Polyamphoteric electrolyte surface modified PES high anti-fouling ultrafiltration membrane, and preparation method and application thereof

Abstract

This invention relates to a polyamphoteric electrolyte-modified PES high-fouling-resistant ultrafiltration membrane, its preparation method, and its application. The preparation process of the PES high-fouling-resistant ultrafiltration membrane is as follows: first, the PES base membrane is subjected to ozone activation treatment, then immersed in a polyethyleneimine (PEI) solution, followed by plasma grafting of PEI to strengthen its bonding on the membrane surface. Then, it is sequentially immersed in a crosslinking agent solution, a tannic acid (TA) solution, and an aluminum ion solution. Finally, after water equilibration, an aluminum ion-crosslinked PEI / TA polyamphoteric electrolyte-modified PES hollow fiber ultrafiltration membrane (D-PES) is obtained. The modified ultrafiltration membrane obtained by this invention has strong stability; the modified layer is not easily detached, and the flexible polymer chains dissipate energy due to chain slippage, improving the mechanical properties of the membrane fibers. It has broad application prospects in the field of hydrophilic modified PES hollow fiber ultrafiltration membranes for water treatment.

Description

Technical Field

[0001] This invention relates to the field of PES ultrafiltration membrane modification, specifically to a PES high-fouling-resistant ultrafiltration membrane with a polyampholyte surface modified with amphoteric electrolyte, its preparation method, and its application. Background Technology

[0002] Membrane separation technology is a selective permeation technology. When filtering mixtures of multi-molecular substances with different particle sizes, the surface and intrinsic properties of the membrane determine the selective permeability of the target substance. Specific substance selective permeation can be achieved by adjusting the surface properties of the membrane material through physical and chemical methods. Polyethersulfone (PES) ultrafiltration membrane materials are gradually becoming the mainstream membrane material due to their good chemical stability, heat resistance (operating at high temperatures), and ease of membrane formation, especially in applications requiring high precision and high temperature resistance. The PES molecular chain contains sulfone (-SO2-) polar groups, which can form dipole-dipole interactions with water molecules, giving it a certain intrinsic water molecule binding force. Simultaneously, the rigid aromatic ring structure on the PES backbone forms a highly aromatic structure with very high chemical bond energy, making it resistant to acids and alkalis, high temperatures, and hydrolysis. However, the rigid aromatic backbone structure means that under external forces, the molecular chain segments are difficult to disperse and absorb energy through conformational changes. Therefore, PES membranes also exhibit high modulus and low ductility, i.e., "hard and brittle." Meanwhile, the porous structure (especially finger-like pores) formed when using the solvent-free phase-inducing separation (NIPS) process to prepare PES membranes in pursuit of high flux further weakens the already limited mechanical strength. This makes them prone to damage under high pressure and repeated washing. Furthermore, the inherent low surface energy and strong hydrophobicity of PES lead to poor wetting properties, low separation efficiency, and susceptibility to oily contamination during water treatment, often requiring membrane material modification and control during the membrane fabrication process or post-film treatment.

[0003] Currently, the main methods for hydrophilic modification of PES hollow fiber ultrafiltration membranes include surface modification and bulk modification. Surface modification can be divided into surface coating and surface grafting, and the methods widely reported in recent years mainly include wet chemical processing, radiation, atomic layer deposition (ALD), and surface coating. CN111111470A grafts a natural hydrogel coating onto the surface of a hollow polyethersulfone fiber membrane. The modified membrane surface has extremely high hydrophilicity and good biocompatibility, but the robustness and antifouling performance of the coating have not been evaluated, which often limits its practical application.

[0004] Bulk modification is also a common matrix modification method, which involves blending different materials to change the structure and properties of the filter membrane matrix. This method is relatively simple, low-cost, and allows for a wide range of material choices; it is also relatively mature in its development. Mahdie Safarpour et al. improved the hydrophilicity of PES membranes using a titanium-tin-carbon (Ti2SnC)-MAX phase (MP) through blending. When the MP mass fraction was 0.5%, the pure water flux of the PES membrane at 0.3 MPa pressure increased from 286 L / (m³) to... 2 The ratio of ·h) was increased to 355 L / (m 2 The flux recovery rate (the percentage of pure water flux after one cycle to the initial pure water flux) increased from 44% to 65%, and the oil-water separation efficiency for oil-water mixed emulsions reached over 80%, successfully improving the membrane's filtration performance and antifouling properties. However, due to the weak interaction between the introduced inorganic particles and the PES matrix, they are prone to aggregation in the modified membrane, leading to defects in the continuous phase of the membrane material. Therefore, the antifouling ability of the ultrafiltration membrane cannot be stably improved, and after long-term use in complex aquatic environments, particles will detach from the membrane, causing secondary pollution while the separation membrane performance deteriorates. Therefore, the synergistic improvement of the mechanical properties and antifouling properties of PES hollow fiber ultrafiltration membranes reported so far is difficult to achieve in practical applications. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing a polyamphoteric electrolyte surface-modified PES high-fouling-resistant ultrafiltration membrane that is simple to process, easy to operate, uses readily available raw materials, has low cost, and exhibits high mechanical and antifouling properties.

