Preparation method of electrically neutral in-situ antibacterial loose nanofiltration membrane

Abstract

The invention discloses a preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane, and belongs to the technical field of nanofiltration membranes. The method comprises the following steps: S1, taking a polymeric membrane matrix material, a membrane modifier and an organic solvent as raw materials, and preparing a base membrane through a phase inversion process; s2, taking the synthesized micromolecular organic matter containing the antibacterial imidazole structure as a water-phase monomer; and S3, selection of organic phase monomers: at least one of halogenated aromatic hydrocarbons such as tribromotrimethylbenzene, sym-tribromobenzene, sym-trichlorobenzene and the like. And S4, carrying out interfacial polymerization reaction on the water-phase monomer and the organic-phase monomer on the base membrane to prepare the electrically neutral in-situ antibacterial loose nanofiltration membrane. The membrane material prepared by the invention has high flux, excellent dye / salt separation performance and efficient antibacterial performance, and remarkable application potential.

Description

Technical Field

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

[0002] Loose nanofiltration (LNF) membranes, as an innovative membrane separation technology, stand out for their high flux and high salt and dye separation performance. Their retention capacity falls between that of ultrafiltration and nanofiltration membranes, a characteristic that gives them enormous application potential in the treatment of dyeing and printing wastewater, and they have rapidly become a research hotspot. LNF membranes not only effectively retain organic dyes but also allow inorganic salt ions to permeate, achieving highly efficient separation of inorganic salts and dyes. Furthermore, LNF membranes feature high water flux and low operating pressure, significantly reducing energy consumption and demonstrating significant energy-saving advantages.

[0003] However, LNF membranes also face significant challenges in separating organic pollutants such as dyes. Microorganisms in water easily accumulate on the membrane surface, forming biofilms, which not only lead to membrane fouling but also significantly reduce water flux. Traditional solutions, such as frequent addition of bactericides and chemical cleaning, can damage the membrane separation layer and potentially cause secondary pollution. To address these challenges, researchers are actively exploring new methods to improve the antibacterial performance of membranes. Currently, methods such as layer-by-layer self-assembly, surface functionalization modification, and nanomaterial doping are widely used to enhance membrane antibacterial properties. Among these, using metals and their oxides to prepare antibacterial separation membranes is a common strategy, but its antibacterial mechanism relies on the release of metal ions, which may lead to a weakening of antibacterial performance over time, and the diffusion of metal ions may also cause environmental pollution. Furthermore, although synthesizing antibacterial modifiers and preparing zwitterionic loose nanofiltration membranes through coating and grafting can yield membranes with high flux and excellent antibacterial performance, its complex preparation process limits its widespread application. To address these technical challenges, this invention proposes an innovative method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, aiming to overcome the limitations of existing technologies and provide a new strategy for LNF membrane design. A previously filed patent (patent application number: CN202410554464.0) proposed a novel antibacterial bisimidazoline aqueous monomer and demonstrated its excellent antibacterial properties. However, the resulting nanofiltration membrane had a relatively dense functional layer, exhibiting high retention rates for both organic dyes and inorganic salts, which is detrimental to resource recovery and utilization. Therefore, using a less reactive oil-phase monomer (such as tribromotrimethylbenzene) to replace the traditional organic-phase monomer pyromellitic acid chloride can prepare a nanofiltration membrane with a more porous functional layer. This patent proposes a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane based on the functional layer microstructure design, providing a technically feasible solution for wastewater treatment in industries such as textiles. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane. The aqueous monomer used has an antibacterial imidazole structure, and the organic monomer does not contain easily hydrolyzable acyl chloride groups. The electrically neutral in-situ antibacterial loose nanofiltration membrane is prepared by interfacial polymerization. This loose nanofiltration membrane has high flux, high salt / dye separation performance and excellent antibacterial properties.

[0005] To achieve the above objectives, the present invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, the specific preparation steps of which are as follows: S1. Preparation of the loose nanofiltration membrane base membrane: The polymer membrane matrix material and membrane modifier are dissolved in an organic solvent and stirred at a constant temperature until a uniform casting solution is formed. After removing air bubbles, the casting solution is poured onto a glass plate, allowed to stand in air to stabilize, and then immersed in distilled water to solidify, thus obtaining the base membrane.

[0006] Preferably, the organic solvent is selected from... N 2-Methylpyrrolidone, acetone N , N -Dimethylacetamide, chloroform, N , N - One of dimethylformamide, cyclohexane, or dimethyl sulfoxide.

