Ultrafiltration membrane for sewage treatment and preparation method thereof

Abstract

The application discloses an ultrafiltration membrane for sewage treatment and a preparation method thereof, and relates to the field of membrane separation technology. The method comprises the following steps: firstly, ZnO@PHEMA-Ag nanoparticles are prepared, and the nanoparticles are pretreated, modified, grafted and loaded with silver nanoclusters; then, maleic anhydride grafted PVDF and modified MXene are prepared; then, a composite casting solution is prepared, and the solution is cast into a film and then immersed into a polyvinyl alcohol coagulation bath containing dimethylformamide to form a film; finally, the finished ultrafiltration membrane is obtained through ultraviolet crosslinking post-processing. The ultrafiltration membrane has excellent anti-pollution performance through functional nanoparticles, substrate modification and process optimization.

Description

An ultrafiltration membrane for wastewater treatment and its preparation method Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to an ultrafiltration membrane for wastewater treatment and its preparation method. Background Technology

[0002] Polyvinylidene fluoride (PVDF) ultrafiltration membranes, with their superior comprehensive performance, have become one of the core materials in water treatment and industrial separation. The high-energy CF bonds in their molecular structure endow the material with excellent high-temperature resistance and chemical corrosion resistance, allowing it to operate stably in acidic and alkaline environments with pH values ​​of 1-13 and in common oxidants and organic solvents, far exceeding conventional membrane materials such as polypropylene and polyethersulfone. Simultaneously, the membrane's tensile strength can reach 30-50 MPa, and it can withstand transmembrane pressure differences of 0.1-0.2 MPa. It is not easily deformed or broken under high flow rates and high pollution loads, exhibiting outstanding operational stability. Based on these advantages, PVDF ultrafiltration membranes are widely used in scenarios such as advanced municipal tap water treatment, industrial circulating water reuse, protein separation in food processing, and clarification of biopharmaceutical fermentation broths. With precise pore size control of 0.01-0.1 μm, they meet the dual requirements of water purification and substance separation.

[0003] However, the antifouling performance of ordinary PVDF ultrafiltration membranes is generally weak, a shortcoming that severely restricts their application range and service life. Membrane fouling is the core issue affecting its performance. With the deterioration of global water quality, pollutants such as organic matter (e.g., humic acid, proteins), colloidal particles, and microorganisms in the water accumulate on the membrane surface, forming a dense fouling layer or clogging the membrane pores, directly leading to a significant decrease in membrane flux. When treating slightly polluted surface water, the flux of ordinary PVDF ultrafiltration membranes may decrease by 30%-50% within 1-2 weeks of operation, while the retention performance deteriorates, and even pollutants may "penetrate," affecting the quality of the effluent. The root cause of this problem lies in the strong hydrophobicity of the PVDF material itself. Its surface contact angle is usually greater than 90°, exhibiting strong repulsion towards water molecules while having a high affinity for hydrophobic or amphiphilic pollutants in the water (e.g., organic matter, microorganisms). Based on the principle of "like dissolves like," these pollutants are easily and firmly adsorbed onto the membrane surface and are difficult to remove through physical methods such as backwashing. Compared with hydrophilic membrane materials such as cellulose acetate and hydrophilically modified polyethersulfone, ordinary PVDF membranes can adsorb 2-3 times more pollutants. More seriously, the types and concentrations of pollutants in current water sources are continuously increasing, easily forming a complex fouling layer of organic matter, colloids, and microorganisms, further exacerbating membrane fouling. This forces companies to frequently perform chemical cleaning, increasing operation and maintenance costs and shortening the membrane's lifespan. Summary of the Invention

[0004] The purpose of this invention is to provide an ultrafiltration membrane for wastewater treatment and its preparation method, thereby solving the technical problem of poor antifouling performance of polyvinylidene fluoride (PVDF) ultrafiltration membranes mentioned in the background art. The PVDF ultrafiltration membrane prepared by this invention has excellent antifouling performance.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing an ultrafiltration membrane for wastewater treatment includes the following steps:

[0007] S1. Zinc oxide nanoparticles were pretreated with sodium dodecylbenzenesulfonate, then modified with γ-aminopropyltriethoxysilane, grafted with poly(hydroxyethyl methacrylate), and finally loaded with silver nanoclusters to obtain ZnO@PHEMA-Ag nanoparticles.

[0008] S2. Preparation of maleic anhydride-grafted polyvinylidene fluoride and modified MXene;

[0009] S3. Maleic anhydride-grafted polyvinylidene fluoride, ZnO@PHEMA-Ag nanoparticles and modified MXene are dispersed in N,N-dimethylformamide solvent to prepare a composite casting solution.

[0010] S4. The composite casting solution is scraped into a film and immersed in a polyvinyl alcohol aqueous solution coagulation bath to form a wet film.

[0011] S5. The wet membrane is immersed in an ethanol-water mixed solvent of benzoin dimethyl ether and tripropylene glycol diacrylate, removed and subjected to ultraviolet crosslinking treatment, then washed and dried to obtain an ultrafiltration membrane.

