A PVDF / PFA composite filter material for wastewater treatment and its preparation method

Abstract

This invention discloses a PVDF / PFA composite filter material for wastewater treatment and its preparation method, relating to the field of water treatment technology. In preparing the filter material, the invention first reacts N-propenylimidazolium with 1-chloro-3-phenylpropane to obtain a vinylimidazolium salt; then, alkali-treated PVDF is grafted with the vinylimidazolium salt and reacted with 5-azauracil to obtain modified PVDF; secondly, resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde are reacted to obtain porous microspheres, which are then sulfonated with chlorosulfonic acid to obtain modified microspheres; finally, PVDF, PFA, polyethylene oxide, and modified microspheres are mixed and melt-spun to prepare a fiber membrane; then, iron(III) oxide is generated in situ and activated with hypochlorous acid to obtain the PVDF / PFA composite filter material for wastewater treatment. The filter material prepared by this invention exhibits excellent antibacterial, hydrophilic, and photocatalytic degradation properties.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a PVDF / PFA composite filter material for wastewater treatment and its preparation method. Background Technology

[0002] Polyvinylidene fluoride (PVDF) possesses excellent chemical stability, resisting the erosion of strong acids, strong alkalis, and various organic solvents, making it one of the best-performing membrane materials worldwide and promising for wide application in wastewater treatment and other fields. However, PVDF materials have low surface energy and strong hydrophobicity, which can lead to two problems in water treatment separation processes: firstly, the separation process requires a large driving force, resulting in low flux; secondly, in the separation of oil / water systems, organic pollutants (such as proteins) are easily adsorbed on the membrane surface or inside the membrane pores, causing membrane fouling, which leads to decreased membrane separation performance, reduced water flux, and shortened membrane lifespan.

[0003] PFA is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether. It has excellent chemical corrosion resistance and can withstand almost all chemical media, except for molten alkali metals, fluorine carriers, and fluorine gas at high temperatures. Its chemical stability and temperature resistance are second only to PTFE (polytetrafluoroethylene), and it can be used for a long time over a wide temperature range. PFA also has good mechanical properties, dimensional stability, electrical insulation, and creep resistance. Its mechanical properties are superior to PTFE, and it has non-adhesive and self-lubricating properties over a wide temperature range. By combining PVDF and PFA, the advantages of both can be fully utilized to achieve complementary performance. At the same time, the hydrophilicity, antifouling, and photocatalytic degradation performance of the composite material can be further improved, which can better meet the high-performance requirements of filter materials in wastewater treatment, improve wastewater treatment efficiency, and reduce operating costs. Summary of the Invention

[0004] The purpose of this invention is to provide a PVDF / PFA composite filter material for wastewater treatment and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for preparing a PVDF / PFA composite filter material for wastewater treatment includes the following preparation steps:

[0007] (1) N-propenylimidazolium and 1-chloro-3-phenylpropane were reacted to obtain vinylimidazolium salt; PVDF was treated with alkali and reacted with vinylimidazolium salt to obtain pre-modified PVDF; pre-modified PVDF was reacted with 5-azauracil and aluminum chloride to obtain modified PVDF;

[0008] (2) Resorcinol, 3,5-dihydroxybenzoic acid and formaldehyde were reacted to obtain porous microspheres; the porous microspheres were sulfonated to obtain modified microspheres;

[0009] (3) Modified PVDF, PFA, modified microspheres and PEO are mixed and melt-spun into a film. After soaking in pure water, a fiber membrane is obtained. The modified fiber membrane is obtained by reacting ferric chloride hexahydrate and ferrous sulfate heptahydrate with the fiber membrane.

[0010] (4) The modified fiber membrane was activated by immersing it in sodium hypochlorite solution to obtain PVDF / PFA composite filter material for wastewater treatment.

[0011] As an optimization, the preparation method of the vinylimidazolium salt in step (1) is as follows: N-propenylimidazolium and 1-chloro-3-phenylpropane are mixed and dissolved in acetonitrile. Under argon protection, the mixture is refluxed at 80-85℃ for 20-24h to obtain vinylimidazolium salt; the molar ratio of N-propenylimidazolium to 1-chloro-3-phenylpropane is 1:(1.05-1.15); the mass of the acetonitrile is 5-6 times the mass of N-propenylimidazolium.

