Preparation method of in-situ antibacterial polyamide loose nanofiltration membrane

Abstract

The invention discloses a preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane, and relates to the technical field of nanofiltration membranes. The method mainly comprises the following steps: S1, preparing a substrate by taking a polymeric membrane matrix material, a membrane modifier and an organic solvent as raw materials through a phase inversion process; s2, preparing an antibacterial water-phase monomer containing a quaternary ammonium imidazole structure through quaternization reaction; and S3, carrying out interfacial polymerization reaction on the water-phase monomer and the organic-phase monomer on the substrate to obtain the in-situ antibacterial polyamide loose nanofiltration membrane. According to the preparation method for preparing the novel in-situ antibacterial loose nanofiltration membrane through the interfacial polymerization process, the obtained membrane material not only has an excellent separation effect on dye and inorganic salt, but also shows efficient antibacterial performance.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane technology, and specifically to a method for preparing an in-situ antibacterial polyamide porous nanofiltration membrane. Background Technology

[0002] The large amounts of wastewater discharged from the textile industry contain complex organic dyes and inorganic salts, posing a serious challenge to the sustainable reuse of water and resource recycling. To address this problem, loose nanofiltration membrane technology, due to its unique pore structure, achieves high salt permeability and high dye retention, making it a preferred strategy. However, membrane fouling, especially biofouling caused by microbial biofilm formation, can compromise membrane separation efficiency and stability. Therefore, developing novel nanofiltration membranes with antifouling and antibacterial properties will be beneficial in solving this problem.

[0003] Currently, improving membrane antibacterial properties mainly focuses on antibacterial agents, including silver nanoparticles, copper hydroxide nanoparticles, graphene oxide, and quaternized polymers, as effective strategies to mitigate biofouling. Among these, quaternized polymers have attracted considerable attention due to their antibacterial properties and hydrophilicity. They can exert antibacterial effects by electrostatically disrupting bacterial cell membranes, while simultaneously increasing the hydrophilicity of the membrane surface to reduce microbial adhesion, thereby enhancing membrane performance. However, most of these methods rely on post-processing modification or doping, often leading to uneven distribution of antibacterial drugs, poor membrane stability, and secondary environmental pollution. This has spurred increasing interest in the development of in-situ antibacterial loose nanofiltration (LNF) membranes, which directly integrate antibacterial structures into the selective layer during membrane formation to improve structural uniformity and operational stability. In a previous patent (application number: CN202410554464.0, published), the prepared aqueous monomer exhibited good antibacterial properties due to its antibacterial imidazole structure. This patent, based on the aforementioned patent, modifies the aqueous monomer with quaternization to obtain a novel aqueous monomer containing a quaternary ammonium imidazole structure. The quaternary ammonium cation of this monomer can generate a strong electrostatic interaction with the negatively charged phospholipid layer of the bacterial cell membrane, disrupting cell membrane integrity and ultimately leading to bacterial death, thereby further improving the membrane's antibacterial properties. This patent converts the tertiary amine structure in the imidazole-containing aqueous monomer into a quaternary ammonium structure through a quaternization reaction, increasing steric hindrance while retaining the terminal amino reaction site. This structure retains interfacial polymerization reactivity while improving antibacterial properties, giving the novel aqueous monomer the dual advantages of antibacterial function and structural regulation. Therefore, compared to the dense polyamide nanofiltration membranes for desalination prepared based on imidazoline-type aqueous monomers in previous patents, the quaternized aqueous monomers in this patent, due to their stereo-quaternary ammonium structure which significantly reduces crosslinking density, can be used to prepare loose polyamide nanofiltration membranes for salt / dye separation, further improving the membrane's antibacterial properties. By optimizing interfacial polymerization parameters, the prepared loose nanofiltration (LNF) membrane exhibits excellent pure water permeability, salt / dye separation performance, and antibacterial properties. This patent provides a technically feasible solution to the problems of severe membrane fouling and low separation efficiency in wastewater from industries such as textiles through molecular design and functional layer construction. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. The obtained quaternized aqueous monomer has an antibacterial structure and a greater steric hindrance effect. An in-situ antibacterial loose nanofiltration membrane is prepared by interfacial polymerization. This loose nanofiltration membrane has high flux, high dye rejection, high salt permeability and excellent antibacterial properties.