[0012] In the technical solution of this invention, the antifouling performance of the ultrafiltration membrane is improved synergistically from the following two aspects:

[0013] On one hand, the zinc oxide nanoparticles were ultrasonically dispersed using sodium dodecylbenzenesulfonate (SDBS). The hydrophilic ends of SDBS bind to the positive charge on the zinc oxide surface through electrostatic interaction, while the hydrophobic ends form steric hindrance, preventing zinc oxide agglomeration (and thus preventing clogging of the membrane pores during subsequent film formation). Then, the surface was modified with γ-aminopropyltriethoxysilane (KH550). The ethoxy groups of KH550 hydrolyze to generate silanol groups, which condense with the hydroxyl groups on the zinc oxide surface to form chemical bonds. The grafted amino groups not only improve the compatibility of zinc oxide with organic materials but also provide active sites for subsequent grafting of poly(hydroxyethyl methacrylate) (PHEMA). Subsequently, methyl groups were added... Hydroxyethyl acrylate (HEMA) was copolymerized and grafted onto the zinc oxide surface using azobisisobutyronitrile (AIBN) as an initiator and triethylamine as a catalyst. This process anchored HEMA chains containing a large number of hydroxyl groups onto the surface of zinc oxide. The strong hydrophilicity of the hydroxyl groups reduced the interfacial tension between the membrane surface and organic pollutants such as proteins and oils, thus reducing the physical adsorption of pollutants. Finally, silver nitrate was reduced with ascorbic acid to load silver nanoclusters onto the zinc oxide@PHEMA surface. The silver nanoclusters and zinc oxide formed a synergistic antibacterial system (zinc oxide photocatalytically assisted in destroying bacterial cell membranes, while silver nanoclusters inhibited bacterial reproduction), effectively preventing biofilm formation and reducing biological pollution at the source.

[0014] On the other hand, maleic anhydride grafting is performed on polyvinylidene fluoride (PVDF) to introduce carboxyl groups into the PVDF backbone. This not only enhances the hydrophilicity of PVDF to reduce the adsorption of pollutants by the bulk, but also enhances the compatibility between the two by forming hydrogen bonds between the carboxyl groups and the hydroxyl groups of the nanoparticles, thus avoiding membrane defects caused by component separation. Furthermore, titanium carbide (Ti3AlC2) is modified to prepare monolayer / few-layer titanium carbide. Its two-dimensional sheet structure can regulate the formation of a gradient porous structure during film formation, slowing down the diffusion of pollutants into the depth of the membrane pores and avoiding membrane fouling caused by clogging of the ultrafiltration membrane.

[0015] Preferably, in step S1, the mass ratio of zinc oxide nanoparticles to sodium dodecylbenzenesulfonate is 4:0.2 to 0.5.

[0016] Preferably, in step S1, the mass ratio of the pretreated zinc oxide nanoparticles to γ-aminopropyltriethoxysilane is 10:0.3-0.8.

[0017] Preferably, in step S1, the mass ratio of zinc oxide nanoparticles modified with γ-aminopropyltriethoxysilane during the grafting of polyhydroxyethyl methacrylate to polyhydroxyethyl methacrylate is 4:10-14.

[0018] Preferably, in step S2, the method for preparing maleic anhydride-grafted polyvinylidene fluoride is as follows:

[0019] Polyvinylidene fluoride, maleic anhydride, and dicumyl peroxide were reacted in a twin-screw extruder, extruded, pelletized, and dried to obtain maleic anhydride-grafted polyvinylidene fluoride.

[0020] Preferably, in step S2, the modified MXene is prepared by:

[0021] Ti3AlC2 powder was reacted with hydrochloric acid, LiF and ascorbic acid, etched, centrifuged and washed to obtain multilayer MXene;

[0022] The above-mentioned multilayer MXene was ultrasonically exfoliated in N,N-dimethylformamide and polyethylene glycol, and then centrifuged and dried to obtain modified MXene.

[0023] Preferably, in step S3, the mass ratio of maleic anhydride-grafted polyvinylidene fluoride, ZnO@PHEMA-Ag nanoparticles, and modified MXene is 8:2 to 3:1 to 2.

[0024] Preferably, in step S4, the polyvinyl alcohol aqueous solution coagulation bath also contains N,N-dimethylformamide.

[0025] Preferably, the N,N-dimethylformamide has a mass concentration of 0.5 to 1.0 wt%.

[0026] In the technical solution of this invention, the R&D team discovered a technical problem of phase transformation kinetic imbalance during the ultrafiltration membrane preparation process through in-depth research: ZnO@PHEMA-Ag nanoparticles have strong hydrophilicity due to the large number of hydroxyl groups in the polymethyl methacrylate chains. This hydrophilicity changes the interfacial tension between the composite casting solution and the coagulation bath. Without the addition of ZnO@PHEMA-Ag nanoparticles, the interfacial tension between the casting solution and the coagulation bath is adapted to the phase transformation rate requirement, and the phase transformation process is stable. However, when ZnO@PHEMA-Ag nanoparticles are added, the interfacial tension is significantly reduced, accelerating the penetration of non-solvents into the casting solution. This leads to an excessively rapid phase transformation on the membrane surface, and the modified titanium carbide sheets are solidified before they can be stacked in an orderly manner. This compresses the macroporous layer that should have formed inside the membrane, ultimately forming an abnormal structure with an excessively thick dense surface layer and narrow internal pores, thereby affecting the flux and antifouling performance of the ultrafiltration membrane.

[0027] To address the aforementioned technical challenges, the research team added a specified amount of N,N-dimethylformamide (0.5–1.0 wt%) to the polyvinyl alcohol aqueous solution coagulation bath. Within this concentration range, N,N-dimethylformamide reduces the solvent concentration difference between the casting solution and the coagulation bath. Based on Fick's diffusion law, this slows down the permeation rate of non-solvents into the casting solution, thereby offsetting the phase transformation acceleration effect caused by the hydrophilicity of ZnO@PHEMA-Ag nanoparticles. This allows the interfacial tension between the coagulation bath and the casting solution to rise back to a range suitable for the orderly stacking of MXene sheets, thus preventing the ZnO@PHEMA-Ag nanoparticles from affecting the flux and antifouling performance of the ultrafiltration membrane.

