Preparation method and application of PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness

Abstract

The invention provides a preparation method and application of a PVDF (polyvinylidene fluoride)-based hollow fiber nanofiltration membrane with piezoelectric responsiveness. Specifically, firstly, PVDF, an inorganic pore-foaming agent, a carbon-based conductive material with a piezoelectric property, an organic reactive monomer (TMC) and an organic solvent are prepared into a uniform viscous dispersion liquid according to a certain proportion, then polyamine molecules and water are mixed according to a certain proportion to serve as a core liquid, finally, spinning is conducted through a non-solvent induced phase separation-interfacial polymerization synchronous preparation technology (NIPS-IP), and the PVDF / TMC composite material is obtained. And the PVDF hollow fiber nanofiltration membrane with piezoelectric responsiveness is prepared in one step. The method is simple and convenient to operate, and the prepared nanofiltration membrane is high in beta-PVDF crystal form content (the relative proportion of the beta crystal form is not lower than 90%). In addition, a carbon-based conductive material which can form a continuous phase and has a piezoelectric property is added into the dispersion liquid, so that the content of a beta-PVDF crystal form can be further increased, a continuous path can be formed in the membrane after the dispersion liquid is combined with PVDF, the surface charge density of the membrane is remarkably improved under the driving of nanofiltration pressure, and an internal electric field is generated in a membrane body; the selective separation performance of multivalent / monovalent mixed ions is enhanced through the triple synergistic effect of size screening, surface strong electrostatic interaction and internal electric field strengthening.

Description

Technical Field

[0001] The present invention belongs to the field of polymer separation membranes, and particularly relates to a preparation method and application of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness Background Art

[0002] The separation of mixed salt ions with different valence states has important research significance in the fields of lithium extraction from salt lake brine, industrial wastewater treatment, seawater desalination, and brackish water desalination. For example, seawater and brackish water contain a large amount of salts, mainly in the form of monovalent ions such as Na + and multivalent ions such as Mg 2+ , Ca 2+ . Usually, one or several specific ions need to be separated. Traditional separation methods such as precipitation, solvent extraction, and distillation are restricted in development due to disadvantages such as complex operations, poor separation effects, and high costs. Compared with traditional mixed ion separation technologies, membrane separation methods have attracted much attention due to their advantages of low cost and low energy consumption

[0003] Currently, the commercial products applied to the separation of mixed ions with different valence states are mainly spiral wound nanofiltration membranes. This technology first prepares a polysulfone (PSF) or polyethersulfone (PES) ultrafiltration membrane on the surface of a non-woven support by the non-solvent induced phase separation method (NIPS), and then forms a dense separation layer of dozens to 200 nm on the surface of the ultrafiltration membrane by interfacial polymerization (usually using piperazine (PIP) as the aqueous phase monomer and trimesoyl chloride (TMC) as the organic phase monomer). The hollow fiber type is another industrialized membrane module form, which has advantages such as high packing density and no need for a support. Although many studies have been carried out on the preparation of hollow fiber nanofiltration membranes, there are few industrial products. For example, Chinese invention patent CN114471181A discloses a preparation method of a highly permeable zwitterionic hollow fiber nanofiltration membrane. This method has two preparation methods: internal pressure type and external pressure type. The internal pressure type is to first make an organic hollow fiber substrate into a membrane module, inject an aqueous solution containing inorganic salts and zwitterionic polyamine, then remove the residual aqueous phase, and then inject an organic phase solution containing polyacyl chloride for interfacial polymerization. Finally, it is heat-treated and immersed in deionized water for storage; the external pressure type is to infiltrate the hollow fiber substrate with an aqueous solution, remove the residual aqueous phase on the outer surface, then soak it in an organic phase solution for polymerization, and the subsequent steps are similar to those of the internal pressure type. The hollow fiber nanofiltration membrane prepared by this method has a maximum pure water flux of about 25Lm -2 h -1 and a MgSO 4Removal rate. However, the interfacial polymerization in the preparation process is carried out in two steps, and the parameters are difficult to control under the action of gravity, and the price of the zwitterionic polyamine used is very expensive. Therefore, it is not suitable for large-scale industrial production considering cost and structural controllability. Another example is that Chinese invention CN115155339A discloses a hollow fiber nanofiltration membrane and its preparation method. This invention first prepares a hollow fiber nanofiltration membrane substrate, and then immerses it in modified solution A, modified solution B, and crosslinking solution C in sequence, and after air-drying, heat treatment is carried out at 80 °C to obtain a hollow fiber nanofiltration membrane. The hollow fiber nanofiltration membrane prepared by this invention has a maximum permeation flux of about 30L m -2 h -1 and a maximum Na 2 SO 4 removal rate of about 98%. However, the operation steps of this invention are relatively complex, the controllability is poor, it is time-consuming (the interfacial polymerization is still carried out in two steps), and the production efficiency is low. Therefore, it is not suitable for modern industrial production either.

