Dynamic covalent bond in-situ self-repairing composite nanofiltration membrane based on temperature response and preparation method and application thereof

Abstract

The invention discloses a dynamic covalent bond in-situ self-repairing composite nanofiltration membrane based on temperature response and a preparation method and application thereof, and belongs to the technical field of nanofiltration membranes. A functional layer of the nanofiltration membrane is a cross-linked network containing dynamic covalent bonds and formed by common reaction of aromatic diamine, a cross-linking agent and trimesoyl chloride, and the dynamic covalent bonds are imine bonds or disulfide bonds. When the surface of the membrane is damaged, dynamic covalent bond breakage and recombination can be triggered through mild heating at 60-80 DEG C, in-situ self-repairing of the membrane is achieved, and the repairing efficiency is larger than or equal to 90%. Compared with an existing beta-cyclodextrin system, pH adjustment is not needed, the elastic modulus is increased by 40% or above, the new membrane dye retention rate is larger than or equal to 98%, the method is suitable for printing and dyeing wastewater treatment and fine chemical engineering separation scenes, and the service life of the membrane can be remarkably prolonged.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane separation technology, specifically relating to a temperature-responsive dynamic covalent bond in-situ self-healing composite nanofiltration membrane, its preparation method, and its application, which is particularly suitable for water treatment and solution separation scenarios requiring long-term stable operation. Background Technology

[0002] Nanofiltration membranes are widely used in seawater desalination, industrial wastewater treatment, and food and pharmaceutical purification due to their excellent separation performance, lack of chemical changes, and ease of operation. However, in actual use, nanofiltration membranes are prone to surface cracks and scratches caused by factors such as operating pressure fluctuations, contaminant friction, and mechanical impacts. This damage can lead to a significant decrease in membrane separation performance, reduced rejection rate, abnormally high water flux, and even loss of separation function, greatly shortening the membrane's lifespan.

[0003] To address membrane damage, existing technologies have proposed using β-cyclodextrin supramolecular systems, leveraging host-guest interactions between β-cyclodextrin and guest molecules to achieve damage repair. Chinese patent document CN118286884A discloses a self-healing nanofiltration composite membrane based on β-cyclodextrin and its preparation method. This method uses pH adjustment of the feed solution to protonate or deprotonate the membrane, resulting in a significant pH-responsive behavior. However, self-healing membrane systems based on β-cyclodextrin supramolecular systems have significant drawbacks: the repair process requires precise pH adjustment, typically between pH 7 and 9, which is complex and easily affects the membrane's chemical stability; the supramolecular interactions are weak, resulting in low elastic modulus and insufficient mechanical properties after repair; and the repair efficiency is limited, typically restoring only 70%-80% of the separation performance, making it unsuitable for demanding applications. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of β-cyclodextrin-based self-healing nanofiltration composite membranes by providing a temperature-responsive, dynamically covalently bonded in-situ self-healing composite nanofiltration membrane, its preparation method, and its applications. By introducing dynamic covalent bonds of imine or disulfide, a cross-linked network is constructed between the polyamide matrix and these dynamic covalent bonds. At a specific temperature, the dynamic covalent bonds break and recombine, enabling rapid in-situ self-healing of membrane damage without pH adjustment, while simultaneously improving the membrane's mechanical properties.

[0005] To achieve the above-mentioned objectives, this invention provides a method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane, comprising the following steps: (1) Dissolve the aromatic diamine in deionized water to obtain an aromatic diamine solution, add a dynamic covalent crosslinking agent, stir, and obtain an aqueous solution; (2) Dissolve pyromellitic chloride in an organic solvent to obtain an oil phase solution; (3) Immerse the base film in the aqueous solution of step (1), take it out and drain the excess solution on the surface, and then immerse it in the oil solution of step (2). An interfacial polymerization reaction occurs on the surface of the base film to form a film containing a polyamide matrix and dynamic covalent bonds. (4) The membrane obtained in step (3) is dried at 60-80℃ for 1-2 hours and cooled to room temperature to obtain a composite nanofiltration membrane with dynamic covalent bond in situ self-healing based on temperature response.

[0006] Preferably, in step (1), the aromatic diamine is m-phenylenediamine; the mass concentration of the aromatic diamine solution is 1%-3%.

