Multifunctional nanofiltration membrane, preparation method and application thereof

Abstract

The application provides a multifunctional nanofiltration membrane and a preparation method and application thereof, and the preparation method comprises the following steps: first, preparing a hydrophilic polydopamine oxidation layer on a polyamide nanofiltration membrane; then, grafting a PHFBM self-cleaning layer with low surface energy on the polydopamine layer; then, grafting a PMTAC layer with sterilization performance on the PHFBM layer; finally, grafting a zwitterionic polymer PSBMA layer with a defense function on the PMTAC layer, so as to obtain a multifunctional nanofiltration membrane with the functions of defense, resistance and self-cleaning. The multifunctional nanofiltration membrane prepared by the application can effectively improve the pollution phenomenon of microorganisms by the defense of the hydrophilic material and the sterilization effect of the quaternary ammonium salt while maintaining the advantage of high water flux, and the low surface energy material can make dead cells and extracellular polymers automatically fall off from the membrane surface under low shear force, so that the effect of self-cleaning is realized.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane technology, specifically relating to a multifunctional nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Membrane filtration is an effective method for separating large numbers of highly active microorganisms and nutrients. However, this also makes the membrane surface highly susceptible to biofouling, leading to a reduction in membrane flux and lifespan. When nanofiltration membranes are used for reclaimed water production, the secondary effluent to be treated is complex in quality, has low salinity, and contains a large number of highly active microorganisms and abundant nutrients. These microorganisms are enriched during the membrane filtration process, making the membrane surface highly susceptible to biofouling. This results in a series of problems, including reduced water flux, increased effluent salinity, increased operating energy consumption, and a sharp decline in the water production efficiency of the nanofiltration system. The main factors contributing to membrane fouling are: the inherent properties of the membrane, the properties of the mixed liquor, and the system operating environment. Controlling and resolving membrane fouling should involve corresponding measures from these three aspects.

[0003] Compared to other membrane fouling control strategies based on operational processes, membrane material modification can more directly affect the interfacial interaction between the membrane surface and pollutants, inhibiting the formation and development of biofouling layers at the source. It also alleviates pretreatment and membrane cleaning stress, reduces chemical reagent usage, and minimizes process byproducts, making it a necessary strategy for membrane biofouling prevention. Traditional anti-biofouling membrane modification strategies mainly fall into two categories: one involves introducing substances with hydrophilicity, electroneutrality, hydrogen bond acceptors, and no hydrogen bond donors to construct a hydrophilic membrane surface, establishing a "defense" mechanism—forming a dense hydration layer or steric hindrance effect on the membrane surface to reduce non-specific adsorption of pollutants and prevent their deposition; the other involves introducing antibacterial substances to construct an antibacterial membrane surface, establishing an active "resistance" mechanism—killing bacteria or inhibiting bacterial growth, thus cutting off the pathways of biofouling. Both passive "defense" mechanisms and active "resistance" antibacterial mechanisms can mitigate biofouling to some extent, but a single mechanism cannot simultaneously possess antibacterial and anti-adhesion properties, limiting its effectiveness in addressing biofouling problems under long-term, complex operating conditions.

[0004] How to effectively reduce the adhesion strength of pollutants on the membrane surface, and transform the biofouling layer that is inevitably formed due to complex wastewater composition and long-term filtration from being difficult to remove to being easy to remove, has become another important strategy for membrane material modification. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multifunctional nanofiltration membrane, its preparation method and application, so as to solve the technical problems of poor antifouling performance of nanofiltration membrane and difficulty in removing biological fouling layer.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a multifunctional nanofiltration membrane is provided, which comprises, from bottom to top: a base membrane, a polydopamine oxide layer, a fluoride self-cleaning layer, a quaternary ammonium salt bactericidal layer, and an amphoteric ion defense layer.