[0028] An ultrafiltration membrane for wastewater treatment is prepared by the method described above.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. On the one hand, the functionalized ZnO@PHEMA-Ag nanoparticles, after multi-layer modification, reduce the interfacial tension between the membrane surface and organic pollutants by leveraging the hydroxyl groups of the PHEMA chain, thereby reducing physical adsorption. They also prevent biofilm formation through the synergistic antibacterial effect of ZnO and silver nanoclusters, thus inhibiting organic and biological pollution at the source. On the other hand, maleic anhydride grafted onto polyvinylidene fluoride enhances the hydrophilicity of the substrate to reduce bulk adsorption, while the modified MXene's two-dimensional sheet-like structure regulates the gradient porous structure, slowing the diffusion of pollutants into the depth of the membrane pores and preventing pore blockage. The dual mechanisms work together to enhance the antifouling effect.

[0031] 2. To address the imbalance in phase transformation kinetics caused by the hydrophilicity of ZnO@PHEMA-Ag nanoparticles, N,N-dimethylformamide can be added to the coagulation bath to adjust the solvent concentration difference between the casting solution and the coagulation bath, slowing down the non-solvent permeation rate. This allows the interfacial tension to adapt to the orderly stacking requirements of MXene sheets, avoiding the formation of abnormal structures with excessively thick surface layers and narrow internal pores, thus ensuring membrane flux and antifouling performance. Attached Figure Description

[0032] Figure 1 is a SEM image of the surface of the ultrafiltration membrane prepared in this invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for preparing an ultrafiltration membrane for wastewater treatment includes the following steps:

[0036] Step 1: Weigh 4g of zinc oxide nanoparticles (particle size 20nm), add 300mL of mixed solvent (225mL of ethanol and 75mL of deionized water), then add 0.4g of sodium dodecylbenzenesulfonate, disperse by ultrasonication at 300W for 40min at 35℃, heat to 76℃ and stir and reflux at 300r / min for 2.5h, centrifuge (10000r / min, 20min), wash twice with deionized water, and vacuum dry at 65℃ for 9h to obtain pretreated zinc oxide;

[0037] Take 4.0 g of pretreated zinc oxide, add 200 mL of mixed solvent (180 mL of ethanol and 20 mL of deionized water), adjust the pH to 4-5 with 0.1 mol / L hydrochloric acid, sonicate for 18 min, add 0.25 g of γ-aminopropyltriethoxysilane, purge with nitrogen to remove oxygen, stir and reflux at 250 r / min for 4 h in an oil bath at 78 °C, centrifuge (10000 r / min, 25 min), wash 4 times with anhydrous ethanol, and vacuum dry at 72 °C for 7 h to obtain γ-aminopropyltriethoxysilane modified zinc oxide;

[0038] Take 4.0 g of modified zinc oxide, add 150 mL of N,N-dimethylformamide, and sonicate for 22 min. Then add 13 g of hydroxyethyl methacrylate and 0.23 g of azobisisobutyronitrile. After purging with nitrogen for 30 min, stir the mixture in an oil bath at 80 °C at 250 r / min for 6 h. After centrifugation (12000 r / min, 30 min), wash twice with N,N-dimethylformamide and dry under vacuum at 60 °C for 5 h to obtain solid ZnO@PHEMA.

[0039] Take 3g ZnO@PHEMA and add 100mL N,N-dimethylformamide. Disperse by sonication for 30min. Add 0.2g polyvinylpyrrolidone and adjust the pH to 5.5 with 0.01mol / L acetic acid. Stir at 28℃ and add 20mL of 0.08mol / L silver nitrate solution dropwise. Continue stirring for 30min and then add 20mL of 0.04mol / L ascorbic acid solution dropwise. Stir in the dark for 1.5h. Centrifuge (10000r / min, 20min) and vacuum dry at 60℃ for 5h to obtain solid ZnO@PHEMA-Ag nanoparticles.

[0040] Step 2: Weigh 100g of polyvinylidene fluoride, 4g of maleic anhydride, and 0.2g of dicumyl peroxide, mix them, and add them to a twin-screw extruder. Set the temperature to 175℃ in zone 1, 180℃ in zone 2, and 185℃ in zone 3, and the screw speed to 50r / min. After extrusion, cut the extruder into pellets and vacuum dry them at 80℃ for 4h to obtain solid maleic anhydride-grafted polyvinylidene fluoride.

[0041] Weigh 10g Ti3AlC2 powder, add 200mL 6mol / L hydrochloric acid, 9g LiF and 0.05g ascorbic acid, stir at 25℃ for 30h, centrifuge (8000r / min, 15min), wash with deionized water containing 0.1% ascorbic acid until pH 6.5-7.0, and vacuum dry at 60℃ for 8h to obtain solid multilayer MXene; take 2.5g multilayer MXene, add 250mL N,N-dimethylformamide and 1g polyethylene glycol-6000, sonicate at 200W for 25min, centrifuge (1500r / min, 15min) and take the supernatant after exfoliation, vacuum dry at 60℃ for 6h to obtain solid modified MXene.

[0042] Step 3: Weigh 8g of solid maleic anhydride-grafted polyvinylidene fluoride, add 100mL of N,N-dimethylformamide, and stir at 300r / min at 70℃ until completely dissolved; add 2.8g of ZnO@PHEMA-Ag nanoparticles, stir at 250r / min at 52℃ for 3h, and then ultrasonically disperse for 20min; add 1.7g of modified MXene, continue stirring for 2.5h, ultrasonically degas at 80W for 15min, and let stand at 52℃ for 14h to obtain the composite casting solution.