[0012] As an optimization, the modified PVDF in step (1) is prepared by dissolving potassium hydroxide in pure water, heating to 60-70°C, adding PVDF and ethanol and mixing for 20-30 min to obtain alkali-treated PVDF; dissolving alkali-treated PVDF, vinylimidazolium salt and initiator in N,N-dimethylformamide, and reacting at 60-70°C for 8-10 h under nitrogen protection to obtain pre-modified PVDF; mixing pre-modified PVDF, 5-azauracil, aluminum chloride and N-methylpyrrolidone, and reacting at 90-100°C for 4-5 h under nitrogen protection to obtain modified PVDF; wherein the PVDF is polyvinylidene fluoride.

[0013] As an optimization, the mass ratio of PVDF, potassium hydroxide, pure water, and ethanol is 1:(4.5-5.5):(25-30):(1.5-2.0); the mass ratio of alkali-treated PVDF, vinylimidazole salt, initiator, and N,N-dimethylformamide is 1:(1-1.5):(0.003-0.005):(20-30); and the mass ratio of pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone is 1:(1.5-2.0):(8-10):(20-30).

[0014] As an optimization, the modified microspheres in step (2) are prepared by mixing resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia, pure water, pore-forming agent and dispersant, and heating at 200-250°C for 20-24 hours to obtain porous microspheres; under nitrogen protection and ice-water bath conditions, the porous microspheres, dichloromethane and chlorosulfonic acid are mixed for 10-12 hours, and quenched by adding 50wt% ethanol aqueous solution to obtain modified microspheres.

[0015] As an optimization, the molar ratio of resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde is 1:(0.5-0.7):(1.5-3.0); the mass ratio of resorcinol, pore-forming agent, pure water, and dispersant is 1:(1-1.5):(10-12):(0.3-0.5); the mass of ammonia is 4%-6% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid; the specification of ammonia is 28wt%, and the specification of formaldehyde is 40wt%; the mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid, and 50wt% ethanol aqueous solution is 1:(10-12):(8-10):(300-400).

[0016] As an optimization, the modified fiber membrane in step (3) is prepared by mixing modified PVDF, PFA, modified microspheres and PEO in a high-speed pulverizer, melting and plasticizing and granulating them in a twin-screw extruder, then melting and spinning them into a film, soaking them in pure water for 24 hours to obtain a fiber membrane, dissolving ferric chloride hexahydrate and ferrous sulfate heptahydrate in pure water under nitrogen protection, adding the fiber membrane, heating to 60-70℃, adjusting the pH to 9-10 with ammonia water, and continuing the reaction for 3-4 hours to obtain the modified fiber membrane.

[0017] As an optimization, the modified PVDF, PFA, modified microspheres, and PEO have a mass ratio of 1:(0.3-0.5):(0.1-0.2):(0.5-0.7); the melt spinning process is as follows: spinning temperature is 200-210℃, post-drawing temperature is 90℃, draw ratio is 100%, and nitrogen gas is introduced during spinning at a pressure of 0.1 MPa; the Fe in the ferric chloride hexahydrate and ferrous sulfate heptahydrate is... 3+ and Fe 2+ The molar ratio is 2:1; the mass ratio of fiber membrane, ferric chloride hexahydrate, and pure water is 1:(2-3):(20-30); the PFA is tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer; and the PEO is polyethylene oxide.

[0018] As an optimization, the feature is that the immersion time in step (4) is 1-2 hours, the mass fraction of the sodium hypochlorite solution is 0.5%-1.0%, and the solid-liquid ratio of the modified fiber membrane and the sodium hypochlorite solution is 1 g:(20-30) L.

[0019] The present invention also provides a PVDF / PFA composite filter material for wastewater treatment prepared according to the above-described method for preparing PVDF / PFA composite filter material for wastewater treatment.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0021] In preparing the PVDF / PFA composite filter material for wastewater treatment, the present invention firstly reacts N-propenylimidazolium and 1-chloro-3-phenylpropane to obtain vinylimidazolium salt, then grafts the vinylimidazolium salt onto alkali-treated polyvinylidene fluoride, and then reacts it with 5-azauracil to obtain modified polyvinylidene fluoride; secondly, resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde are reacted to obtain porous microspheres, which are then sulfonated with chlorosulfonic acid to obtain modified microspheres; finally, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, polyethylene oxide, and modified microspheres are mixed and melt-spun to prepare a fiber membrane; then, iron(III) oxide is generated in situ and activated with hypochlorous acid to obtain the PVDF / PFA composite filter material for wastewater treatment.

