Enhanced zwitterionic polyelectrolyte modified PES ultrafiltration membrane, its preparation method and application

Abstract

The application belongs to the technical field of organic separation membrane material modification, and particularly discloses a reinforced amphoteric polyelectrolyte modified PES ultrafiltration membrane as well as a preparation method and application thereof. A PES / P(A-D) casting solution is prepared by using a one-pot method, PES is activated by an amphoteric electrolyte, P(A-D) amphoteric polyelectrolyte is grafted to PES in situ, and after film formation, the film is transferred to a solution containing metal Al 3+ for coordination crosslinking to construct a stable network structure, and then phase separation balance in water to obtain a PES / P(A-D)@Al 3+ modified ultrafiltration membrane. The application constructs a multi-synergistic structure of covalent bond-ion bond-metal coordination bond, anchors the hydrophilic component in the membrane matrix stably, significantly improves the hydrophilicity, water flux and anti-fouling performance of the membrane, avoids the loss of the modified component, has excellent long-term running stability, and is suitable for a complex water treatment system.

Description

Technical Field

[0001] This invention belongs to the field of organic separation membrane material modification technology, specifically relating to reinforced amphoteric polyelectrolyte modified PES ultrafiltration membranes, their preparation methods, and applications. Background Technology

[0002] Membrane technology plays a crucial role in modern separation and purification. PES ultrafiltration membranes, with their polymer backbone featuring alternating aromatic rings, ether bonds (-O-), and sulfone groups (-SO2-), possess excellent rigidity and chemical inertness, enabling them to meet the filtration requirements of complex water qualities and harsh environments. Furthermore, PES materials exhibit excellent thermal stability, mechanical strength, and membrane processing performance, making them one of the most widely used membrane materials in water treatment and biological separation systems. However, the lack of hydrophilic functional groups in the PES molecular framework results in a strong intrinsic hydrophobicity of the membrane material. In actual separation processes, this hydrophobic surface readily induces non-specific adsorption of contaminants such as proteins, natural organic matter (NOM), and lipids through hydrophobic interactions, leading to severe membrane pore narrowing, clogging, and fouling of the surface gel layer. This not only causes a sharp increase in transmembrane pressure drop and an irreversible rapid decline in pure water flux, but also leads to problems such as deterioration of wetting properties, high cleaning energy consumption, and shortened separation lifespan in long-term operation.

[0003] Currently, hydrophilic modification strategies for PES ultrafiltration membranes mainly include surface modification and bulk modification. Surface modification involves grafting or coating a hydrophilic polymer layer onto the PES membrane surface to reduce the thermodynamic adhesion tendency of organic matter at the interface. For example, CN116212640A discloses a method for surface modification of polyethersulfone using sulfonation and quaternization reagents to introduce zwitterionic groups onto the membrane surface to improve antifouling properties. However, this traditional surface-modified composite layer exhibits poor stability under the high shear forces and dynamic chemical environments of complex water bodies, and is prone to swelling, aging, and peeling. Furthermore, the improvement in water flux after modification has an upper limit, and the antifouling durability is weak, making it difficult to meet the needs of large-scale continuous production and application.

[0004] For bulk modification, CN117181022A achieves bulk hydrophilicity of the membrane by directly blending hydrophilic nanoparticles and additives such as trimesic acid into the PES casting solution and utilizing the phase inversion process. Although this method is simple and improves the hydrophilicity of the base membrane to some extent, traditional small molecule or inorganic hydrophilic agents are prone to thermodynamic aggregation or loss to the aqueous phase during film formation and operation, resulting in a limited increase in water flux of the modified ultrafiltration membrane. In addition, densification and phase separation defects often sacrifice the original mechanical strength of the PES membrane, and the exploration of the membrane antifouling mechanism is still limited to changes in apparent hydrophilicity and hydrophobicity, lacking in-depth interfacial electrostatic repulsion design.

