Preparation method of antifouling super-hydrophilic separation membrane based on zwitterionic polymer-ceramic compounding

Abstract

The invention belongs to the technical field of oily wastewater treatment, and particularly relates to a preparation method of an antifouling super-hydrophilic separation membrane based on zwitterionic polymer-ceramic compounding, which comprises the following two steps of: firstly, grafting protocatechuic acid on a polyvinylidene fluoride base material; and then the composite coating is formed through co-deposition and in-situ hydrolysis of the silane functionalized zwitterionic polymer and a zirconium precursor. A synergistic interface is constructed in which the zwitterionic polymer establishes a strong hydration layer to prevent fouling, while the formed nano-zirconia provides a durable inorganic framework to enhance mechanical and chemical stability. The prepared antifouling super-hydrophilic separation membrane has excellent super-hydrophilicity and underwater super-oleophobicity, still shows excellent stability and separation efficiency under severe chemical conditions, and solves the problem of typical durability of a zwitterionic polymer coating.

Description

Technical Field

[0001] This invention belongs to the field of oily wastewater treatment technology, and relates to a method for preparing an oil-water separation membrane, particularly a method for preparing an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite. Background Technology Over the past 20 years, global fossil fuel consumption has surged by 62%, directly resulting in approximately 470 million cubic meters of oily wastewater annually. How to treat this oily wastewater is a significant challenge. The main challenge lies in treating highly stable nanoemulsion oil droplets (<1 micrometer) in the wastewater. These tiny droplets are extremely stable and cannot be effectively treated by traditional separation methods. In particular, these droplets can act as carriers of toxic pollutants, bioaccumulating in the food chain and posing a serious threat to ecosystems and human health. Therefore, there is an urgent need to separate petroleum from such large oil-in-water emulsions, not only for economic reasons but also for environmental sustainability. Among various separation methods, membrane separation technology has attracted considerable attention due to its unique advantages such as small footprint, low energy consumption, and high separation efficiency. However, the practical application of membranes faces a critical and persistent challenge: membrane fouling. Membrane fouling refers to the irreversible changes in permeate flow rate and separation characteristics that occur during membrane filtration when particulate matter, colloidal particles, or large solute molecules in the water adsorb and deposit on the membrane surface or within the pores due to physicochemical or mechanical interactions with the membrane. The persistent challenge of membrane fouling, particularly the irreversible adhesion of oil droplets, severely restricts the long-term operational stability and efficiency of membrane technologies used for treating oily wastewater.

[0002] Polyvinylidene fluoride (PVDF) possesses excellent chemical stability, thermal stability, and mechanical strength, making it a high-performance separation membrane material. However, the inherent hydrophobicity of traditional polymer membranes leads to a strong van der Waals effect and hydrophobic-hydrophobic interactions, making it easy for oil droplets to adsorb, combine, and ultimately clog the membrane pores. This fouling phenomenon causes a sharp decline in membrane flux and separation efficiency, becoming a major bottleneck restricting the long-term stable operation and large-scale industrialization of membrane technology. Therefore, designing and manufacturing novel membrane materials with strong antifouling properties is key to fundamentally solving this challenge, thereby improving membrane separation performance and paving the way for the widespread practical application of membrane separation technology in this crucial field.

[0003] Inspired by natural surfaces such as fish scales, the use of superhydrophilic surfaces is an effective method to reduce membrane fouling during oil-water separation. These surfaces can trap water molecules, forming a robust hydration layer that acts as a physical barrier, preventing direct contact and adhesion of oil droplets, thus endowing the material with excellent oil-resistant properties. Various methods have been developed to impart hydrophilicity to surfaces, including surface graft polymerization, coating deposition, plasma treatment, and doping. Among these methods, the surface graft functionalization of zwitterionic polymers has emerged as a particularly promising approach. Zwitterionic polymers possess both cationic and anionic groups on the same molecular chain, giving them strong hydration capabilities to form highly stable hydration layers. Furthermore, they exhibit excellent chemical stability, tolerating a wide range of pH values ​​and high salinity environments. Due to these unique advantages, zwitterionic polymers have become the preferred materials for manufacturing high-performance, fouling-resistant superhydrophilic separation membranes.

[0004] Chinese Patent Publication No. CN108404684B discloses a method for preparing a superhydrophilically modified antifouling PVDF separation membrane. The method involves treating the PVDF surface with an alkaline solution to generate double bonds, and then chemically crosslinking hyperbranched polyethyleneimine on the PVDF membrane surface through an amino-olefin addition reaction and an amino-epoxy ring-opening reaction. The hyperbranched polyethyleneimine on the membrane surface undergoes an amino-epoxy ring-opening reaction with an epoxypropanol solution to obtain a PVDF membrane with antifouling properties. The modified PVDF membrane possesses a large number of active groups such as amino and hydroxyl groups, significantly improving the hydrophilicity of the membrane surface.

[0005] Chinese patent CN107096398A discloses a method for modifying PVDF films with amphiphilic copolymers. It discloses that by grafting amphiphilic copolymer P (AMPS-co-MMA) onto the surface of PVDF films, the hydrophilicity and antifouling properties of the film surface are significantly improved.

[0006] Lai et al. prepared a superhydrophilic zwitterionic modified binder-coated membrane using dopamine, polyethyleneimine, and AMAO via a simple one-step co-deposition method. This membrane exhibited strong hydrophilicity, significantly improving its oil resistance. Zhang et al. synthesized an electrospun membrane by synergistically combining the zwitterionic polymer betaine methacrylate sulfonate with a PAN fiber network. The resulting membrane could establish a hydration layer barrier to provide antifouling capabilities, thereby achieving high separation flux and efficiency.

[0007] While these improvements significantly enhance separation performance, steric hindrance results in low coverage of the modified layer on the membrane surface and a limited number of introduced hydrophilic groups, thus limiting the improvement in antifouling performance. Furthermore, the ionomer layer is prone to dissolution or detachment in practical applications. This vulnerability stems from the combined effects of fluid shear stress under pressure-driven filtration and the demanding chemical cleaning cycles required for treating oily wastewater. Therefore, developing a zwitterionic polymer-based membrane that simultaneously possesses excellent hydrophilicity, high mechanical stability, and long-term durability remains a formidable challenge. Summary of the Invention

[0008] To address the aforementioned problems, the present invention aims to provide an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite, thereby solving one or more technical problems existing in the prior art and at least providing a beneficial alternative or creating conditions.