[0007] Preferably, in step (1), the dynamic covalent crosslinking agent is an aldehyde-containing crosslinking agent or a crosslinking agent containing disulfide bonds with amino groups at both ends; the aldehyde-containing crosslinking agent is preferably glutaraldehyde; the stirring conditions are 20-30℃ and stirring for 30-60 min; the crosslinking agent containing disulfide bonds with amino groups at both ends is preferably 3,3'-dithiodipropylamine.

[0008] Preferably, in step (1), the amount of the aldehyde-containing crosslinking agent is 5%-15% of the mass of the aromatic diamine; the amount of the crosslinking agent containing disulfide bonds with amino groups at both ends is 8%-20% of the mass of the aromatic diamine.

[0009] Preferably, in step (2), the organic solvent is n-hexane; and the mass concentration of the trimesoyl chloride is 0.05%-0.2%.

[0010] Preferably, in step (3), the base membrane is a polysulfone ultrafiltration membrane or a polypropylene microporous membrane; the interfacial polymerization reaction temperature is 20-30℃.

[0011] This invention also provides a method for repairing composite nanofiltration membranes based on temperature response and in-situ self-repair of dynamic covalent bonds. When cracks or scratches appear on the membrane surface, the membrane is heated in an environment of 60-80℃ for 20-40 minutes to trigger the breaking and recombination of dynamic covalent bonds, thereby achieving in-situ self-repair of membrane damage.

[0012] During repair, there is no need to disassemble the membrane module. The membrane module can be directly heated or hot water at 60-80℃ can be introduced to achieve in-situ self-repair of the composite nanofiltration membrane, which is simple to operate. The repair efficiency is ≥90%, and the elastic modulus is increased by more than 40% compared with the β-cyclodextrin repair system.

[0013] Two implementations of dynamic covalent bonds: 1. Imine bond system: When preparing an aqueous solution, an aldehyde-containing crosslinking agent is mixed with an aromatic diamine. The aldehyde and amine groups initially come into contact and undergo a Schiff base reaction (-NH2+-CHO→-CH=N-+H2O). The Schiff base reaction rate is positively correlated with temperature. The higher the temperature, the more vigorous the reaction. Therefore, temperature and time must be strictly controlled. In the method of this invention, when the dynamic covalent crosslinking agent used to prepare the aqueous solution is an aldehyde-containing crosslinking agent, the stirring temperature is controlled at 20-30℃ for 30-60 minutes. Under these conditions, the reaction rate is relatively slow, and the aldehyde and amine groups can only initially contact each other. Approximately 30%-40% of the amine groups participate in the initial reaction to form a small amount of imine bonds, which is insufficient for complete reaction. 60%-70% of the free amine groups are retained for subsequent interfacial polymerization. During the interfacial polymerization stage, the amine groups preferentially react with acyl chlorides to generate a polyamide matrix. In the post-treatment stage, the temperature is raised to the repair temperature range of 60-80℃. At this point, the polyamide matrix has been formed through interfacial polymerization, and the remaining aldehyde and amine groups further react at a higher temperature to complete the formation of the remaining 60%-70% of imine bonds. This allows the imine bonds to be uniformly distributed in the polyamide matrix, forming a crosslinked network where the polyamide matrix and dynamic covalent bonds coexist. This network retains the high retention capacity of the polyamide and also possesses repair potential due to the dynamic reversibility of the imine bonds.

[0014] Mechanism of imine bond repair: Heating triggers bond breaking: The bond energy of an imine bond is approximately 30-40 kJ / mol, and that of an amide bond is approximately 380 kJ / mol. The heat energy provided at 60-80℃ can break imine bonds, but is insufficient to destroy the amide bonds in the polyamide matrix, effectively preventing damage to the film structure. Heating at 60-80℃ causes the imine bonds near the crack to absorb energy and break, regenerating active aldehyde and amine groups. The breaking reaction is: -N=CH- → -NH2 + O=CH-. Spontaneous filling and recombination: Aldehyde and amine groups diffuse freely on the crack surface and spontaneously undergo Schiff base reaction due to intermolecular forces, forming new imine bonds to fill the crack gaps. This process is simple to operate and does not require pH adjustment. Unlike the supramolecular action of β-cyclodextrin which requires pH adjustment, the Schiff base reaction can occur under neutral conditions.

