PVDF / PFA composite filter material for sewage treatment and preparation method of PVDF / PFA composite filter material

Abstract

The invention discloses a PVDF / PFA composite filter material for sewage treatment and a preparation method of the PVDF / PFA composite filter material, and relates to the technical field of water treatment. When the filtering material is prepared, firstly, N-propenylimidazole and 1-chloro-3-phenylpropane react to prepare vinyl imidazolium salt, PVDF subjected to alkali treatment is grafted with the vinyl imidazolium salt, then the PVDF and 5-aza-uracil react, and modified PVDF is obtained; secondly, enabling resorcinol, 3, 5-dihydroxybenzoic acid and formaldehyde to react to obtain porous microspheres, and sulfonating the porous microspheres through chlorosulfonic acid to obtain modified microspheres; finally, PVDF, PFA, polyoxyethylene and the modified microspheres are mixed and subjected to melt spinning, and a fiber membrane is prepared; and carrying out in-situ generation of ferroferric oxide, and activating with hypochlorous acid to obtain the PVDF / PFA composite filter material for sewage treatment. The filter material prepared by the invention has good antibacterial, hydrophilic and photocatalytic degradation properties.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to a PVDF / PFA composite filter material for sewage treatment and a preparation method thereof. Background Art

[0002] Polyvinylidene fluoride (PVDF) has excellent chemical stability and can withstand corrosion from strong acids, strong alkalis and a variety of organic solvents, making it one of the membrane materials with the best comprehensive performance in the world. It has broad application prospects in fields such as sewage treatment. PVDF material has low surface energy and strong hydrophobicity, which can cause two problems in the water treatment and separation process. First, the separation process requires a large driving force and low flux. Second, in the process of separating oil / water systems, organic pollutants (such as proteins, etc.) are easily adsorbed on the membrane surface or in the membrane pores, causing membrane fouling, resulting in a decrease in membrane separation performance, a decrease in water flux, and a shortened membrane service life.

[0003] PFA is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether. It has excellent chemical corrosion resistance and is resistant to 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 in a wide temperature range. PFA also has good mechanical properties, dimensional stability, electrical insulation and creep resistance. Its mechanical properties are better than PTFE, and it has non-adhesive and self-lubricating properties in a wide temperature range. Through the compounding of PVDF and PFA, the advantages of both can be fully utilized to achieve complementary performance. At the same time, the hydrophilicity, anti-pollution, and photocatalytic degradation properties of the composite material can be further improved, which can better meet the high performance requirements of filter materials in the sewage treatment process, improve sewage treatment efficiency and reduce operating costs. Summary of the Invention

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

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for preparing a PVDF / PFA composite filter material for sewage treatment comprises the following steps:

[0007] (1) reacting N-propylene imidazole and 1-chloro-3-phenylpropane to obtain vinyl imidazole salt; reacting alkali-treated PVDF and vinyl imidazole salt to obtain pre-modified PVDF; reacting pre-modified PVDF, 5-azauracil and aluminum chloride to obtain modified PVDF;

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

[0009] (3) Modified PVDF, PFA, modified microspheres, and PEO are mixed, melt-spun into a membrane, and then soaked in pure water to obtain a fiber membrane; ferric chloride hexahydrate and ferrous sulfate heptahydrate are dissolved and reacted with the fiber membrane to obtain a modified fiber membrane;

[0010] (4) The modified fiber membrane was immersed in a sodium hypochlorite solution to activate it and obtain a PVDF / PFA composite filter material for sewage treatment.

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

[0012] As an optimization, it is characterized in that the preparation method of the modified PVDF in step (1) is: dissolving potassium hydroxide in pure water, heating to 60-70°C, adding PVDF and ethanol and mixing for 20-30 minutes to obtain alkali-treated PVDF; dissolving alkali-treated PVDF, vinyl imidazole salt, and initiator in N,N-dimethylformamide, heating to 60-70°C under nitrogen protection and reacting for 8-10 hours to obtain pre-modified PVDF; mixing pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone, heating to 90-100°C under nitrogen protection and reacting for 4-5 hours to obtain modified PVDF; the PVDF is polyvinylidene fluoride.

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

[0014] As an optimization, it is characterized in that the preparation method of the modified microspheres in step (2) is: resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia water, pure water, porogen, and dispersant are mixed, and heated at 200-250°C 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 50wt% ethanol aqueous solution is added to quench the mixture to obtain modified microspheres.