[0009] This invention aims to prepare a zwitterionic polymer-ceramic composite antifouling superhydrophilic membrane using a simple method. First, a uniform protocatechuic acid layer rich in carboxyl and hydroxyl groups is stably deposited on the original hydrophobic porous base membrane, improving the membrane's hydrophilicity and providing abundant anchoring points for robust grafting. Subsequently, a silane-functionalized zwitterionic polymer (SBSI) and the precursor zirconium (TPOZ) are co-deposited onto the pretreated surface to form a polymer-ceramic composite coating.

[0010] Therefore, the aforementioned antifouling superhydrophilic membrane based on zwitterionic polymer-ceramic composite comprises a porous base membrane and a protocatechuic acid layer grafted onto its surface, and a zwitterionic polymer-ceramic composite layer. It is prepared through two-step surface modification, specifically: Step 1, grafting protocatechuic acid onto the porous base membrane to obtain a hydroxyl-functionalized hydrophilic membrane, which is obtained by grafting protocatechuic acid onto the surface and / or pores of the porous base membrane, thereby depositing a uniform protocatechuic acid layer with abundant carboxyl and hydroxyl groups on its surface; Step 2, co-depositing the hydroxyl-functionalized hydrophilic layer onto the pretreated surface using a silane-functionalized zwitterionic polymer and the precursor zirconium, forming a zwitterionic polymer-ceramic composite layer, and finally obtaining an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite.

[0011] First, the preparation method of the silane-functionalized zwitterionic polymer is as follows: S1, (N,N-dimethylaminopropyl)trimethoxysilane and 1,3-propanesulfonate lactone are dissolved in anhydrous acetone and reacted under nitrogen protection at a temperature of 25-35°C for 5-8 hours with stirring to form a suspension containing a white solid precipitate. The mass ratio of (N,N-dimethylaminopropyl)trimethoxysilane to 1,3-propanesulfonate lactone is 4-5:2-3.

[0012] S2, the suspension is filtered to obtain a white solid, which is washed 2 to 3 times with anhydrous acetone, and then dried overnight under vacuum at 50 to 60°C to obtain the final product, a white powder, which is the silane-functionalized zwitterionic polymer, denoted as SBSI.

[0013] Furthermore, the preparation method of the hydroxyl-functionalized hydrophilic membrane is specifically as follows: S01, Porous base membrane pretreatment: The porous base membrane is ultrasonically cleaned with acetone, ethanol and deionized water for 20-40 minutes respectively, and then dried at 60°C; the dried membrane is then ultrasonically cleaned in anhydrous ethanol for 5-8 minutes to ensure complete wetting and removal of trapped air, and then stored in anhydrous ethanol to obtain a pre-wetted porous base membrane. The porous base membrane is a polyvinylidene fluoride (PVDF) ultrafiltration membrane with a pore size of 0.2–0.5 micrometers. SO2 is used to dissolve protocatechuic acid, CuCl2, and hydrogen peroxide in deionized water by continuous stirring. Stirring is continued for 30 to 50 minutes until a homogeneous active solution is obtained.

[0014] S03, the pre-wetted porous base membrane is transferred to the active solution and soaked for a period of time. Finally, the membrane is taken out and dried in an oven at 50-60℃ for 30-50 minutes to obtain a polyvinylidene fluoride ultrafiltration membrane with a protocatechuic acid layer rich in carboxyl and hydroxyl groups, namely a hydroxyl-functionalized hydrophilic membrane, denoted as PP. The mass ratio of protocatechuic acid, CuCl2, hydrogen peroxide, and water is 2–3:1–1.2:5–6:200; the pre-wetted porous base membrane is transferred to the active solution and soaked for 12–15 hours; the hydrogen peroxide concentration is 30%.

[0015] Finally, an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite was prepared, specifically as follows: S001, immerse the hydroxyl-functionalized hydrophilic membrane in a silane-functionalized zwitterionic polymer-anhydrous ethanol solution and sonicate for 5-8 minutes to obtain a silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane. S002, under constant stirring, the precursor zirconium (TPOZ) and 3-aminopropyltriethoxysilane were added dropwise to glacial acetic acid, and the mixture was stirred at room temperature for 1 to 2 hours until a homogeneous premix was formed.

[0016] In step S003, the premixture is poured into the silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane in step S001. The entire system is then sonicated for 5–8 minutes to ensure complete dispersion of the silane-functionalized zwitterionic polymer and promote its hydrolysis. The mixture is then placed on a shaker at room temperature for 2–3 cycles. After the reaction is complete, the membrane is thoroughly rinsed with anhydrous ethanol to remove loosely bound particles from the surface. Finally, the washed membrane is recovered and dried in an oven at 80°C to obtain an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite, denoted as PPZP.

[0017] This innovative composite design provides unique synergistic advantages: the grafted zwitterionic polymer chains generate a strong hydration layer responsible for the membrane's superhydrophilicity (WCA=0°) and excellent underwater superoleophobicity (UWOCA>150°), while the simultaneously formed ZrO2 nanoparticles contribute surface roughness and act as a robust inorganic framework. This results in a high and stable permeation flux of approximately 1200 L / m³. -2 h -1 bar -1 It exhibits a very low permeation flux decay rate (as low as 5.67%). During the continuous separation of a variety of challenging surfactant-stabilized oil-in-water emulsions, the separation efficiency remained above 99.9%, and it demonstrated excellent durability under harsh chemical environments (pH 2–12, saturated sodium chloride) and physical stress (ultrasound). This work not only provides a highly efficient solution for oily wastewater treatment but also inspires general design principles for developing advanced separation materials with superior performance and durability suitable for a wide range of applications.