[0043] The composite casting solution was poured onto a clean glass plate and a liquid film was formed by scraping with a film scraper at a speed of 2.5 cm / s (wet film thickness 110 μm). After standing at room temperature for 8 min, it was immersed in a 22℃ coagulation bath (containing an aqueous solution of 2 wt% polyvinyl alcohol and 0.9 wt% N,N-dimethylformamide) for 20 min, and the wet film was obtained by peeling.

[0044] Step 4: Immerse the wet membrane in an ethanol-water mixed solvent (volume ratio 1:1) containing 0.2% benzoin dimethyl ether and 1% tripropylene glycol diacrylate for 5 min. After draining, place it in a UV instrument and irradiate it at a wavelength of 254 nm and a power of 12 W for 20 min (turning it over every 10 min). Then immerse the membrane in deionized water at 6 °C for 8 h. After absorbing the surface moisture, dry it at 5 °C and 0.001 MPa vacuum for 10 h to obtain the ultrafiltration membrane.

[0045] Example 2

[0046] A method for preparing an ultrafiltration membrane for wastewater treatment includes the following steps:

[0047] Step 1: Weigh 4g of zinc oxide nanoparticles (particle size 20nm), add 300mL of mixed solvent (225mL of ethanol and 75mL of deionized water), then add 0.3g of sodium dodecylbenzenesulfonate, disperse by ultrasonication at 300W for 40min at 35℃, heat to 76℃ and stir and reflux at 300r / min for 2.5h, centrifuge (10000r / min, 20min), wash twice with deionized water, and vacuum dry at 65℃ for 9h to obtain pretreated zinc oxide;

[0048] Take 4.0 g of pretreated zinc oxide, add 200 mL of mixed solvent (180 mL of ethanol and 20 mL of deionized water), adjust the pH to 4-5 with 0.1 mol / L hydrochloric acid, sonicate for 18 min, add 0.18 g of γ-aminopropyltriethoxysilane, purge with nitrogen to remove oxygen, stir and reflux in an oil bath at 78 °C at 250 r / min for 4 h, centrifuge (10000 r / min, 25 min), wash 4 times with anhydrous ethanol, and vacuum dry at 72 °C for 7 h to obtain γ-aminopropyltriethoxysilane modified zinc oxide;

[0049] Take 4.0 g of modified zinc oxide, add 150 mL of N,N-dimethylformamide, and sonicate for 22 min. Then add 11 g of hydroxyethyl methacrylate and 0.23 g of azobisisobutyronitrile. After purging with nitrogen for 30 min, stir the mixture in an oil bath at 80 °C at 250 r / min for 6 h. After centrifugation (12000 r / min, 30 min), wash twice with N,N-dimethylformamide and dry under vacuum at 60 °C for 5 h to obtain solid ZnO@PHEMA.

[0050] Take 3g ZnO@PHEMA and add 100mL N,N-dimethylformamide. Disperse by sonication for 30min. Add 0.2g polyvinylpyrrolidone and adjust the pH to 5.5 with 0.01mol / L acetic acid. Stir at 28℃ and add 20mL of 0.08mol / L silver nitrate solution dropwise. Continue stirring for 30min and then add 20mL of 0.04mol / L ascorbic acid solution dropwise. Stir in the dark for 1.5h. Centrifuge (10000r / min, 20min) and vacuum dry at 60℃ for 5h to obtain solid ZnO@PHEMA-Ag nanoparticles.

[0051] Step 2: Weigh 100g of polyvinylidene fluoride, 4g of maleic anhydride, and 0.2g of dicumyl peroxide, mix them, and add them to a twin-screw extruder. Set the temperature to 175℃ in zone 1, 180℃ in zone 2, and 185℃ in zone 3, and the screw speed to 50r / min. After extrusion, cut the extruder into pellets and vacuum dry them at 80℃ for 4h to obtain solid maleic anhydride-grafted polyvinylidene fluoride.

[0052] Weigh 10g Ti3AlC2 powder, add 200mL 6mol / L hydrochloric acid, 9g LiF and 0.05g ascorbic acid, stir at 25℃ for 30h, centrifuge (8000r / min, 15min), wash with deionized water containing 0.1% ascorbic acid until pH 6.5-7.0, and vacuum dry at 60℃ for 8h to obtain solid multilayer MXene; take 2.5g multilayer MXene, add 250mL N,N-dimethylformamide and 1g polyethylene glycol-6000, sonicate at 200W for 25min, centrifuge (1500r / min, 15min) and take the supernatant after exfoliation, vacuum dry at 60℃ for 6h to obtain solid modified MXene.

[0053] Step 3: Weigh 8g of solid maleic anhydride-grafted polyvinylidene fluoride, add 100mL of N,N-dimethylformamide, and stir at 300r / min at 70℃ until completely dissolved; add 2.3g of ZnO@PHEMA-Ag nanoparticles, stir at 250r / min at 52℃ for 3h, and then ultrasonically disperse for 20min; add 1.2g of modified MXene, continue stirring for 2.5h, ultrasonically degas at 80W for 15min, and let stand at 52℃ for 14h to obtain the composite casting solution.

[0054] The composite casting solution was poured onto a clean glass plate and a film was formed by scraping with a film scraper at a speed of 2.5 cm / s (wet film thickness 110 μm). After standing at room temperature for 8 min, the film was immersed in a 22℃ coagulation bath (containing an aqueous solution of 2 wt% polyvinyl alcohol and 0.6 wt% N,N-dimethylformamide) for 20 min and then peeled off to obtain a wet film.

