A polyvinylidene fluoride microporous filter and a preparation method and application thereof

Abstract

The application belongs to the technical field of microporous filtration, and particularly relates to a polyvinylidene fluoride microporous filter and a preparation method and application thereof. The polyvinylidene fluoride, acetone, N,N-dimethylformamide and sodium chloride are mixed to obtain a mixed slurry, the mixed slurry is placed and formed in an environment containing water vapor, then the solvent is evaporated and removed in an air environment, and finally the polyvinylidene fluoride microporous filter is obtained by washing with water. The polyvinylidene fluoride is dissolved by using acetone and N,N-dimethylformamide, and sodium chloride is used as a pore-forming agent, so that the obtained polyvinylidene fluoride microporous filter has a significant purification effect on sewage, has strong mechanical stability, is low in cost, and is suitable for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of microporous filtration technology, specifically relating to a polyvinylidene fluoride microporous filter, its preparation method, and its application. Background Technology

[0002] Wastewater generally refers to polluted wastewater from domestic and industrial processes. With industrial development and improved living standards, the amount of wastewater generated in both urban and rural areas is increasing year by year. Urban wastewater includes not only domestic sewage from urban residents but also industrial wastewater from factories, making its composition more complex. Rural wastewater mainly consists of domestic sewage and rainwater. The main pollutants in wastewater include pathogens, oxygen-consuming pollutants, plant nutrients, toxic pollutants, and impurities.

[0003] Wastewater treatment filters are primarily used to treat wastewater, enabling it to be recycled. Currently, the main wastewater treatment filtration methods include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. These are mainly classified according to the size of the pores and the size of particles they can remove from the wastewater, utilizing the pore size to categorize particles of different sizes.

[0004] There are many precedents both domestically and internationally for using polymers in filter fabrication. Polyvinylidene fluoride (PVDF), as a polymer material, has been documented in existing papers as a potential candidate for filter preparation. However, current wastewater filters made from PVDF exhibit poor filtration efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a polyvinylidene fluoride microporous filter, its preparation method, and its application. The polyvinylidene fluoride microporous filter prepared by this invention has a significant effect on wastewater purification, and is low in cost, making it suitable for industrial application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a polyvinylidene fluoride microporous filter, comprising the following steps:

[0008] Polyvinylidene fluoride, acetone, N,N-dimethylformamide and sodium chloride are mixed to obtain a mixed slurry;

[0009] The mixed slurry is placed in a mold and left to stand in an environment containing water vapor to form a first molded body.

[0010] The first molded body is evaporated in air to remove the solvent, resulting in the second molded body;

[0011] The second molded body is washed with water to obtain the polyvinylidene fluoride microporous filter.

[0012] Preferably, the mass ratio of polyvinylidene fluoride to acetone is 0.8 to 1:3;

[0013] The mass ratio of acetone to N,N-dimethylformamide is 2.8–3.2:2.

[0014] Preferably, the mass ratio of the total mass of the polyvinylidene fluoride, acetone, and N,N-dimethylformamide to the mass of the sodium chloride is 100:(1-20).

[0015] Preferably, the relative humidity of the water vapor-containing environment is 60-80%, and the static molding temperature is room temperature for 2-3 days.

[0016] Preferably, the relative humidity of the air environment is ≤30%, and the temperature for evaporation to remove the solvent is room temperature, and the time is 2 to 3 days.

[0017] The present invention provides a polyvinylidene fluoride microporous filter prepared by the preparation method described in the above technical solution.

[0018] Preferably, the pore size of the polyvinylidene fluoride microporous filter is 1.18 to 23.52 μm.

[0019] Preferably, the pore density of the polyvinylidene fluoride microporous filter is 4161 to 14111 pores / cm². 2 ;

[0020] The porosity of the polyvinylidene fluoride microporous filter is 64.2–77.3%.

[0021] This invention provides the application of the polyvinylidene fluoride microporous filter described above in wastewater treatment.

[0022] Preferably, the filtration device used for wastewater filtration by the polyvinylidene fluoride microporous filter includes a purification storage container 2 with one open end. A movable sealing piston 3 is provided at the open end of the purification storage container 2. The other end of the purification storage container 2, corresponding to the open end, is connected to a wastewater flow pipe 5. The polyvinylidene fluoride microporous filter 1 is provided at one end of the wastewater flow pipe 5 near the purification storage container 2.

