A bifunctionalized terpolymer modified polyacrylonitrile ultrafiltration membrane, a preparation method and application thereof

Abstract

This invention belongs to the field of membrane separation technology and discloses a bifunctional ternary polymer-modified polyacrylonitrile (PAN) ultrafiltration membrane, its preparation method, and its application. Preparation method: A monomer containing quaternary ammonium salt groups, a monomer containing zwitterionic groups, and a monomer containing primary amine groups are mixed uniformly with water to obtain a mixed system. Under a nitrogen atmosphere, the mixed system is reacted with an initiator to obtain a polymer solution. Polyacrylonitrile powder is subjected to alkali treatment and activation treatment sequentially to obtain activated powder. The activated powder is then subjected to a chemical condensation grafting reaction with the polymer solution to obtain a modified powder. The modified powder, a pore-forming agent, and a solvent are mixed to obtain a casting solution, which is poured onto a moistened nonwoven fabric to obtain a precursor membrane and undergo phase inversion to form a modified PAN ultrafiltration membrane. This invention prepares a ternary polymer with both bactericidal and anti-adhesion functions, and uses powder grafting and chemical modification processes to modify the PAN powder before membrane fabrication, ensuring the long-term stability of the membrane functionalization.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and more specifically, relates to a bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane, its preparation method, and its application. Background Technology

[0002] Membrane fouling, especially biofouling, is a major obstacle to the long-term operational efficiency of ultrafiltration membranes. Biofouling, caused by the adhesion, proliferation, and biofilm formation of microorganisms on the membrane surface, is characterized by its complex composition and difficulty in complete removal, leading to a significant decrease in membrane flux, increased operating energy consumption, and deterioration of effluent quality. Traditional anti-biofouling strategies often focus on modifying the membrane surface for sterilization, such as introducing quaternary ammonium salts (QAS) and metal nanoparticles as antibacterial agents. However, these materials often lead to loss of membrane hydrophilicity and flux due to their hydrophobicity, and also pose a risk of drug resistance. Balancing antibacterial performance with the inherent physicochemical properties of the membrane (such as hydrophilicity and pore size distribution) has become the core challenge in the development of anti-biofouling membranes.

[0003] Designing sterilization membrane surfaces is a mainstream approach to mitigating biofouling. Modified membrane surfaces can damage or kill bacteria upon attachment, effectively inhibiting biofouling formation. Strategies for achieving antibacterial effects through membrane surface modification can be broadly categorized into electrical interference with bacterial activity, physical penetration and destruction of bacterial structure, and inhibition of cellular enzyme activity. Commonly used sterilization materials include metal particles, nanomaterials, and cationic salts (quaternary ammonium salts, ionic liquids). Among these, QAS (quaternary ammonium salts) are widely used as a common antibacterial material due to their high antibacterial rate and low drug resistance. However, QAS itself is hydrophobic; modification weakens the hydrophilic properties of the membrane surface, leading to a decrease in the membrane's permeability and antifouling performance.

[0004] Furthermore, existing modification methods (such as surface coating and blending) often suffer from unstable grafts (external components grafted onto polyacrylonitrile membranes), which can damage the membrane structure, leading to decreased flux or weakened physicochemical properties. Meanwhile, traditional membrane surface grafting modifications often employ post-treatment processes (such as alkali treatment activation), which can easily cause problems such as membrane pore swelling and uneven pore size distribution, limiting their practical application.

[0005] Therefore, there is an urgent need to propose a bifunctional ternary polymer-modified polyacrylonitrile ultrafiltration membrane, its preparation method, and its application. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a bifunctional ternary polymer-modified polyacrylonitrile (PAN) ultrafiltration membrane, its preparation method, and its applications. This invention prepares a ternary polymer with both bactericidal and anti-adhesion functions. The PAN powder is modified before membrane fabrication using powder grafting and chemical modification processes to ensure the long-term stability of the membrane's functionalization.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane, the method comprising the following steps:

[0008] S1: A monomer containing a quaternary ammonium salt group, a monomer containing a zwitterionic group, and a monomer containing a primary amino group are mixed with water to obtain a mixed system; under a nitrogen atmosphere, the mixed system is mixed with an initiator and reacted under heating conditions to obtain a ternary polymer; the ternary polymer is mixed with a buffer solution to obtain a polymer solution;

[0009] S2: Polyacrylonitrile (PAN) powder is subjected to alkali treatment and activation treatment in sequence to obtain activated powder;

[0010] S3: The activated powder is mixed with the polymer solution and subjected to a chemical condensation grafting reaction. After centrifugation, washing, and drying, the modified powder is obtained.

