A quaternary ammonium salt modified antibacterial polysulfone membrane, its preparation method and application

Abstract

This application discloses a quaternary ammonium salt modified antibacterial polysulfone membrane, its preparation method, and its application. First, isonicotinamide propanesulfonic acid is prepared by amidation of isonicotinic acid and 3-aminopropanesulfonic acid; then, polysulfone is chloromethylated to obtain chloromethylated polysulfone; next, isonicotinamide propanesulfonic acid is quaternized with chloromethylated polysulfone, covalently grafting pyridine quaternary ammonium salt and sulfonic acid groups onto the polysulfone backbone; finally, a solvent-free phase separation method is used to prepare the membrane. In the resulting membrane, the pyridine quaternary ammonium salt provides efficient, long-lasting, and oxidation-resistant contact antibacterial properties, while the sulfonic acid groups endow the membrane with hydrophilicity and resistance to organic fouling. This membrane combines high flux, high rejection rate, long-term antibacterial stability, and antifouling and easy-to-clean characteristics, making it suitable for water treatment and other fields.

Description

Technical Field

[0001] This invention belongs to the field of modified polysulfone materials technology, and particularly relates to a quaternary ammonium salt modified antibacterial polysulfone film, its preparation method and application. Background Technology

[0002] Polysulfone is a high-performance engineering plastic with excellent mechanical strength, thermal stability, chemical resistance, and film-forming properties, making it widely used in the preparation of separation membrane materials such as ultrafiltration and microfiltration membranes. Polysulfone-based ultrafiltration technology plays a crucial role in water treatment, food and beverage clarification, biopharmaceutical separation, and hemodialysis. Polysulfone membranes are typically prepared using solvent-free phase separation methods and possess finger-like or sponge-like pore structures, enabling highly efficient material separation.

[0003] Polysulfone membrane materials are inherently hydrophobic, resulting in poor resistance to organic fouling. When filtering water containing hydrophobic organic matter such as proteins, humic acids, and polysaccharides, these pollutants are easily adsorbed and deposited on the membrane surface or inside the pores, causing severe membrane fouling. This manifests as rapid flux decline, increased transmembrane pressure differential, and the need for frequent chemical cleaning, increasing operating costs and maintenance difficulty. Polysulfone membranes themselves do not possess antibacterial properties. During long-term operation, bacteria, fungi, and other microorganisms present in the water can easily adhere to, multiply, and secrete extracellular polymers on the membrane surface, forming a biofilm. Biofilms not only further exacerbate membrane fouling but may also cause a decline in effluent quality and even pose biosafety risks. These problems severely restrict the long-term stable operation and widespread application of polysulfone ultrafiltration membranes.

[0004] To overcome the drawbacks of polysulfone membranes, such as strong hydrophobicity and poor antibacterial properties, researchers have attempted to modify them for hydrophilicity and antibacterial properties. Quaternary ammonium salt modification is a commonly used strategy. Quaternary ammonium salts carry a positive charge and can adsorb and disrupt negatively charged bacterial cell membranes through electrostatic interactions, thereby endowing the membrane material with antibacterial activity. Simultaneously, quaternary ammonium salts possess a certain degree of hydrophilicity, which helps improve the antifouling ability of the membrane surface. Existing technologies often employ physical blending or surface coating to introduce small-molecule quaternary ammonium salts into polysulfone membranes, but these methods often suffer from problems such as easy dissolution of quaternary ammonium salts, short-lasting antibacterial effects, and unstable modified layers. Chemical grafting can improve the stability of the polysulfone structure. For example, Chinese invention patent application number 202410376313.0 introduces highly lipophilic long-chain quaternary ammonium salt functional groups and highly hydrophilic short-chain quaternary ammonium salt functional groups into the polysulfone structure, enabling the control of the hydrophilicity, antibacterial properties, and compatibility with other functional plastics of the polysulfone material. However, the types of alkyl quaternary ammonium salts introduced in conventional methods are relatively limited, and their broad-spectrum antibacterial activity, antioxidant properties, and synergistic resistance to complex organic pollution still need to be improved. More importantly, existing quaternary ammonium salt-modified polysulfone membranes often fail to simultaneously address inorganic or organic scaling issues, especially when treating complex water bodies containing high concentrations of organic matter and microorganisms. The synergistic effect of membrane fouling and biofouling leads to rapid degradation of membrane performance.

[0005] Therefore, developing a novel polysulfone membrane that combines efficient and long-lasting antibacterial properties, excellent resistance to organic pollution, good hydrophilicity, and chemical stability, and establishing a simple and controllable preparation method, has significant academic value and promising industrial application prospects. Summary of the Invention

[0006] In view of the above situation and to overcome the shortcomings of the prior art, the present invention provides a quaternary ammonium salt modified antibacterial polysulfone membrane, which has comprehensive advantages such as high efficiency in antibacterial activity, antifouling, high throughput, chemical stability and easy large-scale preparation. It can be widely used in drinking water purification, municipal sewage treatment, industrial wastewater reuse, biopharmaceutical separation and other fields, demonstrating technological progress and industrial applicability.