[0015] 2. Disulfide Bond System: The formation of disulfide bonds depends on copolymerization. Disulfide bonds are embedded as functional units in the polyamide matrix, forming a dynamic cross-linked structure. In preparing the aqueous solution, a cross-linking agent containing disulfide bonds and end-capped amine groups is mixed with an aromatic diamine. The cross-linking agent, with end-capped amine groups, serves as an amine source along with the aromatic diamine, participating in interfacial polymerization as a monomer. During the interfacial polymerization stage, the amine groups of the disulfide-bonded cross-linking agent undergo an amidation reaction with acyl chloride (-NH2+-COCl→-CONH-+HCl), embedding the disulfide bonds as "spacer units" into the polyamide molecular chain. In the post-treatment stage, the molecular chain is further regularized, and the disulfide bonds are uniformly distributed in the polyamide matrix, forming a cross-linked structure of "polyamide backbone tandem disulfide bonds." The dynamic reversibility of the disulfide bonds does not affect the hydrophilicity and selectivity of the polyamide and provides reversible sites for subsequent repair.

[0016] Disulfide bond repair mechanism: Heating triggers bond breaking: The bond energy of a disulfide bond is about 25-35 kJ / mol. Heating at 60-80℃ causes the disulfide bond near the crack to break, generating two active thiol groups. The breaking reaction is: -SS-→2-SH. Oxidation-driven bond recombination: Thiol groups have strong reducing properties and spontaneously oxidize to reform disulfide bonds (2-SH→-SS-+H2) under the influence of trace amounts of oxygen on the membrane surface or dissolved oxygen in water, filling cracks. This process does not require additional oxidants, as the trace amounts of oxygen in the membrane operating environment are sufficient to trigger the oxidation reaction, further simplifying the operation.

[0017] This invention also provides an application of the temperature-responsive dynamic covalent bond in-situ self-healing composite nanofiltration membrane prepared by the above preparation method, wherein the composite nanofiltration membrane is used in the fields of water treatment and solution system separation; the water treatment includes seawater desalination and industrial wastewater purification; the solution system separation includes separation of small or large organic molecules and dye removal.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By constructing a dynamic covalent cross-linked network, in-situ efficient repair without pH adjustment is achieved, significantly simplifying the operation process. This invention innovatively introduces imine or disulfide bonds into the polyamide matrix, forming a temperature-responsive dynamic cross-linked network. During repair, only gentle heating to 60-80℃ by introducing hot water or heating the membrane module is needed to trigger the breaking and recombination of dynamic covalent bonds, spontaneously filling cracks or scratches on the membrane surface. Unlike β-cyclodextrin repair systems that require precise pH control of 7-9, this method does not require additional pH adjustment, avoiding interference from pH fluctuations on membrane chemical stability and water treatment processes. Furthermore, it eliminates the need to disassemble the membrane module, shortening the repair time to 20-40 minutes. It can be directly adapted to existing membrane system operating procedures, effectively avoiding process interruptions caused by repair and significantly reducing operating costs.

[0019] 2. By optimizing the dynamic bond type and distribution, a dual guarantee of high repair efficiency and long-term cycling stability is achieved. Targeting the characteristics of imine and disulfide bonds, this invention ensures that dynamic covalent bonds are uniformly dispersed in the polyamide matrix through precise control of the crosslinking agent dosage and interfacial polymerization process. This design enables the membrane's repair efficiency to be ≥90%, and the separation performance to recover to over 90% of the level of a new membrane. After five "damage-repair" cycles, the Congo red rejection rate remains above 95%, far superior to the cycling stability of the β-cyclodextrin system, significantly extending the actual service life of the membrane.

[0020] 3. The cross-linking effect of dynamic covalent bonds significantly improves the mechanical properties and damage resistance of the membrane. Dynamic covalent bonds form stable cross-linking sites between polyamide molecular chains, effectively enhancing the bonding force between the chains. This results in an elastic modulus of 2.7-2.9 GPa, more than 40% higher than the 2.0 GPa of the β-cyclodextrin system and more than 80% higher than ordinary polyamide membranes without cross-linking agents. The optimized mechanical properties give the membrane stronger resistance to mechanical friction and pressure fluctuations, enabling it to adapt to complex operating environments in industrial settings and further extending the replacement cycle of membrane modules.

