Nanoarray-fortified ultra-durable nanofiber membrane via sequential crystallization

Domain: chemistry
Published: 2025-12-19
Editorial outcome: major_revision

Abstract
Advanced polymeric nanofiber membranes (PNMs) are hindered by intrinsically low mechanical strength and stability, especially under harsh conditions of oily water separation. Here, we report an approach to simultaneously enhance the tensile strength, stability and hydrophilicity of PNMs by sequentially crystallizing the covalent organic framework (COF) and poly(ether ether ketone) (PEEK). During the process, a superhydrophilic pine-needle-shaped COF nanoarray layer is inserted into the PEEK nanofibers to form a mechanical interlocking structure through the entanglement between PEEK non-crystallizing polymer chains and the hetero-interpenetration crystal structure consisting of COF crystal and PEEK crystal regions. Both simulation and experimental results show that the mechanical interlocking structure enhances the mechanical properties (16.2 MPa) and harsh-condition stability of the PNMs. In addition, the rigid COF nanoarray layer significantly improves the affinity with water, thereby enhancing the emulsion permeance up to 3.4 × 104 L m−2 h−1 bar−1 (968% increment) with nearly zero irreversible fouling during 100 fouling-cleaning cycles, which exceeds that of the state-of-the-art membranes.

Introduction
3D printing-based electron-spinning techniques can produce nano- to micron fibers with customized characteristics, and integrated advanced polymeric nanofiber membranes (PNMs) has the characteristics of high porosity, high surface area, and adjustable structure and surface properties1–3. The superwetting nanofiber membrane developed based on the above characteristics is considered to be an indispensable tool for the oily water separation process, which rely on the different capillary force generated by the wetting properties of the membranes in water and oil4,5. However, the poor tensile strength (below 5.0 MPa) and stability of PNMs hamper their wide application because of the low crystallinity of the polymeric materials during the electrospun process, the intrinsic low strength of each nanofibers with nanoscale diameter, and low interaction between each nanofibers (Supplementary Fig. 1)6–8. Several efforts have been made to improve the tensile strength of nanofibers through inducing the force between the fibers and the regulation of the polymer crystal region7–9. The strength of nanofiber membranes can be effectively improved by inducing the formation of interaction forces, such as hydrogen bonds between fibers. However, due to its low bond energy, it is easy to destroy under extreme conditions, especially in the complex environment of water remediation9. Adjusting the crystalline region by filling the nanomaterial can also effectively improve the membrane strength, but it will destroy the stability of the non-Newtonian fluid, resulting in difficulties in the spinning process10. The development of self-supporting nanofiber membranes with high tensile strength (>15 MPa) that can be applied in various extreme environments may enhance their use in water treatment fields and promote technological change in related application fields.

Adopting the high-performance polymer as the membrane substrate can also validly facilitate the strength of the prepared membrane7. PEEK, as a typical semicrystalline polymer containing one ketone bond and two ether bonds in the main chain, has excellent high-temperature resistance, high tensile strength, good corrosion resistance and excellent stability, which is enough to cope with the extreme conditions under water environment restoration11. However, the strong solvent resistance of PEEK polymers results in extremely low solubility in various organic solvents, making membrane manufacturing a challenging process12. In addition, the inherent hydrophobicity and molecular inertness of PEEK are barriers to its application. Although the sulfonation process was used to adjust the sulfonation degree of PEEK to increase the solubility of PEEK in organic solvent, excessive sulfonation leads to poor solvent resistance in PEEK, and the corrosion of strong sulfonic acid solutions makes it difficult to modify the surface of PEEK by blending13. Moreover, the tensile strength of the membrane is still low, due to the poor molecular chain orientation during the short and weak stretching process of the non-Newtonian liquid, even if adopting the high-performance polymer, which will weaken the long-term stability in the water treatment process7. It is still a challenge to develop high-strength PEEK-based functional nanofiber membranes via mild preparation technology and modification schemes.

Herein, we conceived a facile approach to construct high-strength and stable PNMs by sequential crystallization of COF-TpPa and polyether ether ketone (PEEK). First, the Pa monomers were dissolved and uniformly distributed in a polyether ether ketone imine (PEEKi, the precursor of PEEK and transform into noncrystalline PEEK after a typical oxime hydrolysis reaction) solution and electrospun to form nanofiber membranes (PIMs-Pa). Subsequently, the crystallization process of the COF-TpPa crystal and PEEK was regulated. In this process, the existing COF crystal region will induce the crystallization process of PEEK to form a hetero-interpenetrating structure. Moreover, the amorphous polymer chains interpenetrate with each other in the crystal region to form a physically crosslinked network with a mechanical interlocking structure, thereby enhancing the strength and excellent stability (even in strong solvents, strong acid and strong base solutions) of the CPMs. Interestingly, because the dissolution of Pa and the diffusion rate are lower than the rate of COF formation, the COF crystal could grow along the radial direction of the nanofiber to form a regularly patterned COF nanoarray layer. The formation of COF nanoarrays also enhances the mechanical properties and surface hydrophilicity of CPMs and broadens their application. When deployed for the separation of an oil-in-water emulsion, owing to its intrinsic hydrophilicity and axial distribution, the regularly patterned COF-TpPa layer promoted the formation of a hydrated layer and increased the capillary force (Fig. 1a). Together with the high porosity and rigidity of the COF-TpPa, the as-prepared CPMs could provide a superhydrophilic surface, increasing the impetus and repulsion of water and defending against attack from oil droplets or oily filter cakes, thereby simultaneously improving permeances, separation efficiency and antifouling performance.

Results
The PEEK in nanofiber membranes (PIMs), PEEK nanofiber membranes (PMs), and COF-TpPa-modified PEEK nanofiber membranes (CPMs) before and after thermal compression treatment were developed (if not emphasized later, CPMs refer to CPMs-II in the Supplementary Information). The mean diameter of the PMs was approximately 0.16 ± 0.1 μm (Supplementary Figs. 3–5), and no obvious adhesion between individual nanofibers was observed. Due to the increase of the viscosity of the casting solution, the diameter of PIMs-Pa increased to 1.02 μm, which may significantly influence the characteristics of the prepared membrane (Supplementary Table 1). For the CPMs, axially distributed pine-needle-shaped COF nanoarrays uniformly appeared on the surface of the nanofibers, and the diameter and length of the pine-needle-shaped COF-TpPa nanoarray were 45.4 and 151.6 nm, respectively (Fig. 1e, f). The diameter of the CPMs (approximately 1.44 μm) was approximately equal to the sum of the diameter of the pure PIM-Pa membrane (1.02 μm) and the thickness of the nanoarrays, indicating that the growth of the COF-TpPa nanoarray layer greatly increased the diameter of the fibers (Fig. 1b, c and Supplementary Fig. 5). Notably, the morphology of the PMs and CPMs after thermal compression treatment was identical to that of the PMs and CPMs without thermal compression treatment (Supplementary Fig. 6), indicating that the as-prepared nanofibers could maintain shape stability even under a pressure of 5.0 MPa during the thermal treatment. In addition, the thickness of the as-prepared nanofiber membranes increased from 59.1 to 90.2 μm after the in situ growth of the COF-TpPa nanoarray due to the uncompacted stacking of thicker fibers, which may also reduce the mass transfer resistance during the separation process (Supplementary Fig. 7)4. Moreover, the growth of nanoarrays greatly improves the specific surface area of the prepared membrane, expanding the steric hindrance between the oil molecules and membrane surface (Supplementary Fig. 8).

Interestingly, the in situ growth of the COF nanoarray layer regulates the crystallinity of PEEK molecules, and transmission electron microscopy confirmed the formation of interpenetrated structures between crystal regions (Fig. 1g)14,15. Before thermal compression, the PMs were amorphous, while one type of lattice fringe with the 0.22 nm d-spacing was observed for the PMs after thermal treatment (Supplementary Fig. 9a, b). The lattice fringe of COF-TpPa with d-spacing of 0.3 nm appeared on the CPMs before thermal compression (Supplementary Fig. 9c)16. Notably, the introduction of COFs led to the disappearance of most of the lattice fringes of the PMs, and the electron diffraction pattern demonstrated the transformation from a single crystal to polycrystalline with a variety of lattice fringes with different d-spacings after thermal treatment (Fig. 1g and Supplementary Fig. 9c). Furthermore, d-spacings within the crystalline domains of PEEK and COF-TpPa exhibited a marginal increase, attributable to lattice distortion arising from the thermally induced slip of COF crystals by PEEK16,17. Moreover, the surface roughness of the nanofiber membranes increased by 30%-85% after the formation of the COF-TpPa nanoarray layer (Supplementary Fig. 10), which could affect the surface energy of the membrane18,19. Interestingly, the membrane aperture and membrane porosity increased by 105% and 102%, respectively (Supplementary Figs. 11 and 12), because the COF-TpPa nanoarray increased the distance between the nanofibers.