[0023] This invention provides a method for preparing a polyvinylidene fluoride (PVDF) microporous filter, comprising the following steps: mixing PVDF, acetone, N,N-dimethylformamide, and sodium chloride to obtain a mixed slurry; placing the mixed slurry in a mold and allowing it to stand in an environment containing water vapor to form a first molded body; evaporating the first molded body in an air environment to remove the solvent, thereby obtaining a second molded body; and washing the second molded body with water to obtain the PVDF microporous filter. This invention utilizes acetone and N,N-dimethylformamide to dissolve polyvinylidene fluoride (PVDF), while using sodium chloride as a pore-forming agent. Then, in an environment containing water vapor, taking advantage of the fact that PVDF is insoluble in water, but water is soluble in both solvents, the water vapor in the environment contacts the PVDF, causing it to precipitate. Simultaneously, the mutual solubility of acetone, N,N-dimethylformamide, and water vapor further reduces the solubility of PVDF, leading to further precipitation and obtaining a pre-formed first molded body. Acetone, N,N-dimethylformamide, and water are then evaporated in an air environment to remove them, allowing all the PVDF to precipitate. During solvent evaporation, since the first molded body has already been pre-formed, pore structures are formed in the original solvent locations after solvent evaporation. Simultaneously, during solvent removal, sodium chloride precipitates along with PVDF, occupying some positions between PVDF particles. Finally, water washing removes the sodium chloride from the PVDF, thus preserving a large number of interconnected pore structures within the PVDF. Therefore, the polyvinylidene fluoride microporous filter prepared by this invention has a significant effect on wastewater purification, strong mechanical stability, low cost, and is suitable for industrial application.

[0024] This invention provides a polyvinylidene fluoride (PVDF) microporous filter prepared by the method described above. The PVDF microporous filter provided by this invention can filter impurities in wastewater, purify wastewater, thereby alleviating the problem of water scarcity, and can be applied in filtration, purification, and other fields.

[0025] In this invention, the filtration device used for wastewater filtration by the polyvinylidene fluoride (PVDF) microporous filter includes a purification storage container 2 with one open end. A movable sealing piston 3 is provided at the open end of the purification storage container 2. The other end of the purification storage container 2, corresponding to the open end, is connected to a wastewater flow pipe 5. The PVDF microporous filter 1 is located at the end of the wastewater flow pipe 5 closest to the purification storage container 2. The filtration device provided by this invention can provide negative pressure through the movable sealing piston 3, enabling simple suction filtration of wastewater by the PVDF microporous filter. Attached Figure Description

[0026] Figure 1 The filtration device used in the embodiments of the present invention;

[0027] Figure 1In the middle: 1 is a polyvinylidene fluoride microporous filter, 2 is a purification storage container, 3 is a movable sealing piston, 4 is a connecting rod, 5 is a sewage flow pipe, and 6 is a connecting handle;

[0028] Figure 2 Scanning electron microscope image of the polyvinylidene fluoride microporous filter prepared for Comparative Example 1;

[0029] Figure 3 A scanning electron microscope image of the polyvinylidene fluoride microporous filter prepared in Example 2;

[0030] Figure 4 A scanning electron microscope image of the polyvinylidene fluoride microporous filter prepared in Example 3;

[0031] Figure 5 A scanning electron microscope image of the polyvinylidene fluoride microporous filter prepared in Example 4;

[0032] Figure 6 A scanning electron microscope image of the polyvinylidene fluoride microporous filter prepared in Example 5;

[0033] Figure 7 The transmittance test results are for the filtered liquid and simulated wastewater obtained in Comparative Example 2 and Example 6;

[0034] Figure 8 The flowcharts for the preparation of polyvinylidene fluoride microporous filters are shown in the examples and comparative examples.

[0035] Figure 9 The curves showing the changes in pore size and pore density of polyvinylidene fluoride microporous filters prepared in the examples and comparative examples as a function of the concentration of sodium chloride nanoparticles added during the preparation process are shown.

[0036] Figure 10 This is a schematic diagram showing the colors of the carbon ink before and after filtration in Comparative Example 2 and Example 6;

[0037] Figure 11 The images show actual laboratory-assembled filtration devices for Comparative Example 2 and Example 6. Detailed Implementation

[0038] This invention provides a method for preparing a polyvinylidene fluoride microporous filter, comprising the following steps:

[0039] Polyvinylidene fluoride, acetone, N,N-dimethylformamide and sodium chloride are mixed to obtain a mixed slurry;

[0040] The mixed slurry is placed in a mold and left to stand in an environment containing water vapor to form a first molded body.