[0006] The corresponding technical solution is as follows: A method for preparing a PES high-fouling-resistant ultrafiltration membrane with a polyampholyte surface modified with PES includes the following steps: (1) The PES hollow fiber membrane is treated with ozone, then soaked in polyethyleneimine (PEI) solution, taken out and subjected to plasma activation treatment, and then soaked in crosslinking agent solution to obtain S-PES hollow fiber ultrafiltration membrane. (2) The obtained S-PES hollow fiber ultrafiltration membrane was washed and then soaked in tannic acid TA solution; (3) After soaking in TA solution, take it out and soak it again in aluminum ion solution; (4) The obtained PES hollow fiber membrane is in water equilibrium to obtain aluminum ion crosslinked PEI / TA polyampholyte surface modified PES hollow fiber ultrafiltration membrane D-PES.

[0007] Furthermore, the ozone treatment can be performed using an ultraviolet / ozone surface cleaning machine, with treatment conditions at room temperature and pressure, and a treatment time of 10-20 minutes.

[0008] Furthermore, prior to ozone treatment, the PES hollow fiber ultrafiltration membrane may optionally be washed and dried in anhydrous ethanol. This yields a clean and dry fiber membrane.

[0009] Ozone treatment strongly oxidizes the surface of PES membranes, generating oxygen-containing polar groups such as –COOH and –SO3H, which activates the condensed PES membrane surface, increases the surface roughness and effective water permeable area, enhances hydrophilicity, and provides active sites for the next reaction.

[0010] Further, in step (1), the PES hollow fiber membrane is taken out of the PEI solution and subjected to plasma treatment before being soaked in the crosslinking agent solution.

[0011] The amino group (-NH2) on the PEI molecular chain has a lone pair of electrons on its nitrogen atom, exhibiting strong nucleophilicity. Under the action of plasma high-energy particles, reactive groups such as -OH are formed on the aromatic ring molecular chain of the base film PES, and leaving units with activation points are generated on the aromatic ring. The nucleophile PEI undergoes a bimolecular nucleophilic aromatic substitution reaction with the leaving units on the aromatic ring, and is "grafted" onto the aromatic ring molecular chain of PES through chemical bonds. At the same time, plasma high-energy particles also directly generate active free radicals on the PEI molecular chain segments, generating a large number of new surface free radicals, which in turn trigger the grafting reaction of PEI. These free radicals can react with the PES substrate to firmly anchor PEI to the surface and prevent it from falling off, or they can trigger cross-linking between PEI molecules to form a more stable functional layer.

[0012] Furthermore, the plasma treatment employs a plasma surface treatment machine, with a treatment time of 20-30 minutes.

[0013] PEI is a strong cationic polymer containing a large number of –NH2, –NH–, and –N= groups. Under specific conditions of synergistic ozone and plasma treatment, it can firmly bond with PES through multiple dynamic crosslinking processes involving both chemical and physical methods. The bonding mechanism between PEI and PES includes the following three aspects: First, electrostatic interaction, where the Coulomb attraction between positive and negative charges causes PEI to be rapidly adsorbed onto the PES surface; second, hydrogen bonding, where the hydrogen bond network significantly enhances the cohesive strength and interfacial bonding of the PEI layer, inhibiting desorption; and finally, covalent bonding, where the numerous positively charged free radicals on the PEI molecular chain, such as amino groups, undergo amidation reactions with negatively charged groups on PES, such as carboxyl groups. These three interactions work synergistically to firmly bond PEI to the PES surface, resulting in a PEI-modified PES hollow fiber ultrafiltration membrane, thereby endowing the fiber membrane with stronger wettability.

[0014] Furthermore, in the PEI solution, the molecular weight of PEI is 10 kDa to 25 kDa. The molecular weight of PEI should ensure an appropriate charge density of the hydrophilic polymer to satisfy the dynamic cross-linking of TA and the coupling of metal ions, while avoiding a weakening of the hydrophilic polymer's permeability.

[0015] Furthermore, the concentration of PEI in the PEI solution is 0.004 wt% to 0.008 wt%.

[0016] Furthermore, in the PEI solution, the solvent is a mixed solution of ethanol and water, preferably an aqueous solution of ethanol with a volume ratio of 1:1.

[0017] Furthermore, the soaking time in the PEI solution is 3 to 6 hours.

[0018] Furthermore, the crosslinking agent contains two or more aldehyde functional groups, such as glyoxal, glutaraldehyde, succinaldehyde, adipaldehyde, trimethylolpropionate, and propyltrialdehyde.