According to density functional theory, the Gibbs free energy of molecules in different reaction stages was calculated to clarify the limit of the thermodynamic direction of the chemical reaction process20. The energy barrier of p-phenylenediamine bound to PEEKi is 72.3 kcal/mol, which is less than that bound to aniline. Therefore, p-phenylenediamine alleviated the hydrolysis process of PEEKi oxime (Fig. 1h)18. Interestingly, aniline, the byproduct of oxime hydrolysis, would not exert significant negative feedback on the formation process of COF-TpPa due to the large Gibbs free energy of reaction between aniline and Tp (Supplementary Fig. 13)21. On the basis of the above experimental and simulation results, the mechanism of the formation of the unique microstructure of the CPMs was speculated. As mentioned above, the hydrolysis of PEEKi and in situ growth of COF-TpPa simultaneously occurred in n-octanoic acid solutions. Since the solubility and diffusion rate of Pa in n-octanoic acid were far lower than the rate of COF-TpPa formation, especially the -CHO of Tp, which was activated to -C+HOH by n-octanoic acid in the solvent (Supplementary Fig. 14)22, the in situ growth of the COF-TpPa layer mainly occurred at the interface between the nanofibers and n-octanoic acid. With the continuous diffusion and dissolution of an appropriate content of Pa, the formation of an axially distributed pine-needle-shaped COF-TpPa nanoarray on the top surface of PEEK nanofiber membranes (PMs) was induced and inserted (Fig. 2a). Notably, as the Pa content increased, the COF-TpPa layer formed distinct nanostructures, including nanobulges, pine-needle-shaped nanoarrays, and nanoflowers (Fig. 1c and Supplementary Fig. 3c, d). This morphological evolution was driven by the number of surface Pa reactive sites and the enhanced diffusion rate (Fig. 2a and Supplementary Fig. 15). After the formation of the COF-TpPa nanoarray, the hydrolysis of PEEKi became easier without the inhibition caused by Pa. Simultaneously, the hydrolysis of PEEKi released aniline, which reduced the steric hindrance of the subsequent thermal rearrangement crystallization process so that the thermal rearrangement of the polymer chain was easier to carry out (Fig. 2b).

This sequential crystallization could optimize the compatibility between COF and PEEK crystals and avoid phase separation. Therefore, the molecules of crystalline PEEK and COF-TpPa formed a hetero-interpenetration crystal structure, and the noncrystalline PEEK molecules wrapped the interpenetrating crystals to form mechanically interlocked structures23–25. The changes in the chemical structure and properties of the as-prepared nanofiber membranes further confirmed the above speculation (Supplementary Figs. 16–19 and Supplementary Table 2), which are discussed in detail in the Supplementary Infomation11,26,27. The sequential crystallization of COF-TpPa and PEEK could be confirmed by the X-ray diffraction (XRD) patterns of the as-prepared nanofiber membranes (Fig. 2c and Supplementary Fig. 20). PEEKi and PEEK were fully amorphous after electron pinning, with no characteristic diffraction peaks. Notably, only the COF-TpPa crystal pattern (2θ = 4.6°) appeared in the XRD pattern of the CPMs before thermal treatment. The crystallinity of COF-TpPa was approximately 13.0%. After thermal compression treatment, new characteristic peaks belonging to the PEEK crystal region (2θ = 18.2°) in the PMs and CPMs were observed28. In addition, the XRD characteristic diffraction peaks of both COF-TpPa and PEEK shifted to the left, which also confirmed the increase in d-spacing caused by the interpenetration between the COF crystal and the PEEK crystal23,27–30. The crystallinity (41.4%) of PEEK in CPMs was slightly lower than that in PMs (43.3%) since COF-TpPa restricted the rearrangement of the molecular chain of PEEK, thereby limiting their crystallization (Supplementary Table 3)29–31. The melting temperature of PMs was approximately 250 °C, but the CPMs did not melt even at 400 °C (Supplementary Fig. 21). Moreover, the (Tg) of the CPMs increased by 15.1 °C after the introduction of the COF-TpPa layer and the sequential crystallization of the COF and PEEK (Fig. 2d and Supplementary Fig. 22)32. Molecular dynamics (MD) calculations show that compared with the original PEEK, the free volume of PEEK containing COF-TpPa is reduced by 37.8%, indicating that the introduction of COF-TpPa limits the movement of the PEEK main chain and causes a decrease in crystallinity, as mentioned above (Supplementary Fig. 23). Consequently, the glass transition temperature of CPMs is higher than that of PMs. The tensile strength of the PIM was approximately 2.3 MPa (Fig. 2e). The rigid structure of PEEK contributes to its high tensile strength. Interestingly, the crystallization process of PEEK increased its tensile strength by 121.7%. The strength of the CPMs after sequential crystallization increased to 16.2 MPa, which was comparable with that of laboratory-made ultrafiltration membranes fabricated by nonsolvent-induced phase inversion (Supplementary Fig. 24). Notably, the increase in tensile strength was positively correlated with the content of the COF-TpPa (Supplementary Table 4), which showed that the introduction of a COF had a great influence on the mechanical properties of PEEK. As mentioned above, COF-TpPa is a crystalline material composed of conjugated aromatic rings, showing strong intrinsic rigidity11. Moreover, the molecular rearrangement transforms randomly because the thermal compression arranges the molecular chain segments of PEEK into long-range ordered arrangements. The hetero-interpenetration crystal structure formed by COF-TpPa and crystalline PEEK molecules contributed to the increase in the tensile strength of each nanofiber33. Interestingly, the introduction of COF led to an increase in the proportion of the amorphous region, which could absorb energy through slip and conformational changes in the molecular chain when subjected to external force, thereby increasing the elongation at break of the nanofiber membrane (Fig. 2f)34,35. The mechanical interlocking structure formed by amorphous molecules and hetero-interpenetration crystal structures optimistically increases the mechanical properties of nanofiber membranes. In addition, the nanofiber membranes were stacked by every single nanofiber of the CPMs, as mentioned above. The stacking of the axially distributed pine-needle-shaped COF-TpPa nanoarray improved the interactive force (friction force) between different nanofibers, which could increase the mechanical strength of the prepared membrane by dispersing the force between the fibers through friction (Fig. 2f). Significantly, compared with PMs, CPMs have unparalleled stability in most organic solvents. The CPMs still maintained the shape of intact fibers after soaking in various organic solvents for 180 days, but the fibers of the PMs partially collapsed, which may have been caused by incomplete hydrolysis (Supplementary Fig. 25). Interestingly, the COF nanoarrays collapsed in some solvents, resulting in a slight decrease in tensile strength, which also proved that pine-needle-like nanoarrays between different fibers could enhance the tensile properties of the prepared membranes by dispersing external forces via friction. Notably, the prepared CPMs still had high tensile strength and elongation at break (Fig. 2g).

Interestingly, the COF-TpPa nanoarray excellently increased the surface energy of the PMs. The PMs demonstrated high hydrophobicity and underwater superoleophilicity, with a stable water contact angle of approximately 135.1° and a zero degree of underwater oil contact angle (UWOCA). However, water droplets could spread on the surface of the CPMs in less than 1.0 s, and the UWOCA of the CPM membranes was above 150.3°, indicating that the hydrophobic surface of the PM had transformed into a superhydrophilic surface after in situ radical growth of the COF-TpPa nanoarray (Fig. 3a; Supplementary Movies 1, 2 and Fig. 26). The underwater oil rolling angle of the as-prepared nanofiber membranes decreased to 5.4° after the introduction of the COF-TpPa nanoarrays (Supplementary Figs. 27, 28 and Supplementary Movie 3). In addition, unlike the superoleophilic PMs, the CPMs exhibited excellent oil repellency, and the adhesion force of the underwater oil droplets was less than 1.0 μN (Fig. 3b; Supplementary Movie 4 and Supplementary Fig. 29). The increase (51.8 times) in the apparent surface tension of the polar components caused by the abundant conjugated oxygen-containing groups in COF-TpPa and increased surface roughness (58.5%) on the nanofiber surface account for the reversal of surface hydrophilicity (Fig. 2c and Supplementary Fig. 30)36.

As a kind of hydrophobic material, the water adsorption capacity of PM is as low as 0.8 g g−1. After the formation of the COF-TpPa crystal nanoarray layer, the water adsorption capacity was nearly 14.8 times greater than that of the PMs since the CPMs contained many water adsorption sites and conjugated oxygen-containing groups (Fig. 3d and Supplementary Fig. 31)37. Moreover, the endothermic peak of the water-melting process shifted from 0.29 to 4.26 °C with more melting enthalpy (156.49 J/g) after the introduction of the COF-TpPa nanoarray. Similarly, the content of nonrefrigerated water in the CPMs (37.7%) was much greater than that in the PMs (18.4%) (Fig. 3e). In addition, the peak area ratios of intermediate water (3216 and 3400 cm−1) and free water (3544 and 3700 cm−1) increased from 0.21 to 1.75 according to Raman spectroscopy (Fig. 3f; Supplementary Fig. 32 and Supplementary Table 5), which further proved that the water binding capacity of the as-prepared nanofiber membranes significantly increased as well38. According to the MD simulation, the CPM membranes exhibited stronger electrostatic interactions with water (Ecoul), which could induce a stronger binding ability with water (Fig. 3g, h)39. The water molecular diffusion coefficients in the hydration layers of the PM and CPMs were 2.6 and 2.0 m2/s, respectively. Moreover, the residence time of the CPM hydration layer was also greater than that of the PM hydration layer. The lower diffusion coefficient and greater water residence time in the CPMs could also account for their greater ability to form a hydration layer (Supplementary Fig. 33)40. In addition, the ability to form hydrogen bonds between water and the PNMs and the lifetime of the hydrogen bonds increased by 62.5% and 58.6%, respectively, after the introduction of COF-TpPa nanoarrays (Fig. 3j and Supplementary Fig. 34), which was attributed to the formation of hydrophilic COF nanoarrays on the fiber providing a large number of potential hydrogen bond acceptor sites and donor sites. (Supplementary Fig. 35)37.

