Preparation method of zwitterionic copolymer ultrafiltration membrane

Abstract

The invention discloses a preparation method of a zwitterionic copolymer ultrafiltration membrane. The preparation method of the zwitterionic copolymer ultrafiltration membrane comprises the following steps: preparing a zwitterionic piperidine monomer; preparing a zwitterionic copolymer; and preparing the zwitterionic ultrafiltration membrane. The zwitterionic copolymer is synthesized by carrying out Friedel-Crafts copolycondensation on terphenyl, a piperidine monomer and a zwitterionic piperidine monomer in a specific proportion. The copolymer has high hydrophilicity and can be directly processed into an ultrafiltration membrane. The ultra-filtration membrane prepared by the preparation method disclosed by the invention is of a compact and interconnected spongy porous structure; the amphoteric ion copolymer membrane prepared by the preparation method can efficiently separate pollutants, shows excellent antifouling performance, can be repeatedly used, solves the problems of poor antifouling capability, low filtering efficiency, short service life and the like of the traditional ultrafiltration membrane, paves a way for directly manufacturing the amphoteric ion copolymer membrane, and provides an effective way for promoting the practical application of the high-performance anti-pollution membrane in a water treatment system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ultrafiltration membrane preparation, and particularly relates to a preparation method of a zwitterionic copolymer ultrafiltration membrane. BACKGROUND

[0002] In membrane separation processes, ultrafiltration (UF) membranes are widely used due to their excellent removal of suspended solids and macromolecular contaminants, and are particularly suitable for municipal and industrial wastewater treatment, drinking water reuse, and purification of complex wastewater. Commercial ultrafiltration membranes are mainly made of polymeric materials such as polyether sulfone (PES), polyvinylidene fluoride (PVDF), and polysulfone (PS). Although these polymers can provide reliable filtration performance, their inherent hydrophobicity makes them prone to adsorption of contaminants and surface fouling, which can compromise the long-term operational efficiency and durability of the membranes. Therefore, developing the next generation of ultrafiltration membranes with enhanced anti-fouling performance and high separation efficiency remains a key and active research direction in this field.

[0003] One widely studied strategy to enhance membrane performance is to modify with zwitterionic substances. This modification can significantly improve the anti-fouling properties of the membrane, while also imparting excellent hydrophilicity, durability, and stability. Zwitterionic polymer-modified membranes can maintain ideal permeation performance while retaining excellent anti-fouling ability. These advantages not only stem from their inherent hydrophilicity, but also from their ability to form a unique hydration structure at the molecular interface. This structure helps to build a strong hydration layer around the polymer chain, effectively inhibiting fouling by establishing a high-energy barrier between the membrane surface and potential contaminants.

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

[0005] However, despite the obvious advantages of zwitterionic modification, it often faces challenges such as multi-step synthesis processes and the generation of undesirable byproducts, which complicate large-scale production and restrict its practical application. Solving these technical bottlenecks is crucial for fully realizing the practical potential of zwitterionic membrane technology. SUMMARY

[0006] The technical solution of the present application proposes a new method for preparing ultrafiltration membranes using zwitterionic copolymers, mainly providing a zwitterionic copolymer ultrafiltration membrane and its preparation method and application, to effectively overcome the shortcomings of traditional surface modification techniques and avoid key defects such as leakage of nanomaterials and interfacial incompatibility in hybrid matrix membranes.

[0007] The present application aims to provide a kind of zwitterionic copolymer (referred to as ZCP) and its preparation method, by triphenyl with piperidine and zwitterionic piperidine monomer (referred to as zwPip) Friedel-Crafts copolycondensation with controlled proportion synthesis, this copolymer has high hydrophilicity.

[0008] Another purpose of the present application is to provide a kind of ultrafiltration membrane and its preparation method, using the high hydrophilicity of zwitterionic copolymer, prepare the ultrafiltration membrane with excellent antifouling ability.

[0009] The present application also aims to provide a kind of application of ultrafiltration membrane, for wastewater treatment.

[0010] The present application provides a kind of zwitterionic copolymer membrane and its preparation method, comprising the following steps:

[0011] Step one: N-methyl-4-piperidone is mixed and dissolved with 1,4-butanesulfonic acid lactone in solvent, heated reaction, then cooled to room temperature, washed, vacuum dried, to obtain zwitterionic piperidine monomer.

