Preparation method of super-hydrophobic membrane material and application of super-hydrophobic membrane material in concentrating trace organic matters in water

Abstract

The invention discloses a preparation method of a super-hydrophobic membrane material and application of the super-hydrophobic membrane material in the aspect of concentrating trace organic matter in water, the preparation method of the super-hydrophobic membrane material comprises the following steps: (1) soaking a PVDF base membrane in a Tris-HCl buffer solution containing dopamine, taking out the PVDF base membrane after soaking, and cleaning the PVDF base membrane to obtain a PVDF membrane with the surface modified with dopamine; (2) dispersing silicon dioxide nanoparticles in a Tris-HCl buffer solution, and performing ultrasonic dispersion to obtain a solution A; soaking the PVDF membrane of which the surface is modified with dopamine in the solution A, taking out the PVDF membrane after soaking, and cleaning the PVDF membrane to obtain the PVDF membrane of which the surface has a micro-nano structure; and (3) soaking the PVDF membrane with the micro-nano structure on the surface in an ethanol solution containing perfluorinated substances, taking out the PVDF membrane after soaking, cleaning and drying to obtain the super-hydrophobic PVDF membrane.

Description

Technical Field

[0001] This invention relates to a method for preparing a superhydrophobic membrane material, and also to the application of the superhydrophobic membrane material prepared by the above method in the treatment of trace organic matter in concentrated water. Background Technology

[0002] Ultrapure water is a crucial raw material in the semiconductor manufacturing industry, widely used in various cleaning processes. Trace organic matter in water is a key indicator of ultrapure water quality, often expressed as total organic carbon (TOC). For advanced semiconductor manufacturing processes, the TOC concentration of ultrapure water should be below 1 μg / L; exceeding this limit can severely impact semiconductor product yield.

[0003] However, ultrapure water has a low concentration of trace organic matter. For example, the TOC concentration in reverse osmosis permeate from ultrapure water systems is typically between 10 and 5 μg / L. Current technologies can only identify about 30% of the organic matter, including volatile organic compounds, halogenated organic compounds, nitrogen-containing organic compounds, and oxidation byproducts of aldehydes, ketones, and acids. Approximately 70% of the organic matter remains unknown. Existing instruments such as GC-MS and HPLC-MS are insufficient for the quantitative detection of these individual organic compounds, resulting in a lack of targeted treatment processes and a high risk of exceeding TOC limits in ultrapure water. Therefore, pre-concentration measures are necessary to concentrate and enrich trace organic matter before detection.

[0004] Chinese invention patent (application number 2016109206121) discloses a device for concentrating organic matter in water by combining reverse osmosis concentration with macroporous adsorption resin enrichment. This device is only suitable for large-molecule organic matter in water, mainly including humic acid, fulvic acid, and other substances with a molecular weight greater than 200 Da. It is not suitable for small-molecule substances such as polypeptides, polysaccharides, amino acids, and urea. Therefore, in actual ultrapure water engineering cases, the measured rejection rate of the reverse osmosis system for small-molecule substances such as urea is only about 70%.

[0005] During the aforementioned reverse osmosis membrane concentration process, some small molecule organic matter dissolves in the water and passes through the hydrophilic membrane surface, resulting in the small molecule organic matter failing to achieve the expected concentration effect. Therefore, existing methods for concentrating organic matter in water are difficult to effectively concentrate trace small molecule organic matter in ultrapure water. Experimental results show that after concentrating the volume of ultrapure water containing 10 μg / L TOC to 1 / 4, the TOC concentration in the permeate is still 5 μg / L, and the TOC concentration in the concentrate is about 25 μg / L, which cannot achieve effective concentration. Summary of the Invention