The superhydrophilic surface of the engineered membrane significantly expands its potential applications in diverse operational environments, such as oil-water separation. Owing to the intrinsically hydrophobic surface, the pristine PM had a low permeance of 3.2 × 103 L m−2 h−1 bar−1, with a separation efficiency of 92.7% for water-in-octane emulsions. The permeance of the CPMs increased significantly by at least 968% and was positively correlated with the content of COF-TpPa (Fig. 4a; Supplementary Figs. 36 and 37), and the separation efficiency of the CPMs was above 99.9% (Fig. 4a). The increased permeance and separation efficiency after in situ radical growth of the COF-TpPa crystal layer could be attributed to the finely tailored membrane structures and affinities with water during the dynamic crystal engineering process, according to both the experimental and simulation results mentioned above. The COF-TpPa nanoarray layer increased the mean pore size of the nanofiber membranes, reducing the mass transfer resistance (Supplementary Fig. 38). The improvement in the affinity between the nanofiber membranes and water caused by the introduction of the COF-TpPa nanoarray layer during the sequential crystallization process promoted the formation of a rigid hydration layer and encouraged water to pass through the nanofiber membranes while preventing the formation of oil droplets (Fig. 4d). More importantly, the mean particle size of the oil droplets in the filtrate of CPM was less than 100 nm, which was far smaller than that in the feed emulsion (1000 nm) and in the filtrate of PMs (500 nm) (Supplementary Fig. 38). Notably, the average pore diameter of the CPMs was greater than 3 μm, indicating that the separation of the oil-water emulsions was dependent mainly on the different Laplace repulsions caused by the different wettabilities toward water and oil2,39,40. The CPMs were also effective at disposing of various oil-in-water emulsions, such as toluene-in-water emulsions and soybean-in-water emulsions (Supplementary Figs. 39–41).

During the separation process of nanofiber membranes, the oil droplets tend to adhere and embed into the nanofiber membranes via hydrophobic interactions under transmembrane pressure due to the flexible segment and hydrophobicity of the polymer, resulting in severe irreversible membrane fouling, which limits the application of nanofiber membranes in oil/water separation (Supplementary Fig. 42). The PM exhibited severe irreversible fouling since the permeance decreased to 7.0 × 102 L m−2 h−1 bar−1, and the separation efficiency correspondingly decreased to 80% after 100 fouling-washing cycles. The interaction between the oily cake layer and the hydrophobic segment in PEEK and the underwater lipophilicity of PEEK are the main reasons for severe membrane fouling41,42. Interestingly, the permeance of CPM remained 100% (3.4 × 104 L m−2 h−1 bar−1) even after 100 fouling-washing cycles, which was approximately 3800% greater than that of PM after fouling, indicating that the CPM did not exhibit irreversible fouling (Fig. 4b and Supplementary Figs. 43–47). This was due to the hetero-interpenetration crystal structure in the mechanical interlocking structure, which increased the rigidity of the fibers and prevented oil droplets from being embedded in the membrane due to gravity. Importantly, the rigidity of the membrane prevented it from swelling in various solvents, which greatly improved the service life of the membrane (Supplementary Tables 6 and 7). In addition, the excellent antifouling performance of the prepared membrane was due to the underwater superoleophobic characteristics endowed by the introduction of COF-TpPa nanoarrays, which prevented the adhesion of oil droplets to the surface due to hydrophobic interactions. In addition, due to the formation of mechanically interlocked hydrophilic rigid COF nanoarrays, which could prevent acid/oil droplets from eroding PEEK molecular chains, the CPMs were strongly stable in various solvents and at various pH values (Supplementary Figs. 48–51), with excellent separation performance after immersion for 180 days (Fig. 4c). Interestingly, the rigid COF-TpPa nanoarray layer promoted the demulsification of the oil-in-water emulsion. The nanoscale oil-in-water emulsion enters the channel between the COF nanoarrays during the separation process. Owing to the narrow pores, the emulsion droplets continuously collided between the nanoarrays and interacted with the hydration layer, which might destroy the stability of the emulsion. Therefore, demulsification occurred inside the nanoarray, which floated on the water surface after continuous aggregation (Fig. 4d)39. In summary, the comprehensive performance of the CPMs was far greater than that of the state-of-the-art PNMs reported (Fig. 4e)43–46. Moreover, while maintaining the same retention performance, the CPM membrane achieves a permeance 59.1–90.2 μm over 8 times greater than commercial microfiltration membranes and surpasses commercial ultrafiltration membranes by two orders of magnitude (Supplementary Tables 8 and 9), showing substantial promise in oily wastewater treatment.

Methods
Preparation of as-prepared nanofiber membranes

Preparation of PIMs. PEEKi (2.0 g) was dissolved in 8.0 g of NMP and stirred at 30 °C for 8 h to obtain a homogeneous solution. Then, a uniform PEEKi solution was poured into a disposable syringe equipped with a 0.9 mm spinneret. The applied electric voltage and solution feed rate were 13 kV and 0.0010 mm/s, respectively. The spinneret had translational oscillatory motion perpendicular to the collector rotation direction (the oscillation distance was 18 cm). A rotating collector (diameter: 10 cm, width: 20 cm) covered with glossy aluminum foil was used to collect the PEEKi nanofibers at a rotating speed of 180 rpm. The distance between the spinneret and the collector was 15 cm, and the collection time was 6 h.

Preparation of PMs. The obtained PIMs were hydrolyzed to PEEK nanofiber membranes in n-octanoic acid at 80 °C for 24 h. After that, the membranes were removed and thoroughly rinsed with deionized water. Finally, the PEEK nanofiber membranes were thermally compressed at 250 °C under 5.0 MPa for 30 min. During this procedure, the amorphous PEEK nanofiber membranes could transform into semicrystalline PEEK nanofiber membranes (PMs), thereby improving the tensile strength of the nanofiber membranes.

Preparation of CPMs. Pa (1.0, 2.0 or 3.0 g) was added to the PEEKi solution to form a uniform solution. Then, uniform PEEKi-Pa solution was poured into a disposable syringe equipped with a 0.9 mm spinneret. The applied electric voltage and solution feed rate were 13 kV and 0.0010 mm/s, respectively. The spinneret had translational oscillatory motion perpendicular to the collector rotation direction (the oscillation distance was 18 cm). A rotating collector (diameter: 10 cm, width: 20 cm) covered with glossy aluminum foil was used to collect the PEEKi-Pa nanofibers at a rotating speed of 180 rpm. The distance between the spinneret and the collector was 15 cm, and the collection time was 6 h. After that, the PEEKi-Pa nanofiber membranes were soaked in Tp-n-octanoic acid solutions at 80 °C for 24 h. During this process, the Pa monomers reacted with the Tp monomers to form a COF-TpPa nanoarray layer, and PEEKi was hydrolyzed to PEEK. The as-prepared membranes were subsequently thermally compressed to obtain CPMs. The CPMs with different COF contents were labeled CPM-I, CPM-II, and CPM-III.