[0011] S4: Mix the modified powder, pore-forming agent and solvent evenly to obtain a casting solution; pour the casting solution onto a moistened nonwoven fabric; when the moistened nonwoven fabric is in a semi-dry state, use a doctor blade to scrape a membrane onto the semi-dry nonwoven fabric to obtain a precursor membrane, and perform phase transformation in a coagulation bath to separate the phases and form the bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane.

[0012] According to the present invention, preferably, in step S1:

[0013] The monomer containing the quaternary ammonium salt group is [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC).

[0014] The monomer containing the zwitterionic group is [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA);

[0015] The monomer containing the primary amino group is aminoethyl methacrylate (AEMA).

[0016] The molar ratio of the monomer containing a primary amino group, the monomer containing a quaternary ammonium salt group, and the monomer containing a zwitterionic group is 10:(10-80):(10-80), preferably 10:10:80, 10:30:60, 10:45:45, 10:60:30, 10:80:10, and more preferably 10:45:45.

[0017] In the reaction system formed by mixing the mixed system and the initiator, the molar concentration of the initiator is 0.5-2 mmol / L; the initiator is at least one of AIBN (azobisisobutyronitrile), AIBA (azobisisobutyramidine hydrochloride) and ABVN (azobisisoheptanenitrile), preferably AIBN;

[0018] The reaction temperature is 50-80℃, preferably 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, more preferably 70℃, and the reaction time is 6-48h, preferably 6h, 12h, 18h, 24h, 36h, 48h, more preferably 24h;

[0019] The buffer solution is PBS buffer solution and / or Tris-HCl buffer solution (preferably, the pH value of Tris-HCl buffer solution is 7.4); the concentration of the polymer solution is 90-450 mg / L (preferably 90 mg / L, 180 mg / L, 270 mg / L, 360 mg / L, 450 mg / L, more preferably 360 mg / L).

[0020] According to the present invention, preferably, after the reaction is completed, a product solution is obtained, and the product solution is subjected to evaporation purification and freeze-drying treatment in sequence to obtain ternary polymer powder. The ternary polymer powder is then mixed with the buffer solution to obtain a polymer solution.

[0021] This invention utilizes free radical polymerization technology to prepare a ternary polymer with dual functional modifications, achieving both bactericidal and anti-adhesion properties (hydrophilicity). The sulfonic acid groups in the zwitterionic material, due to their strong hydrophilicity and hydration capacity, effectively inhibit pollutant adhesion; while the quaternary ammonium salt achieves efficient bactericidal effects by disrupting microbial cell membranes. Combining these two elements to construct a ternary copolymer not only kills bacteria but also reduces biofilm formation through a hydration layer, providing a new approach to the design of anti-biofouling membranes.

[0022] According to the present invention, preferably, in step S2:

[0023] The polyacrylonitrile powder has a molecular weight of 50-300 kDa, preferably 50 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, or 300 kDa, and more preferably 150 kDa.

[0024] The alkaline solution used in the alkaline treatment is a sodium hydroxide aqueous solution with a concentration of 1-10 mol / L, preferably 1 mol / L, 3 mol / L, 5 mol / L, 7 mol / L, or 10 mol / L, and more preferably 5 mol / L;

[0025] The alkali treatment temperature is 40-80℃, preferably 40℃, 50℃, 60℃, 70℃, or 80℃, more preferably 60℃, and the time is 0.5-4h, preferably 0.5h, 1h, 2h, 3h, or 4h, more preferably 1h;

[0026] The activation solution used in the activation treatment is a mixture of EDC (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride), NHS (methacryloyloxyethyltrimethylammonium chloride) and PBS buffer solution with pH 3-6, wherein the molar ratio of EDC to NHS is (1-5):1;

[0027] The activation treatment is performed at a temperature of 30-60℃ (preferably 30℃, 40℃, 50℃, 60℃, more preferably 50℃), for a reaction time of 0.5-2h (preferably 0.5h, 1.0h, 1.5h, 2.0h, more preferably 1.0h), and the pH of the reaction system is 3-6 (preferably 5.0).

[0028] This invention converts the surface nitrile groups of polyacrylonitrile (PAN) powder into carboxyl groups through alkali treatment, forming active sites suitable for chemical condensation grafting. The carboxyl groups on the PAN powder are then activated using EDC / NHS, and subsequently, a ternary functionalized polymer is grafted onto the PAN powder via chemical condensation grafting, thereby endowing the PAN ultrafiltration membrane with anti-biofouling properties. This invention, through powder grafting, allows the modified PAN ultrafiltration membrane to retain the original membrane's physical and chemical properties. The pre-grafting process modifies the PAN powder before membrane fabrication, avoiding membrane pore swelling caused by alkali treatment and preserving the original membrane's permeability and pore size distribution.