[0022] First, vinylimidazolium salt is prepared by reacting N-propenylimidazolium with 1-chloro-3-phenylpropane. Polyvinylidene fluoride (PVDF) is then treated with alkali to induce defluorination, introducing carbon-carbon unsaturated bonds on the membrane surface. Vinylimidazolium salt can be grafted onto the membrane under the action of an initiator. The vinylimidazolium salt can improve the hydrophilicity of PVDF and adsorb negatively charged impurities in wastewater through electrostatic adsorption. At the same time, a benzene ring is introduced. The benzene ring undergoes an arylation reaction with 5-azauracil under the catalysis of aluminum chloride to generate a haloamine precursor. Under the activation of hypochlorous acid, the material is endowed with good antibacterial properties.

[0023] The arylation reaction is shown in the following equation:

[0024] ;

[0025] Secondly, phenolic microspheres are obtained by reacting resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde. Adding a pore-forming agent during the synthesis of the microspheres can generate porous microspheres with a larger specific surface area. These microspheres are then sulfonated with chlorosulfonic acid to obtain modified microspheres. The carboxyl and sulfonic acid groups on the modified microspheres can further enhance the hydrophilicity of the material. They can also adsorb positively charged heavy metal ions from wastewater through electrostatic interactions. Furthermore, during the mixing process with the modified microspheres, electrostatic interactions promote the uniform dispersion of the modified microspheres in the matrix. In addition, during the generation of iron(III) oxide, the carboxyl and sulfonic acid groups on the modified microspheres form chemical bonds with iron(III) oxide through coordination, enabling the particles to be firmly anchored to the material surface. Iron(III) oxide and the modified microspheres together constitute a self-Fenton catalytic system. Resorcinol and formaldehyde form an electron donor-acceptor pair structure under hydrothermal conditions. This structure generates a large number of delocalized electrons through π-π conjugation and stacking. In an aqueous system, these delocalized electrons can reduce oxygen, generating hydrogen peroxide through a two-step single-electron reduction reaction. The hydrogen peroxide is activated by Fe²⁺, producing hydroxyl radicals with strong oxidizing properties. These hydroxyl radicals can oxidize and degrade pollutants such as Rhodamine B, breaking them down into smaller organic molecules or completely mineralizing them into titanium dioxide and water. Simultaneously, Fe²⁺ is oxidized to Fe³⁺ in the reaction, and Fe³⁺ can be promptly reduced back to Fe²⁺ with the help of electrons carried by the microspheres, thereby promoting the cyclical progress of the Fenton reaction. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0027] In the following examples and comparative examples, the PVDF is polyvinylidene fluoride, model Solef 6010, purchased from DuPont; the PEO is polyethylene oxide, model P823143, purchased from Maclean Biochemical Co., Ltd.; the PFA is tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, model AP-202, purchased from Dakin; and the polyvinyl alcohol is PVA1788, purchased from Shandong Maofa Chemical Co., Ltd.

[0028] Example 1:

[0029] A method for preparing a PVDF / PFA composite filter material for wastewater treatment, the method comprising the following steps:

[0030] (1) N-propenylimidazole and 1-chloro-3-phenylpropane were mixed in a molar ratio of 1:1.05 and dissolved in acetonitrile in 6 times the mass of N-propenylimidazole. The mixture was refluxed at 85°C for 24 h under argon protection. After the reaction was completed, the acetonitrile was removed and the product was dried under vacuum at room temperature to obtain vinylimidazole salt. The washing temperature of the acetonitrile was 5°C. Potassium hydroxide was dissolved in pure water and heated to 70°C. PVDF and ethanol were added and mixed for 30 min. The mixture was filtered, washed, and dried to obtain alkali-treated PVDF. The mass ratio of PVDF, potassium hydroxide, pure water, and ethanol was 1:4.5:25:1.5. The alkali-treated PVDF was then... Vinyl imidazole salt and initiator benzoyl peroxide were dissolved in N,N-dimethylformamide. Under nitrogen protection, the mixture was heated to 70℃ and reacted for 10 h. After precipitation with methanol, filtration, washing, and drying, pre-modified PVDF was obtained. The mass ratio of alkali-treated PVDF, vinyl imidazole salt, initiator, and N,N-dimethylformamide was 1:1:0.003:20. The pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone were mixed at a mass ratio of 1:1.5:8:20 and reacted at 100℃ for 5 h under nitrogen protection. After precipitation with methanol, filtration, washing, and drying, modified PVDF was obtained.