Full experimental procedures are available in the Supplementary Information.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors constructed a mechanical interlocking structure of heterogenous interpenetrating crystals and amorphous regions with chain entanglement through sequential crystallization of COF-TpPa and PEEK, thereby simultaneously improving the strength and hydrophilicity of the CPMs. This paper is structurally complete and provides sufficient experimental data. If the authors can supplement the paper with mechanism verification and application arguments, it will significantly improve the scientific rigor and industrial reference value of their work. Therefore, I recommend that the paper be accepted for publication after major revisions. The following are specific issues.\n1. How is sequential crystallization achieved? Please describe the principle and process in detail. How does sequential crystallization differ from conventional crystallization methods? What are the key factors affecting the sequential crystallization process?\n2. When comparing the mechanical properties and separation efficiency of materials, only laboratory-made membranes were compared, and commercial ultrafiltration membranes (such as PVDF and PES membranes) were not included. It is recommended that performance comparison data with commercial membranes be added.\n3. The preparation of CPMs involves complex processes such as electrospinning, n-octanoic acid treatment, and heat treatment. Have the authors considered production costs and efficiency, and whether large-scale production is feasible? What challenges will be encountered in the process of achieving large-scale production, and how should these challenges be addressed?\n4. Please explain in detail how nanoarrays enhance the strength, stability, and hydrophilicity of the CPMs, and supplement with relevant schematic diagrams of the mechanism.\n5. The caption for Figure 2b is missing; the format of the references is also inconsistent. Please carefully check the abbreviations used for journals and make any necessary corrections.", "reviewer_2": "The authors combined COF-TpPa with PEEK through heterogeneous interpenetrating crystal structure and mechanical interlocking network, and improved the mechanical properties, hydrophilicity and stability of nanofiber membranes. More importantly, the author introduced pine needle-like COF nanoarrays and clarified the mechanism, which have novel structure, clear morphology control and functional orientation. Although the manuscript has solid data and clear organization, some content in the manuscript are suggested to be further clarified to improve the quality of the paper to meet the publishing standards of Nature Commications.\n1.The authors proposed that the COF-TpPa nanoarray led to an increase in the distance between the fibers, which affected the porosity, pore size and thickness of the membrane. However, the increase of fiber diameter will also cause the above situation. Please consider the expression of this part carefully.\n2.The authors proposed that the appearance of nanoflower structure in CPM-III was due to the high diffusion rate of high concentration of Pa. However, the explanation still puzzles me. The mechanism of different structure formation at different Pa concentrations should be described in detail.\n3.The author believed that the process of Pa inhibiting the typical oxime hydrolysis reaction of PEEKi was very important for the performance of membrane. Please offer the sufficient reasons.\n4.The author proposed that membrane separation mainly depended on the different Laplace forces generated by the membrane surface on water droplets and oil droplets. But later, COF nanoarrays were proposed to promote demulsification. Which of these two mechanisms is dominant or how to cooperate ? The author should clarify the critical mechanism.\n5.The author needs to supplement the relevant characterization of TpPa-COF, such as XRD, Fourier transform infrared, etc., to prove that the growth of the membrane surface was TpPa-COF.", "reviewer_3": "This paper addressed the challenge of insufficient mechanical strength and stability in polymeric nanofiber membranes (PNMs) by introducing a sequential crystallization strategy of COF and PEEK to construct a ‘mechanical interlocking structure’, supported by both experimental and simulation evidence. The results demonstrate remarkable enhancements in terms of physical, chemical stability and oil-water separation performance, highlighting the novelty and practical significance of the research. In general, the article has met the publication requirements of Nature communications, but some modifications are still needed to improve the overall quality of the article.\n1. After in-situ growth of COF-TpPa nanoarrays, the thickness of the nanofiber membrane increased from 59.1 μm to 90.2 μm. What is the reason for the increase in thickness, and will it affect the mass transfer process of the membrane?\n2. Although the Gibbs free energy of the reaction of aniline with Tp was greater than that of p-phenylenediamine and Tp, it could not be simply considered that aniline had no effect on the growth process of COF-TpPa. The author should consider the expression in this part.\n3. The author did not elaborate on the root cause of lattice distortion, but simply believed that the mutual penetration of the two types of crystals occurred. To be precise, the lattice distortion should be caused by the defects of COF crystals caused by the thermal motion of PEEK crystallization process. The should consider this part carefully and explore the reasons in depth.\n4. It can be seen from the XRD spectrum that the crystallinity of COF decreased after hot pressing. Will this cause a decrease in membrane performance.\n5. The author should supplement the basic characterization of COF-TpPa.\n6. Whether the author can supplement BET and other characterizations to improve the basic properties of nanofiber membranes after in-situ growth of COF to build solid structural advantages.\n7. The author needs to supplement the swelling ratio in each solvent to confirm that it can have excellent stability in harsh environments."}, "author_response": "Responses for\nTitle ‘Nanoarray-fortified Ultra-durable Nanofiber Membrane via Sequential\nCrystallization’\nManuscript Number: NCOMMS-25-59373-T\nDear Editor and Reviewers,\nWe gratefully thank the editor and all reviewers for the time they spent making\nconstructive remarks and useful suggestions, which significantly improved the\nquality of the manuscript. After careful consideration of the Reviewers'\nprofessional comments, we have revised the manuscript and made more works to\nenhance the quality of this manuscript. Below are the comments of the reviewers,\nresponses point by point and the revisions indicated.\nIn our point-by-point response, reviewers’ comments are in BLACK, and our\nresponses are in BLUE. The modified sentences in the marked manuscript are in\nRED. The suggested modifications have also been incorporated into the revised\nmanuscript.\nWe are looking forward to your further advice on our work.\nYours sincerely,\nLu Shao\nPoint-by-Point Responses to the Reviewers’ Comments\nReviewer #1:\nThe authors constructed a mechanical interlocking structure of heterogenous\ninterpenetrating crystals and amorphous regions with chain entanglement through\nsequential crystallization of COF-TpPa and PEEK, thereby simultaneously improving\nthe strength and hydrophilicity of the CPMs. This paper is structurally complete and\nprovides sufficient experimental data. If the authors can supplement the paper with\nmechanism verification and application arguments, it will significantly improve the\nscientific rigor and industrial reference value of their work. Therefore, I recommend\nthat the paper be accepted for publication after major revisions. The following are\nspecific issues.\nResponse: Thank you for reviewing our manuscript and for your valuable insights\naimed at enhancing its quality. According to your suggestions, we have supplemented\nand modified the relevant content in our previous draft and the detailed corrections are\nlisted below. After revisions, we believe that the scientific rigor and industry reference\nvalue of manuscript have been effectively improved, and meet the criteria for Nature\nCommunications.\n1. How is sequential crystallization achieved? Please describe the principle and process\nin detail. How does sequential crystallization differ from conventional crystallization\nmethods? What are the key factors affecting the sequential crystallization process?\nResponse: Thanks for your review on our article. Sequential crystallization was\nachieved by the kinetic and thermodynamic difference in the crystallization process of\nPEEK and COF-TpPa. The crystallization temperature of PEEK is 250 °C, while the\nsynthesis temperature of COF-TpPa is usually about 120 °C (Polym. Sci, 2024, 63, 876-\n883. J. Am. Chem. Soc, 2012, 134, 19524-19527). Specifically, the reaction monomer\nPa of COF inhibited the typical hydrolysis reaction of oxime in PEEKi, thereby\npreventing the formation of PEEK (Fig. 1h). Meanwhile COF would quickly form and\ninsert into the polymer chain of PEEKi. With the gradual completion of the COF\nreaction, the oxime hydrolysis process was quickly carried out and aniline was released,\nwhich would provide sufficient thermal motion space for the subsequent PEEK thermal\nmotion crystallization process at 250 °C. The crystallization process of COF is based\non the reversible process of Schiff base reaction, while PEEK crystallization belongs to\nthe thermal motion rearrangement of polymer chain, which requires sufficient thermal\nmotion space. However, the traditional one-step crystallization method under 250 ℃\nwill lead to defects, disordered structure and even phase separation due to compatibility\nand kinetic differences, especially for polymer with long-chain molecules. (Prog.\nPolym. Sci, 2021, 115, 101376. Acc. Chem. Res, 2006, 39,314-323. Macromol. Rapid\nCommun, 2024, 46, 2400724.). Therefore, we hope to achieve the formation of\nmechanical interlocking structure with crystal interpenetrating structure by regulating\nthe crystallization process of COF and PEEK. In general, the insertion of COF crystals\nin the fibers would reduce the space for thermal motion of PEEK and limited the\ncrystallization process of PEEK. Sequential crystallization can effectively solve the\nabove problems. In this process, controlling the temperature in the process of sequential\ncrystallization is the key to realize the preparation of mechanical interlocking structure\nwith heterogeneous interpenetrating crystal structure by sequential crystallization.