[0007] To achieve the above objectives, the following technical solution is adopted: This invention provides a method for preparing a quaternary ammonium salt modified antibacterial polysulfone membrane, comprising the following steps: S1. Add isonicotinic acid and 3-aminopropanesulfonic acid to a first organic solvent, add a condensing agent and an organic base, and carry out an amidation reaction. After the reaction is completed, add to ice water, filter, wash and dry to obtain isonicotinamide propanesulfonic acid. S2. Polysulfone is dissolved in chloroform, paraformaldehyde and trimethylchlorosilane are added, and anhydrous tin tetrachloride is added as a catalyst under inert gas protection. After the reaction is completed, chloromethylated polysulfone is obtained by precipitation, washing and drying. S3. Dissolve isonicotinamide propanesulfonic acid and triethylamine together in NMP, stir until clear, then add chloromethylated polysulfone and potassium iodide to react. After the reaction is completed, precipitate, wash and dry to obtain quaternary ammonium salt modified polysulfone. S4. Quaternary ammonium salt modified polysulfone and pore-forming agent are added to a second organic solvent, and then non-solvent additives are added. After stirring, a casting solution is obtained. After degassing, the film is scraped and then gelled in deionized water. After washing and drying, the quaternary ammonium salt modified antibacterial polysulfone film is obtained.

[0008] In step S1, the carboxyl group in the isonicotinic acid molecule is activated using a condensing agent, and then undergoes a nucleophilic substitution reaction with the amino group in the 3-aminopropanesulfonic acid molecule, resulting in dehydration and the formation of a stable amide bond. An organic base is used to neutralize the acid generated during the reaction, shifting the reaction equilibrium towards the product. The final product is an intermediate containing both a pyridine ring and a sulfonic acid group.

[0009] In step S2, paraformaldehyde depolymerizes to formaldehyde in the presence of a Lewis acid catalyst. Formaldehyde reacts with trimethylchlorosilane, undergoing an electrophilic substitution reaction at the active hydrogen positions of the aromatic ring in the polysulfone molecular chain to generate chloromethyl groups. This reaction is a Friedel-Crafts chloromethylation reaction, in which trimethylchlorosilane acts as both a reactant and a solvent or auxiliary. Inert gas protection prevents oxidation side reactions of the polysulfone backbone during the reaction. The chloromethylated polysulfone product introduces reactive chloromethyl active sites onto the benzene ring side groups.

[0010] In step S3, the chloromethyl group on the chloromethylated polysulfone undergoes a nucleophilic substitution reaction (quaternization) with the pyridine nitrogen atom in the isonicotinamide propanesulfonic acid molecule. Triethylamine acts as an acid-binding agent, neutralizing the hydrogen chloride generated in the reaction and promoting the forward reaction. Potassium iodide acts as a catalyst, accelerating the quaternization process through a halide exchange reaction. After the reaction, the pyridine nitrogen atom becomes positively charged and forms a covalent bond with the carbon atom of the chloromethyl group, thereby stably grafting an amphoteric structure containing both pyridine quaternary ammonium cations and sulfonic acid anions onto the polysulfone molecular chain, yielding the target product, quaternary ammonium salt modified polysulfone.

[0011] In step S3, a non-solvent-induced phase separation method is used to form a film. Quaternary ammonium salt modified polysulfone is dissolved in a polar organic solvent, and a pore-forming agent (to regulate the pore structure) and a non-solvent additive (to adjust the thermodynamic properties and kinetic processes) are added. After being coated into a uniform liquid film, it is immersed in a deionized water coagulation bath. Due to the strong mutual solubility and diffusion between the solvent and the non-solvent, solvent-non-solvent exchange occurs inside the liquid film, leading to a decrease in polymer solubility and solidification, forming a porous structure.

[0012] Further, in step S1, the molar ratio of isonicotinic acid to 3-aminopropanesulfonic acid is 1:(1.0~1.5), the condensing agent is selected from at least one of EDC・HCl and DCC, and the molar ratio of the condensing agent to isonicotinic acid is (1.0~1.5):1; the organic base is one of N,N-diisopropylethylamine or triethylamine, and the amount of the organic base is 1.5~2.0 times the molar amount of isonicotinic acid.

[0013] Furthermore, the first organic solvent is one of N,N-dimethylformamide or dichloromethane, the reaction temperature is 20~60℃, and the reaction time is 6~24h.