[0019] During the soaking process of the crosslinking agent solution, the crosslinking agent crosslinks the PEI inside the membrane pores, giving the PES hollow fiber ultrafiltration membrane a more stable hydrophilic modification effect.

[0020] Furthermore, in the crosslinking agent solution, the mass fraction of the crosslinking agent is 10 wt% to 15 wt%.

[0021] If the concentration of the crosslinking agent is too low, the PEI molecular network will have insufficient crosslinking, making it prone to breakage and detachment due to the opening of the molecular chain interaction under external force; if the concentration of the crosslinking agent is too high, it will cause membrane pore blockage and reduce water flux.

[0022] Furthermore, the crosslinking agent solution also contains 1.5 wt% to 2.5 wt% of an acid, such as citric acid, acrylic acid, acetic acid, or hydrochloric acid.

[0023] Under acidic conditions, the crosslinking agent undergoes a Schiff base reaction with the primary and secondary amines on the PEI chain to form C=N covalent bonds, constructing a three-dimensional crosslinked network. Simultaneously, the crosslinked network binds to polar groups on the membrane surface through hydrogen bonds, significantly improving coating stability and interfacial adhesion. Furthermore, in an acidic environment, the reaction between the crosslinking agent and PEI is relatively slow, allowing it to gradually penetrate into the membrane pores without causing violent reactions that could clog them.

[0024] In a preferred embodiment, the preparation method of the crosslinking agent solution includes the following steps: Step a: Under light-shielding conditions, mix glutaraldehyde and deionized water at a volume ratio of 1:1 until homogeneous. Step b: Add citric acid to the mixed solution obtained in step a, stir well, and obtain glutaraldehyde solution.

[0025] Furthermore, in the above reaction system for preparing glutaraldehyde solution, the mass concentration of glutaraldehyde accounts for 0.12~0.13 g / mL of the total reaction system; the amount of citric acid added accounts for 1.5 wt%~2 wt% of the total reaction system.

[0026] Furthermore, the temperature for soaking the crosslinking agent solution is room temperature, and the soaking time is 2 to 12 hours.

[0027] Further, the mass fraction of tannic acid in the TA solution is 0.002 wt% to 0.01 wt%, more preferably 0.002 wt% to 0.006 wt%.

[0028] Furthermore, the TA solution was soaked at room temperature for 3 to 6 hours.

[0029] Negatively charged tannic acid molecules are rapidly adsorbed onto the positively charged cross-linked PEI layer through electrostatic interactions. Multiple phenolic hydroxyl groups in the tannic acid molecules form a high-density hydrogen bond network with N and O atoms on the membrane surface and PEI chains. At the same time, phenolic hydroxyl groups can undergo addition and condensation reactions with residual C=N double bonds or aldehyde groups on the membrane surface to form a small number of covalent bonds. Further π–π stacking occurs between aromatic rings, ultimately constructing a stable, dense PES / PEI–TA composite membrane layer with strong antifouling properties.

[0030] Furthermore, the concentration of aluminum ions in the aluminum ion-containing solution is 0.05 mol / L to 0.08 mol / L; the source of the aluminum ions is, for example, aluminum chloride hexahydrate.

[0031] Furthermore, the temperature for immersion in the aluminum ion-containing solution is room temperature, and the immersion time is 2 to 12 hours.

[0032] The tannic acid-modified membrane surface is rich in catechol structures and phenolic hydroxyl groups. When immersed in aluminum ion solution, it mainly undergoes metal coordination complexation: the ortho-phenolic hydroxyl groups in the tannic acid molecule deprotonate and react with Al³⁺. + A stable five-membered chelate ring is formed, generating an O→Al coordination bond; simultaneously, the negatively charged phenoxy anion reacts with the high-valence Al³⁺ ion. + Strong electrostatic interactions between the molecules drive the rapid adsorption of aluminum ions. Hydrated aluminum ions can also form a hydrogen bond network with the membrane surface and act as ionic crosslinking bridges connecting adjacent tannic acid molecules and lower PEI segments, further densifying and crosslinking the entire functional layer. These multiple interactions synergistically construct a structurally stable, firmly bonded PES–PEI–TA–Al³ membrane with excellent antifouling properties. + Composite separation membrane.

[0033] Furthermore, the water balance period is 20-24 hours, with the water changed every 4 hours.

[0034] The second objective of this invention is to provide a highly antifouling poly(ampholyte) surface-modified polyethersulfone (PES) hollow fiber ultrafiltration membrane, which is prepared using the method described above.

[0035] The third objective of this invention is to provide the application of the above-mentioned high-fouling-resistant poly(ampholyte) surface-modified polyethersulfone (PES) hollow fiber ultrafiltration membrane in wastewater treatment materials.