[0005] Conventional surface grafting and bulk blending modification methods often suffer from mechanical property degradation and instability of the modified layer, making it difficult to achieve a simultaneous leap in water flux and antifouling performance of PES ultrafiltration membranes in practical applications. Therefore, this application proposes an enhanced amphoteric polyelectrolyte-modified PES polyethersulfone ultrafiltration membrane to address the aforementioned problems. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing an enhanced amphoteric polyelectrolyte-modified PES ultrafiltration membrane that is low in cost, convenient in process, simple in operation, and has high water flux and strong antifouling ability.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing an enhanced amphoteric polyelectrolyte-modified PES ultrafiltration membrane includes the following steps: (1) Using the "one-pot method", 2-acrylamide-2-methylpropanesulfonic acid AMPS, diethanolamine DEA, PES, pore-forming agent, initiator and organic solvent are mixed. The mixture is first reacted at 60-90℃ for 1-6 hours, and then reacted at 110-130℃ for 1-4 hours. The reaction solution is degassed to obtain the casting solution. (2) The casting solution is applied to the substrate and then subjected to a coagulation bath to obtain a flat film; (3) The obtained flat sheet membrane is immersed in a metal-containing Al 3+ PES / P(AD)@Al was obtained by soaking in a solution with a concentration range of 0.02-0.05 mol / L for 1-12 hours, followed by equilibration in pure water. 3+ Ultrafiltration membrane.

[0008] Furthermore, in the casting solution obtained in step (1), the molar ratio of AMPS to DEA is 1:0.8-1.2, for example, 1:0.9, 1:1, or 1:1.1.

[0009] Further, in the casting solution obtained in step (1), the mass fraction of PES is 16.5 wt%~18.5 wt%, more preferably 17.0 wt%~17.5 wt%.

[0010] Further, in the casting solution obtained in step (1), the mass fraction of AMPS is 0.8 wt%~1.2 wt%, more preferably 0.9 wt%~1.0 wt%.

[0011] Further, in the casting solution obtained in step (1), the mass fraction of the pore-forming agent is 1.5 wt%~3.5 wt%, more preferably 2.0 wt%~3.0 wt%.

[0012] Furthermore, in the casting solution obtained in step (1), the mass fraction of organic solvent is 78 wt%~82 wt%, more preferably 79 wt%~81 wt%.

[0013] Further, in the casting solution obtained in step (1), the amount of initiator is 0.01% to 0.03% of the molar amount of AMPS, and more preferably 0.015% to 0.02%.

[0014] Further, in step (1), the porogen is selected from one or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polyacrylamide (PAM); the initiator is selected from one of ammonium persulfate (APS), benzoyl peroxide (BPO), and potassium persulfate (KPS); and the organic solvent is selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF).

[0015] Furthermore, in step (1), the mixed solution is first reacted at 60-90℃ for 1-6 hours to carry out polymerization and crosslinking, preferably at 75℃ in an oil bath environment for 5-6 hours.

[0016] Further, in step (1), after the mixed solution polymerization and cross-linking reaction, the temperature is raised to 110~130℃ to carry out the grafting reaction of amphoteric electrolyte activation, preferably at 120℃ with stirring for 3~4 hours.

[0017] Furthermore, in step (1), the temperature of vacuum degassing is 60~80℃, the pressure is -0.08 ~ -0.1 MPa, and the time of vacuum degassing is 30~90 minutes.

[0018] Furthermore, the casting liquid is applied to the glass substrate and leveled.

[0019] Furthermore, the leveling methods include, but are not limited to, scraping, spraying, spinning, and casting.

[0020] In a preferred embodiment, a casting blade can be used to scrape the casting solution on the glass plate into a film at a uniform speed. The casting solution is applied at a speed of 7-8 cm·s. -1 The material is evenly scraped onto the glass plate at a speed of 100~300 μm, preferably 200 μm, and then left to stand in the air for 30 s to level.

[0021] The thickness of the film formed after coagulation in the coagulation bath is generally slightly less than the thickness of the selected scraper. The thickness of the flat sheet membrane is preferably 100~300 μm. This is because a film thickness of less than 100 μm results in poor mechanical properties, while a thickness greater than 300 μm can easily lead to membrane pore collapse and a low equilibrium water flux.

[0022] Furthermore, in step (2), before the coagulation bath treatment, a pre-phase separation treatment is also included: the poor solvent is brought into contact with the surface of the casting liquid in the form of gas phase or microdroplets, so that phase separation occurs on the film surface and multi-segment finger-shaped pores are generated.

[0023] Furthermore, the unsuitable solvent is pure water; the coagulation bath solution is water or a solution containing metallic Al. 3+ The solution, the Al 3+ The concentration range is 0.02-0.05 mol / L.

[0024] The coagulation bath treatment continues until the flat sheet membrane can be easily peeled off the substrate, or until the flat sheet membrane floats to the surface of the water.

[0025] Furthermore, the prephase separation process takes 10s to 200s.