[0018] The antifouling superhydrophilic separation membrane PPZP of the present invention can be applied to the separation of oil-water mixtures and the treatment of oily wastewater.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: 1) A robust and durable zwitterionic polymer-ceramic composite antifouling superhydrophilic separation membrane was successfully prepared through a simple and effective two-step surface modification strategy. First, a uniform protocatechuic acid layer rich in carboxyl and hydroxyl groups was stably deposited on the original hydrophobic porous substrate membrane. This not only improved the membrane's hydrophilicity but also provided abundant anchoring points for robust grafting. Subsequently, a silane-functionalized zwitterionic polymer and precursor zirconium (TPOZ) were co-deposited onto the pretreated surface to form a polymer-ceramic composite coating. The hydroxyl groups generated by the dehydration condensation reaction between the silane-functionalized zwitterionic polymer and the precursor zirconium readily form stable covalent bonds with the substrate layer, ensuring stable grafting of the silane-functionalized zwitterionic polymer. Simultaneously, nano-zirconia generated in situ from the precursor zirconium hydrolysate exists in the form of an inorganic framework. This framework not only increases the micro-roughness of the coating surface, facilitating the establishment of a stable underwater superoleophobic interface, but also significantly improves the mechanical strength and wear resistance of the coating during actual separation processes. In addition, they exhibit excellent chemical stability and can tolerate a wide range of pH values ​​and high salinity environments.

[0020] 2) Utilizing surface grafting technology, protocatechuic acid is grafted onto the surface of a porous membrane, introducing carboxyl groups rich in both carboxyl and hydroxyl groups. Furthermore, silane-functionalized zwitterionic polymers are introduced. These zwitterionic polymers possess both cationic and anionic groups on the same molecular chain, giving them strong hydration capabilities and forming a highly stable hydration layer. This further enhances the hydrophilicity of the membrane surface and strengthens its stability. The hydrophilic polymer molecules exhibit excellent anti-oil adhesion properties, allowing the fabricated PPZP membrane to establish a hydration layer barrier to provide antifouling capabilities, thereby achieving high separation flux and efficiency. It can effectively capture and separate highly stable nanoemulsion oil droplets (<1 micrometer) from wastewater. Simultaneously, it offers high water flux, simple operation, and no additional energy consumption besides mass transfer energy. The membrane surface has a self-cleaning function, making it easy to clean and reuse, and exhibits slow flux decay. Moreover, it can withstand harsh conditions, being immersed in strong acid (pH=2), strong alkali (pH=12), and saturated sodium chloride solutions for 30 days respectively. Even after being exposed to this harsh chemical environment for 30 consecutive days, the PPZP membrane still largely maintained its excellent wettability and exhibited outstanding durability and excellent separation efficiency.

[0021] 3) This innovative composite design provides unique synergistic advantages: the grafted zwitterionic polymer chains generate a strong hydration layer responsible for the membrane's superhydrophilicity (WCA=0°) and excellent underwater superoleophobicity (UWOCA>150°), while the simultaneously formed ZrO2 nanoparticles contribute surface roughness and act as a robust inorganic framework. This achieves a high and stable permeation flux of approximately 1200 L / m³. -2 h -1 bar -1It exhibits a very low permeation flux decay rate (as low as 5.67%). During the continuous separation of a variety of challenging surfactant-stabilized oil-in-water emulsions, the separation efficiency remained above 99.9%.

[0022] 4) The preparation method of the present invention is simple, easy to operate, mild, and highly applicable, and is suitable for large-scale production. Attached Figure Description

[0023] Figure 1 a. Electron microstructure diagram of the original porous base membrane, namely the polyvinylidene fluoride ultrafiltration membrane; Figure 1 b. Electron microstructure of the hydroxyl-functionalized hydrophilic membrane; Figure 1 c, Electron micrograph of an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite; Figure 1 d, EDS energy dispersive spectroscopy image of an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite; Figure 2 a. FTIR images of polyvinylidene fluoride ultrafiltration membrane, hydroxyl-functionalized hydrophilic membrane, and antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite. Figure 2 b. XPS spectra of polyvinylidene fluoride ultrafiltration membrane, hydroxyl-functionalized hydrophilic membrane and antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite; Figure 2 cf, high-resolution spectra of C1S, O1S, S2P and N1S of an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite. Figure 3 a. Water contact angle WCA of PVDF, PP and PPZP in Example 1; Figure 3 b. The oil contact angle (UWOCA) of the PPZP prepared in Example 1 for various oils; Figure 3 c, Water contact angle WCA and oil contact angle UWOCA of PPZP at different reaction times; Figure 3 d. Dynamic underwater oil resistance test of PPZP; Figure 4 .PPZP WCA and UWOCA after treatment at (a) pH=2, (b) pH=12, (c) saturated salt solution and (d) ultrasonic treatment for different times; Figure 5 a. Real-time permeation flux of I / W emulsions separated by PVDF, PP and PPZP respectively; Figure 5b. Real-time permeation flux of T / W emulsion, D / W emulsion and K / W emulsion separated by PPZP; Figure 5 c. Different membranes for separating oil-in-water emulsions (DR); Figure 5 Microscopic and digital images of de, I / W and T / W emulsions and filtrates; Figure 6 a. Droplet size analysis of I / W filtrate and emulsion separated by PPZP; Figure 6 b. Total organic carbon content and separation efficiency of PPZP in separating various oil-in-water emulsions. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims. Example 1 A method for preparing an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite first requires the preparation of a silane-functionalized zwitterionic polymer, specifically: Five parts of (N,N-dimethylaminopropyl)trimethoxysilane and three parts of 1,3-propanesulfonate lactone were dissolved in 20 parts of anhydrous acetone. The mixture was stirred and reacted for 5 hours under nitrogen protection at 35°C to form a suspension containing a white solid precipitate. The suspension was filtered to obtain a white solid, which was washed 2-3 times with anhydrous acetone and then dried overnight under vacuum at 60°C to obtain the final product, a white powder, which is the silane-functionalized zwitterionic polymer (SBSI).