[0029] In this invention, as a preferred embodiment, step S2 includes:

[0030] The polyacrylonitrile powder was dried overnight in a 60°C oven and stored in a desiccator. The dried polyacrylonitrile powder was then placed in an aqueous sodium hydroxide solution and stirred vigorously under heating conditions to obtain the alkali-treated powder (i.e., carboxylated powder, denoted as HPAN powder).

[0031] HPAN powder was washed and centrifuged three times with deionized water and a washing solvent (the washing solvent is at least one of methanol, ethanol, DMF and triethyl ether, preferably ethanol) (the centrifugation conditions include: centrifugation speed of 4000-12000 rpm (preferably 4000 rpm, 6000 rpm, 8000 rpm, 10000 rpm, 12000 rpm), centrifugation time of 3-6 min (preferably 3 min, 4 min, 5 min, 6 min), more preferably 6000 rpm, 3 min) to remove residual sodium hydroxide aqueous solution. The washed and centrifuged powder was then vacuum dried (drying temperature is 40-70℃, preferably 40℃, 45℃, 50℃, 60℃, 65℃, 70℃, more preferably 60℃) to obtain dried HPAN powder.

[0032] EDC and NHS were dissolved in PBS buffer solution to obtain an activation solution. Dry HPAN powder was placed in the activation solution and activated in a constant-temperature shaker (150 rpm) to obtain activated powder (increasing the carboxyl activity in the powder). The activated powder was washed three times with deionized water and three times with ethanol. The washed and centrifuged powder was then vacuum dried to obtain activated powder.

[0033] According to the present invention, preferably, in step S3: the temperature of the chemical condensation grafting reaction is 40-70℃ (preferably 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, more preferably 50℃), and the time is 2-12h (preferably 2h, 4h, 6h, 8h, 10h, 12h, more preferably 4h).

[0034] According to the present invention, preferably, in step S4:

[0035] The mass ratio of the modified powder, pore-forming agent, and solvent is (14-20):1:(85-79), preferably 14:1:85, 15:1:84, 16:1:83, 17:1:82, 18:1:81, 19:1:80, 20:1:79, and more preferably 16:1:83;

[0036] The pore-forming agent is PVP (polyvinylpyrrolidone).

[0037] The solvent is DMF (N,N-dimethylformamide).

[0038] The nonwoven fabric is moistened with ethanol to obtain the moistened nonwoven fabric; the temperature when the casting solution is poured onto the moistened nonwoven fabric is 20-30℃ and the air humidity is 50-60%, preferably 20℃ and 50%; 20℃ and 55%; 20℃ and 60%; 25℃ and 50%; 25℃ and 55%; 25℃ and 60%; 30℃ and 50%; 30℃ and 55%; 30℃ and 60%, preferably 25℃ and 55%.

[0039] The coagulation bath is a DMF aqueous solution with a volume concentration of 10%-50%, preferably 10%, 20%, 30%, 40%, or 50%, and more preferably 10%.

[0040] In this invention, the modified powder, pore-forming agent and solvent can be mixed evenly by heating and stirring. The heating temperature is 40-70℃, preferably 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, or 70℃, and more preferably 65℃.

[0041] In this invention, the thickness of the scraper is 100-250μm, preferably 100μm, 150μm, 200μm, or 250μm, and more preferably 200μm.

[0042] This invention proposes an innovative modification path of "powder grafting-dual-functional synergy":

[0043] This invention uses MTAC, SBMA, and AEMA as monomers to synthesize a bifunctional ternary polymer that simultaneously possesses antibacterial and hydrophilic (anti-adhesion) properties. The quaternary ammonium groups in the ternary polymer provide highly efficient bactericidal ability (by disrupting bacterial cell membranes), while the zwitterions in the polymer inhibit bioadhesion through strong hydration. These two components synergistically enhance the anti-biofouling performance, achieving the goal of antibacterial modification and bifunctionalization of polyacrylonitrile ultrafiltration membranes.

[0044] This invention uses polyacrylonitrile (PAN) powder as a base and introduces a random terpolymer (PAMS) containing quaternary ammonium salt groups and zwitterionic (sulfonic acid group) groups into the polyacrylonitrile (PAN) powder through chemical condensation grafting. Then, the functionalized membrane of this invention (i.e., bifunctionalized terpolymer modified polyacrylonitrile ultrafiltration membrane) is prepared by phase inversion molding.

[0045] This invention utilizes the condensation reaction of activated carboxyl and amino groups by EDC / NHS to achieve chemical condensation grafting of polyacrylonitrile powder with active carboxyl groups and ternary polymer with primary amine groups (groups for chemical condensation grafting), thus ensuring the long-term stability of the ultrafiltration membrane of this invention.