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

[0016] As an optimization, it is characterized in that the preparation method of the modified fiber membrane in step (3) is: modifying PVDF, PFA, modified microspheres and PEO are mixed in a high-speed pulverizer, melt-plasticized and granulated by a twin-screw extruder, and then melt-spinned into a film, and soaked in pure water for 24 hours to obtain a fiber membrane, and under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate are dissolved in pure water, added to the fiber membrane, heated to 60-70°C, and ammonia water is used to adjust the pH to 9-10, and the reaction is continued for 3-4 hours to obtain a modified fiber membrane.

[0017] As an optimization, it is characterized in that the mass ratio of the 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: the spinning temperature is 200-210 ° C, the post-stretching temperature is 90 ° C, the stretching ratio is 100%, nitrogen is introduced during the spinning process, and the nitrogen pressure is 0.1 MPa; the Fe in the hexahydrate ferric chloride and the heptahydrate ferrous sulfate is 0.1 MPa. 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, it is 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 1g:(20-30)L.

[0019] The present invention also provides a PVDF / PFA composite filter material for sewage treatment prepared according to the preparation method of the PVDF / PFA composite filter material for sewage treatment.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] When preparing the PVDF / PFA composite filter material for sewage treatment, the present invention comprises the following steps: first, reacting N-propylene imidazole and 1-chloro-3-phenylpropane to obtain vinyl imidazole salt, grafting vinyl imidazole salt onto alkali-treated polyvinylidene fluoride, and then reacting with 5-azauracil to obtain modified polyvinylidene fluoride; secondly, reacting resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde to obtain porous microspheres, and then sulfonating with chlorosulfonic acid to obtain modified microspheres; finally, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, polyethylene oxide, and the modified microspheres are mixed and melt-spun to prepare a fiber membrane; and then in-situ generating ferrosoferric oxide and activating with hypochlorous acid to obtain the PVDF / PFA composite filter material for sewage treatment.

[0022] First, N-propylene imidazole and 1-chloro-3-phenylpropane are reacted to produce vinyl imidazole salt. Polyvinylidene fluoride is treated with an alkali to cause a dehydrofluorination reaction on the polyvinylidene fluoride, introducing carbon-carbon unsaturated bonds on the membrane surface. Vinyl imidazole salt can then be grafted onto the membrane under the action of an initiator. The vinyl imidazole salt can increase the hydrophilicity of the polyvinylidene fluoride and adsorb negatively charged impurities in wastewater through electrostatic interaction. At the same time, a benzene ring is introduced. Under the catalysis of aluminum chloride, the benzene ring undergoes an arylation reaction with 5-azauracil to produce a halamine precursor. Activated by hypochlorous acid, the material is endowed with excellent antibacterial properties.

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

[0024] ;

[0025] Secondly, resorcinol, 3,5-dihydroxybenzoic acid and formaldehyde are reacted to obtain phenolic microspheres. The addition of a porogen during the synthesis of the microspheres can generate porous microspheres with a larger specific surface area, which 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, and can also adsorb positively charged heavy metal ions in wastewater through electrostatic action. In the process of mixing with the modified microspheres, the electrostatic action can promote the uniform dispersion of the modified microspheres in the matrix. In addition, in the process of generating ferric oxide, the carboxyl and sulfonic acid groups on the modified microspheres form chemical bonds through coordination with ferric oxide, enabling the particles to be firmly anchored on the surface of the material. Ferric 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 produces a large number of delocalized electrons through π-π conjugation and stacking. In a water system, these delocalized electrons can reduce oxygen and generate hydrogen peroxide through a two-step single-electron reduction reaction. Hydrogen peroxide is activated by Fe²⁺ to produce hydroxyl radicals with strong oxidizing properties. Hydroxyl radicals can oxidize and degrade pollutants such as rhodamine B, decomposing them into smaller molecular organic matter or completely mineralizing them into titanium dioxide and water. At the same time, Fe²⁺ is oxidized to Fe³⁺ in the reaction, and Fe³⁺ can be promptly reduced to Fe²⁺ with the help of the electrons carried by the microspheres, thereby promoting the cycle of the Fenton reaction. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] In the following examples and comparative examples, the PVDF is polyvinylidene fluoride, model number Solef 6010, purchased from DuPont; the PEO is polyethylene oxide, model number P823143, purchased from McLean Biochemical Co., Ltd.; the PFA is tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer, model number 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 sewage treatment, the preparation method comprising the following steps:

[0030] (1) N-propylene imidazole and 1-chloro-3-phenylpropane were mixed in a molar ratio of 1:1.05, dissolved in acetonitrile with a mass of 6 times that of N-propylene imidazole, and refluxed at 85°C for 24 hours under argon protection. After the reaction, the acetonitrile was removed and the mixture was dried at room temperature under vacuum to obtain vinyl imidazole salt; the acetonitrile temperature for washing was 5°C; potassium hydroxide was dissolved in pure water, heated to 70°C, PVDF and ethanol were added and mixed for 30 minutes, and alkali-treated PVDF was obtained by filtration, washing and drying; the mass ratio of PVDF, potassium hydroxide, pure water and ethanol was 1:4.5:25:1.5; alkali-treated PVDF was prepared. , vinyl imidazole salt, and initiator benzoyl peroxide are dissolved in N,N-dimethylformamide, and the reaction is heated to 70°C for 10 hours under nitrogen protection, and the pre-modified PVDF is obtained by precipitation with methanol, filtration, washing, and drying; the mass ratio of alkali-treated PVDF, vinyl imidazole salt, initiator, and N,N-dimethylformamide is 1:1:0.003:20; the pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone are mixed in a mass ratio of 1:1.5:8:20, and the reaction is heated to 100°C for 5 hours under nitrogen protection, and the modified PVDF is obtained by precipitation with methanol, filtration, washing, and drying;

[0031] (2) Resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia water and pure water were mixed, porogen toluene and dispersant polyvinyl alcohol were added and continued to mix, and heated at 250 ° C for 24 h 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 water was 4% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid; the specification of ammonia water was 28wt%, and the specification of formaldehyde was 40wt%; under nitrogen protection and ice water bath conditions, the porous microspheres, dichloromethane and chlorosulfonic acid were mixed for 12 h, quenched by adding 50wt% ethanol aqueous solution, and filtered and washed to obtain modified microspheres; the mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid and 50wt% 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, 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°C, the post-stretching temperature was 90°C, the stretching ratio was 100%, and nitrogen was introduced during the spinning process at a nitrogen pressure of 0.1 MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 70°C, and the pH was adjusted to 10 with ammonia water. The reaction was continued for 4 hours, filtered, ultrasonically washed, and dried to obtain a modified fiber membrane. Fe3+ and Fe 2+ The molar ratio of 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 a sodium hypochlorite solution for 2 h, filtered, washed, and dried to obtain a PVDF / PFA composite filter material for sewage treatment. The mass fraction of the sodium hypochlorite solution was 1.0%; the solid-liquid ratio of the modified fiber membrane to the sodium hypochlorite solution was 1 g:20 L.

[0034] Example 2:

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

[0036] (1) N-propylene imidazole and 1-chloro-3-phenylpropane were mixed in a molar ratio of 1:1.07, dissolved in acetonitrile with a mass of 5.5 times that of N-propylene imidazole, and refluxed at 82°C for 22 hours under argon protection. After the reaction, the acetonitrile was removed and the mixture was dried at room temperature under vacuum to obtain vinyl imidazole salt; the acetonitrile temperature for washing was 4°C; potassium hydroxide was dissolved in pure water, heated to 65°C, PVDF and ethanol were added and mixed for 25 minutes, and alkali-treated PVDF was obtained by filtration, washing and drying; the mass ratio of PVDF, potassium hydroxide, pure water and ethanol was 1:5.0:27:1.7; alkali-treated PVDF was prepared. , vinyl imidazole salt, and initiator benzoyl peroxide are dissolved in N,N-dimethylformamide, and the temperature is raised to 65°C for reaction for 9 hours under nitrogen protection, and the pre-modified PVDF is obtained by precipitation with methanol, filtration, washing, and drying; the mass ratio of alkali-treated PVDF, vinyl imidazole salt, initiator, and N,N-dimethylformamide is 1:1.3:0.003:25; the pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone are mixed in a mass ratio of 1:1.7:9:25, and the temperature is raised to 95°C for reaction for 4.5 hours under nitrogen protection, and the modified PVDF is obtained by precipitation with methanol, filtration, washing, and drying;

