslinked nanofilm. The novelty of this work is high,\nand the results are very interesting. For example, the TACA-MPD membrane exhibits\nexceptional dye/salt selectivity and structural stability, showing great potential for treating\ncomplex water bodies, such as textile wastewater. Considering the overall high quality of\nthis work, I recommend its acceptance by Nature Communications after some minor\nrevisions. The specific comments are as follows.\nResponse: Thank you for your positive comments and valuable suggestions on this\nmanuscript. The point-by-point responses to the related comments and questions are\nprovided below.\n1. The abstract section is slightly wordy and it is recommended that a more concise and\nemphasized abstract be provided.\nResponse: We sincerely thank the reviewer for careful reading and pointing this out. We\nhave streamlined the content of the abstract and effectively highlighted the key points of\nthis work. Below are the revisions made to the “Abstract” section of original manuscript.\nPage 2, Line 28-29; Line 43-44\n“Membrane processes offer a promising solution by selectively separating organics and\nsalts for water reuse and resource recovery, which are critical for advancing circular water\neconomies.”\n“This work highlights the potential of our macrocycle-assembled membranes for the\ntreatment and reuse of organic-laden saline industrial wastewaters.”\n2. What are the characteristics and advantages of TACA macrocyclic molecules compared\nto typical ones, like cyclodextrins and cucurbiturils? Why are they suited as building blocks\nfor separation membranes?\nResponse: Thank you for your good questions. Classical macrocyclic molecules such as\ncyclodextrins and cucurbiturils have been widely used in the construction of separation\nmembranes. However, because cyclodextrins contain numerous hydroxyl groups with\ncomparable reactivity, they tend to result in disordered packing in films hundreds of\nnanometers thick, hindering the interconnection of cavities and the formation of through-\npores (Adv. Mater. 29, 1606641 (2017); Adv. Mater. 30, 1705933 (2018); Chem. Eng. J.\n492, 152165 (2024)). On the other hand, cucurbiturils exhibit exceptionally strong host-\nguest interactions with monomers, enabling them to act as nano-fillers during interfacial\npolymerization while regulating the local distribution of monomer concentration and\ndiffusion behavior. However, due to compatibility issues, their doping level in polymer\nmatrices is generally low, which limits the full utilization of their structural advantages\n(Nano Lett. 23, 4167-4175 (2023)).\nCompared to traditional cyclodextrins and cucurbiturils, our synthesized TACA shows\nthe following advantages: (i) TACA that features multiple reactive aldehyde groups\nexhibits a moderate reactivity. It can react with diamines through a controlled Schiff base\ncondensation reaction, allowing regulation of the structural compactness of TFC\nmembranes. (ii) Its unique amphiphilic nature and tunable cavities enhance water flux and\ncreate pore sizes suitable for organic/salt separation. (iii) Its hydrophobicity and high\nmolecular weight confine it to the organic phase boundary, while the diamine monomer in\nthe aqueous phase unidirectionally diffuses across the phase boundary.\nWe would like to highlight the advantages of TACA macrocycles in the fabrication of\nloose-structured TFC membranes for dye/salt separation. These advantages have been\nshown in the “Introduction” section. To maintain the coherence, logic, and readability of\nthis section, we did some revisions to this part. Thank you for your understanding.\nPage 2, Line 64-66:\n“The unique 3D stereochemical configurations and diverse chemical functionalities of\nmacrocyclic molecules enable precise control over monomer diffusion kinetics in both bulk\nand interfacial environments.16,17”\nPage 3, Line 73-80:\n“However, the commonly used amide condensation reaction during fabrication often\nproduces an excessively dense crosslinked network with sub-nanoscale pores. This limits\nits ability to separate molecular/ion mixtures and hinders its effectiveness in treating saline\norganic-rich waters. In contrast, calixarenes maintain the structural characteristics of\ntraditional macrocyclic molecules while offering tunable configurations and easy chemical\nmodification. This provides a foundation for precise control over membrane architecture.\nBy altering chemical bonding type, polymer membranes with adjustable network structures\nare fabricated.”\n3. Is the ability to self-assemble at the interface a property common to macrocyclic\nmolecules? Does this self-assembly occur in the UDIP process? Why are TFC membranes\nthicker than free-standing films?\nResponse: We appreciate this important question regarding the effect of TACA assembly\nduring the UDIP process. Interfacial self-assembly results from the combined effects of\nstructural design (e.g., amphiphilicity and functional groups) and environmental conditions\n(e.g., interface type and medium) (Physical Chemistry Chemical Physics 15, 125-128\n(2013); Matter 5, 3883-3900 (2022)). Whether macrocyclic molecules can self-assemble\nat interfaces depends on their ability to meet two conditions: (i) interface affinity, where\nthe molecule must be capable of adsorption at the interface (e.g., liquid-gas, liquid-liquid,\nliquid-solid), typically requiring amphiphilic properties; and (ii) intermolecular\ninteractions, where sufficiently strong forces (e.g., hydrogen bonding, hydrophobic\ninteractions, electrostatic forces, π-π stacking) drive ordered assembly rather than random\ndispersion. Therefore, self-assembly at interfaces is not an inherent property of macrocyclic\nmolecules (Organic Chemistry Frontiers 6, 1027-1031 (2019); Coord. Chem. Rev. 337,\n145-177 (2017)).\nFor instance, although cyclodextrin has a hydrophobic cavity and a hydrophilic outer\nrim, its amphiphilic nature is weak due to the strong hydrophilicity of the hydroxyl groups,\nwhich limits its ability to self-assemble at interfaces. However, by regulating the interfacial\nenvironment and incorporating guest molecules, the self-assembly capability of\ncyclodextrins at interfaces can be enhanced (Angew. Chem. Int. Ed. 63, e202312187 (2024);\nJ. Membr. Sci. 652, 120466 (2022)).\nThe self-assembly also occurs in the UDIP process. TACA possesses hydrophobic\ncavities and hydrophilic outer edges, exhibiting strong hydrophobicity that enables it to\nadsorb at the phase interface. Consequently, it can self-assemble at the phase interface.