[0005] To achieve the above objectives, the present invention provides a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane, the method specifically comprising the following steps: S1. Steps for preparing a loose nanofiltration membrane substrate: Dissolve the polymer membrane matrix material and membrane modifier in an organic solvent, and continuously stir under constant temperature to obtain a uniform casting solution. After degassing, coat the casting solution onto a glass plate, evaporate it in the air for a certain period of time, and then immerse it in deionized water to complete the phase transformation, finally obtaining the nanofiltration membrane substrate.

[0006] Preferably, in step S1, the organic solvent is selected from... N, N - Dimethylacetamide, acetone, dimethyl sulfoxide, chloroform N, N - Dimethylformamide, cyclohexane, n-hexane or N At least one of methylpyrrolidone.

[0007] Preferably, in step S1, the polymeric membrane matrix material is at least one of polysulfone, polyethersulfone, cellulose acetate, polypropylene, polyvinylidene fluoride, polyvinyl chloride, and polyamide; preferably, based on the total mass of the casting solution, the mass percentage of the polymeric membrane matrix material is 16% to 22%.

[0008] Preferably, in step S1, the membrane modifier includes at least one of a pore-forming agent, a hydrophilic agent, or a surfactant.

[0009] S2. Steps for preparing quaternized aqueous monomers: Polyene polyamines and polyacids are sequentially subjected to amidation and cyclization reactions. The reaction products are purified to obtain an aqueous monomer with an imidazole structure and a terminal amino group. Subsequently, this monomer is reacted with a quaternizing reagent to prepare an aqueous monomer containing a quaternized imidazole structure.

[0010] Preferably, in step S2, the polydicarboxylic acid is selected from at least one of glutaric acid, malonic acid, or succinic acid.

[0011] Preferably, in step S2, the amide reaction temperature is 120~170℃, and the reaction time is 4~6 hours. A water-carrying agent may be added during the reaction to promote the reaction; the water-carrying agent is selected from at least one of chloroform, toluene, petroleum ether, isoamyl acetate, xylene, or cyclohexane.

[0012] Preferably, in step S2, the ring reaction temperature is 190~210℃ and the reaction time is 4~6 hours.

[0013] Preferably, in step S2, each molecule of the obtained aqueous monomer containing an imidazole structure simultaneously contains an imidazole structure and a terminal amino group.

[0014] Preferably, in step S2, the quaternizing agent is selected from at least one of the following halogenated quaternizing agents: hexadecyl dimethyl quaternary ammonium salt, 2-bromoethylamine hydrobromide, sodium bromoethylsulfonate, bromoethane, benzyl chloride, dimethyl octadecyl quaternary ammonium salt bromide, etc.

[0015] Preferably, in step S2, the solvent for the quaternization reaction is selected from at least one of tetrahydrofuran, methanol, dimethylformamide, acetonitrile, dimethyl sulfoxide, water, or ethanol; the quaternization reaction temperature is 30~100℃; and the quaternization reaction time is 10~72 hours.

[0016] S3. Steps for preparing an in-situ antibacterial polyamide loose nanofiltration membrane: An aqueous solution and an organic solution are sequentially coated onto the substrate, and a functional layer is prepared through an interfacial polymerization reaction between the two. The aqueous solution contains an aqueous monomer and a solvent, and the organic solution contains an organic monomer and a solvent. After heat treatment, a polyamide loose nanofiltration membrane with in-situ antibacterial function can be prepared.

[0017] Preferably, in step S3, the mass ratio of the aqueous monomer to the solution is 1:10 to 1:100.

[0018] Preferably, in step S3, the mass ratio of the organic phase monomer to the solution is 1:10 to 1:100.