[0036] This invention introduces polyethyleneimine, tannic acid, and aluminum ion coordination structures onto the surface of a PES hollow fiber membrane, constructing a super-hydrophilic surface layer rich in hydroxyl and amino groups. PES itself is reactive in the condensed state; ozone treatment strongly oxidizes the PES membrane surface, introducing reactive groups onto the aromatic rings of PES in the condensed state. Further, a strongly nucleophilic PEI with polyamine groups is introduced. Under the action of high-energy plasma particles, nitrogen atoms in PEI undergo a bimolecular nucleophilic aromatic substitution reaction with leaving units on the aromatic rings of PES. The high-energy plasma particles also directly generate active free radicals on the PEI molecular chain segments, generating a large number of new surface free radicals, which in turn trigger the graft polymerization of PEI, firmly anchoring PEI to the PES surface. This surface layer can rapidly form a stable hydration layer, significantly reducing the interfacial transport resistance of water. Simultaneously, because the coating is ultra-thin and uniform, it will not clog the membrane pores, ultimately enabling the membrane fibers to achieve higher water flux. Meanwhile, under the action of external force, the flexible polymer chains dissipate energy due to the slippage of the molecular chains, thereby improving the mechanical properties of the membrane.

[0037] The abundant hydrophilic groups in the polyamphoteric electrolyte formed by PEI / TA allow the hydrophilic polymer to swell rapidly in water while retaining a large amount of water, endowing the modified fiber membrane with high hydrophilicity. The stable hydration layer formed on the surface of the modified membrane effectively isolates pollutants such as proteins and humic acids, reducing their direct contact with the membrane surface. Simultaneously, the surface layer exhibits suitable negative charge, generating electrostatic repulsion with most pollutants in the water. The smooth and dense chelate layer formed by tannic acid and aluminum ions reduces the adhesion strength of pollutants. Furthermore, covalent cross-linking and metal coordination endow the coating with excellent structural stability, enabling the membrane fibers to exhibit high antifouling ability and good mechanical properties. This will become a common method for preparing hydrophilic PES hollow fiber ultrafiltration membranes with high mechanical properties and high antifouling properties.

[0038] 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 utilizes a hydrophilic modified PES hollow fiber ultrafiltration membrane with high mechanical properties and high antifouling performance, obtained through surface modification with a polyamphoteric electrolyte. The highly hydrophilic polyamphoteric electrolyte imparts high water flux to the fiber membrane, while the strong coordination and complexation of metal ions and the strong electrostatic interaction at the interface endow the fiber membrane with strong mechanical properties and strong interfacial interaction with the PES substrate, resulting in strong stability and resistance to detachment. The flexible polymer chains dissipate energy through chain slippage, further enhancing the mechanical properties of the membrane fibers. This invention has broad application prospects in the field of hydrophilic modified PES hollow fiber ultrafiltration membranes for water treatment. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the preparation process of the polyamphoteric electrolyte surface-modified PES high-fouling-resistant ultrafiltration membrane of this application.

[0040] Figure 2 This is a schematic diagram illustrating the principle of the polyamphoteric electrolyte surface-modified PES high-fouling-resistant ultrafiltration membrane of this application. Detailed Implementation

[0041] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0042] In the following embodiments: The hydrophilically modified PES hollow fiber ultrafiltration membranes were purchased from Hubei Jufu Co., Ltd., with an outer diameter of 1.38~1.4 mm, a wall thickness of 0.45~0.5 mm, and an average pore size of 0.005~0.01 μm.

[0043] The ozone pretreatment process involves washing the dried PES hollow fiber ultrafiltration membrane in anhydrous ethanol and then drying it. After cleaning, the membrane is placed in an ultraviolet / ozone surface cleaning machine and treated with ozone at normal pressure for 10-20 minutes to obtain an ozone-pretreated PES hollow fiber ultrafiltration membrane.

[0044] The plasma treatment is performed directly using a plasma surface treatment machine, with a processing time of 20-30 minutes.

[0045] The PEI solution is a mixture of PEI, ethanol, and water, wherein the mass fraction of PEI in the mixture is 0.004 wt% to 0.008 wt%, and the volume ratio of ethanol to water is 1:1.

[0046] The experimental procedure and the corresponding principles are as follows: Figure 1 As shown.

[0047] Example 1 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.006 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a crosslinking solution (containing glutaraldehyde at a mass fraction of 12.5 wt% and citric acid at a mass fraction of 1.5 wt%) at room temperature for 12 hours; Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then immerse it in a modified solution with a tannic acid mass fraction of 0.004 wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and immerse it in a solution with an aluminum ion molar concentration of 0.05 mol / L for 12 hours; Step 5: Take out the fiber membrane obtained in Step 4 and put it into deionized water for 24 hours. After swelling equilibrium, the PES hollow fiber membrane D-PES with aluminum ion crosslinked PEI / TA double network polymer hydrophilic modification is obtained.