\nHowever, the presence of the Kevlar substrate effectively suppresses this self-assembly\nbehavior to some extent, thereby significantly enhancing the film thickness and density.\nDuring the UDIP process, using Kevlar hydrogel as a porous support would induce\nelectrostatic interactions and hydrogen bonding with TACA molecules. This strong\ninteraction between the Kevlar and TACA impedes its self-assembly, resulting in the lower\ncompactness of the assembled TACA film compared to the free water-DCM system. The\nresultant loose film structure allows sustained diamine supply, promoting continuous\npolymerization of TACA at the interface and ultimately forming a thicker film. To make\nthe effect of TACA-assembled film clearer during the UDIP process, we made the\nfollowing major revisions in the main text.\nPage 5, Line 170-178:\n“Based on its strong hydrophobicity and stable intermolecular hydrogen bonding\ninteractions, TACA preferentially adsorbs and self-assembles into a thin film at the oil-\nwater interface formed when an aqueous phase is added. This assembly behavior aligns\nwith established principles of interfacial self-organization, where sufficiently strong\ninteractions such as hydrogen bonding, hydrophobic effects, electrostatic forces, or π–π\nstacking enable film formation39,40. During the growth of the TACA-MPD nanofilm, a\nTACA-rich layer forms initially. This interfacial layer serves a dual function in the\nsubsequent interfacial polymerization: (i) it forms an effective physical barrier that restricts\ndiamine diffusion and (ii) it enables confined growth of the polyimine nanofilm with\nnanoscale increments in thickness41.”\nPage 6, Line 204-206:\n“The mechanism of film thickness enhancement during the UDIP process closely relates\nto the Kevlar hydrogel, which mitigates the TACA self-assembly by establishing\nelectrostatic and hydrogen-bonding interactions with the TACA molecules.”\nPage 6-7, Line 206-209:\n“This results in a less compact TACA-assembled film structure compared to that formed at\na free water- interface. This loose structure sustains diamine transport, which in turn\nfacilitates the continuous polymerization with TACA at the interface, ultimately leading to\nthicker film formation.”\n4. XPS confirms that the oxygen-rich functional groups of TACA increase the oxygen\ncontent on the membrane surface, which is proposed to enhance the membrane-water\naffinity. However, the water contact angles indicate surface hydrophobicity. This seems to\npresent two contradictory results. Please explain how a hydrophobic surface can exhibit\nhigh hydrophilicity.\nResponse: Thank you for your valuable question. XPS is employed to analyze the\nelemental composition and concentration, chemical state, and molecular structure of\nmembrane surfaces, which is capable of detecting elemental information at depths of 10\nnm beneath the surface. The water contact angle is the angle formed between the membrane\nsurface and a water droplet upon contact, which is determined solely by the top 1–2 atomic\nlayers of the membrane surface. Given that TACA is rich in oxygen-containing functional\ngroups such as hydroxyl and aldehyde groups, XPS data indicate that TACA-MPD-TFC\nexhibits higher oxygen content than the Kevlar substrate. Furthermore, XPS has a finite\npenetration depth, analyzing the elemental composition and concentration on the TFC\nmembrane surface and near-surface regions. This indicates the presence of abundant\noxygen-containing functional groups within nanochannels throughout the TFC membrane\nstructure. These internal polar hydrophilic functional groups can enhance interactions with\nwater molecules via hydrogen bonding, thus significantly improving water adsorption and\ntransport properties of the membrane (Angew. Chem. Int. Ed. 64, e202502204 (2025);\nEnvironmental Science & Technology 58, 16204-16214 (2024) ).\nWhen the hydrophobic benzene ring of TACA is oriented toward the surface, it\nincreases the hydrophobicity of the TFC membrane. To comprehensively understand the\ncomplex interaction mechanisms between the membrane structure and water molecules,\nthe wettability of the membrane and its variations need to be analyzed by integrating the\nwater contact angle data of the outermost layer with the near-surface elemental\ncomposition revealed by XPS characterization (Environmental Science & Technology 59,\n902-912 (2025); Adv. Mater. 37, 2501092 (2025); Desalination 549, 116365 (2023)).\nPage 7, Line 226-229:\n“While the membrane surface maintains hydrophobic, the presence of internal polar\nhydrophilic functional groups (as evidenced by XPS results) augment interactions with\nwater molecules through hydrogen bonding. This in turn facilitates the enhanced water\ntransport across the TACA-assembled layer.”\n5. The pore size of the TFC membrane is 3.4 nm. Please explain how such a large pore size\ncan achieve high rejection of dye molecules.\nResponse: Thank you for your insightful comment. The rejection of dye molecules by the\nTFC membrane is primarily attributed to the synergistic effects of size sieving and the\nDonnan effect (Chem. Eng. J. 467, 143456 (2023)). Experimental data indicate that the\nTFC membrane exhibits excellent rejection of various dyes. Although the TFC membrane\nhas a relatively large MWCO of 11480 Da and a pore size of 3.4 nm, the negative charges\non its surface and the presence of TACA within the polymer structure, which has electron-\nrich cavities, enable effective repulsion of anionic dyes through electrostatic interactions.\nMore importantly, their hydrophobic interactions lead to the aggregation of dye molecules\ninto larger clusters, reducing their diffusivity in aqueous solutions (Nature\nCommunications 16, 3671 (2025); J. Membr. Sci. 685, 121908 (2023)). These clusters are\nretained by the membrane pores through enhanced size exclusion. Both experimental\nresults and molecular dynamics simulations confirm the efficient rejection of various dye\nmolecules by the TFC membrane. We have rewritten this part to make our description and\nexplanation much clearer.\nPage 10, Line 319-327:\n“Dye molecules exhibit a strong tendency to agglomerate into larger, less diffusive clusters\nin aqueous media, a phenomenon resulting from hydrophobic and π−π stacking interactions\nwithin their aromatic moieties52,53. These inherent characteristics make loose-structured\nmembranes (e.g., TACA-MPD) particularly well-suited for dye purification. This is\nbecause dense-structured membranes inevitably reject both dyes and salts and lead to an\nundesirable elevation of osmotic pressure that compromises separation efficiency.