[0025] Furthermore, the preparation method of the hydroxyl-functionalized hydrophilic membrane is as follows: Porous base membrane pretreatment: A 10*10cm polyvinylidene fluoride ultrafiltration membrane with a pore size of 0.45 micrometers was ultrasonically cleaned for 30 minutes with acetone, ethanol and deionized water respectively, and then dried at 60°C; the dried membrane was then ultrasonically cleaned in anhydrous ethanol for 5 minutes to ensure complete wetting and removal of trapped air, and then stored in anhydrous ethanol to obtain a pre-wetted porous base membrane. By continuous stirring, 2 parts protocatechuic acid, 1 part CuCl2 and 5 parts hydrogen peroxide were dissolved in 200 parts deionized water, and stirring was continued for 50 minutes until a uniform active solution was obtained. The pre-wetted porous base membrane was transferred to the active solution and soaked for 12 hours. Finally, the membrane was removed and dried in an oven at 60°C for 50 minutes to obtain a hydroxyl-functionalized hydrophilic membrane (PP). Finally, an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite was prepared, specifically as follows: The hydroxyl-functionalized hydrophilic membrane was immersed in a 5 mM solution of silane-functionalized zwitterionic polymer-anhydrous ethanol and ultrasonically treated for 8 minutes to obtain a silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane. Under constant stirring, 2 parts of precursor zirconium (TPOZ) and 2 parts of 3-aminopropyltriethoxysilane were added dropwise to 1 part of glacial acetic acid, and the mixture was stirred at room temperature for 2 hours until a homogeneous premix was formed. The premixture was poured into a solution of silane-functionalized zwitterionic polymer containing a hydroxyl-functionalized hydrophilic membrane. The entire system was then sonicated for 5 minutes to ensure complete dispersion of the silane-functionalized zwitterionic polymer and to promote its hydrolysis. The mixture was then placed on a shaker at room temperature for 2-3 cycles. After the reaction was completed, the membrane was thoroughly rinsed with anhydrous ethanol to remove loosely bound particles from the surface. Finally, the cleaned membrane was recovered and dried in an oven at 80°C to obtain an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite.

[0026] Example 2 A method for preparing an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite first requires the preparation of a silane-functionalized zwitterionic polymer, specifically: Four parts of (N,N-dimethylaminopropyl)trimethoxysilane and three parts of 1,3-propanesulfonate lactone were dissolved in 20 parts of anhydrous acetone. The mixture was stirred and reacted for 6 hours under nitrogen protection at 35°C to form a suspension containing a white solid precipitate. The suspension was filtered to obtain a white solid, which was washed 2-3 times with anhydrous acetone and then dried overnight under vacuum at 60°C to obtain the final product, a white powder, which is the silane-functionalized zwitterionic polymer (SBSI).

[0027] Furthermore, the preparation method of the hydroxyl-functionalized hydrophilic membrane is as follows: Porous base membrane pretreatment: A 10*10cm polyvinylidene fluoride ultrafiltration membrane with a pore size of 0.2 micrometers was ultrasonically cleaned with acetone, ethanol and deionized water for 40 minutes respectively, and then dried at 60°C; the dried membrane was then ultrasonically cleaned in anhydrous ethanol for 5 minutes to ensure complete wetting and removal of trapped air, and then stored in anhydrous ethanol to obtain a pre-wetted porous base membrane. By continuous stirring, 3 parts protocatechuic acid, 1.2 parts CuCl2 and 5 parts hydrogen peroxide were dissolved in 200 parts deionized water, and stirring was continued for 50 minutes until a homogeneous active solution was obtained. The pre-wetted porous base membrane was transferred to the active solution and soaked for 12 hours. Finally, the membrane was removed and dried in an oven at 60°C for 50 minutes to obtain a hydroxyl-functionalized hydrophilic membrane (PP). Finally, an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite was prepared, specifically as follows: The hydroxyl-functionalized hydrophilic membrane was immersed in a 5 mM solution of silane-functionalized zwitterionic polymer-anhydrous ethanol and ultrasonically treated for 5-8 minutes to obtain a silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane. Under constant stirring, 2 parts of precursor zirconium (TPOZ) and 2 parts of 3-aminopropyltriethoxysilane were added dropwise to 1 part of glacial acetic acid, and the mixture was stirred at room temperature for 1 hour until a homogeneous premix was formed. The premixture was poured into a solution of silane-functionalized zwitterionic polymer containing a hydroxyl-functionalized hydrophilic membrane. The entire system was then sonicated for 5–8 minutes to ensure complete dispersion of the silane-functionalized zwitterionic polymer and to promote its hydrolysis. The mixture was then placed on a shaker at room temperature for 2–3 cycles. After the reaction was complete, the membrane was thoroughly rinsed with anhydrous ethanol to remove loosely bound particles from the surface. Finally, the cleaned membrane was recovered and dried in an oven at 80°C to obtain an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite.

[0028] Example 3 A method for preparing an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite first requires the preparation of a silane-functionalized zwitterionic polymer, specifically: Five parts of (N,N-dimethylaminopropyl)trimethoxysilane and two parts of 1,3-propanesulfonate lactone were dissolved in 20 parts of anhydrous acetone. The mixture was stirred and reacted for 7 hours under nitrogen protection at 30°C to form a suspension containing a white solid precipitate. The suspension was filtered to obtain a white solid, which was washed 2-3 times with anhydrous acetone and then dried overnight under vacuum at 50°C to obtain the final product, a white powder, which is the silane-functionalized zwitterionic polymer (SBSI).

[0029] Furthermore, the preparation method of the hydroxyl-functionalized hydrophilic membrane is as follows: S01, Porous base membrane pretreatment: A 10*10cm polyvinylidene fluoride ultrafiltration membrane with a pore size of 0.5 micrometers was ultrasonically cleaned for 30 minutes with acetone, ethanol and deionized water respectively, and then dried at 60°C; the dried membrane was then ultrasonically cleaned in anhydrous ethanol for 8 minutes to ensure complete wetting and removal of trapped air, and then stored in anhydrous ethanol to obtain a pre-wetted porous base membrane. By continuous stirring, 3 parts protocatechuic acid, 1 part CuCl2 (0.2688 g) and 6 parts hydrogen peroxide were dissolved in 200 parts deionized water, and stirring was continued for 40 minutes until a homogeneous active solution was obtained. The pre-wetted porous base membrane was transferred to the active solution and soaked for 15 hours. Finally, the membrane was removed and dried in an oven at 50°C for 50 minutes to obtain a hydroxyl-functionalized hydrophilic membrane (PP). Finally, an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite was prepared, specifically as follows: The hydroxyl-functionalized hydrophilic membrane was immersed in a 5 mM solution of silane-functionalized zwitterionic polymer-anhydrous ethanol and ultrasonically treated for 8 minutes to obtain a silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane. Under constant stirring, 2 parts of precursor zirconium (TPOZ) and 2 parts of 3-aminopropyltriethoxysilane were added dropwise to 1 part of glacial acetic acid, and the mixture was stirred at room temperature for 2 hours until a homogeneous premix was formed. The premixture was poured into a solution of silane-functionalized zwitterionic polymer containing a hydroxyl-functionalized hydrophilic membrane. The entire system was then sonicated for 8 minutes to ensure complete dispersion of the silane-functionalized zwitterionic polymer and to promote its hydrolysis. The mixture was then placed on a shaker at room temperature for 2-3 cycles. After the reaction was completed, the membrane was thoroughly rinsed with anhydrous ethanol to remove loosely bound particles from the surface. Finally, the cleaned membrane was recovered and dried in an oven at 80°C to obtain an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite.