[0007] This invention also discloses a method for preparing a multifunctional nanofiltration membrane, comprising the following steps:

[0008] S1: Pretreatment of the base film: Immerse the base film in a 25-35 wt% isopropanol solution for 30-45 min, then rinse with a cleaning solution for 10-20 min, and then immerse it in the cleaning solution for 4-6 h.

[0009] S2: Preparation of polydopamine oxide layer: At room temperature, the active layer of the base film treated in step S1 is placed in reaction solution A and shaken to react. Then, the base film is rinsed with cleaning solution for 10-20 min to obtain a base film with a polydopamine oxide layer. Reaction solution A is a mixture of N,N-dimethylformamide, dopamine hydrochloride, and a 0.4-0.5 g / mL solution of tris(hydroxymethyl)aminomethane in a ratio of 15-25 mL: 0.3-0.5 g: 90-110 mL.

[0010] S3: Preparation of the fluoride self-cleaning layer: Dissolve hexafluorobutyl methacrylate in a 45-55 wt% isopropanol solution and remove oxygen from the solution. Then, add the base film obtained in step S2 and reaction solution B sequentially. Under dark conditions, purge with nitrogen for 10-30 min. Then, add a reducing agent and continue the reaction for 1-2 h. Finally, rinse the base film with a cleaning solution for 10-20 min to obtain a base film with a fluoride self-cleaning layer. Reaction solution B is a mixture of ligand, catalyst, and 50 wt% isopropanol solution in a ratio of 0.05-0.09 g: 0.005-0.008 g: 5-10 mL. The ratio of hexafluorobutyl methacrylate, 45-55 wt% isopropanol solution, reaction solution B, and reducing agent is 1-2 g: 180-220 mL: 5-10 mL: 10-15 mL.

[0011] S4: Preparation of the quaternary ammonium salt sterilization layer: Dissolve methacryloyloxyethyltrimethylammonium chloride in a 45-55wt% isopropanol solution and remove oxygen from the solution. Then, add the base film obtained in step S3 and reaction solution B in sequence. Under dark conditions, remove the film with nitrogen gas for 10-30 min. Then, add a reducing agent and continue the reaction for 22-26 h. Finally, rinse the base film with a washing solution for 10-20 min to obtain a base film with a quaternary ammonium salt sterilization layer. The ratio of methacryloyloxyethyltrimethylammonium chloride, 45-55wt% isopropanol solution, reaction solution B and reducing agent is 13-16g: 180-220mL: 5-10mL: 10-15mL.

[0012] S5: Preparation of zwitterion defense layer: Dissolve [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 45-55wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S4 and reaction solution B in sequence. Under dark conditions, purge with nitrogen for 10-30 min. Then, add reducing agent and continue the reaction for 1-2 h. Finally, rinse the base membrane with washing solution for 10-20 min to prepare a multifunctional nanofiltration membrane. The ratio of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, 45-55wt% isopropanol solution, reaction solution B and reducing agent is 13-16g: 180-220mL: 5-10mL: 10-15mL.

[0013] The modification method employed in this invention is ARGET-ATRP. In an aerobic environment, dopamine is dissolved in a buffer solution and reacted at room temperature. Dopamine undergoes self-oxidative polymerization to generate a dark brown polydopamine, which adheres tightly to the base film through hydrogen bonds or π-π bonds, while simultaneously fixing the initiator to the base film surface. Atom transfer radical polymerization enables uniform chain growth to obtain low-dispersion polymers, primarily relying on the transition metal catalyst. The catalyst creates an equilibrium between the actively growing polymer chains and the dormant, inactive polymer chains. Because the dormant polymers are more dominant in this equilibrium, the concentration of active species is reduced, thereby effectively suppressing side reactions. Furthermore, this equilibrium reduces the concentration of free radicals in the system, inhibiting premature chain termination reactions (bimolecular termination) and achieving the goal of controlling the polymer molecular weight.

[0014] Based on the above technical solution, the present invention can be further improved as follows:

[0015] Furthermore, the cleaning solution is distilled water.