[0007] Preferably, the polymer membrane matrix material is selected from at least one of polyvinyl chloride, polysulfone, cellulose acetate, polyethersulfone, polypropylene, polyamide, or polyvinylidene fluoride.

[0008] Preferably, based on the total mass of the casting solution, the mass percentage of the polymeric membrane matrix material is 16wt%~22wt%.

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

[0010] S2. Preparation of aqueous monomers containing antibacterial structures: Polyene polyamines and polyacids are dissolved in a water-carrying agent, and an amidation reaction is carried out at 120-170℃ for 4-6 hours, followed by a cyclization reaction at 190-210℃ for 4-6 hours. After the reaction, the monomers are purified to obtain antibacterial aqueous monomers containing antibacterial imidazole structures and terminal amino groups.

[0011] Preferably, the polydicarboxylic acid is selected from at least one of malonic acid, succinic acid, or glutaric acid.

[0012] Preferably, the water-carrying agent is selected from at least one of petroleum ether, cyclohexane, xylene, chloroform, toluene, or isoamyl acetate.

[0013] Preferably, the aqueous monomer containing the antibacterial imidazole structure and the terminal amino group contains an imidazole structure and a terminal amino group, and its structural formula is shown below: Where n is an integer.

[0014] Preferably, the polyacid is selected from at least one of oxalic acid, malonic acid, or succinic acid.

[0015] Preferably, the water-carrying agent is selected from at least one of xylene, benzene, or toluene.

[0016] S3. Selection of organic phase monomers: The organic phase monomers can be at least one of the following: tribromotrimethylbenzene, mesbromotribromobenzene, mesbromotrichlorobenzene, etc.

[0017] S4. Preparation of an electrically neutral, in-situ antibacterial, loose nanofiltration membrane: An aqueous solution and an organic solution are sequentially coated onto the base membrane obtained in S1, and a functional layer is formed on the surface of the base membrane through an interfacial polymerization reaction. The aqueous solution contains a solvent and the aqueous monomer prepared in S2, while the organic solution contains a solvent and the organic monomer selected in S3. After the reaction, heat treatment is performed to finally obtain a loose nanofiltration membrane with electrically neutral and in-situ antibacterial functions.

[0018] Preferably, the mass ratio of the aqueous monomer to the aqueous solution is 1:10 to 1:100.

[0019] Preferably, the mass ratio of the organic phase monomer to the organic phase solution is 1:10 to 1:100.

[0020] The antibacterial aqueous monomer prepared by this invention contains an imidazole structure. This imidazole structure is easily protonated. After protonation, it can disrupt the integrity of the bacterial surface through electrostatic interaction, leading to leakage of cell contents and subsequent bacterial death.

[0021] The organic phase monomer selected in this invention is a haloaromatic hydrocarbon, which does not form amide bonds and carboxyl groups during interfacial polymerization, and its reactivity is lower than that of the traditional organic phase monomer trimesoyl chloride (TMC). Therefore, it is beneficial to prepare membrane materials with neutral surface charge and loose functional layers.

[0022] In terms of base membrane preparation, this invention employs a non-solvent-induced phase separation method (liquid-solid phase inversion method). The film formation mechanism is as follows: a polymeric membrane matrix material, a membrane modifier, and an organic solvent are blended to prepare a casting solution. Subsequently, through the exchange process between the solvent and the non-solvent, the polymer solid phase is precipitated to form a porous base membrane.

[0023] In terms of functional layer construction, this invention employs interfacial polymerization. Its film-forming mechanism is as follows: difunctional or trifunctional reactive monomers dissolved in the aqueous and organic phases respectively undergo polymerization at the interface between the two phases, thereby forming a loose functional separation layer on the surface of the base film.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) The aqueous monomer contains an antibacterial imidazole structure, which allows the antibacterial structure to be directly constructed in the separation layer through interfacial polymerization, thereby achieving in-situ antibacterial function. The separation layer is rich in imidazole groups, which are easily protonated in water. The protonated imidazole structure can disrupt the integrity of the cell wall through electrostatic interaction with the bacterial surface, leading to leakage of intracellular substances and ultimately causing bacterial death, thus significantly endowing the membrane with antibacterial properties.