[0014] Further, in step S2, the molar ratio of polysulfone to paraformaldehyde is 1:(0.5~1.2); the mass ratio of polysulfone to trimethylchlorosilane is 1:(5~10); the mass ratio of polysulfone to anhydrous tin tetrachloride is 1:(0.15~0.2); the inert gas is nitrogen or argon; the reaction temperature is 45~55℃, and the reaction time is 24~48h.

[0015] Further, in step S3, the molar ratio of chloromethylated polysulfone to isonicotinamide propanesulfonic acid is 1:(2.0~2.5), the molar ratio of isonicotinamide propanesulfonic acid to triethylamine is 1:1, and the amount of potassium iodide used is 5~10% of the molar amount of chloromethyl.

[0016] Furthermore, in step S3, the reaction temperature is 80~100℃ and the reaction time is 48~72h.

[0017] Further, in step S4, the casting solution, by mass percentage, comprises 12-18% quaternary ammonium salt modified polysulfone, 60-80% second organic solvent, 5-15% porogen, and 2-8% non-solvent additive; the second organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; the porogen is selected from at least one of polyethylene glycol or polyvinylpyrrolidone; and the non-solvent additive is water or ethanol.

[0018] Further, in step S4, the degassing is performed under vacuum at 25~40℃ for 1~3 hours; the film coating is performed using a doctor blade on a glass plate or non-woven fabric substrate, with a doctor blade thickness of 100~300μm; the gelation film formation is carried out in deionized water at 20~30℃ for 10~30 minutes; the washing involves immersing the gelled film in deionized water for 24~48 hours, changing the deionized water 3~5 times during this period; and the drying is performed under vacuum at 40~60℃ for 12~24 hours.

[0019] On the other hand, the present invention provides a quaternary ammonium salt modified antibacterial polysulfone membrane, which is prepared by the aforementioned preparation method.

[0020] Furthermore, the present invention also provides the application of the aforementioned quaternary ammonium salt modified antibacterial polysulfone membrane in ultrafiltration.

[0021] The beneficial effects of this invention are: This invention introduces a pyridine-type quaternary ammonium salt structure onto the polysulfone molecular chain. The quaternary ammonium ions in this structure can be adsorbed onto the negatively charged bacterial cell wall or cell membrane surface through electrostatic interactions, thereby disrupting the integrity of the lipid bilayer of the cell membrane and causing intracellular leakage. This achieves efficient and broad-spectrum contact sterilization. Unlike traditional small-molecule antibacterial agents, the quaternary ammonium salt of this invention is covalently grafted onto the polysulfone backbone and will not dissolve during use. Therefore, it endows the membrane material with long-lasting and stable antibacterial activity, effectively inhibits the formation of biofilm on the membrane surface, and extends the continuous operating life of the membrane module. The pyridine ring also has aromaticity, giving the polymer chain high rigidity and chemical inertness. Furthermore, the aromatic heterocyclic quaternary ammonium salt has stronger resistance to oxidants and can withstand the oxidative environment in the routine chemical cleaning of the membrane module, avoiding the degradation of antibacterial performance due to the degradation of the quaternary ammonium group.

[0022] The modified polysulfone structure incorporates sulfonic acid groups, which can form a dense water molecule layer in an aqueous environment through hydrogen bonding and ion hydration. This effectively prevents hydrophobic organic pollutants (such as proteins, polysaccharides, and humic substances) from directly contacting the membrane surface, reducing the tendency of pollutants to adsorb and deposit on the membrane surface. The sulfonic acid groups are negatively charged, which generates electrostatic repulsion with common natural organic pollutants that are also negatively charged, further mitigating membrane fouling. Therefore, the membrane material of this invention has both hydrophilicity and antistatic adsorption capabilities, reducing the frequency of chemical cleaning.

[0023] The introduction of quaternary ammonium salts and sulfonic acid groups effectively enhances the surface energy of the polysulfone bulk, transforming the originally hydrophobic polysulfone membrane into a hydrophilic membrane. This increased hydrophilicity facilitates rapid water molecule penetration, improving pure water flux while maintaining a high rejection rate. Attached Figure Description

[0024] Figure 1 The chemical structural diagram of the quaternary ammonium salt modified polysulfone prepared in this invention is shown. Figure 2 Fourier transform infrared (FTIR) images of the quaternary ammonium salt modified polysulfone and polysulfone raw materials prepared in Example 3 of this invention.

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are commercially available. The chemical structural formula of the quaternary ammonium salt modified polysulfone prepared by this invention is attached. Figure 1 As shown.