[0019] This invention significantly enhances the antibacterial properties of a monomer by introducing an antibacterial quaternary ammonium imidazole structure into the aqueous phase. This structure can generate a strong electrostatic interaction with the bacterial cell membrane, disrupting the normal metabolic pathways and cell membrane integrity of bacteria, ultimately leading to bacterial death.

[0020] In terms of substrate preparation, this invention employs a liquid-solid phase transformation method. Its film-forming mechanism involves mixing a polymeric membrane matrix material, a membrane modifier, and an organic solvent to prepare a casting solution, which then forms a substrate with a finger-like pore structure through a phase transformation process.

[0021] In terms of functional layer construction, this invention employs interfacial polymerization. Its film-forming mechanism involves the polymerization of two reactants containing bifunctional or multifunctional groups at the interface between two phases, forming a loose polyamide selective layer, thereby endowing the nanofiltration membrane with specific separation and antibacterial functions.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) A novel aqueous monomer with an antibacterial quaternized imidazole structure was successfully synthesized by amidation, cyclization and quaternization reactions. An in-situ antibacterial loose nanofiltration membrane was prepared based on interfacial polymerization technology. The modified membrane obtained has excellent dye / salt separation performance and antibacterial performance while maintaining high flux, and exhibits good continuous operation stability. (2) The antibacterial quaternary ammonium imidazole structure introduced into the aqueous monomer is firmly integrated into the separation layer through interfacial polymerization. The quaternized imidazole group in this structure can disrupt the integrity of the bacterial cell membrane through electrostatic interactions, leading to bacterial death, thereby improving the membrane's long-lasting antibacterial properties; (3) The separation layer contains quaternary ammonium imidazole structures and terminal amino groups, which makes the membrane surface exhibit a weaker negative charge than traditional piperazine nanofiltration membranes. This characteristic helps to enhance the membrane's retention of cationic dyes; (4) The preparation process of this invention is simple, the reaction conditions are easy to control, the energy consumption is low, and it has good process scalability and application potential, providing a new strategy for efficient dye / salt separation and anti-biocontamination applications.

[0023] 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

[0024] Figure 1Infrared image of the novel quaternized aqueous monomer in Example 1 of the preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane of the present invention; Figure 2 The NMR spectrum of the novel quaternized aqueous monomer in Example 1 of the preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane of the present invention is shown. Figure 3 The images show the co-culture of novel quaternized aqueous monomers with Escherichia coli in Example 1 of the preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane of the present invention, wherein the left image is a blank sample and the right image is an image of the aqueous monomers. Figure 4 The images show the co-culture of a novel quaternized aqueous monomer with Staphylococcus aureus in Example 1 of the preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane of the present invention. The left image is a blank sample, and the right image is a picture of the co-culture of the aqueous monomer. Figure 5 This invention relates to a novel quaternized aqueous monomer used in Example 1 of a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. OD 600nm Values, where the left side is the blank sample and the right side is the aqueous monomer value. OD 600nm Value diagram; Figure 6 The image shows a plate count of the novel quaternized aqueous monomer in Example 1 of the preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane of the present invention. The left side is the blank sample and the right side is the plate count of the aqueous monomer. Figure 7 The infrared image is of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention. Figure 8 XPS image of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention; Figure 9 The contact angle and water flux diagram of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention are shown. Figure 10 This is a molecular weight cutoff diagram of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention. Figure 11 The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to the present invention includes the zeta potential diagram of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1; Figure 12 The dye rejection rate of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention is shown in the figure. Figure 13 The inorganic salt rejection rate of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention is shown in the figure. Figure 14 The salt / dye separation performance of the in-situ antibacterial polyamide loose nanofiltration membrane in Example 1 of the preparation method of the in-situ antibacterial polyamide loose nanofiltration membrane of the present invention is shown in the figure. Figure 15 The present invention discloses a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. Example 1 shows the co-culture of the in-situ antibacterial polyamide loose nanofiltration membrane with bacteria. Figure 16 The present invention discloses a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. Example 1 shows a plate count diagram after co-culturing the in-situ antibacterial polyamide loose nanofiltration membrane with bacteria. Figure 17 The present invention discloses a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. Example 1 shows the SEM image of the membrane surface after co-culturing the in-situ antibacterial polyamide loose nanofiltration membrane with bacteria. Figure 18 The present invention discloses a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. Example 1 shows a continuous salt / dye separation diagram of the in-situ antibacterial polyamide loose nanofiltration membrane. Detailed Implementation

[0025] 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.