[0004] The selective separation mechanism of the nanofiltration membrane for mixed ions is based on the "size sieving - electrostatic interaction" synergistic separation mechanism, which requires the separation layer to have high density and high positive charge density. Obviously, the negatively charged nanofiltration membrane prepared by PIP is not applicable, and using polyethyleneimine (PEI) instead of PIP can increase the positive charge density on the membrane surface and eliminate the acid-binding agent, but the too dense separation layer also increases the retention of monovalent ions and reduces the effect of selective separation. That is to say, it is difficult for a positively charged nanofiltration membrane driven only by pressure to achieve efficient selective separation of mixed ions. It is found that by applying an electric field on both sides of the membrane, the selective separation performance of the nanofiltration membrane for mixed ions can be significantly improved, but the technical difficulty of applying an electric field on the inner and outer sides of the hollow fiber is relatively large. Therefore, the key is how to form a high charge density on the membrane surface and generate an electric field inside the hollow fiber nanofiltration membrane under pressure operation.

[0005] The piezoelectric effect refers to the phenomenon that certain dielectrics are polarized internally when subjected to external forces in a certain direction, resulting in a potential difference (electric field) on the two opposite surfaces of the material. Researchers have found that polyvinylidene fluoride (PVDF) has a piezoelectric effect, and its piezoelectric effect mainly comes from the β-crystalline form inside the material. Therefore, using PVDF as the film-making raw material and optimizing the relative content of the β-crystalline form in the film to improve the piezoelectric performance is a new method to solve the poor selective separation performance and the difficulty in commercialization of hollow fiber nanofiltration membranes. However, the conventional film-making process has limited improvement in the relative content of the β-crystalline form inside the PVDF membrane, making it insufficient to rely solely on the piezoelectric output of PVDF. Introducing other carbon-based conductive materials with piezoelectric properties can not only increase the content of the β-crystalline form of PVDF, but also enhance the surface charge density of the membrane under the driving of nanofiltration pressure, and the continuous path formed can create an internal electric field, which can generate different forces with the same ions of different valence states migrating inside it to further differentiate their mass transfer rates, ultimately achieving the efficient separation of mixed ions of different valence states.

[0006] To address the above problems, the present invention prepares a piezoelectric-responsive PVDF-based hollow fiber nanofiltration membrane by a one-step method. Specifically, using PVDF as the film-making raw material, inorganic additives as pore-forming agents, carbon-based materials with piezoelectric properties to construct a conductive path, TMC as the organic-phase reaction monomer, and formulating the above substances with organic solvents into a uniform dispersion liquid. Then, mixing polyamine molecules and water in a certain proportion as the core liquid, and finally spinning through the synchronous preparation technology of "non-solvent induced phase separation-interfacial polymerization" (NIPS-IP) to directly prepare a piezoelectric-responsive PVDF hollow fiber nanofiltration membrane in one step. This method is simple to operate and the prepared nanofiltration membrane has a high content of β-PVDF crystalline form (the relative proportion of the β-crystalline form is not less than 90%). In addition, adding carbon-based conductive materials with piezoelectric properties that can form a continuous phase in the dispersion liquid can not only further increase the content of the β-PVDF crystalline form, but also form a continuous path in the membrane after combining with PVDF, significantly enhancing the surface charge density of the membrane under the driving of nanofiltration pressure and generating an internal electric field in the membrane body, and enhancing the selective separation performance of "multivalent / monovalent" mixed ions through the triple synergistic effect of "size sieving-surface strong electrostatic interaction-internal electric field strengthening". Summary of the Invention

[0007] Aiming at the existing problems, the purpose of the present invention is to provide a preparation method and product of a piezoelectric-responsive PVDF hollow fiber nanofiltration membrane.