[0048] Example 2 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.008 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a crosslinking solution (in which the mass fraction of glutaraldehyde is 12.5 wt% and the mass fraction of citric acid is 1.5 wt%) at room temperature for 12 hours; Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then soak it in a modified solution with a tannic acid mass fraction of 0.004wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and immerse it in a solution containing aluminum ions with a molar concentration of 0.05 mol / L for 12 hours; Step 5: Take out the fiber membrane obtained in Step 4 and put it into deionized water for 24 hours. After swelling equilibrium, the PES hollow fiber membrane D-PES with aluminum ion crosslinked PEI / TA double network polymer hydrophilic modification is obtained.

[0049] Example 3 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.004 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a crosslinking solution (containing glutaraldehyde at a mass fraction of 12.5 wt% and citric acid at a mass fraction of 1.5 wt%) at room temperature for 12 hours; Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then soak it in a modified solution with a tannic acid mass fraction of 0.004 wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and immerse it in a solution containing aluminum ions with a molar concentration of 0.05 mol / L for 12 hours; Step 5: Take out the fiber membrane obtained in Step 4 and put it into deionized water for 24 hours. After swelling equilibrium, the PES hollow fiber membrane D-PES with aluminum ion crosslinked PEI / TA double network polymer hydrophilic modification is obtained.

[0050] Example 4 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.006 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a glutaraldehyde crosslinking solution with a total mass fraction of 14 wt% (where the mass fraction of glutaraldehyde is 12.5 wt% and the mass fraction of citric acid is 1.5 wt%) at room temperature for 12 hours. Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then soak it in a modified solution with a tannic acid mass fraction of 0.006 wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and immerse it in a solution containing aluminum ions with a molar concentration of 0.05 mol / L for 12 hours; Step 5: Take out the fiber membrane obtained in Step 4 and put it into deionized water for 24 hours. After swelling equilibrium, the PES hollow fiber membrane D-PES with aluminum ion crosslinked PEI / TA double network polymer hydrophilic modification is obtained.

[0051] Example 5 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.006 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a glutaraldehyde crosslinking solution with a total mass fraction of 14 wt% (where the mass fraction of glutaraldehyde is 12.5 wt% and the mass fraction of citric acid is 1.5 wt%) at room temperature for 12 hours. Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then soak it in a modified solution with a tannic acid mass fraction of 0.002wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and immerse it in a solution containing aluminum ions with a molar concentration of 0.05 mol / L for 12 hours; Step 5: Take out the fiber membrane obtained in Step 4 and put it into deionized water for 24 hours. After swelling equilibrium, the PES hollow fiber membrane D-PES with aluminum ion crosslinked PEI / TA double network polymer hydrophilic modification is obtained.

[0052] Comparative Example 1 Step 1: The dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.006 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a crosslinking solution (containing glutaraldehyde at a mass fraction of 12.5 wt% and citric acid at a mass fraction of 1.5 wt%) at room temperature for 12 hours; Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then soak it in a modified solution with a tannic acid mass fraction of 0.004 wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and immerse it in a solution containing aluminum ions with a molar concentration of 0.05 mol / L for 12 hours; Step 5: Take out the fiber membrane obtained in Step 4 and put it into deionized water for 24 hours. After swelling equilibrium, the PES hollow fiber membrane D-PES with aluminum ion crosslinked PEI / TA double network polymer hydrophilic modification is obtained.

[0053] Comparative Example 2 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.006 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a glutaraldehyde crosslinking solution with a total mass fraction of 14 wt% (where the mass fraction of glutaraldehyde is 12.5 wt% and the mass fraction of citric acid is 1.5 wt%) at room temperature for 12 hours. Step 3: Take out the fiber membrane obtained in Step 2 and put it into deionized water for 24 hours. After swelling equilibrium, a PES hollow fiber ultrafiltration membrane with glutaraldehyde crosslinked PEI monolayer surface hydrophilic modification is obtained.

[0054] Comparative Example 3 Step 1: The ozone-pretreated dried PES hollow fiber ultrafiltration membrane is immersed in a PEI solution with a mass fraction of 0.006 wt% at room temperature for 3 hours, and then placed in a plasma treatment machine for 30 min to obtain a PEI monolayer modified PES hollow fiber ultrafiltration membrane S-PES. Step 2: The S-PES obtained in Step 1 is immersed in a glutaraldehyde crosslinking solution with a total mass fraction of 14 wt% (where the mass fraction of glutaraldehyde is 12.5 wt% and the mass fraction of citric acid is 1.5 wt%) at room temperature for 12 hours. Step 3: Take out the fiber membrane obtained in Step 2, soak and wash it in deionized water, and then soak it in a modified solution with a tannic acid mass fraction of 0.004wt% at room temperature for 4 hours. Step 4: Take out the fiber membrane obtained in Step 3 and put it into deionized water for 24 hours. After swelling equilibrium, the non-ion-crosslinked PEI / TA dual-network polymer hydrophilically modified PES hollow fiber membrane D-PES is obtained.