[0021] 4. By precisely controlling reaction priority and process parameters, the core separation performance of the membrane is ensured to remain unaffected. This invention employs a step-by-step strategy of "mild preparation of aqueous solution at 20-30℃ + preferential formation of polyamide backbone through interfacial polymerization + deep construction of cross-linked network through post-treatment," ensuring that the introduction of dynamic covalent bonds does not damage the separation properties of the polyamide. The new membrane exhibits a Congo red rejection rate ≥98%, and a stable water flux of 27-29 L / (m²). 2 The membrane separation performance fully meets the requirements of industrial applications such as dyeing and printing wastewater treatment and fine chemical separation; compared with the membrane densification problem caused by excessive crosslinking agent, the water flux of Comparative Example 4 is only 22.1 L / (m²). 2 The process parameters optimized in this invention achieve a perfect balance between "repair function and separation performance".

[0022] 5. With compatibility with existing processes and low-cost raw materials, this invention possesses strong potential for industrial-scale mass production. The preparation process of this invention is fully compatible with existing interfacial polymerization technology for polyamide nanofiltration membranes, requiring no additional specialized equipment. The unit price of the crosslinking agents used is all below 50 RMB / kg, making raw material costs controllable. β-Cyclodextrin, as a supramolecular reagent, typically costs approximately 80-120 RMB / kg in the industry, far exceeding the crosslinking agent of this invention, and requires the addition of a pH adjuster. It can be estimated that the raw material cost of this invention is 20%-40% lower than that of the β-cyclodextrin system, with no additional auxiliary reagent consumption, resulting in significantly better raw material economy. Furthermore, the membrane is compatible with various base membranes such as polysulfone and polypropylene, making it suitable for seawater desalination, industrial wastewater purification, and the separation of small organic molecules, among other fields. It has a wide range of application scenarios and the feasibility of large-scale production, providing an economical and efficient solution for upgrading the performance of industrial membranes. Attached Figure Description

[0023] Figure 1 The image shows a scanning electron microscope (SEM) image of the surface of the composite nanofiltration membrane prepared in Example 1. Figure 2 This is a cross-sectional SEM image of the composite nanofiltration membrane prepared in Example 1; Figure 3 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the composite nanofiltration membrane prepared in Example 1. Detailed Implementation

[0024] The present invention will be described in detail below with reference to embodiments and comparative examples, but the present invention is not limited thereto. The embodiments and comparative examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Example 1

[0025] (1) Dissolve 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, add 0.2g of glutaraldehyde, stir at 25℃ for 40min to obtain an aqueous solution; (2) Dissolve 0.1 g of trimesoyl chloride in 99.9 g of n-hexane and disperse by ultrasonication for 12 min to obtain a 0.1 wt% oil phase solution; (3) Immerse a polysulfone ultrafiltration membrane with a diameter of 47 mm, a thickness of 120 μm, and a molecular weight cutoff of 30 kDa in an aqueous solution for 2 min. After taking it out, use a dust-free filter paper to dry the surface solution. Keep the temperature at 25 °C and immediately immerse it in an oil solution for 2 min to form a membrane containing a polyamide matrix and dynamic covalent bonds. (4) The membrane containing polyamide matrix and dynamic covalent bond obtained in step (3) is placed in a 70℃ forced-air drying oven and dried for 1.5h, and then cooled to room temperature to obtain a composite nanofiltration membrane with in-situ self-healing dynamic covalent bond based on temperature response. Example 2

[0026] (1) Dissolve 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, add 0.3g of 3,3'-dithiodipropylamine, stir to obtain an aqueous solution; (2) Dissolve 0.1 g of trimesoyl chloride in 99.9 g of n-hexane and disperse by ultrasonication for 12 min to obtain a 0.1 wt% oil phase solution; (3) Immerse a polysulfone ultrafiltration membrane with a diameter of 47 mm, a thickness of 120 μm, and a molecular weight cutoff of 30 kDa in an aqueous solution for 2.5 min. After taking it out, use a dust-free filter paper to dry the surface solution. Keep the temperature at 25 °C and immediately immerse it in an oil solution for 3 min to form a membrane containing a polyamide matrix and dynamic covalent bonds. (4) The membrane containing polyamide matrix and dynamic covalent bond obtained in step (3) is placed in a 75°C forced-air drying oven and dried for 1 hour, and then cooled to room temperature to obtain a composite nanofiltration membrane with in-situ self-healing dynamic covalent bond based on temperature response. Example 3

