Preparation method of positively charged thin-layer composite membrane

Abstract

The invention discloses a preparation method of a positively charged thin-layer composite membrane, and relates to the technical field of separation membranes. The method comprises the following steps: S1, preparing a base membrane from a polymeric membrane matrix material, a membrane modifier and an organic solvent through a phase inversion method; s2, synthesizing a novel antibacterial water-phase monomer containing a quaternary ammonium imidazole structure through quaternization reaction; and S3, constructing the positively charged thin-layer composite membrane with the in-situ antibacterial function on the base membrane prepared in S1 through secondary interfacial polymerization by using the antibacterial aqueous-phase monomer prepared in S2 and an organic-phase monomer prepared in S2. According to the method disclosed by the invention, the novel monomer containing the quaternary ammonium imidazole structure participates in interfacial polymerization, so that the thin-film composite nanofiltration membrane with high flux, excellent salt / dye separation performance and efficient antibacterial performance is successfully prepared.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology, and specifically to a method for preparing a positively charged thin-film composite membrane. Background Technology

[0002] The textile industry is a significant source of industrial wastewater, which typically contains high concentrations of organic dyes and inorganic salts, resulting in complex compositions that severely restrict water reuse and the recovery of valuable resources. For this type of difficult-to-treat wastewater, thin-layer composite membranes, with their unique pore size distribution, can efficiently retain dye molecules while allowing salt permeation, making them an ideal technology for dye / salt separation. However, in actual operation, membrane materials are susceptible to microbial contamination. Bacteria adhere to the membrane surface and form biofilms, leading to a significant decrease in separation performance and a shortened operating cycle, severely limiting the large-scale application of this technology. Therefore, constructing novel thin-layer composite membranes that simultaneously possess high-efficiency separation capabilities and resistance to biofouling has become a key research focus in the field of membrane technology.

[0003] Currently, common strategies for improving the antibacterial properties of membrane surfaces mainly rely on the addition of external antibacterial agents, such as silver nanoparticles, graphene oxide, and quaternary ammonium polymers. Quaternary ammonium compounds, in particular, have been widely studied due to their positively charged properties, which can effectively disrupt bacterial cell membrane structures and inhibit microbial adhesion by enhancing surface hydrophilicity. However, most of these methods employ post-modification or blending techniques, leading to problems such as uneven dispersion and insufficient binding strength between the introduced antibacterial components and the membrane matrix. This can not only cause secondary pollution due to the dissolution of active components but also make it difficult to ensure the performance stability of the membrane during continuous operation.

[0004] To address the aforementioned issues, research trends are increasingly shifting towards in-situ fixation of antibacterial groups during film formation. By designing functional monomers at the molecular level, the antibacterial structure can be directly bonded to the separation layer network during interfacial polymerization, effectively improving the uniformity of functional distribution and the operational stability of the membrane structure. Based on this approach, our team developed an aqueous monomer with an antibacterial imidazoline structure in our previous patent (CN202410554464.0) and successfully prepared a nanofiltration membrane with certain antibacterial functions. This patent represents a significant development based on that. We designed and synthesized a novel aqueous monomer, QBAIE, with quaternary ammonium cations, by quaternizing the aforementioned imidazoline monomer. This modification not only retains the amino activity at the monomer's end, ensuring its effective participation in interfacial polymerization, but also significantly enhances its electrostatic destructive effect on bacterial cell membranes by introducing strongly positively charged quaternary ammonium groups, thereby greatly improving the material's antibacterial efficacy. Furthermore, the steric hindrance effect of the quaternary ammonium groups can moderately suppress the crosslinking density during polymerization, which is beneficial for forming a looser separation layer structure. Based on this, the core of this patent lies in utilizing the QBAIE functional monomer, combined with secondary interfacial polymerization technology, to construct a positively charged QBAIE-TMC-QBAIE thin-layer composite membrane with in-situ antibacterial function. This design aims to synergistically integrate highly efficient antibacterial properties with a loose separation layer structure, ultimately producing an advanced membrane material that combines high water flux, excellent dye / salt separation selectivity, and strong resistance to biofouling. This provides a new technical solution for addressing membrane fouling and improving separation efficiency in textile wastewater treatment. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a positively charged thin-layer composite membrane. This method involves designing and synthesizing quaternized antibacterial aqueous monomers with antibacterial functions, and then using interfacial polymerization technology to firmly bond them to a separation layer. This successfully prepares a thin-layer composite membrane that combines a loose nanofiltration structure, positively charged properties, and excellent antibacterial performance. The membrane material exhibits high water flux, high dye rejection rate, high salt permeability, and excellent resistance to biofouling in applications such as textile wastewater treatment.