[0016] Furthermore, reaction solution A is a mixture of N,N-dimethylformamide, dopamine hydrochloride, and a 0.45 g / mL solution of tris(hydroxymethyl)aminomethane in a ratio of 20 mL: 0.4 g: 100 mL.

[0017] Furthermore, in step S2, the oscillation speed is 40-50 r / min, and the oscillation reaction time is 20-30 min.

[0018] Furthermore, reaction solution B is a mixture of ligand, catalyst and 50wt% isopropanol solution in a ratio of 0.07g:0.0063g:10mL.

[0019] Furthermore, the ligand is tris(2-pyridinemethyl)amine, and the catalyst is CuCl2.

[0020] Furthermore, the reducing agent is a mixture of ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

[0021] Furthermore, the ratio of hexafluorobutyl methacrylate, methacryloyloxyethyltrimethylammonium chloride, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, 45-55wt% isopropanol solution, reaction solution B and reducing agent is 1g:15.64g:15.64g:200mL:8mL:12mL.

[0022] This invention also discloses the application of a multifunctional nanofiltration membrane in wastewater treatment.

[0023] The present invention has the following beneficial effects:

[0024] 1. This invention effectively improves microbial contamination through the defense of hydrophilic materials and the bactericidal effect of quaternary ammonium salts. Furthermore, the low surface energy material allows dead cells and extracellular polymers to automatically detach from the membrane surface, achieving a self-cleaning effect. At the same time, the resulting multifunctional nanofiltration membrane has high pure water flux and high salt removal rate.

[0025] 2. Compared with traditional modification methods, this invention has the advantages of controllable activity, mild reaction conditions, wide range of applicable monomers, low preparation cost, easy industrialization, and no environmental pollution. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention;

[0027] Figure 2 This is a schematic diagram of the pure water flux decay of the multifunctional nanofiltration membrane prepared in Example 1.

[0028] Figure 3 Flux recovery rate (FRR) is the value of the multifunctional nanofiltration membrane prepared in Example 1. Detailed Implementation

[0029] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. Unless otherwise specified in the examples, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are conventional products that can be purchased commercially.

[0030] The base membrane used in the following embodiments is a nanofiltration membrane, model NF270, provided by Dow Chemical Company, USA.

[0031] Example 1:

[0032] A method for preparing a multifunctional nanofiltration membrane, the preparation process is as follows: Figure 1As shown, it includes the following steps:

[0033] S1: Pretreatment of the base membrane: Soak the 10cm×10cm nanofiltration membrane in 30wt% isopropanol solution for 35min, then rinse with distilled water for 15min, and then soak in distilled water for 5h.

[0034] S2: Preparation of polydopamine oxide layer: N,N-dimethylformamide, dopamine hydrochloride and tris(hydroxymethyl)aminomethane solution with a concentration of 0.45 g / mL were mixed at room temperature in a ratio of 20 mL: 0.4 g: 100 mL. The active layer of the base film obtained in step S1 was then placed in the mixture and shaken on a constant temperature shaker at a speed of 45 r / min for 25 min. The base film was then rinsed with distilled water for 15 min to obtain a base film with a polydopamine oxide layer grown on it.

[0035] S3: Preparation of the fluoride self-cleaning layer: 1.5g of hexafluorobutyl methacrylate was dissolved in 200mL of 50wt% isopropanol solution, and the oxygen in the solution was removed. Then, the base film obtained in step S2 and 8mL of reaction solution B were added sequentially. The mixture was stripped with nitrogen for 20min in the dark, followed by the addition of 12mL of reducing agent. The reaction was continued for 1.5h. Finally, the base film was rinsed with distilled water for 15min to obtain a base film with a fluoride self-cleaning layer. Reaction solution B was prepared by mixing tris(2-pyridinemethyl)amine, CuCl2, and 50wt% isopropanol solution in a ratio of 0.07g:0.0063g:10mL. The reducing agent was prepared by mixing ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