[0031] (2) Resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia, and pure water were mixed, and toluene, a porogen, and polyvinyl alcohol, a dispersant, were added and mixed again. The mixture was heated at 250°C for 24 hours to obtain porous microspheres. The molar ratio of resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde was 1:0.5:1.5. The mass ratio of resorcinol, porogen, pure water, and dispersant was 1:1:10:0.3. The mass of ammonia was 4% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid. The ammonia was 28 wt% and the formaldehyde was 40 wt%. Under nitrogen protection and ice-water bath conditions, porous microspheres, dichloromethane, and chlorosulfonic acid were mixed for 12 hours. The mixture was quenched by adding 50 wt% ethanol aqueous solution and then filtered and washed to obtain modified microspheres. The mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid, and 50 wt% ethanol aqueous solution was 1:10:8:300.

[0032] (3) Modified PVDF, PFA, modified microspheres, and PEO were mixed in a high-speed pulverizer at a mass ratio of 1:0.3:0.1:0.5, then melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a film. After soaking in pure water for 24 hours, a fiber membrane was obtained. During the melt spinning process, the spinning temperature was 210℃, the post-stretching temperature was 90℃, and the stretching ratio was 100%. Nitrogen gas was introduced during the spinning process at a pressure of 0.1MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 70℃, and the pH was adjusted to 10 using ammonia water. The reaction was continued for 4 hours. After filtration, ultrasonic washing, and drying, the modified fiber membrane was obtained. The Fe content in ferric chloride hexahydrate and ferrous sulfate heptahydrate was...3+ and Fe 2+ The molar ratio is 2:1; the mass ratio of fiber membrane, ferric chloride hexahydrate, and pure water is 1:2:20.

[0033] (4) The modified fiber membrane was immersed in sodium hypochlorite solution for 2 hours, and after filtration, washing and drying, PVDF / PFA composite filter material for sewage treatment was obtained. The mass fraction of sodium hypochlorite solution was 1.0%; the solid-liquid ratio of modified fiber membrane and sodium hypochlorite solution was 1g:20L.

[0034] Example 2:

[0035] A method for preparing a PVDF / PFA composite filter material for wastewater treatment, the method comprising the following steps:

[0036] (1) N-propenylimidazole and 1-chloro-3-phenylpropane were mixed in a molar ratio of 1:1.07 and dissolved in acetonitrile in 5.5 times the mass of N-propenylimidazole. The mixture was refluxed at 82°C for 22 h under argon protection. After the reaction was completed, the acetonitrile was removed and the product was dried under vacuum at room temperature to obtain vinylimidazole salt. The washing temperature of the acetonitrile was 4°C. Potassium hydroxide was dissolved in pure water and heated to 65°C. PVDF and ethanol were added and mixed for 25 min. The mixture was filtered, washed, and dried to obtain alkali-treated PVDF. The mass ratio of PVDF, potassium hydroxide, pure water, and ethanol was 1:5.0:27:1.7. The alkali-treated PVDF was then... Vinyl imidazole salt and initiator benzoyl peroxide were dissolved in N,N-dimethylformamide. Under nitrogen protection, the mixture was heated to 65℃ and reacted for 9 hours. After precipitation with methanol, filtration, washing, and drying, pre-modified PVDF was obtained. Alkali-treated PVDF, vinyl imidazole salt, initiator, and N,N-dimethylformamide were mixed in a mass ratio of 1:1.3:0.003:25. Pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone were mixed in a mass ratio of 1:1.7:9:25 and reacted at 95℃ for 4.5 hours under nitrogen protection. After precipitation with methanol, filtration, washing, and drying, modified PVDF was obtained.

[0037] (2) Resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia, and pure water were mixed, and toluene, a porogen, and polyvinyl alcohol, a dispersant, were added and mixed again. The mixture was heated at 230°C for 22 hours to obtain porous microspheres. The molar ratio of resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde was 1:0.6:2.5. The mass ratio of resorcinol, porogen, pure water, and dispersant was 1:1.3:11:0.4. The mass of ammonia was 5% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid. The ammonia was 28 wt% and the formaldehyde was 40 wt%. Under nitrogen protection and ice-water bath conditions, porous microspheres, dichloromethane, and chlorosulfonic acid were mixed for 11 hours. A 50 wt% ethanol aqueous solution was added to quench the mixture. The mixture was then filtered and washed to obtain modified microspheres. The mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid, and 50 wt% ethanol aqueous solution was 1:11:9:350.

