Preparation method of zwitterionic copolymer ultrafiltration membrane

Abstract

The application discloses a preparation method of a zwitterionic copolymer ultrafiltration membrane, and the preparation of the zwitterionic copolymer ultrafiltration membrane comprises the following steps: preparation of a zwitterionic piperidine monomer, preparation of a zwitterionic copolymer, and preparation of a zwitterionic ultrafiltration membrane. The zwitterionic copolymer is synthesized through Friedel-Crafts copolycondensation of terphenyl, piperidine monomer and zwitterionic piperidine monomer in a specific proportion. The copolymer can be directly processed into an ultrafiltration membrane while having high hydrophilicity. The prepared ultrafiltration membrane has a dense, interconnected sponge-like porous structure, can efficiently separate pollutants, has excellent antifouling performance, and can be used for multiple times, thereby solving the problems of poor antifouling ability, low filtration efficiency and short service life of traditional ultrafiltration membranes, paving the way for direct manufacturing of zwitterionic copolymer membranes, and providing an effective approach for promoting practical application of high-performance antifouling membranes in water treatment systems.

Description

Technical Field

[0001] This invention belongs to the field of ultrafiltration membrane preparation, specifically relating to a method for preparing a zwitterionic copolymer ultrafiltration membrane. Background Technology

[0002] In membrane separation processes, ultrafiltration (UF) membranes are widely used due to their excellent removal capabilities of suspended solids and large molecular pollutants, particularly suitable for municipal and industrial wastewater treatment, drinking water reuse, and the purification of complex wastewater. Commercial ultrafiltration membranes are mainly made of polymer materials such as polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polysulfone (PS). Although these polymers provide reliable filtration performance, their inherent hydrophobicity makes them susceptible to pollutant adsorption and surface fouling. This persistent problem can impair the long-term operating efficiency and durability of the membrane. Therefore, developing next-generation ultrafiltration membranes that combine enhanced antifouling performance with high separation efficiency remains a key and active research direction in this field.

[0003] One widely studied strategy for improving membrane performance is modification with zwitterionic materials. This modification significantly enhances the membrane's antifouling properties while imparting excellent hydrophilicity, durability, and stability. Zwitterionic polymer-modified membranes maintain ideal permeability while retaining superior antifouling capabilities. These advantages stem not only from their inherent hydrophilicity but also from their ability to form unique hydration structures at the molecular interface. This structure facilitates the construction of a robust hydration layer around the polymer chains, effectively inhibiting fouling by establishing a high-energy barrier between the membrane surface and potential contaminants.

[0004] Compared to other membrane performance enhancement technologies (such as incorporating nanomaterials into a polymer matrix to prepare hybrid matrix membranes), zwitterionic modified membranes offer significant advantages. Hybrid matrix membranes are often limited by the interfacial compatibility issues between nanomaterials and the polymer matrix, which can easily lead to structural defects and thus affect solute retention performance. In contrast, zwitterionic modified membranes typically achieve higher chemical homogeneity and more stable performance.

[0005] However, despite the significant advantages of zwitterionic modification, it often faces challenges such as multi-step synthesis processes and the generation of undesirable byproducts, which complicates large-scale production and limits its practical application. Overcoming these technical bottlenecks is crucial to fully realizing the actual potential of zwitterionic membrane technology. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technical solutions by proposing a novel method for preparing ultrafiltration membranes using zwitterionic copolymers. It mainly provides a zwitterionic copolymer ultrafiltration membrane, its preparation method, and its application, effectively overcoming the deficiencies of traditional surface modification techniques and avoiding key defects such as leakage of nanomaterials and interfacial incompatibility in mixed matrix membranes.

[0007] The purpose of this invention is to provide a zwitterionic copolymer (referred to as ZCP) and its preparation method, which is synthesized by Friedel-Crafts copolymerization of terphenyl with piperidine and zwitterionic piperidine monomer (referred to as zwPip) in a controlled ratio. This copolymer has high hydrophilicity.

[0008] Another objective of this invention is to provide an ultrafiltration membrane and its preparation method, which utilizes the high hydrophilicity of zwitterionic copolymers to prepare an ultrafiltration membrane with excellent antifouling ability.

[0009] Another objective of this invention is to provide an application of an ultrafiltration membrane for wastewater treatment.