[0025] (2) The selected organic phase monomer, haloaromatic hydrocarbon, does not contain easily hydrolyzable acyl chloride groups. Therefore, the surface charge of the membrane material prepared from it tends to be close to electroneutrality, which helps to improve the separation selectivity of the membrane for mixed solutions of inorganic salts and dyes. At the same time, compared with traditional organic phase monomers TMC, haloaromatic hydrocarbons have lower reactivity, which is conducive to the formation of a looser nanofiltration separation layer during interfacial polymerization.

[0026] (3) The preparation process described in this invention is simple, easy to control, and has low energy consumption, and has good development potential and application prospects.

[0027] 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

[0028] Figure 1 Infrared image of the aqueous monomer in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention; Figure 2 The NMR spectrum of the aqueous monomer in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention; Figure 3 The images shown are of an aqueous monomer and Escherichia coli co-cultured in Example 1 of the preparation method of an electrically neutral in situ antibacterial loose nanofiltration membrane according to the present invention. The left image is a blank sample, and the right image is an image of the aqueous monomer. Figure 4 The images shown are of the aqueous monomer and Staphylococcus aureus co-cultured in Example 1 of the preparation method of an electrically neutral in situ antibacterial loose nanofiltration membrane of the present invention. The left image is a blank sample, and the right image is a picture of the aqueous monomer co-culture. Figure 5 The aqueous monomer in Example 1 of the method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane according to the present invention... 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 This is a plate count image of the aqueous monomer in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention, wherein the left side is a blank sample and the right side is a plate count image of the aqueous monomer. Figure 7 Infrared image of the membrane material in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention; Figure 8 XPS image of the membrane material in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention; Figure 9 This is a diagram showing the contact angle and water flux of the membrane material in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane according to the present invention. Figure 10 This is a molecular weight cutoff diagram of the membrane material in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane according to the present invention; Figure 11 The zeta potential diagram of the membrane material in Example 1 of the present invention is shown in the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane. Figure 12 The dye rejection rate diagram of the membrane material in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention; Figure 13 The inorganic salt rejection rate of the membrane material in Example 1 of the present invention is shown in the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane. Figure 14 The salt / dye separation performance diagram of the membrane material in Example 1 of the preparation method of an in-situ antibacterial polyamide loose nanofiltration membrane of the present invention; Figure 15 The present invention discloses a method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane. In Example 1, a plate count diagram is shown after co-culturing the membrane material with bacteria. The left diagram is a blank sample, and the right diagram is an antibacterial effect diagram of the membrane material. Figure 16 The present invention provides a method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane. Example 1 shows the SEM image of the membrane surface after co-culturing the membrane material with bacteria. Figure 17 The salt / dye separation stability diagram of the membrane material in Example 1 of the preparation method of an electrically neutral in-situ antibacterial loose nanofiltration membrane of the present invention. Detailed Implementation

[0029] 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.

[0030] Example 1 This invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, mainly comprising the following steps: S1. Steps for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane base: Dissolve 18g of polyethersulfone resin (PES), 3g of polyvinylpyrrolidone (PVP), and 3g of polyethylene glycol 400 (PEG-400) in... N, N A homogeneous PES casting solution was obtained by stirring in dimethylacetamide (DMAc) at 60°C for 12 hours. This casting solution was then placed in a vacuum drying oven at 60°C and allowed to stand for 12 hours to remove air bubbles. Subsequently, the casting solution was uniformly coated onto a glass plate, allowed to stand in air for 30 seconds, and then immersed in deionized water for curing for 12 hours to obtain the PES base film. The film material was stored in deionized water.

[0031] S2. Preparation of the antibacterial aqueous monomer: 6.19 mL of diethylenetriamine (DETA), 2.95 g of succinic acid (SA), and 30 mL of toluene were reacted at 160 °C for 4 h under a nitrogen atmosphere. The temperature was then increased to 200 °C and reacted for another 6 h. After purification, the antibacterial aqueous monomer 1,2-bis( N -Aminoethylimidazoline) ethane (BAIE).

[0032] S3. Steps for preparing an electrically neutral in-situ loose antibacterial nanofiltration membrane: Remove moisture from the surface of the base membrane and air dry for 5 min. Fix the base membrane in a mold, pour in an aqueous solution containing 0.5 wt% BAIE to completely cover the membrane surface, and let it stand for 2 min. After removing excess aqueous solution, air dry for 5 min. Subsequently, pour a cyclohexane organic phase solution containing 0.1 wt% tribromotrimethylbenzene (TBB) under the membrane surface and hold for 1 min. Finally, heat-treat the membrane in an 80 ℃ oven for 30 s to obtain the target membrane material.