[0037] (2) Resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia water and pure water were mixed, porogen toluene and dispersant polyvinyl alcohol were added and continued to mix, and 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 water was 5% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid; the specification of ammonia water was 28wt%, and the specification of formaldehyde was 40wt%; under nitrogen protection and ice water bath conditions, the porous microspheres, dichloromethane and chlorosulfonic acid were mixed for 11 hours, quenched by adding 50wt% ethanol aqueous solution, and filtered and washed to obtain modified microspheres; the mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid and 50wt% 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, 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°C, the post-stretching temperature was 90°C, the stretching ratio was 100%, and nitrogen was introduced during the spinning process at a nitrogen pressure of 0.1 MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 65°C, and the pH was adjusted to 9 with ammonia water. The reaction was continued for 3.5 hours, filtered, ultrasonically washed, and dried to obtain a modified fiber membrane. The Fe 3+ and Fe 2+ The molar ratio of is 2:1; the mass ratio of fiber membrane, ferric chloride hexahydrate and pure water is 1:2.5:25;

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

[0040] Example 3:

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

[0042] (1) N-propylene imidazole and 1-chloro-3-phenylpropane were mixed in a molar ratio of 1:1.15, dissolved in acetonitrile with a mass of 6 times that of N-propylene imidazole, and refluxed at 80°C for 20 hours under argon protection. After the reaction, the acetonitrile was removed and the mixture was dried at room temperature in a vacuum to obtain vinyl imidazole salt; the acetonitrile temperature for washing was 0°C; potassium hydroxide was dissolved in pure water, heated to 60°C, PVDF and ethanol were added and mixed for 20 minutes, and alkali-treated PVDF was obtained by filtration, washing and drying; the mass ratio of PVDF, potassium hydroxide, pure water and ethanol was 1:5.5:30:2.0; alkali-treated PVDF was prepared. , vinyl imidazole salt, and initiator benzoyl peroxide are dissolved in N,N-dimethylformamide, and the temperature is raised to 60°C for reaction for 8 hours under nitrogen protection, and the pre-modified PVDF is obtained by precipitation with methanol, filtration, washing, and drying; the mass ratio of alkali-treated PVDF, vinyl imidazole salt, initiator, and N,N-dimethylformamide is 1:1.5:0.005:30; the pre-modified PVDF, 5-azauracil, aluminum chloride, and N-methylpyrrolidone are mixed in a mass ratio of 1:2.0:10:30, and the temperature is raised to 90°C for reaction for 4 hours under nitrogen protection, and the modified PVDF is obtained by precipitation with methanol, filtration, washing, and drying;

[0043] (2) Resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia water and pure water were mixed, porogen toluene and dispersant polyvinyl alcohol were added and continued to mix, and 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 water was 6% of the total mass of resorcinol and 3,5-dihydroxybenzoic acid; the specification of ammonia water was 28wt%, and the specification of formaldehyde was 40wt%; under nitrogen protection and ice water bath conditions, the porous microspheres, dichloromethane and chlorosulfonic acid were mixed for 10 hours, quenched by adding 50wt% ethanol aqueous solution, and filtered and washed to obtain modified microspheres; the mass ratio of porous microspheres, dichloromethane, chlorosulfonic acid and 50wt% 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. The fiber membrane was soaked in pure water for 24 hours. During the melt spinning process, the spinning temperature was 200°C, the post-stretching temperature was 90°C, the stretching ratio was 100%, and nitrogen was introduced during the spinning process at a nitrogen pressure of 0.1 MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 60°C, and the pH was adjusted to 9 with ammonia water. The reaction was continued for 3 hours, filtered, ultrasonically washed, and dried to obtain a modified fiber membrane. The Fe3+ and Fe 2+ The molar ratio of 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 a sodium hypochlorite solution for 1 h, filtered, washed, and dried to obtain a PVDF / PFA composite filter material for sewage treatment. The mass fraction of the sodium hypochlorite solution was 0.5%; the solid-liquid ratio of the modified fiber membrane to the sodium hypochlorite solution was 1 g:30 L.

[0046] Comparative Example 1:

[0047] The preparation method of the PVDF / PFA composite filter material for sewage treatment in Comparative Example 1 differs from that in Example 2 in 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 crusher 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 sewage treatment is obtained. During the melt spinning process, the spinning temperature is 205°C, the post-stretching temperature is 90°C, the stretching ratio is 100%, and nitrogen is introduced during the spinning process at a nitrogen pressure of 0.1 MPa.