[0046] Polyacrylonitrile (PAN) powder is grafted with a terpolymer (PAMS) to obtain chemically modified functionalized powder. This chemically modified functionalized powder is then uniformly dispersed in a casting solution (PVP and DMF), and after phase inversion, it forms a membrane with a porous structure, fully preserving the water permeability and narrow pore size distribution of the ultrafiltration membrane. Simultaneously, the chemical condensation grafting on the surface of the PAN powder improves the grafting density and efficiency. Through chemical bonding (effectively utilizing the stability of chemical bonding), the terpolymer is fixedly grafted into the membrane material, overcoming the lifespan bottleneck of traditional modification technologies. This provides a reliable guarantee for long-term stable operation in complex and harsh environments (such as high-salt, strong-acid, and bacterial wastewater), significantly reducing membrane replacement and maintenance costs.

[0047] According to the present invention, preferably, the thickness of the bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane is 100-250 μm.

[0048] The second aspect of the present invention provides a method for preparing the bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane.

[0049] The third aspect of this invention provides the application of the bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane in water treatment.

[0050] According to the present invention, preferably, the water treatment is the treatment of wastewater containing bacteria, and more preferably, the bacteria in the wastewater containing bacteria are Staphylococcus aureus and / or Escherichia coli.

[0051] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0052] Based on the use of quaternary ammonium salt (QAS) as an antibacterial material, this invention introduces a hydrophilic material (zwitterionic (containing sulfonic acid groups)). The hydrophilic material can reduce the adhesion of bacteria on the membrane by forming a hydration layer while bringing about flux recovery. This gives the ultrafiltration membrane of this invention hydrophilic properties while introducing excellent bactericidal performance.

[0053] This invention utilizes a powder grafting (chemical condensation grafting) method to perform surface bifunctional modification of polyacrylonitrile powder with ternary polymers, thereby anchoring the ternary polymers to the membrane surface and improving the stability of the ultrafiltration membrane of this invention.

[0054] This invention solves the problem of significantly reduced flux caused by membrane pore swelling by first grafting powder and then transforming it into a membrane, providing a technical path for the large-scale production of high-performance separation membranes.

[0055] The ultrafiltration membrane of the present invention has good anti-interference performance against two types of bacteria (Staphylococcus aureus and Escherichia coli).

[0056] The powder grafting and chemical modification process of this invention is highly compatible with industrial film-making processes, requires no additional complex equipment, and is suitable for large-scale production of film surfaces.

[0057] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0058] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.

[0059] Figure 1 This is a diagram showing the surface morphology of the membrane sample obtained in Comparative Example 1 (PAN).

[0060] Figure 2 This is a diagram showing the surface morphology of the membrane sample obtained in Comparative Example 2 (HPAN).

[0061] Figure 3 This is a surface morphology diagram of the membrane sample obtained in Example 1 (PAMS).

[0062] Figure 4 This is a diagram showing the surface morphology of the membrane sample obtained in Comparative Example 3 (PAM).

[0063] Figure 5 Infrared absorption spectra of the membrane samples obtained in Comparative Examples 1-3 and Example 1 are shown.

[0064] Figure 6 The X-ray photoelectron spectra of the membrane samples obtained in Comparative Examples 1-3 and Example 1 are shown.

[0065] Figure 7 The antibacterial test results of the membrane samples obtained in Comparative Examples 1-3 and Example 1 are shown in the figure. Figure 7 (This demonstrates the antibacterial effect against Escherichia coli).

[0066] Figure 8 The antibacterial test results of the membrane samples obtained in Comparative Examples 1-3 and Example 1 are shown in the figure. Figure 8 (This demonstrates the antibacterial effect against Staphylococcus aureus).

[0067] Figure 9 The water flux effect diagrams of the membrane samples obtained in Comparative Examples 1-3 and Example 1 are shown.

[0068] Figure 10 The anti-biofouling performance of the membrane samples obtained in Comparative Examples 1-3 and Example 1 is shown in the figure. Figure 10 (This represents flux changes over 12 hours).

[0069] Figure 11 The anti-biofouling performance of the membrane samples obtained in Comparative Examples 1-3 and Example 1 is shown in the figure. Figure 11 (Fluorescence loss and recovery rate before and after membrane sample cleaning).

[0070] Figure 12 The present invention illustrates the synthetic route for preparing a bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane. Detailed Implementation

[0071] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0072] The sources of the various materials in the following embodiments and comparative examples are not particularly limited, and they can be commercially available products.