[0026] Example 1 This invention provides a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane, comprising the following steps: S1. Preparation of in-situ antibacterial loose nanofiltration membrane substrate: Dissolve 18 g of polyethersulfone resin, 3 g of polyvinylpyrrolidone and 3 g of polyethylene glycol 400 in... N, N The modified polyethersulfone casting solution was prepared by stirring in dimethylacetamide at 60 °C for 12 h to obtain a uniform solution. The solution was placed in a vacuum drying oven at 60 °C for 12 h to remove air bubbles. The casting solution was spread evenly on a glass plate using a 250 μm thick doctor blade. After stabilizing in air for 30 s, the solution was immersed in distilled water for 12 h. Then, it was washed and soaked in distilled water for 24 h to obtain the in-situ antibacterial nanofiltration membrane substrate.

[0027] Preparation of S2, Quaternized Aqueous Monomer: 6.19 ml of diethylenetriamine (DETA), 2.95 g of succinic acid (SA), and 30 mL of toluene were added to a reactor, and the mixture was stirred and heated at 160 ℃ under a N2 atmosphere for 4 h. The temperature was then increased to 200 ℃ and maintained for 6 h until no water remained in the water separator. The mixture was then dried to obtain the antibacterial aqueous monomer, 1,2-di( N 2.28 g of BAIE and 4.30 g of 2-bromoethylamine hydrobromide were dissolved in deionized water and kept at 80 °C for 24 h. The product was then centrifuged in anhydrous ethanol. Finally, the precipitate was dried under vacuum to obtain quaternized 1,2-di(aminoethylimidazoline)ethane (BAIE). N -Aminoethylimidazoline) ethane (QBAIE).

[0028] S3. Preparation of In-situ Antibacterial Loose Nanofiltration Membrane: A nanofiltration membrane with an antibacterial PA layer was prepared by the IP method using quaternized aqueous monomers and organic monomers. Water was removed from the substrate surface, and the membrane was dried in vacancy for 5 min. The substrate was placed in a mold, and the aqueous phase was applied for 2 min. The aqueous phase solution contained 0.5 wt% QBAIE. Before proceeding to the next step, the solution on the membrane surface was removed, and the membrane was air-dried for 5 min. An organic phase containing 0.1 wt% TMC and n-hexane was applied to the membrane surface for 1 min at 50 °C. Finally, the membrane was heat-treated at 80 °C for 30 s and stored in deionized water for subsequent characterization.

[0029] like Figure 1 The infrared spectrum of QBAIE shown is at 3262 cm⁻¹. -1 and 2937 cm -1 The peaks at 1653 cm⁻¹ are attributed to the stretching vibrations of NH₄⁺ and CH₄, respectively. The peaks at 1653 cm⁻¹ are attributed to the stretching vibrations of NH₄⁺ and CH₄, respectively. -1 and 1256 cm -1 The peaks at these locations are attributed to C=N and CN, respectively. This indicates the successful synthesis of the QBAIE aqueous monomer with a bisimidazoline structure. Figure 2 The NMR spectrum showed a resonance peak around 1.51 ppm, attributed to H near the amino group, while peaks in the ranges of 2.93 ppm and 3.50–3.68 ppm were associated with hydrogen on C-CH2-C and C-CH2-N, respectively. The peak around 3.92 ppm was attributed to H on C=N-CH2-C (the b peak of the imidazole ring), strongly confirming the successful synthesis of QBAIE.