[0033] like Figure 1 As shown, the successful synthesis of the aqueous monomer can be verified by infrared spectroscopy. The values ​​at 3299 and 2934 cm⁻¹ in the spectrum are also relevant. -1 The absorption peaks at 1644 cm⁻¹ are attributed to the stretching vibrations of NH₃ and CH₄, respectively; -1 The absorption peak at 1275 cm⁻¹ corresponds to the stretching vibration of the C=N bond. -1 The peaks at this location originate from CN bond vibrations. These characteristic peaks indicate the successful synthesis of the BAIE aqueous monomer with a bisimidazoline structure. Further... Figure 2 The nuclear magnetic resonance hydrogen spectrum ( 1¹H NMR analysis revealed that the peak at a chemical shift of 2.20 ppm was attributed to a hydrogen atom in the amino group; the peak at 2.52 ppm corresponded to a hydrogen atom in the C-CH₂-C structure; and the multiplets in the 2.60–2.80 ppm range were associated with hydrogen atoms in the C-CH₂-N structure. Furthermore, the signal at 3.28 ppm was attributed to a hydrogen atom in the C=N-CH₂-C structure of the imidazole ring (corresponding to the b-position in the ring). These spectral data collectively confirm the successful synthesis of the target product BAIE.

[0034] like Figure 3 and Figure 4 The BAIE shown is related to Escherichia coli ( E. coli Staphylococcus aureus ( S.aureus The co-culture images show that the culture medium in the BAIE-treated group was clear and transparent compared to the turbid blank control group. Figure 5 The corresponding OD 600 The value further confirms this phenomenon: BAIE processing E. coli and S.aureus After OD 600 The values ​​were only 0.004 and 0.006, respectively, significantly lower than the control group, indicating that BAIE has a strong antibacterial effect. Furthermore, Figure 6 The plate count results clearly showed that the BAIE-treated group had extremely low colony counts, further confirming its highly effective antibacterial properties. Quantitative data indicated that BAIE... E. coli and S.aureus The inhibition rate was as high as 99.0%. This excellent antibacterial activity is mainly attributed to the imidazole structure in the BAIE molecule. Its antibacterial mechanism is that the imidazole group is easily protonated, which can destroy the integrity of the bacterial cell wall, ultimately leading to bacterial death.

[0035] like Figure 7 and Figure 8 The images show the infrared and XPS spectra of an electrically neutral, in-situ antibacterial, porous nanofiltration membrane. In the infrared spectrum, 1489 and 1071 cm⁻¹ are shown. -1 The absorption peaks at 1668 cm⁻¹ are attributed to the stretching vibrations of C=N and CN, respectively. -1 The peak at 701 cm⁻¹ represents the stretching vibration of C=O. -1 The characteristic peak of C-Br appears at this point. In the XPS spectrum, the binding energy peaks at 531.3 eV, 399.1 eV, 284.5 eV, 231.5 eV, 168.0 eV, and 66.8 eV correspond to the O 1s, N 1s, C 1s, S 2s, S 2p, and Br 3d signals, respectively. These results collectively confirm that a successful interfacial polymerization reaction occurred between BAIE and TBB.

[0036] like Figure 9 The contact angle and water flux data of the membrane are presented. The contact angle of the prepared membrane is 76.2°, indicating its good hydrophilicity; at the same time, thanks to its loose porous structure, its water flux reaches 157 L / m³. -2 h -1 bar -1 .from Figure 10 Based on the molecular weight cutoff of the membrane, the molecular weight cutoff of this loose nanofiltration membrane is approximately 1957 Da, corresponding to a Stokes radius of approximately 1.14 nm. Figure 11 The zeta potential results of the membrane showed that the zero point of the membrane appeared at pH 6.4, and its surface potential was -3.0 mV at pH 7.0, further proving that the prepared membrane has near-electrically neutral surface properties.