[0008] Technical solution of the present invention: A preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness. Specifically, first, a certain proportion of PVDF, inorganic additives, carbon-based conductive materials with piezoelectric properties, organic reaction monomers (TMC), and organic solvents are formulated into a uniform viscous dispersion liquid. Then, polyamine molecules and water are mixed in a certain proportion as the core liquid. Finally, through the non-solvent induced phase separation-interfacial polymerization synchronous preparation technology (NIPS-IP) spinning, a PVDF hollow fiber nanofiltration membrane with piezoelectric responsiveness is prepared in one step. This method is simple to operate and the prepared nanofiltration membrane has a high content of β-PVDF crystal form (the relative proportion of β crystal form is not less than 90%). In addition, adding carbon-based conductive materials with piezoelectric properties that can form a continuous phase in the dispersion liquid can not only further increase the content of β-PVDF crystal form, but also form a continuous path in the membrane after binding with PVDF and significantly increase the surface charge density of the membrane under the driving of nanofiltration pressure to generate an internal electric field in the membrane body, enhancing the selective separation performance of "multivalent / monovalent" mixed ions through the triple synergistic effect of "size sieving-surface strong electrostatic interaction-internal electric field strengthening".

[0009] The aforementioned preparation method of a PVDF hollow fiber nanofiltration membrane with piezoelectric responsiveness is specifically as follows:

[0010] S1. Dry the PVDF powder at 80 °C for 24 h. Take PVDF powder, inorganic pore-forming agent, carbon-based material, organic phase reaction monomer (TMC), and organic solvent with a mass ratio of 18-22:1-5:0.5-3:1-3:67-80 and stir at 60 °C for 8 h, and then degas for 8 h to obtain a uniform dispersion liquid;

[0011] S2. Dilute polyamine molecules with deionized water into an aqueous solution with a concentration of 5-15% as the core liquid;

[0012] S3. Extrude the dispersion liquid and the core liquid using a spinning device, pass through an air gap, and then enter the coagulation bath for phase inversion, and finally wind up to obtain a hollow fiber nanofiltration membrane.

[0013] In the aforementioned preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, the inorganic additive in step S1 is one of lithium chloride (LiCl), magnesium chloride (MgCl 2 ), and calcium chloride (CaCl 2 ).

[0014] In the aforementioned preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, the carbon-based material in step S1 is one of carbon nanotubes (CNT), graphene (GE), carbon quantum dots (CQD), and graphitic carbon nitride (g-C 3 N 4 ).

[0015] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the organic solvent described in step S1 is one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and hexamethylphosphoric triamide (HMPA).

[0016] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the polyamine molecule described in step S2 is one of piperazine (PIP), polyethyleneimine (PEI), and polyvinylamine (PVAm).

[0017] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the temperatures of the uniform dispersion liquid and the core liquid described in step S3 are 40-70°C and 25-50°C, respectively.

[0018] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the air gap described in step S3 is 1-10 cm.

[0019] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the coagulation bath temperature described in step S3 is 40-80°C.

[0020] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, for the preset conditions of spinning in step S3, the extrusion rate of the dispersion liquid is 2-5 mL / min, the basic rate of the core liquid is 1-3 mL / min, the ambient temperature is 25-35°C, and the ambient humidity is 20%-50%.

[0021] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the winding rate in step S3 is 10-20 m / min.

[0022] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the content of β-crystalline form in the prepared PVDF hollow fiber nanofiltration membrane is not less than 90%.

[0023] The foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, wherein the operating pressure of the prepared PVDF hollow fiber nanofiltration membrane is 0.3-1 MPa.

[0024] The product prepared by the foregoing preparation method of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness.

[0025] Advantages of the present invention

[0026] The principle of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness described in the present invention is as follows: PVDF is a polymorphic polymer, and its β-crystalline form has been proven to have piezoelectric responsiveness through research. Moreover, the higher the relative content of the β-crystalline form, the more prominent the piezoelectric responsiveness, that is, the greater the potential difference between the inner and outer surfaces of the material. Therefore, using PVDF as the raw material for membrane preparation and optimizing the relative content of the β-crystalline form in the membrane to enhance the piezoelectric performance is a new method to solve the poor selective separation performance and difficulty in commercialization of hollow fiber nanofiltration membranes. However, the conventional membrane preparation process has limited ability to increase the relative content of the β-crystalline form in the PVDF membrane body, which makes it insufficient to rely solely on the piezoelectric output of PVDF itself. Introducing other carbon-based conductive materials with piezoelectric properties can not only further increase the content of β-crystalline PVDF, but also form a continuous pathway in the membrane after combining with PVDF, and significantly increase the surface charge density of the membrane under the driving force of nanofiltration pressure and form an internal electric field in the membrane body. Thus, the selective separation performance of "multivalent / monovalent" mixed ions is enhanced through the triple synergistic effect of "size sieving - surface strong electrostatic interaction - internal electric field strengthening".