[0006] To achieve the above objectives, the present invention provides a method for preparing a positively charged thin-film composite film, comprising the following steps: S1. Preparation of base film: The polymer membrane matrix material and membrane modifier are dissolved in an organic solvent, and after constant temperature stirring and degassing, a homogeneous casting solution is prepared. The casting solution is then coated onto a glass plate and then immersed in a pure water coagulation bath to form a thin-layer composite membrane base film through the liquid-solid phase inversion method.

[0007] Preferably, the organic solvent is selected from acetone, dimethyl sulfoxide, cyclohexane, chloroform, N-methylpyrrolidone, etc. N, N-Dimethylacetamide, N,N At least one of dimethylformamide.

[0008] Preferably, the polymeric membrane matrix material is at least one of polyvinylidene fluoride, polyethersulfone, polysulfone, polyamide, cellulose acetate, polypropylene, and polyvinyl chloride. Preferably, based on the total mass of the casting solution, the mass percentage of the polymeric membrane matrix material is 16wt% to 20wt%.

[0009] Preferably, the intermediate film modifier is at least one of a pore-forming agent, a hydrophilic agent, or a surfactant.

[0010] S2. Preparation of Quaternized Aqueous Monomer: Polyene polyamines and polyacids are dissolved in a water-carrying agent for amidation and cyclization reactions. After purification, a bisimidazoline aqueous monomer containing an imidazole ring and a terminal amino group is obtained. Subsequently, the monomer is reacted with a quaternizing agent in a suitable solvent to prepare a quaternized bisimidazoline aqueous monomer.

[0011] Preferably, the polydicarboxylic acid can be at least one of malonic acid, succinic acid, or glutaric acid.

[0012] Preferably, the amide reaction temperature is 120~170℃ and the reaction time is 4~6h; the cyclization reaction temperature is 190~210℃ and the reaction time is 4~6h; the water-carrying agent is selected from at least one of toluene, xylene, petroleum ether, chloroform, cyclohexane, and isoamyl acetate.

[0013] Preferably, the quaternizing agent is at least one of the following halogenated quaternizing agents: 2-bromoethylamine hydrobromide, bromoethane, sodium bromoethylsulfonate, benzyl chloride, hexadecyl dimethyl quaternary ammonium chloride, and dimethyl octadecyl quaternary ammonium bromide.

[0014] Preferably, the solvent for the quaternization reaction in step S2 includes methanol, dimethyl sulfoxide, ethanol, acetonitrile, water, tetrahydrofuran, dimethylformamide, etc.; the quaternization reaction temperature is 30~100℃; and the quaternization reaction time is 10~72h.

[0015] S3. Construction of positively charged thin-film composite membrane: The base membrane obtained in S1 is sequentially immersed in an aqueous solution containing monomers prepared in S2 and an organic solution containing polyfunctional acyl chlorides. A functional separation layer is formed on the surface of the base membrane through interfacial polymerization reaction. The positively charged thin-film composite membrane is obtained after subsequent heat treatment.

[0016] Preferably, the mass ratio of monomer to solvent in the aqueous solution is 1:10 to 1:100.

[0017] Preferably, the mass ratio of monomer to solvent in the organic phase solution is 1:10 to 1:100.

[0018] This invention enhances the antibacterial properties of the separation membrane by loading more antibacterial structures through secondary interfacial polymerization. The antibacterial structures disrupt the metabolic pathways of bacteria through electrostatic interactions, thereby damaging the integrity of the bacteria and ultimately leading to their death.