[0010] This invention provides a zwitterionic copolymer film and its preparation method, comprising the following steps:

[0011] Step 1: Mix N-methyl-4-piperidinone with 1,4-butyryl lactone in a solvent, heat to react, cool to room temperature, wash, and vacuum dry to obtain zwitterionic piperidine monomer.

[0012] Step 2: The zwitterionic piperidine monomer obtained in Step 1 is mixed and dispersed with p-terphenyl and N-methyl-4-piperidinone in a solvent. Trifluoroacetic acid and trifluoromethanesulfonic acid are added at low temperature to react, precipitate, wash, and vacuum dry to obtain the zwitterionic copolymer.

[0013] Step 3: Dissolve the zwitterionic copolymer obtained in Step 2 in a solvent, degas it, and then cast the membrane to obtain the ultrafiltration membrane.

[0014] Further, in step one, the molar ratio of N-methyl-4-piperidinone to 1,4-butyryl lactone is 1:1 to 1:1.2, preferably 1:1.8.

[0015] Furthermore, the solvent in step one is acetonitrile.

[0016] Furthermore, the heating reaction in step one refers to heating at 60±5℃ for 24-48 hours. Preferably, the reaction temperature is 60℃ and the reaction time is 24 hours.

[0017] Furthermore, in step one, the product is washed with acetonitrile.

[0018] Furthermore, in step one, the vacuum drying is carried out in a vacuum drying oven at 80±2℃ for 12-24 hours.

[0019] Further, in step two, the masses of zwPip, p-terphenyl, and N-methyl-4-piperidinone are 0.03-0.2g, 2.0-3.0g, and 1.0-2.0g, respectively, preferably 0.1416g, 2.525g, and 1.546g, respectively.

[0020] Furthermore, the solvent in step two is dichloromethane.

[0021] Furthermore, the low-temperature reaction in step two refers to a low-temperature reaction at 0°C for 2-12 hours, preferably 8 hours.

[0022] Further, in step two, the amount of trifluoroacetic acid is 0.1-5 mL and the amount of trifluoromethanesulfonic acid is 10-20 mL. Preferably, the amount of trifluoroacetic acid is 0.5 mL and the amount of trifluoromethanesulfonic acid is 13 mL.

[0023] Furthermore, in step two, the rate at which trifluoroacetic acid and trifluoromethanesulfonic acid are added is controlled to be 1 drop every 2 seconds.

[0024] Furthermore, in step two, the precipitation occurs in ethanol.

[0025] Furthermore, in step two, the vacuum drying is carried out in a vacuum drying oven at 60±2℃ for 12-24 hours.

[0026] Furthermore, the solvent in step three is N-methylpyrrolidone (NMP).

[0027] Furthermore, in step three, the mass concentration of ZCP in the casting solution is 10-25%; preferably 20%.

[0028] Furthermore, in step three, the mass ratio of ZCP to solvent is 2:8.

[0029] Further, in step three, ZCP is dissolved in a solvent and stirred at 25±2℃ for 12-24 hours.

[0030] Furthermore, in step three, degassing refers to degassing in a vacuum drying oven at 60±2℃ for 3 hours.

[0031] Further, the casting conditions in step three are as follows: Under ambient air conditions, the deaerated casting solution is evenly poured onto a clean glass plate. Using a scraper with a height adjusted to 150±2μm, the casting solution is evenly spread onto the glass plate at a speed of 1.5±0.1m / min. The casting solution spread on the glass plate is then transferred to deionized water at 25±2℃ for phase inversion, precipitating into a membrane. The membrane is then immersed in deionized water for 48±2h, with the water changed every 6-7h to completely remove residual solvent from the membrane, thus obtaining the ultrafiltration membrane.

[0032] This invention provides a zwitterionic copolymer ultrafiltration membrane, which is prepared by the above method.

[0033] This invention provides an application of the above-mentioned zwitterionic copolymer ultrafiltration membrane for wastewater treatment.