[0036] S4: Preparation of quaternary ammonium salt sterilization layer: Dissolve 15.64g of methacryloyloxyethyltrimethylammonium chloride in 200mL of 50wt% isopropanol solution and remove oxygen from the solution. Then, add the base film obtained in step S3 and 8mL of reaction solution B in sequence. Under dark conditions, blow off with nitrogen for 20min. Then add 12mL of reducing agent and continue the reaction for 24h. Finally, rinse the base film with distilled water for 15min to obtain the base film with quaternary ammonium salt sterilization layer.

[0037] S5: Preparation of zwitterion defense layer: Dissolve 15.64 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 200 mL of 50 wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S4 and 200 mL of reaction solution B in sequence. Under dark conditions, strip with nitrogen for 20 min. Then add 12 mL of reducing agent and continue the reaction for 1.5 h. Finally, rinse the base membrane with distilled water for 15 min to prepare a multifunctional nanofiltration membrane.

[0038] The main objective of this embodiment is to improve the biofouling resistance of nanofiltration membranes. By preventing microbial adhesion and sterilization, and simultaneously providing a self-cleaning function, the active layer (i.e., polyamide layer) of existing nanofiltration membranes is surface modified. Through the self-polymerization of dopamine and atom transfer radical polymerization, multifunctional polymers are sequentially grown on the membrane surface, reducing the adsorption and easy removal characteristics of pollutants on the membrane surface, thereby effectively improving the membrane's biofouling resistance.

[0039] This embodiment employs atom transfer radical polymerization modification technology, which is relatively mature and the modification results can be controlled. Simultaneously, the selected fluoride material has low surface energy and weak adhesion; the bactericidal material, quaternary ammonium salt, exhibits good bactericidal properties and is safe, non-toxic, and non-irritating; and the zwitterionic material possesses strong hydration capabilities, effectively resisting bacterial adhesion. Since this embodiment first utilizes dopamine coating on the TFC membrane, and dopamine can undergo an oxidation-crosslinking reaction under dissolved oxygen to form polymeric dopamine that strongly adheres to the surface of solid materials, dopamine can adhere to various surfaces beyond the polyamide of the TFC membrane. Therefore, the method in this embodiment is not only applicable to TFC membranes but also to the antifouling modification of other surfaces.

[0040] Example 2:

[0041] A method for preparing a multifunctional nanofiltration membrane includes the following steps:

[0042] S1: Pretreatment of the base membrane: The nanofiltration membrane with a specification of 10cm×10cm was soaked in 25wt% isopropanol solution for 45min, then rinsed with distilled water for 10min, and then soaked in distilled water for 4h.

[0043] S2: Preparation of polydopamine oxide layer: N,N-dimethylformamide, dopamine hydrochloride and tris(hydroxymethyl)aminomethane solution with a concentration of 0.4 g / mL were mixed at room temperature in a ratio of 25 mL: 0.3 g: 110 mL. The active layer of the base film obtained in step S1 was then placed in the mixture and shaken in a constant temperature shaker at a speed of 40 r / min for 30 min. The base film was then rinsed with distilled water for 10 min to obtain a base film with a polydopamine oxide layer.

[0044] S3: Preparation of the fluoride self-cleaning layer: 1g of hexafluorobutyl methacrylate was dissolved in 180mL of 45wt% isopropanol solution, and the oxygen in the solution was removed. Then, the base film obtained in step S2 and 10mL of reaction solution B were added sequentially. The mixture was stripped with nitrogen for 10min in the dark, followed by the addition of 10mL of reducing agent. The reaction was continued for 2h. Finally, the base film was rinsed with distilled water for 20min to obtain a base film with a fluoride self-cleaning layer. Reaction solution B was prepared by mixing tris(2-pyridinemethyl)amine, CuCl2 and 50wt% isopropanol solution in a ratio of 0.05g:0.008g:5mL. The reducing agent was prepared by mixing ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