\nAdditionally, the TACA-MPD nanofilm features electron-rich cavities and a negatively\ncharged surface, which establishes significant electrostatic repulsion against anionic dyes,\nsubstantially contributing to the observed high rejections41.”\n6. Please provide more details on the relationship between partition coefficients,\nhydrophilicity, and monomer diffusion or reaction regions.\nResponse: Thank you for your valuable comment. The partition coefficient refers to the\nratio of the equilibrium concentrations of a compound in the organic and aqueous phases,\ndenoted as logP. It reflects the compound's relative affinity for the organic and aqueous\nphases and is widely used to describe its lipophilicity or hydrophobicity. A higher logP\nvalue indicates a stronger affinity for the organic phase (oil), whereas a lower value\nsuggests a stronger affinity for the aqueous phase (water) (Sun, C. (2018). Partitioning and\nPartition Coefficients.; ACS Applied Materials & Interfaces 17, 47659-47671 (2025); Anal.\nChem. 91, 10371-10375 (2019)).\nThe logP of TACA between dichloromethane and water is 3.33, indicating strong\nlipophilicity and poor water solubility. In contrast, MPD has a logP value of -0.45,\ndemonstrating good hydrophilicity. According to the calculation formula of logP, MPD\nalso exhibits certain solubility in the oil phase. As a result, MPD can diffuse from the\naqueous phase to the oil-water interface and into the oil phase, while TACA is directionally\ndistributed at the oil-water interface, where it reacts with MPD through a Schiff base\ncondensation reaction. During the interfacial polymerization between MPD and TACA,\nthe reaction is confined to the oil-water interface. Furthermore, during the diffusion process\nof MPD, the abundant hydrogen bonds in the Kevlar hydrogel effectively regulate its\ndiffusion rate, thereby enhancing the controllability of the interfacial polymerization. In\nresponse to the reviewer’s suggestion, we have incorporated additional details as presented\nbelow.\nPage 8, Line 251-254:\n“The partition coefficient (logP) is a measure of the relative distribution of a compound\nbetween an organic phase and an aqueous phase. A higher logP value corresponds to an\nincreased lipophilicity and preferential partitioning into the organic medium, while a lower\nvalue denotes enhanced aqueous solubility and a dominant affinity for the aqueous phase.”\nReviewer #2\nIn response to the insightful comments provided by the reviewers, we have revised the\nmanuscript accordingly and provided a point-by-point response to each comment. The\nmajor revisions include:\n1. Elucidated the distinctions between the UDIP process and conventional interfacial\npolymerization, as well as their impact on polymer structure. Analyzed the\nnanofilm growth mechanisms of the UDIP process versus those of free-standing\nfilms.\n2. Determined the feasible concentration range for fabricating TACA membranes via\nsolubility tests (new Figure S1-2 and Table S1), characterized the membranes after\ntest by SEM and FTIR (new Figure S32), and added a monomer leaching test (new\nFigure S33) to confirm the safety and long-term stability of the TACA-MPD\nmembrane.\n3. Provided a comparison of membrane performance fabricated by various methods\nacross different substrates, interfacial polymerization strategies, and reactive\nmonomers (new Figure S34) to validate the superiority of the TACA-MPD\nmembrane fabrication process.\n4. Clarified unclear aspects (such as the research background, rejection mechanisms\nand physical and chemical properties), and highlighted the innovations of this study.\nThis study presents the fabrication of loosely structured macrocycle-assembled membranes\nas a promising approach for effective dye/salt separation in high-salinity organic\nwastewater treatment. The authors systematically evaluate the optimal concentrations of\nMPD and TACA, along with reaction time, to optimize membrane formation. The\nseparation performance of the fabricated membranes is subsequently assessed, revealing\nhigh rejection rates for a broad range of organic dyes (most exceeding 99%). Furthermore,\nmolecular-level mechanisms are provided to substantiate the observed separation behavior.\nOverall, the research strategy is well-conceived, and the methodology is clearly described.\nThe results are thoroughly presented and interpreted, offering strong support for the\nconclusions. I recommend this article for publication after revisions. Detailed comments\nare as follows:\nResponse: We would like to express our gratitude for the Reviewer’s appreciation of our\nresults as well as the critical reading and helpful suggestions. The point-by-point responses\nto the comments and questions are provided below.\n1. In lines 216-219, it is mentioned that “A negative surface charge is observed across a\nwide pH range for the TACA-MPD membrane (Fig. 3g), attributed to the electron-rich\ncavity of TACA and its phenolic hydroxyl groups. This negative charge can promote strong\nelectrostatic repulsion against negatively charged organic molecules, such as organic dyes,\nand enhance their rejection.” Given that the surface charge becomes positive below pH 5,\ndoes this imply that the TACA-MPD membrane should be operated at pH ≥ 5 to maintain\na negatively charged surface and thus achieve effective electrostatic exclusion of anionic\norganic dyes?\nResponse: Thanks for your valuable comments. As noted by the reviewers, when the pH\nfalls below 5, the membrane surface becomes positively charged, which typically\ndiminishes electrostatic interactions and may partially reduce dye rejection. However, dye\nrejection depends not only on membrane surface charge but also on pore size and the\npolymer network structure and functional groups. The synergy between these pathways\nenables TACA-MPD membranes to achieve highly efficient rejection of dye molecules,\neven without charge-based exclusion. (i) Dye molecules aggregate through hydrophobic\ninteractions between their benzene ring structures, forming larger dye clusters with reduced\ndiffusivity. As a result of this aggregation, TACA-MPD membrane can achieve high dye\nrejection rates. (ii) Furthermore, the densely crosslinked and interwoven network\nstrengthens the size exclusion effect. (ⅲ) Due to its electron-rich cavities, TACA strongly\nrepels dye molecules electrostatically within the polymer network, thereby retaining them\non the membrane surface and enhancing dye rejection. As a result, even membranes with\na weak positive charge can achieve high rejection of anionic dyes (J. Membr. Sci. 584, 324-\n332 (2019); Journal of Water Process Engineering 68, 106488 (2024)). Therefore, we\nconclude that the TACA-MPD membranes maintain effective dye separation performance\neven at pH values below 5.