[0034] The main drawback of ultrafiltration membrane separation is membrane fouling, which severely reduces permeate flux. The hydrophilicity or hydrophobicity of the membrane surface has a significant impact on membrane morphology, separation performance, and fouling. In ultrafiltration processes, the membrane surface should be hydrophilic, as hydrophilic surfaces exhibit good tolerance to membrane fouling. Permeate flux is directly related to the porosity, pore size distribution, thickness of the upper and lower membrane layers, and the hydrophilicity of the membrane. Rejection rate is another crucial parameter in ultrafiltration separation; excellent ultrafiltration rejection rate is strictly dependent on the pore size distribution and porosity of the membrane. Modifying the nodular microstructure during the phase inversion process of membrane preparation plays a vital role in controlling the removal rate of macromolecules. Zwitterionic copolymers can overcome various problems in ultrafiltration membranes; introducing zwitterionic groups into the copolymer can improve the hydrophilicity of the polymer membrane, thereby enhancing its antifouling performance.

[0035] This invention innovatively synthesizes a zwitterionic piperidine monomer by reacting the tertiary amine group on N-methyl-4-piperidinone with 1,4-butyryl lactone, based on the highly hydrophilic structure of zwitterionic copolymers. The zwitterionic copolymer is then synthesized through Friedel-Crafts copolymerization of terphenyl with piperidine and zwPip. The synthesis was achieved by proton nuclear magnetic resonance spectroscopy (1H NMR spectroscopy). 1 The structure of ZCP was confirmed by 1H NMR, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Subsequently, a series of ZCPs with different ratios (ZCP-1, ZCP-2) were synthesized to regulate the structure and properties of the film.

[0036] Compared with existing technologies, this invention provides a simple and effective method for synthesizing novel zwitterionic copolymers. N-methyl-4-piperidinone and 1,4-butyryl lactone are dissolved in acetonitrile solvent. Through high-temperature heating, the tertiary amino group on N-methyl-4-piperidinone and the 1,4-butyryl lactone undergo a quaternization reaction, forming a quaternary ammonium group (-CN). + ) and -SO3 on the side chain - A zwitterionic piperidine monomer is formed. Subsequently, ZCP is synthesized through Friedel-Crafts copolymerization of terphenyl with piperidine and the zwitterionic piperidine monomer. ZCP exhibits high hydrophilicity and antifouling properties. 1The chemical structure of ZCP was confirmed by 1H NMR, FTIR, and XPS. The membrane surface morphology and properties were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and static water contact angle measurements. It was clearly observed from the electron micrographs that the surface porosity of the ZCP ultrafiltration membrane was significantly increased, and the pore structure of the membrane cross-section changed from finger-like pores to sponge-like pores. The ZCP-2 ultrafiltration membrane exhibited optimal performance: an initial pure water flux of 234.51 Lm. -2 h -1 bar -1 The bovine serum albumin (BSA) rejection rate was 98.35%. After three contamination-wash cycles, the flux recovery rate (FRR) was 95.02%. Attached Figure Description

[0037] Figure 1 This is the synthetic route for zwitterionic piperidine monomers.

[0038] Figure 2 This is the synthetic route for zwitterionic copolymers.

[0039] Figure 3 For zwPip, CP, ZCP-1 and ZCP-2 1 HNMR spectrum.

[0040] Figure 4 The FTIR spectra of zwPip, CP, ZCP-1, and ZCP-2 are shown.

[0041] Figure 5 XPS full-spectrum scans of zwPip, CP, ZCP-1, and ZCP-2.

[0042] Figure 6 For the N-fine spectrum scan of ZCP-2.

[0043] Figure 7 For the water contact angle and free energy of the membrane.

[0044] Figure 8 This is an AFM image of the membrane surface.

[0045] Figure 9 These are SEM images of the membrane surface and cross-section.

[0046] Figure 10 The pure water flux and BSA rejection rate of the membrane are given.

[0047] Figure 11 This is a graph showing the flux change over time under 1 bar conditions (with BSA as the pollutant).

[0048] Figure 12 The FRR value is the result of three BSA filters. Detailed Implementation

[0049] The present invention will be further described below with reference to specific embodiments.

[0050] Experimental materials used in this invention:

[0051] p-Triphenyl (C 18 H 14 ), N-methyl-4-piperidinone (C6H 11 NO), 1,4-butyric acid lactone (C4H8O3S), acetonitrile (C2H3N), dichloromethane (CH2Cl2), trifluoroacetic acid (C2HF3O2), trifluoromethanesulfonic acid (CHF3O3S), N-methylpyrrolidone (C5H9NO), and ethanol (C2H6O) were purchased from a biochemical technology company in Shanghai.