[0029] Example 1 A method for preparing a quaternary ammonium salt modified antibacterial polysulfone membrane includes the following steps: S1. Isonicotinic acid and 3-aminopropanesulfonic acid are added to a first organic solvent at a molar ratio of 1:1.0, along with a condensing agent and an organic base, to carry out an amidation reaction; the condensing agent is EDC·HCl, and the molar ratio of the condensing agent to isonicotinic acid is 1.0:1; the organic base is N,N-diisopropylethylamine, and the amount of organic base used is 1.5 times the molar amount of isonicotinic acid; the first organic solvent is N,N-dimethylformamide; the reaction temperature is 20℃, and the reaction time is 6 hours; after the reaction is completed, the mixture is added to ice water, filtered, washed, and dried to obtain isonicotinamide propanesulfonic acid; S2. Polysulfone is dissolved in chloroform, paraformaldehyde and trimethylchlorosilane are added, and anhydrous tin tetrachloride is added as a catalyst under inert gas protection; the molar ratio of polysulfone to paraformaldehyde is 1:0.5; the mass ratio of polysulfone to trimethylchlorosilane is 1:5; the mass ratio of polysulfone to anhydrous tin tetrachloride is 1:0.15; the inert gas is nitrogen; the reaction temperature is 45℃, and the reaction time is 24h; after the reaction is completed, chloromethylated polysulfone is obtained by precipitation, washing, and drying. S3. Isonicotinamide propanesulfonic acid and triethylamine are dissolved together in NMP at a molar ratio of 1:1 and stirred until clear. Then, chloromethylated polysulfone and potassium iodide are added to carry out the reaction. The molar ratio of chloromethylated polysulfone to isonicotinamide propanesulfonic acid is 1:2.0. The amount of potassium iodide is 5% of the molar amount of chloromethyl. The reaction temperature is 80℃ and the reaction time is 48h. After the reaction is completed, the polysulfone is obtained by precipitation, washing and drying. S4. Quaternary ammonium salt modified polysulfone and a porogen are added to a second organic solvent, and then a non-solvent additive is added. After stirring, a casting solution is obtained. After degassing, the film is coated and gelled in deionized water. The film is then washed and dried to obtain the quaternary ammonium salt modified antibacterial polysulfone membrane. The casting solution, by mass percentage, contains 12% quaternary ammonium salt modified polysulfone, 80% second organic solvent, 5% porogen, and 3% non-solvent additive. The second organic solvent is N,N-dimethylformamide. The porogen is polyethylene glycol. The non-solvent additive is water. Degassing is performed under vacuum at 25°C for 1 hour. Coating is performed using a doctor blade on a glass plate with a blade thickness of 100 μm. Gel formation is carried out in deionized water at 20°C for 10 minutes. Washing involves immersing the gelled membrane in deionized water for 24 hours, changing the deionized water three times during this period. Drying is performed under vacuum at 40°C for 12 hours.

[0030] Example 2 A method for preparing a quaternary ammonium salt modified antibacterial polysulfone membrane includes the following steps: S1. Isonicotinic acid and 3-aminopropanesulfonic acid are added to a first organic solvent at a molar ratio of 1:1.5, along with a condensing agent and an organic base, to carry out an amidation reaction; the condensing agent is DCC, and the molar ratio of the condensing agent to isonicotinic acid is 1.5:1; the organic base is triethylamine, and the amount of the organic base is 2.0 times the molar amount of isonicotinic acid; the first organic solvent is dichloromethane; the reaction temperature is 60℃, and the reaction time is 24h; after the reaction is completed, the mixture is added to ice water, filtered, washed, and dried to obtain isonicotinamide propanesulfonic acid; S2. Polysulfone is dissolved in chloroform, paraformaldehyde and trimethylchlorosilane are added, and anhydrous tin tetrachloride is added as a catalyst under inert gas protection; the molar ratio of polysulfone to paraformaldehyde is 1:1.2; the mass ratio of polysulfone to trimethylchlorosilane is 1:10; the mass ratio of polysulfone to anhydrous tin tetrachloride is 1:0.2; the inert gas is argon; the reaction temperature is 55℃, and the reaction time is 48h; after the reaction, chloromethylated polysulfone is obtained by precipitation, washing, and drying. S3. Isonicotinamide propanesulfonic acid and triethylamine are dissolved together in NMP at a molar ratio of 1:1 and stirred until clear. Then, chloromethylated polysulfone and potassium iodide are added to carry out the reaction. The molar ratio of chloromethylated polysulfone to isonicotinamide propanesulfonic acid is 1:2.5. The amount of potassium iodide is 10% of the molar amount of chloromethyl. The reaction temperature is 100℃ and the reaction time is 72h. After the reaction is completed, the polysulfone is obtained by precipitation, washing and drying. S4. Quaternary ammonium salt modified polysulfone and a porogen are added to a second organic solvent, and then a non-solvent additive is added. After stirring, a casting solution is obtained. After degassing, the film is coated and gelled in deionized water. The film is then washed and dried to obtain the quaternary ammonium salt modified antibacterial polysulfone film. The casting solution, by mass percentage, contains 18% quaternary ammonium salt modified polysulfone, 60% second organic solvent, 15% porogen, and 7% non-solvent additive. The second organic solvent is N-methylpyrrolidone. The porogen is polyvinylpyrrolidone. The non-solvent additive is ethanol. Degassing is performed under vacuum at 40°C for 3 hours. Coating is performed on a non-woven fabric substrate using a doctor blade with a thickness of 300 μm. Gel formation is carried out in deionized water at 30°C for 30 minutes. Washing involves immersing the gelled film in deionized water for 48 hours, changing the deionized water 5 times during this period. Drying is performed under vacuum at 60°C for 24 hours.