[0030] like Figure 3 and Figure 4 Images of a novel aqueous monomer co-cultured with Escherichia coli and Staphylococcus aureus, and... Figure 5 of OD 600nmThe values ​​showed that, compared to the turbid blank sample, the QBAIE co-culture medium was clear and transparent, with significantly higher concentrations of monomers in the aqueous phase, including Escherichia coli (0.011) and Staphylococcus aureus (0.013). OD 600nm The values ​​were all low, indicating that BAIE has strong antibacterial properties. For example... Figure 6 Plate count images of the aqueous monomer against Escherichia coli and Staphylococcus aureus clearly show that BAIE has high antibacterial activity. E. coli ) and Staphylococcus aureus ( S. aureus The inhibition rates of QBAIE were all high (>99.0%), which is related to the antibacterial structure of quaternized imidazole. The antibacterial mechanism of the quaternized imidazole structure is to disrupt the integrity of bacteria, thereby causing their death.

[0031] like Figure 7 and Figure 8 Infrared and XPS images of the in-situ antibacterial polyamide loose nanofiltration membrane. 1483 cm⁻¹ -1 and 1325 cm -1 The peak values ​​at these locations are related to the C=N and CN stretching vibrations, respectively, with the C=O stretching vibration peak located at 1660 cm⁻¹. The peaks at 533.1 eV, 399.2 eV, 284.6 eV, 231.0 eV, and 168.6 eV represent O 1s, N 1s, C 1s, S 2s, and S 2s, respectively, which demonstrates the successful amidation reaction between QBAIE and TMC.

[0032] like Figure 9 The figure shows the contact angle and water flux of the in-situ antibacterial polyamide loose nanofiltration membrane. As can be seen from the figure, after adding the modifier, the contact angle of the prepared membrane is 74.2°, indicating that the membrane has excellent hydrophilic properties. Its water flux is 165.1 L / m². -2 h -1 bar -1 .

[0033] like Figure 10 The figure shows the molecular weight cutoff of the in-situ antibacterial polyamide nanofiltration membrane. As can be seen from the figure, the molecular weight cutoff of the prepared nanofiltration membrane is 2772 Da, and its corresponding Stock radius is 1.38 nm. Figure 11 As shown, the zero potential point of the membrane appears at pH 4.5, and its surface zeta potential is -8.7 mV at pH 7, indicating that a weakly electronegative membrane has been successfully prepared.

[0034] like Figure 12The dye rejection rates of the in-situ antibacterial polyamide loose nanofiltration membrane are shown in the order: Congo Red (CR) > Victoria Blue (VBB) > Chrome Black T (EBT) > Methyl Blue (MB). The membrane rejection rates for the four dyes are relatively close, all exceeding 94.2%. The membrane surface exhibits weak negative charge; therefore, the membrane rejection rate mainly depends on particle size sieving and electrostatic repulsion. Dyes mainly exist in clusters in aqueous solutions; suitable pore size contributes to the membrane's high dye rejection performance, and the negative charge on the membrane surface also aids in the rejection of anionic dyes. Figure 13 The inorganic salt rejection rates of the in-situ antibacterial polyamide loose nanofiltration membranes are shown to be Na2SO4 > MgSO4 > MgCl2 > NaCl. The membranes' removal rates for all four salts are below 3.0%. Due to their loose functional layer structure, most salts permeate, meaning their pore structure is conducive to high dye rejection and high salt permeability.

[0035] Figure 14 The salt / dye separation capability of the in-situ antibacterial polyamide loose nanofiltration membrane was studied. With increasing salt concentration, the membrane's CR rejection rate gradually decreased. At different salt concentrations, the membrane exhibited high CR rejection rates (>98.0%) and high salt permeability (>97.0%). The decrease in CR rejection rate with increasing salt concentration is attributed to the presence of inorganic salt ions, which to some extent reduces CR aggregation, resulting in a more uniform distribution in the solution and allowing it to pass through the membrane pores. Simultaneously, the membrane's rejection rate for Na₂SO₄ or NaCl gradually decreased, primarily due to concentration polarization caused by high Na₂SO₄ or NaCl concentrations.