[0026] Furthermore, the pre-phase separation treatment involves pretreating the surface of the casting solution with water vapor in a constant temperature and humidity chamber. The temperature of the chamber is 15-25℃, the humidity is 80%-90%, and the treatment time is 60-120 seconds, which causes phase separation to occur on the membrane surface, resulting in multiple finger-like pores.

[0027] Furthermore, in step (3), the flat sheet membrane is immersed in pure water until phase separation reaches equilibrium. The water equilibrium time is 20-24 hours, and the water is changed every 6-12 hours.

[0028] The second objective of this invention is to provide an enhanced amphoteric polyelectrolyte-modified PES ultrafiltration membrane, which is prepared using the method described above.

[0029] The third objective of this invention is to provide applications for the above-mentioned enhanced amphoteric polyelectrolyte modified PES ultrafiltration membrane, specifically for water purification, food and pharmaceutical separation, concentration and sterilization, liquid filtration in chemical processes, oily wastewater treatment, adsorption materials, anti-adhesion coating materials, and gas filtration materials.

[0030] Traditional hydrophilic modification strategies often suffer from weak interfacial bonding between the modifier and the matrix, leading to easy loss during cleaning and a decline in hydrophilicity and antifouling properties. This invention, PES / P(AD)@Al³, addresses this issue. + Ultrafiltration membranes introduce metallic Al³⁺ + Mediated coordination crosslinking to construct Al³ + The stable coordination network between the sulfonic acid group and the amino group greatly enhances the interfacial interaction between the amphoteric polyelectrolyte and the PES matrix. Relying on this multi-level anchoring mechanism of "covalent bond-ionic bond-metal coordination bond", the functional polymer is locked in the PES matrix network for a long time, fundamentally solving the problem of loss of modified components.

[0031] Furthermore, by utilizing gas-liquid mixing and solvent-induced prephase separation (V-LIPS), undesirable solvents were introduced into the casting solution surface in the form of gaseous phase or microdroplets. This effectively induced the migration of hydrophilic amphoteric polyelectrolytes to the membrane surface, forming a gradient distribution in the PES matrix that is beneficial for antifouling. This V-LIPS process induced delayed phase separation, inhibiting the through-growth of large-sized finger pores, and successfully developing a regular multi-segmented finger pore structure on and inside the membrane. This gradient distribution and regular multi-segmented pore morphology facilitate subsequent immersion in metallic Al³⁺. + This provides excellent mass transfer channel advantages, which is beneficial to Al³ + Uniform diffusion and full penetration within the membrane matrix enable the efficient construction of a metal coordination crosslinking network.

[0032] This application improves the antifouling performance of PES membranes from the perspectives of structural stability, film formation kinetics, and pore morphology control, resulting in multiple synergistic effects. Morphological characterization shows that the membrane exhibits a highly dense and regular multi-segmented pore structure, a thickened active skin layer, and a complete cross-sectional microstructure without obvious phase separation defects, thereby greatly improving the antifouling performance of the PES membrane during multiple cycle separations. The obtained PES membrane exhibits desirable initial water flux and circulating water flux in complex wastewater environments.

[0033] The method for modifying PES polyethersulfone ultrafiltration membranes with enhanced amphoteric polyelectrolytes provided by this invention has a simple and easy-to-control modification process, and the modified flat sheet membrane PES / P(AD)@Al³ is obtained. + It possesses both high water flux and high antifouling performance. In the preparation of its ultrafiltration membrane, reactive leaving unit "anchors" are generated on the aromatic ring of PES pre-activated by introducing negatively charged AMPS into the system. The strong nucleophilicity of the nitrogen atom in the introduced positively charged DEA causes a nucleophilic substitution reaction with the aromatic ring of PES. Further, the AMPS monomer undergoes a free radical polymerization reaction under the action of an initiator to form PAMPS. An amphoteric electrolyte activation reaction grafts DEA onto the PES chain. The oppositely charged DEA and PAMPS form an amphoteric polymer through electrostatic recombination. + It can undergo crosslinking reactions with electrolytes DEA and PAMPS. This will become a common method for preparing reinforced amphoteric polyelectrolyte-modified PES polyethersulfone ultrafiltration membranes.