[0055] Step 4: Immerse the wet membrane in an ethanol-water mixed solvent (volume ratio 1:1) containing 0.2% benzoin dimethyl ether and 1% tripropylene glycol diacrylate for 5 min. After draining, place it in a UV instrument and irradiate it at a wavelength of 254 nm and a power of 12 W for 20 min (turning it over every 10 min). Then immerse the membrane in deionized water at 6 °C for 8 h. After absorbing the surface moisture, dry it at 5 °C and 0.001 MPa vacuum for 10 h to obtain the ultrafiltration membrane.

[0056] Example 3

[0057] A method for preparing an ultrafiltration membrane for wastewater treatment includes the following steps:

[0058] Step 1: Weigh 4g of zinc oxide nanoparticles (particle size 20nm), add 300mL of mixed solvent (225mL of ethanol and 75mL of deionized water), then add 0.35g of sodium dodecylbenzenesulfonate, disperse by ultrasonication at 300W for 40min at 35℃, heat to 76℃ and stir and reflux at 300r / min for 2.5h, centrifuge (10000r / min, 20min), wash twice with deionized water, and vacuum dry at 65℃ for 9h to obtain pretreated zinc oxide;

[0059] Take 4.0 g of pretreated zinc oxide, add 200 mL of mixed solvent (180 mL of ethanol and 20 mL of deionized water), adjust the pH to 4-5 with 0.1 mol / L hydrochloric acid, sonicate for 18 min, add 0.2 g of γ-aminopropyltriethoxysilane, purge with nitrogen to remove oxygen, stir and reflux at 250 r / min for 4 h in an oil bath at 78 °C, centrifuge (10000 r / min, 25 min), wash 4 times with anhydrous ethanol, and vacuum dry at 72 °C for 7 h to obtain γ-aminopropyltriethoxysilane modified zinc oxide;

[0060] Take 4.0 g of modified zinc oxide, add 150 mL of N,N-dimethylformamide, and sonicate for 22 min. Then add 12 g of hydroxyethyl methacrylate and 0.23 g of azobisisobutyronitrile. After purging with nitrogen for 30 min, stir the mixture in an oil bath at 80 °C at 250 r / min for 6 h. After centrifugation (12000 r / min, 30 min), wash twice with N,N-dimethylformamide and dry under vacuum at 60 °C for 5 h to obtain solid ZnO@PHEMA.

[0061] Take 3g ZnO@PHEMA and add 100mL N,N-dimethylformamide. Disperse by sonication for 30min. Add 0.2g polyvinylpyrrolidone and adjust the pH to 5.5 with 0.01mol / L acetic acid. Stir at 28℃ and add 20mL of 0.08mol / L silver nitrate solution dropwise. Continue stirring for 30min and then add 20mL of 0.04mol / L ascorbic acid solution dropwise. Stir in the dark for 1.5h. Centrifuge (10000r / min, 20min) and vacuum dry at 60℃ for 5h to obtain solid ZnO@PHEMA-Ag nanoparticles.

[0062] Step 2: Weigh 100g of polyvinylidene fluoride, 4g of maleic anhydride, and 0.2g of dicumyl peroxide, mix them, and add them to a twin-screw extruder. Set the temperature to 175℃ in zone 1, 180℃ in zone 2, and 185℃ in zone 3, and the screw speed to 50r / min. After extrusion, cut the extruder into pellets and vacuum dry them at 80℃ for 4h to obtain solid maleic anhydride-grafted polyvinylidene fluoride.

[0063] Weigh 10g Ti3AlC2 powder, add 200mL 6mol / L hydrochloric acid, 9g LiF and 0.05g ascorbic acid, stir at 25℃ for 30h, centrifuge (8000r / min, 15min), wash with deionized water containing 0.1% ascorbic acid until pH 6.5-7.0, and vacuum dry at 60℃ for 8h to obtain solid multilayer MXene; take 2.5g multilayer MXene, add 250mL N,N-dimethylformamide and 1g polyethylene glycol-6000, sonicate at 200W for 25min, centrifuge (1500r / min, 15min) and take the supernatant after exfoliation, vacuum dry at 60℃ for 6h to obtain solid modified MXene.

[0064] Step 3: Weigh 8g of solid maleic anhydride-grafted polyvinylidene fluoride, add 100mL of N,N-dimethylformamide, and stir at 300r / min at 70℃ until completely dissolved; add 2.5g of ZnO@PHEMA-Ag nanoparticles, stir at 250r / min at 52℃ for 3h, and then ultrasonically disperse for 20min; add 1.5g of modified MXene, continue stirring for 2.5h, ultrasonically degas at 80W for 15min, and let stand at 52℃ for 14h to obtain the composite casting solution.

[0065] The composite casting solution was poured onto a clean glass plate and a liquid film was formed by scraping with a film scraper at a speed of 2.5 cm / s (wet film thickness 110 μm). After standing at room temperature for 8 min, it was immersed in a 22℃ coagulation bath (containing an aqueous solution of 2 wt% polyvinyl alcohol and 0.7 wt% N,N-dimethylformamide) for 20 min, and the wet film was obtained by peeling.

[0066] Step 4: Immerse the wet membrane in an ethanol-water mixed solvent (volume ratio 1:1) containing 0.2% benzoin dimethyl ether and 1% tripropylene glycol diacrylate for 5 min. After draining, place it in a UV instrument and irradiate it at a wavelength of 254 nm and a power of 12 W for 20 min (turning it over every 10 min). Then immerse the membrane in deionized water at 6 °C for 8 h. After absorbing the surface moisture, dry it at 5 °C and 0.001 MPa vacuum for 10 h to obtain the ultrafiltration membrane.