\nFor comparison, we supplemented the XRD and mechanical properties of nanofiber\nmembranes prepared using the traditional one-step co-crystallization scheme to\nhighlight the superiority of the sequential crystallization. Specifically, PIMs-Pa was\nplaced in an aqueous solution of n-octanoic acid containing Tp and reacted at 250 °C\nfor 24 h. As shown in Fig. R1a, PEEK and COF exhibited low crystallinity, which was\ncaused by the incompatibility between the lattices of COF and PEEK. As a result, the\ntensile strength of the prepared membrane decreased to 5.4 MPa, which is 66.7% less\nthan CPM membranes fabricated by sequential crystallization (Fig. R1b and Fig. R2).\nWe have supplemented the relevant content in the text, in the hope of better expounding\nthe superiority of sequential crystallization.\nFig. R1: Characterizations of membranes prepared by traditional crystallization\nmethod; (a) XRD, (b) stress‒strain curves.\nFig. R2: Characterizations of membranes prepared by sequential crystallization; (a)\nXRD, (b) stress‒strain curves.\nWe have modified the content in the manuscript:\nAfter the formation of the COF-TpPa nanoarray, the hydrolysis of PEEKi became easier\nwithout the inhibition caused by Pa. Simultaneously, the hydrolysis of PEEKi released\naniline, which reduced the steric hindrance of the subsequent thermal rearrangement\ncrystallization process so that the thermal rearrangement of the polymer chain was\neasier to carry out (Fig. 2b). This sequential crystallization could optimize the\ncompatibility between COF and PEEK crystals and avoid phase separation. Therefore,\nthe molecules of crystalline PEEK and COF-TpPa formed a hetero-interpenetration\ncrystal structure, and the non-crystalline PEEK molecules wrapped the interpenetrating\ncrystals to form mechanically interlocked structures.23-25\n[23] Xiong, P. et al. Two-dimensional organic-inorganic superlattice-like\nheterostructures for energy storage applications. Energ Environ. Sci. 13, 4834-4853\n(2020).\n[24] Ou, Z. et al. Oriented Growth of Thin Films of Covalent Organic Frameworks with\nLarge Single-Crystalline Domains on the Water Surface. J. Am. Chem. Soc. 144, 3233\n-3241 (2022).\n[25] Tang, Z. et al. Synthesis of a crystalline two-dimensional [c2] daisy chain\nhoneycomb network. Nature Synth. 4, 922-930 (2025)\nWe have supplemented the content in the supplementary materials:\nThe XRD characteristic peaks of PEEK did not appear in the PM or CPM samples\nwithout thermal compression treatment, indicating that the initial PEEK material was\nin an amorphous state. After thermal compression, the characteristic peaks of PEEK\nappeared in the PM and CPM samples (Supplementary Fig. 20), confirming the\nprocess of sequential crystallization.20 Interestingly, the COF-TpPa characteristic peak\nof the CPMs after thermal treatment shifted to the left, which confirmed that the\ncrystallization process of PEEK caused distortion of the COF-TpPa lattice.28 Similarly,\nthe introduction of COFs also caused a shift in the characteristic peaks of PEEK to the\nleft. The formation of the hetero-interpenetration crystal structure by sequential\ncrystallization was the main reason leading to an increase in the d-spacings of the two\ntypes of lattices.29 Notably, the characteristic peak intensities of both COF and PEEK\nin the CPM prepared by the one-step crystallization method were attenuated to varying\ndegrees, indicating a reduction in their crystallinity. This was because the rapid reaction\nof COF under the co-crystallization conditions at 250°C generates defects. Meanwhile,\nhigh temperature also accelerated the hydrolysis of oxime, which would accelerate the\nformation of PEEK. The rapid formation of crystals would lead to a significant decrease\nin the compatibility of the two crystals, which may affect the membrane performance.\nFig. S20. XRD spectrum of the prepared membranes.\nThe as-prepared CPMs (6 cm 2 cm100 μm) could withstand a mass of 700 g without\nbreaking. The tensile strength of the CPMs was superior to that of commercial\nultrafiltration and microfiltration membranes (Supplementary Fig. 24 and Table 4).37-\ncrystallinity.\nCPM-III\nCPM-III (without heat treatment)\n25\n) CPM-II (one-step crystallization)\na\nP Cellulose acetate plate membrane\nM20 PAN nanofiber membrane\n( PAN plate membrane\ns\ns15\ne\nr\nt\nS10\n5\n0\n0 10 20 30 40 50\nStrain (%)\nFig. S24. Mechanical properties of the prepared membranes.\n2. When comparing the mechanical properties and separation efficiency of materials,\nonly laboratory-made membranes were compared, and commercial ultrafiltration\nmembranes (such as PVDF and PES membranes) were not included. It is recommended\nthat performance comparison data with commercial membranes be added.\nResponse: Thank you very much for this insightful comment, which improved the\nscientific rigor and industry reference value of the manuscript. We purchased several\ncommon PES and PAN ultrafiltration membranes (containing non-woven substrates)\nand several typical hydrophilic microfiltration membranes on the market, and measured\ntheir mechanical properties and separation performance. The results show that the\nprepared membrane showed the same mechanical properties as the commercial\nmembrane, but the separation performance was much higher than that of the\ncommercial membrane. We supplemented the relevant content in the text to highlight\nthe superiority of the prepared nanofiber membrane.\nWe have modified the content in the manuscript:\nIn summary, the comprehensive performance of the CPMs was far greater than that of\nthe state-of-the-art polymeric nanofiber membranes reported (Fig. 4e).43-46 Moreover,\nwhile maintaining the same retention performance, the CPM membrane achieves a\npermeance over 8 times greater than commercial microfiltration membranes and\nsurpasses commercial ultrafiltration membranes by two orders of magnitude\n(Supplementary Table 9), showing substantial promise in oily wastewater treatment.\nWe have modified the content in the supplementary materials:\n1. Materials and methods\nPVDF (MF) was Purchased at Delvstlab and PES membrane (MF) was Purchased at\nJinteng. PAN membrane (UF) and PES membrane (UF) were purchased at Zhongke\nRuiyang Membrane Technology (Beijing) Co., Ltd.\nTable S9 Comparison with commercial membrane\nMembrane Tensile Strain Permeance Separation\nStrength (%) (L·m-2·h-1·bar-1) rate (%)\n(MPa)\nOur work 11.0 (CPM-I) 34.7 2.8104 99.9\n16.2 (CPM-II) 41.0 3.4104 99.9\n22.5 (CPM-III) 47.0 4.2104 99.8\nPVDF (MF) 7.5 18.1 4230.4 99.2\nPES membrane 6.3 10.2 3546.5 99.1\n(MF)\nPAN membrane 23.6 20 162.4 99.9\n(UF)\nPES membrane 29.2 13.3 101.1 99.9\n(UF)\n3. The preparation of CPMs involves complex processes such as electrospinning, n-\noctanoic acid treatment, and heat treatment. Have the authors considered production\ncosts and efficiency, and whether large-scale production is feasible? What challenges\nwill be encountered in the process of achieving large-scale production, and how should\nthese challenges be addressed.\nResponse: Thank you very much for this insightful comment. The advantage of\nelectrospinning is that it can prepare organic, inorganic and other materials, which can\nbe applied in water treatment and energy, etc. (Prog Polym Sci, 2018, 86, 40-84. Renew\nSust Energ Rev, 2018, 81, 1825-1858.). However, the current dilemma facing\nelectrospinning is how to manufacture on a large scale. Our laboratory has been able to\nmake 300 mm*400 mm CPMs at present, which is comparable to the scale of the\nultrafiltration membrane prepared by the phase inversion method in the laboratory.\nThere are also several attempts to develop electrospun nanofiber membranes, such as\nmodifying the shape of the needle, increasing the number of needles and the area of the\nreceiving plate, which can further achieve large-scale manufacturing (Mater Design,\n2019, 179, 107885. Renew Sust Energ Rev, 2018, 81, 1825-1858). Inspired by the\naforementioned works, we will try to manufacture the CPMs on a large scale through\nincreasing the number of needles and using roll-to-roll receiver. It is should be\nmentioned that the cost of the raw materials (PEEK) ($1143.8/kg from Aladdin reagent\nnetwork) is cheaper than that of polyimide ($1177.8/kg from Aladdin reagent network)\nwhich has been developed as commercial nanofiber membranes (Dupont). Moreover,\nthe electrospinning process enables solvent recovery and operates without wastewater\ndischarge, which substantially lowers wastewater treatment expenses and shows strong\npromising in substituting the phase inversion. Taken together, although the\nmanufacturing of CPMs also needs heat-treatment and in-situ growth in n-octanoic as\nthe reviewer mentioned, it is still a promising method to develop highly-durable and\nhigh-separation performance CPMs for applications under extreme conditions such as\nstrong acids, alkalis and organic solvents.\nFig. R3: Prices of PI and PEEK from Aladdin reagent network\n4. Please explain in detail how nanoarrays enhance the strength, stability, and\nhydrophilicity of the CPMs, and supplement with relevant schematic diagrams of the\nmechanism.\nResponse: Thanks for your insightful comments. Specifically, COF crystals and PEEK\ncrystals form lattice interpenetrating structures, which greatly improved the mechanical\nstrength of the membrane. Meanwhile, the lattice interpenetrating structure and PEEK\namorphous region form a mechanical interlocking structure, so that the toughness of\nthe membrane was improved by the slip of the molecules in the amorphous region to\neffectively disperse the force (Fig. R4) (Compos. Part. B-Eng, 2021, 213, 108737.\nNano Lett, 2024, 24, 3826-3834.). The increase (51.8 times) in the apparent surface\ntension of the polar components caused by the abundant conjugated oxygen-containing\ngroups in COF-TpPa and increased surface roughness (58.5%) on the nanofiber surface\naccount for the reversal of surface hydrophilicity (Fig. 2c and Supplementary Fig. 28).\nMeanwhile, the skeleton structure of COF-TpPa, especially the nitrogen atom of -C=N-\nand the oxygen/hydrogen atom of -OH, which are the core components of COF-TpPa,\nprovide a large number of potential hydrogen bond acceptor sites and donor sites. By\nvirtue of its strong polarity and bifunctional (donor and acceptor) properties, water\nmolecules can form hydrogen bond networks with these sites very effectively (Small,\n2025, 21, 2505330. Adv. Funct. Mater, 2021, 49, 2106507). Coupled with the inherent\nhigh specific surface area and pore structure of the COF material, water molecules can\nfully contact these sites, resulting in a significant hydrogen bond interaction between\nCOF-TpPa and water (Fig. R5). According to the reviewer’s suggestion, we have\nrevised and supplemented the relevant mechanism diagram in order to expect readers\nto understand our point of view.\nFig. R4: The schematic diagram of nanoarrays to improve the mechanical properties\nof the membrane.\nFig. R5: The schematic diagram of improving the hydrophilicity of the membrane by\nnanoarrays.