[0045] S4: Preparation of quaternary ammonium salt sterilization layer: Dissolve 13g of methacryloyloxyethyltrimethylammonium chloride in 220mL of 45wt% isopropanol solution and remove oxygen from the solution. Then add the base film obtained in step S3 and 5mL of reaction solution B in sequence. Under dark conditions, remove the base film with nitrogen gas for 30min. Then add 10mL of reducing agent and continue the reaction for 22h. Finally, rinse the base film with distilled water for 20min to obtain the base film with quaternary ammonium salt sterilization layer.

[0046] S5: Preparation of zwitterion defense layer: Dissolve 16g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 180mL of 55wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S4 and 220mL of reaction solution B in sequence. Under dark conditions, strip with nitrogen for 10min. Then add 15mL of reducing agent and continue the reaction for 2h. Finally, rinse the base membrane with distilled water for 10min to prepare a multifunctional nanofiltration membrane.

[0047] Example 3:

[0048] A method for preparing a multifunctional nanofiltration membrane includes the following steps:

[0049] S1: Pretreatment of the base membrane: The nanofiltration membrane with a specification of 10cm×10cm was soaked in 35wt% isopropanol solution for 30min, then rinsed with distilled water for 20min, and then soaked in distilled water for 6h.

[0050] S2: Preparation of polydopamine oxide layer: N,N-dimethylformamide, dopamine hydrochloride and tris(hydroxymethyl)aminomethane solution with a concentration of 0.5 g / mL were mixed at room temperature in a ratio of 15 mL: 0.5 g: 90 mL. The active layer of the base film obtained in step S1 was then placed in the mixture and shaken in a constant temperature shaker at a speed of 50 r / min for 20 min. The base film was then rinsed with distilled water for 10 min to obtain a base film with a polydopamine oxide layer.

[0051] S3: Preparation of the fluoride self-cleaning layer: 2g of hexafluorobutyl methacrylate was dissolved in 220mL of 55wt% isopropanol solution, and the oxygen in the solution was removed. Then, the base film obtained in step S2 and 5mL of reaction solution B were added sequentially. The mixture was stripped with nitrogen for 30min in the dark. Then, 10mL of reducing agent was added, and the reaction was continued for 1h. Finally, the base film was rinsed with distilled water for 10min to obtain a base film with a fluoride self-cleaning layer. Reaction solution B was prepared by mixing tris(2-pyridinemethyl)amine, CuCl2, and 50wt% isopropanol solution in a ratio of 0.09g:0.005g:10mL. The reducing agent was prepared by mixing ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

[0052] S4: Preparation of quaternary ammonium salt sterilization layer: Dissolve 16g of methacryloyloxyethyltrimethylammonium chloride in 180mL of 55wt% isopropanol solution and remove oxygen from the solution. Then add the base film obtained in step S3 and 10mL of reaction solution B in sequence. Under dark conditions, remove nitrogen gas for 10min. Then add 15mL of reducing agent and continue the reaction for 26h. Finally, rinse the base film with distilled water for 10min to obtain the base film with quaternary ammonium salt sterilization layer.

[0053] S5: Preparation of zwitterion defense layer: Dissolve 13g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 220mL of 45wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S4 and 180mL of reaction solution B in sequence. Under dark conditions, remove nitrogen gas for 30min. Then add 10mL of reducing agent and continue the reaction for 1h. Finally, rinse the base membrane with distilled water for 20min to prepare a multifunctional nanofiltration membrane.

[0054] Comparative Example 1:

[0055] A method for preparing a multifunctional nanofiltration membrane includes the following steps:

[0056] S1: Preparation of polydopamine oxide layer: N,N-dimethylformamide, dopamine hydrochloride and tris(hydroxymethyl)aminomethane solution with a concentration of 0.45 g / mL were mixed at room temperature in a ratio of 20 mL: 0.4 g: 100 mL. Then, a nanofiltration membrane with a size of 10 cm × 10 cm was placed in the mixture and shaken on a constant temperature shaker at a speed of 45 r / min for 25 min. Then, the base membrane was rinsed with distilled water for 15 min to obtain a base membrane with a polydopamine oxide layer grown on it.