[0052] Example 1

[0053] A method for preparing a zwitterionic copolymer, specifically comprising:

[0054] (1) Synthetic route of zwitterionic piperidine monomer Figure 1 As shown, specifically: 2.17 g of N-methyl-4-piperidinone and 3.6 mL of 1,4-butyric acid lactone were mixed and dissolved in a three-necked flask containing 10 mL of acetonitrile. The mixture was heated at 60±2 °C and stirred for 24 h at this temperature. Then it was cooled to room temperature, washed 5 times with acetonitrile, and placed in a vacuum drying oven at 80±2 °C for 12 h to obtain the synthesized product zwPip.

[0055] (2) Synthetic routes of zwitterionic copolymers Figure 2As shown. 2.525 g of terphenyl, 1.610 g of N-methyl-4-piperidinone, and 10 mL of dichloromethane were mixed. Under ice bath conditions (0-4℃), 1 drop of trifluoroacetic acid (0.5 mL) and trifluoromethanesulfonic acid (13 mL) were added dropwise every 2 seconds. After the addition was complete, the mixture was stirred for 8 h. Subsequently, the precipitate was precipitated in 300 mL of ethanol. The precipitate was filtered, washed further with ethanol, and then placed in a vacuum drying oven at 60±2℃ to obtain the original copolymer (referred to as CP). 2.525 g of terphenyl, 1.578 g of N-methyl-4-piperidinone, 0.0708 g of zwPip and 10 mL of dichloromethane were mixed. Under ice bath conditions (0-4℃), 1 drop of trifluoroacetic acid (0.5 mL) and trifluoromethanesulfonic acid (13 mL) were added dropwise every 2 seconds. After the addition was complete, the mixture was stirred and reacted for 8 h. The precipitate was then precipitated in 300 mL of ethanol. The precipitate was filtered, washed further with ethanol, and then placed in a vacuum drying oven at 60±2℃ to obtain ZCP-1. 2.525 g of terphenyl, 1.546 g of N-methyl-4-piperidinone, 0.1416 g of zwitterionic piperidine monomer, and 10 mL of dichloromethane were mixed. Under ice bath conditions (0-4℃), 1 drop of trifluoroacetic acid (0.5 mL) and trifluoromethanesulfonic acid (13 mL) were added dropwise every 2 seconds. After the addition was complete, the mixture was stirred and reacted for 8 h. The precipitate was then precipitated in 300 mL of ethanol. The precipitate was filtered, washed further with ethanol, and then placed in a vacuum drying oven at 60±2℃ to obtain ZCP-2.

[0056] Use at room temperature 1 The molecular structures of zwPip and ZCP were determined by HNMR, FTIR and XPS.

[0057] exist 1 HNMR spectrum ( Figure 3 The characteristic signal observed between 7.00 and 8.00 ppm can be attributed to aromatic protons in the main chain structure of the copolymer terphenyl. The peaks at 2.6 to 3.8 ppm indicate the presence of H atoms from the methyl and methylene groups of the piperidine ring, while the peak at 1.6 to 1.7 ppm indicates that the H atom of the methylene group is attached to –SO3. - This indicates that zwPip is incorporated into the polymer structure.

[0058] In FTIR spectra ( Figure 4 ZCP at 1058cm -1 A slight peak is shown at this point, indicating a correlation with –SO3. - Symmetric tensile vibrations related to the O=S=O portion of the functional groups. At 3460 cm⁻¹ -1 A prominent absorption peak was observed, which is attributed to the NH stretching vibration associated with the quaternary ammonium salt present in the copolymer. The successful synthesis of the zwitterionic piperidine monomer and copolymer was confirmed by FTIR spectroscopy.

[0059] XPS was used to further confirm the chemical composition of ZCP. Figure 5 , Figure 6 The spectra in the N1s and S2p regions provide strong evidence for the successful introduction of zwitterionic groups. Analysis of the N1s region shows that the primary peak (399.9 eV) of the nitrogen in the zwitterionic copolymer corresponds to CN, while the secondary peak (402.4 eV) corresponds to quaternary ammonium CN. + The presence of a distinct peak corresponding to S2p on the copolymer indicates the presence of zwitterionic groups (-SO3). - The results showed that ZCP was successfully synthesized via quaternization of tertiary amines involving the piperidine segments of the copolymer, mediated by 1,4-butyryl lactone.