\nWe have modified the content in the manuscript:\nInterestingly, the introduction of COF led to an increase in the proportion of the\namorphous region, which could absorb energy through slip and conformational changes\nin the molecular chain when subjected to external force, thereby increasing the\nelongation at break of the nanofiber membrane (Fig. 2f).34,35 The mechanical\ninterlocking structure formed by amorphous molecules and hetero-interpenetration\ncrystal structures optimistically increases the mechanical properties of nanofiber\nmembranes. In addition, the nanofiber membranes were stacked by every single\nnanofiber of the CPMs, as mentioned above. The stacking of the axially distributed\npine-needle-shaped COF-TpPa nanoarray improved the interactive force (friction force)\nbetween different nanofibers, which could increase the mechanical strength of the\nprepared membrane by dispersing the force between the fibers through fiction (Fig. 2f).\nSignificantly, compared with PMs, CPMs have unparalleled stability in most organic\nsolvents. The CPMs still maintained the shape of intact fibers after soaking in various\norganic solvents for 180 days, but the fibers of the PMs partially collapsed, which may\nhave been caused by incomplete hydrolysis (Supplementary Fig. 25). Interestingly,\nthe COF nanoarrays collapsed in some solvents, resulting in a slight decrease in tensile\nstrength, which also proved that pine-needle-like nanoarrays between different fibers\ncould enhance the tensile properties of the prepared membranes by dispersing external\nforces via friction. Notably, the prepared CPMs still had high tensile strength and\nelongation at break (Fig. 2g).\n[34] Zhang, L. et al., SiC Nanowire -Si N Nanobelt Interlocking Interfacial\n3 4\nEnhancement of Carbon Fiber Composites with Boosting Mechanical and Frictional\nProperties. Acs Appl. Mater. Interfaces. 13, 20746-20753 (2021).\n[35] Li, Y. et al., Mechanically interlocked stretchable nanofibers for multifunctional\nwearable triboelectric nanogenerator. Nano Energy. 78, 105358 (2020).\nFig. 2: (a) Mechanistic diagram of the formation of the nanoarray: (b) The hydrolysis\nof PEEKi releases aniline to generate enough space to promote the thermal motion of\nPEEK molecules. (c) X-ray diffraction (XRD) and (d) DSC curves; (e) stress‒strain\ncurves of the as-prepared membranes; (f) crystalline microdomain structure and\nmechanical interlocking structure in the CPMs; and the diagram of the increase in\nfriction between nanofibers in the nanoarray; (g) mechanical properties of the prepared\nmembranes after immersion in different organic solvents for 180 days.\nThe lower diffusion coefficient and greater water residence time in the CPMs could\nalso account for their greater ability to form a hydration layer (Supplementary Fig.\n33).40 In addition, the ability to form hydrogen bonds between water and the PNMs and\nthe lifetime of the hydrogen bonds increased by 62.5% and 58.6%, respectively, after\nthe introduction of COF-TpPa nanoarrays (Fig. 3j and Supplementary Fig. 34), which\nwas attributed to the formation of hydrophilic COF nanoarrays on the fiber providing a\nlarge number of potential hydrogen bond acceptor sites and donor sites.\n(Supplementary Fig. S35).37\n[40] Zhao, Y. et al. Surface manipulation for prevention of migratory viscous crude oil\nfouling in superhydrophilic membranes. Nat. Commun. 14, 2679 (2023).\n[37] Shi, B. et al., Short hydrogen-bond network confined on COF surfaces enables\nultrahigh proton conductivity. Nat. Commun. 13, 6666 (2022).\nWe have supplemented the content in the supplementary:\nFig. S35: The schematic diagram of improving the hydrophilicity of the membrane by\nnanoarrays\n5. The caption for Figure 2b is missing; the format of the references is also inconsistent.\nPlease carefully check the abbreviations used for journals and make any necessary\ncorrections\nResponse: We are sorry for our carelessness and thanks for your careful review.\nWe have carefully reviewed the manuscript and corrected it according to the requirements\nof Nature Communications. Because there are too many references and modified parts\nof the text, we only extract part of the content on detailed response to reviewers. More\nrevisions are included in the revised manuscript. We are once again sorry for these\navoidable mistakes.\nWe have modified the content in the manuscript:\nFig. 2: (a) Mechanistic diagram of the formation of the nanoarray: (b) The hydrolysis\nof PEEKi releases aniline to generate enough space to promote the thermal motion of\nPEEK molecules. (c) X-ray diffraction (XRD) and (d) DSC curves; (e) stress‒strain\ncurves of the as-prepared membranes; (f) crystalline microdomain structure and\nmechanical interlocking structure in the CPMs; and the diagram of the increase in\nfriction between nanofibers in the nanoarray; (g) mechanical properties of the prepared\nmembranes after immersion in different organic solvents for 180 days.\nReferences format revisions:\n[2] Ji, D. et al. Electrospinning of nanofibres. Nat Rev Methods Primers. 4, 1 (2024).\n[3] Rahmati, M. et al. Electrospinning for tissue engineering applications. Prog. Mater\nSci. 117, 100721 (2021).\n[4] Cheng, X. et al. Biodegradable electrospinning superhydrophilic nanofiber\nmembranes for ultrafast oil-water separation. Sci. Adv. 9, eadh8195 (2023).\nReviewer #2:\nThe authors combined COF-TpPa with PEEK through heterogeneous interpenetrating\ncrystal structure and mechanical interlocking network, and improved the mechanical\nproperties, hydrophilicity and stability of nanofiber membranes. More importantly, the\nauthor introduced pine needle-like COF nanoarrays and clarified the mechanism, which\nhave novel structure, clear morphology control and functional orientation. Although the\nmanuscript has solid data and clear organization, some content in the manuscript are\nsuggested to be further clarified to improve the quality of the paper to meet the\npublishing standards of Nature Communications.\nResponse: We are truly grateful for this reviewer’s insightful review and\nacknowledgment of our work. We have carefully considered all valuable suggestions\nand made revisions for improvement. Below, you will find our detailed point-by-point\nresponses.\n1. The authors proposed that the COF-TpPa nanoarray led to an increase in the distance\nbetween the fibers, which affected the porosity, pore size and thickness of the\nmembrane. However, the increase of fiber diameter will also cause the above situation.\nPlease consider the expression of this part carefully.\nResponses: Thank you very much for this insightful comment. As the reviewer\nmentioned, the increase in nanofiber diameter due to the increase of the viscosity of the\ncasting solution would also affect the pore size, porosity and thickness of the membrane\n(Supplementary Fig. 3a-3b). Notably, the diameter was further increased by about\n0.42 μm after the formation of in-situ nanoarrays (Fig. 3d), which would also have a\ngreat influence on the physical properties of the prepared membrane. In order to further\nclarify our statement and not ignore the impact of the increase in fiber diameter, we\ncarefully revised the relevant content according to the reviewer’s opinion.\nWe have modified the content of the manuscript.\nThe PEEKi nanofiber membranes (PIMs), PEEK nanofiber membranes (PMs), and\nCOF-TpPa-modified PEEK nanofiber membranes (CPMs) before and after thermal\ncompression treatment were developed (if not emphasized later, CPMs refer to CPMs-\nII in the supplementary information). The mean diameter of the PMs was approximately\n0.16 ± 0.1 μm (Supplementary Fig. 3-S5), and no obvious adhesion between\nindividual nanofibers was observed. Due to the increase of the viscosity of the casting\nsolution, the diameter of PIMs-Pa increased to 1.02 μm, which may significantly\ninfluence the characteristics of the prepared membrane (Supplementary Table 1). For\nthe CPMs, axially distributed pine-needle-shaped COF nanoarrays uniformly appeared\non the surface of the nanofibers and The diameter and length of the pine-needle-shaped\nCOF-TpPa nanoarray were 45.4 nm and 151.6 nm, respectively (Fig. 1e-f). The\ndiameter of the CPMs (approximately 1.44 μm) was approximately equal to the sum of\nthe diameter of the pure PIM-Pa membrane (1.02 μm) and the thickness of the\nnanoarrays, indicating that the growth of the COF-TpPa nanoarray layer greatly\nincreased the diameter of the fibers (Fig. 1b-c, and Supplementary Fig. S5).\n2. The authors proposed that the appearance of nanoflower structure in CPM-III was\ndue to the high diffusion rate of high concentration of Pa. However, the explanation still\npuzzles me. The mechanism of different structure formation at different Pa\nconcentrations should be described in detail.\nResponses: We appreciate you mentioned about this point. CPM-I, CPM-II and CPM-\nIII obtained different surface morphologies due to the different Pa content in the surface\nof the PEEKi nanofibers and different diffusion rate of Pa (Fig. 1b and Supplementary\nFig. 3). For CPM-I, only little Pa on the surface could react with Tp in n-octanoic acid,\nand a small amount of Pa inside the fiber was difficult to diffuse to the solid-liquid\ninterface. Therefore, CPM-I exhibits a rough structure (Supplementary Fig. 3c and\nFig. R6). For CPM-II, the surface of PEEKi nanofiber membranes contained enough\nPa, providing sufficient reactive site to form nanoarrays. Meanwhile, the Pa inside the\nfiber diffused along the nanoarrays to the solid-liquid interface and reacted with the Tp\nin the solvent to form nanoarrays (Fig. 1c and Fig. R6). While the concentration of Pa\nincreased further, the surface of fiber contained a large number of reaction sites, and\nthe rate of diffusion of Pa inside the fiber to the interface was accelerated. Therefore,\nnanoflower structure was formed on the surface of CPM-III (Supplementary Fig. 3d\nand Fig. R6). To clarify the reaction mechanism, we have supplemented the content\nand increased the mechanism diagram in the corresponding part of the manuscript.\nFig. R6: The reaction mechanism diagram of different membrane surface.\nWe have modified the content in the manuscript:\nWith the continuous diffusion and dissolution of an appropriate content of Pa, the\nformation of an axially distributed pine-needle-shaped COF-TpPa nanoarray on the top\nsurface of PEEK nanofiber membranes (PMs) was induced and inserted (Fig. 2a).\nNotably, as the Pa content increased, the COF-TpPa layer formed distinct\nnanostructures, including nanobulges, pine-needle-shaped nanoarrays, and nanoflowers\n(Fig. 1c and Supplementary Fig. 3c-d). This morphological evolution was driven by\nthe number of surface Pa reactive sites and the enhanced diffusion rate (Fig. 2a and\nSupplementary Fig. 15).\nWe have supplemented the content in the supplementary materials:\nFig. S15: The reaction mechanism diagram of CPM-I and CPM-III\nFor CPM-I, only little Pa on the surface could react with Tp in n-octanoic acid, and a\nsmall amount of Pa inside the fiber was difficult to diffuse to the solid-liquid interface.