\nPage 7, Line 237-242:\n“Moreover, the synergistic effect of the multi-pathway dye rejection mechanism in the\nTACA-MPD membrane enables it to achieve highly efficient rejection of dye molecules,\neven close to their isoelectric point: (i) dye molecules aggregate through hydrophobic\ninteractions, reducing their diffusivity; (ii) enhanced size exclusion effects from the densely\ncross-linked network; and (iii) strong electrostatic repulsion provided by the electron-rich\ncavities in TACA.”\n2. In Fig. 3h and 3j, the effects of varying MPD and TACA concentrations on membrane\nperformance are examined. To improve clarity and practical applicability, it is\nrecommended that the authors specify the optimal concentration ranges of MPD and TACA\nidentified in this study. Providing these ranges would help readers better understand the\ndesign window for achieving favorable membrane performance.\nResponse: We sincerely thank the reviewer for the constructive feedback. During the\nexperiments, the concentrations of TACA used were 0.4, 0.5, 0.6, and 0.7 mM, while the\nconcentrations of MPD were 0.25, 0.50, 0.75, and 1.0 mM. The reaction times were set at\n1, 3, 5, and 7 hours. As the reaction time or monomer concentration increased, both the\ndegree of crosslinking and the density of the membrane were enhanced. Although this\neffectively improved the dye rejection, it also reduced water permeance. Taking all factors\ninto consideration, the optimal conditions were determined to be a TACA concentration of\n0.5 mM, an MPD concentration of 0.5 mM, and a reaction time of 3 hours. The membrane\nprepared under these conditions was designated TACA -MPD -3. We have already made\n0.5 0.5\nthe changes in our resubmitted manuscript.\nPage 15, Line 491-496:\n“The prepared membranes were designated as TACA MPD -Z, where X represents the\nX Y\nTACA concentration (0.4, 0.5, 0.6, and 0.7 mM), Y represents the MPD concentration (0.25,\n0.50, 0.75, and 1.0 mM), and Z represents the reaction time (1, 3, 5, and 7 h). By balancing\ndye rejection and water permeance, we identified the optimal membrane, which was\nfabricated using 0.5 mM TACA and 0.5 mM MPD under a 3 h reaction condition (referred\nto as TACA -MPD -3), and used it for subsequent dye/salt separation tests.”\n0.5 0.5\n3. In Fig. 4d, the long-term filtration performance of the membrane is evaluated. Although\nthe permeance and rejection of the mixed solution demonstrate exceptional long-term\noperational stability, could the authors clarify whether any physicochemical or structural\nchanges occurred in the membrane material after prolonged operation? Specifically, were\nthere any post-filtration characterizations (e.g., SEM, FTIR) conducted to assess potential\nfouling, degradation, or structural integrity loss?\nResponse: We appreciate your constructive suggestions. In response to the reviewers'\nsuggestions, we have included SEM and FTIR analyses of the TACA-MPD membrane\nbefore and after long-term operation, confirming its excellent operational stability and\nantifouling performance.\nPage 11, Line 355-360:\n“SEM and FTIR characterizations further exhibit the superior stability of the TACA-MPD\nmembranes. The SEM results (Supplementary Fig. 32a-b) reveal minimal dye\naccumulation on the surface following prolonged testing, directly indicating remarkable\nantifouling capabilities. Moreover, the near-perfect overlap between the FTIR spectra\nobtained before and after operation (Supplementary Fig. 32c) serves as compelling\nevidence for their structural integrity and resilience under prolonged operational\nconditions.”\nSupplementary Fig. 32 SEM images of the TACA-MPD membrane surface (a) before and\n(b) after the performance test (mild rinsing with ethanol was performed for SEM sample\npreparation, which is not expected to remove irreversible fouling). (c) FTIR spectra of the\nTACA-MPD membrane before and after the test.\n4. While the fabrication of TACA–MPD membranes demonstrates excellent dye/salt\nseparation performance, both MPD and TACA (or their precursors) may pose potential\nrisks to human health and the environment due to their chemical toxicity and reactivity.\nHave the authors considered the environmental and occupational safety aspects associated\nwith the use of these monomers, particularly in terms of residuals, disposal, and potential\nleaching from the membrane?\nResponse: Thank you for your valuable advice. As rightly noted by the reviewers, the\nenvironmental and occupational safety of monomer materials is a critical issue, as it\ninvolves not only potential environmental risks but also has significant implications for\nhuman health. Accordingly, we conducted additional experiments to investigate whether\nthe TACA-MPD membrane poses a risk of monomer leakage. The specific experimental\ndetails and data are presented below.\nPage 11, Line 364-369:\n“UV-Vis spectral analysis (Supplementary Fig. 33) was conducted to evaluate potential\nmonomer leaching from the TACA-MPD membranes, which may lead to safety concerns.\nNo detectable leaching of either MPD or TACA was observed under static (prolonged\nimmersion) or dynamic (filtration) conditions. This finding strongly confirms the\nexceptional stability of the polyimine membrane, supporting both the chemical robustness\nand environmental safety of the membrane.”\nSupplementary Fig. 33 (a) UV-Vis spectrum of different MPD concentration in water. (b)\nMPD concentration vs. absorbance standard curve at 289 nm. UV-Vis absorbance curves\nat different testing times (c) and immersion times (d).\nPage 36 in Supplementary Information\n“The stability of the TACA-MPD membrane was rigorously verified by monitoring\nmonomer leaching (MPD maximum absorption at 289 nm and TACA maximum absorption\nat 237 nm; Supplementary Figs. S33a-b and S21) using UV-Vis spectroscopy. The stability\nwas assessed under a filtration test. Prior to testing, the membrane reached steady state\nafter compaction with deionized water (2 bar, 30 min). Under continuous operation (1 bar,\ndeionized water), hourly collection of the permeate demonstrated no evidence of MPD or\nTACA monomer leaching over 12 hours (Supplementary Fig. 33c). To confirm long-term\nsafety, the membrane was also statically stored in deionized water, with UV-Vis analysis\n(Supplementary Fig. 33d) showing no evidence of leaching for the duration of the 7-day\nmonitoring period.”