[0034] Compared with the prior art, the present invention has the following advantages and significant progress: 1) The preparation process of this invention is simple, the production cycle is short, the process conditions are simple, the raw materials are readily available, and the production cost is low; 2) This invention constructs a PES / P(AD)@Al³ structure with a stable bulk modified structure by grafting polyamplifier P(AD) onto the PES molecular chain and then using a metal ion coordination strategy. +Ultrafiltration membranes, with their unique multi-interaction network of "covalent bonds-ionic bonds-metal coordination bonds", exhibit significant advantages in permeability, hydrophilicity, antifouling and antibacterial properties, and have broad application prospects in the field of PES ultrafiltration membranes for water treatment. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the hydrophilic modification principle of the PES polyethersulfone ultrafiltration membrane modified with the enhanced amphoteric polyelectrolyte of this application.

[0036] Figure 2 This is a schematic diagram of the hydrophilic modification preparation process of the PES polyethersulfone ultrafiltration membrane modified with the enhanced amphoteric polyelectrolyte of this application. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] In the following embodiments: The PES powder used for hydrophilic modification was purchased from the Siasco Group, grade 3000P.

[0039] The preparation method of the casting solution of the enhanced amphoteric polyelectrolyte modified polyethersulfone ultrafiltration membrane PES / P(AD) is as follows: PVP, AMPS, APS, DEA and PES are added to 80 g NMP, and the mixture is stirred and reacted in an oil bath at 75℃ for 5 h. Then the temperature is raised to 120℃ and stirred for another 3 h.

[0040] The preparation method of PES polyethersulfone ultrafiltration membrane modified with V-LIPS induced phase separation enhancement is as follows: The obtained casting solution is uniformly scraped onto a glass plate, allowed to stand in air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting solution. After that, it is placed in an Al-containing metal chamber. 3+ Subsequent phase separation is performed in the solution to remove residual unreacted small molecules.

[0041] Example 1 Step 1: Using the "one-pot method," first weigh out 0.0048 mol of AMPS powder, 0.0048 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP. Add 80 g of solvent NMP and stir at 300 rpm for 30 min at room temperature to ensure complete dissolution of the solids. Add thermal initiator APS (0.02% of the AMPS monomer molar) to the system, and then purge the system with nitrogen until the reaction is complete. At this point, raise the temperature to 75°C and continue vigorous stirring for 5 h, then raise the temperature to 120°C and maintain a stirring speed of 300 rpm for another 3 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / P(AD) casting solution.

[0042] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0043] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface. Then, place it in a container containing metallic Al. 3+ Subsequent ionic crosslinking was completed in a 0.025 mol / L solution. After 6 hours, the solution was replaced with deionized water and soaked for 24 hours. The water was then changed every 6 hours thereafter to remove residual unreacted small molecules, resulting in a reinforced amphoteric polyelectrolyte-modified polyethersulfone (PES / P(AD)@Al) after phase separation equilibrium. 3+ Ultrafiltration membrane.

[0044] Example 2 Step 1: Using the "one-pot method," first weigh 0.0043 mol of AMPS powder and 0.0043 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP, and add them to 80 g of solvent NMP. Stir at 300 rpm for 30 min at room temperature using a mechanical stirrer until the solids are completely dissolved in the solvent. Add thermal initiator APS (0.02% of the AMPS monomer molar amount) to the system, and then purge the system with nitrogen until the reaction is complete. Then, raise the temperature to 75℃ and continue vigorous stirring for 5 h, followed by raising the temperature to 120℃ and stirring at 300 rpm for another 3 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / P(AD) casting solution.

[0045] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0046] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface. Then, place it in a container containing metallic Al. 3+ Subsequent ionic crosslinking was completed in a 0.025 mol / L solution. After 6 hours, the solution was replaced with deionized water and soaked for 24 hours. The water was then changed every 6 hours thereafter to remove residual unreacted small molecules, resulting in a reinforced amphoteric polyelectrolyte-modified polyethersulfone (PES / P(AD)@Al) after phase separation equilibrium. 3+ Ultrafiltration membrane.

[0047] Example 3 Step 1: Using the "one-pot method," first weigh 0.0039 mol of AMPS powder and 0.0039 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP, and add them to 80 g of solvent NMP. Stir at 300 rpm for 30 min at room temperature using a mechanical stirrer until the solids are completely dissolved in the solvent. Add thermal initiator APS (0.02% of the molar amount of AMPS monomer) to the system, and then purge the system with nitrogen until the reaction is complete. Then, raise the temperature to 75℃ and continue vigorous stirring for 5 h, followed by raising the temperature to 120℃ and stirring at 300 rpm for another 3 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / P(AD) casting solution.