[0067] Example 4

[0068] A method for preparing an ultrafiltration membrane for wastewater treatment includes the following steps:

[0069] Step 1: Weigh 4g of zinc oxide nanoparticles (particle size 20nm), add 300mL of mixed solvent (225mL of ethanol and 75mL of deionized water), then add 0.5g of sodium dodecylbenzenesulfonate, disperse by ultrasonication at 300W for 40min at 35℃, heat to 76℃ and stir and reflux at 300r / min for 2.5h, centrifuge (10000r / min, 20min), wash twice with deionized water, and vacuum dry at 65℃ for 9h to obtain pretreated zinc oxide;

[0070] Take 4.0 g of pretreated zinc oxide, add 200 mL of mixed solvent (180 mL of ethanol and 20 mL of deionized water), adjust the pH to 4-5 with 0.1 mol / L hydrochloric acid, sonicate for 18 min, add 0.32 g of γ-aminopropyltriethoxysilane, purge with nitrogen to remove oxygen, stir and reflux in an oil bath at 78 °C at 250 r / min for 4 h, centrifuge (10000 r / min, 25 min), wash 4 times with anhydrous ethanol, and vacuum dry at 72 °C for 7 h to obtain γ-aminopropyltriethoxysilane modified zinc oxide;

[0071] Take 4.0 g of modified zinc oxide, add 150 mL of N,N-dimethylformamide, and sonicate for 22 min. Then add 14 g of hydroxyethyl methacrylate and 0.23 g of azobisisobutyronitrile. After purging with nitrogen for 30 min, stir the mixture in an oil bath at 80 °C at 250 r / min for 6 h. After centrifugation (12000 r / min, 30 min), wash twice with N,N-dimethylformamide and dry under vacuum at 60 °C for 5 h to obtain solid ZnO@PHEMA.

[0072] Take 3g ZnO@PHEMA and add 100mL N,N-dimethylformamide. Disperse by sonication for 30min. Add 0.2g polyvinylpyrrolidone and adjust the pH to 5.5 with 0.01mol / L acetic acid. Stir at 28℃ and add 20mL of 0.08mol / L silver nitrate solution dropwise. Continue stirring for 30min and then add 20mL of 0.04mol / L ascorbic acid solution dropwise. Stir in the dark for 1.5h. Centrifuge (10000r / min, 20min) and vacuum dry at 60℃ for 5h to obtain solid ZnO@PHEMA-Ag nanoparticles.

[0073] Step 2: Weigh 100g of polyvinylidene fluoride, 4g of maleic anhydride, and 0.2g of dicumyl peroxide, mix them, and add them to a twin-screw extruder. Set the temperature to 175℃ in zone 1, 180℃ in zone 2, and 185℃ in zone 3, and the screw speed to 50r / min. After extrusion, cut the extruder into pellets and vacuum dry them at 80℃ for 4h to obtain solid maleic anhydride-grafted polyvinylidene fluoride.

[0074] Weigh 10g Ti3AlC2 powder, add 200mL 6mol / L hydrochloric acid, 9g LiF and 0.05g ascorbic acid, stir at 25℃ for 30h, centrifuge (8000r / min, 15min), wash with deionized water containing 0.1% ascorbic acid until pH 6.5-7.0, and vacuum dry at 60℃ for 8h to obtain solid multilayer MXene; take 2.5g multilayer MXene, add 250mL N,N-dimethylformamide and 1g polyethylene glycol-6000, sonicate at 200W for 25min, centrifuge (1500r / min, 15min) and take the supernatant after exfoliation, vacuum dry at 60℃ for 6h to obtain solid modified MXene.

[0075] Step 3: Weigh 8g of solid maleic anhydride-grafted polyvinylidene fluoride, add 100mL of N,N-dimethylformamide, and stir at 300r / min at 70℃ until completely dissolved; add 3g of ZnO@PHEMA-Ag nanoparticles, stir at 250r / min at 52℃ for 3h, and then ultrasonically disperse for 20min; add 2g of modified MXene, continue stirring for 2.5h, ultrasonically degas at 80W for 15min, and let stand at 52℃ for 14h to obtain the composite casting solution.

[0076] The composite casting solution was poured onto a clean glass plate and a liquid film was formed by scraping with a film scraper at a speed of 2.5 cm / s (wet film thickness 110 μm). After standing at room temperature for 8 min, it was immersed in a 22℃ coagulation bath (containing an aqueous solution of 2 wt% polyvinyl alcohol and 1.0 wt% N,N-dimethylformamide) for 20 min, and the wet film was obtained by peeling.

[0077] Step 4: Immerse the wet membrane in an ethanol-water mixed solvent (volume ratio 1:1) containing 0.2% benzoin dimethyl ether and 1% tripropylene glycol diacrylate for 5 min. After draining, place it in a UV instrument and irradiate it at a wavelength of 254 nm and a power of 12 W for 20 min (turning it over every 10 min). Then immerse the membrane in deionized water at 6 °C for 8 h. After absorbing the surface moisture, dry it at 5 °C and 0.001 MPa vacuum for 10 h to obtain the ultrafiltration membrane.