\n5. In lines 404–406, the conclusion states that “This combination enables energy-efficient\ndiafiltration without the need for high hydraulic pressures commonly required in\ntraditional processes.” However, the manuscript does not present any quantitative or\nstatistical data on energy consumption to support this claim. Could the authors clarify or\nprovide relevant data to substantiate this conclusion?\nResponse: Thank you for your helpful and valuable suggestions. In the experimental\nsection, we conducted a diafiltration process to achieve dye enrichment and concentration,\nrecording the required water consumption and processing time. Based on the 15 W\noperating power and the average of permeance per batch, calculating the energy\nconsumption during the filtration process shows that the TACA-MPD membrane requires\n131 kWh m-3, much lower than the 228 kWh m-3 reported for the NF270 membrane in the\nliterature (Environ. Sci. Technol. 2022, 56, 17998−1800). By comparing our data with\nthose reported in the literature, we demonstrated the advantage of the TACA-MPD\nmembrane in improving process efficiency.\nPage 10-11, Line 346-351:\n“To reduce the NaCl concentration in the feed to below 0.5 g/L, the total water consumption\nusing the TACA-MPD membrane was 1750 mL, substantially lower than that required by\ncommercial nanofiltration (NF) membranes. Furthermore, the energy consumption of the\nTACA-MPD diafiltration process was only 131 kWh m-3, substantially lower than that of\nthe NF 270 membrane (228 kWh m-3), demonstrating significant advantage of TACA-MPD\nmembrane in enhancing process efficiency (Supplementary Table 4)52”\nPage 14, Line 456-462:\n“The macrocycle-assembled membranes developed in this study offer a distinct advantage\nover conventional polyamide nanofiltration membranes by coupling high water permeance\nwith exceptional organic/salt selectivity. This combination facilitates energy-efficient\ndiafiltration, eliminating the need for the high hydraulic pressures commonly required in\ntraditional separation processes. Their capacity for the selective recovery of organic\ncompounds and salts makes them particularly well-suited for treating high-salinity organic\nwastewaters, providing a sustainable, cost-effective solution that strongly supports\nresource recovery and the circular economy.”\nPage 50 in Supplementary Information\nTable S4. Comparison of energy consumption between TACA MPD -3 and NF270\n0.5 0.5\nmembranes.\nPump power Operation time Water consumption Energy\nMembranes Ref\n/W /min /mL /kWh m-3\nTACA-MPD 15 1050 1750 131 This work\nNF270 15 2348 2500 228 4\nReviewer #3\nIn response to the insightful comments provided by the reviewers, we have revised the\nmanuscript accordingly and provided a point-by-point response to each comment. The\nmajor revisions include:\n1. Elucidated the distinctions between the UDIP process and conventional interfacial\npolymerization, as well as their impact on polymer structure. Analyzed the\nnanofilm growth mechanisms of the UDIP process versus those of free-standing\nfilms.\n2. Determined the feasible concentration range for fabricating TACA membranes via\nsolubility tests (new Figure S1-2 and Table S1), characterized the membranes after\ntest by SEM and FTIR (new Figure S32), and added a monomer leaching test (new\nFigure S33) to confirm the safety and long-term stability of the TACA-MPD\nmembrane.\n3. Provided a comparison of membrane performance fabricated by various methods\nacross different substrates, interfacial polymerization strategies, and reactive\nmonomers (new Figure S34) to validate the superiority of the TACA-MPD\nmembrane fabrication process.\n4. Clarified unclear aspects (such as the research background, rejection mechanisms\nand physical and chemical properties), and highlighted the innovations of this study.\nThis article reports development of macrocyclic water treatment membranes via a new\ndiffusion-assisted interfacial polymerization (IP) method. Nanoporous films containing\ncalixarene macrocycles with intrinsic internal cavities exhibited a noteworthy combination\nof high dye rejection and high permeances for separation of aqueous salt and dye mixtures\n(Fig 4E). While incorporation of aligned macrocycles into polymer membranes has been\npreviously reported for similar small molecule separations, this work establishes new\nmethods of controlled film formation with enhanced control over membrane microstructure\nand increased separation performance. The use of a Kevlar hydrogel as a substrate for\ninterfacial polymerization is innovative, and the authors clearly demonstrated how\ndirectional polymer growth can be controlled at the organic solvent interface. These\nmaterials could have potential for use as high performance sieving membranes for current\nand emerging water treatment applications. Experimental and simulation methods are\nsufficiently detailed to aid reproducibility. The conclusions that these materials exhibit high\nseparation performance are supported by evidence provided. Conclusions about how\nmacrocycle incorporation and diffusion-assisted IP affect molecular diffusion pathways\nand how those in turn affect macroscopic transport still require additional supporting\nevidence. Recommended revisions or clarifications:\nResponse: Thanks for your constructive suggestions on this manuscript. We provide\nadditional experimental evidence and compensate for many shortcomings. The point-by-\npoint responses to all comments raised are provided below.\nComments:\n1. It would help the reader to clarify the difference between “unidirectional” diffusion for\ninterfacial polymerization (IP) and the conventional method of IP which also primarily\noccurs via growth in one dimension perpendicular to the membrane’s surface. The authors\nobserved nodular structures on TACA membranes – how do these compare with nodular\nstructures of other IP membranes?\nResponse: Thank you for your insightful and constructive suggestions. The differences\nbetween the two methods and their unique features are outlined below.