[0048] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0049] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface. Then, place it in a container containing metallic Al. 3+ Subsequent ionic crosslinking was completed in a 0.025 mol / L solution. After 6 hours, the solution was replaced with deionized water and soaked for 24 hours. The water was then changed every 6 hours thereafter to remove residual unreacted small molecules, resulting in a reinforced amphoteric polyelectrolyte-modified polyethersulfone (PES / P(AD)@Al) after phase separation equilibrium. 3+ Ultrafiltration membrane.

[0050] Example 4 Step 1: Using the "one-pot method," first weigh 0.0048 mol of AMPS powder, 0.0043 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP, and add them to 80 g of solvent NMP. Stir at 300 rpm for 30 min at room temperature using a mechanical stirrer until the solids are completely dissolved in the solvent. Add thermal initiator APS (0.02% of the AMPS monomer molar amount) to the system, and then purge the system with nitrogen gas until the reaction is complete. Then, raise the temperature to 75℃ and continue vigorous stirring for 5 h, followed by raising the temperature to 120℃ and stirring at 300 rpm for another 3 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / P(AD) casting solution.

[0051] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0052] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface. Then, place it in a container containing metallic Al. 3+ Subsequent ionic crosslinking was completed in a 0.025 mol / L solution. After 6 hours, the solution was replaced with deionized water and soaked for 24 hours. The water was then changed every 6 hours thereafter to remove residual unreacted small molecules, resulting in a reinforced amphoteric polyelectrolyte-modified polyethersulfone (PES / P(AD)@Al) after phase separation equilibrium. 3+ Ultrafiltration membrane.

[0053] Example 5 Step 1: Using the "one-pot method," first weigh 0.0043 mol of AMPS powder, 0.0048 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP, and add them to 80 g of solvent NMP. Stir at 300 rpm for 30 min at room temperature using a mechanical stirrer until the solids are completely dissolved in the solvent. Add thermal initiator APS (0.02% of the AMPS monomer molar amount) to the system, and then purge the system with nitrogen until the reaction is complete. Then, raise the temperature to 75°C and continue vigorous stirring for 5 h, followed by raising the temperature to 120°C and stirring at 300 rpm for another 3 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / P(AD) casting solution.

[0054] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0055] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface. Then, place it in a container containing metallic Al. 3+ Subsequent ionic crosslinking was completed in a 0.025 mol / L solution. After 6 hours, the solution was replaced with deionized water and soaked for 24 hours. The water was then changed every 6 hours thereafter to remove residual unreacted small molecules, resulting in a reinforced amphoteric polyelectrolyte-modified polyethersulfone (PES / P(AD)@Al) after phase separation equilibrium. 3+ Ultrafiltration membrane.

[0056] Comparative Example 1 Step 1: First, weigh 17.5 g of PES powder and 2.5 g of pore-forming agent PVP and add them to 80 g of solvent NMP. Stir at 300 rpm for 3 hours at room temperature until the solids are completely dissolved in the solvent. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / PVP casting solution.

[0057] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0058] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface. Then, put it back into deionized water and change the water every 6 hours to remove residual unreacted small molecules and obtain the modified general hydrophilic compound blended modified PES / PVP filter membrane after phase separation equilibrium.

[0059] Comparative Example 2 Step 1: Using a one-pot method, first weigh 0.0048 mol of AMPS powder and 0.0048 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP, and add them to 80 g of solvent NMP. Stir at 300 rpm for 30 min at room temperature until the solids are completely dissolved in the solvent. Add thermal initiator APS (0.02% of the AMPS monomer molar amount) to the system, and then purge the system with nitrogen until the reaction is complete. Continue vigorous stirring at 75°C for 8 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain ungrafted PES / P(AD) casting solution.

[0060] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0061] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface of the water. Then put it back into deionized water and change the water every 6 hours to remove residual unreacted small molecules and obtain the ungrafted polyethersulfone PES / P(AD) ultrafiltration membrane after phase separation equilibrium.

[0062] Comparative Example 3 Step 1: Using the "one-pot method," first weigh 0.0048 mol of AMPS powder and 0.0048 mol of DEA, 17.5 g of PES powder, and 2.5 g of pore-forming agent PVP, and add them to 80 g of solvent NMP. Stir at 300 rpm for 30 min at room temperature using a mechanical stirrer until the solids are completely dissolved in the solvent. Add thermal initiator APS (0.02% of the molar amount of AMPS monomer) to the system, and then purge the system with nitrogen until the reaction is complete. At this point, raise the temperature to 75℃ and continue vigorous stirring for 5 h, then raise the temperature to 120℃ and continue stirring at 300 rpm for 3 h. Finally, stop stirring and degas the casting solution in a vacuum oven to obtain the PES / P(AD) casting solution.