[0006] Objective of this invention: The objective of this invention is to provide a method for preparing a superhydrophobic membrane material. This method overcomes the problem of membrane wettability leading to permeation of the concentrate during membrane distillation in existing superhydrophobic membranes, thereby achieving effective concentration of trace small-molecule organic compounds in ultrapure water. Another objective of this invention is to provide the application of the superhydrophobic membrane prepared by the above method in concentrating trace organic compounds in water. Technical solution: The preparation method of the superhydrophobic film material of the present invention includes the following steps: (1) Modification of PVDF membrane with adhesive coating: Immerse the PVDF membrane in Tris-HCl buffer solution with a dopamine concentration of 0.3~1.5wt% for 12~24 hours, and then wash with ultrapure water to modify a cross-linked polydopamine coating layer on the surface of the PVDF membrane; providing a large number of hydroxyl attachment active sites for the next step of silica nanoparticles; (2) Surface attachment of silica nanoparticles: Silica nanoparticles were dispersed in Tris-HCl buffer solution with pH 7.8, sonicated for 20-60 minutes and then allowed to stand at room temperature for 15-30 minutes to obtain solution A; The PVDF membrane with surface modified dopamine obtained in step (1) was immersed in solution A, and after immersion for 2-4 hours, it was taken out, washed several times with deionized water, and then washed several times with ethanol to obtain a PVDF membrane with micro-nano structure on the surface; (3) Surface modification with perfluorinated low surface energy material: The PVDF film with micro-nano structure obtained in step (2) is immersed in an ethanol solution containing perfluorinated material. After immersion for 12 to 24 hours, it is taken out, washed several times with ethanol, and then placed in an oven at 40 to 60°C to dry for 1 to 3 hours.

[0007] In this invention, the membrane substrate material is PVDF, and the membrane preparation method is a solvent-inducible phase inversion method to prepare a PVDF-based membrane.

[0008] In step (2), the particle size of the silica nanoparticles is 100~200nm; in the dispersion, the mass concentration of the silica nanoparticles is 0.1~0.3%.

[0009] In step (3), the perfluorinated substance is at least one of heptadecafluorodecyltrimethoxysilane (CAS: 83048-65-1), perfluorooctyltrimethoxysilane, or perfluorodecyltriethoxysilane (CAS: 101947-16-4); the volume concentration of the perfluorinated substance in the ethanol solution is 0.1~0.3%.

[0010] The prepared membrane was used in a direct contact membrane distillation apparatus to treat ultrapure water containing 5-10 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively, to concentrate the volume of the treated ultrapure water to 1 / 10 to 1 / 5, thereby achieving the concentration of trace organic matter.

[0011] This invention utilizes membrane distillation to concentrate trace organic matter in water. During membrane distillation, due to the surface tension of water, liquid water cannot permeate through the micropores of the membrane, thus preventing trace organic matter from passing through with the liquid water. However, water vapor can permeate through the micropores. When a temperature difference exists across the membrane, due to the difference in vapor pressure, water vapor molecules pass through the micropores and condense on the other side, gradually concentrating the feed solution. Furthermore, the temperature during membrane distillation is relatively mild, preventing even extremely low concentrations of trace organic matter from evaporating, thus retaining the organic matter in the feed solution. By increasing the concentration of trace organic matter in water through membrane distillation, the specific components and concentrations can be quantitatively identified for targeted treatment. Traditional membrane distillation processes often use hydrophobic membrane materials with wettability issues; as the distillation process progresses, the feed solution penetrates into the membrane pores, wetting or partially wetting the membrane channels, thereby reducing the rejection rate and affecting the concentration effect. The superhydrophobic membrane material prepared by this invention constructs micro-nano structures and low surface energy substances on the surface of a traditional PVDF hydrophobic membrane, which can significantly increase the water contact angle, thereby effectively preventing membrane wetting and ensuring that trace organic pollutants to be concentrated will not permeate through the membrane and affect the concentration factor.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention uses membrane distillation process to concentrate trace organic matter in water. During operation, only gaseous water vapor can pass through the membrane, while liquid water and trace organic matter dissolved in water cannot pass through, thereby concentrating trace organic matter in water. This facilitates the increase of organic matter concentration in water and further quantitative detection of its components. It effectively solves the problem that traditional reverse osmosis can only concentrate large molecular organic matter, while small molecular organic matter can easily pass through the membrane. (2) The present invention effectively improves the hydrophobicity of the membrane by constructing micro-nano structures on the membrane surface and modifying it with low surface energy materials. The water contact angle of the membrane reaches more than 165°. Therefore, during the membrane distillation application, the membrane wetting can be effectively avoided, ensuring that the trace organic pollutants to be concentrated will not pass through the membrane and affect the concentration ratio. Attached Figure Description