[0027] (1) Dissolve 1.5g of m-phenylenediamine in 98.5g of deionized water to obtain a 1.5wt% m-phenylenediamine solution, add 0.12g of glyoxal, stir at 28℃ for 35min to obtain an aqueous solution; (2) Dissolve 0.08 g of trimesoyl chloride in 99.92 g of n-hexane and disperse by ultrasonication for 14 min to obtain a 0.08 wt% oil phase solution; (3) Immerse a polypropylene microporous membrane with a diameter of 47 mm, a thickness of 100 μm, and a porosity of 50% in an aqueous solution for 2.5 min. After taking it out, use a dust-free filter paper to dry the surface solution. Keep the temperature at 28℃ and immediately immerse it in an oil solution for 2.5 min to form a membrane containing a polyamide matrix and dynamic covalent bonds. (4) The membrane containing polyamide matrix and dynamic covalent bond obtained in step (3) is placed in a 75°C forced-air drying oven and dried for 1.2 h, and then cooled to room temperature to obtain a composite nanofiltration membrane with in-situ self-healing dynamic covalent bond based on temperature response. Example 4

[0028] (1) Dissolve 2.5g of m-phenylenediamine in 97.5g of deionized water to obtain a 2.5wt% m-phenylenediamine solution, add 0.3g of 2,2'-dithiodimethyldiethylamine, stir, and obtain an aqueous solution; (2) 0.15 g of pyromellitic chloride was dissolved in 99.85 g of n-hexane and ultrasonically dispersed for 11 min to obtain a 0.15 wt% oil phase solution; (3) Immerse the polysulfone ultrafiltration membrane with a molecular weight cutoff of 50 kDa in an aqueous solution for 3 min, remove it and blot the surface solution with dust-free filter paper; keep it at a constant temperature of 22℃ and immediately immerse it in an oil solution for 4 min to form a membrane containing a polyamide matrix and dynamic covalent bonds. (4) The membrane containing polyamide matrix and dynamic covalent bond obtained in step (3) is placed in a 65°C forced-air drying oven and dried for 2 hours, and then cooled to room temperature to obtain a composite nanofiltration membrane with in-situ self-healing dynamic covalent bond based on temperature response. Comparative Example 1

[0029] This comparative example is the β-cyclodextrin repair system.

[0030] The difference from Example 1 is that step (1) uses β-cyclodextrin instead of glutaraldehyde.

[0031] Step (1) involves dissolving 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, adding 0.2g of β-cyclodextrin, adjusting the pH to 8.0, and stirring at 25℃ for 40min to obtain an aqueous solution.

[0032] Everything else is the same as the process in Example 1. Comparative Example 2

[0033] The difference between this comparative example and Example 1 is that glutaraldehyde is not added.

[0034] Step (1) involves dissolving 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, stirring at 25°C for 40 minutes to obtain an aqueous solution.

[0035] Everything else is the same as the process in Example 1. Comparative Example 3

[0036] The difference between this comparative example and Example 1 is that the amount of glutaraldehyde added is 0.06g.

[0037] Step (1) involves dissolving 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, adding 0.06g of glutaraldehyde, and stirring at 25℃ for 40min to obtain an aqueous solution.

[0038] Everything else is the same as the process in Example 1. Comparative Example 4

[0039] The difference between this comparative example and Example 1 is that the amount of glutaraldehyde added is 0.4g.

[0040] Step (1) involves dissolving 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, adding 0.4g of glutaraldehyde, stirring at 25℃ for 40min to obtain an aqueous solution. The solution is slightly yellow because the excess glutaraldehyde did not react completely.

[0041] Everything else is the same as the process in Example 1. Comparative Example 5

[0042] The difference between this comparative example and Example 1 is that the aqueous solution was prepared at a temperature of 45°C.

[0043] Step (1) involves dissolving 2g of m-phenylenediamine in 98g of deionized water to obtain a 2wt% m-phenylenediamine solution, adding 0.2g of glutaraldehyde, stirring at 45℃ for 40min to obtain an aqueous solution. The solution is dark yellow because the aldehyde and amine groups react excessively, generating a large number of prematurely cross-linked aggregates.

[0044] Everything else is the same as the process in Example 1. Application examples

[0045] The composite nanofiltration membranes prepared using the above examples and comparative examples were tested. The test steps were as follows: (1) Test the water flux, dye rejection rate and elastic modulus of the composite nanofiltration membranes prepared in Examples 1-3 and Comparative Examples 1-4.