[0063] Step 2: Pour the casting solution obtained in Step 1 at a speed of 7-8 cm·s -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (the thickness of the film scraper is selected), allowed to stand in the air for 30 s to level, and then subjected to a 60 s constant temperature and humidity chamber pre-phase separation treatment on the surface of the casting liquid.

[0064] Step 3: Transfer the substrate containing the casting solution obtained in Step 2 to deionized water to complete phase separation until the flat sheet membrane floats to the surface of the water. Then put it back into deionized water and change the water every 6 hours to remove residual unreacted small molecules and obtain the modified polyethersulfone PES / P(AD) ultrafiltration membrane after phase separation equilibrium.

[0065] Antifouling performance test: Step 1: Humic acid (HA) solution and bovine serum albumin (BSA) solution were prepared to simulate real wastewater with biological metabolic pollution faced by ultrafiltration membranes in real-world application scenarios, in order to evaluate the wastewater separation performance of the membrane: 0.05 g HA / BSA was added to 500 mL of deionized water, and then stirred with a stirrer for 30 min to obtain 0.1 mg / mL HA solution and 0.1 mg / mL BSA solution.

[0066] Step 2: At room temperature, compact the membrane under a negative pressure of 0.1 MPa for 30 min to achieve a stable water flux before starting the wastewater separation test. Each cycle is defined as testing the deionized water flux for 30 min, followed by filtering the HA / BSA solution obtained in Step 1 for 90 min.

[0067] Step 3: Immerse the membrane after separation in Step 2 in a 0.5 mol / L sodium hydroxide (NaOH) solution and perform ultrasonic washing for 1-2 minutes. Repeat this process for three cycles, recording the wastewater flux in each cycle. J p1 , J p2 , J p3 Water flux is denoted as J w1 , J w2 , J w3 .

[0068] Step 4: Use the flux recovery rate after the second cycle. FRR Flux decay rate FDR The following formula is used to determine the antifouling performance of the filter membrane:

[0069]

[0070] In the formula, J w2 This is the steady-state water flux of the filter membrane during the second test, measured in L·m. -2 ·h -1 ·bar -1 , J w3This is the steady-state water flux of the filter membrane in the third test, measured in L·m. -2 ·h -1 ·bar -1 ; J p2 The wastewater flux measured during the second test of the filtration membrane is expressed in L·m. -2 ·h -1 ·bar -1 .

[0071] Water flux test: Step 1: Cut the ultrafiltration membrane into 5 cm × 5 cm samples.

[0072] Step 2: Fix the sample obtained in Step 1 on the area S 1.32×10 -3 m 2 On the water flux tester, ensure good airtightness between the sample and the tester.

[0073] Step 3: Add an appropriate amount of deionized water to the measuring cup above the sample fixed in Step 2, and adjust the test negative pressure of the water flux tester. P The pressure was stabilized at -0.1 MPa. Once the deionized water could be stably extracted through the flat sheet membrane, the timing was started. After pre-pressurization for 30 minutes, the first wastewater separation cycle was performed, and the stable water flux of the first water cycle was recorded.

[0074] Step 4: Calculate the water flux of the filtration membrane by the ratio of the volume of deionized water extracted to the product of the test time, the test membrane area, and the test pressure. J w， The calculation formula is as follows:

[0075] In the formula, J w This is the pure water flux during the initial wastewater separation process, measured in L·m⁻². -2 ·h -1 ·bar -1 ; V The volume of deionized water pumped out is expressed in liters (L). ΔT The test time is in hours (h). S The membrane area is expressed in meters (m²). 2 ; P The applied pressure is measured in bar.