\nTherefore, CPM-I exhibits a rough structure (Supplementary Fig. 3c and Fig. 15). For\nCPM-II, the surface of PEEKi nanofiber membranes contained enough Pa, providing\nsufficient reactive site to form nanoarrays (Fig. 1c and Fig. 2a). Meanwhile, the Pa\ninside the fiber diffused along the nanoarrays to the solid-liquid interface and reacted\nwith the Tp in the solvent to form nanoarrays. While the concentration of Pa increased\nfurther, the surface of fiber contained a large number of reaction sites, and the rate of\ndiffusion of Pa inside the fiber to the interface was accelerated. Therefore, nanoflower\nstructure was formed on the surface of CPM-III (Supplementary Fig. 3d and Fig. 15).\n3.The author believed that the process of Pa inhibiting the typical oxime hydrolysis\nreaction of PEEKi was very important for the performance of membrane. Please offer\nthe sufficient reasons.\nResponses: Thank you very much for this insightful comment. Specifically, the reaction\nmonomer Pa of COF inhibited the typical hydrolysis reaction of oxime in PEEKi,\nthereby preventing the formation of PEEK. Meanwhile COF would quickly form and\ninsert into the polymer chain of PEEKi. With the gradual completion of the COF\nreaction, the oxime hydrolysis process was quickly carried out and aniline was released,\nwhich would provide sufficient thermal motion space for the subsequent PEEK thermal\nmotion crystallization process at 250 °C. If there was no inhibitory effect of Pa on the\nhydrolysis process of PEEKi, it would lead to difficulties in the subsequent\ncrystallization process of PEEK, and it was difficult to form a stable lattice\ninterpenetrating structure (Fig. R7).\nFig. R7: The hydrolysis of PEEKi released aniline which generated enough space to\npromote the thermal motion of PEEK molecules\nWe have modified the content in the manuscript:\nAfter the formation of the COF-TpPa nanoarray, the hydrolysis of PEEKi became easier\nwithout the inhibition caused by Pa. Simultaneously, the hydrolysis of PEEKi released\naniline, which reduced the steric hindrance of the subsequent thermal rearrangement\ncrystallization process so that the thermal rearrangement of the polymer chain was\neasier to carry out (Fig. 2b). This sequential crystallization could optimize the\ncompatibility between COF and PEEK crystals and avoid phase separation. Therefore,\nthe molecules of crystalline PEEK and COF-TpPa formed a hetero-interpenetration\ncrystal structure, and the non-crystalline PEEK molecules wrapped the interpenetrating\ncrystals to form mechanically interlocked structures.23-25\nFig. 2: (a) Mechanistic diagram of the formation of the nanoarray: (b) The hydrolysis\nof PEEKi releases aniline to generate enough space to promote the thermal motion of\nPEEK molecules. (c) X-ray diffraction (XRD) and (d) DSC curves; (e) stress‒strain\ncurves of the as-prepared membranes; (f) crystalline microdomain structure and\nmechanical interlocking structure in the CPMs; and the diagram of the increase in\nfriction between nanofibers in the nanoarray; (g) mechanical properties of the prepared\nmembranes after immersion in different organic solvents for 180 days.\n4.The author proposed that membrane separation mainly depended on the different\nLaplace forces generated by the membrane surface on water droplets and oil droplets.\nBut later, COF nanoarrays were proposed to promote demulsification. Which of these\ntwo mechanisms is dominant or how to cooperate? The author should clarify the critical\nmechanism.\nResponses: Thank you for your comments on our article. We fundamentally think that\nthe difference Laplace force generated by the membrane surface on oil droplets and\nwater droplets was the main mechanism in the membrane separation process, which is\nmainly used to separate large oil droplets. However, oil droplets smaller than 100 nm\ncannot be effectively separated by simple Laplace force (Sci. Adv. 2023, 9, adh8195).\nThe existence of nanoarrays could make the nano scale oil-in-water emulsion (< 100\nnm) continuously collide with the hydrophilic COF in the nanochannel and effectively\ndemulsify them, which could greatly improve the separation efficiency. Therefore, the\nprepared membrane can effectively remove oil droplets larger than 70 nm. In order to\nfurther clarify the relationship between the two, we have made corresponding\nsupplements in the text.\nWe have modified the content in the manuscript:\nInterestingly, the rigid COF-TpPa nanoarray layer promoted the demulsification of the\noil-in-water emulsion. The nanoscale oil-in-water emulsion enters the channel between\nthe COF nanoarrays during the separation process. Owing to the narrow pores, the\nemulsion droplets continuously collided between the nanoarrays and interacted with the\nhydration layer, which might destroy the stability of the emulsion. Therefore,\ndemulsification occurred inside the nanoarray, resulting in the flotation of oil on the\nwater surface after continuous aggregation (Fig. 4d). 39\n[39] Guo, X. et al., Janus channel of membranes enables concurrent oil and water\nrecovery from emulsions. Science. 386, 654-659 (2024)\n5.The author needs to supplement the relevant characterization of TpPa-COF, such as\nXRD, Fourier transform infrared, etc., to prove that the growth of the membrane surface\nwas TpPa-COF.\nResponses: We appreciate this comment for comprehensiveness improvement in our\npaper. According to the reviewer’s comment, we supplemented the X-Ray diffraction\n(XRD) and Fourier Transform Infrared (FT-IR) of COF-TpPa powder. The\ncharacteristic peak at 1650 cm-1 was attributed to -C=O, and the occurrence of -C=C-\nN- at 1563 cm-1 and Ar-OH at 1450 cm-1 indicated the successful formation of COF-\nTpPa. For the prepared membrane, the new peak at 1650 cm-1 was attributed to -C=O-,\nindicating the transformation of the PEEKi nanofiber membranes (PIMs) to PEEK\nnanofiber membranes (PMs) after hydrolysis. The occurrence of -C=C-N- at 1510 cm-\n1 and Ar-OH at 1450 cm-1 indicated the successful formation of COF-TpPa on the\nsurface of the PMs. The red shift of the -C=C-N- characteristic peak may be due to the\nconjugation between COF-TpPa and PEEK.\nFig. R8. Fourier transform infrared spectroscopy (FT-IR) of PIM, PM, CPM and COF-\nTpPa.\nCOF-TpPa powder possessed peaks at 2θ values of 4.7° (100), 8.2° (210), and 26.8°\n(001), which correspond to the typical reflections of the hexagonal COF-TpPa crystals.\nNotably, the same diffraction peak appeared in CPM, which confirmed that COF-TpPa\nwas successfully loaded on PEEK nanofiber membrane. Meanwhile, we further\nsupplement the corresponding part of the paper.\nFig. R9: XRD of PIM, PM, CPM and COF-TpPa\nWe have modified the content in the manuscript:\nFig. 2: (a) Mechanistic diagram of the formation of the nanoarray: (b) The hydrolysis\nof PEEKi releases aniline to generate enough space to promote the thermal motion of\nPEEK molecules. (c) X-ray diffraction (XRD) and (d) DSC curves; (e) stress‒strain\ncurves of the as-prepared membranes; (f) crystalline microdomain structure and\nmechanical interlocking structure in the CPMs; and the diagram of the increase in\nfriction between nanofibers in the nanoarray; (g) mechanical properties of the prepared\nmembranes after immersion in different organic solvents for 180 days.\nWe have modified the content in the supplementary materials:\nThe changes in the chemical structure of the as-prepared nanofiber membranes confirmed the\naforementioned processes (Supplementary Fig. 14). The new peak at 1658 cm-1 was\nattributed to -C=O-, indicating the transformation of the PEEKi nanofiber membranes (PIMs)\nto PEEK nanofiber membranes (PMs) after hydrolysis. The characteristic peak at 1650 cm-\n1 was attributed to -C=O, and the occurrence of -C=C-N- at 1563 cm-1 and Ar-OH at\n1450 cm-1 indicated the successful formation of COF-TpPa. For the prepared membrane,\nthe new peak at 1650 cm-1 was attributed to -C=O-, indicating the transformation of the\nPEEKi nanofiber membranes (PIMs) to PEEK nanofiber membranes (PMs) after\nhydrolysis. The occurrence of -C=C-N- at 1510 cm-1 and Ar-OH at 1450 cm-1 indicated\nthe successful formation of COF-TpPa on the surface of the PMs. The red shift of the -\nC=C-N- characteristic peak may be due to the conjugation between COF-TpPa and\nPEEK.20,33\nReviewer #3:\nThis paper addressed the challenge of insufficient mechanical strength and stability in\npolymeric nanofiber membranes (PNMs) by introducing a sequential crystallization\nstrategy of COF and PEEK to construct a ‘mechanical interlocking structure’,\nsupported by both experimental and simulation evidence. The results demonstrate\nremarkable enhancements in terms of physical, chemical stability and oil-water\nseparation performance, highlighting the novelty and practical significance of the\nresearch. In general, the article has met the publication requirements of Nature\ncommunications, but some modifications are still needed to improve the overall quality\nof the article.\nWe appreciate your detailed and positive comments on our manuscript. We have\nresponded your comments as best as we can. After revision, we hope that the manuscript\ncan meet the standard of Nature Communications.\n1. After in-situ growth of COF-TpPa nanoarrays, the thickness of the nanofiber\nmembrane increased from 59.1 μm to 90.2 μm. What is the reason for the increase in\nthickness, and will it affect the mass transfer process of the membrane?\nResponses: Thanks for your insightful comments. The increase of membrane thickness\nwas mainly due to the formation of nanoarrays. The diameter was further increased by\nabout 0.42 μm after the formation of in-situ nanoarrays (Fig. 3d), which caused the\nspacing between the fibers to widen. The increase in thickness means that the fiber stack\nis not dense and the porosity increases, which will lead to a decrease in the mass transfer\nresistance of the permeate during the separation process and improve the permeance of\nthe prepared membrane. (ACS Nano, 2022, 16, 4684-4692). Meanwhile, due to the\ngrowth of surface COF nanoarrays, the hydrophilicity of the membrane surface is\nimproved, so the separation efficiency is also greatly improved.\nWe have modified the content in the manuscript:\nIn addition, the thickness of the as-prepared nanofiber membranes increased from 59.1\nto 90.2 μm after the in situ growth of the COF-TpPa nanoarray due to the uncompacted\nstacking of thicker fibers, which may also reduce the mass transfer resistance during\nthe separation process (Supplementary Fig. 7).[4] Moreover, the growth of nanoarrays\ngreatly improves the specific surface area of the prepared membrane, which provides\nmore active sites (Supplementary Fig. 8).\n[4] Cheng, X. et al., Biodegradable electrospinning superhydrophilic nanofiber\nmembranes for ultrafast oil-water separation. Sci. Adv. 9, eadh8195 (2023).\n2. Although the Gibbs free energy of the reaction of aniline with Tp was greater than\nthat of p-phenylenediamine and Tp, it could not be simply considered that aniline had\nno effect on the growth process of COF-TpPa. The author should consider the\nexpression in this part.\nResponses: We appreciated you for pointing out the mistakes in our manuscript. We are\nsorry that our inaccurate description has caused ambiguity and we revised the\nexpression of the relevant part according to the reviewer’s suggestion to express our\nopinion accurately.