[0019] This invention uses a liquid-solid phase inversion method to prepare a base membrane for a loose nanofiltration membrane. The membrane formation mechanism is as follows: a casting solution is prepared by using a polymer membrane matrix material, a membrane modifier, and an organic solvent, and the base membrane for the loose nanofiltration membrane is prepared by using a liquid-solid phase inversion method.

[0020] This invention uses a two-stage interfacial polymerization method to prepare thin-layer composite films. The film formation mechanism is as follows: organic reactants with bifunctional or trifunctional groups are polymerized between two immiscible systems to form a network structure.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The antibacterial properties of the separation membrane are further improved by secondary polymerization of quaternized antibacterial aqueous monomers. Its antibacterial structure can effectively destroy bacterial cell membranes through electrostatic interaction, achieving efficient, long-lasting, and in-situ antibacterial activity, overcoming the problems of easy loss and uneven distribution of antibacterial agents; (2) The secondary quaternized antibacterial aqueous monomer forms a more loose network structure through the steric hindrance effect of the quaternary ammonium group, thereby improving the membrane flux and salt dye separation ability; in addition, the quaternary ammonium cations in the separation layer make the membrane surface positively charged, which can enhance the membrane's ability to retain cationic dyes and improve separation selectivity. (3) The process of this invention is simple, the conditions are mild and easy to control, and it is suitable for large-scale production. The prepared positively charged antibacterial thin-film composite membrane has important application value in fields such as high-difficulty wastewater treatment and resource recycling.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 The infrared image is shown in Example 1 of the preparation method of a positively charged thin-film composite film of the present invention. Figure 2 XPS image of the positively charged thin-film composite film in Example 1 of the preparation method of the positively charged thin-film composite film of the present invention; Figure 3 This is a molecular weight cutoff diagram of the positively charged thin-film composite membrane in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention; Figure 4 The zeta potential diagram of the positively charged thin-film composite film in Example 1 of the preparation method of the positively charged thin-film composite film of the present invention; Figure 5The diagram shows the contact angle and water flux of the positively charged thin-film composite membrane in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention. Figure 6 The dye rejection diagram of the positively charged thin-film composite film in Example 1 of the preparation method of the positively charged thin-film composite film of the present invention; Figure 7 Salt cutoff diagram of the positively charged thin-film composite membrane in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention; Figure 8 The separation diagram of anions and inorganic salts in the positively charged thin-film composite membrane in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention; Figure 9 The separation diagram of cations and inorganic salts in the positively charged thin-film composite membrane in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention; Figure 10 The positively charged thin-film composite membrane of the present invention is prepared by a method for preparing a positively charged thin-film composite membrane. The figure in Example 1 shows the positively charged thin-film composite membrane after co-culturing with bacteria. Figure 11 The plate count diagram of the positively charged thin-film composite membrane after co-culturing with bacteria in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention; Figure 12 The SEM image of the positively charged thin-film composite membrane co-cultured with bacteria in Example 1 of the preparation method of the positively charged thin-film composite membrane of the present invention; Figure 13 The method for preparing a positively charged thin-film composite membrane according to the present invention is illustrated in Example 1, which shows the continuous separation performance of the positively charged thin-film composite membrane for anionic dyes and inorganic salts. Figure 14 The method for preparing a positively charged thin-film composite membrane according to the present invention is illustrated in Example 1, which shows the continuous separation performance of the positively charged thin-film composite membrane for cationic dyes and inorganic salts. Detailed Implementation

[0024] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] Example 1 This invention provides a method for preparing a positively charged thin-film composite film, comprising the following steps: S1. Base film preparation: Weigh 9 g of polyethersulfone resin (PES), 1.5 g of polyvinylpyrrolidone (PVP), and 1.5 g of polyethylene glycol 400 (PEG-400) and dissolve them in an appropriate amount of... N,N- Dimethylacetamide (DMAc) was added. The mixture was stirred continuously at 60°C for 12 hours to obtain a homogeneous PES casting solution. The casting solution was then placed in a vacuum drying oven at 60°C and allowed to stand for 12 hours to completely remove air bubbles. The casting solution was then uniformly coated onto a clean glass plate, allowed to stand at room temperature for 30 seconds, and then transferred to a deionized water coagulation bath to complete phase separation. After soaking for 12 hours, the membrane sample was removed and stored in deionized water.