[0041] The first molded body is evaporated in air to remove the solvent, resulting in the second molded body;

[0042] The second molded body is washed with water to obtain the polyvinylidene fluoride microporous filter.

[0043] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0044] This invention mixes polyvinylidene fluoride (PVDF), acetone, N,N-dimethylformamide (NDM), and sodium chloride to obtain a mixed slurry. In this invention, the PVDF is preferably PVDF particles, and the particle size of the PVDF particles is not particularly important. The sodium chloride is preferably sodium chloride nanoparticles, and the particle size of the sodium chloride nanoparticles is preferably 1.1–1.52 μm. The mass ratio of PVDF to acetone is preferably 0.8–1:3, more preferably 0.85–0.95:3. The mass ratio of acetone to N,N-dimethylformamide is preferably 2.8–3.2:2, more preferably 2.9–3.1:2, and most preferably 3.03:2. The mass ratio of the total mass of PVDF, acetone, and N,N-dimethylformamide to the mass of sodium chloride is preferably 100:(1–20), specifically preferably 100:1, 100:5, 100:10, or 100:20.

[0045] In this invention, the mixing preferably includes the following steps: dissolving the polyvinylidene fluoride (PVDF) in acetone and N,N-dimethylformamide to obtain a PVDF solution; and mixing the PVDF solution with sodium chloride. The dissolution is carried out under stirring conditions, preferably magnetic stirring, with a preferred stirring speed of 1000 r / min, a preferred dissolution temperature of 80°C, and a preferred dissolution time of 1 h. Preferably, the obtained PVDF solution is cooled to room temperature before being mixed with the sodium chloride.

[0046] After obtaining the mixed slurry, the present invention places the mixed slurry in a mold and allows it to stand in an environment containing water vapor to form a first molded body.

[0047] In this invention, the mixed slurry is formed into a cylindrical shape in a mold, and the base area of ​​the cylinder is 3-4 cm². 2 The height is 0.2-3 cm. The relative humidity of the water vapor-containing environment is preferably 60-80%, more preferably 65-75%, and the settling temperature is preferably room temperature, with a settling time of 2-3 days. In a specific embodiment of the invention, the mold is preferably a wide-mouthed beaker. Preferably, the wide-mouthed beaker containing the mixed slurry is placed in another container with a larger volume and a certain amount of water is injected into the container. After sealing the container, the settling process is carried out.

[0048] In this invention, during the static molding process, water vapor in the environment comes into contact with polyvinylidene fluoride in the mixed slurry, causing polyvinylidene fluoride to precipitate. At the same time, acetone and N,N-dimethylformamide, as well as water vapor in the environment, dissolve in each other, reducing the solubility of polyvinylidene fluoride and causing further precipitation of polyvinylidene fluoride, thereby obtaining the first molded body in the preliminary stage.

[0049] After obtaining the first molded body, the solvent is evaporated in the air to obtain the second molded body.

[0050] In this invention, during the solvent removal evaporation process, the first molded body is preferably still retained in the mold. The relative humidity of the air environment is preferably ≤30%, more preferably ≤20%; the solvent removal temperature is preferably room temperature, and the time is preferably 2-3 days. This invention removes acetone, N,N-dimethylformamide, and water by evaporation in an air environment, causing all polyvinylidene fluoride to precipitate. During the solvent evaporation process, since the first molded body has already been preliminarily formed, a porous structure is formed at the original solvent locations after solvent evaporation. Simultaneously, during the solvent removal process, sodium chloride precipitates together with polyvinylidene fluoride, occupying some positions between polyvinylidene fluoride layers.

[0051] After obtaining the second molded body, the present invention washes the second molded body with water to obtain the polyvinylidene fluoride microporous filter.

[0052] In this invention, the water is preferably deionized water. The washing is preferably performed 2 to 3 times. This invention removes sodium chloride from polyvinylidene fluoride (PVDF) through water washing, thereby preserving a relatively large interconnected pore structure within the PVDF.

[0053] The present invention provides a polyvinylidene fluoride microporous filter prepared by the preparation method described in the above technical solution.

[0054] In this invention, the pore size of the polyvinylidene fluoride microporous filter is preferably 1.18–23.52 μm, more preferably 1.2–23 μm, and even more preferably 1.5–20 μm.

[0055] In this invention, the pore density of the polyvinylidene fluoride microporous filter is preferably 4161 to 14111 pores / cm². 2 More preferably, 4200–14000 per cm 2 .