[0057] S2: Preparation of the fluoride self-cleaning layer: 1.5g of hexafluorobutyl methacrylate was dissolved in 200mL of 50wt% isopropanol solution, and the oxygen in the solution was removed. Then, the base film obtained in step S1 and 8mL of reaction solution B were added sequentially. The mixture was stripped with nitrogen for 20min in the dark, followed by the addition of 12mL of reducing agent. The reaction was continued for 1.5h. Finally, the base film was rinsed with distilled water for 15min to obtain a base film with a fluoride self-cleaning layer. Reaction solution B was prepared by mixing tris(2-pyridinemethyl)amine, CuCl2, and 50wt% isopropanol solution in a ratio of 0.07g:0.0063g:10mL. The reducing agent was prepared by mixing ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

[0058] S3: Preparation of quaternary ammonium salt sterilization layer: Dissolve 15.64g of methacryloyloxyethyltrimethylammonium chloride in 200mL of 50wt% isopropanol solution and remove oxygen from the solution. Then, add the base film obtained in step S2 and 8mL of reaction solution B in sequence. Under dark conditions, remove the base film with nitrogen gas for 20min. Then add 12mL of reducing agent and continue the reaction for 24h. Finally, rinse the base film with distilled water for 15min to obtain the base film with quaternary ammonium salt sterilization layer.

[0059] S4: Preparation of zwitterion defense layer: Dissolve 15.64 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 200 mL of 50 wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S3 and 200 mL of reaction solution B in sequence. Under dark conditions, purge with nitrogen for 20 min. Then add 12 mL of reducing agent and continue the reaction for 1.5 h. Finally, rinse the base membrane with distilled water for 15 min to prepare a multifunctional nanofiltration membrane.

[0060] Comparative Example 2:

[0061] A method for preparing a multifunctional nanofiltration membrane includes the following steps:

[0062] S1: Pretreatment of the base membrane: Soak the 10cm×10cm nanofiltration membrane in 30wt% isopropanol solution for 35min, then rinse with distilled water for 15min, and then soak in distilled water for 5h.

[0063] S2: Preparation of polydopamine oxide layer: N,N-dimethylformamide, dopamine hydrochloride and tris(hydroxymethyl)aminomethane solution with a concentration of 0.45 g / mL were mixed at room temperature in a ratio of 20 mL: 0.4 g: 100 mL. The active layer of the base film obtained in step S1 was then placed in the mixture and shaken on a constant temperature shaker at a speed of 45 r / min for 25 min. The base film was then rinsed with distilled water for 15 min to obtain a base film with a polydopamine oxide layer grown on it.

[0064] S3: Preparation of the fluoride self-cleaning layer: 1.5g of hexafluorobutyl methacrylate was dissolved in 200mL of 50wt% isopropanol solution, and the oxygen in the solution was removed. Then, the base film obtained in step S2 and 8mL of reaction solution B were added sequentially. The mixture was stripped with nitrogen for 20min in the dark, followed by the addition of 12mL of reducing agent. The reaction was continued for 1.5h. Finally, the base film was rinsed with distilled water for 15min to obtain a base film with a fluoride self-cleaning layer. Reaction solution B was prepared by mixing tris(2-pyridinemethyl)amine, CuCl2, and 50wt% isopropanol solution in a ratio of 0.07g:0.0063g:10mL. The reducing agent was prepared by mixing ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

[0065] S4: Preparation of zwitterion defense layer: Dissolve 15.64 g of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 200 mL of 50 wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S3 and 200 mL of reaction solution B in sequence. Under dark conditions, purge with nitrogen for 20 min. Then add 12 mL of reducing agent and continue the reaction for 1.5 h. Finally, rinse the base membrane with distilled water for 15 min to prepare a multifunctional nanofiltration membrane.