[0027] The advantages and positive effects of the present invention are as follows: (1) The operation method is simple. A PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness can be prepared only through a conventional spinning method; (2) The pure water flux of the membrane is high, the divalent cation rejection rate is high, and the monovalent cation rejection rate is low; (3) It effectively solves many limitations existing in hollow fiber nanofiltration membranes, such as poor separation efficiency, complex preparation process, and difficulty in industrial production, etc.; (4) This method is also applicable to various configurations such as spiral wound membranes and multi-channel hollow fiber membranes. Detailed implementation mode

[0028] The technical route in the specific implementation process of the present invention will be described in detail and completely. It should be noted that the above-mentioned implementation process and technical route of the present invention are only a small part of the key achievements involved in the present invention, and all the technical requirements are not listed in detail. Based on the specific implementation scheme, all other specific embodiments obtained by other technical personnel under the technical route of the present invention without creative labor are within the protection scope of the present invention.

[0029] Example 1:

[0030] S1. Dry the PVDF powder at 80 °C for 24 h. By mass fraction, take 18 parts of PVDF powder, 3 parts of inorganic additive (LiCl), 1 part of carbon-based material (CNT), 2 parts of organic phase reaction monomer (TMC), and 76 parts of organic solvent (DMAc). Stir at 60 °C for 8 h, and then degas for 8 h to obtain a uniform dispersion;

[0031] S2. Dilute the polyamine molecule (PIP) with deionized water to an aqueous solution with a concentration of 5% as the core liquid;

[0032] S3. At environmental temperature and humidity of 25°C / 40% respectively, extrude the dispersion liquid (at 50°C, extrusion rate 2 mL / min) and the core liquid (at 30°C, extrusion rate 1 mL / min) using a spinning device, pass through an air gap of 6 cm, and then enter a coagulation bath at 50°C for phase inversion. Finally, wind up at a rate of 10 m / min to obtain a hollow fiber nanofiltration membrane.

[0033] It is measured that the relative content of the p crystal form in the hollow fiber nanofiltration membrane is 96.2%, and the pure water flux is 27 L m -2 h -1 (operating pressure 3 bar), the zeta potential on the membrane surface is 30 mV (pH = 7), and the rejection rate of Mg 2+ is 99.3%, and the rejection rate of Na + is 18% (the test solution is a MgSO 4 / NaCl mixed solution, the concentration of MgSO 4 is 100 mg / L, and the concentration of NaCl is 1900 mg / L). For a commercially available dNF40 model from a certain company, the pure water flux is 20 L m -2 h -1 , and the rejection rate of MgSO 4 is 91%.

[0034] Example 2:

[0035] S1. Dry the PVDF powder at 80°C for 24 h. By mass fraction, take 18 parts of PVDF powder, 3 parts of inorganic additive (MgCl 2 ), 1 part of carbon-based material (GE), 2 parts of organic phase reaction monomer (TMC), and 76 parts of organic solvent (DMF). Stir at 60°C for 8 h, and then degas for 8 h to obtain a uniform dispersion liquid;

[0036] S2. Dilute the polyamine molecule (PEI) with deionized water to an aqueous solution with a concentration of 7% as the core liquid;

[0037] S3. At environmental temperature and humidity of 30°C / 45% respectively, extrude the dispersion liquid (at 50°C, extrusion rate 3 mL / min) and the core liquid (at 30°C, extrusion rate 2 mL / min) using a spinning device, pass through an air gap of 7 cm, and then enter a coagulation bath at 55°C for phase inversion. Finally, wind up at a rate of 12 m / min to obtain a hollow fiber nanofiltration membrane.