[0073] The CAS number for AEMA (aminoethyl methacrylate) is 7659-36-1;

[0074] The CAS number for MTAC ([2-(methacryloyloxy)ethyl]trimethylammonium chloride) is 5039-78-1;

[0075] The CAS number for SBMA ([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide) is 3637-26-1;

[0076] The CAS number for EDC (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride) is 25952-53-8;

[0077] The CAS number for NHS (methacryloyloxyethyltrimethylammonium chloride) is 5039-78-1.

[0078] Example 1

[0079] This embodiment provides a method for preparing a bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane, the preparation method comprising the following steps:

[0080] S1: [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC), [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide (SBMA), and aminoethyl methacrylate (AEMA) were selected as monomers for polymerization. First, 10 mmol of AEMA, 45 mmol of MTAC, and 45 mmol of SBMA were placed in a three-necked flask and dissolved in 1000 mL of deionized water to obtain a mixed system. Then, under a nitrogen atmosphere, 1 mmol of AIBA was added to the mixed system, and the flask was placed in a 70°C water bath for 24 h. After the reaction was completed, the product solution was purified by rotary evaporation at 50°C and 60 rpm, and the purified substance was freeze-dried to obtain a ternary polymer powder. The ternary polymer powder was mixed with Tris-HCl buffer (pH 7.4) to obtain a polymer solution (360 mg / L).

[0081] S2: Dry the polyacrylonitrile powder (150 kDa molecular weight) overnight in a 60°C oven and store it in a desiccator. Place the dried polyacrylonitrile powder into a 5 mol / L sodium hydroxide aqueous solution and stir vigorously at 60°C for 1 hour to obtain the alkali-treated powder (i.e., carboxylated powder, denoted as HPAN powder).

[0082] HPAN powder was washed with deionized water and ethanol and centrifuged three times (6000 rpm, 3 min) to remove residual sodium hydroxide solution. The washed and centrifuged powder was then vacuum dried (drying temperature was 60℃) to obtain dried HPAN powder.

[0083] 10 mmol EDC and 5 mmol NHS were dissolved in 100 mL of PBS buffer (0.1 mol / L, pH=5.0) to obtain an activation solution. Dry HPAN powder was placed in the activation solution and activated in a constant temperature shaker (50℃, 150 rpm) for 1.0 h to obtain activated powder (increasing the carboxyl activity in the powder). The activated powder was washed three times with deionized water and ethanol (6000 rpm, 3 min). The washed and centrifuged powder was then vacuum dried at 60℃ to obtain activated powder.

[0084] S3: Mix 1.2g of activated powder with the polymer solution (360mg / L, 100mL), and then carry out a chemical condensation grafting reaction in a constant temperature shaker at 50℃ for 4h to obtain product powder; wash the product powder with deionized water and ethanol three times (6000 rpm, 3 min) respectively, and centrifuge. Dry the washed and centrifuged powder under vacuum at 60℃ to obtain modified powder.

[0085] S4: The modified powder, PVP, and DMF were mixed at a mass ratio of 16:1:83 and heated and stirred at 65°C for 16 hours to prepare a casting solution. The casting solution was placed in a vacuum chamber for degassing. Then, the degassed casting solution was poured onto a moistened nonwoven fabric (with a small amount of anhydrous ethanol sprayed onto the surface of the nonwoven fabric) at 25°C and 50% humidity. When the moistened nonwoven fabric was semi-dry, a precursor membrane with a thickness of 150 μm was scraped out at a uniform speed using a 200 μm thick doctor blade. The precursor membrane was then placed in a 10% DMF aqueous solution for 5 minutes for phase inversion, resulting in phase separation to form the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane. Finally, the obtained ultrafiltration membrane was placed in deionized water and stored at 4°C.

[0086] Comparative Example 1

[0087] The only difference between this comparative example and Example 1 is that:

[0088] The modified powder was replaced with polyacrylonitrile powder; a blank control PAN ultrafiltration membrane was obtained by step S4 of Example 1, placed in deionized water, and stored at 4°C.

[0089] Comparative Example 2

[0090] The only difference between this comparative example and Example 1 is that:

[0091] The modified powder was replaced with the HPAN powder from step S2 of Example 1; an ultrafiltration membrane with carboxyl grafting sites on the surface was obtained by step S4 of Example 1, placed in deionized water, and stored at 4°C.

[0092] Comparative Example 3

[0093] The only difference between this comparative example and Example 1 is that:

[0094] In step S1: only MTAC and AEMA are selected as polymerization monomers.