[0046] (2) Artificially create 0.4-0.7μm cracks and test the water flux and dye rejection rate of the composite nanofiltration membrane after damage.

[0047] (3) Place the membrane in an environment of 60-80℃ and heat for 20-40 minutes or change the pH of the solution to achieve in-situ self-repair of membrane damage. Test the water flux and dye rejection rate of the composite nanofiltration membrane after repair and calculate the repair efficiency.

[0048] (4) Repeat steps (2)-(3) above on the composite nanofiltration membrane of Example 1 to perform a “damage-repair” cycle test.

[0049] The specific parameters and related calculation formulas are as follows: Water flux test: 0.6MPa operating pressure, 25℃, deionized water, test for 30 minutes and take the average value; Retention rate test: 100 mg / L Congo red solution, 0.6 MPa, 25℃, high performance liquid chromatography to determine the concentration of the permeate; Elastic modulus test: universal tensile testing machine, tensile rate 1 mm / min, sample size 10 mm × 50 mm; Water flux recovery rate calculation: (Water flux after repair - Water flux after damage) / (Water flux of new membrane - Water flux after damage) × 100%; Repair efficiency calculation: (Retention rate after repair - Retention rate after damage) / (Retention rate of new membrane - Retention rate after damage) × 100%.

[0050]

[0051]

[0052]

[0053] Table 1 shows the performance test results of the composite nanofiltration membrane without damage. The comparison between the examples and comparative examples directly confirms that the initial performance of the composite nanofiltration membrane prepared by this invention fully meets the standards and satisfies industrial requirements. The water flux of the composite nanofiltration membranes prepared in Examples 1-4 of this invention is consistently between 27.1-28.5 L / (m²). 2 (h) The membrane is within the high rejection-suitable flux balance range for industrial applications; the dye rejection rate is consistently between 98.1% and 98.6%, all ≥98%, far exceeding the basic requirement of ≥95% dye rejection rate for industrial nanofiltration membranes; the elastic modulus reaches 2.7-2.9 GPa, more than 40% higher than the β-cyclodextrin system of Comparative Example 1, fully meeting the index of superior mechanical properties compared to the β-cyclodextrin system. Dynamic covalent bonds form uniform cross-linking sites between molecular chains, enhancing inter-chain bonding and laying the foundation for the membrane's resistance to mechanical damage. Comparative Example 1 has a slightly lower rejection rate and insufficient elastic modulus. Although the water flux is close to that of the example, supramolecular interactions cannot balance rejection, flux, and mechanical properties like dynamic covalent bonds, highlighting the advantages of the dynamic covalent bonds in this invention. Comparative Example 2 has an excellent rejection rate, but its elastic modulus is only 1.5 GPa, resulting in poor mechanical properties, proving that dynamic covalent bonds are the core of mechanical enhancement. Without cross-linking, the membrane is easily damaged and cannot be repaired. Comparative Example 3 showed insufficient crosslinking agent, resulting in sparse crosslinking and slightly larger pores in the separation layer, higher water flux, slightly lower retention rate, and lower elastic modulus. This indicates that a crosslinking agent dosage below 5%-15% leads to a sparse dynamic network and performance imbalance. Comparative Example 4 showed excessive crosslinking agent, resulting in over-densification of the functional layer, lower water flux, and excessively high elastic modulus leading to brittleness. Although the retention rate of 98.0% met the standard, the flux and mechanical brittleness failed to meet industrial requirements, thus validating the scientific validity of the upper limit for crosslinking agent dosage in this invention. Comparative Example 5 showed excessively high aqueous solution temperature, leading to defects in main chain formation and excessively large pores, abnormally high water flux, failure to meet the standard retention rate, and low elastic modulus. This demonstrates that an aqueous solution temperature exceeding 20-30℃ will destroy main chain formation, resulting in a comprehensive deterioration of initial performance, highlighting the necessity of limiting the process temperature in this invention.