[0038] It is measured that the relative content of the β crystal form in the hollow fiber nanofiltration membrane is 97.5%, and the pure water flux is 51 L m -2 h -1 (operating pressure 5 bar), the zeta potential on the membrane surface is 43 mV (pH = 7), and Mg2+ The removal rate is 99.5%, Na + The removal rate is 19% (the test solution is a MgSO 4 / NaCl mixed solution, with a MgSO 4 concentration of 100 mg / L and an NaCl concentration of 1900 mg / L). The pure water flux of a commercially available dNF40 model from a certain company is 20 L m -2 h -1 , and the MgSO 4 removal rate is 91%.

[0039] Example 3:

[0040] S1. Dry the PVDF powder at 80 °C for 24 h. By mass fraction, take 20 parts of PVDF powder, 3 parts of inorganic additive (MgCl 2 ), 1 part of carbon-based material (CQD), 2 parts of organic phase reaction monomer (TMC), and 74 parts of organic solvent (NMP). Stir at 60 °C for 8 h, and then degas for 8 h to obtain a uniform dispersion;

[0041] S2. Dilute the polyamine molecule (PVAm) with deionized water to an aqueous solution with a concentration of 10% as the core liquid;

[0042] S3. Extrude the dispersion (50 °C, extrusion rate 3 mL / min) and the core liquid (30 °C, extrusion rate 3 mL / min) under the conditions of environmental temperature and humidity of 30 °C / 35% respectively. Use a spinning device to extrude and enter a coagulation bath at 55 °C after passing through an 8 cm air gap for phase inversion, and finally wind up at a rate of 15 m / min to obtain a hollow fiber nanofiltration membrane.

[0043] It was measured that the relative content of β-crystalline form in the hollow fiber nanofiltration membrane was 97%, the pure water flux was 84 L m -2 h -1 (operating pressure 7 bar), the zeta potential on the membrane surface was 56 mV (pH = 7), the Mg 2+ removal rate was 99.5%, and the Na + removal rate was 20% (the test solution was a MgSO 4 / NaCl mixed solution, with a MgSO 4 concentration of 100 mg / L and an NaCl concentration of 1900 mg / L). The pure water flux of a commercially available dNF40 model from a certain company is 20 L m -2 h -1 , and the MgSO 4 removal rate was 91%.

[0044] Example 4:

[0045] S1. Dry the PVDF powder at 80 °C for 24 h. By mass fraction, take 21 parts of PVDF powder, 5 parts of inorganic additive (CaCl 2 ), 2 parts of carbon-based material (g-C 3 N 4 ), 3 parts of organic phase reaction monomer (TMC), and 69 parts of organic solvent (DMSO). Stir at 60 °C for 8 h, then degas for 8 h to obtain a homogeneous dispersion;

[0046] S2. Dilute the polyamine molecule (PEI) with deionized water to an aqueous solution with a concentration of 10% as the core liquid;

[0047] S3. Under the conditions of ambient temperature and humidity of 25 °C / 40%, extrude the dispersion (60 °C, extrusion rate 5 mL / min) and the core liquid (25 °C, extrusion rate 3 mL / min) using a spinning device, pass through an air gap of 9 cm, and then enter a coagulation bath at 55 °C for phase inversion. Finally, wind up at a rate of 18 m / min to obtain a hollow fiber nanofiltration membrane.

[0048] It is measured that the relative content of β-crystalline form in the hollow fiber nanofiltration membrane is 97.5%, the pure water flux is 127 Lm -2 h -1 (operating pressure 9 bar), the zeta potential on the membrane surface is 73 mV (pH = 7), the rejection rate of Mg 2+ is 99.6%, and the rejection rate of Na + is 16% (the test solution is a MgSO 4 / NaCl mixed solution, the concentration of MgSO 4 is 100 mg / L, and the concentration of NaCl is 1900 mg / L). The pure water flux of a commercially available dNF40 model from a certain company is 20 Lm -2 h -1 , and the rejection rate of MgSO 4 is 91%.