[0037] like Figure 12 The membrane exhibits its retention performance for four dyes: Congo Red (CR), Victoria Blue (VBB), Methylene Blue (MB), and Reactive Brilliant Blue (KN-R). The retention capacity of the membrane for the four dyes is ranked as follows: CR > VBB > MB > KN-R, with all retention rates exceeding 99.6%, demonstrating excellent dye retention capabilities. Due to the near-electrical neutrality of the membrane surface, its dye retention mechanism is primarily size sieving. Dye molecules tend to form clusters in aqueous solutions, and the membrane has a matching pore size, thus achieving highly efficient dye retention. Figure 13 The membranes demonstrated exhibit retention performance for four inorganic salts. The retention rates are in the order of MgSO4 > MgCl2 > Na2SO4 > NaCl, with all inorganic salts having a retention rate below 3.9%. This is mainly attributed to the porous structure and large pore size of the membrane's functional layers, which allows salt ions to permeate freely, thus achieving high dye rejection and low inorganic salt rejection.

[0038] like Figure 14 The separation performance of the membrane in the salt / dye coexistence system was further demonstrated. With increasing salt concentration, the membrane's rejection rate for dye CR decreased slightly, but remained above 99.0% at all concentrations. The presence of salt weakens the aggregation of CR molecules, resulting in a more uniform size distribution. Some smaller dye aggregates may permeate through the membrane pores, leading to a slight decrease in rejection rate. Meanwhile, the membrane's rejection rates for MgSO4 and NaCl remained below 2%, and decreased further with increasing salt concentration. This is mainly attributed to the concentration polarization effect caused by high salt concentration.

[0039] After co-culturing the membrane sample with bacterial suspension, the sample was removed to remove non-adhesive or loosely attached bacteria from the surface. The sample was then immersed in 10 mL of sterile water and sonicated for 10 minutes to separate firmly adhered bacteria from the membrane surface. The obtained bacterial suspension was serially diluted, spread onto nutrient agar plates, and incubated at 37°C for 12 hours. Colonies on each plate were then observed and recorded.

[0040] like Figure 15 and Figure 16 As shown, under the action of the antibacterial imidazole structure, the prepared loose nanofiltration membrane has the effect of... S. aureus and E. coli The antibacterial rates reached 98.79% and 98.83% respectively, indicating that the membrane possesses excellent antibacterial properties. For example... Figure 17 The results of continuous filtration experiments on the membrane were presented. During the 24-hour test, the membrane's salt / contamination separation performance did not show a significant decrease, indicating its excellent operational stability. This is mainly attributed to the stable and robust structure of the in-situ antibacterial functional layer formed by the interfacial polymerization of BAIE and TBB on the PES-based membrane surface.

[0041] Example 2 This invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, mainly comprising the following steps: S1. Steps for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane base: Dissolve 18g PES, 3g PVP, and 3g PEG-400 in DMAC and stir at 60℃ for 12h to obtain a homogeneous PES casting solution. Place the casting solution in a 60℃ vacuum drying oven and let it stand for 12h to remove air bubbles. Then, uniformly coat the casting solution onto a glass plate, let it stand in air for 30s, and then immerse it in deionized water to cure for 12h to obtain the PES base membrane. The membrane material is stored in deionized water.

[0042] S2. Preparation of the antibacterial aqueous monomer: 6.29 ml DETA, 3.00 g succinic acid (SA), and 30 mL toluene were stirred and heated at 160℃ under a N2 atmosphere for 4 h. Then the temperature was increased to 200℃ and the reaction was carried out for 6 h. The product was then purified to obtain the antibacterial aqueous monomer.

[0043] S3. Steps for preparing an electrically neutral in-situ loose antibacterial nanofiltration membrane: Remove moisture from the surface of the base membrane and air dry for 5 min. Fix the base membrane in a mold, pour in an aqueous solution containing 0.5 wt% BAIE to completely cover the membrane surface, and let it stand for 2 min. After removing excess aqueous solution, air dry for 5 min. Subsequently, pour a cyclohexane organic phase solution containing 0.05 wt% TBB under the membrane surface and hold for 1 min. Finally, heat-treat the membrane in an 80 ℃ oven for 30 s to obtain the target membrane material.

[0044] The water flux of the loose nanofiltration membrane prepared in this embodiment is 104.0 L / m³. -2 h -1 bar -1 The membrane exhibited retention rates of 99.3%, 99.4%, 98.7%, and 98.6% for dyes VBB, CR, MB, and KN-R, respectively, while the retention rates for inorganic salts MgSO4, MgCl2, Na2SO4, and NaCl were 6.2%, 3.8%, 2.7%, and 1.4%, respectively. The loose nanofiltration membrane achieved an inhibition rate of 95.56% against Staphylococcus aureus and 97.67% against Escherichia coli. Compared to Example 1, reducing the concentration of the oil phase monomer facilitated the preparation of a loose functional layer, which is beneficial for improving the salt dye separation performance.