[0013] Figure 1 Here is a scanning electron microscope image of the superhydrophobic film material prepared in Example 1; Figure 2 Photographs showing the water contact angle of the superhydrophobic film material prepared in Example 1; Figure 3 The image shows a scanning electron microscope (SEM) image of the hydrophobic film material prepared in Comparative Example 1. Figure 4 Photographs showing the water contact angle of the hydrophobic film material prepared in Comparative Example 1. Detailed Implementation

[0014] Example 1 The method for preparing the superhydrophobic film material of the present invention includes the following steps: (1) Preparation of PVDF-based film: (1.1) Preparation of casting solution: 14 parts by weight of commercial PVDF polymer solid particles and 6 parts by weight of pore-forming agent PEG4000 are added to 80 parts by weight of N-methylpyrrolidone. The mixture is mechanically stirred for 4 hours under a water bath heating condition of 60°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (1.2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in a 60°C water bath for 4 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (1.3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 200μm to form a nascent film. (1.4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The membrane is then removed and placed in deionized water to remove residual organic solvents, thus obtaining a PVDF-based membrane. (2) Modification of the surface adhesive coating of dopamine: The PVDF base film obtained in step (1) was immersed in Tris-HCl buffer solution with a dopamine concentration of 0.3wt% for 12 hours, and then washed with ultrapure water. (3) Surface attachment of silica nanoparticles: Silica nanoparticles were placed in a Tris-HCl buffer solution with a pH of 7.8, sonicated for 20 minutes, and then allowed to stand at room temperature for 15 minutes to obtain a silica nanoparticle dispersion; the dopamine-modified PVDF membrane obtained in step (2) was immersed in the silica nanoparticle dispersion, and after 2 hours it was taken out, washed several times with deionized water, and then washed several times with ethanol to obtain a PVDF membrane with micro-nano structures on the surface; the concentration of silica nanoparticles in the silica nanoparticle dispersion was 0.1 wt%; (4) Surface modification with perfluorinated low surface energy material: The PVDF membrane with surface micro-nano structure obtained in step (3) was immersed in an ethanol solution containing heptadecafluorodecyltrimethoxysilane. After immersion for 12 hours, it was taken out, washed several times with ethanol, and dried in an oven at 40°C for 1 hour to obtain a superhydrophobic PVDF membrane. The volume concentration of heptadecafluorodecyltrimethoxysilane in the ethanol solution was 0.1%.

[0015] (5) The prepared membrane was used in a direct contact membrane distillation device to treat ultrapure water containing 10 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 98 μg / L, thus achieving effective concentration.

[0016] The superhydrophobic PVDF film prepared in Example 1 exhibits high resistance to water droplets, with a water contact angle reaching 168.2°. Scanning electron microscopy of the surface micro / nano structure and the water contact angle are shown in the figures below. Figure 1 , Figure 2 As shown.

[0017] Example 2 The method for preparing the superhydrophobic film material of the present invention includes the following steps: (1) Preparation of PVDF-based film: (1.1) Preparation of casting solution: 16 parts by weight of commercial PVDF polymer solid particles and 8 parts by weight of pore-forming agent PEG4000 are added to 76 parts by weight of dimethyl sulfoxide and mechanically stirred for 8 hours under water bath heating at 70°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (1.2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in a 70°C water bath for 6 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (1.3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 220μm to form a nascent film. (1.4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The membrane is then removed and placed in deionized water to remove residual organic solvents, thus obtaining a PVDF-based membrane. (2) Modification of the surface adhesive coating of dopamine: The PVDF base film obtained in step (1) was immersed in Tris-HCl buffer solution with a dopamine concentration of 0.9wt% for 18 hours, and then washed with ultrapure water. (3) Surface attachment of silica nanoparticles: Silica nanoparticles were placed in a Tris-HCl buffer solution with a pH of 7.8, sonicated for 40 minutes, and then allowed to stand at room temperature for 25 minutes to obtain a silica nanoparticle dispersion; the dopamine-modified PVDF membrane obtained in step (2) was immersed in the silica nanoparticle dispersion, and after immersion for 3 hours, it was taken out, washed several times with deionized water, and then washed several times with ethanol to obtain a PVDF membrane with micro-nano structures on the surface; the concentration of silica nanoparticles in the silica nanoparticle dispersion was 0.2 wt%; (4) Surface modification with perfluorinated low surface energy material: The PVDF membrane with surface micro-nano structure obtained in step (3) was immersed in an ethanol solution containing perfluorooctyltrimethoxysilane. After immersion for 18 hours, it was taken out, washed several times with ethanol, and dried in an oven at 50°C for 2 hours to obtain a superhydrophobic PVDF membrane. The volume concentration of perfluorooctyltrimethoxysilane in the ethanol solution was 0.2%.