[0038] (3) Modified PVDF, PFA, modified microspheres, and PEO were mixed in a high-speed pulverizer at a mass ratio of 1:0.4:0.15:0.6, then melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a film. After soaking in pure water for 24 hours, a fiber membrane was obtained. During the melt spinning process, the spinning temperature was 205℃, the post-stretching temperature was 90℃, and the stretching ratio was 100%. Nitrogen gas was introduced during the spinning process at a pressure of 0.1MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 65℃, and the pH was adjusted to 9 using ammonia water. The reaction continued for 3.5 hours. After filtration, ultrasonic washing, and drying, the modified fiber membrane was obtained. The Fe content in ferric chloride hexahydrate and ferrous sulfate heptahydrate was... 3+ and Fe 2+ The molar ratio of the components is 2:1; the mass ratio of the fiber membrane, ferric chloride hexahydrate, and pure water is 1:2.5:25.

[0039] (4) The modified fiber membrane was immersed in sodium hypochlorite solution for 1.5 h, and after filtration, washing and drying, PVDF / PFA composite filter material for sewage treatment was obtained. The mass fraction of sodium hypochlorite solution was 0.7%; the solid-liquid ratio of modified fiber membrane to sodium hypochlorite solution was 1 g: 25 L.

[0040] Example 3:

[0041] A method for preparing a PVDF / PFA composite filter material for wastewater treatment, the method comprising the following preparation steps:

[0042] (1) N-propenylimidazole and 1-chloro-3-phenylpropane were mixed in a molar ratio of 1:1.15 and dissolved in acetonitrile in 6 times the mass of N-propenylimidazole. The mixture was refluxed at 80°C for 20 h under argon protection. After the reaction was completed, the acetonitrile was removed and the product was dried under vacuum at room temperature to obtain vinylimidazole salt. The acetonitrile used for washing was at 0°C. Potassium hydroxide was dissolved in pure water and heated to 60°C. PVDF and ethanol were added and mixed for 20 min. The mixture was filtered, washed, and dried to obtain alkali-treated PVDF. The mass ratio of PVDF, potassium hydroxide, pure water, and ethanol was 1:5.5:30:2.0. The alkali-treated PVDF was then... Vinyl imidazole salt and initiator benzoyl peroxide were dissolved in N,N-dimethylformamide. Under nitrogen protection, the mixture was heated to 60℃ and reacted for 8 hours. After precipitation with methanol, filtration, washing, and drying, pre-modified PVDF was obtained. Alkali-treated PVDF, vinyl imidazole salt, initiator, and N,N-dimethylformamide were mixed in a mass ratio of 1:1.5:0.005:30. Pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone were mixed in a mass ratio of 1:2.0:10:30 and reacted at 90℃ for 4 hours under nitrogen protection. After precipitation with methanol, filtration, washing, and drying, modified PVDF was obtained.

[0043] (2) Resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia, and pure water were mixed, and toluene, a porogen, and polyvinyl alcohol, a dispersant, were added and mixed again. The mixture was heated at 200°C for 20 hours to obtain porous microspheres. The molar ratio of resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde was 1:0.7:3.0. The mass ratio of resorcinol, porogen, pure water, and dispersant was 1:1.5:12:0.5. The mass of ammonia was 6% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid. The ammonia was 28 wt% and the formaldehyde was 40 wt%. Under nitrogen protection and ice-water bath conditions, porous microspheres, dichloromethane, and chlorosulfonic acid were mixed for 10 hours. The mixture was quenched by adding 50 wt% ethanol aqueous solution and then filtered and washed to obtain modified microspheres. The mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid, and 50 wt% ethanol aqueous solution was 1:12:10:400.

[0044] (3) Modified PVDF, PFA, modified microspheres, and PEO were mixed in a high-speed pulverizer at a mass ratio of 1:0.5:0.2:0.7, melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a film. After soaking in pure water for 24 hours, a fiber membrane was obtained. During the melt spinning process, the spinning temperature was 200℃, the post-stretching temperature was 90℃, and the stretching ratio was 100%. Nitrogen gas was introduced during the spinning process at a pressure of 0.1MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 60℃, and the pH was adjusted to 9 using ammonia water. The reaction was continued for 3 hours. After filtration, ultrasonic washing, and drying, the modified fiber membrane was obtained. The Fe content in ferric chloride hexahydrate and ferrous sulfate heptahydrate was...3+ and Fe 2+ The molar ratio is 2:1; the mass ratio of fiber membrane, ferric chloride hexahydrate, and pure water is 1:3:30.

[0045] (4) The modified fiber membrane was immersed in sodium hypochlorite solution for 1 hour, and after filtration, washing and drying, PVDF / PFA composite filter material for sewage treatment was obtained. The mass fraction of sodium hypochlorite solution was 0.5%; the solid-liquid ratio of modified fiber membrane to sodium hypochlorite solution was 1g:30L.