[0056] In this invention, the porosity of the polyvinylidene fluoride microporous filter is preferably 64.2-77.3%, more preferably 64.5-77%.

[0057] In this invention, the polyvinylidene fluoride microporous filter is cylindrical in shape with a base area of ​​3-4 cm².2 The height is 0.2 to 0.3 cm.

[0058] The polyvinylidene fluoride microporous filter provided by this invention is a filter with a certain thickness and a block-like morphology. Compared with the polyvinylidene fluoride filter membranes disclosed in the prior art, the polyvinylidene fluoride filter provided by this invention has better mechanical strength and is not easily damaged during use.

[0059] The preparation method provided by this invention uses sodium chloride as a pore-forming agent. It utilizes not only solvent evaporation to form pores but also the pores induced by sodium chloride particles. This invention allows polyvinylidene fluoride (PVDF) to slowly precipitate in a water vapor environment, gradually settling at the bottom of a mold. The resulting PVDF microporous filter, formed by stacking layers of membranes, exhibits a pore structure that includes not only diffuse pores from solvent evaporation but also interconnected pores left by the washing away of sodium chloride. The PVDF filter provided by this invention offers better wastewater filtration than existing PVDF filter membranes and is less prone to damage.

[0060] This invention provides the application of the polyvinylidene fluoride microporous filter described above in wastewater treatment.

[0061] like Figure 1 As shown, in this invention, the filtration device used for wastewater filtration by the polyvinylidene fluoride microporous filter preferably includes a purification storage container 2 with one open end. A movable sealing piston 3 is provided at the open end of the purification storage container 2. The other end of the purification storage container 2, corresponding to the open end, is connected to a wastewater flow pipe 5. The polyvinylidene fluoride microporous filter is located at the end of the wastewater flow pipe 5 near the purification storage container 2. In this invention, the sealing piston 3 is preferably fixedly connected to a connecting rod 4, and the connecting rod 4 is fixedly connected to a connecting handle 6. In this invention, the preferred application is as follows: the polyvinylidene fluoride microporous filter 1 described above is placed at the end of the wastewater flow pipe 5 near the purification storage container 2. Wastewater is introduced into the wastewater flow pipe 5. The movable sealing piston 3, via the connecting rod 4 and the connecting handle 6, creates a negative pressure less than atmospheric pressure in the purification storage container 2. Under the action of this pressure difference, the wastewater in the wastewater flow pipe 5 is filtered through the polyvinylidene fluoride microporous filter, resulting in filtered clean water in the purification storage container 2.

[0062] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0063] The following examples and comparative examples adopt Figure 8 The preparation process shown is carried out.

[0064] Example 1

[0065] Place 1g of polyvinylidene fluoride into a beaker, add 2.2mL of N,N-dimethylformamide, then add 4mL of acetone. Place a magnetic rotor in the beaker, seal it, and then use a temperature-controlled magnetic stirrer to stir at a constant temperature of 80℃ for one hour at 1000 revolutions per minute. Let it stand for three hours to cool.

[0066] Comparative Example 1

[0067] The liquid in Example 1 was subjected to the following operation: the sealing cap of the beaker was opened, 0.65g of the liquid was pipetted into a new small beaker, and then placed into a large beaker with a volume of 200mL and containing 50mL of water. The large beaker was then sealed and left for three days. After that, the sealing cap was opened, the beaker was removed, and it was left to stand in the atmosphere for three days to evaporate the remaining liquid. The beaker was then rinsed three times with deionized water to obtain a polyvinylidene fluoride microporous filter.

[0068] Example 2

[0069] The liquid in Example 1 was processed as follows: the sealed cap of the beaker was opened, 0.65g of the liquid was pipetted into a new small beaker, 0.0065g of sodium chloride nanoparticles were added, and then the beaker was placed into a large beaker with a capacity of 200mL and containing 50mL of water. The large beaker was then sealed and left for three days. After that, the sealed cap was opened, the beaker was removed, and it was left to stand in the atmosphere for three days to allow the remaining liquid to evaporate. The beaker was then rinsed three times with deionized water to obtain a polyvinylidene fluoride microporous filter.