[0026] Synthesis of S2, Quaternized Imidazoline Monomer in Aqueous Phase: In a reaction apparatus, 12.38 mL of diethylenetriamine, 5.90 g of succinic acid, and 30 mL of toluene were added sequentially. Under nitrogen protection, the reaction was refluxed at 160 °C for 4 hours; subsequently, the system temperature was raised to 200 °C, and the reaction continued for 6 hours until no more water was distilled off from the separator. After the reaction, the product was purified to obtain the intermediate product bisimidazoline (BAIE). Then, 4.56 g of the above BAIE product and 8.60 g of 2-bromoethylamine hydrobromide were dissolved together in deionized water and reacted at 80 °C for 24 hours. The reaction product was purified to obtain the target product, quaternized imidazoline monomer (QBAIE).

[0027] S3. Construction of Positively Charged Thin-Layer Composite Membrane: A positively charged antibacterial functional layer is constructed on the surface of the base membrane using a two-stage interfacial polymerization process. First, the surface moisture of the base membrane is removed, and it is allowed to air dry at room temperature for 5 minutes, then fixed in a dedicated mold. The following steps are performed sequentially: the base membrane surface is immersed in an aqueous solution containing 0.5 wt% QBAIE for 2 minutes, excess droplets are removed, and it is air-dried for 5 minutes; then, a hexane solution containing 0.1 wt% trimesoyl chloride is applied to the membrane surface for 1 minute; after air-drying for another 5 minutes, a second immersion treatment is performed with an aqueous solution containing 4 wt% QBAIE for 2 minutes. Finally, the membrane is heat-treated in an 80℃ oven for 30 seconds to complete cross-linking and curing. The resulting product is stored in deionized water for later use.

[0028] Figure 1 and Figure 2 Infrared and XPS images of the positively charged thin-film composite film. 1485 cm⁻¹ -1 and 1409 cm -1 The peak values ​​at these locations are related to the C=N and CN stretching vibrations, respectively, while the C=O stretching vibration peak is located at 1660 cm⁻¹. The peaks at 531.5 eV, 399.3 eV, 284.6 eV, 231.5 eV, and 168.3 eV are O 1s, N 1s, C 1s, S 2s, and S 2p, respectively, which demonstrates the construction of a functionally separated layer with a loose structure.

[0029] Figure 3The molecular weight cutoff for the positively charged thin-film composite film is 2377 Da, corresponding to a Stokes radius of approximately 1.69 nm. Furthermore, as... Figure 4 As shown, the Zeta potential on the membrane surface is +2.1 mV at pH = 7, proving that it has successfully achieved positive charge characteristics. The figure also shows that the molecular weight cutoff of the prepared nanofiltration membrane is 2377 Da, and its corresponding Stock radius is 1.69 nm. Figure 5 As shown, when the pH is 7, the surface zeta potential is +2.1 mV, indicating that a positively charged membrane has been successfully prepared.

[0030] Figure 5 The hydrophilicity and permeability of the composite membrane were demonstrated. Test results showed a contact angle of 37.2°, indicating excellent hydrophilicity. Simultaneously, the water flux of this membrane reached 183.8 L / m². -2 h -1 bar -1 It exhibits good water permeability.

[0031] Figure 6 The figure shows the dye rejection capacity of the positively charged thin-film composite membrane. The rejection rates of the membrane for the four dyes, in descending order, are: Victoria Blue (VBB) > Congo Red (CR) > Chrome Black T (EBT) > Methyl Blue (MB), with rejection rates exceeding 94.1% for all four. This is mainly attributed to the size sieving effect caused by the membrane pore size and the electrostatic repulsion between the positive charge on the membrane surface and the anionic dyes. Dye molecules often exist in clusters in water, and a suitable membrane pore size helps to achieve efficient rejection, while the positive charge of the membrane further enhances the separation effect of anionic dyes. Figure 7 The figure shows the inorganic salt rejection capacity of the positively charged thin-layer composite membrane. The rejection capacity of the membrane for four inorganic salts is as follows: MgSO4 > Na2SO4 > MgCl2 > NaCl, and the rejection rate is less than 1.9%. This reflects that the functional layer structure of the membrane is relatively loose, which allows most salt ions to pass through. Its pore structure is conducive to high dye rejection rate and high salt permeability.