[0018] (5) The prepared membrane was used in a direct contact membrane distillation device to treat ultrapure water containing 5 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 49 μg / L, thus achieving effective concentration.

[0019] The superhydrophobic PVDF membrane prepared in Example 2 has high resistance to water droplets, with a water contact angle of up to 169.5°.

[0020] Example 3 The method for preparing the superhydrophobic film material of the present invention includes the following steps: (1) Preparation of PVDF-based film: (1.1) Preparation of casting solution: 18 parts by weight of commercial PVDF polymer solid particles and 10 parts by weight of pore-forming agent PEG4000 are added to 72 parts by weight of N,N-dimethylacetamide and mechanically stirred for 10 hours under water bath heating at 80°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (1.2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in an 80°C water bath for 8 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (1.3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 240μm to form a nascent film. (1.4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The membrane is then removed and placed in deionized water to remove residual organic solvents, thus obtaining a PVDF-based membrane. (2) Modification of the surface adhesive coating of dopamine: The PVDF base film obtained in step (1) is immersed in Tris-HCl buffer solution with a dopamine concentration of 1.5wt% for 24 hours, and then washed with ultrapure water. (3) Surface attachment of silica nanoparticles: Silica nanoparticles were placed in a Tris-HCl buffer solution with a pH of 7.8, sonicated for 60 minutes, and then allowed to stand at room temperature for 30 minutes to obtain a silica nanoparticle dispersion; the dopamine-modified PVDF membrane obtained in step (2) was immersed in the silica nanoparticle dispersion, and after immersion for 4 hours, it was taken out, washed several times with deionized water, and then washed several times with ethanol to obtain a PVDF membrane with micro-nano structures on the surface; the concentration of silica nanoparticles in the silica nanoparticle dispersion was 0.3 wt%; (4) Surface modification with perfluorinated low surface energy material: The PVDF membrane with surface micro-nano structure obtained in step (3) was immersed in an ethanol solution containing perfluorodecyltriethoxysilane. After immersion for 18 hours, it was taken out, washed several times with ethanol, and dried in an oven at 60°C for 3 hours to obtain a superhydrophobic PVDF membrane. The volume concentration of perfluorodecyltriethoxysilane in the ethanol solution was 0.3%.

[0021] (5) The prepared membrane was used in a direct contact membrane distillation device to treat ultrapure water containing 8 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 79 μg / L, thus achieving effective concentration.

[0022] The superhydrophobic PVDF membrane prepared in Example 3 has high resistance to water droplets, with a water contact angle of up to 169.7°.

[0023] Comparative Example 1 A method for preparing a PVDF hydrophobic membrane includes the following steps: (1) Preparation of casting solution: 14 parts by weight of commercial PVDF polymer solid particles and 6 parts by weight of pore-forming agent PEG4000 are added to 80 parts by weight of N-methylpyrrolidone. The mixture is mechanically stirred for 4 hours under a water bath heating condition of 60°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in a 60°C water bath for 4 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 200μm to form a nascent film. (4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The obtained membrane is then placed in deionized water to remove residual organic solvents, yielding a PVDF-based membrane. The surface scanning electron microscope and water contact angle are shown in the figures below. Figure 3 , Figure 4 As shown, the water contact angle is 81.9°, and the surface does not have superhydrophobic properties.

[0024] (5) The prepared membrane was used in a direct contact membrane distillation device to treat ultrapure water containing 10 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 39 μg / L. Effective concentration was not achieved.