\nWe have modified the content in the manuscript:\nInterestingly, aniline, the byproduct of oxime hydrolysis, would not exert significant\nnegative feedback on the formation process of COF-TpPa due to the large Gibbs free\nenergy of reaction between aniline and Tp (Supplementary Fig. 13).21 On the basis of\nthe above experimental and simulation results, the mechanism of the formation of the\nunique microstructure of the CPMs was speculated.\n[21] Kalia, J. & Raines, R. T., Hydrolytic stability of hydrazones and oximes. Angew\nChem Int Edit. 47 7523-7526 (2008).\n3. The author did not elaborate on the root cause of lattice distortion, but simply\nbelieved that the mutual penetration of the two types of crystals occurred. To be precise,\nthe lattice distortion should be caused by the defects of COF crystals caused by the\nthermal motion of PEEK crystallization process. The author should consider this part\ncarefully and explore the reasons in depth.\nResponses: We appreciated your insightful comment for comprehensiveness\nimprovement in our paper. It can also be seen from Fig. 2c that the crystallinity of COF\ndecreases greatly after PEEK crystallization, which was due to the lattice strain of COF\ncrystal caused by the thermal motion during PEEK crystallization. According to the\nreviewer 's comments, we have revised the relevant sections in the hope of better\nelaborating the relevant mechanisms.\nWe have modified the content in the manuscript:\nNotably, the introduction of COFs led to the disappearance of most of the lattice fringes\nof the PMs, and the electron diffraction pattern demonstrated the transformation from\na single crystal to polycrystalline with a variety of lattice fringes with different d-\nspacings after thermal treatment (Fig. 1g and Supplementary Fig. 8c). Furthermore,\nd-spacings within the crystalline domains of PEEK and COF-TpPa exhibited a marginal\nincrease, which was attributed to the lattice strain of COF crystal caused by PEEK\nthermal motion.16,17\n[16] De Bolos, E. et al., Interlocked 2D Covalent Organic Frameworks from\nOvercrowded Nodes. J. Am. Chem. Soc. 147,2579-2586 (2025).\n[17] Zhang, S. et al., Integration of Multiple Heterointerfaces in a Hierarchical\n0D@2D@1D Structure for Lightweight, Flexible, and Hydrophobic Multifunctional\nElectromagnetic Protective Fabrics. Nano-Micro Lett. 15, 204 (2023).\n4. It can be seen from the XRD spectrum that the crystallinity of COF decreased after\nhot pressing. Will this cause a decrease in membrane performance.\nResponses: We appreciated your mentioned about this point. The weakening\ncrystallinity of COF is mainly due to the slip of the COF crystal during the thermal\nmotion of PEEK. We compared the separation performance of CPM before and after\ncrystallization, and the results were not much different. Notably, the mechanical\nproperties of PEEK improved significantly after crystallization. The separation process\nof the membrane to the emulsion mainly depends on the surface morphology and\nsurface wettability of the membrane. The change of COF crystallinity did not affect the\napparent morphology and contact angle (Fig. R10b and Fig. R11), so the decrease of\nCOF crystallinity had little effect on the separation performance of the membrane (Fig.\nR10a).\nFig. R10. (a) Separation performance of the prepared membrane before and after heat\ntreatment, (b) Initial water contact angle of the prepared membrane before and after hot\npressing.\nFig. R11. SEM images of the prepared; (a) CPM (without heat treatment), and (b) CPM\n(heat treatment).\n5. The author should supplement the basic characterization of COF-TpPa.\nResponses: We appreciate this comment for comprehensiveness improvement in our\npaper. According to the reviewer’s comment, we supplemented the X-Ray diffraction\n(XRD) and Fourier Transform Infrared (FT-IR) of COF-TpPa powder. The\ncharacteristic peak at 1650 cm-1 was attributed to -C=O, and the occurrence of -C=C-\nN- at 1563 cm-1 and Ar-OH at 1450 cm-1 indicated the successful formation of COF-\nTpPa. For the prepared membrane, the new peak at 1650 cm-1 was attributed to -C=O-,\nindicating the transformation of the PEEKi nanofiber membranes (PIMs) to PEEK\nnanofiber membranes (PMs) after hydrolysis. The occurrence of -C=C-N- at 1510 cm-\n1 and Ar-OH at 1450 cm-1 indicated the successful formation of COF-TpPa on the\nsurface of the PMs. The red shift of the -C=C-N- characteristic peak may be due to the\nconjugation between COF-TpPa and PEEK.\nFig. R12. Fourier transform infrared spectroscopy (FT-IR) of PIM, PM, CPM and COF-\nTpPa\nCOF-TpPa powder possessed peaks at 2θ values of 4.7° (100), 8.2° (210), and 26.8°\n(001), which correspond to the typical reflections of the hexagonal COF-TpPa crystals.\nNotably, the same diffraction peak appeared in CPM, which confirmed that COF-TpPa\nwas successfully loaded on PEEK nanofiber membrane.\nFig. R13. XRD of PIM, PM, CPM and COF-TpPa\nMeanwhile, we further supplement the corresponding part of the paper.\nWe have modified the content in the manuscript:\nFig. 2: (a) Mechanistic diagram of the formation of the nanoarray: (b) The hydrolysis\nof PEEKi releases aniline to generate enough space to promote the thermal motion of\nPEEK molecules. (c) X-ray diffraction (XRD) and (d) DSC curves; (e) stress‒strain\ncurves of the as-prepared membranes; (f) crystalline microdomain structure and\nmechanical interlocking structure in the CPMs; and the diagram of the increase in\nfriction between nanofibers in the nanoarray; (g) mechanical properties of the prepared\nmembranes after immersion in different organic solvents for 180 days.\nWe have modified the content in the supplementary materials:\nThe changes in the chemical structure of the as-prepared nanofiber membranes\nconfirmed the aforementioned processes (Supplementary Fig. 14). The new peak at\n1658 cm-1 was attributed to -C=O-, indicating the transformation of the PEEKi\nnanofiber membranes (PIMs) to PEEK nanofiber membranes (PMs) after hydrolysis.\nThe characteristic peak at 1650 cm-1 was attributed to -C=O, and the occurrence of -\nC=C-N- at 1563 cm-1 and Ar-OH at 1450 cm-1 indicated the successful formation of\nCOF-TpPa. For the prepared membrane, the new peak at 1650 cm-1 was attributed to -\nC=O-, indicating the transformation of the PEEKi nanofiber membranes (PIMs) to\nPEEK nanofiber membranes (PMs) after hydrolysis. The occurrence of -C=C-N- at\n1510 cm-1 and Ar-OH at 1450 cm-1 indicated the successful formation of COF-TpPa on\nthe surface of the PMs. The red shift of the -C=C-N- characteristic peak may be due to\nthe conjugation between COF-TpPa and PEEK.20,33\n6. Whether the author can supplement BET and other characterizations to improve the\nbasic properties of nanofiber membranes after in-situ growth of COF to build solid\nstructural advantages.\nResponses: We appreciate your suggestion. We supplemented the BET adsorption curve\nand specific surface area test of CPMs and PMs. The results showed that the adsorption\nisotherm of CPMs belonged to type IV isotherm, and there was a significant increase\nin the amount of adsorption in the high relative pressure area. The CPMs on the surface\nhad a certain porous structure. The adsorption capacity of PMs was almost zero,\nindicating that fibers of PMs had almost no pore structure. Moreover, the specific\nsurface area of CPMs was significantly higher than that of PMs, which was due to the\ncontribution of CPM surface nanoarrays. The larger specific surface area increased the\ncontact interface between the membrane and water, expanding the steric hindrance\nbetween the oil molecules and membrane surface (Nat. Commun. 2015, 14, 2679).\nFig. R14. Nitrogen adsorption and desorption isotherms of the prepared membranes and\nthe specific surface area of the prepared membranes\nWe have supplemented the content in the manuscript:\nThe diameter of the CPMs (approximately 1.44 μm) was approximately equal to the\nsum of the diameter of the pure PIM-Pa membrane (1.02 μm) and the thickness of the\nnanoarrays, indicating that the growth of the COF-TpPa nanoarray layer greatly\nincreased the diameter of the fibers (Fig. 1b-c, and Supplementary Fig. S5). Notably,\nthe morphology of the PMs and CPMs after thermal compression treatment was\nidentical to that of the PMs and CPMs without thermal compression treatment\n(Supplementary Fig. 6), indicating that the as-prepared nanofibers could maintain\nshape stability even under a pressure of 5.0 MPa during the thermal treatment. In\naddition, the thickness of the as-prepared nanofiber membranes increased from 59.1 to\n90.2 μm after the in situ growth of the COF-TpPa nanoarray due to the uncompacted\nstacking of thicker fibers, which may also reduce the mass transfer resistance during\nthe separation process (Supplementary Fig. S7).[4] Moreover, the growth of nanoarrays\ngreatly improves the specific surface area of the prepared membrane, expanding the\nsteric hindrance between the oil molecules and membrane surface (Supplementary Fig.\nS8).\nWe have supplemented the content in the supplementary materials:\nFig. S8. Nitrogen adsorption and desorption isotherms of the prepared membranes and\nthe specific surface area of the prepared membranes.\n7. The author needs to supplement the swelling ratio in each solvent to confirm that it\ncan have excellent stability in harsh environments.\nResponses: We appreciate your detailed comments on our manuscript. According to the\nreviewer’s comment, we supplemented the swelling ratio of the membrane immersed\nin each solvent. However, we only supplemented the data for 50 days due to time\nproblems. The specific data are as shown in Table 1, and the results showed that our\nmembrane exhibits excellent anti-swelling ability in various organic solvents, which\npresented an excellent stability in harsh environments.\nWe have supplemented the content in the manuscript:\nThis was due to the hetero-interpenetration crystal structure in the mechanical\ninterlocking structure, which increased the rigidity of the fibers and prevented oil\ndroplets from being embedded in the membrane due to gravity. Importantly, the rigidity\nof the membrane prevented it from swelling in various solvents, which greatly\nimproved the service life of the membrane (Supplementary Table 6-7).\nWe have supplemented the content in the supplementary materials:\nTable S7 Swelling rate after soaking in each solution for 50 days\nMembrane Chloroform Acetonitrile Acetone NMP Ethyl Dichlorom\n(CPM) acetate ethane\nSwelling 0 0 0 0 0 0\nratio (%)"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The reviewer is glad to see that the issues he raised have been addressed in the revised manuscript. Recommended for acceptance and publication.", "reviewer_2": "Nice work, it can be accepted for publication.", "reviewer_3": "The authors have addressed my concerns satifactorily, and it's suitable for piblication in its present form."}, "author_response": ""}]

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