[0030] Comparative Example 1: A commercially available polyvinylidene fluoride ultrafiltration membrane with a pore size of 0.45 micrometers was purchased from Longjin Thin Film Technology Co., Ltd. Comparative Example 2, using the same preparation method as in Example 1, except for the first step of surface treatment, yielded a hydroxyl-functionalized hydrophilic membrane PP. Comparative Example 3: The surface of the hydroxyl-functionalized hydrophilic membrane PP was first treated with protocatechuic acid, and then the surface was treated with a silane-functionalized zwitterionic polymer to obtain a zwitterionic polymer and a hydroxyl-functionalized hydrophilic membrane. Other aspects were the same as in Example 1. Comparative Example 4: A commercially available PVDF superhydrophilic membrane treated with zwitterionic polymers.

[0031] Experimental data and results analysis 1. Surface morphology analysis The morphology and structure of the material were observed using field emission scanning electron microscopy (Thermo Scientific Verios G4 UC) and energy scattering X-ray spectroscopy (EDS).

[0032] The morphological analysis of the polyvinylidene fluoride ultrafiltration membrane PVDF in Comparative Example 1, the hydroxyl-functionalized hydrophilic membrane PP in Comparative Example 2, and the antifouling superhydrophilic separation membrane PPZP based on zwitterionic polymer-ceramic composite in Example 1 was performed as described above. Figure 1 ; The surface morphology evolution at each stage of modification was carefully studied using scanning electron microscopy, with representative images such as... Figure 1 As shown. Figure 1 Image a shows the microstructure of the original porous membrane, namely a polyvinylidene fluoride (PVDF) ultrafiltration membrane. It exhibits a characteristic porous structure with interconnected pores of different sizes, and the pores are relatively uniformly distributed on the surface. Hydroxyl-functionalized hydrophilic membranes obtained through preliminary modification with protocatechuic acid (…) Figure 1 b) Subsequently, a significant change in surface appearance was observed. The color of the PVC ultrafiltration membrane changed from white to dark. Crucially, the inherent porous structure of the PVC ultrafiltration membrane was largely preserved. However, closer examination revealed that some of the larger original pores appeared to be partially blocked by the protocatechuic acid coating, effectively reducing their apparent diameter. This improvement in pore size is advantageous because it enhances the membrane's particle size screening capability, potentially improving its ability to intercept and retain smaller emulsion oil droplets during oil-water emulsion separation. This improvement was further demonstrated in the subsequent preparation of an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite using surface functionalization with zwitterionic polymers (see...). Figure 1 c) The overall macroporous framework remains evident, indicating that the modification did not lead to significant pore blockage. However, the surface morphology becomes quite rough, characterized by the presence of numerous fine nanoparticles distributed on the membrane surface and within the pore walls. These particles are attributed to in-situ formed ZrO2 nanoparticles, as well as the aggregation of the zwitterionic polymer itself. According to Cassie-Baxter theory, the creation of this hierarchical micro / nanostructure is crucial for achieving a stable superwetting state, increasing surface roughness, which is essential for capturing a stable hydration layer, thereby promoting robust superhydrophilicity and underwater superoleophobicity. Figure 1 d is an EDS image of an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite, such as... Figure 1 As shown in d, the uniform distribution of S, N, O and Zr elements provides compelling evidence for the successful grafting of zirconium oxide onto the zwitterionic polymer and the formation of zirconium oxide on the PPZP film surface.

[0033] 2. Chemical composition analysis Its chemical structure was characterized using Fourier transform infrared spectroscopy (FTIR, Thermo Fisher Scientific Nicolet iN 10). The chemical state and elemental composition of the sample were analyzed using X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific Nexsa).

[0034] The chemical composition analysis of the three membranes—the polyvinylidene fluoride (PVDF) ultrafiltration membrane from Example 1, the hydroxyl-functionalized hydrophilic membrane (PP), and the antifouling superhydrophilic separation membrane (PPZP) based on zwitterionic polymer-ceramic composite—was performed as described above. (See attached image.) Figure 2 ; The surface chemical composition of the membrane was analyzed using FTIR. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 2 In the spectrum of a, 1172 and 1400 cm⁻¹ -1 The strong absorption peak at [value missing] is attributed to the stretching vibrations of the inherent -CH2 and -CF2 groups in the polyvinylidene fluoride (PVDF) ultrafiltration membrane. For the spectrum of the hydroxyl-functionalized hydrophilic membrane, a distinct new peak appeared compared to the PVDF ultrafiltration membrane. Specifically, a peak appeared at 1726 cm⁻¹. -1 The nearby peak originates from the PCA's -COO-, while another new one is at 1512 cm⁻¹. -1 The absorption peak at 3440 cm⁻¹ corresponds to the C=C stretching vibration on the aromatic benzene ring of the grafted protocatechuic acid. -1 A broad absorption peak can be observed at 675 cm⁻¹, which is a result of the action of the hydroxyl groups in protocatechuic acid. As for the spectrum of the superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite, a peak is observed at 675 cm⁻¹. -1 and 1042cm -1 The prominent spectral bands observed nearby are attributed to the -SO42- of the silane-functionalized zwitterionic polymer. 3- The symmetrical S=O stretching vibration occurs. Furthermore, at 775 cm⁻¹... -1 The new absorption peak that appears is due to the Zr-O-Zr stretching vibration on the membrane, indicating the presence of nano-ZrO2 on the PPZP membrane.