[0070] Example 3

[0071] The liquid in Example 1 was processed as follows: the sealed cap of the beaker was opened, 0.65g of the liquid was pipetted into a new small beaker, 0.0325g of sodium chloride nanoparticles were added, and then the beaker was placed into a large beaker with a capacity of 200mL and containing 50mL of water. The large beaker was then sealed and left for three days. After that, the sealed cap was opened, the beaker was removed, and it was left to stand in the atmosphere for three days to evaporate the remaining liquid. The beaker was then rinsed three times with deionized water to obtain a polyvinylidene fluoride microporous filter.

[0072] Example 4

[0073] The liquid in Example 1 was subjected to the following operation: the sealed cap of the beaker was opened, 0.65g of the liquid was pipetted into a new small beaker, 0.065g of sodium chloride nanoparticles were added, and then the beaker was placed into a large beaker with a capacity of 200mL and containing 50mL of water. The large beaker was then sealed and left for three days. After that, the sealed cap was opened, the beaker was removed, and it was left to stand in the atmosphere for three days to evaporate the remaining liquid. The beaker was then washed three times with deionized water to obtain a polyvinylidene fluoride microporous filter.

[0074] Example 5

[0075] The liquid in Example 1 was processed as follows: the sealed cap of the beaker was opened, 0.65g of the liquid was pipetted into a new small beaker, 0.13g of sodium chloride nanoparticles were added, and then the beaker was placed into a large beaker with a capacity of 200mL and containing 50mL of water. The large beaker was then sealed and left for three days. After that, the sealed cap was opened, the beaker was removed, and it was left to stand in the atmosphere for three days to evaporate the remaining liquid. The beaker was then rinsed three times with deionized water to obtain a polyvinylidene fluoride microporous filter.

[0076] Comparative Example 2

[0077] Take a pipette tip and fully fill it with the filter obtained in Comparative Example 1. Then, select a 5mL syringe, remove the needle, and insert the pipette tip containing the filter into the syringe syringe in reverse, ensuring a tight seal at the connection point (e.g., ...). Figure 11 As shown). Wastewater was simulated using carbon ink (Hero brand carbon ink) and deionized water (volume ratio of carbon ink to deionized water was 1:1). Figure 10 (As shown in the "unfitted" sample) Pour wastewater into the upper part of the filter device, pull the piston (from the 0mL position to the 1mL position), and use a square piece of wood to wedge between the piston and the tube body to prevent the syringe piston from retracting, continuously providing negative pressure. After the wastewater is filtered, the filtered sample solution is obtained. Remove the syringe and the pipette tip, and aspirate the filtered liquid to obtain the filtered wastewater, as shown in the image. Figure 10 The actual product is shown as 0 wt%.

[0078] Example 6

[0079] Take a pipette tip and fill it completely with the filter obtained in Example 4. Then, select a 5mL syringe, remove the syringe needle, and insert the pipette tip containing the filter into the syringe needle in reverse, ensuring a thorough seal at the connection point (e.g., ...). Figure 11 As shown). Wastewater was simulated using carbon ink (Hero brand carbon ink) and deionized water (volume ratio of carbon ink to deionized water was 1:1). Figure 10 (As shown in the "unfitted" sample) Pour wastewater into the upper part of the filter device, pull the piston (from the 0mL position to the 1mL position), and use a square piece of wood to wedge between the piston and the tube body to prevent the syringe piston from retracting, continuously providing negative pressure. After the wastewater is filtered, the filtered sample solution is obtained. Remove the syringe and the pipette tip, and aspirate the filtered liquid to obtain the filtered wastewater, as shown in the image. Figure 10 The actual sample is shown as 10 wt%.

[0080] Scanning electron microscopy was performed on the polyvinylidene fluoride microporous filters obtained in Comparative Examples 1 and Examples 2-5. The results are as follows: Figures 2-6 ,Depend on Figures 2-6 The scanning electron microscope images of the polyvinylidene fluoride (PVDF) microporous filters obtained in Comparative Examples 1 and Examples 2-5 show that as the mass of sodium chloride nanoparticles added increases, the number of pores in the PVDF microporous filters increases, and the pore density decreases. This is likely because more sodium chloride nanoparticles occupy more space, increasing the probability of them agglomerating into larger pores, resulting in larger pore sizes, fewer pores, and lower pore density.