[0036] Using Staphylococcus aureus as a bacterial model, the membrane was co-cultured with the bacterial solution. After removing the membrane sample, any non-adhesive or loosely adhering bacteria on the surface were removed, and the sample was immersed in 10 ml of sterile water and sonicated for 10 min to separate the bacteria adhering to the membrane surface. The obtained bacterial solution was serially diluted and spread on nutrient agar plates. After incubation at 37°C for 12 h, the number of CFUs on each plate was observed and compared.

[0037] like Figure 15 and Figure 16 The images show the antibacterial effect of the in-situ antibacterial polyamide loose nanofiltration membrane. Under the influence of the sterilization performance of the antibacterial imidazole structure, the prepared loose nanofiltration membrane achieved an inhibition rate of 98.8% against Staphylococcus aureus and 99.2% against Escherichia coli, indicating that the modified membrane has excellent antibacterial properties.

[0038] like Figure 17The continuous filtration test of the in-situ antibacterial polyamide loose nanofiltration membrane is shown. During the 24-hour filtration experiment, the salt / dye separation performance of the prepared loose nanofiltration membrane did not decrease significantly, indicating that the loose nanofiltration membrane has good salt / dye separation stability. This is mainly because QBAIE and TMC form a stable in-situ antibacterial polyamide loose layer on the PES substrate.

[0039] Example 2: Aqueous phase formulation: 0.3 wt% aqueous monomer. The rest is the same as in Example 1.

[0040] Example 3: Aqueous phase formulation: 0.6 wt% aqueous monomer. The rest is the same as in Example 1.

[0041] Example 4: Oil phase formulation: 0.2 wt% oil phase monomer. The rest is the same as in Example 1.

[0042] Example 5: Oil phase formulation: 0.05 wt% oil phase monomer. The rest is the same as in Example 1.

[0043] Example 6: Substrate formulation: 16 g polyethersulfone resin, 3 g polyvinylpyrrolidone, and 3 g polyethylene glycol. The rest is the same as in Example 1.

[0044] Test method for separation performance of loose nanofiltration membrane.

[0045] Test solution: 100 mg / L dye, 1000 mg / L inorganic salt solution.

[0046] Operating pressure: 4 bar.

[0047] 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.

[0048] flux J w = V / ( A t P ), V For the volume of water produced, 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.

[0049] Table 1 shows the running results of different examples compared to Example 1. Table 1

[0050] As shown in the above embodiments, this invention prepares a loose nanofiltration membrane substrate by dissolving a polymeric membrane matrix material and a membrane modifier in an organic solvent through a blending method. An antibacterial aqueous monomer containing a quaternary ammonium imidazole structure is synthesized through amidation-cyclization and quaternization reactions, and an in-situ antibacterial loose nanofiltration membrane is prepared on the substrate via interfacial polymerization. The prepared loose nanofiltration membrane exhibits excellent salt / dye separation performance and antibacterial properties, making it suitable for application in wastewater treatment in the papermaking and dyeing industries.

[0051] Therefore, this invention provides a method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane. The introduced antibacterial quaternized imidazole structure enhances the antibacterial properties of the loose nanofiltration membrane. An in-situ antibacterial polyamide loose layer is prepared by interfacial polymerization of quaternary imidazole-type aqueous monomers and organic monomers. The prepared loose nanofiltration membrane exhibits separation stability. The loose nanofiltration membrane with the in-situ antibacterial quaternized imidazole structure of this invention is applied as a filter medium in the treatment and reuse of dyeing and printing wastewater.