[0012] Step two: the zwitterionic piperidine monomer prepared in step one is mixed and dispersed with p-triphenyl and N-methyl-4-piperidone in solvent, trifluoroacetic acid and trifluoromethanesulfonic acid are added at low temperature to carry out reaction, precipitate, wash, vacuum dried, to obtain zwitterionic copolymer.

[0013] Step three: the zwitterionic copolymer prepared in step two is dissolved in solvent, after defoaming, film casting, to obtain ultrafiltration membrane.

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

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

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

[0017] Further, in step one, the washing is to wash the product with acetonitrile.

[0018] Further, in step one, the vacuum drying is to place in 80±2℃ vacuum drying box for 12-24h.

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

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

[0021] Further, the low temperature reaction in step two refers to a reaction at 0℃ for 2-12h, preferably, the reaction time is 8h.

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

[0023] Further, the speed of adding the trifluoroacetic acid and the trifluoromethanesulfonic acid in step two is controlled to 1 drop per 2s.

[0024] Further, the precipitation in step two is precipitation in ethanol.

[0025] Further, the vacuum drying in step two is placing in a vacuum drying oven at 60±2℃ for 12-24h.

[0026] Further, the solvent in step three is N-methyl pyrrolidone (NMP).

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

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

[0029] Further, the ZCP is dissolved in the solvent in step three, and stirring is performed at 25±2℃ for 12-24h.

[0030] Further, the defoaming in step three refers to defoaming in a vacuum drying oven at 60±2℃ for 3h.

[0031] Further, the casting conditions in step three are as follows: the defoamed casting solution is uniformly poured on a clean glass plate under room temperature and air conditions, a doctor blade with a height of 150±2μm is used to uniformly coat the casting solution on the glass plate at a speed of 1.5±0.1m / min. The casting solution on the glass plate is transferred to deionized water at 25±2℃ for phase inversion, and a membrane is precipitated. The membrane is placed in deionized water for immersion for 48±2h, and the water is changed every 6-7h to completely remove the residual solvent in the membrane, thereby obtaining an 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. 1HNMR, FTIR and XPS confirmed the chemical structure of ZCP; the surface morphology and properties of the membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), static water contact angle measurement, etc. It can be observed from the electron micrographs that the surface porosity of ZCP ultrafiltration membranes increased significantly, and the pore structure of the membrane cross-section changed from finger-like pores to sponge-like pores. ZCP-2 ultrafiltration membrane had the best performance: the initial pure water flux was 234.51 Lm -2 h -1 bar -1 , and the bovine serum albumin (BSA) rejection rate was 98.35%. After three pollution-cleaning cycles, the flux recovery rate (FRR) was 95.02%. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a synthetic route for the zwitterionic piperidine monomer.

[0038] Figure 2 is a synthetic route for the zwitterionic copolymer.

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

[0040] Figure 4 is the FTIR spectrum of zwPip, CP, ZCP-1 and ZCP-2.

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

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

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

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

[0045] Figure 9 is the SEM image of the membrane surface and cross-section.

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

[0047] Figure 11 is the flux change graph over time (with BSA as the pollutant) at 1 bar.

[0048] Figure 12 is the FRR value after three BSA filtrations. DETAILED DESCRIPTION

[0049] The application is further described below in conjunction with the specific embodiments.

[0050] Experimental materials used in the application:

[0051] The synthesis of the zwitterionic piperidinium monomer (C6H 18 H 14 ), N-methyl-4-piperidone (C6H 11 NO), 1,4-butanedisulfonyl lactone (C4H8O3S), acetonitrile (C2H3N), dichloromethane (CH2Cl2), trifluoroacetic acid (C2HF3O2), trifluoromethanesulfonic acid (CHF3O3S), N-methylpyrrolidone (C5H9NO), ethanol (C2H6O) were purchased from Shanghai Biochem-Pharm Co., Ltd.