[0031] Example 3 A method for preparing a quaternary ammonium salt modified antibacterial polysulfone membrane includes the following steps: S1. Isonicotinic acid and 3-aminopropanesulfonic acid are added to a first organic solvent at a molar ratio of 1:1.25, along with a condensing agent and an organic base, to carry out an amidation reaction. The condensing agent is DCC, and the molar ratio of the condensing agent to isonicotinic acid is 1.25:1. The organic base is a mixture of N,N-diisopropylethylamine and triethylamine at a mass ratio of 1:1, and the amount of organic base used is 1.75 times the molar amount of isonicotinic acid. The first organic solvent is a mixture of N,N-dimethylformamide and dichloromethane at a mass ratio of 1:1. The reaction temperature is 40°C, and the reaction time is 15 hours. After the reaction is completed, the mixture is added to ice water, filtered, washed, and dried to obtain isonicotinamide propanesulfonic acid. S2. Polysulfone is dissolved in chloroform, paraformaldehyde and trimethylchlorosilane are added, and anhydrous tin tetrachloride is added as a catalyst under inert gas protection; the molar ratio of polysulfone to paraformaldehyde is 1:0.85; the mass ratio of polysulfone to trimethylchlorosilane is 1:7.5; the mass ratio of polysulfone to anhydrous tin tetrachloride is 1:0.175; the inert gas is a mixture of nitrogen and argon in a mass ratio of 1:1; the reaction temperature is 50℃, and the reaction time is 36h; after the reaction is completed, chloromethylated polysulfone is obtained by precipitation, washing, and drying. S3. Isonicotinamide propanesulfonic acid and triethylamine are dissolved together in NMP at a molar ratio of 1:1 and stirred until clear. Then, chloromethylated polysulfone and potassium iodide are added to carry out the reaction. The molar ratio of chloromethylated polysulfone to isonicotinamide propanesulfonic acid is 1:2.25. The amount of potassium iodide is 7.5% of the molar amount of chloromethyl. The reaction temperature is 90℃ and the reaction time is 60h. After the reaction is completed, the polysulfone is obtained by precipitation, washing and drying. S4. Quaternary ammonium salt modified polysulfone and a porogen are added to a second organic solvent, followed by the addition of a non-solvent additive. After stirring, a casting solution is obtained. The solution is then degassed and coated, followed by gelation in deionized water. The resulting film is then washed and dried to obtain the quaternary ammonium salt modified antibacterial polysulfone membrane. The casting solution, by mass percentage, comprises 15% quaternary ammonium salt modified polysulfone, 70% second organic solvent, 10% porogen, and 5% non-solvent additive. The second organic solvent is dimethyl sulfoxide; the porogen is polyethylene glycol and... The mixture consists of polyvinylpyrrolidone in a mass ratio of 1:1; the non-solvent additive is a mixture of water and ethanol in a mass ratio of 1:1; the degassing is performed under vacuum at 32.5°C for 2 hours; the film is coated using a doctor blade on a glass plate with a blade thickness of 200 μm; the gelation is carried out in deionized water at 25°C for 20 minutes; the washing involves immersing the gelled film in deionized water for 36 hours, changing the deionized water 4 times during this period; and the drying is performed under vacuum at 50°C for 18 hours.

[0032] Comparative Example 1 An unmodified pure polysulfone membrane differs from Example 1 in that the modification steps S1, S2, and S3 are not performed. Instead, commercial polysulfone raw materials are used directly, and the polysulfone membrane is prepared according to the same formulation and process as step S4 of Example 1.

[0033] Comparative Example 2 A physically blended small molecule quaternary ammonium salt modified polysulfone membrane differs from Example 1 in that: the chemical modification steps S1, S2, and S3 are not performed; instead, a small molecule quaternary ammonium salt (hexadecyltrimethylammonium bromide, CTAB) is directly physically added during the preparation of the casting solution in step S4, and the amount added is calculated as 5% of the mass of polysulfone in the final casting solution.