[0060] Example 2

[0061] Ultrafiltration membranes were prepared using the ZCP prepared in Example 1, and the specific method is as follows:

[0062] ZCP was dissolved in NMP, degassed, and then coated to obtain the ultrafiltration membrane. All membranes were prepared using the non-solvent-induced phase separation (NIPS) method. The specific steps are as follows: ZCP was dissolved in NMP and stirred continuously at 25±2℃ for 12 hours, followed by degasing in a vacuum drying oven at 60±2℃ for 3 hours. Finally, the resulting casting solution was evenly poured onto a clean glass plate, and a scraper with a height adjusted to 150±2μm was used to evenly coat the glass plate at a speed of 1.5m / min. The mixture was then transferred to deionized water at 25±2℃ for phase inversion, precipitating the membrane. The membrane was then immersed in deionized water for 48 hours, with the water changed every 6 hours to completely remove residual NMP, thus obtaining the ultrafiltration membrane. Based on the different copolymers in the casting solution, the membranes were labeled CPM, ZCPM-1, and ZCPM-2.

[0063] The following table shows the composition of the casting solution:

[0064] Membrane labeling Copolymer types copolymer mass / g NMP / g CPM CP 2 8 ZCPM-1 ZCP-1 2 8 ZCPM-2 ZCP-2 2 8

[0065] The structure and surface properties of a membrane have a significant impact on its separation and antifouling performance, including the membrane's surface pore structure, cross-sectional morphology, surface hydrophilicity, and surface roughness.

[0066] Hydrophilicity test: The ultrafiltration membrane was dried in a 60°C oven for 12 hours to characterize the hydrophilicity of the membrane.

[0067] At room temperature, the contact angle values ​​at three different locations on each group of membranes were measured using a contact angle meter (OCA60), and the average value was calculated. The membrane-liquid interfacial free energy (-ΔG) was further calculated using the equation. MWThe wettability of the membrane surface is measured using atomic force microscopy (AFM). Higher surface wettability corresponds to higher interfacial free energy. The surface roughness of the membrane is determined using AFM. The average roughness (R0) of the AFM images is quantitatively calculated using nanoscale analysis software. a ) and root mean square roughness (R q ), and is used to represent the surface roughness of the membrane. -ΔG MW The equation (Equation (1)) is calculated using the modified Y–Dupréequation:

[0068]

[0069] In the formula, γL is the surface tension of water (72.8 mJ / m²). -2 (20℃), θ is the average water contact angle, and the roughness area parameter Δ is the ratio of the actual area of ​​the membrane surface to its geometric area.

[0070] The hydrophilicity of all ultrafiltration membranes was calculated by measuring the water contact angle and interfacial free energy. Surface hydrophilicity is widely considered a key factor controlling the permeability and antifouling performance of liquid filtration membranes, such as... Figure 7 As shown.

[0071] Surface wettability analysis showed that CPM exhibited a water contact angle of 78.86°, while ZCPM-1 and ZCPM-2 showed gradually decreasing angles of 68.83° and 63.37°, respectively. The corresponding film-water interfacial free energies (-ΔG) for CPM, ZCPM-1, and ZCPM-2 were also described. MW The values ​​were 30.79 mJm. -2 123.09mJm -2 and 134.94mJm -2 This indicates the membrane's high hydrophilicity, a result consistent with the water contact angle of the copolymer membrane. This will benefit the improvement of the ultrafiltration membrane's permeability and antifouling properties.

[0072] The surface roughness of the film was studied using atomic force microscopy (AFM). Figure 8 The 2D and 3D surface morphologies of ultrafiltration membranes are shown. a and R q Used to represent the surface roughness of the membrane. The surface roughness (R0) of the ZCPM-2 membrane was observed from the AFM images. a =42.40, R q =52.00) is significantly higher than CPM(R) a =10.40, R q =13.90) and ZCPM-1 membrane (R a =35.80, R q =43.10). This phenomenon may be attributed to excessive surface swelling of the membrane caused by the high water absorption capacity of zwitterionic groups.