[0048] Comparative Example 2:

[0049] The preparation method of the PVDF / PFA composite filter material for sewage treatment in Comparative Example 2 differs from that in Example 2 in that modified microspheres are not added, specifically, step (2) is not included; 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 in a twin-screw extruder, and then melt-spun to form a film. The film is then soaked in pure water for 24 hours to obtain the PVDF / PFA composite filter material for sewage treatment. During the melt spinning process, the spinning temperature is 205°C, the post-stretching temperature is 90°C, the stretching ratio is 100%, and nitrogen is introduced during the spinning process at a nitrogen pressure of 0.1 MPa. The remaining steps are the same as those in Example 2.

[0050] Comparative Example 3:

[0051] The preparation method of the PVDF / PFA composite filter material for sewage treatment in Comparative Example 3 differs from that in Example 2 in that PVDF is not modified, specifically, steps (1) and (4) are not included; 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 to form a film, and then soaked in pure water for 24 hours to obtain a fiber membrane. During the melt spinning process, The spinning temperature was 205°C, the post-stretching temperature was 90°C, the stretching ratio was 100%, and nitrogen was introduced during the spinning process with a nitrogen pressure of 0.1 MPa. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate were dissolved in pure water, added to the fiber membrane, heated to 65°C, and the pH was adjusted to 9 with ammonia water. The reaction was continued for 3.5 hours, and the PVDF / PFA composite filter material for sewage treatment was obtained after filtration, ultrasonic washing, and drying. The Fe in ferric chloride hexahydrate and ferrous sulfate heptahydrate was 1.34 wt. % and 1.37 wt. % respectively. 3+ and Fe 2+ The molar ratio of the fiber membrane, ferric chloride hexahydrate, and pure water 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 those in Example 2.

[0052] Test Example 1:

[0053] Antibacterial performance test:

[0054] Test method: Under light-proof conditions, the antibacterial rate test of the filter materials prepared in the examples and comparative examples was carried out in accordance with the standard GB / T 37206-2018. The test bacteria species 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] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, it can be found that the PVDF / PFA composite filter material for sewage treatment prepared by the present invention has good antibacterial properties.

[0058] The antibacterial properties of Examples 1 to 3 are better than those of Comparative Examples 1 and 3, indicating that, first, N-propylene imidazole and 1-chloro-3-phenylpropane are reacted to prepare vinyl imidazole salt, and polyvinylidene fluoride is treated with an alkali to cause a dehydrofluorination reaction of the polyvinylidene fluoride, thereby introducing a carbon-carbon unsaturated bond on the membrane surface. Under the action of an initiator, vinyl imidazole salt can be grafted, and a benzene ring is introduced at the same time. The benzene ring undergoes an arylation reaction with 5-azauracil under the catalysis of aluminum chloride to generate a halamine precursor, which imparts good antibacterial properties to the material under the activation of hypochlorous acid.

[0059] Test Example 2:

[0060] Hydrophilic performance test:

[0061] Testing Method: The static water contact angles of the films prepared in Examples and Comparative Examples were measured using an optical contact angle meter (DSA100, KRUSS, Germany). The volume of the water droplet was fixed at 0.5 μL during titration. 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] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 2, it can be found that the PVDF / PFA composite filter material for sewage treatment prepared by the present invention has good hydrophilic properties.

[0065] The hydrophilic properties of Examples 1 to 3 are better than those of Comparative Examples 1 to 3, indicating that, first, N-acrylimidazole and 1-chloro-3-phenylpropane are reacted to prepare vinyl imidazole salt, and polyvinylidene fluoride is treated with an alkali to cause a dehydrofluorination reaction of the polyvinylidene fluoride, thereby introducing carbon-carbon unsaturated bonds on the membrane surface. Vinyl imidazole salt can then be grafted under the action of an initiator, and the vinyl imidazole salt can improve the hydrophilicity of the polyvinylidene fluoride.

[0066] Secondly, resorcinol, 3,5-dihydroxybenzoic acid and formaldehyde are reacted to obtain phenolic microspheres. During the synthesis of the microspheres, toluene is used as a porogen to generate porous microspheres with a larger specific surface area, which 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] Test of photocatalytic degradation performance:

[0069] Test method: 2×2 cm2 of the materials prepared in the embodiment and comparative example were placed in a beaker containing 20 mL of 0.05 mmol / L rhodamine B solution, stirred in the dark for 24 h, and after reaching adsorption equilibrium, the absorbance (A0) at 550 nm was measured. 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-A0) / 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] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 3, it can be found that the PVDF / PFA composite filter material for sewage treatment prepared by the present invention has good photocatalytic performance.