[0055] Water flux and fouling resistance testing: Step 1: Cut the hydrophilically modified and dried D-PES hollow fiber membrane into 11 cm long samples and test the outer diameter D of the fiber membrane.

[0056] Step 2: Seal one end of the sample obtained in Step 1 and fix the other end to the self-made water flux tester, so that the effective length in the middle is 10 cm, and ensure good airtightness between the sample and the tester.

[0057] Step 3: Completely immerse the sample fixed in Step 2 in a water bath containing deionized water and conduct the test at 25°C. Adjust the test pressure of the water flux analyzer to stabilize at 0.1 MPa. Start timing after the solution is stably extracted through the fiber membrane. Pre-pressurize for 30 minutes and record the solution volume every 2 minutes. V w1 The test lasted 10 minutes.

[0058] Step 4: Replace the deionized water in the water tank from Step 3 with a 0.1 g / L bovine serum albumin solution, keeping the pressure constant, and conduct the test at 25°C. Start timing after the solution is stably extracted through the fiber membrane, and record the solution volume every 2 minutes. V p The test lasted 60 minutes.

[0059] Step 5: Remove the fiber membrane from Step 4, backwash with deionized water for 5 minutes, then soak it in a 0.5 mol / L sodium hydroxide (NaOH) solution and ultrasonically wash for 3 minutes. Next, replace the bovine serum albumin solution in the water tank from Step 4 with deionized water, maintaining constant pressure, and conduct the test at 25°C. Start timing after the solution is stably extracted through the fiber membrane, and record the solution volume every 2 minutes. V w2 The test lasted 10 minutes.

[0060] Step 6: Calculate the water flux of the fiber membrane by the ratio of the volume of deionized water extracted to the product of the test time and the test membrane area. J The calculation formula is as follows:

[0061] In the formula, J This is the flux during the testing of a single fiber membrane, measured in L·m. -2 ·h -1 The data obtained in steps 3, 4, and 5 represent the initial flux of deionized water, respectively. J w1 Bovine serum albumin solution flux J p Deionized water recovery flux J w2 ; V The volume of solution removed is expressed in liters (L). The data obtained in steps 3, 4, and 5 represent the initial volume of deionized water, respectively. V w1 Volume of bovine serum albumin solution V p Deionized water restores volume V w2 ;Δ T The test time is in hours (h). S The membrane area is expressed in meters (m²). 2 ; D The outer diameter of the fiber membrane is in meters (m).

[0062] Step 7: Use the results calculated in Step 6 J w1 and J w2 The flux recovery rate of the membrane before and after testing with bovine serum albumin solution was calculated. FRR The calculation formula is as follows:

[0063] The result calculated using step 6 J w2 and J p The difference andJ w1 The reversible fouling rate of the membrane before and after testing with bovine serum albumin solution was calculated. R r The calculation formula is as follows:

[0064] The result calculated using step 6 J w1 and J w2 The difference and J w1 The ratio of the irreversible fouling rate of the membrane before and after testing with bovine serum albumin solution was calculated. R ir The calculation formula is as follows:

[0065] Mechanical property testing: The mechanical properties of the membrane filaments were analyzed using a universal testing machine. The membrane filaments were cut into 10 cm long strips using a cutter, and the inner and outer diameters of the strips were measured. The strips were then fixed at both ends using upper and lower clamps, and tested at room temperature at 50 mm / min. -1 Mechanical properties were tested at the specified rate to obtain force-displacement curves for the membrane fiber samples. Each sample group underwent at least three parallel tests. Tensile strength at break was also measured. σ This refers to the maximum tensile force per unit area that the spline can withstand during the stretching process. The calculation formula is as follows:

[0066] In the formula, F The maximum load on the spline during the stretching process is expressed in Newtons (N). S The interfacial area of ​​the spline in the stretching direction, in mm. 2 .

[0067] Elongation at break of the spline during the stretching process ε The calculation formula is as follows:

[0068] In the formula, L 0 represents the initial gauge length of the spline before testing, in mm; L The gauge length at which the spline breaks during the stretching process is in mm.

[0069] The elastic modulus E of the sample can be calculated from the stress-strain curve, which is the slope value of the linear region of the curve (between 5% and 10%).

[0070] The water flux and antifouling properties of the hydrophilic modified PES hollow fiber ultrafiltration membranes obtained in the above embodiments and comparative examples are shown in Table 1 below: Table 1. Water flux and antifouling performance of ultrafiltration membranes obtained in each embodiment and comparative example.