[0066] Results analysis:

[0067] Figure 2 This is a schematic diagram illustrating the pure water flux decay during the biological pollution treatment process of the multifunctional nanofiltration membrane prepared in Example 1. Figure 3The flux recovery rate (FRR) of the multifunctional nanofiltration membrane prepared in Example 1 after a 20-minute water rinse following a biofouling experiment is shown in the figure. As can be seen from the figure, the original TFC membrane exhibits a rapid decrease in water flux, reaching approximately 32.73% after 6 hours of biofouling development, indicating the most severe biofouling tendency. In contrast, the PHFBM membrane shows a slightly reduced fouling tendency, with a flux decrease of 29.5%, indicating that the introduction of the PHFBM membrane imparts a slight resistance to biofouling. The superhydrophobic properties generated by the fluoropolymer reduce surface energy, thereby inhibiting bacterial adhesion and thus providing some antifouling performance. The low surface energy of the PHFBM membrane segment loosens the interaction between contaminants and the membrane surface, resulting in a higher FRR (91.1%) for the PHFBM membrane compared to Comparative Example 1 (79.1%), demonstrating the self-cleaning ability of the PHFBM membrane. However, the water flux of the PHFBM membrane continues to decrease over time, increasing by only 3.2% compared to the original membrane after 6 hours of contact with contaminants. This may be attributed to the poor durability of fluoropolymers under direct exposure, thus causing the imparted antifouling properties to gradually decline over time. In contrast, the bifunctional PHFBM-PMTAC membrane exhibited a milder water flux decrease of 22.3%, with a reduced fouling tendency, confirming that the antifouling performance was further improved due to the introduction of a contact sterilization mechanism. Furthermore, the flux recovery rate of the PHFBM-PMTAC membrane was further improved to 93.28%, possibly because dead bacteria were more easily removed from the membrane by shear forces. Clearly, the water flux of the PHFBM-PMTAC-PSBMA membrane remained relatively stable throughout the biofouling process, with a flux decrease of 13.8%, compared to 18.9% for the original TFC.