[0052] 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 an in-situ antibacterial polyamide loose nanofiltration membrane, characterized in that, Includes the following steps: S1. The substrate is prepared using a phase inversion process, with the following specific steps: A casting solution containing a polymer membrane matrix material, a membrane modifier, and an organic solvent is stirred and degassed under constant temperature conditions, and then uniformly coated onto a clean glass plate. It is then allowed to stand in air to evaporate for a certain period of time, and then immersed in a coagulation bath (usually deionized water) to complete the phase inversion process, ultimately obtaining the desired substrate. S2. The steps for preparing quaternized aqueous monomers are as follows: First, the imidazole-structured aqueous monomer undergoes a quaternization reaction with a quaternization reagent; then, the reaction product is washed to remove residual reagents and by-products, and then centrifuged and dried to finally obtain a quaternized monomer containing an antibacterial structure. S3. The in-situ antibacterial polyamide loose nanofiltration membrane of the present invention is prepared by the following steps: First, an aqueous solution and an organic solution are successively coated onto the obtained substrate, causing an interfacial polymerization reaction to form a functional layer. The aqueous solution is prepared by dissolving the aforementioned quaternized monomer in a corresponding solvent; the organic solution is prepared by dissolving the organic monomer in an organic solvent. After the functional layer is formed, subsequent processing yields the polyamide loose nanofiltration membrane with in-situ antibacterial properties.

2. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S1, the polymeric membrane matrix material is selected from at least one of polysulfone, polyethersulfone, cellulose acetate, polypropylene, polyvinylidene fluoride, polyvinyl chloride, and polyamide; preferably, the mass percentage of the polymeric membrane matrix material is 16% to 20% based on the total mass of the casting solution.

3. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S1, the membrane modifier includes at least one of a pore-forming agent, a hydrophilic agent, or a surfactant.

4. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S1, the organic solvent is selected from... N, N - Dimethylformamide, acetone, chloroform N, N -Dimethylacetamide cyclohexane, dimethyl sulfoxide or N At least one of methylpyrrolidone.

5. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: The aqueous monomer containing the imidazole structure is prepared by the following steps: Diethylenetriamine and a polybasic acid are dissolved in a water-carrying agent, followed by amidation and cyclization reactions. The product is then washed, filtered, and dried to obtain an aqueous monomer with an imidazole structure and a terminal amino group, the structural formula of which is: , , Where n is an integer greater than or equal to 0.

6. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S2, the quaternizing agent is selected from halogenated compounds, such as halogenated amino compounds, halogenated alkyl compounds, and halogenated alkyl sulfonate reagents, specifically at least one of quaternizing agents such as 2-bromoethylamine hydrobromide, bromoethane, sodium bromoethylsulfonate, benzyl chloride, hexadecyl dimethyl quaternary ammonium salt, and dimethyl octadecyl quaternary ammonium salt bromide.

7. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S2, the aqueous monomer containing the imidazole structure may contain a monoimidazoline structure or a bisimidazoline structure. The monomer molecule has a tertiary amine active site, and a quaternization reaction is carried out based on the site to graft quaternary ammonium salt groups. The resulting quaternized aqueous monomer contains at least two functional groups that can participate in interfacial polymerization reactions.

8. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S2, the solvent used for the quaternization reaction is at least one of tetrahydrofuran, methanol, dimethylformamide, acetonitrile, dimethyl sulfoxide, water, or ethanol; the reaction is carried out in a temperature range of 30°C to 180°C; and the reaction time is 10 hours to 72 hours.

9. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S2, the aqueous monomer containing the antibacterial quaternized structure, each monomer contains an antibacterial quaternary ammonium imidazole structure and a terminal amino structure, and its structure can be: , ， Where R is an amino chain, alkyl chain, or zwitterionic chain, etc., and R1 is an amino chain.

10. The method for preparing an in-situ antibacterial polyamide loose nanofiltration membrane according to claim 1, characterized in that: In step S3, the mass ratio of the aqueous phase monomer, the organic phase monomer and its solvent is 1:10 to 1:100; the organic phase monomer is selected from polyfunctional acyl chlorides or halogenated aromatic hydrocarbons, etc., preferably, the organic phase monomer is at least one of adipyl chloride, trimesoyl chloride, m-tribromomethylbenzene, sebacyl chloride, m-trichloromethylbenzene, etc.

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