[0052] Example 1

[0053] A preparation method of a zwitterionic copolymer, specifically:

[0054] (1) Synthesis path of zwitterionic piperidinium monomer Figure 1 As shown in the figure, specifically: 2.17 g of N-methyl-4-piperidone and 3.6 mL of 1,4-butanedisulfonyl lactone were mixed and dissolved in a three-necked flask containing 10 mL of acetonitrile, heated at 60±2℃, stirred at this temperature for 24 h, then cooled to room temperature, washed with acetonitrile for 5 times and placed in a vacuum drying oven at 80±2℃ for 12 h to obtain the synthesis product zwPip.

[0055] (2) Synthesis path of zwitterionic copolymer Figure 2The mixture of p-terphenyl 2.525 g, N-methyl-4-piperidone 1.610 g and dichloromethane 10 mL was prepared and 1 drop of trifluoroacetic acid (0.5 mL) and trifluoromethanesulfonic acid (13 mL) was added dropwise every 2 s under ice bath condition (0-4 °C). After the completion of the addition, the reaction was stirred for 8 h and then precipitated in 300 mL of ethanol. The precipitate was filtered and further washed with ethanol and kept in a vacuum oven at 60 ± 2 °C to obtain the pristine copolymer (referred as CP). The mixture of p-terphenyl 2.525 g, N-methyl-4-piperidone 1.578 g, zwPip 0.0708 g and dichloromethane 10 mL was prepared and 1 drop of trifluoroacetic acid (0.5 mL) and trifluoromethanesulfonic acid (13 mL) was added dropwise every 2 s under ice bath condition (0-4 °C). After the completion of the addition, the reaction was stirred for 8 h and then precipitated in 300 mL of ethanol. The precipitate was filtered and further washed with ethanol and kept in a vacuum oven at 60 ± 2 °C to obtain ZCP-1. The mixture of p-terphenyl 2.525 g, N-methyl-4-piperidone 1.546 g, zwitterionic piperidine monomer 0.1416 g and dichloromethane 10 mL was prepared and 1 drop of trifluoroacetic acid (0.5 mL) and trifluoromethanesulfonic acid (13 mL) was added dropwise every 2 s under ice bath condition (0-4 °C). After the completion of the addition, the reaction was stirred for 8 h and then precipitated in 300 mL of ethanol. The precipitate was filtered and further washed with ethanol and kept in a vacuum oven at 60 ± 2 °C to obtain ZCP-2.

[0056] The FTIR spectra of the copolymers were recorded at room temperature using 1 HNMR, FTIR and XPS were used to determine the molecular structure of the zwPip and ZCP.

[0057] The FTIR spectra of the copolymers were recorded at room temperature using 1 HNMR spectra of the copolymers (Fig. 1), Figure 3 ), the characteristic signals observed between 7.00-8.00 ppm were attributed to the aromatic protons in the copolymer terphenyl backbone structure. The peaks between 2.6 to 3.8 ppm indicated 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 represented the methylene H atoms attached to the -SO3 - group, indicating the incorporation of the zwPip into the polymer structure.

[0058] In the FTIR spectra of the copolymers (Fig. 2), Figure 4 ), ZCP showed a slight peak at 1058 cm -1 , indicating the symmetric stretching vibration associated with the O=S=O moiety of the -SO3 - group. A prominent absorption peak was observed at 3460 cm -1 , which was 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 the copolymer was confirmed by the FTIR spectra.

[0059] The chemical composition of ZCP was further confirmed by XPS. Figure 5 , Figure 6 ) The spectra of N1s and S2p regions provide strong evidence for the successful introduction of zwitterionic groups. Analysis of the N1s region indicates that the primary peak (399.9 eV) of nitrogen in the zwitterionic copolymer corresponds to C-N, while the secondary peak (402.4 eV) is associated with quaternary ammonium C-N + . A unique peak corresponding to S2p was obviously observed on the copolymer, indicating the presence of zwitterionic groups (-SO3 - ). The results show that ZCP was successfully synthesized through quaternization involving tertiary amines within the copolymer piperidine segments, mediated by 1,4-butane sultone.