[0034] Comparative Example 3 A quaternary ammonium salt modified polysulfone membrane differs from Example 1 in that the raw materials used in steps S1 and S3 are different, and sulfonic acid groups are not introduced. Specifically, step S1 is omitted, and in step S3, N,N-dimethyldodecylamine is used instead of isonicotinamide propanesulfonic acid to react with chloromethylated polysulfone.

[0035] Results Analysis Test Example 1: Characterization of Quaternary Ammonium Salt Modified Polysulfone Structure Fourier transform infrared spectroscopy was performed on the quaternary ammonium salt modified polysulfone and polysulfone raw materials prepared in Example 3. The images are shown in [images not provided]. Figure 2 The solid and dashed lines represent quaternary ammonium salt modified polysulfone and unmodified polysulfone, respectively. From Figure 2 As can be seen from the data, compared with unmodified polysulfone, modified polysulfone exhibits the following significant changes in its infrared spectrum: at 1648 cm⁻¹... -1A new strong absorption peak appears at 3200-3500 cm⁻¹, attributed to the C=O stretching vibration of the amide, indicating the successful introduction of the isonicotinamide structure; [further details about the absorption peak and its relationship to absorption peaks are needed]. -1 A broad and strong absorption band appears within the range of 1040–1200 cm⁻¹, attributed to the stretching vibrations of the amide NH group and the sulfonic acid OH group; simultaneously, in the range of 1040–1200 cm⁻¹... -1 The enhanced S=O absorption peak within the region indicates successful grafting of the sulfonic acid group; furthermore, the absorption peak at 1350–1450 cm⁻¹... -1 CN appeared nearby + The characteristic peaks indicate the formation of the quaternary ammonium salt structure, thus proving that the present invention has successfully prepared quaternary ammonium salt modified polysulfone.

[0036] Test Example 2: Membrane hydrophilicity and permeation separation performance test (1) Purpose of the test: The hydrophilicity (contact angle), pure water permeation flux, and retention performance of the polysulfone membrane before and after modification were evaluated.

[0037] (2) Testing process: Sample preparation: The membrane samples prepared in Examples 1-3 and Comparative Examples 1-3 were immersed in deionized water for 24 hours to remove residual solvent. Before testing, the membrane surface moisture was blotted dry with filter paper. Three parallel samples were prepared for each type of membrane, and the average value of the test results was taken.

[0038] Water contact angle test: Instrument: Optical contact angle measuring instrument.

[0039] Test solution: deionized water, droplet volume 2 μL.

[0040] Procedure: Secure the dried membrane sample flat on a glass slide and place it on the sample stage. Use a microsyringe to drop 2 μL of deionized water onto the membrane surface. After the droplet has stabilized for 10 seconds, use the instrument's built-in software to calculate the contact angle using the Young-Laplace equation. Test at five different locations randomly selected on the surface of each membrane and calculate the average value.

[0041] Pure water flux test: Apparatus: Laboratory ultrafiltration cup (effective filtration area, e.g., 28.7 cm²) 2 (or as recorded by the actual device), connect a nitrogen cylinder to provide pressure.

[0042] Pre-compression: Load the membrane sample into the ultrafiltration cup and pre-compress it with deionized water at 0.15 MPa for 30 min until the flux stabilizes.

[0043] Test conditions: operating pressure 0.1 MPa, water temperature 25±1℃.

[0044] Procedure: Collect the volume (V) of permeate over 10 minutes and record the time (t).

[0045] Calculation formula: Pure water flux J w =V / (A·t), where A is the effective membrane area. Bovine serum albumin (BSA) retention rate test: Feed solution: 1 g / L bovine serum albumin (BSA, molecular weight 67 kDa) in phosphate buffer (PBS, pH 7.4).

[0046] Test conditions: operating pressure 0.1 MPa, water temperature 25±1℃.

[0047] Procedure: After pre-pressurization, replace the deionized water in the ultrafiltration cup with BSA solution (solvent is phosphate buffer solution with pH=7.4). After stable operation for 10 minutes, collect the permeate sample. At the same time, collect the feed sample.

[0048] Concentration determination: The concentration of the feed liquid (C) was determined using a UV-Vis spectrophotometer at a wavelength of 280 nm. f ) and permeate (C p The absorbance of the sample was used to calculate the BSA concentration based on the standard curve.

[0049] Calculation formula: Retention rate R = (1 - C) p / C f ) × 100%.