[0046] Comparative Example 1:

[0047] The difference between the preparation method of the PVDF / PFA composite filter material for wastewater treatment in Comparative Example 1 and Example 2 is that PVDF is not modified and modified microspheres are not added; specifically, steps (1) to (2) and (4) are not included, and step (3) is modified as follows: PVDF, PFA and PEO are mixed in a high-speed pulverizer at a mass ratio of 1:0.4:0.6, melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a film. After soaking in pure water for 24 hours, the PVDF / PFA composite filter material for wastewater treatment is obtained. During the melt spinning process, the spinning temperature is 205℃, the post-stretching temperature is 90℃, the stretching ratio is 100%, and nitrogen gas is introduced during the spinning process at a pressure of 0.1MPa.

[0048] Comparative Example 2:

[0049] The difference between the preparation method of the PVDF / PFA composite filter material for wastewater treatment in Comparative Example 2 and Example 2 is that modified microspheres are not added, specifically step (2) is omitted; step (3) is modified as follows: modified PVDF, PFA, and PEO are mixed in a high-speed pulverizer at a mass ratio of 1:0.4:0.6, melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a film. After soaking in pure water for 24 hours, the PVDF / PFA composite filter material for wastewater treatment is obtained. During the melt spinning process, the spinning temperature is 205℃, the post-stretching temperature is 90℃, the stretching ratio is 100%, and nitrogen gas is introduced during the spinning process at a pressure of 0.1 MPa. The remaining steps are the same as in Example 2.

[0050] Comparative Example 3:

[0051] The difference between the preparation method of the PVDF / PFA composite filter material for wastewater treatment in Comparative Example 3 and Example 2 is that the PVDF is not modified, specifically steps (1) and (4) are omitted; step (3) is modified as follows: PVDF, PFA, modified microspheres, and PEO are mixed in a high-speed pulverizer at a mass ratio of 1:0.4:0.15:0.6, melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a film. After soaking in pure water for 24 hours, a fiber film is obtained. During the melt spinning process, The spinning temperature was 205℃, the post-stretching temperature was 90℃, and the stretching ratio was 100%. Nitrogen gas was introduced during the spinning process at a pressure of 0.1 MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, and a fiber membrane was added. The temperature was raised to 65℃, and the pH was adjusted to 9 using ammonia. The reaction continued for 3.5 hours. After filtration, ultrasonic washing, and drying, a PVDF / PFA composite filter material for wastewater treatment was obtained. The Fe content in ferric chloride hexahydrate and ferrous sulfate heptahydrate was... 3+ and Fe 2+ The molar ratio of the components is 2:1; the mass ratio of the fiber membrane, ferric chloride hexahydrate, and pure water is 1:2.5:25. The remaining steps are the same as in Example 2.

[0052] Test Example 1:

[0053] Antibacterial performance testing:

[0054] Test method: Under light-protected conditions, the antibacterial rate of the filter materials prepared in the examples and comparative examples was tested according to standard GB / T 37206-2018. The test strain was Escherichia coli. The results are shown in Table 1.

[0055] Table 1

[0056] Antibacterial rate (%) Antibacterial rate (%) Example 1 98.74 Comparative Example 1 11.34 Example 2 98.37 Comparative Example 2 96.41 Example 3 98.41 Comparative Example 3 37.41

[0057] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 1 reveals that the PVDF / PFA composite filter material for wastewater treatment prepared in this invention exhibits excellent antibacterial properties.

[0058] The antibacterial properties of Examples 1-3 are superior to those of Comparative Examples 1 and 3. This indicates that, firstly, vinylimidazolium salt is prepared by reacting N-propenylimidazolium with 1-chloro-3-phenylpropane. Polyvinylidene fluoride is then treated with alkali to induce defluorination of the polyvinylidene fluoride, introducing carbon-carbon unsaturated bonds on the membrane surface. Under the action of an initiator, vinylimidazolium salt can be grafted onto the membrane, and a benzene ring is introduced. The benzene ring undergoes an arylation reaction with 5-azauracil under the catalysis of aluminum chloride to generate a haloamine precursor. Activation with hypochlorous acid imparts good antibacterial properties to the material.

[0059] Test Example 2:

[0060] Hydrophilicity testing:

[0061] Test method: The static water contact angle of the membranes prepared in the examples and comparative examples was tested using an optical contact angle meter (DSA100, KRUSS GmbH, Germany). During titration, the volume of the water droplet was fixed at 0.5 μL. The results are shown in Table 2.