[0045] Example 3 This invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, comprising the following steps: S1. Steps for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane base: Dissolve 18g PES, 3g PVP, and 3g PEG-400 in DMAC and stir at 60℃ for 12h to obtain a homogeneous PES casting solution. Place the casting solution in a 60℃ vacuum drying oven and let it stand for 12h to remove air bubbles. Then, uniformly coat the casting solution onto a glass plate, let it stand in air for 30s, and then immerse it in deionized water to cure for 12h to obtain the PES base membrane. The membrane material is stored in deionized water.

[0046] S2. Preparation of the antibacterial aqueous monomer: 6.25 ml DETA, 3.10 g SA, and 30 mL toluene were stirred and heated at 160℃ under a N2 atmosphere for 4 h. Then the temperature was increased to 200℃ and maintained for 6 h. After the reaction was completed, the mixture was purified to obtain the antibacterial aqueous monomer.

[0047] S3. Steps for preparing an electrically neutral in-situ loose antibacterial nanofiltration membrane: Remove moisture from the surface of the base membrane and air dry for 5 min. Fix the base membrane in a mold, pour in an aqueous solution containing 0.5 wt% BAIE to completely cover the membrane surface, and let it stand for 2 min. After removing excess aqueous solution, air dry for 5 min. Subsequently, pour a cyclohexane organic phase solution containing 0.2 wt% TBB under the membrane surface and hold for 1 min. Finally, heat-treat the membrane in an 80 ℃ oven for 30 s to obtain the target membrane material.

[0048] The water flux of the nanofiltration membrane prepared in this embodiment is 106.9 L / m³. -2 h -1 bar -1The membrane exhibited rejection rates of 97.8%, 97.9%, 95.9%, and 95.8% for dyes VBB, CR, MB, and KN-R, respectively, while the rejection rates for inorganic salts MgSO4, MgCl2, Na2SO4, and NaCl were 3.5%, 3.3%, 3.1%, and 2.2%, respectively. The loose nanofiltration membrane achieved an inhibition rate of 97.98% against Staphylococcus aureus and 98.05% against Escherichia coli. Compared to Example 1, increasing the TBB content made the functional layer more porous, which is beneficial for improving the membrane's hydrophilicity and the permeability of inorganic salts.

[0049] Example 4 This invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, comprising the following steps: S1. Steps for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane base: Dissolve 18g PES, 3g PVP, and 3g PEG-400 in DMAC and stir at 60℃ for 12h to obtain a homogeneous PES casting solution. Place the casting solution in a 60℃ vacuum drying oven and let it stand for 12h to remove air bubbles. Then, uniformly coat the casting solution onto a glass plate, let it stand in air for 30s, and then immerse it in deionized water to cure for 12h to obtain the PES base membrane. The membrane material is stored in deionized water.

[0050] S2. Preparation of the antibacterial aqueous monomer: 6.19 ml DETA, 2.95 g SA, and 30 mL toluene were stirred and heated at 160℃ under a N2 atmosphere for 4 h. Then the temperature was increased to 200℃ and maintained for 6 h. After the reaction was completed, the mixture was purified to obtain the antibacterial aqueous monomer.

[0051] S3. Steps for preparing an electrically neutral in-situ loose antibacterial nanofiltration membrane: Remove moisture from the surface of the base membrane and air dry for 5 min. Fix the base membrane in a mold, pour in an aqueous solution containing 0.5 wt% BAIE to completely cover the membrane surface, and let it stand for 2 min. After removing excess aqueous solution, air dry for 5 min. Subsequently, pour a cyclohexane organic phase solution containing 0.4 wt% TBB under the membrane surface and hold for 1 min. Finally, heat-treat the membrane in an 80 ℃ oven for 30 s to obtain the target membrane material.

[0052] The water flux of the nanofiltration membrane prepared in this embodiment is 10.4 L / m³. -2 h -1 bar -1The retention rates of the membrane for dyes VBB, CR, MB, and KN-R were 94.6%, 95.7%, 92.4%, and 92.2%, respectively, while the retention rates for inorganic salts MgSO4, MgCl2, Na2SO4, and NaCl were 7.1%, 6.9%, 4.0%, and 2.2%, respectively. The loose nanofiltration membrane showed an inhibition rate of 96.5% against Staphylococcus aureus and 97.8% against Escherichia coli. Compared to Example 1, further increasing the TBB content improved the membrane's hydrophilicity, but slightly decreased the retention and antibacterial capabilities of the loose nanofiltration membrane. This indicates that when the TBB content exceeds a certain proportion, the overall performance of the membrane slightly decreases.