[0078] Example 5

[0079] A method for preparing an ultrafiltration membrane for wastewater treatment includes the following steps:

[0080] Step 1: Weigh 4g of zinc oxide nanoparticles (particle size 20nm), add 300mL of mixed solvent (225mL of ethanol and 75mL of deionized water), then add 0.2g of sodium dodecylbenzenesulfonate, disperse by ultrasonication at 300W for 40min at 35℃, heat to 76℃ and stir and reflux at 300r / min for 2.5h, centrifuge (10000r / min, 20min), wash twice with deionized water, and vacuum dry at 65℃ for 9h to obtain pretreated zinc oxide;

[0081] Take 4.0 g of pretreated zinc oxide, add 200 mL of mixed solvent (180 mL of ethanol and 20 mL of deionized water), adjust the pH to 4-5 with 0.1 mol / L hydrochloric acid, sonicate for 18 min, add 0.12 g of γ-aminopropyltriethoxysilane, purge with nitrogen to remove oxygen, stir and reflux in an oil bath at 78 °C at 250 r / min for 4 h, centrifuge (10000 r / min, 25 min), wash 4 times with anhydrous ethanol, and vacuum dry at 72 °C for 7 h to obtain γ-aminopropyltriethoxysilane modified zinc oxide;

[0082] Take 4.0 g of modified zinc oxide, add 150 mL of N,N-dimethylformamide, and sonicate for 22 min. Then add 10 g of hydroxyethyl methacrylate and 0.23 g of azobisisobutyronitrile. After purging with nitrogen for 30 min, stir the mixture in an oil bath at 80 °C at 250 r / min for 6 h. After centrifugation (12000 r / min, 30 min), wash twice with N,N-dimethylformamide and dry under vacuum at 60 °C for 5 h to obtain solid ZnO@PHEMA.

[0083] Take 3g ZnO@PHEMA and add 100mL N,N-dimethylformamide. Disperse by sonication for 30min. Add 0.2g polyvinylpyrrolidone and adjust the pH to 5.5 with 0.01mol / L acetic acid. Stir at 28℃ and add 20mL of 0.08mol / L silver nitrate solution dropwise. Continue stirring for 30min and then add 20mL of 0.04mol / L ascorbic acid solution dropwise. Stir in the dark for 1.5h. Centrifuge (10000r / min, 20min) and vacuum dry at 60℃ for 5h to obtain solid ZnO@PHEMA-Ag nanoparticles.

[0084] Step 2: Weigh 100g of polyvinylidene fluoride, 4g of maleic anhydride, and 0.2g of dicumyl peroxide, mix them, and add them to a twin-screw extruder. Set the temperature to 175℃ in zone 1, 180℃ in zone 2, and 185℃ in zone 3, and the screw speed to 50r / min. After extrusion, cut the extruder into pellets and vacuum dry them at 80℃ for 4h to obtain solid maleic anhydride-grafted polyvinylidene fluoride.

[0085] Weigh 10g Ti3AlC2 powder, add 200mL 6mol / L hydrochloric acid, 9g LiF and 0.05g ascorbic acid, stir at 25℃ for 30h, centrifuge (8000r / min, 15min), wash with deionized water containing 0.1% ascorbic acid until pH 6.5-7.0, and vacuum dry at 60℃ for 8h to obtain solid multilayer MXene; take 2.5g multilayer MXene, add 250mL N,N-dimethylformamide and 1g polyethylene glycol-6000, sonicate at 200W for 25min, centrifuge (1500r / min, 15min) and take the supernatant after exfoliation, vacuum dry at 60℃ for 6h to obtain solid modified MXene.

[0086] Step 3: Weigh 8g of solid maleic anhydride-grafted polyvinylidene fluoride, add 100mL of N,N-dimethylformamide, and stir at 300r / min at 70℃ until completely dissolved; add 2g of ZnO@PHEMA-Ag nanoparticles, stir at 250r / min at 52℃ for 3h, and then ultrasonically disperse for 20min; add 1g of modified MXene, continue stirring for 2.5h, ultrasonically degas at 80W for 15min, and let stand at 52℃ for 14h to obtain the composite casting solution.

[0087] The composite casting solution was poured onto a clean glass plate and a film was formed by scraping with a film scraper at a speed of 2.5 cm / s (wet film thickness 110 μm). After standing at room temperature for 8 min, the film was immersed in a 22℃ coagulation bath (containing an aqueous solution of 2 wt% polyvinyl alcohol and 0.5 wt% N,N-dimethylformamide) for 20 min and then peeled off to obtain a wet film.

[0088] Step 4: Immerse the wet membrane in an ethanol-water mixed solvent (volume ratio 1:1) containing 0.2% benzoin dimethyl ether and 1% tripropylene glycol diacrylate for 5 min. After draining, place it in a UV instrument and irradiate it at a wavelength of 254 nm and a power of 12 W for 20 min (turning it over every 10 min). Then immerse the membrane in deionized water at 6 °C for 8 h. After absorbing the surface moisture, dry it at 5 °C and 0.001 MPa vacuum for 10 h to obtain the ultrafiltration membrane.

[0089] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that step 1 is omitted in the ultrafiltration membrane preparation process, and the casting solution in step 3 does not contain ZnO@PHEMA-Ag nanoparticles.

[0090] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that in step 3 of the ultrafiltration membrane preparation process, maleic anhydride-grafted polyvinylidene fluoride is replaced with polyvinylidene fluoride.

[0091] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that in step 3 of the ultrafiltration membrane preparation process, the modified MXene is replaced with ordinary MXene.

[0092] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the coagulation bath in step 3 of the ultrafiltration membrane preparation process does not contain N,N-dimethylformamide.