[0054] Table 2 shows the performance changes of the membrane after damage and repair. The comparison of repair efficiency and water flux recovery rate confirms that the system of this invention has high repair efficiency and is easy to operate. The composite nanofiltration membranes prepared in Examples 1-4 of this invention, after being repaired by heating at 60-80℃ for 20-40 minutes, showed a repair efficiency of 93.5%-96.3%, all ≥90%, meeting the core indicators of the claims and proving the effective reversibility of the bonds; the water flux recovery rate was 91.2%-94.2%, and the water flux after repair was 28.1-29.5 L / (m²). 2 (h) The return to the new membrane level indicates that the repair not only restores retention but also corrects abnormally high water flux, demonstrating a comprehensive recovery of separation performance. Comparative Example 1 showed lower repair efficiency and water flux recovery rate than the examples, indicating weak supramolecular interaction bond energies, hindering efficient recombination and requiring pH adjustment, making the operation complex and demonstrating the repair advantage of dynamic covalent bonds. The membrane in Comparative Example 2 lacked self-repairing capabilities. In Comparative Example 3, insufficient crosslinking agent resulted in a sparse dynamic network with insufficient recombination sites, incomplete repair, and low membrane repair efficiency, failing to meet requirements. In Comparative Example 4, excessive crosslinking restricted bond breakage and diffusion, preventing the formation of new bonds near cracks, weakening repair ability, and resulting in low repair efficiency. In Comparative Example 5, the excessively high aqueous phase temperature caused the superposition of main chain defects and uneven dynamic network, making it impossible to fill cracks and main chain pores even with heating, resulting in the worst repair effect.

[0055] Table 3 shows the results of the "damage-repair" cycle test of the membrane in Example 1, verifying that the membrane prepared by the system of the present invention has excellent cycle stability, which can reduce the frequency of membrane module replacement during use, thereby reducing replacement costs and process interruption losses. After 5 "damage-repair" cycle tests, the repair efficiency of the composite nanofiltration membrane in Example 1 steadily decreased from 96.3% to 95.2% without significant decay. This characteristic indicates that the reversible activity of dynamic covalent bonds can be stably maintained during long-term use, enabling continuous damage repair, significantly extending the service life of the membrane, and reducing replacement costs in industrial applications.

[0056] Depend on Figure 1 It can be observed that the membrane surface prepared in Example 1 exhibits a continuous, smooth, and dense structure, without any visible voids, protrusions, or localized agglomerations. This characteristic stems from the synergistic control of gentle stirring at 20-30°C during the aqueous phase preparation stage and the isothermal reaction at 25°C during the interfacial polymerization stage. The gentle conditions ensure that the aldehyde-containing crosslinking agent and the aromatic diamine only undergo a preliminary Schiff base reaction, preventing premature formation of crosslinked clusters. In the subsequent interfacial polymerization, the amine groups preferentially react with the acyl chloride to form a regular polyamide backbone. The drying at 60-80°C during the post-treatment stage further ensures the uniform distribution of imine bonds, ultimately forming a surface structure with a continuous backbone and uniform crosslinking. This smooth and dense surface is key to the membrane's high rejection rate. Congo red cannot penetrate the dense functional layer, hence the new membrane in Example 1 achieves a rejection rate of 98.6%, confirming the direct correlation between surface structure and separation performance.

[0057] Depend on Figure 2 A magnified view of the cross section reveals that the membrane consists of a functional layer and a support layer. The thickness of the functional layer is about 70-80 nm, which is within the optimal thickness range of 50-100 nm. This thickness ensures both compactness and high rejection rate, without causing a decrease in water flux due to excessive thickness. There are no obvious gaps or peeling phenomena at the interface between the functional layer and the support layer, and the bonding is firm.

[0058] Depend on Figure 3 The XPS full spectrum clearly shows that the main elements on the membrane surface are C, N, and O, with no other impurity elements or impurity peaks, proving that there are no unreacted monomer residues during the membrane preparation process. The post-treatment can effectively remove residual solvents and impurities, further confirming the rationality of the post-treatment process design for stabilizing the membrane structure in this invention. The high-resolution C1s spectrum shows that the 284.8 eV peak corresponds to saturated carbon, mainly originating from the methylene group of the polyamide backbone and the alkyl chain of glutaraldehyde; the 286.2 eV peak corresponds to nitrogen-containing carbon, originating from the amide bond of the polyamide, and is a characteristic peak of the polyamide matrix, proving that the backbone was successfully formed; the 287.8 eV peak corresponds to double-bonded carbon, -C=O / C=N, with the -C=O peak of the polyamide bond near 287.2 eV and the -C=N peak of the imine bond near 287.8 eV. The appearance of the -C=N peak is crucial, directly proving that glutaraldehyde and the amino group of m-phenylenediamine undergo a Schiff base reaction, and the imine bond is successfully introduced into the polyamide matrix. Moreover, the peak shape is symmetrical and without shift, indicating that the chemical environment of the imine bond is uniform and the crosslinking network is well-distributed.