[0095] First, 10 mmol of AEMA and 90 mmol of MTAC were placed in a three-necked flask and dissolved in 1000 mL of deionized water to obtain a mixed system. Then, under a nitrogen atmosphere, 1 mmol of AIBA was added to the mixed system, and the flask was placed in a 70°C water bath for 24 h. After the reaction was completed, the product solution was purified by rotary evaporation at 50°C and 60 rpm, and the purified substance was freeze-dried to obtain a ternary polymer powder. The ternary polymer powder was mixed with Tris-HCl buffer (pH 7.4) to obtain a polymer solution (360 mg / L).

[0096] Steps S2-4 are the same as in Example 1.

[0097] The comparative example yielded an antibacterial functionalized binary polymer-modified ultrafiltration membrane that lacks hydrophilicity.

[0098] Test Example 1

[0099] The membrane samples obtained from Comparative Examples 1-3 and Example 1 were characterized by their microstructure (SEM characterization), such as... Figures 1-4 As shown, Figures 1-4 The images show the surface morphology of the membrane samples obtained in Comparative Examples 1-3 and Example 1. Figures 1-4 The images shown are, in order, surface morphology diagrams of the membrane samples obtained from Comparative Example 1, Comparative Example 2, Example 1, and Comparative Example 3.

[0100] The morphological comparison of Comparative Examples 1-2 shows that the ultrafiltration membrane prepared by the phase inversion reaction in this invention has the smoothest surface morphology and a uniform pore distribution without obvious defects. In contrast, the membrane prepared from the alkali-treated HPAN powder in Comparative Example 2 exhibited enlarged and unevenly distributed pores. This is because the alkali-treated powder (HPAN powder) has poor dispersibility, and the low viscosity of the casting solution leads to varying degrees of phase inversion on the membrane surface. Furthermore, alkali treatment of polyacrylonitrile generates a large number of carboxyl groups, which may enhance the hydrogen bonding between powder particles, making them more prone to aggregation and reducing dispersibility.

[0101] As can be seen from the comparison between Example 1 and Comparative Examples 1-3, the grafting modification of the ternary polymer consumed most of the carboxyl groups, the dispersibility of the powder was improved, and the film surface after phase inversion was more uniform.

[0102] In addition, the surface roughness results also show the same results, especially the surface roughness of the ternary polymer modified film prepared in Experimental Example 1 is the same as that of the original film.

[0103] Test Example 2

[0104] The membrane samples obtained from Comparative Examples 1-3 and Example 1 were characterized by Fourier Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS), respectively.

[0105] Figure 5 The infrared absorption spectra of the membrane samples obtained in Comparative Examples 1-3 and Example 1 are shown below. Figure 5 It can be known that:

[0106] In Comparative Example 2, after alkali treatment, the -CN groups on the polyacrylonitrile were hydrolyzed into -COOH. Therefore, the three membranes obtained in Comparative Example 2, Experimental Example 1, and Comparative Example 3 showed improved performance at 1590 cm⁻¹. -1 The peak performance originates from the vibration of the carbonyl group;

[0107] After grafting the binary polymer (MTAC-AEMA) with EDC / NHS activation, the modified ultrafiltration membrane obtained in Comparative Example 3 was used at 956 cm⁻¹. -1 The appearance of a new peak indicates that the modified ultrafiltration membrane contains quaternary ammonium groups;

[0108] In addition to the above characteristic peaks, the ternary polymer-modified membrane obtained in Experimental Example 1 also exhibits peaks at 1095 cm⁻¹. -1 The presence of sulfonic acid group extension peaks indicates that the ternary polymer was successfully grafted onto the activated powder via chemical condensation, and that the ultrafiltration membrane underwent specific functionalization after phase inversion.

[0109] Figure 6 The X-ray photoelectron spectra of the film samples obtained in Comparative Examples 1-3 and Example 1 are shown below. Figure 6 It can be seen that the intensity of the N 1s peak at 398 eV in the X-ray photoelectron spectrum of Example 1 is increased compared with that of Comparative Example 1 and Comparative Example 2. The S element in the sulfonic acid group also significantly increases the intensity of the S 2p peak at 164 eV in the film of Example 1.

[0110] The above experimental results show that the bifunctionalized ternary polymer, synthesized from nitrogen-containing antibacterial quaternary ammonium salt monomers and sulfur-containing sulfonic acid monomers, has successfully functionalized polyacrylonitrile membranes.

[0111] Test Example 3

[0112] The antibacterial activity of the ultrafiltration membrane samples prepared in this invention was measured using the colony-forming unit (CFU) counting method.