[0053] Example 5 This invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, comprising the following steps: S1. Steps for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane base: Dissolve 16g PES, 3g PVP, and 3g PEG-400 in DMAC and stir at 60℃ for 12h to obtain a homogeneous PES casting solution. Place the casting solution in a 60℃ vacuum drying oven and let it stand for 12h to remove air bubbles. Then, uniformly coat the casting solution onto a glass plate, let it stand in air for 30s, and then immerse it in deionized water to cure for 12h to obtain the PES base membrane. The membrane material is stored in deionized water.

[0054] S2. Preparation of the antibacterial aqueous monomer: 6.5 ml DETA, 3.10 g SA, and 30 mL toluene were stirred and heated at 160℃ under a N2 atmosphere for 4 h. Then the temperature was 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.

[0055] S3. Preparation of in-situ antibacterial loose nanofiltration membrane: Remove moisture from the surface of the base membrane and air dry for 5 min. Fix the base membrane in a mold, pour in an aqueous solution containing 0.5 wt% BAIE to completely cover the membrane surface, and let it stand for 2 min. After removing excess aqueous solution, air dry for 5 min. Subsequently, pour a cyclohexane organic phase solution containing 0.1 wt% TBB under the membrane surface and hold for 1 min. Finally, heat-treat the membrane in an 80 ℃ oven for 30 s to obtain the target membrane material.

[0056] The water flux of the loose nanofiltration membrane prepared in this embodiment is 160.3 L / m³. -2 h -1 bar -1The membrane exhibited rejection rates of 99.5%, 99.42%, 99.12%, and 98.91% for dyes VBB, CR, MB, and KN-R, respectively, while the rejection rates for inorganic salts MgSO4, MgCl2, Na2SO4, and NaCl were 3.8%, 3.6%, 3.0%, and 2.8%, respectively. The loose nanofiltration membrane achieved an inhibition rate of 98.85% against Staphylococcus aureus and 98.81% against Escherichia coli. Compared to Example 1, reducing the solid content in the base membrane facilitates the diffusion of monomers in the aqueous phase, thereby increasing the membrane's water flux.

[0057] Example 6 This invention provides a method for preparing an electrically neutral, in-situ antibacterial, loose nanofiltration membrane, comprising the following steps: S1. Steps for preparing the in-situ antibacterial loose nanofiltration membrane base: Dissolve 18g PES, 3g PVP, and 3g PEG-400 in DMAC and stir at 60℃ for 12h to obtain a homogeneous PES casting solution. Place the casting solution in a 60℃ vacuum drying oven and let it stand for 12h to remove air bubbles. Then, uniformly coat the casting solution onto a glass plate, let it stand in air for 30s, and then immerse it in deionized water to cure for 12h to obtain the PES base membrane. The membrane material is stored in deionized water.

[0058] S2. Preparation of the antibacterial aqueous monomer: 6.19 ml DETA, 3.30 g glutaric acid (GA) and 30 mL toluene were stirred and heated at 160℃ under a N2 atmosphere for 4 h. Then the temperature was raised 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.

[0059] S3. Steps for preparing in-situ antibacterial loose nanofiltration membrane: Remove moisture from the surface of the base membrane and air dry for 5 minutes. Fix the base membrane in a mold, pour in an aqueous solution containing 0.2 wt% BAIE to completely cover the membrane surface, and let it stand for 2 minutes. After removing excess aqueous solution, air dry for 5 minutes. Subsequently, pour a cyclohexane organic phase solution containing 0.1 wt% TBB under the membrane surface and hold for 1 minute. Finally, heat-treat the membrane in an 80 ℃ oven for 30 seconds to obtain the target membrane material.

[0060] The water flux of the nanofiltration membrane prepared in this embodiment is 210.4 L / m³. -2 h -1 bar -1The membrane exhibited rejection rates of 92.11%, 91.85%, 90.52%, and 90.22% for dyes VBB, CR, MB, and KN-R, respectively, while the rejection rates for inorganic salts MgSO4, MgCl2, Na2SO4, and NaCl were 2.2%, 1.8%, 1.5%, and 1.2%, respectively. The loose nanofiltration membrane achieved an inhibition rate of 99.1% against Staphylococcus aureus and 99.3% against Escherichia coli. Compared to Example 1, reducing the monomer content in the aqueous phase resulted in a more porous functional layer, thereby improving the membrane's water flux and antibacterial properties.