[0073] The evolution of the film surface and cross-sectional morphology was observed using scanning electron microscopy (SEM). Figure 9 All membrane samples were sputter-coated with gold to obtain SEM images. Additionally, the membrane samples were immersed in liquid nitrogen and subjected to cryogenic fracture for SEM observation to study the cross-sectional morphology of the membranes. The average surface pore size and surface porosity were calculated using ImageJ software. With increasing zwitterionic group content, the surface porosity increased from 21.34% (CPM) to 31.84% (ZCPM-2), while the average surface pore size increased from 10 nm (CPM) to 15 nm (ZCPM-2). The CPM membrane exhibited a significant asymmetric cross-sectional structure with finger-like pores in the sublayers, while the ZCPM-1 and ZCPM-2 ultrafiltration membranes exhibited a sponge-like structure.

[0074] CPM exhibits a typical asymmetric structure, with a dense top layer and finger-like pores in the sublayer. This finger-like structure is attributed to the rapid exchange of solvent and non-solvent during the NIPS process. The solvent diffusion rate influences the formation of finger pores. The reduced viscosity of the copolymer casting solution allows for faster solvent diffusion, promoting the development of larger finger pores and the formation of a thinner skin layer. The increase in surface porosity is primarily due to the incorporation of zwitterionic groups, which interact more effectively with water during phase inversion, thereby increasing membrane porosity. The change in cross-sectional structure is attributed to the delayed solvent-non-solvent exchange rate during the NIPS process in zwitterionic copolymers. This morphological transformation is attributed to the delayed solvent-non-solvent exchange rate during phase inversion in zwitterionic copolymers. Specifically, the addition of zwitterionic groups to ZCPM-1 and ZCPM-2 slows the precipitation rate, inhibits finger pore formation, and promotes a denser, more porous, sponge-like structure. This phenomenon is consistent with the known ability of zwitterionic materials to delay phase separation, thereby modulating the membrane substrate morphology.

[0075] Ultrafiltration experiment: An effective membrane area of ​​22 cm² was used. 2 The filtration device was used to determine the permeability of the ultrafiltration membrane, the BSA retention capacity, and the antifouling performance. In this system, a pump provided pressure. To stabilize the pure water flux of the membrane, it was pre-pressurized with deionized water at 0.15 MPa for 60 min. Then, it was continued at 0.1 MPa for 30 min to obtain the initial pure water flux of the membrane. Next, the BSA solution (0.5 g / L) was filtered for 30 min. Finally, the membrane was rinsed with deionized water and filtered for another 30 min to test the water flux recovered after membrane cleaning. The BSA filtration and water washing were repeated 3 times. The permeate was weighed every 2 min using an electronic balance connected to the computer. The membrane flux was calculated using formula (2). J(Lm -2 h -1 bar -1 ):

[0076]

[0077] Where m is the mass of permeate water in kg; A is the effective membrane area in m². 2 ρ refers to the density of the permeate, 1.0 kg / L; Δt is the permeation time of deionized water, in hours.

[0078] The BSA rejection rate (R) of the membrane is calculated according to equation (3).

[0079]

[0080] Where C f This is the concentration of the original BSA solution, in mg / L, C p The concentration of the BSA solution after permeation is determined by measuring the absorbance at 278 nm using ultraviolet-visible spectrophotometry.

[0081] The antifouling performance of ultrafiltration membranes for BSA is expressed by flux recovery rate (FRR), which is calculated using equation (4):

[0082]

[0083] In the formula, J wv It is the initial steady-state pure water flux, J wc This is the recovery water flux after filtering the BSA solution.

[0084] Ultrafiltration performance of the membrane: The effects of zwitterion content on the water flux and BSA rejection rate of the copolymer ultrafiltration membrane were investigated through ultrafiltration experiments. Water flux measurements and BSA rejection performance of UF membranes with different zwitterion concentrations are shown below. Figure 10 As shown, with the increase of amphoteric groups in the copolymer, the water flux gradually increases, from 151.15 Lm. -2 h -1 bar -1 Increased to 234.51 Lm -2 h -1 bar -1This enhancement can be attributed to the presence of zwitterionic groups in the polymer, which significantly improves the hydrophilicity of the ultrafiltration membrane, resulting in higher porosity and improved water permeability. The water flux of the ZCPM-2 membrane is 1.5 times higher than that of the CPM membrane. In terms of BSA retention, the ZCPM-2 membrane exhibits significantly enhanced performance, with the retention efficiency increasing from 91.79% (CPM) to 98.35% (ZCPM-1). The introduction of zwitterionic groups minimizes the direct interaction between BSA and the membrane, thereby inhibiting BSA permeation. This mechanism involves hydrogen bonds between the zwitterionic groups and water molecules, driven by their inherent hydrophilicity. This copolymer is a high-performance material for ultrafiltration membrane fabrication.