[0093] Performance testing:

[0094] 1. Membrane flux and flux recovery rate test:

[0095] The ultrafiltration membranes prepared in each embodiment and comparative example were cut into membrane sheets with a diameter of 47 mm. Under the conditions of 0.1 MPa transmembrane pressure and 25°C, they were first pre-pressed with deionized water for 30 min, and the amount of water permeating the membrane within 30 min was recorded. The initial water flux was calculated according to the formula: membrane flux = permeate volume / (effective membrane area × time). Subsequently, the solution was switched to 1 g / L bovine serum albumin (BSA) solution (simulating organic pollutants), and filtration was carried out for 2 h at the same pressure and temperature. After that, the membrane sheets were backwashed with deionized water for 10 min (backwashing pressure 0.12 MPa), and the water flux was tested again. The flux recovery rate (reflecting antifouling ability) was calculated according to the formula: flux recovery rate = (flux after backwashing / initial water flux) × 100%. The test results are shown in Table 1.

[0096] 2. Retention Rate Test: A 1 g / L BSA solution was prepared and filtered through various membranes at a transmembrane pressure of 0.1 MPa and a temperature of 25°C. The unfiltered stock solution and the permeate were collected separately. The absorbance at 280 nm was measured using a UV-Vis spectrophotometer. The concentrations of the stock solution and the permeate were calculated using the BSA standard curve. The BSA retention rate was calculated using the formula: Retention Rate = [1 - (Permeate Concentration / Stock Solution Concentration)] × 100%. The test was performed in triplicate, and the average value was taken. The test results are shown in Table 1.

[0097] 3. Antibacterial performance test: The antibacterial performance of the membrane was tested using the inhibition zone method, with *Escherichia coli* (ATCC 25922) as the test strain. Each membrane was cut into a 10mm diameter circle, sterilized, and then placed in a bacterial solution (concentration 10). 6 The culture was carried out on LB agar plates containing CFU / mL at 37℃ for 24 hours. The diameter of the inhibition zone around the membrane was measured. An inhibition zone diameter ≥7mm was considered to have antibacterial activity. The test was performed in triplicate and the average value was taken. The test results are shown in Table 1.

[0098] Table 1:

[0099] Initial Water Flux (LMH) Flux Recovery Rate (%) BSA Retention Rate (%) E. coli Inhibition Zone Diameter (mm) Example 1 465 96.4 93.8 14.6 Example 2 453 95.7 94.9 13.7 Example 3 460 96.2 94.5 14.0 Example 4 469 96.8 93.2 15.2 Example 5 447 95.3 95.1 13.3 Comparative Example 1 319 75.2 92.70 Comparative Example 2 357 79.7 89.2 11.6 Comparative Example 3 386 81.3 86.4 9.7 Comparative Example 4 318 72.4 93.1 13.9 surface

[0100] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an ultrafiltration membrane for wastewater treatment, characterized in that, Includes the following steps: S1. Zinc oxide nanoparticles were pretreated with sodium dodecylbenzenesulfonate, then modified with γ-aminopropyltriethoxysilane, grafted with poly(hydroxyethyl methacrylate), and finally loaded with silver nanoclusters to obtain ZnO@PHEMA-Ag nanoparticles; S2. Maleic anhydride-grafted polyvinylidene fluoride and modified MXene were prepared; S3. Maleic anhydride-grafted polyvinylidene fluoride, ZnO@PHEMA-Ag nanoparticles and modified MXene were dispersed in N,N-dimethylformamide solvent to prepare a composite casting solution; S4. The composite casting solution was scraped into a membrane and immersed in a polyvinyl alcohol aqueous solution coagulation bath to form a wet membrane; S5. The wet membrane was immersed in an ethanol-water mixed solvent of benzoin dimethyl ether and tripropylene glycol diacrylate, removed and subjected to ultraviolet crosslinking treatment, then washed and dried to obtain an ultrafiltration membrane.

2. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S1, the mass ratio of zinc oxide nanoparticles to sodium dodecylbenzenesulfonate is 4:0.2-0.

5.

3. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S1, the mass ratio of the pretreated zinc oxide nanoparticles to γ-aminopropyltriethoxysilane is 10:0.3-0.

8.

4. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S1, the mass ratio of zinc oxide nanoparticles modified with γ-aminopropyltriethoxysilane to polymethyl methacrylate during the grafting of polyhydroxyethyl methacrylate is 4:10-14.

5. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S2, the preparation method of maleic anhydride-grafted polyvinylidene fluoride is as follows: polyvinylidene fluoride, maleic anhydride and dicumyl peroxide are reacted in a twin-screw extruder, extruded, pelletized and dried to obtain maleic anhydride-grafted polyvinylidene fluoride.

6. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S2, the modified MXene is prepared by reacting Ti3AlC2 powder with hydrochloric acid, LiF and ascorbic acid, etching, centrifuging and washing to obtain multilayer MXene; ultrasonically peeling the above multilayer MXene in N,N-dimethylformamide and polyethylene glycol, centrifuging and drying to obtain modified MXene.

7. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S3, the mass ratio of maleic anhydride-grafted polyvinylidene fluoride, ZnO@PHEMA-Ag nanoparticles, and modified MXene is 8:2-3:1-2.

8. The method for preparing an ultrafiltration membrane for wastewater treatment according to claim 1, characterized in that, In step S4, the polyvinyl alcohol aqueous solution coagulation bath also contains N,N-dimethylformamide.

9. A method for preparing an ultrafiltration membrane for wastewater treatment according to claim 8, characterized in that, The mass concentration of the N,N-dimethylformamide is 0.5 to 1.0 wt%.

10. An ultrafiltration membrane for wastewater treatment, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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