[0025] Comparative Example 2 A method for preparing a PVDF hydrophobic membrane includes the following steps: (1) Preparation of PVDF-based film: (1.1) Preparation of casting solution: 18 parts by weight of commercial PVDF polymer solid particles and 10 parts by weight of pore-forming agent PEG4000 are added to 72 parts by weight of N,N-dimethylacetamide and mechanically stirred for 10 hours under water bath heating at 80°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (1.2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in an 80°C water bath for 8 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (1.3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 240μm to form a nascent film. (1.4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The membrane is then removed and placed in deionized water to remove residual organic solvents, thus obtaining a PVDF-based membrane. (2) Modification of the surface adhesive coating of dopamine: The PVDF base film obtained in step (1) is immersed in Tris-HCl buffer solution with a dopamine concentration of 1.5wt% for 24 hours, and then washed with ultrapure water. (3) Surface attachment of silica nanoparticles: Silica nanoparticles were placed in Tris-HCl buffer solution with a pH of 7.8, sonicated for 60 minutes, and then allowed to stand at room temperature for 30 minutes to obtain a silica nanoparticle dispersion; the PVDF membrane with surface modified dopamine obtained in step (2) was immersed in the silica nanoparticle dispersion, and after immersion for 4 hours, it was taken out, washed several times with deionized water, and then washed several times with ethanol to obtain a PVDF membrane with micro-nano structure on the surface; the concentration of silica nanoparticles in the silica nanoparticle dispersion was 0.3wt%.

[0026] The membrane prepared in Comparative Example 2 was used in a direct contact membrane distillation apparatus to treat ultrapure water containing 8 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 37.6 μg / L, which did not achieve effective concentration.

[0027] Comparative Example 3 A method for preparing a PVDF hydrophobic membrane includes the following steps: (1) Preparation of PVDF-based film: (1.1) Preparation of casting solution: 18 parts by weight of commercial PVDF polymer solid particles and 10 parts by weight of pore-forming agent PEG4000 are added to 72 parts by weight of N,N-dimethylacetamide and mechanically stirred for 10 hours under water bath heating at 80°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (1.2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in an 80°C water bath for 8 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (1.3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 240μm to form a nascent film. (1.4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The membrane is then removed and placed in deionized water to remove residual organic solvents, thus obtaining a PVDF-based membrane. (2) Modification of the surface adhesive coating of dopamine: The PVDF base film obtained in step (1) is immersed in Tris-HCl buffer solution with a dopamine concentration of 1.5wt% for 24 hours, and then washed with ultrapure water. (3) Surface modification with perfluorinated low surface energy material: The PVDF membrane with surface-modified dopamine obtained in step (2) was immersed in an ethanol solution containing perfluorodecyltriethoxysilane. After immersion for 18 hours, it was taken out, washed several times with ethanol, and dried in an oven at 60°C for 3 hours to obtain a PVDF hydrophobic membrane. The volume concentration of perfluorodecyltriethoxysilane in the ethanol solution was 0.3%.

[0028] The membrane prepared in Comparative Example 3 was used in a direct contact membrane distillation apparatus to treat ultrapure water containing 8 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 44 μg / L, which did not achieve effective concentration.