[0113] The E. coli cultured in Luria-Bertani (LB) liquid medium to the exponential stage was washed three times by centrifugation with sterile phosphate-buffered saline (PBS), and then resuspended to a concentration of 5 × 10⁻⁶. 5 CFU / mL. Then add the membrane sample (1cm). 2 The surface impurities and bacteria were removed by soaking in alcohol for 10 minutes, followed by rinsing three times with sterile water. 20 μL of bacterial solution was dropped onto the membrane sample surface and incubated at 37°C for 6 hours. The membrane from Comparative Example 1 served as a blank control. After contact, the membrane was placed in PBS buffer solution and ultrasonically cleaned for 10 minutes to remove bacteria. 100 μL of the cleaned bacterial solution was evenly spread on LB solid medium and incubated at 37°C for 12 hours. The number of viable bacterial colonies was recorded. The number of surviving bacterial colonies after contact with the membrane of Example 1 was compared with that of the blank control (Comparative Example 1) to obtain the antibacterial efficiency of the membrane of Example 1.

[0114] like Figure 7 As shown, the antibacterial effect of the membrane in Example 1 is significantly improved and the best compared with that of the membrane in Comparative Example 1. This indicates that the membrane in Example 1 not only retains the excellent antibacterial properties of the antibacterial quaternary ammonium salt modified ultrafiltration membrane, but also improves the antibacterial properties on this basis. This is due to the antifouling ability of the hydrophilic sulfonic acid groups on the surface.

[0115] The antibacterial efficiency test method for Staphylococcus aureus is the same as that for Escherichia coli, and the results are as follows: Figure 8 As shown.

[0116] Test Example 4

[0117] The flux performance of the ultrafiltration membranes prepared in the examples and comparative examples was measured using a cross-flow filtration device to evaluate the change in water flux of the ultrafiltration membranes modified with the bifunctional ternary polymer of the present invention.

[0118] The ultrafiltration membranes prepared in the examples and comparative examples were cut to a size suitable for the filtration system (2.5 cm diameter discs) and soaked in deionized water overnight.

[0119] The pure water flux was determined using deionized water. First, the filtration system was pre-pressurized at 0.2 MPa for 2 hours to stabilize it. After the flux stabilized, the pressure was adjusted to 0.1 MPa, and the flux change data was continuously measured for 30 minutes. Figure 9 As shown, the flux of the membrane obtained in Example 1 was not significantly different from that of the membrane in Comparative Example 1, indicating that the ultrafiltration membrane of the present invention maintains the same flux while having bactericidal ability.

[0120] Test Example 5

[0121] The improved resistance to biofouling of the ultrafiltration membrane prepared in this invention was tested using a cross-flow filtration device.

[0122] The ultrafiltration membranes prepared in the examples and comparative examples were cut to a size of 3×4 cm. First, the filtration system was pre-pressurized with deionized water at a pressure of 0.2 MPa for 1.5 h to stabilize it. The membranes contained 1.16 mM C6H5Na3O7, 0.94 mM NH4Cl, 0.45 mM KH2PO4, 0.5 mM CaCl2, 0.5 mM NaHCO3, 2.0 mM NaCl, and 0.6 mM MgSO4, with an initial E. coli concentration of 10. 4 Simulated bacterial wastewater (CFU / mL) was used as the feed solution. The system pressure was adjusted to approximately 0.1 MPa at 37°C and a flow rate of 60 LPH to maintain a consistent initial flux. Filtration was stabilized for 12 hours, and membrane flux changes were recorded every half hour. Chemical modification with the ternary polymer slightly improved the membrane flux in Example 1, partly due to the increased pore size and partly due to the introduction of hydrophilic substances. For example... Figures 10-11 As shown, the bifunctionalized ternary polymer powder modified polyacrylonitrile ultrafiltration membrane of Example 1 has significantly improved anti-biofouling performance compared with the blank polyacrylonitrile ultrafiltration membrane of Comparative Example 1 because it has both bactericidal quaternary ammonium salt monomer and antifouling sulfonate monomer.

[0123] The characterization of the ternary polymer and the modified polyacrylonitrile ultrafiltration membrane of the present invention demonstrates the successful synthesis of the ternary polymer and the success of the powder grafting-chemical modification, while preserving the basic properties of the ultrafiltration membrane.

[0124] This invention demonstrates the anti-biofouling properties of the ultrafiltration membrane through static antibacterial and simulated bacterial wastewater treatment experiments. The modified polyacrylonitrile ultrafiltration membrane of this invention exhibits significant advantages compared to Comparative Example 1. As a novel antifouling and antibacterial membrane material, the modified polyacrylonitrile ultrafiltration membrane of this invention can effectively prevent the adhesion of bacteria in wastewater and kill bacteria trapped on the membrane surface, thereby alleviating the problem of membrane surface biofouling. The synergistic application of powder grafting and chemical modification, through a molecular design-structure regulation-process optimization approach, enables the modified polyacrylonitrile ultrafiltration membrane of this invention to exhibit excellent performance in terms of hydrophilicity, pore size distribution, flux, retention rate, and antibacterial properties. These performance improvements make the modified polyacrylonitrile ultrafiltration membrane of this invention promising for broad application in complex water treatment scenarios.