[0071] The flux of bovine serum albumin solution obtained from D-PES in Examples 1-5 was 130.6-140.0 L·m⁻¹. -2 ·h -1 The flux recovery rate (83.3%~87.3%), non-contamination rate (12.6%~16.6%), reversible contamination rate (41.4%~46.1%), tensile strength (2.98~3.04MPa), and Young's modulus (72.1~74.2) of the D-PES:bovine serum albumin solution obtained in Comparative Example 1 without ozone treatment (62 L·m) were all significantly better than those of the D-PES:bovine serum albumin solution obtained in Comparative Example 1. -2 ·h -1 The flux recovery rate (68.9%), irreversible contamination rate (31.1%), reversible contamination rate (25.2%), tensile strength (2.24 MPa), and Young's modulus (57.5 MPa) were also measured. Ozone treatment efficiently oxidizes the inert aromatic rings on the surface of polyethersulfone (PES) and introduces oxygen-containing functional groups such as hydroxyl and carboxyl groups. This step provides chemical sites for subsequent PEI grafting. In contrast, the surface of untreated PES is hydrophobic and has strong surface inertness. PEI can only adhere through weak physical entanglement, resulting in poor adhesion. During long-term operation, the surface layer is prone to delamination and detachment, exposing membrane pores and drastically reducing separation efficiency. Secondly, the membrane fiber surface after ozone treatment carries an electronegative layer, which can attract more polycationic PEI through electrostatic attraction. In contrast, the PEI in untreated membrane fibers tends to accumulate on the surface in a coiled and irregular form, resulting in low and uneven coverage, which leads to uneven modification effects and exacerbates membrane fouling. Finally, the strong initial anchoring effect of ozone treatment ensures the structural stability of PEI adhesion, providing multi-point crosslinking for subsequent modification. However, the membrane fibers without ozone treatment have unstable PEI adhesion. During plasma treatment, some physically attached PEI molecular chains may be directly eroded away, leading to insufficient cross-linking. Coatings with insufficient cross-linking are prone to swelling or dissolution in practical applications, which not only affects their mechanical properties but also greatly shortens their service life. However, its flux recovery rate, irreversible fouling rate, reversible fouling rate, tensile strength, and Young's modulus are all superior to those of comparative examples 2 and 3.

[0072] The flux of bovine serum albumin solution obtained from D-PES in Examples 1-5 was 130.6-140.0 L·m⁻¹. -2 ·h -1The flux recovery rate (83.3%~87.3%), non-contamination rate (12.6%~16.6%), reversible contamination rate (41.4%~46.1%), tensile strength (2.98~3.04 MPa), and Young's modulus (72.1~74.2 MPa) of the PEI polycationic monolayer hydrophilic modified S-PES:bovine serum albumin solution obtained in Comparative Example 2 were all significantly better than those of the PEI obtained in Comparative Example 2. -2 ·h -1 The parameters included flux recovery rate (60.9%), irreversible fouling rate (22.9%), reversible fouling rate (23.0%), tensile strength (2.08 MPa), and Young's modulus (47 MPa). When the PEI mass fraction was 0.004~0.008 wt%, the polycations could interact with the base membrane through various interactions such as transient electrostatic interactions and covalent bonding, causing PEI to "adhere" to the PES base membrane and imparting strong hydrophilicity to the PES base membrane. The high-energy particles of the plasma could also break the chemical bonds on the PEI molecular chain segments, generating a large number of free radicals on its surface. These free radicals could react with the PES substrate or initiate cross-linking between PEI molecules, forming a denser and more stable functional layer. Cross-linking enhanced the strength of the PEI modified layer and greatly improved the mechanical properties of the membrane. However, the PEI molecular chain is highly flexible and lacks a rigid structure. Using it alone can easily cause pollutants to embed into the membrane pores and form entanglements, resulting in irreversible fouling. Meanwhile, amino groups are hydrophilic but lack strong hydration groups, exhibiting strong positive charge. They form only a thin and unstable hydration layer on the PES surface, allowing pollutants (such as proteins and humic acids) to easily break through this layer and be directly adsorbed. Furthermore, the introduction of tannic acid and aluminum ions into the surface further enhances the adsorption capacity of Al. 3+ As a crosslinking agent, it forms coordination / ionic bonds with the amino groups (-NH2) of PEI and the phenolic hydroxyl groups (-OH) of tannic acid (TA) to construct a three-dimensional stable network. This crosslinking network results in a smoother surface and more regular pores, ensuring contaminants remain on the surface and do not easily enter the pores, making cleaning easier. The abundant phenolic hydroxyl groups on TA form a high-density, strongly hydrated hydration layer after crosslinking, effectively preventing direct contact between contaminants and the membrane surface and significantly reducing adsorption free energy. Addressing the strong positive charge issue of the PEI monolayer, the phenolic hydroxyl groups of TA dissociate and introduce a negative charge, synergistically modulating the positive charge of PEI to achieve near-neutral or weak charge, significantly weakening electrostatic attraction and enhancing repulsion, making contaminants easier to remove through cleaning. Through the interaction of TA and Al... 3+ Assisted modification enables dynamic cross-linking of PEI flexible molecular chains with TA and subsequent cross-linking with Al. 3+ The coordination coupling transforms the adverse effects of flexible polymer chains into beneficial improvements in mechanical properties.