[0076] The water flux and antifouling properties of the enhanced amphoteric polyelectrolyte-modified PES polyethersulfone ultrafiltration membranes obtained in the above embodiments and comparative examples are shown in Table 1 below: Table 1: Water flux and antifouling properties of enhanced amphoteric polyelectrolyte modified PES polyethersulfone ultrafiltration membranes

[0077] Examples 1-5, under identical conditions, controlled the total mass of the casting solution system to 100g, and only changed the contents of AMPS and DEA to prepare reinforced amphoteric polyelectrolyte-modified polyethersulfone PES / P(AD)@Al. 3+ Ultrafiltration membrane; Comparative Example 1, based on the examples, omits the addition of the amphoteric electrolyte modifier, initiator, and crosslinking agent, containing only the pore-forming agent PVP, to prepare a general hydrophilic compound blend-modified PES / PVP filtration membrane; Comparative Example 2, based on the examples, does not involve the amphoteric electrolyte activation reaction, nor does it involve the addition of metal Al. 3+ Ionic crosslinking was completed in the solution, and the ungrafted PES / P(AD) filter membrane was prepared by crosslinking reaction only at 75°C; Comparative Example 3, based on the examples, eliminated the crosslinking reaction in metal Al. 3+ Modified PES / P(AD) filter membranes were prepared by ionic cross-linking in solution.

[0078] Referring to Table 1, it can be seen from Examples 1-5 and Comparative Example 1 that the sample PES / P(AD)@Al of the present invention... 3+ The steady-state water flux (214.56~209.55 L·m) -2 ·h -1 ·bar -1 The flux recovery rates of the second and third wastewater separation cycles (90.5–88.5%) and the flux decay rate of the second wastewater separation cycle (39.3–36.3%) were significantly better than the stable water flux (86.96 L·m) of the PES / PVP filter membrane modified with general-purpose hydrophilic compounds. -2 ·h -1 ·bar -1 The flux recovery rate of the second and third wastewater separation cycles was 82.8%, and the flux decline rate of the second wastewater separation cycle was 45.1%. During multiple cycles and washing processes, the PES / PVP membrane matrix modified with general-purpose hydrophilic compounds and the pore-forming agent PVP only relied on weak van der Waals forces for physical blending. Due to the lack of chemical bonding, the hydrophilic components were easily lost as solutes under water flow shear, leading to a rapid decline in membrane flux. In contrast, the PES / P(AD)@Al example... 3+ By in-situ initiating polymerization, copolymers containing sulfonic acid groups and amine groups are introduced into the PES matrix, transforming simple physical doping into strong chemical entanglement and polar interaction, fundamentally enhancing the interfacial stability of the hydrophilic modified layer in complex wastewater environments.

[0079] As can be seen from Examples 1-5 and Comparative Example 2, the sample of the present invention, PES / P(AD)@Al, exhibits [the following characteristics]. 3+The steady-state water flux (214.56~209.55 L·m) -2 ·h -1 ·bar -1 The flux recovery rates of the second and third wastewater separation cycles (90.5–88.5%) and the flux decay rate of the second wastewater separation cycle (39.3–36.3%) were significantly better than the stable water flux of the ungrafted PES / P(AD) filter membrane (90.58 L·m). -2 ·h -1 ·bar -1 The recovery rate of the second and third wastewater separation cycle flux (83.4%) and the decrease rate of the second wastewater separation cycle flux (41.3%) were compared. This is because the PES / P(AD) filter membrane in Comparative Example 2 did not undergo the amphoteric electrolyte activation reaction and heat treatment, and the polymer chain segments failed to achieve effective depolymerization, recombination, and chemical activation, making it difficult to form a stable covalent graft network in the PES matrix. In this system lacking chemical bond anchoring, the modified components are maintained only by low-energy hydrogen bonds or electrostatic attraction, and it is impossible to establish effective spatial topological constraints, making the modified layer thermodynamically unstable and difficult to control to produce dense and uniform multi-segment finger pores. In contrast, the PES / P(AD)@Al example 3+ By introducing a high-temperature induction step, the filtration membrane achieves the recombination and activation of polymer chain segments, constructing a strong chemical grafting system. This strong chemical driving force provides an effective regulatory mechanism during the film formation process, inducing the formation of a multi-segmented dense pore structure, thereby making its stable water flux much higher than that of the comparative example.