[0032] Figure 8 and Figure 9 The salt-dye separation capability of the positively charged thin-film composite membrane was investigated. With increasing salt concentration, the membrane's rejection rate for Congo red decreased slightly, but remained above 98.6% under all concentration conditions, and the salt permeability consistently exceeded 98.1%. The decrease in rejection rate may be related to the salt ions inhibiting dye aggregation and promoting more uniform dispersion and passage through the membrane pores. Simultaneously, the membrane's rejection rate for inorganic salts decreased with increasing concentration, which can be attributed to the intensified concentration polarization effect under high-salt conditions.

[0033] Figure 10 , Figure 11 andFigure 12 The image illustrates the antibacterial effect of the positively charged thin-layer composite membrane against *Escherichia coli* and *Staphylococcus aureus*. The results show that, due to the combined contribution of the bactericidal effect of the quaternary ammonium imidazole structure and the membrane's hydrophilic antibacterial adhesion ability, the membrane exhibits excellent antibacterial performance against both bacteria. The antibacterial and inhibitory rates against *Escherichia coli* and *Staphylococcus aureus* were 99.3% and 98.8%, respectively. Figure 13 and Figure 14 The operational stability of the positively charged thin-film composite membrane is shown. A 24-hour filtration experiment revealed no significant decrease in the membrane's water flux and salt / dye separation performance, indicating good operational stability. This is mainly attributed to the stable, porous structure layer formed by secondary interfacial polymerization, which possesses in-situ antibacterial properties.

[0034] Example 2: Aqueous phase formulation: 0.5 wt% aqueous monomer. The rest is the same as in Example 1.

[0035] Example 3: Aqueous phase formulation: 6 wt% aqueous monomer. The rest is the same as in Example 1.

[0036] Example 4: Oil phase formulation: 0.2 wt% oil phase monomer. The rest is the same as in Example 1.

[0037] Example 5: Oil phase formulation: 0.05 wt% oil phase monomer. The rest is the same as in Example 1.

[0038] Example 6: Base film formulation: 16 g polyethersulfone resin, 3 g polyvinylpyrrolidone, and 3 g polyethylene glycol. The rest is the same as in Example 1.

[0039] Test method for separation performance of thin-layer composite membranes.

[0040] Test solution: 100 mg / L dye, 1000 mg / L inorganic salt solution.

[0041] Operating pressure: 4 bar.

[0042] Calculation formula: Retention rate R ( C f - C p ) / C f , C f and C p These are the concentrations of the feed liquid and the discharge liquid, respectively.

[0043] flux J w = V / (A t P ), V For water production volume, A For the test area, t For testing time, P For testing stress Antibacterial rate A e N a - N b ) / N a , A e For better antibacterial efficiency, N a The number of CFUs on the plate co-incubated with the blank membrane. N b The number of CFUs on the plate co-incubated with the test membrane.

[0044] Table 1 shows the running results of different examples compared to Example 1. Table 1. Performance of different instances

[0045] This invention demonstrates a strategy for preparing a high-performance positively charged composite membrane for treating dyeing and printing wastewater. This strategy achieves precise control of membrane structure and function through two key steps: First, a base membrane with ideal mechanical strength and a stable interface is constructed by precisely blending a polymeric membrane matrix material, a membrane modifier, and an organic solvent using phase inversion technology. Then, a novel aqueous monomer containing a quaternary ammonium imidazole structure is synthesized and polymerized in situ with the organic monomer on the base membrane surface via secondary interfacial polymerization, constructing a functional layer with both separation and antibacterial functions.