[0035] XPS analysis was performed to further clarify the surface elemental composition and confirm successful modification. Figure 2As shown in b, polyvinylidene fluoride (PVDF) exhibits two peaks, 284.5 eV and 530.43 eV, attributed to C1S and O1S, respectively. The O1s signal intensity of the hydroxyl-functionalized hydrophilic membrane is significantly increased, while the C1s signal intensity is relatively decreased. This change is consistent with the introduction of protocatechuic acid onto the PVDF ultrafiltration membrane, resulting in oxygen-rich carboxyl and hydroxyl groups on the PVDF ultrafiltration membrane. Compared to the hydroxyl-functionalized hydrophilic membrane, the superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite shows distinct signals corresponding to Si2p (100.94 eV), S2d (166.8 eV), Zr3d (181.33 eV), and N1s (399.14 eV). The detection of N and S confirms the successful grafting of silane-functionalized zwitterionic polymers. The presence of the Zr3d signal verifies the formation of zirconium oxide, while the Si2p signal originates from the silane coupling agent moiety in the silane-functionalized zwitterionic polymer precursor used for grafting. High-resolution XPS spectra of C1s, O1s, S2p, N1s, and Zr3d are as follows: Figure 2 As shown in cf., the C1S spectrum can be fitted with four peaks at 284.6 eV, 285.8 eV, 288.6 eV, and 289.8 eV ( Figure 2 c), attributed to the five peaks in the O1S spectrum at 532.1 eV, 531.3 eV, 530.9 eV, 530.4 eV, 530 eV, and 529 eV, respectively, of the CC / CH, CO / CN, C=O, and -CF2 O1S spectra. Figure 2 d), attributed to Si-OH, C=O, CO-Si, Zr-O-Zr, and Zr-O, respectively. S 2p( Figure 2 The spectrum of e) can be fitted by two peaks at 166.8 eV and 167.8 eV, which are attributed to S2p3 / 2 and S2p1 / 2, respectively. Figure 2 f shows deconvolution peaks of N1s at 398.7-235 eV and 401.2 eV, attributed to -NH2 and NC, respectively. The Zr3d spectrum shows two peaks at 181.28 eV and 184.62 eV, consistent with Zr3d5 / 2 and Zr3d2 / 3, respectively. Overall, the FTIR and XPS results provide compelling supplementary evidence for the stepwise chemical modification of the PPZP ultrafiltration membrane, ultimately leading to the successful preparation of the PPZP membrane.

[0036] 3. Wettability and film stability The surface wettability of PPZP in Example 1, PVDF in Comparative Example 1, and PP in Comparative Example 2 was tested using a contact angle goniometer (JC2000C1, Shanghai).

[0037] The surface wettability of the membrane was quantitatively evaluated by measuring the contact angle between water and oil. The results are as follows: Figure 3 As shown. From Figure 3 As can be seen from a, the PVDF in Comparative Example 1 exhibits hydrophobicity in air, with an average contact angle (WCA) of 110.2° ± 2.6°. After surface modification with protocatechuic acid from Comparative Example 2 to form a PP film, the surface hydrophilicity of the film was significantly improved. The WCA decreased significantly to 51.7° ± 3.1°, indicating that hydrophilic hydroxyl groups were successfully introduced into the film surface. However, its hydrophilicity is still far from sufficient, while the PPZP obtained in Example 1 after a two-step functionalization process involving zwitterionic polymers and nano-ZrO2 exhibits superhydrophilic behavior. Water droplets diffuse completely and instantaneously upon contact with the PPZP surface, resulting in a WCA of 0°. This complete wetting phenomenon is attributed to the synergistic effect of the highly hydrated zwitterionic polymer layer and the enhanced surface roughness imparted by the ZrO2 nanoparticle aggregates. When in contact with water, the micro-nano rough structure helps to form a stable, continuous aqueous film (hydration layer) on the film surface. It also promotes the superoleophobic properties of PPZP underwater. Figure 3 As can be seen from b, PPZP's superoleophobicity (UWOCA) to various oils is above 150°, indicating its superior underwater superoleophobicity.

[0038] The reaction time of the final grafting step of zwitterionic polymers is crucial for surface roughness and polymer density, which directly affects the wettability of the membrane. Therefore, we investigated the effect of different modification times (3 h, 6 h, 12 h, 24 h, and 48 h) on the wettability of PPZP membranes. Figure 3 c) At 3 hours, the WCA of the membrane was 30°. Notably, after 12 hours of reaction, a superhydrophilic surface with a WCA of 0° and an UWOCA greater than 150° was obtained. When the reaction was extended to 24 hours and 48 hours, the UWOCA increased slightly, while the WCA remained at 0°. Considering both time and resource efficiency, 12 hours was determined to be the optimal modification time for preparing PPZP membranes in subsequent experiments.

[0039] To further clarify and visually demonstrate the strong underwater superoleophobic properties and oil-resistant adhesion of the PPZP film, two dynamic underwater oil resistance tests were conducted. From Figure 3As can be seen, by carefully manipulating a droplet of 1,2-dichloromethane with a syringe needle and slowly bringing it into contact with the surface of an immersed PPZP membrane, a slight pressure was applied upon contact to deform the droplet on the membrane. When the needle was retracted, the droplet was observed to completely separate from the membrane surface, leaving no visible oil residue on the PPZP. Similarly, dyed oil (isooctane) was sprayed at a relatively high velocity onto the surface of a PPZP membrane immersed in water. The oil droplet was observed to immediately bounce off or roll off the PPZP surface without adhering. The oil was so effectively repelled that it did not diffuse or wet the membrane, but maintained its flow integrity as discrete droplets before leaving the surface. This is mainly due to the resilience of the hydration layer formed on the superhydrophilic PPZP membrane, which acts as a strong barrier against oil penetration and adhesion. These results strongly demonstrate the excellent anti-oil adhesion properties of PPZP membranes underwater.

[0040] The long-term operational stability of separation membranes is crucial, especially in real-world applications where they are frequently exposed to challenging chemical environments. These conditions can lead to irreversible degradation of the membrane surface microstructure and chemical composition, affecting initial separation efficiency and antifouling properties. The chemical stability of the PPZP membrane prepared in Example 1 was tested through a series of accelerated aging tests, the results of which are shown in Figure 4. Specifically, PPZP membrane samples were immersed in strong acid (pH=2), strong alkali (pH=12), and saturated sodium chloride solutions for 30 days, respectively. The water contact angle in air (WCA) and the underwater oil contact angle (UWOCA) were monitored regularly throughout the immersion period (every 6 days). Figure 4 As shown in Figure ac, the experimental data demonstrate significant stability. Even after 30 days of continuous exposure to this harsh chemical environment, the PPZP membrane largely maintained its excellent wetting properties. The WCA value remained consistently around 0°, indicating sustained superhydrophilicity. Although the UWOCA value showed slight fluctuations over 30 days, it remained consistently around 150°, demonstrating its strong underwater superoleophobic properties. Furthermore, the membrane's resistance to physical stress was assessed by ultrasonic treatment, a common challenge during operation or cleaning. Figure 4 As shown in Figure d, after ultrasonic treatment for 5–25 minutes, the WCA of the PPZP membrane remained at 0° and the UWOCA was above 150°. These findings demonstrate the excellent chemical and mechanical stability of the PPZP membrane, which is mainly attributed to the formation of stable RO-R' bonds (where R or R' represents Zr or Si) through condensation hydrolysis.