[0062] Table 2

[0063] Water contact angle (°) Water contact angle (°) Example 1 29.4 Comparative Example 1 92.7 Example 2 27.3 Comparative Example 2 40.2 Example 3 26.2 Comparative Example 3 67.1

[0064] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 2 reveals that the PVDF / PFA composite filter material for wastewater treatment prepared in this invention has excellent hydrophilic properties.

[0065] The hydrophilicity of Examples 1-3 is better than that of Comparative Examples 1-3, indicating that firstly, vinylimidazolium salt is prepared by reacting N-propenylimidazolium and 1-chloro-3-phenylpropane, and then polyvinylidene fluoride is treated with alkali to induce defluorination of polyvinylidene fluoride, which introduces carbon-carbon unsaturated bonds on the membrane surface. With the help of an initiator, vinylimidazolium salt can be grafted onto the membrane, and the vinylimidazolium salt can improve the hydrophilicity of polyvinylidene fluoride.

[0066] Secondly, phenolic microspheres are obtained by reacting resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde. During the synthesis of the microspheres, toluene is used as a porogen to generate porous microspheres with a larger specific surface area. The microspheres are then sulfonated with chlorosulfonic acid to obtain modified microspheres. The carboxyl and sulfonic acid groups on the modified microspheres can further enhance the hydrophilicity of the material.

[0067] Example 3:

[0068] Testing of photocatalytic degradation performance:

[0069] Test method: The materials prepared in the 2×2cm examples and comparative examples were placed in a beaker containing 20mL of 0.05mmol / L Rhodamine B solution and stirred in the dark for 24h. After reaching adsorption equilibrium, the absorbance (A0) at 550nm was measured at a light intensity of 100mW / cm². 2 The photocatalytic reaction was carried out using a CEL-PF300L-3A uniform xenon lamp light source system. After 2 hours of reaction, the absorbance (A) at 550 nm was measured. The degradation rate of Rhodamine B was calculated according to the formula (degradation rate = (A0-A) / A0×100%). The results are shown in Table 3.

[0070] Table 3

[0071] Degradation rate (%) Degradation rate (%) Example 1 82.56 Comparative Example 1 1.2% Example 2 83.41 Comparative Example 2 0.7% Example 3 83.74 Comparative Example 3 82.74

[0072] A comparison of the experimental data from Examples 1-3 and Comparative Examples 1-3 in Table 3 reveals that the PVDF / PFA composite filter material for wastewater treatment prepared in this invention exhibits excellent photocatalytic performance.

[0073] The superior photocatalytic performance of Examples 1-3 compared to Comparative Examples 1-2 demonstrates that iron(III) oxide and modified microspheres together constitute a self-Fenton catalytic system. Resorcinol and formaldehyde form an electron donor-acceptor pair structure under hydrothermal conditions. This structure generates a large number of delocalized electrons through π-π conjugation and stacking. In the aqueous system, these delocalized electrons can reduce oxygen, generating hydrogen peroxide through a two-step single-electron reduction reaction. Hydrogen peroxide is activated by Fe²⁺, producing highly oxidizing hydroxyl radicals. These hydroxyl radicals can oxidize and degrade pollutants such as Rhodamine B, breaking them down into smaller organic molecules or completely mineralizing them into titanium dioxide and water. Simultaneously, Fe²⁺ is oxidized to Fe³⁺ during the reaction, and Fe³⁺ can be promptly reduced back to Fe²⁺ with the help of electrons carried by the microspheres, thus promoting the cyclical progression of the Fenton reaction.

[0074] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a PVDF / PFA composite filter material for wastewater treatment, characterized in that, The preparation steps include the following: (1) Pre-modified PVDF is obtained by reacting alkali-treated PVDF and vinylimidazolium salt; modified PVDF is obtained by reacting pre-modified PVDF, 5-azauracil, and aluminum chloride; the modified PVDF is prepared by dissolving potassium hydroxide in pure water, heating to 60-70℃, adding PVDF and ethanol and mixing for 20-30 min to obtain alkali-treated PVDF; alkali-treated PVDF, vinylimidazolium salt and initiator are dissolved in N,N-dimethylformamide, and the mixture is heated to 60-70℃ for 8-10 h under nitrogen protection to obtain pre-modified PVDF; pre-modified PVDF, 5-azauracil, aluminum chloride and N-methylpyrrolidone are mixed and the mixture is heated to 90-100℃ for 4-5 h under nitrogen protection to obtain modified PVDF; (2) Resorcinol, 3,5-dihydroxybenzoic acid and formaldehyde are reacted to obtain porous microspheres; the porous microspheres are sulfonated to obtain modified microspheres; the modified microspheres are prepared by mixing resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia, pure water, pore-forming agent and dispersant, and heating at 200-250℃ for 20-24h to obtain porous microspheres; under nitrogen protection and ice-water bath conditions, the porous microspheres, dichloromethane and chlorosulfonic acid are mixed for 10-12h, and quenched by adding 50wt% ethanol aqueous solution to obtain modified microspheres; (3) Modified PVDF, PFA, modified microspheres and PEO are mixed and melt-spun into a film. After soaking in pure water, a fiber membrane is obtained; ferric chloride hexahydrate, ferrous sulfate heptahydrate and fiber membrane are reacted to obtain a modified fiber membrane; (4) The modified fiber membrane was activated by immersing it in sodium hypochlorite solution to obtain PVDF / PFA composite filter material for wastewater treatment.