\nTraditional interfacial polymerization is the primary method for fabricating polyamide\nTFC membranes. In this process: (i) the support membrane first adsorbs the aqueous phase\nand retains a certain amount of amine monomer. It then directly contacts the organic phase\nto form a liquid-liquid interface. (ii) Highly reactive monomers rapidly diffuse to the\ninterface and undergo random, irreversible cross-linking reactions. Once the polymer film\nbegins to form, it restricts further diffusion of monomers, resulting in a self-limiting effect\nthat inhibits additional growth of the polymer film (Chem. Commun. 59, 13258-13271\n(2023); Angew. Chem. Int. Ed. 59, 21840-21856 (2020)). This typically results in the\nformation of a relatively thick and dense selective layer within a very short time (Chem.\nSoc. Rev. 50, 6290-6307 (2021)).\nUnidirectional diffusion assisted interfacial polymerization uses a diffusion cell\ndevice where a base membrane is secured between two chambers, each containing aqueous\nand organic phase monomer solutions. This method relies on the directional diffusion of\nmonomers to facilitate interfacial polymerization (J. Membr. Sci. 663, 121043 (2022); J.\nMembr. Sci. 604, 118090 (2020)). In this process: (i) The porous support prevents direct\ncontact between the two phases, slows the monomer diffusion rate, and thereby makes the\nreaction process more controllable. (ii) Compared to traditional in-situ interfacial\npolymerization, the unidirectional diffusion-assisted mode ensures a more sustained and\nsufficient monomer supply for film formation. (iii) Longer reaction times promote self-\nhealing of the membrane structure, significantly minimizing defect formation and\nfacilitating the formation of defect-free thin films.\nThe nodular morphologies of TACA-MPD membranes differ from those of traditional\nIP membranes in both their formation and structure. In traditional interfacial\npolymerization, the highly exothermic reaction between TMC and MPD significantly\nraises the local temperature at the interface. This temperature rise causes convective flow\nwithin the organic phase, promoting the formation of nodular features on the membrane\nsurface. Additionally, the localized temperature increase, along with the generation of\nhydrochloric acid as a byproduct of the interfacial polymerization reaction, causes\ndissolved gas molecules (such as CO , O , and N ) in the aqueous phase to nucleate\n2 2 2\nmicrobubbles. These bubbles become encapsulated and trapped by the nascent polyamide\nlayer, ultimately resulting in the formation of a ridge-and-valley structure (Environmental\nScience & Technology Letters 5, 123-130 (2018); Nature Communications 13, 7954 (2022);\nSep. Purif. Technol. 379, 134974 (2025)).\nDuring unidirectional diffusion assisted interfacial polymerization, TACA and MPD\nreact to form an imine-linked polymer via a Schiff base reaction, which promotes the\nnucleation and growth of nodular structures. Subsequently, these polymer nodules\naggregate and fuse onto the Kevlar substrate, forming a continuous nanofilm through\ndynamic breakage and reorganization of imine bonds. As the reaction progresses, the\nnodules grow and accumulate, ultimately producing a smooth-surfaced TACA-MPD\nmembrane.\nPage 4, Line 113-117:\n“In contrast to traditional interfacial polymerization, the UDIP process uses a Kevlar\nhydrogel to prevent direct contact between the two-phase solutions, thereby achieving\nsuperior control over the reaction. Furthermore, UDIP provides a sustained and stable\nmonomer supply for film formation, which promotes structural self-healing and leads to\nthe fabrication of defect-free thin films.”\nPage 5, Line 159-162:\n“While nodular structures in traditional interfacial polymerization are driven by convective\nflow from exothermic reactions, the morphology of the TACA-MPD membrane is\ncontrolled by the dynamic assembly and fusion of imine-bonded polymer particles.”\n2. Does TACA remain as nanoparticles during IP or is it fully soluble at the concentrations\nused? If so, is there a solubility limit?\nResponse: Thank you for your valuable question. TACA can be dissolved in a DCM\nsolution, but it has a definite solubility limit. To ensure complete dissolution within the\nexperimental concentration range, we conducted additional experiments to verify this limit.\nThe specific details and results are as follows.\nPage 4-5, Line 136-139:\n“The introduction of formyl group onto the aromatic rings and good solubility in the DCM\nsolution are both essential for subsequent membrane fabrication via Schiff base reaction\n(reaction between aldehyde and amine; Supplementary Fig. 1-2 and Supplementary Table\n1)34.”\nPage 8 in Supplementary Information\nSupplementary Fig. 1 The DCM solutions containing different concentrations of TACA.\n(a)\n0.4 mM TACA. (b) 0.5 mM TACA. (c) 0.6 mM TACA. (d) 0.7 mM TACA.\n“As shown in Supplementary Fig. 1, at all concentrations used in the experiment, the DCM\nsolution of TACA remained clear and transparent, with no Tyndall effect observed. These\nobservations indicate that TACA is completely soluble within the concentration range of\n0.4–0.7 mM.”\nPage 9 in Supplementary Information\nSupplementary Fig. 2 Solubility of TACA in DCM solution. (a) 0.025 w/v% TACA. (b)\n0.05 w/v% TACA. (c) 0.075 w/v% TACA. (d) 0.100 w/v% TACA. (e) 0.125 w/v% TACA.\n(e) 0.150 w/v% TACA.\n“At room temperature, the solubility of TACA was investigated by gradually adding it to\n20 mL of DCM. As shown in Supplementary Fig. 2 and Table S1, the TACA/DCM solution\ntransitioned from clear and transparent to turbid as the mass of TACA increased. When the\nconcentration of TACA was below 0.100 w/v%, it was completely soluble in DCM,\nresulting in a clear solution without a Tyndall effect. When the concentration exceeded\n0.125 w/v%, a distinct Tyndall effect was observed, indicating the formation of TACA\nnanoparticles in the solution. Table R1 further confirms the good solubility of TACA within\nthe experimental range.”\nPage 47 in Supplementary Information\nTable S1. Solubility of TACA in DCM solution.\nSample TACA mass / mg DCM volume / mL w/v% mM\na 5 20 0.025 0.47\nb 10 20 0.050 0.93\nc 15 20 0.075 1.40\nd 20 20 0.100 1.86\ne 25 20 0.125 2.32\nf 30 20 0.150 2.80\n3. Can the authors comment on the reversibility of dynamic imine linkages and the impact\non mechanical and chemical stability in harsh operating conditions (e.g., acidic or basic\nsolutions, exposure to bleach during washing and regeneration)? Why are these linkages\nexpected to be stable under practical operating conditions based on previous literature or\nnew observations?