[0073] The flux of bovine serum albumin solution obtained from D-PES in Examples 1-5 was 130.6-140.0 L·m⁻¹. -2 ·h-1 The flux recovery rate (83.3%~87.3%), non-fouling rate (12.6%~16.6%), reversible fouling rate (41.4%~46.1%), tensile strength (2.98~3.04 MPa), and Young's modulus (72.1~74.2 MPa) of the non-ion-crosslinked PES hollow fiber ultrafiltration membrane obtained in Comparative Example 3 were all significantly better than those of the bovine serum albumin solution flux (87.6 L·m⁻¹). -2 ·h -1 The parameters included flux recovery rate (57%), irreversible contamination rate (42.7%), reversible contamination rate (14.0%), tensile strength (2.24 MPa), and Young's modulus (57.5 MPa). Tannic acid is rich in o-diphenol and gallic acid groups, which can react with Al... 3+ Strong coordination bonds are formed to construct a high-strength three-dimensional network structure. These coordination bonds possess both good dynamic reversibility and enhanced mechanical strength of the membrane fibers. However, the single hydrogen bond attachment causes these non-covalent forces to break under hydraulic scouring or chemical cleaning, resulting in poor structural stability and unstable retention rate during long-term operation; Al 3+ The introduction of [a specific substance] alters the zeta potential of the membrane surface, which helps to prevent negatively charged pollutants through electrostatic repulsion. A single tannic acid coating, rich in uncoordinated hydroxyl groups, easily dissociates in water and carries a strong negative charge, adsorbing positively charged organic matter to form complex pollutants. Uncrosslinked membrane fibers have weaker resistance to pollution in complex water bodies and are more prone to irreversible pollutant deposition, leading to a higher flux decay rate. 3+ It inherently possesses certain antibacterial properties, which are present in the formation of TA-Al. 3+ After the network is in place, the composite layer can significantly enhance the antibacterial / anti-biodeposition properties of the membrane. While pure tannic acid has a certain oxidizing property, it lacks the synergistic effect of metal ions and has a weaker effect in inhibiting the reproduction of microorganisms on the membrane surface. Therefore, it is more likely to cause biofilm fouling when treating wastewater containing microorganisms.

[0074] The above embodiments are merely illustrative examples of the technical solutions of the present invention. The modification method for poly(amphoteric electrolyte) surface-modified polyethersulfone (PES) hollow fiber 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 a polyamphoteric electrolyte-modified PES high-fouling-resistant ultrafiltration membrane, characterized in that, Includes the following steps: (1) The PES hollow fiber membrane is treated with ozone, then soaked in polyethyleneimine (PEI) solution, taken out and subjected to plasma activation treatment, and then soaked in crosslinking agent solution to obtain S-PES hollow fiber ultrafiltration membrane. (2) The obtained S-PES hollow fiber ultrafiltration membrane was washed and then soaked in tannic acid TA solution; (3) Remove and soak again in an aluminum ion solution; (4) The obtained PES hollow fiber membrane is in water equilibrium to obtain aluminum ion crosslinked PEI / TA polyampholyte surface modified PES hollow fiber ultrafiltration membrane D-PES.

2. The preparation method according to claim 1, characterized in that, The ozone treatment in step (1) involves exposing the PES hollow fiber membrane to an ultraviolet or ozone environment for 10-20 minutes.

3. The preparation method according to claim 1, characterized in that, In step (1), the plasma activation treatment time is 20-30 minutes.

4. The preparation method according to claim 1, characterized in that, In the PEI solution: The molecular weight of PEI is 10 kDa~25 kDa; The concentration of PEI was 0.004 wt% to 0.008 wt%. The solvent is a mixture of ethanol and water.

5. The preparation method according to claim 1, characterized in that, The crosslinking agent contains two or more aldehyde functional groups; the mass fraction of the crosslinking agent in the crosslinking agent solution is 10 wt% to 15 wt%.

6. The preparation method according to claim 1, characterized in that, The crosslinking agent solution contains 1.5 wt% to 2.5 wt% acid.

7. The preparation method according to claim 1, characterized in that, The mass fraction of tannic acid in the TA solution is 0.002 wt% to 0.01 wt%.

8. The preparation method according to claim 1, characterized in that, The concentration of aluminum ions in the aluminum ion-containing solution is 0.05 mol / L to 0.08 mol / L.

9. A highly antifouling polyamphoteric electrolyte surface-modified polyethersulfone (PES) hollow fiber 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 high-fouling-resistant poly(ampholyte) surface-modified polyethersulfone (PES) hollow fiber ultrafiltration membrane as described in claim 9 in wastewater treatment materials.

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