2. The method for preparing a PVDF / PFA composite filter material for wastewater treatment according to claim 1, characterized in that, The method for preparing the vinylimidazolium salt in step (1) is as follows: N-propenylimidazolium and 1-chloro-3-phenylpropane are mixed and dissolved in acetonitrile. Under argon protection, the mixture is refluxed at 80-85℃ for 20-24 hours to obtain the vinylimidazolium salt. The molar ratio of N-propenylimidazolium to 1-chloro-3-phenylpropane is 1:(1.05-1.15). The mass of the acetonitrile is 5-6 times the mass of N-propenylimidazolium.

3. The method for preparing a PVDF / PFA composite filter material for wastewater treatment according to claim 1, characterized in that, The mass ratio of PVDF, potassium hydroxide, pure water and ethanol is 1:(4.5-5.5):(25-30):(1.5-2.0); the mass ratio of alkali-treated PVDF, vinylimidazole salt, initiator and N,N-dimethylformamide is 1:(1-1.5):(0.003-0.005):(20-30); the mass ratio of pre-modified PVDF, 5-azauracil, aluminum chloride and N-methylpyrrolidone is 1:(1.5-2.0):(8-10):(20-30).

4. The method for preparing a PVDF / PFA composite filter material for wastewater treatment according to claim 1, characterized in that, The molar ratio of resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde is 1:(0.5-0.7):(1.5-3.0); the mass ratio of resorcinol, pore-forming agent, pure water, and dispersant is 1:(1-1.5):(10-12):(0.3-0.5); the mass of ammonia is 4%-6% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid; the specification of ammonia is 28wt%, and the specification of formaldehyde is 40wt%; the mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid, and 50wt% ethanol aqueous solution is 1:(10-12):(8-10):(300-400).

5. The method for preparing a PVDF / PFA composite filter material for wastewater treatment according to claim 1, characterized in that, The modified fiber membrane in step (3) is prepared by mixing modified PVDF, PFA, modified microspheres and PEO in a high-speed pulverizer, melting and plasticizing and granulating it in a twin-screw extruder, then melting and spinning it into a membrane. After soaking in pure water for 24 hours, a fiber membrane is obtained. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate are dissolved in pure water, the fiber membrane is added, the temperature is raised to 60-70℃, the pH is adjusted to 9-10 with ammonia water, and the reaction continues for 3-4 hours to obtain the modified fiber membrane.

6. The method for preparing a PVDF / PFA composite filter material for wastewater treatment according to claim 5, characterized in that, The mass ratio of modified PVDF, PFA, modified microspheres, and PEO is 1:(0.3-0.5):(0.1-0.2):(0.5-0.7); the melt spinning process is as follows: spinning temperature is 200-210℃, post-stretching temperature is 90℃, stretching ratio is 100%, nitrogen gas is introduced during spinning, and nitrogen pressure is 0.1MPa; the molar ratio of Fe3+ and Fe2+ in ferric chloride hexahydrate and ferrous sulfate heptahydrate is 2:1; the mass ratio of fiber membrane, ferric chloride hexahydrate, and pure water is 1:(2-3):(20-30).

7. The method for preparing a PVDF / PFA composite filter material for wastewater treatment according to claim 1, characterized in that, The immersion time in step (4) is 1-2 hours, the mass fraction of the sodium hypochlorite solution is 0.5%-1.0%, and the solid-liquid ratio of the modified fiber membrane and the sodium hypochlorite solution is 1 g:(20-30) L.

8. A PVDF / PFA composite filter material for wastewater treatment prepared by a method according to any one of claims 1-7.