[0046] The resulting thin-layer composite membrane exhibits superior performance. Its positively charged characteristics, combined with the porous functional layer, result in a dye rejection rate exceeding 94.1% while maintaining a high permeability of over 98.1% for inorganic salts, achieving highly efficient separation of dyes and salts. The firmly bonded quaternary ammonium imidazole structure within the membrane provides durable in-situ antibacterial capabilities, effectively inhibiting biofouling and ensuring operational stability.

[0047] This technology provides an innovative solution to address pain points in the treatment of dyeing and papermaking wastewater, such as difficulty in dye recovery, high desalination costs, and severe membrane biofouling, and provides technical support for the resource-based recycling and green sustainable development of wastewater.

[0048] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a positively charged thin-film composite film, characterized in that, Includes the following steps: S1. Preparation of the base membrane: The base membrane is prepared by phase inversion of the casting solution, wherein the casting solution contains a polymeric membrane matrix material, a membrane modifier, and an organic solvent. The prepared casting solution is stirred at a constant temperature to remove air bubbles, then coated onto a glass plate. After standing in air, it is immersed in distilled water to obtain the base membrane of the nanofiltration membrane. S2. Preparation of novel quaternized aqueous monomers: The previously synthesized aqueous monomers containing imidazole structures were reacted with quaternizing reagents, and the reaction products were purified to obtain aqueous monomers containing quaternization. S3. Preparation of a positively charged thin-film composite membrane: An aqueous solution, an organic solution, and another aqueous solution are sequentially coated onto the base membrane. A functional layer is then prepared on the base membrane via a secondary interfacial polymerization reaction. The aqueous solution contains an aqueous monomer and a solvent, and the organic solution contains an organic monomer and a solvent. Finally, the membrane is heat-treated to obtain the positively charged thin-film composite membrane.

2. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S1, the polymeric membrane matrix material is selected from at least one of polyvinylidene fluoride, polyethersulfone, polysulfone, polyamide, cellulose acetate, polypropylene, and polyvinyl chloride. Preferably, based on the total mass of the casting solution, the mass percentage of the polymeric membrane matrix material is 16wt% to 20wt%.

3. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S1, the membrane modifier is selected from at least one of pore-forming agents, hydrophilic agents, or surfactants.

4. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S1, the organic solvent is selected from acetone, dimethyl sulfoxide, cyclohexane, chloroform, N-methylpyrrolidone, etc. N,N -Dimethylacetamide, N,N At least one of dimethylformamide, etc.

5. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S2, the quaternizing agent can be a halogenated compound, including at least one of halogenated amino compounds, halogenated alkyl compounds, or halogenated alkyl sulfonates, specifically selected from at least one of quaternizing agents such as 2-bromoethylamine hydrobromide, bromoethane, sodium bromoethylsulfonate, benzyl chloride, hexadecyl dimethyl quaternary ammonium chloride, and dimethyl octadecyl quaternary ammonium bromide.

6. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S2, the aqueous monomer containing the imidazole structure can be a compound containing a monoimidazoline structure or a bisimidazoline structure. Its characteristic is that the molecular structure has a tertiary amine group that can serve as a quaternization reaction site. After grafting quaternary ammonium salt groups through the quaternization reaction, the resulting quaternized aqueous monomer contains at least two amino groups that can participate in the interfacial polymerization reaction.

7. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S2, the quaternization reaction solvent includes N , N - At least one of dimethylformamide, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, water, methanol, ethanol, etc.; reaction temperature is 30~180℃; reaction time is 10~72h.

8. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S2, the aqueous monomer containing the antibacterial quaternized imidazole structure, each molecule of which contains an antibacterial quaternized imidazole structure and a terminal amino group, has the following structure: , ， Where R is an amino chain, alkyl chain, or zwitterionic chain, etc., and R1 is an amino chain.

9. The method for preparing a positively charged thin-film composite film according to claim 1, characterized in that: In step S3, the mass ratio of the aqueous monomer, the organic monomer, and the solvent is 1:10 to 1:

100. The organic monomer can be at least one of a polyfunctional acyl chloride or a halogenated aromatic hydrocarbon, selected from benzotrimethylol chloride, adipicoyl chloride, sebacyl chloride, m-tribromomethylbenzene, m-trichloromethylbenzene, etc.

Images