[0061] In summary, the present invention prepares a loose nanofiltration membrane base membrane via a blending method and synthesizes an antibacterial aqueous monomer using an amidation-cyclization reaction. This monomer is then combined with a halogenated aromatic hydrocarbon via interfacial polymerization to successfully construct a loose nanofiltration membrane with both electroneutrality and in-situ antibacterial properties on the base membrane surface. This membrane combines excellent salt / dye separation performance with antibacterial properties, making it suitable for applications such as dyeing and printing wastewater treatment.

[0062] Therefore, this invention provides a method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane. This method imparts durable antibacterial capabilities to the membrane by introducing an antibacterial structure into the separation layer; and through interfacial polymerization of low-activity halogenated aromatic hydrocarbon monomers, a stable and loose functional layer is formed, giving the membrane excellent salt / dye separation stability. The prepared membrane can be used as a high-performance filtration medium and is widely applied in the treatment of dyeing and printing wastewater in industries such as textiles and papermaking.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane, characterized in that, Includes the following steps: S1. Base film preparation: The base film is prepared by phase inversion method; specifically, the casting solution containing polymer membrane matrix material, membrane modifier and organic solvent is stirred and degassed under constant temperature conditions, then uniformly coated on a glass plate, and after being allowed to evaporate in the air, it is immersed in a coagulation bath to solidify and obtain the base film. S2. Preparation of antibacterial aqueous monomers: Aqueous monomers containing antibacterial imidazole structures are synthesized by stepwise temperature-controlled reaction using diethylenetriamine and polybasic acids as raw materials. S3. Selection of organic phase monomers: At least one of tribromotrimethylbenzene, mesbromotribromobenzene or mesbromotrichlorobenzene is selected as the organic phase monomer. S4. Preparation of an electrically neutral in-situ antibacterial loose nanofiltration membrane: An aqueous solution and an organic solution are sequentially coated onto a base membrane, and a functional layer is formed on the surface of the base membrane through an interfacial polymerization reaction. The aqueous solution contains a solvent and the aqueous monomer prepared in S2, and the organic solution contains a solvent and the organic monomer prepared in S3. After heat treatment, an electrically neutral in-situ antibacterial loose nanofiltration membrane with antibacterial function is obtained.

2. The method for preparing an electrically neutral in-situ antibacterial 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, polyvinyl chloride, polyamide, polypropylene, polyvinylidene fluoride, cellulose acetate, and polyethersulfone. Preferably, based on the total mass of the casting solution, the mass percentage of the polymeric membrane matrix material is 16% to 20%.

3. The method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane 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 an electrically neutral in-situ antibacterial loose nanofiltration membrane according to claim 1, characterized in that: In step S1, the organic solvent is dimethyl sulfoxide. N -Methylpyrrolidone, N, N -Dimethylacetamide, cyclohexane, N, N - One of dimethylformamide, chloroform, or acetone.

5. The method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane according to claim 6, characterized in that: In step S2, the polydicarboxylic acid is selected from at least one of malonic acid, glutaric acid, or succinic acid.

6. The method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane according to claim 1, characterized in that: In step S2, the amide reaction temperature is 120~160℃, the reaction time is 4~6h, and a water-carrying agent can be added during the reaction to promote the reaction. The water-carrying agent is selected from at least one of isoamyl acetate, xylene, chloroform, toluene, petroleum ether or cyclohexane.

7. The method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane according to claim 1, characterized in that: In step S2, the cyclization reaction temperature is 190~210℃ and the reaction time is 4~6h.

8. The method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane according to claim 1, characterized in that: In step S2, each repeating unit of the aqueous monomer containing the antibacterial structure contains an imidazole structure and a terminal amino group, and its structural formula is as follows: , Where n is an integer greater than or equal to 0.

9. The method for preparing an electrically neutral in-situ antibacterial loose nanofiltration membrane according to claim 1, characterized in that: In step S3, the organic phase monomer is selected from at least one of tribromotrimethylbenzene, mesbromotribromobenzene, mesbromotrichlorobenzene, and other halogenated aromatic hydrocarbons. In step S4, the mass ratio of the aqueous monomer to the solution is 1:10 to 1:100; the mass ratio of the organic monomer to the solution is 1:10 to 1:100.

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