\nResponse: Thanks for your constructive suggestions on this manuscript. As a dynamic\ncovalent bond, the imine bond strikes a balance between reversibility and stability. While\nhigher reversibility facilitates defect repair and structural rearrangement in the network,\ndriving it towards a thermodynamically stable state, excessive reversibility can\ncompromise the stability of the material (Chem. Soc. Rev. 49, 8469-8500 (2020); Advanced\nScience 6, 1801410 (2019); ACS Nano 19, 29934-29960 (2025)). Because of the unique\nreversibility and structural stability of imine bonds, these bonds exhibit promising\napplications in membrane separation.\nNumerous studies demonstrate that imine-based membrane materials possess\nexcellent mechanical and chemical stability under harsh operating conditions. Wang et al.\nprepared imine COF membranes via Schiff base reaction of tetrakis(4-formylphenyl)-\nmethane with 3,3'-Dihydroxybenzidine (Nano Lett. 21, 8355-8362 (2021)). Due to the\nreversibility of the Schiff base reaction, COF microcrystals tend to coalesce with\nneighboring crystals, forming larger crystals through the breaking and rebinding of imine\nlinkages. The simultaneous deposition of crystals and microcrystals onto the substrate\nfacilitates horizontal growth of the COF, leading to continuous film formation. The COF\nfilms exhibit outstanding flexibility and exceptional tolerance to a wide range of extreme\nconditions (e.g., hot organic solvents). Wen et al. fabricated cross-linked crown-ether-based\npolyimine nanofilms through interfacial polymerization of p-phenylenediamine and\n4,4′,5,5′-terabenzaldehyde dibenzo-14-crown-4 (Angew. Chem. Int. Ed. 62, e202300167\n(2023)). The incorporation of flexible crown ether units into the rigid aryl conjugated\nskeleton chains forms a “flexible-in-rigid” structural framework within the polyimine\nmembrane. The membrane exhibits both robustness and flexibility, demonstrating excellent\nmechanical properties (Young's modulus ca. 8.2 GPa). Zachary P. Smith and colleagues\nused triaminotriptycene and tetraformylspirobifluorene as building blocks to fabricate\nmicroporous polyimine TFC membranes via interfacial polymerization (Science 388, 839-\n844 (2025)). By incorporating molecular units with rigid and contorted structures, the\nmicroporosity and hydrophobicity of the membrane were significantly enhanced. The\npolyimine membrane achieved exceptionally high swelling and plasticization resistance,\nremarkable operational stability, and great potential for crude oil fractionation processes.\nThe studies cited above collectively demonstrate that polyimine membranes maintain\nexcellent mechanical and chemical stability even under harsh conditions.\nAs discussed above, dynamic imine bonds can maintain good stability even in harsh\noperating environments. Therefore, it follows that the TAC-MPD membrane is also\nexpected to exhibit good stability. The Schiff base reaction between TACA and MPD\ngenerates imine polymer nodules, which assemble into a continuous nanofilm through the\nbreaking and reformation of imine bonds. The continuous accumulation of particles on the\nfilm promotes vertical growth, thereby increasing its thickness. First, the interlocking\nchemical bonds within the polymer network are more stable than those in crystalline imine\nstructure. Second, the rigid three-dimensional structure of TACA enhances the\nmicroporosity and structural stability of the polyimine film. Consequently, we propose that\nthe imine-linked TACA-MPD film exhibits favorable structural and chemical stability\nunder practical operating conditions.\nPage 11, Line 360-364:\n“The synergy between dynamic imine bonds and the UDIP self-healing process enables the\nTACA-MPD membrane to reach a state of thermodynamic stability. Furthermore, the rigid\nthree-dimensional structure of TACA enhances its microporosity and structural stability,\nwhich holds considerable potential for practical application.”\n4. The study would benefit from more clear comparisons with control materials to better\nestablish the mechanism of separation improvement. How do the permeances and\nrejections of membranes formed by “unidirectional diffusion-assisted IP” differ from those\nformed either (A) from the same monomers by conventional IP using other substrates like\nPES or (B) from conventional monomers such as TMC+MPD using the diffusion-assisted\nKevlar hydrogel substrates (refs 32 and 33)? Can the authors quantify any flux\nenhancement for macrocycle membranes formed by diffusion-assisted IP compared to\nsimilar membranes without macrocycles or using conventional IP? This would provide\nstrong evidence that the resulting structures are distinctly unique.\nResponse: We appreciate the reviewer’s careful assessment of our manuscript. In response\nto the reviewers' comments, we conducted additional experiments to better illustrate the\nadvantages of TACA macrocyclic molecules as building blocks for TFC membranes in\nenhancing microporous interconnectivity and the distinctive features of the UDIP strategy.\nThe results are presented below.\nPage 11, Line 373-378\n“By preparing TFC membranes using either conventional monomers or in situ IP strategies,\nwe further demonstrate the potential of TACA macrocyclic molecules for constructing\npolyimine membranes. The resulting performance demonstrates the superior advantages of\nboth the UDIP approach and TACA monomers for fabricating high-flux and high-selective\npolyimine-TFC membranes (see detailed analyses in Supplementary information and\nSupplementary Fig. 34).”\nIn addition, we added more detailed analyses and discussions in the Supplementary\ninformation.\nPage 37-38 in Supplementary Information\nSupplementary Fig. 34 (a) Performance comparison of TFC membranes prepared using\nTACA and conventional monomers. All membranes were fabricated via the UDIP strategy\non a Kevlar hydrogel substrate, with the same monomer concentrations (MPD: 0.5 mM;\nTACA: 0.5 mM; TMC: 0.5 mM) and a reaction time of 3 hours. (b) Performance\ncomparison of TFC membranes fabricated using different strategies. The membranes were\nprepared using UDIP/Kevlar, conventional interfacial polymerization/Kevlar (CIP/Kevlar),\nand CIP/PAN, with the same monomer concentrations (MPD: 0.5 mM; TACA: 0.5 mM)\nand a reaction time of 3 hours.\nAs shown in Supplementary Fig. 34a, the TFC membrane prepared from TACA and\nMPD features loose and interconnected pore channels, which facilitate excellent water\npermeance and high dyes rejection. In contrast, the conventional monomers TMC and\nMPD are planar and highly reactive, leading to the formation of a dense and relatively thick\nselective layer. This results in a water permeance of only 0.53 L m-2 h-1 bar-1, despite its\nhigh NaCl rejection. The intrinsic cavity of the TACA monomer confers pronounced\nmicroporosity to the nanofilm, significantly reducing water permeation resistance and\nenabling efficient separation of dye molecules and inorganic salts.