[0050] Table 1 Comparison of Membrane Hydrophilicity and Permeation Separation Performance Test Results ; As shown in Table 1, the water contact angles (55-58°) of all embodiments were lower than those of the three comparative examples, indicating that the modification of the polysulfone membrane by the present invention improved its hydrophilicity. Comparative Example 1 had the highest contact angle due to its strong hydrophobicity. Although Comparative Example 2 showed some improvement, CTAB was easily dissolved during film formation and cleaning, so its effect was not as good as the chemically grafted examples. The quaternary ammonium salt introduced in Comparative Example 3 had some hydrophilicity, but lacked sulfonic acid groups, so the improvement in hydrophilicity was limited. The embodiments contained both pyridine quaternary ammonium salt and sulfonic acid groups, and their synergistic effect resulted in the best hydrophilicity. The high hydrophilicity endowed the embodiments with higher pure water flux and BSA rejection rate. Comparative Example 1 had the lowest flux, and the hydrophobic surface easily adsorbed BSA, resulting in a low rejection rate. The performance of Comparative Examples 2 and 3 was in the middle. The high flux of the embodiments stemmed from the rapid capture and transfer of water molecules by the hydrophilic surface; the high rejection rate benefited from the uniform pore structure and the reduced non-specific adsorption by the hydrophilic surface.

[0051] Test Example 3: Resistance to Organic Pollution Test (1) Purpose of the test: To evaluate the membrane's antifouling ability and flux recovery capability when filtering organic pollutant solutions.

[0052] (2) Testing process: Sample preparation: Same as test example 2.

[0053] Initial pure water flux (J) w1 Measurement: Measured according to the method in Test Example 2, denoted as J. w1 .

[0054] Pollution experiment: Contaminant solution: a mixed solution of 1 g / L BSA + 0.5 g / L humic acid (prepared with deionized water, pH adjusted to 7.0).

[0055] Procedure: Replace the deionized water in the ultrafiltration vessel with the contaminant solution, and continuously filter for 60 min at 0.1 MPa and 25°C. Record the initial flux (Jp0) and the flux at the end of 60 min (Jp). 60 ).

[0056] Pollution assessment index: Flux Decay Rate (FDR) = (1 - Jp) 60 / Jp0)×100%. The lower the FDR, the better the pollution resistance.

[0057] Cleaning and flux recovery: Physical cleaning: After the contamination experiment, pour off the contaminant solution and gently rinse the membrane surface three times with deionized water.

[0058] Procedure: Fill the ultrafiltration cup with deionized water and run it at 0.1 MPa and 25℃ for 10 minutes for hydraulic cleaning.

[0059] Resumption of flux measurement: After cleaning, the deionized water flux was measured again at 0.1 MPa and recorded as J. w2 .

[0060] Recovery evaluation index: Flux recovery rate (FRR) = (J w2 / J w1 () × 100%. The higher the FRR, the less reversible fouling the membrane has and the better its antifouling performance.

[0061] Table 2 Comparison of Test Results for Resistance to Organic Pollution ; As shown in Table 2, the flux decay rate of each embodiment was much lower than that of the comparative example, and the flux recovery rate was also much higher, demonstrating excellent resistance to organic pollution. Comparative Example 1 had a hydrophobic surface, making it highly susceptible to the adsorption of BSA and humic acid, resulting in severe irreversible pollution and the highest FDR and lowest FRR. Comparative Example 2 showed limited improvement in hydrophilicity, and its surface properties were unstable after the quaternary ammonium salt dissolved. Comparative Example 3 achieved some anti-pollution effect due to the charge and partial hydrophilicity of the quaternary ammonium salt, but it still lagged behind the embodiments. This is because the chemically grafted sulfonic acid groups in the embodiments formed a strong hydration layer, effectively repelling hydrophobic organic matter. Simultaneously, the positive charge of the pyridine quaternary ammonium salt electrostatically repelled negatively charged organic matter; the synergistic effect of both greatly inhibited the adsorption and deposition of pollutants.

[0062] Test Example 4: Antibacterial Properties and Durability Test (1) Purpose of the test: The antibacterial activity and antibacterial persistence (anti-dissolution) of the membrane against Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) were evaluated.

[0063] (2) Testing process: Sample preparation: Cut the membrane sample into a circle with a diameter of 2cm.

[0064] Membrane surface antibacterial rate test: Procedure: Place the membrane sample in a 24-well plate and seed the membrane surface with 100 μL of a 10⁻⁶ solution. 6 CFU / mL of Escherichia coli and Staphylococcus aureus bacterial suspensions were prepared. The suspensions were spread evenly using a sterile coverslip. The suspensions were incubated at 37°C and >90% relative humidity for 24 hours.

[0065] Elution and Counting: After incubation, transfer the membrane sample to a centrifuge tube containing 10 mL PBS and vortex vigorously for 3 min to elute the bacteria surviving on the membrane surface. Spread 100 μL of elution buffer or serially diluted buffer onto LB agar plates and incubate at 37°C for 18 h before counting the colony counts (CFU).