[0081] The porosity of the polyvinylidene fluoride microporous filters obtained in Comparative Examples 1 and Examples 2-5 was tested, and the results are shown in Table 1 and... Figure 9 As shown in Table 1. The specific procedure involves completely immersing the polyvinylidene fluoride (PVDF) microporous filter in water for 4 hours, then drying it in a dryer for 2 hours to evaporate the moisture. The change in the filter's mass before and after the process is measured. Then, using the density-volume-mass formula, the porosity of the PVDF filter is calculated. Porosity is specifically the percentage of the filter's volume relative to the volume of the pores. (See Table 1 and...) Figure 9 It can be seen that the porosity of the filter with added sodium chloride nanoparticles is significantly improved compared to the filter without added sodium chloride nanoparticles. Furthermore, as the amount of added sodium chloride nanoparticles increases, the maximum pore size and the middle pore size in the filter structure increase, while the pore density decreases.

[0082] Table 1 shows the porosity test results of the polyvinylidene fluoride microporous filters prepared in Comparative Example 1 and Examples 2-5.

[0083] 0 0.35 1 64.21 5 66.26 10 66.05 20 77.29

[0084] The transmittance of the filtered liquids obtained in Comparative Example 2 and Example 6, and the simulated wastewater, was tested. First, the instrument was normalized using a glass plate without added liquid. Then, the three liquids were each dripped onto the glass plate, and their transmittance was measured. The results are as follows: Figure 7 .Depend on Figure 7 It can be seen that the transmittance of different liquids varies. The main difference is the increase in transmittance between unfiltered, unfiltered, and filtered liquids with added sodium chloride nanoparticles. This indicates that the filter without added sodium chloride nanoparticles also has a certain purification effect on wastewater. The filter with added sodium chloride nanoparticles has a better filtration effect than the one without. This may be because the filter with added sodium chloride nanoparticles has a more suitable pore size and pore density, or it may be that the passages in the filter without added sodium chloride nanoparticles are not sufficiently connected, and wastewater cannot pass through the pores, so it cannot effectively filter impurities.

[0085] The polyvinylidene fluoride (PVDF) microporous filter preparation method provided by this invention uses low-cost materials and requires common experimental equipment. The manufacturing process is simple and convenient for preparing PVDF microporous filters. More importantly, the filtration performance is significantly improved after adding sodium chloride nanoparticles, which can be used to make microporous filters. The matching filtration device can also filter automatically. The device is simple to prepare and only requires pulling open the syringe to form a negative pressure, which can continuously filter sewage.

[0086] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride microporous filter, characterized in that, Includes the following steps: Polyvinylidene fluoride, acetone, N,N-dimethylformamide, and sodium chloride are mixed to obtain a mixed slurry. The mass ratio of polyvinylidene fluoride to acetone is 0.8~1:3, the mass ratio of acetone to N,N-dimethylformamide is 2.8~3.2:2, and the mass ratio of the total mass of polyvinylidene fluoride, acetone, and N,N-dimethylformamide to the mass of sodium chloride is 100:(5~20). The sodium chloride is sodium chloride nanoparticles with a particle size of 1.1~1.52 μm; The mixed slurry is placed in a mold and left to stand in a sealed environment containing water vapor to form a first molded body; the relative humidity of the water vapor-containing environment is 60-80%, the standing temperature is room temperature, and the time is 2-3 days. The first molded body is evaporated in an air environment to remove the solvent, thereby obtaining the second molded body. The relative humidity of the air environment is ≤30%, and the temperature for evaporation to remove the solvent is room temperature, and the time is 2 to 3 days. The second molded body was washed with water to obtain the polyvinylidene fluoride microporous filter; The pore size of the polyvinylidene fluoride microporous filter is 1.18~23.52μm; The pore density of the polyvinylidene fluoride microporous filter is 4161~14111 pores / cm³. 2 ; The porosity of the polyvinylidene fluoride microporous filter is 66.26~77.3%.

2. The polyvinylidene fluoride microporous filter prepared by the method of claim 1; wherein the pore size of the polyvinylidene fluoride microporous filter is 1.18~23.52 μm; The pore density of the polyvinylidene fluoride microporous filter is 4161~14111 pores / cm³. 2 ; The porosity of the polyvinylidene fluoride microporous filter is 66.26~77.3%.

3. The application of the polyvinylidene fluoride microporous filter according to claim 2 in wastewater treatment.

4. The application according to claim 3, characterized in that, The filtration device used for wastewater filtration by the polyvinylidene fluoride microporous filter includes a purification storage container (2) with one open end. A movable sealing piston (3) is provided at the open end of the purification storage container (2). The other end of the purification storage container (2) corresponding to the open end is connected to a wastewater flow pipe (5). The polyvinylidene fluoride microporous filter (1) is provided at one end of the wastewater flow pipe (5) near the purification storage container (2).

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