[0085] Membrane antifouling performance: To further investigate the antifouling performance of the ultrafiltration membrane, three ultrafiltration cycle experiments were conducted. Figure 11 The changes in membrane flux during three cycles of BSA solution filtration are shown. After filtration with BSA solution, the flux decrease of ZCPM is significantly less than that of CPM, indicating enhanced antifouling performance of ZCPM. Simultaneously, the FRR (Fluid Flow Rate) value, obtained by analyzing the water washing efficiency after three filtration cycles, further reveals the membrane's antifouling performance. FRR is a key indicator of antifouling durability, reflecting the membrane's ability to recover permeability after multiple cleaning cycles. Higher FRR values ​​are associated with enhanced antifouling properties. Figure 12 As shown, compared with CPM (90.40%), the FRR of ZCPM-1 and ZCPM-2 membranes (92.95% and 95.02%, respectively) showed significant improvement. This means that ZCPM has better antifouling performance. The introduction of zwitterionic groups can enhance the surface hydrophilicity of the membrane, making it easier for a hydration layer to form on the membrane surface and bind with water, reducing BSA deposition on the membrane surface, and improving the membrane's antifouling performance. The results highlight the synergistic effect of zwitterionic groups in improving hydrophilicity and antifouling robustness.

[0086] This invention synthesizes a zwitterionic copolymer via Friedel-Crafts copolymerization of terphenyl with piperidine and zwitterionic piperidine monomers. Compared to the original membrane, the zwitterionic copolymer ultrafiltration membrane exhibits higher total porosity and a larger average surface pore size, thus resulting in higher permeability. All zwitterionic copolymer ultrafiltration membranes show higher FRR values ​​than the original membranes, primarily due to the enhanced hydrophilicity of the zwitterionic copolymer ultrafiltration membranes. The results demonstrate that the one-step synthesis of zwitterionic copolymer ultrafiltration membranes offers a simple structure, good scalability, and is an effective method for preparing high-performance ultrafiltration membranes.

[0087] The above are preferred embodiments of the present invention. The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope of the present invention. All such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a zwitterionic copolymer ultrafiltration membrane, characterized in that, The preparation method is specifically as follows: Step 1: N-methyl-4-piperidinone and 1,4-butyryl lactone are mixed and dissolved in a solvent, heated to react, then cooled to room temperature, washed, and vacuum dried to obtain zwitterionic piperidine monomer; Step 2: The zwitterionic piperidine monomer obtained in Step 1 is mixed and dispersed with p-terphenyl and N-methyl-4-piperidinone in a solvent. Trifluoroacetic acid and trifluoromethanesulfonic acid are added at low temperature to react, precipitate, wash, and vacuum dry to obtain the zwitterionic copolymer. Step 3: Dissolve the zwitterionic copolymer obtained in Step 2 in a solvent, degas it, and then scrape the membrane to obtain the ultrafiltration membrane.

2. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step one, the molar ratio of N-methyl-4-piperidinone to 1,4-butyryl lactone is 1:1 to 1:

2.

3. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, The solvent in step one is acetonitrile.

4. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, The heating reaction in step one refers to heating at 60±5℃ for 24-48 hours.

5. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step two, the masses of zwitterionic piperidine monomer, p-terphenyl, and N-methyl-4-piperidinone are 0.03-0.2 g, 2.0-3.0 g, and 1.0-2.0 g, respectively.

6. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step two, the low-temperature reaction refers to a reaction at 0℃ for 2-12 hours.

7. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, The solvent in step two is dichloromethane.

8. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step two, the amount of trifluoroacetic acid is 0.1-5 mL, and the amount of trifluoromethanesulfonic acid is 10-20 mL.

9. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, The solvent in step three is N-methylpyrrolidone.

10. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step three, the mass concentration of the zwitterionic copolymer in the casting solution is 10-25%; in step three, degassing refers to degassing in a vacuum drying oven at 60±2℃ for 3 hours.

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