[0073] The superior photocatalytic performance of Examples 1-3 compared to Comparative Examples 1-2 demonstrates that the ferrosoferric oxide and modified microspheres together constitute a self-Fenton catalytic system. Resorcinol and formaldehyde form an electron donor-acceptor pair structure under hydrothermal conditions, which 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. Hydrogen peroxide is activated by Fe²⁺ to produce highly oxidizing hydroxyl radicals, which 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, which can then be promptly reduced to Fe²⁺ by the electrons carried by the microspheres, thereby promoting the cyclic 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 embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A method for preparing a PVDF / PFA composite filter material for sewage treatment, characterized in that: The method comprises the following preparation steps: (1) reacting alkali-treated PVDF with vinyl imidazole salt to obtain pre-modified PVDF; reacting pre-modified PVDF, 5-azauracil, and aluminum chloride to obtain modified PVDF; (2) Resorcinol, 3,5-dihydroxybenzoic acid, and formaldehyde are reacted to obtain porous microspheres; and the porous microspheres are sulfonated to obtain modified microspheres; (3) Modified PVDF, PFA, modified microspheres, and PEO are mixed, melt-spun into a membrane, and then soaked in pure water to obtain a fiber membrane; ferric chloride hexahydrate and ferrous sulfate heptahydrate are dissolved and reacted with the fiber membrane to obtain a modified fiber membrane; (4) The modified fiber membrane was immersed in a sodium hypochlorite solution to activate it and obtain a PVDF / PFA composite filter material for sewage treatment.

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

3. The method for preparing a PVDF / PFA composite filter material for sewage treatment according to claim 1, characterized in that: The preparation method of the modified PVDF in step (1) is as follows: dissolving potassium hydroxide in pure water, heating to 60-70°C, adding PVDF and ethanol and mixing for 20-30 minutes to obtain alkali-treated PVDF; dissolving alkali-treated PVDF, vinyl imidazole salt and initiator in N,N-dimethylformamide, heating to 60-70°C under nitrogen protection and reacting for 8-10 hours to obtain pre-modified PVDF; mixing pre-modified PVDF, 5-azauracil, aluminum chloride and N-methylpyrrolidone, heating to 90-100°C under nitrogen protection and reacting for 4-5 hours to obtain modified PVDF.

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

5. The method for preparing a PVDF / PFA composite filter material for sewage treatment according to claim 1, characterized in that: The preparation method of the modified microspheres in step (2) is as follows: resorcinol, 3,5-dihydroxybenzoic acid, formaldehyde, ammonia water, pure water, a porogen, and a dispersant are mixed, and heated 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 50wt% ethanol aqueous solution is added to quench the mixture to obtain modified microspheres.

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

7. The method for preparing a PVDF / PFA composite filter material for sewage treatment according to claim 1, characterized in that: The preparation method of the modified fiber membrane in step (3) is as follows: the modified PVDF, PFA, modified microspheres and PEO are mixed in a high-speed pulverizer, melt-plasticized and granulated by a twin-screw extruder, and then melt-spun into a membrane. The fiber membrane is obtained after soaking in pure water for 24 hours. Under nitrogen protection, ferric chloride hexahydrate and ferrous sulfate heptahydrate are dissolved in pure water, added to the fiber membrane, heated to 60-70°C, and ammonia water is used to adjust the pH to 9-10. The reaction is continued for 3-4 hours to obtain the modified fiber membrane.

8. The method for preparing a PVDF / PFA composite filter material for sewage treatment according to claim 7, characterized in that: The mass ratio of the 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: the spinning temperature is 200-210°C, the post-stretching temperature is 90°C, the stretching ratio is 100%, nitrogen is introduced during the spinning process, and the nitrogen pressure is 0.1MPa; the Fe in the ferric chloride hexahydrate and the ferrous sulfate heptahydrate is 0.1MPa. 3+ and Fe 2+ The molar ratio of the fiber membrane, ferric chloride hexahydrate and pure water is 2:1; the mass ratio of the fiber membrane, ferric chloride hexahydrate and pure water is 1:(2-3):(20-30).

9. The method for preparing a PVDF / PFA composite filter material for sewage 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%; the solid-liquid ratio of the modified fiber membrane to the sodium hypochlorite solution is 1g:(20-30)L.

10. A PVDF / PFA composite filter material for sewage treatment prepared according to the method for preparing a PVDF / PFA composite filter material for sewage treatment according to any one of claims 1 to 9.