[0059] The specific embodiments described above provide a further detailed explanation of the present invention; however, these descriptions should not be construed as limiting the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane, comprising a support layer and a functional layer, characterized in that, The functional layer is a cross-linked network containing dynamic covalent bonds formed by the reaction of aromatic diamine, cross-linking agent, and trimesoyl chloride; the dynamic covalent bonds are imine bonds or disulfide bonds; The imine bond is formed by the reaction of an aldehyde-containing crosslinking agent with an aromatic diamine and pyromellitic acid chloride in a polyamide matrix; The disulfide bond is introduced by copolymerizing a crosslinking agent containing disulfide bonds with amino groups at both ends and an aromatic diamine as a reactive monomer with pyromellitic trimethylol chloride to form a crosslinking network. The composite nanofiltration membrane can self-repair under heating conditions of 60-80℃.

2. A method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane as described in claim 1, characterized in that, Includes the following steps: (1) Dissolve the aromatic diamine in deionized water to obtain an aromatic diamine solution, add a dynamic covalent crosslinking agent, stir, and obtain an aqueous solution; (2) Dissolve pyromellitic chloride in an organic solvent to obtain an oil phase solution; (3) Immerse the base film in the aqueous solution of step (1), take it out and drain the excess solution on the surface, and then immerse it in the oil solution of step (2). An interfacial polymerization reaction occurs on the surface of the base film to form a film containing a polyamide matrix and dynamic covalent bonds. (4) The membrane obtained in step (3) is dried at 60-80℃ for 1-2 hours and cooled to room temperature to obtain a composite nanofiltration membrane with dynamic covalent bond in situ self-healing based on temperature response.

3. The method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane according to claim 2, characterized in that, In step (1), the aromatic diamine is m-phenylenediamine or p-phenylenediamine; the mass concentration of the aromatic diamine solution is 1%-3%.

4. The method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane according to claim 2, characterized in that, In step (1), the dynamic covalent crosslinking agent is an aldehyde-containing crosslinking agent or a disulfide-containing crosslinking agent with amine groups at both ends.

5. The method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane according to claim 4, characterized in that, The aldehyde-containing crosslinking agent is glutaraldehyde or glyoxal; in step (1), the stirring conditions are 20-30℃ and stirring for 30-60 min; the crosslinking agent containing disulfide bonds with amine groups at both ends is 3,3'-dithiodipropylamine or 2,2'-dithiodimethyldiethylamine.

6. The method for preparing a temperature-responsive, dynamically covalently bonded in-situ self-healing composite nanofiltration membrane according to claim 4, characterized in that, The amount of the aldehyde-containing crosslinking agent is 5%-15% of the mass of the aromatic diamine; the amount of the crosslinking agent containing disulfide bonds with amino groups at both ends is 8%-20% of the mass of the aromatic diamine.

7. The method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane according to claim 2, characterized in that, In step (2), the organic solvent is n-hexane or cyclohexane; the mass concentration of the trimesoyl chloride is 0.05%-0.2%.

8. The method for preparing a temperature-responsive, dynamically covalently bonded, in-situ self-healing composite nanofiltration membrane according to claim 2, characterized in that, In step (3), the base membrane is a polysulfone ultrafiltration membrane or a polypropylene microporous membrane; the interfacial polymerization reaction temperature is 20-30℃.

9. A method for repairing a composite nanofiltration membrane based on temperature response and dynamic covalent bond in-situ self-healing as described in any one of claims 1-8, characterized in that, When cracks or scratches appear on the membrane surface, the membrane is heated in an environment of 60-80℃ for 20-40 minutes to trigger the breaking and recombination of dynamic covalent bonds, thereby achieving in-situ self-repair of membrane damage.

10. An application of the temperature-responsive dynamic covalent bond in-situ self-healing composite nanofiltration membrane as described in claim 1, characterized in that, The composite nanofiltration membrane is used in water treatment and solution system separation; the water treatment includes seawater desalination and industrial wastewater purification; the solution system separation includes separation of small or large organic molecules and dye removal.

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