[0080] As can be seen from Examples 1-5 and Comparative Example 3, the sample of the present invention, PES / P(AD)@Al, exhibits [the following characteristics]. 3+ The steady-state water flux (214.56~209.55 L·m) -2 ·h -1 ·bar -1 The flux recovery rates of the second and third wastewater separation cycles (90.5–88.5%) and the flux decay rate of the second wastewater separation cycle (39.3–36.3%) were significantly better than the stable water flux (109.10 L·m⁻¹) of the modified PES / P(AD) filter membrane. -2 ·h -1 ·bar -1 The flux recovery rate of the second and third wastewater separation cycles was 84.2%, and the flux decline rate of the second wastewater separation cycle was 44.3%. While the modified PES / P(AD) filter membrane in Comparative Example 3 already possessed basic covalent bonding, the lack of a key ionic crosslinking step resulted in the absence of anchoring effects from multidentate coordination centers in its modified layer. During the film formation stage, the lack of Al... 3+The system's ability to inhibit disordered rearrangement of polymer chains is weakened due to the induction and regulation of the modified layer, making it unable to form an efficient supramolecular shielding network. Furthermore, after film formation, the modified layer is prone to swelling and structural loosening in the aqueous phase due to the lack of strong coordination bonds. In contrast, the example PES / P(AD)@Al... 3+ Filter membrane by increasing Al 3+ In the ion crosslinking process, metal ions are introduced as coordination centers, forming stable polydentate coordination bonds with the -SO3- and -NH2 groups of the copolymer side chains. This coordination anchoring effect not only plays a good inductive role in the phase separation stage, but also endows the film with extremely high chemical integrity and interfacial bonding after film formation, demonstrating the superior performance of Al. 3+ A decisive contribution to long-lasting anti-pollution performance.

[0081] The above embodiments are merely illustrative examples of the technical solutions of the present invention. The method for modifying high-flux, high-fouling-resistant, enhanced amphoteric polyelectrolyte-modified PES polyethersulfone ultrafiltration membranes involved in this invention is not limited to the content described in the above embodiments, but is subject to the scope defined by the claims. Any modifications, additions, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed by the claims of this invention.

Claims

1. A method for preparing an enhanced amphoteric polyelectrolyte-modified PES ultrafiltration membrane, characterized in that, Includes the following steps: (1) Mix 2-acrylamide-2-methylpropanesulfonic acid AMPS, diethanolamine DEA, PES, pore-forming agent, initiator and organic solvent. The resulting mixture is first reacted at 60-90℃ for 1-6 hours, and then reacted at 110-130℃ for 1-4 hours. The reaction solution is then degassed to obtain casting solution. (2) The casting solution is applied to the substrate and then subjected to a coagulation bath to obtain a flat film; (3) The obtained flat sheet membrane was soaked in metal Al 3+ The solution was left to stand for 1-12 hours, then soaked in pure water until equilibrium was reached, to obtain metal-coordinated ion polymer-grafted modified PES / P(AD)@Al. 3+ Ultrafiltration membrane.

2. The preparation method according to claim 1, characterized in that, In the casting solution obtained in step (1), the molar ratio of AMPS to DEA is 1:0.8-1.

2.

3. The preparation method according to claim 1, characterized in that, In the casting solution obtained in step (1), The mass fraction of PES is 16.5 wt%~18.5 wt%; The mass fraction of AMPS is 0.8 wt% to 1.2 wt%; The mass fraction of the porogen is 1.5 wt%~3.5 wt%; The mass fraction of the organic solvent is 78 wt%~82 wt%; The molar amount of initiator is 0.01% to 0.03% of the molar amount of AMPS.

4. The preparation method according to claim 1, characterized in that, In step (1), the porogen is selected from one or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polyacrylamide (PAM); the initiator is selected from one of ammonium persulfate (APS), benzoyl peroxide (BPO), and potassium persulfate (KPS); and the organic solvent is selected from one or more of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF).

5. The preparation method according to claim 1, characterized in that, In step (2), before the coagulation bath treatment, a pre-phase separation treatment is also included: the poor solvent is brought into contact with the surface of the casting liquid in the form of gas phase or microdroplets.

6. The preparation method according to claim 5, characterized in that, The prephase separation process takes 10s to 200s.

7. The preparation method according to claim 5, characterized in that, The unsuitable solvent is pure water; the coagulation bath solution is water or contains metal Al. 3+ The solution.

8. The preparation method according to claim 1, characterized in that, The thickness of the flat sheet membrane is 50~300 μm.

9. A reinforced amphoteric polyelectrolyte-modified PES ultrafiltration membrane, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The application of the enhanced amphoteric polyelectrolyte-modified PES ultrafiltration membrane as described in claim 9, characterized in that, Used for water purification, food and pharmaceutical separation, concentration and sterilization, liquid filtration in chemical processes, oily wastewater treatment, adsorption materials, anti-adhesion coating materials, and gas filtration materials.

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