[0049] Example 5:

[0050] S1. Dry the PVDF powder at 80 °C for 24 h. By mass fraction, take 22 parts of PVDF powder, 5 parts of inorganic additive (LiCl), 2 parts of carbon-based material (CNT), 3 parts of organic phase reaction monomer (TMC), and 68 parts of organic solvent (HMPA). Stir at 60 °C for 8 h, then degas for 8 h to obtain a homogeneous dispersion;

[0051] S2. Dilute the polyamine molecule (PEI) with deionized water to an aqueous solution with a concentration of 10% as the core liquid;

[0052] S3. The dispersion liquid (at 60 °C, extrusion rate 5 mL / min) and the core liquid (at 25 °C, extrusion rate 3 mL / min) are extruded using a spinning device under the conditions of ambient temperature and humidity of 25 °C / 40% respectively, pass through an air gap of 10 cm, and then enter a coagulation bath at 55 °C for phase inversion. Finally, the hollow fiber nanofiltration membrane is wound up at a rate of 20 m / min.

[0053] It is measured that the relative content of β-crystal form in the hollow fiber nanofiltration membrane is 99.3%, the pure water flux is 143 Lm -2 h -1 (operating pressure 10 bar), the zeta potential on the membrane surface is 89 mV (pH = 7), and the rejection rate of Mg 2+ is 99.8%, and the rejection rate of Na + is 14% (the test solution is a MgSO 4 / NaCl mixed solution, the concentration of MgSO 4 is 100 mg / L, and the concentration of NaCl is 1900 mg / L). The pure water flux of a commercially available dNF40 model from a certain company is 20 L m -2 h -1 , and the rejection rate of MgSO 4 is 91%.

Claims

1. A preparation method and application of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, characterized in that: PVDF is used as the membrane raw material, inorganic additives are used as porogens, and carbon-based materials with piezoelectric properties are used to construct the conductive path. TMC is used as the organic phase reaction monomer and the above substances are dissolved in an organic solvent to prepare a uniform dispersion. Then, the polyamine molecules and water are mixed in a certain proportion as the core liquid. Through non-solvent induced phase separation (NIPS) spinning, a PVDF hollow fiber nanofiltration membrane with piezoelectric responsiveness is made in one step.

2. A preparation method and application of a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness, characterized in that: The specific steps are as follows: S1. Dry the PVDF powder at 80°C for 24h, take the PVDF powder, inorganic porogen, carbon-based conductive material with piezoelectric properties, organic phase reaction monomer (TMC), and organic solvent in a mass ratio of 18-22:1-5:0.5-3:1-3:67-80 and stir at 60°C for 8h, then degas for 8h to obtain a uniform dispersion; S2, using deionized water to dilute the polyamine molecules into a 5-15% aqueous solution as the core liquid; S3. The dispersion liquid and the core liquid are extruded under preset conditions using a spinning device and enter a coagulation bath after passing through an air gap to undergo phase inversion, and finally rolled up to obtain a hollow fiber nanofiltration membrane.

3. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: The inorganic additive in step S1 is one of lithium chloride (LiCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2).

4. A method for preparing a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness and its application according to claim 2, characterized in that: The carbon-based conductive material with piezoelectric properties in step S1 is one of carbon nanotubes (CNT), graphene (GE), carbon quantum dots (CQD), and graphite carbon nitride (g-C3N4).

5. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: The organic solvent in step S1 is one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and hexamethylphosphoric acid triamide (HMPA).

6. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: The polyamine molecule in step S2 is one of piperazine (PIP), polyethyleneimine (PEI) and polyvinylamine (PVAm).

7. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: In step S3, the temperatures of the dispersion liquid and the core liquid are 40-70° C. and 25-50° C. respectively.

8. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: The air gap in step S3 is 1 to 10 cm.

9. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: The coagulation bath temperature in step S3 is 40-80°C.

10. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness as claimed in claim 2, characterized in that: The preset conditions for spinning in step S3 are that the extrusion rate of the dispersion is 2-5 mL / min, the basic rate of the core liquid is 1-3 mL / min, the ambient temperature is 25-35° C., and the ambient humidity is 20%-50%.

11. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness according to claim 2, characterized in that: The winding rate of the spinning in step S3 is 10 to 20 m / min.

12. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness according to claim 2, characterized in that: The content of beta crystal in the prepared PVDF hollow fiber nanofiltration membrane is not less than 90%.

13. The method for preparing and using a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness according to claim 2, characterized in that: The operating pressure of the prepared PVDF hollow fiber nanofiltration membrane is 0.3-1 MPa.

14. A product obtained by the method for preparing a PVDF-based hollow fiber nanofiltration membrane with piezoelectric responsiveness according to claim 1 or 2.