[0068] The flux curves also reveal that the adsorption degree of the PHFBM-PMTAC-PSBMA membrane is significantly reduced in the early stages of biofouling, primarily due to the protective function of the PSBMA brushes. Simultaneously, the PHFBM-PMTAC-PSBMA membrane exhibits a high FRR value of 96.5%. This enhanced antifouling performance is attributed not only to the antifouling properties of the PSBMA segments but also to the antibacterial properties of the PMTAC segments and the fouling release properties of the PHFBM segments. The hydrophilic PSBMA segments form a strong hydration layer through electrostatic interactions, preventing contaminants from contacting the membrane surface. Simultaneously, the PMTAC segments kill bacteria that breach the hydration layer. Finally, the low surface energy of the PHFBM segments allows dead bacteria to be released from the membrane surface. The defensive properties of PSBMA and the aggressive properties of PMTAC protect the self-cleaning properties of the fluoride. Therefore, in crossflow dynamic filtration, the antifouling performance significantly prevents a decrease in water flux; the fouling release properties destabilize contaminant adhesion, further eliminating water flux decline and improving water flux recovery capability.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multifunctional nanofiltration membrane, characterized in that, The multifunctional nanofiltration membrane comprises, from bottom to top: a base membrane, a polydopamine oxide layer, a fluoride self-cleaning layer, a quaternary ammonium salt bactericidal layer, and a zwitterion defense layer; the preparation method of the multifunctional nanofiltration membrane includes the following steps: S1: Pretreatment of the base film: Immerse the base film in a 25-35 wt% isopropanol solution for 30-45 min, then rinse with a cleaning solution for 10-20 min, and then immerse it in the cleaning solution for 4-6 h. S2: Preparation of polydopamine oxide layer: The active layer of the base film treated in step S1 is placed in reaction solution A and shaken to react at room temperature. Then, the base film is rinsed with cleaning solution for 10-20 min to obtain a base film with a polydopamine oxide layer. The reaction solution A is a mixture of N,N-dimethylformamide, dopamine hydrochloride, and a 0.4-0.5 g / mL solution of tris(hydroxymethyl)aminomethane in a ratio of 15-25 mL: 0.3-0.5 g: 90-110 mL. S3: Preparation of the fluoride self-cleaning layer: Dissolve hexafluorobutyl methacrylate in a 45-55 wt% isopropanol solution and remove oxygen from the solution. Then, add the base film obtained in step S2 and reaction solution B sequentially. Under dark conditions, purge with nitrogen for 10-30 min. Then, add a reducing agent and continue the reaction for 1-2 h. Finally, rinse the base film with a cleaning solution for 10-20 min to obtain a base film with a fluoride self-cleaning layer. The reaction solution B is a mixture of ligand, catalyst, and 50 wt% isopropanol solution in a ratio of 0.05-0.09 g: 0.005-0.008 g: 5-10 mL. The ratio of hexafluorobutyl methacrylate, 45-55 wt% isopropanol solution, reaction solution B, and reducing agent is 1-2 g: 180-220 mL: 5-10 mL: 10-15 mL. S4: Preparation of quaternary ammonium salt sterilization layer: Dissolve methacryloyloxyethyltrimethylammonium chloride in 45-55wt% isopropanol solution and remove oxygen from the solution. Then, add the base film obtained in step S3 and reaction solution B in sequence. Under dark conditions, blow off with nitrogen for 10-30 min. Then, add reducing agent and continue the reaction for 22-26 h. Finally, rinse the base film with washing solution for 10-20 min to obtain a base film with a quaternary ammonium salt sterilization layer. The ratio of methacryloyloxyethyltrimethylammonium chloride, 45-55wt% isopropanol solution, reaction solution B and reducing agent is 13-16g: 180-220mL: 5-10mL: 10-15mL. S5: Preparation of zwitterion defense layer: Dissolve [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide in 45-55wt% isopropanol solution and remove oxygen from the solution. Then, add the base membrane obtained in step S4 and reaction solution B in sequence. Under dark conditions, purge with nitrogen for 10-30 min. Then, add reducing agent and continue the reaction for 1-2 h. Finally, rinse the base membrane with washing solution for 10-20 min to obtain the multifunctional nanofiltration membrane. The ratio of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, 45-55wt% isopropanol solution, reaction solution B and reducing agent is 13-16g:180-220mL:5-10mL:10-15mL.

2. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The cleaning solution is distilled water.

3. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The reaction solution A is a mixture of N,N-dimethylformamide, dopamine hydrochloride, and a 0.45 g / mL solution of tris(hydroxymethyl)aminomethane in a ratio of 20 mL: 0.4 g: 100 mL.

4. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The oscillation speed in step S2 is 40-50 r / min, and the oscillation reaction time is 20-30 min.

5. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The reaction solution B is a mixture of ligand, catalyst and 50wt% isopropanol solution in a ratio of 0.07g:0.0063g:10mL.

6. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The ligand is tris(2-pyridinemethyl)amine, and the catalyst is CuCl2.

7. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The reducing agent is a mixture of ascorbic acid and 50wt% isopropanol solution in a ratio of 1g:10mL.

8. The multifunctional nanofiltration membrane according to claim 1, characterized in that: The ratio of hexafluorobutyl methacrylate, methacryloyloxyethyltrimethylammonium chloride, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide, 45-55wt% isopropanol solution, reaction solution B and reducing agent is 1g:15.64g:15.64g:200mL:8mL:12mL.

9. The application of the multifunctional nanofiltration membrane according to claim 1 in wastewater treatment.

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