[0029] Comparative Example 4 A method for preparing a PVDF hydrophobic membrane includes the following steps: (1) Preparation of PVDF-based film: (1.1) Preparation of casting solution: 18 parts by weight of commercial PVDF polymer solid particles and 10 parts by weight of pore-forming agent PEG4000 are added to 72 parts by weight of N,N-dimethylacetamide and mechanically stirred for 10 hours under water bath heating at 80°C to ensure that the membrane material and pore-forming agent are uniformly dissolved. (1.2) Degassing of casting solution: After obtaining a clear and transparent casting solution, stop stirring and remove the stirring paddle. Let the casting solution stand in an 80°C water bath for 8 hours to degas, ensuring that the air bubbles in the casting solution are completely removed. (1.3) Film scraping: After the casting solution is allowed to stand and degas, it is naturally cooled to room temperature. The casting solution is slowly poured onto one end of the glass plate, and then the casting solution is spread on the glass plate with a thickness of 240μm to form a nascent film. (1.4) Phase transformation: The nascent membrane scraped out above is quickly immersed in a 25°C water bath. After solvent-non-solvent exchange, the casting solution undergoes phase transformation to form a membrane. The membrane is then removed and placed in deionized water to remove residual organic solvents, thus obtaining a PVDF-based membrane. (2) Surface adhesion of silica nanoparticles: Silica nanoparticles were partially dissolved in Tris-HCl buffer solution with a pH of 7.8, sonicated for 60 minutes, and then allowed to stand at room temperature for 30 minutes to obtain a silica nanoparticle dispersion; the PVDF substrate membrane was immersed in the silica nanoparticle dispersion for 4 hours, then removed, washed several times with deionized water, and then washed several times with ethanol to obtain a PVDF membrane; the concentration of silica nanoparticles in the silica nanoparticle dispersion was 0.3 wt%; (3) Surface modification with perfluorinated low surface energy material: The PVDF membrane with surface micro-nano structure obtained in step (3) was immersed in an ethanol solution containing perfluorodecyltriethoxysilane. After immersion for 18 hours, it was taken out, washed several times with ethanol, and dried in an oven at 60°C for 3 hours to obtain a hydrophobically modified PVDF membrane. The volume concentration of perfluorodecyltriethoxysilane in the ethanol solution was 0.3%.

[0030] The membrane prepared in Comparative Example 4 was used in a direct contact membrane distillation apparatus to treat ultrapure water containing 8 μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system were set to 20℃ and 40℃, respectively. The volume of the treated ultrapure water was concentrated to 1 / 10, and the TOC concentration was measured to be 46 μg / L, which did not achieve effective concentration.

Claims

1. A method for preparing a superhydrophobic film material, characterized in that, Includes the following steps: (1) Immerse the PVDF base membrane in Tris-HCl buffer containing dopamine, remove it after immersion, wash it, and obtain a PVDF membrane with surface modified with dopamine. (2) Disperse silica nanoparticles in Tris-HCl buffer solution and sonicate to obtain solution A; A PVDF membrane with dopamine surface modification was immersed in solution A, and after immersion, it was taken out and washed to obtain a PVDF membrane with micro-nano structure on the surface. (3) The PVDF membrane with micro-nano structure on the surface is immersed in an ethanol solution containing perfluorinated substances. After immersion, it is taken out, cleaned and dried to obtain a superhydrophobic PVDF membrane.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass concentration of dopamine in the Tris-HCl buffer is 0.3~1.5%.

3. The preparation method according to claim 1, characterized in that: In step (1), the soaking time is 12 to 24 hours.

4. The preparation method according to claim 1, characterized in that: In step (2), the pH value of the Tris-HCl buffer is 7.8; first, sonicate for 20-60 minutes, then let it stand at room temperature for 15-30 minutes.

5. The preparation method according to claim 1, characterized in that: In step (2), the particle size of the silica nanoparticles is 100~200nm; in solution A, the mass concentration of the silica nanoparticles is 0.1~0.3%.

6. The preparation method according to claim 1, characterized in that: In step (2), the soaking time is 2 to 4 hours.

7. The preparation method according to claim 1, characterized in that: In step (3), the perfluorinated substance is at least one of heptadecafluorodecyltrimethoxysilane, perfluorooctyltrimethoxysilane or perfluorodecyltriethoxysilane; the volume concentration of the perfluorinated substance in the ethanol solution is 0.1~0.3%.

8. The preparation method according to claim 1, characterized in that: In step (3), the soaking time is 12 to 24 hours; the drying temperature is 40 to 60℃ and the drying time is 1 to 3 hours.

9. The application of the superhydrophobic membrane material prepared by the method of claim 1 in the treatment of trace organic matter in concentrated water.

10. The application according to claim 9, characterized in that: The prepared membrane is used in a direct contact membrane distillation apparatus to treat ultrapure water containing 5~10μg / L TOC. The circulating temperatures of the hot and cold sides of the membrane distillation system are set to 20~25℃ and 40~45℃, respectively, to concentrate the volume of the treated ultrapure water to 1 / 10~1 / 5.

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