[0125] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane, characterized in that, The preparation method includes the following steps: S1: A monomer containing a quaternary ammonium salt group, a monomer containing a zwitterionic group, and a monomer containing a primary amino group are mixed with water to obtain a mixed system; under a nitrogen atmosphere, the mixed system is mixed with an initiator and reacted under heating conditions to obtain a ternary polymer; the ternary polymer is mixed with a buffer solution to obtain a polymer solution; S2: Polyacrylonitrile powder is subjected to alkali treatment and activation treatment in sequence to obtain activated powder; S3: The activated powder is mixed with the polymer solution and subjected to a chemical condensation grafting reaction. After centrifugation, washing, and drying, the modified powder is obtained. S4: Mix the modified powder, pore-forming agent and solvent evenly to obtain a casting solution; pour the casting solution onto a moistened nonwoven fabric; when the moistened nonwoven fabric is in a semi-dry state, use a doctor blade to scrape a membrane onto the semi-dry nonwoven fabric to obtain a precursor membrane, and perform phase transformation in a coagulation bath to separate the phases and form the bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane.

2. The method for preparing the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane according to claim 1, wherein, In step S1: The monomer containing the quaternary ammonium salt group is [2-(methacryloyloxy)ethyl]trimethylammonium chloride; The monomer containing the zwitterionic group is [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide; The monomer containing a primary amino group is aminoethyl methacrylate; The molar ratio of the monomer containing a primary amino group, the monomer containing a quaternary ammonium salt group, and the monomer containing a zwitterionic group is 10:(10-80):(10-80). In the reaction system formed by mixing the mixed system with the initiator, the molar concentration of the initiator is 0.5-2 mmol / L; the initiator is at least one of AIBN, AIBA, and ABVN; The reaction is carried out at a temperature of 50-80℃ for a time of 6-48 hours. The buffer solution is PBS buffer solution and / or Tris-HCl buffer solution; the concentration of the polymer solution is 90-450 mg / L.

3. The method for preparing the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane according to claim 2, wherein, After the reaction in step S1 is completed, a product solution is obtained. The product solution is then subjected to evaporation purification and freeze-drying treatment to obtain a ternary polymer powder. The ternary polymer powder is then mixed with the buffer solution to obtain a polymer solution.

4. The method for preparing the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane according to claim 1, wherein, In step S2: The polyacrylonitrile powder has a molecular weight of 50-300 kDa. The alkaline solution used in the alkaline treatment is a sodium hydroxide aqueous solution with a concentration of 1-10 mol / L; The alkaline treatment is carried out at a temperature of 40-80℃ for a time of 0.5-4 hours. The activation solution used in the activation treatment is a mixture of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, methacryloyloxyethyltrimethylammonium chloride and PBS buffer solution at pH 3-6, wherein the molar ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and methacryloyloxyethyltrimethylammonium chloride is (1-5):1; The activation treatment is performed at a temperature of 30-60℃ for 0.5-2 hours, with a pH of 3-6.

5. The method for preparing the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane according to claim 1, wherein, In step S3: the temperature of the chemical condensation grafting reaction is 40-70℃, and the time is 2-12h.

6. The method for preparing the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane according to claim 1, wherein, In step S4: The mass ratio of the modified powder, pore-forming agent, and solvent is (14-20):1:(85-79); The pore-forming agent is PVP; The solvent is DMF; The nonwoven fabric is moistened with ethanol to obtain the moistened nonwoven fabric; the temperature when the casting solution is poured onto the moistened nonwoven fabric is 20-30°C and the air humidity is 50-60%; The coagulation bath is a DMF aqueous solution with a volume concentration of 10%-50%.

7. The method for preparing the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane according to claim 1, wherein, The thickness of the bifunctionalized ternary polymer-modified polyacrylonitrile ultrafiltration membrane is 100-250 μm.

8. The bifunctional ternary polymer modified polyacrylonitrile ultrafiltration membrane prepared by the preparation method of any one of claims 1-7.

9. The application of the bifunctionalized ternary polymer modified polyacrylonitrile ultrafiltration membrane according to claim 8 in water treatment.

10. The application according to claim 9, wherein, The water treatment is for wastewater containing bacteria, and the bacteria in the wastewater are Staphylococcus aureus and / or Escherichia coli.

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