[0060] Example 2

[0061] Ultrafiltration membranes were prepared using ZCP prepared in Example 1, in particular as follows:

[0062] ZCP was dissolved in NMP, and after degassing, a film was scraped, and an ultrafiltration membrane was obtained. All membranes were prepared by non-solvent induced phase separation (NIPS). The specific steps are as follows: ZCP was dissolved in NMP, and stirred at 25±2℃ for 12h, and then degassed in a vacuum drying oven at 60±2℃ for 3h. Finally, the casting solution obtained after degassing was uniformly poured onto a clean glass plate, and a scraper with a height of 150±2μm was used to coat the casting solution uniformly on the glass plate at a speed of 1.5m / min. Then it was transferred to deionized water at 25±2℃ for phase inversion, and the membrane was precipitated, and the membrane was placed in deionized water for 48h, and the water was changed every 6h to completely remove the residual NMP in the membrane, and an ultrafiltration membrane was obtained. According to the different copolymers in the casting solution, the membranes were marked as CPM, ZCPM-1 and ZCPM-2.

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

[0064] Membrane marker Copolymer class 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 the membrane have a great influence on the separation and anti-fouling performance of the membrane, including the surface pore structure, cross-sectional morphology, surface hydrophilicity and surface roughness of the membrane.

[0066] Hydrophilicity detection: the ultrafiltration membrane was placed in a blast drying oven at 60℃ for 12h to characterize the hydrophilicity of the membrane.

[0067] The contact angle values of three different positions on each group of membranes were measured at room temperature using a contact angle meter (OCA60), and the average value was calculated. The membrane-liquid interfacial free energy (-ΔG MW) to measure the wettability of the membrane surface. The higher the surface wettability of the membrane, the higher the interfacial free energy. Atomic force microscopy (AFM) was used to determine the surface roughness of the membranes. The average roughness (R a ) and root mean square roughness (R q ) of the AFM images were quantitatively calculated by the Nanoscopy software and used to represent the surface roughness of the membranes. MW The modified Y-Duprée equation was used to calculate the equation (Equation (1)):

[0068]

[0069] where γLis the surface tension of water (72.8 mJ m -2 , 20 °C), θ is the average water contact angle value, and the roughness area parameter Δ is the ratio of the actual surface area to the geometric area of the membrane.

[0070] By measuring the water contact angle and the interfacial free energy, the hydrophilicity of all the ultrafiltration membranes was calculated. The surface hydrophilicity is widely considered as a key factor to control the permeability and antifouling performance of liquid filtration membranes, as shown in Figure 7 .

[0071] The surface wettability analysis showed that CPM exhibited a water contact angle of 78.86°, while ZCPM-1 and ZCPM-2 exhibited gradually decreasing angles of 68.83° and 63.37°, respectively. The corresponding membrane-water interfacial free energy (-ΔG MW ) values of CPM, ZCPM-1 and ZCPM-2 were 30.79 mJ m -2 , 123.09 mJ m -2 and 134.94 mJ m -2 , respectively. This indicated the high hydrophilicity of the membranes, which was also consistent with the water contact angle of the copolymer membranes. This would be beneficial to improve the permeability and antifouling performance of the ultrafiltration membranes.

[0072] Atomic force microscopy (AFM) was used to study the surface roughness of the membranes. Figure 8 The 2D and 3D surface morphologies of the ultrafiltration membranes. R a and R q were used to represent the surface roughness of the membranes. From the AFM images, it was observed that the surface roughness (R a = 42.40, R q = 52.00) of the ZCPM-2 membrane was significantly higher than that of CPM (R a = 10.40, R q = 13.90) and ZCPM-1 membrane (R a = 35.80, R q = 43.10). This phenomenon could be attributed to the excessive swelling of the membrane surface caused by the high water absorption capacity of the 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 permeated water, kg; A is the effective membrane area, m 2 ; p is the density of the permeate, 1.0 kg / L; At is the permeation time of deionized water, h.

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

[0079]

[0080] where C f is the concentration of the BSA original solution, mg / L, and C p is the concentration of the BSA solution after permeation, which was determined by measuring the absorbance at 278 nm using UV-Vis spectrophotometry.

[0081] The BSA anti-fouling performance of the ultrafiltration membrane was represented by the flux recovery rate (FRR), which was calculated using equation (4):

[0082]

[0083] where J wv is the initial stable pure water flux, J wc is the recovered water flux after BSA solution filtration.