[0041] 4. Separation performance Images of the emulsion and filtrate were observed using an optical microscope (BX53, OLYMPUS, Japan). Dynamic light scattering (DLS) measurements were performed using a Zetasizer Nano ZS90.

[0042] Oil-water emulsion separation experiment: Isooctane, toluene, kerosene, and 1,2-dichloromethane were mixed with water at a ratio of 1:250, and 1 mg / mL sodium dodecyl sulfate was added as an emulsifier. The mixtures were stirred for 6 hours to prepare water-in-isooctane (I / W), water-in-toluene (T / W), water-in-kerosene (K / W), and water-in-dichloromethane (D / W) emulsions, respectively. For visual observation, the oils were stained with Sudan III before the experiment. The emulsification and separation performance of the membrane was evaluated using a self-made laboratory cross-flow filtration device. In a typical filtration process, the membrane was first filtered with pure water for 30 min, followed by emulsification and separation for 4 h. The separation efficiency (R, %) and permeate flux (J, L m) were calculated using the following formulas. -2 h -1 bar -1 ):

[0043]

[0044] in and These represent the oil concentrations in the feed emulsion and filtrate, respectively, and V(L) is the filtrate volume within a predetermined time. A(m 2 ) is the effective filtration area, T(h) is the preset time, and P(bar) is the operating pressure.

[0045] The filtration flux reduction rate (DR) is calculated as follows:

[0046] In the formula, and These represent the permeation flux at the start and end of emulsion separation, respectively.

[0047] The long-term operational stability and antifouling ability of the separation membrane are key indicators for evaluating its practicality. Therefore, a gravity-driven cross-flow filtration device was used to systematically evaluate the permeate flux and antifouling performance of the PPZP membrane prepared in Example 1 for oil-in-water emulsions stabilized with different surfactants. Figure 5 ).like Figure 5As shown in a and 5c, when separating I / W emulsions, the commercial hydrophobic PVDF membrane in Comparative Example 1 experienced a catastrophic flux drop, with the permeate flux plummeting by approximately 78.88% within the first 30 minutes. This was attributed to the strong hydrophobic-hydrophobic interactions between oil droplets and the membrane surface, leading to rapid and irreversible pore blockage. In Comparative Example 2, modification with protocatechuic acid alone resulted in basic hydrophilicity and improved performance, but the permeate flux still decreased significantly by over 50% in the 4-hour test, indicating that oil contamination remained a problem. In stark contrast, the PPZP membrane in Example 1 exhibited excellent antifouling capabilities. Throughout the 4-hour filtration process, the membrane flux remained at 1200 L / m³. -2 h -1 bar -1 The DR (diffusion rate) is negligible, at only 7.78%. This superior performance is attributed to the grafted zwitterionic polymer and the formation of a robust hydration layer through micro / nano-junctions, which acts as a physical barrier preventing oil droplets from adhering and coalescing on the surface, thus ensuring consistently high permeability. To further explore the versatility of PPZP membranes, we tested their antifouling performance against other challenging emulsions (including T / W, D / W, and K / W), such as... Figure 5 As shown in b, for all tested emulsions, the PPZP membrane consistently provided stable high-flux separation, with DR values ​​remaining remarkably low at 13.94%, 5.67%, and 16.15%, respectively. Figure 5 c).

[0048] Furthermore, it is important to note that the separation efficiency was consistently excellent in all tests. We took the filtrate obtained at the end of the separation for further analysis. Taking I / W separation as an example, as... Figure 5 As shown in Figure d, the optical microscopic image of the initial solution clearly shows high-density, finely dispersed oil droplets, a characteristic of stable emulsions. In stark contrast, no visible oil droplets were observed in any of the tested filtrates, providing direct microscopic evidence for effective oil phase interception. Digital photographs further confirm this superior separation; the initially turbid, reddish emulsion became completely transparent and colorless after passing through the PPZP membrane, indicating thorough removal of the dispersed oil. The separation performance was further quantified to confirm these visual observations. DLS analysis of representative I / W initial emulsions showed a wide droplet size distribution, primarily concentrated in the submicron to several micron range. Figure 6 a). Crucially, after filtration, DLS did not detect significant droplet signals in the filtrate, confirming that the emulsified oil droplets had been completely removed. PPZP showed similar results in separating T / W, D / W, and K / W emulsions. Figure 5 e).

[0049] Quantitative assessment of separation efficiency and permeation flux, such as Figure 6 As shown in b. Notably, the PPZP membrane exhibited very high separation efficiencies for all four emulsions, exceeding 99.9%, demonstrating its versatility in treating solvents ranging from light aromatics like toluene to heavier alkanes like kerosene. This high efficiency is reflected in the low TOC content of the collected filtrate. The TOC values ​​for I / W, T / W, D / W, and K / W filtrates were 19.67±13.32, 44.67±18.23, 32.67±13.87, and 71.67±12.22 ppm, respectively. In conclusion, these results demonstrate the powerful versatility of PPZP membranes in purifying complex oily wastewater, offering significant potential for practical environmental remediation applications.

[0050] The separation performance of various membranes involved in Examples 1-3 and Comparative Examples 1-4 for D / W emulsions was tested, as shown in Table 1. Table 1. Separation performance of the separation membrane for D / W emulsions

[0051] As can be seen from the data in Table 1, the separation performance of Examples 1-3 is significantly improved compared with that of Comparative Examples 1-4. This is mainly due to the combined effect of the two surface treatments. The improvement in its anti-fouling and stability performance makes the decrease in filtration flux caused by pore blockage negligible, thereby ensuring the separation efficiency of the entire system.