[0066] Calculation formula: Antibacterial rate = (N) c -N t ) / N c ×100%, where N c N represents the average number of colonies on the membrane surface of Comparative Example 1 (blank control without antibacterial properties). t This represents the average number of colonies on the sample membrane surface.

[0067] Antibacterial durability test: The membrane samples from Examples 1-3 and Comparative Examples 1-3 were immersed in deionized water at 50°C for 7 days (simulating accelerated aging), with the water changed daily. After aging, the surface antibacterial rate against Escherichia coli was retested according to the above method.

[0068] Table 3 Comparison of Antibacterial Properties and Durability Test Results ; Table 3 shows that the surface antibacterial rate of the embodiments is slightly better than that of Comparative Example 3, and higher than that of Examples 1 and 2. This indicates that the pyridine-type quaternary ammonium salt of the present invention has stronger antibacterial activity than conventional long alkyl chain quaternary ammonium salts. This is attributed to the conjugated structure of the pyridine ring, which enhances the positive charge density and more effectively disrupts the bacterial cell membrane. Furthermore, the antibacterial rate of each embodiment did not change significantly after aging.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0070] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a quaternary ammonium salt modified antibacterial polysulfone membrane, characterized in that: Includes the following steps: S1. Add isonicotinic acid and 3-aminopropanesulfonic acid to a first organic solvent, add a condensing agent and an organic base, and carry out an amidation reaction. After the reaction is completed, add to ice water, filter, wash and dry to obtain isonicotinamide propanesulfonic acid. S2. Polysulfone is dissolved in chloroform, paraformaldehyde and trimethylchlorosilane are added, and anhydrous tin tetrachloride is added as a catalyst under inert gas protection. After the reaction is completed, chloromethylated polysulfone is obtained by precipitation, washing and drying. S3. Dissolve isonicotinamide propanesulfonic acid and triethylamine together in NMP, stir until clear, then add chloromethylated polysulfone and potassium iodide to react. After the reaction is completed, precipitate, wash and dry to obtain quaternary ammonium salt modified polysulfone. S4. Quaternary ammonium salt modified polysulfone and pore-forming agent are added to a second organic solvent, and then non-solvent additives are added. After stirring, a casting solution is obtained. After degassing, the film is scraped and then gelled in deionized water. After washing and drying, the quaternary ammonium salt modified antibacterial polysulfone film is obtained.

2. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: In step S1, the molar ratio of isonicotinic acid to 3-aminopropanesulfonic acid is 1:(1.0~1.5), the condensing agent is selected from at least one of EDC・HCl and DCC, and the molar ratio of the condensing agent to isonicotinic acid is (1.0~1.5):1; the organic base is one of N,N-diisopropylethylamine or triethylamine, and the amount of the organic base is 1.5~2.0 times the molar amount of isonicotinic acid.

3. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: The first organic solvent is one of N,N-dimethylformamide or dichloromethane, the reaction temperature is 20~60℃, and the reaction time is 6~24h.

4. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: In step S2, the molar ratio of polysulfone to paraformaldehyde is 1:(0.5~1.2); the mass ratio of polysulfone to trimethylchlorosilane is 1:(5~10); the mass ratio of polysulfone to anhydrous tin tetrachloride is 1:(0.15~0.2); the inert gas is nitrogen or argon; the reaction temperature is 45~55℃; and the reaction time is 24~48h.

5. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: In step S3, the molar ratio of chloromethylated polysulfone to isonicotinamide propanesulfonic acid is 1:(2.0~2.5), the molar ratio of isonicotinamide propanesulfonic acid to triethylamine is 1:1, and the amount of potassium iodide used is 5~10% of the molar amount of chloromethyl.

6. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: In step S3, the reaction temperature is 80~100℃ and the reaction time is 48~72h.

7. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: In step S4, the casting solution, by mass percentage, comprises 12-18% quaternary ammonium salt modified polysulfone, 60-80% second organic solvent, 5-15% porogen, and 2-8% non-solvent additive; the second organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide; the porogen is selected from at least one of polyethylene glycol or polyvinylpyrrolidone; and the non-solvent additive is water or ethanol.

8. The method for preparing the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 1, characterized in that: In step S4, the degassing is performed under vacuum at 25-40°C for 1-3 hours; the film coating is performed using a doctor blade on a glass plate or non-woven fabric substrate, with a doctor blade thickness of 100-300 μm; the gelation film is formed in deionized water at 20-30°C for 10-30 minutes; the washing involves immersing the gelled film in deionized water for 24-48 hours, changing the deionized water 3-5 times during this period; and the drying is performed under vacuum at 40-60°C for 12-24 hours.

9. A quaternary ammonium salt modified antibacterial polysulfone membrane, characterized in that: It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the quaternary ammonium salt modified antibacterial polysulfone membrane according to claim 9 in the preparation of filter materials.

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