[0084] Ultrafiltration performance of the membrane: The effect of the zwitterionic content on the water flux and BSA rejection rate of the copolymer ultrafiltration membrane was studied by ultrafiltration experiments. The water flux measurement and BSA rejection performance of the UF membranes with different concentrations of zwitterionic groups are shown in Figure 10 As the zwitterionic groups in the copolymer increased, the water flux showed a gradual upward trend, increasing from 151.15 Lm -2 h -1 bar -1 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 ZCPM-2 membranes is 1.5 times higher than that of CPM. In terms of BSA rejection, ZCPM-2 membranes exhibit significantly enhanced performance, with rejection efficiency increasing from 91.79% (CPM) to 98.35% (ZCPM-1). The introduction of zwitterionic groups forms a mechanism that minimizes direct interactions between BSA and the membrane, thereby inhibiting BSA permeation. This mechanism involves hydrogen bonding between zwitterionic groups and water molecules, driven by their inherent hydrophilicity. This copolymer is a high-performance material for ultrafiltration membrane manufacturing.

[0085] Anti-fouling performance of the membranes: To further investigate the anti-fouling performance of the ultrafiltration membranes, three ultrafiltration cycles were performed. Figure 11 The change in membrane flux during the filtration of BSA solution over three cycles is shown. After filtration of BSA solution, the flux of ZCPM decreased significantly lower than that of CPM, indicating that the anti-fouling performance of ZCPM was enhanced. At the same time, the water washing efficiency after three filtration cycles was used to further understand the anti-fouling performance of the membranes using the FRR value. FRR is a key indicator of anti-fouling durability, reflecting the ability of the membrane to recover permeability after multiple cleaning cycles. A higher FRR value is associated with enhanced anti-fouling performance. As shown in Figure 12 compared to 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 anti-fouling performance. The introduction of zwitterionic groups can enhance the surface hydrophilicity of the membrane, making it easy for the membrane surface to form a hydration layer and bind with water, reducing the deposition of BSA on the membrane surface and improving the anti-fouling performance of the membrane. The results highlight the synergistic effect of zwitterionic groups in improving hydrophilicity and anti-fouling robustness.

[0086] The present application synthesizes a zwitterionic copolymer by Friedel-Crafts copolycondensation of terphenyl with piperidine and zwitterionic piperidine monomers. Compared with the original membrane, the zwitterionic copolymer ultrafiltration membrane has higher total porosity and larger average surface pore size, thus having higher permeability. The FRR value of all zwitterionic copolymer ultrafiltration membranes is higher than that of the original membrane, which is mainly due to the enhancement of the hydrophilicity of the zwitterionic copolymer ultrafiltration membrane. The results show that the zwitterionic copolymer ultrafiltration membrane synthesized by one-step method has simple structure and good scalability, and is an effective way to prepare high-performance ultrafiltration membranes.

[0087] The above are preferred embodiments of the present application, the basic principles and main features of the present application and the advantages of the present application are shown and described above, those skilled in the art should understand that the present application is not limited to the above embodiments, the above embodiments and the description in the specification are only to illustrate the principles of the present application, various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the claimed present application, the scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a zwitterionic copolymer ultrafiltration membrane, characterized by, The preparation method is specifically as follows: Step one: N-methyl-4-piperidone and 1, 4-butanesultone are mixed and dissolved in a solvent, heated for reaction, then cooled to room temperature, washed, and vacuum dried to obtain the zwitterionic piperidone monomer; Step two: the zwitterionic piperidone monomer obtained in step one is mixed and dispersed with p-terphenyl and N-methyl-4-piperidone in a solvent, trifluoroacetic acid and trifluoromethanesulfonic acid are added at low temperature for reaction, precipitated, washed, and vacuum dried to obtain the zwitterionic copolymer; Step three: the zwitterionic copolymer obtained in step two is dissolved in a solvent, defoamed, and scraped 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-piperidone to 1, 4-butanesultone is 1:1-1:

2.

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

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

5. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step two, the mass of the zwitterionic piperidone monomer, p-terphenyl and N-methyl-4-piperidone is 0.03-0.2g, 2.0-3.0g and 1.0-2.0g, 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 reaction at 0℃ for 2-12h.

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

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

9. The method for preparing a zwitterionic copolymer ultrafiltration membrane according to claim 1, characterized in that, In step three, the solvent 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, the defoaming refers to defoaming in a vacuum drying box at 60±2℃ for 3h.

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