\nWhen only the interfacial polymerization method was modified, the UDIP strategy\nensured continuous and sufficient MPD monomer supply, producing a relatively dense\nTACA-MPD membrane with excellent rejection of CR and MB. In contrast, under the\nconventional interfacial polymerization (CIP) method, the TACA-MPD membrane\nexhibited a looser structure due to insufficient monomer supply. This increased water\npermeance but reduced CR and MB rejection. When different substrates were compared,\nthe Kevlar hydrogel provided a stable reaction interface for the two-phase monomers and\neffectively regulated MPD monomer diffusion compared to the PAN substrate. As a result,\nthe TFC membrane prepared under the CIP/Kevlar condition achieved significantly higher\nwater permeance than that prepared via the CIP/PAN strategy, while maintaining\ncomparable dye rejection.\n5. Additional support is needed for the existence of “high-speed water transport pathway”s\nthrough the macrocycle internal cavities which was mostly speculated. Simulations showed\nnetwork interconnectivity and porosity affected small molecule transport (around the\nmacrocycles), but that is a distinctly different diffusion pathway from transport through\nthe macrocycles. How many of the molecular trajectories in MD passed through the TACA\nmacrocycles and how many went around them? Is this consistent with any observed flux\nenhancement compared to a control material without internal macrocyclic cavities?\nResponse: Thanks for your remarkable and valuable comments. We fully agree with the\nreviewer's suggestion to further investigate the proportion of water molecule transport\npathways, as this is crucial for elucidating the mechanism of transmembrane mass transfer.\nThis perspective offers a highly valuable direction for our future research.\nTo validate the role of the TACA cavity in water transport, we present explanations\nfrom both experimental and simulation perspectives. In response to the Comment #4 from\nReviewer 3, we furthered our study by fabricating a TFC membrane using cavity-free TMC\nand MPD via interfacial polymerization. This control membrane exhibited very low water\npermeance (<1 L m-2 h-1 bar-1). The significant difference in water permeance between the\nTACA-MPD and TMC-MPD membranes conclusively demonstrates the role of the TACA\ncavity in facilitating water transport. From the simulation perspective, evidence from both\nMolecular Dynamics (MD) and Density Functional Theory (DFT) simulations confirms\nthat the TACA cavity acts as an efficient water transport channel. As shown in Fig. R3, the\nmean squared displacement (MSD) of H O from MD simulations reveals a diffusion\n2\ncoefficient significantly higher than those of solutes and ions. This high MSD further\nsupports the conclusion that the TACA-MPD TFC membrane facilitates rapid water\ntransport. Additionally, DFT simulations, which show strong interactions between water\nmolecules and TACA-MPD structural units, confirm that the TACA cavity and molecular\nstructure.\nUnder the current experimental and simulation conditions, precisely quantifying the\nrelative proportion of water molecules passing through the macrocyclic cavity versus the\ncross-linked pores remains technically challenging. First, the water transport pathways are\ninherently stochastic. Second, accurately determining whether water molecules pass\nthrough the cross-linked pores or the cavity within feasible simulation timescales remains\nchallenging to achieve with high precision. Our current simulation efforts focus on\nvalidating that the macrocycle-assembled membrane exhibits excellent water permeance\nand dyes rejection, enabling the selective separation of dyes from salts. Despite these\ntechnical challenges, we agree with the reviewer that elucidating the transport pathways of\nwater molecules is an important research direction that merits further investigation.\nFig. R1 Mean square displacement (MSD) curves of H O and solutes.\n“Investigating the proportion of transport pathways of water molecules within macrocyclic\nmembranes is crucial for elucidating the transmembrane mechanism. Although this\nmechanism falls beyond the scope of the present study, it constitutes a key direction for\nfuture research and will focus on clarifying the specific transport processes and the\ncontribution of macrocyclic cavities.”\n6. Please add citations for the structures shown in Figure 4E.\nResponse: Thank you for your valuable comment. We have supplemented it in the\nmanuscript.\nPage 11, Line 370-373:\n“A comparison of dye retention and permeability of TACA-MPD membranes with\nliterature values is presented in Fig. 4e54-71. Results reveal that macrocycle-assembled\nmembranes exhibit both high water permeance and dye rejection, outperforming many\nstate-of-the-art membranes (Supplementary Table S5).”\n7. Please clarify if “permeances” in Figure 4 subplots are solute or water permeances.\nResponse: Thank you for your kind reminder. In Figure 4, \"permeance\" denotes water\npermeance. We have made the corresponding replacements in our resubmitted manuscript.\nPage 12, Line 385-392:\nFig. 4: Separation Performance of TACA-MPD Membranes. a, Water permeance, Congo\nred and Methyl blue rejection of TACA-MPD membranes synthesized with different MPD\nconcentrations. b, Rejection of various dyes and salts (feed solution was with single dye of\n100 ppm or single salt of 1 g/L). c, A diafiltration process of TACA MPD -3 (blue ball:\n0.5 0.5\nNaCl feed concentration). d, Stability of long-term operation in mixed solutions of Congo\nred/NaCl. e, Filtration performance of TACA MPD -3 compared with previously\n0.5 0.5\nreported membranes. f, Properties of polyimine membranes prepared using various\ndiamine monomers and TACA.\n25"}, {"round": 2, "reviewer_comments": {"reviewer_1": "After the author's revisions, the quality of the article has been improved and can be published in the Nature\nCommunications.", "reviewer_2": "The manuscript has been revised accordingly. All my comments have been addressed. It can now be accepted for\npublication", "reviewer_3": "The authors' revisions and responses to reviewers are appropriate and complete. I recommend acceptance for this article."}, "author_response": ""}]

Decision letter