[0052] Furthermore, the various membranes involved in Examples 1-3 and Comparative Examples 1-4 were immersed in strong acid (pH=2) and strong alkali (pH=12) for 30 days, respectively. Then, the water contact angle and separation efficiency were tested, as shown in Table 2. Table 2 shows that, regardless of whether in strong acid or strong alkali environments, the membranes of Examples 1-3, after two surface treatments, exhibited excellent strength, and the grafted active groups did not detach or weaken. Even after continuous exposure to this harsh chemical environment for 30 days, the PPZP membranes in Examples 1-3 essentially maintained their excellent wetting properties. The WCA remained at approximately 0°, indicating sustained superhydrophilicity. Although the UWOCA value showed slight fluctuations over 30 days, it remained consistently around 150°, indicating strong underwater superoleophobic properties, thus ensuring the separation effect and durability of the prepared antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite. In contrast, under the single-stage active grafting conditions of Comparative Examples 2 and 3, the resulting separation membranes have weak robustness and mechanical strength, which can lead to irreversible degradation of the membrane surface microstructure and chemical composition under harsh conditions, thereby affecting their initial separation effect and antifouling properties.

[0053] Table 2 Separation performance under harsh conditions

[0054] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Equal modifications and variations made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the overall concept of the present invention, shall still fall within the scope of the present invention.

Claims

1. A method for preparing an antifouling superhydrophilic separation membrane based on a zwitterionic polymer-ceramic composite, characterized in that: The aforementioned zwitterionic polymer-ceramic composite antifouling superhydrophilic membrane, comprising a porous base membrane and a protocatechuic acid layer and a zwitterionic polymer-ceramic composite layer grafted onto its surface, is prepared through a two-step surface modification process, specifically: Step 1, grafting protocatechuic acid onto a porous base membrane to obtain a hydroxyl-functionalized hydrophilic membrane, is to graft protocatechuic acid onto the surface and / or pores of a porous base membrane, thereby depositing a uniform protocatechuic acid layer with abundant carboxyl and hydroxyl groups on its surface to obtain a hydroxyl-functionalized hydrophilic membrane. In step 2, the hydroxyl-functionalized hydrophilic layer is co-deposited onto the pretreated surface with silane-functionalized zirconium and precursor zirconium to form a zirconium-ceramic composite layer, and finally a superhydrophilic antifouling separation membrane based on zirconium-ceramic composite is obtained.

2. The method for preparing the antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite according to claim 1, characterized in that, The preparation method of the silane-functionalized zwitterionic polymer is as follows: S1, (N,N-dimethylaminopropyl)trimethoxysilane and 1,3-propanesulfonate lactone are dissolved in anhydrous acetone and reacted under nitrogen protection at a temperature of 25-35°C for 5-8 hours with stirring to form a suspension containing a white solid precipitate. S2, the suspension is filtered to obtain a white solid, which is washed 2 to 3 times with anhydrous acetone, and then dried overnight under vacuum at 50 to 60°C to obtain the final product, a white powder, which is the silane-functionalized zwitterionic polymer.

3. The method for preparing the antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite according to claim 2, characterized in that, The mass ratio of (N,N-dimethylaminopropyl)trimethoxysilane to 1,3-propanesulfonate lactone is 4-5:2-3.

4. The method for preparing the antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite according to claim 1, characterized in that, The preparation method of the hydroxyl-functionalized hydrophilic membrane is as follows: S01, Porous base membrane pretreatment: The porous base membrane is ultrasonically cleaned with acetone, ethanol and deionized water for 20-40 minutes respectively, and then dried at 60°C; the dried membrane is then ultrasonically cleaned in anhydrous ethanol for 5-8 minutes to ensure complete wetting and removal of trapped air, and then stored in anhydrous ethanol to obtain a pre-wetted porous base membrane. SO2, through continuous stirring, dissolve protocatechuic acid, CuCl2 and hydrogen peroxide in deionized water, and continue stirring for 30 to 50 minutes until a uniform active solution is obtained; S03, the pre-wetted porous base membrane is transferred to the active solution and soaked for a period of time. Finally, the membrane is taken out and dried in an oven at 50-60℃ for 30-50 minutes to obtain a polyvinylidene fluoride ultrafiltration membrane with a protocatechuic acid layer rich in carboxyl and hydroxyl groups, namely a hydroxyl-functionalized hydrophilic membrane, denoted as PP.

5. The method for preparing the antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite according to claim 4, characterized in that, The porous base membrane is a polyvinylidene fluoride (PVDF) ultrafiltration membrane with a pore size of 0.2–0.5 micrometers; the mass ratio of protocatechuic acid, CuCl2, hydrogen peroxide, and water is 2–3:1–1.2:5–6:200; the pre-wetted porous base membrane is transferred to the active solution and soaked for 12–15 hours; the concentration of hydrogen peroxide is 30% by mass.

6. The method for preparing the antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite according to claim 1, characterized in that, A superhydrophilic antifouling separation membrane based on a zwitterionic polymer-ceramic composite was prepared, specifically as follows: S001, immerse the hydroxyl-functionalized hydrophilic membrane in a silane-functionalized zwitterionic polymer-anhydrous ethanol solution and sonicate for 5-8 minutes to obtain a silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane. S002, under constant stirring, the precursor zirconium (TPOZ) and 3-aminopropyltriethoxysilane were added dropwise to glacial acetic acid and stirred at room temperature for 1 to 2 hours until a homogeneous premix was formed; S003: Pour the premixed material into the silane-functionalized zwitterionic polymer solution containing the hydroxyl-functionalized hydrophilic membrane in S001; sonicate the entire system for 5-8 minutes to ensure complete dispersion of the silane-functionalized zwitterionic polymer and promote its hydrolysis; then place it on a shaker at room temperature for 2-3 cycles. After the reaction is complete, thoroughly rinse the membrane with anhydrous ethanol to remove loosely bound particles on the surface. Finally, recover the cleaned membrane and dry it in an oven at 80°C to obtain an antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite, denoted as PPZP.

7. The antifouling superhydrophilic separation membrane based on zwitterionic polymer-ceramic composite prepared by the preparation method according to any one of claims 1-6 is applied to environmental pollution control, specifically in the separation of oil-water mixtures and the treatment of oily wastewater.

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