A PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane and its preparation and application

Abstract

This invention relates to a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane, its preparation, and its application. The specific preparation method is as follows: First, the PTFE microporous membrane is impregnated in silica sol for surface hydrophilic modification. Then, functional modification is performed to graft coordinating groups capable of complexing with metal ions onto the polymer macromolecular chains. These groups, along with a surfactant, are added to a solvent and stirred to obtain a web-forming solution. The web-forming solution is then uniformly coated onto the surface of the hydrophilically modified PTFE microporous membrane to form a continuous ultrathin polymer liquid membrane. Finally, a non-solvent is added for negative pressure filtration, causing phase separation of the liquid membrane into a web, thus obtaining a functionalized two-dimensional nanofiber mesh continuously covering the surface of the PTFE microporous membrane. The two-dimensional nanofiber mesh prepared by this invention has a diameter of 10–40 nm and a pore size of 0.5–1 μm; the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane has a porosity ≥90%, a filtration efficiency for metal ions ≥90%, and a mass transfer flux ≥500 L / m³. 2 •h has great application potential in the field of liquid filtration and separation.

Description

Technical Field

[0001] This invention belongs to the field of water filtration materials technology, specifically relating to a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane and its preparation and application. Background Technology

[0002] PTFE (polytetrafluoroethylene) microporous membranes are widely used in waterproofing, filtration, separation, and electronic energy fields due to their small pore size, high temperature resistance, and excellent chemical stability. The interconnected pore structure formed by biaxial stretching of PTFE microporous membranes provides high filtration efficiency for submicron particles. However, the low surface energy caused by the fluorine-containing macromolecular chains makes them highly hydrophobic, and their surface chemical inertness makes them difficult to composite with other materials, thus limiting their practical application in liquid filtration.

[0003] Patent ZL201810441419.9 discloses a high-performance lithium-ion battery composite separator and its preparation method. This method modifies the surfaces of PTFE microporous membranes and PE microporous membranes respectively, and then combines the two microporous membranes through polymer bonding to obtain a sandwich-structured composite separator. This method improves the durability of the PTFE microporous membrane through surface modification and subsequent composite bonding, but it is difficult to further reduce the pore size and increase its porosity, thus failing to improve its functionality. Patent ZL201810966123.9 discloses a method for preparing laminated fabrics from modified PTFE membranes and polyester woven fabrics. This method heat-treats the PTFE microporous membrane to give it surface adhesion, and then composites it with polyester fabric to obtain a laminated fabric. While the heat treatment changes the chemical inertness of the PTFE membrane surface, the melt bonding between fibers easily blocks the original pore structure, causing damage to its pore structure and limiting its practical application. Patent ZL201711386965.9 discloses a heavy metal ion filter paper and its preparation method. This method involves loading porous calcium silicate onto wood pulp fibers to support the filter paper for heavy metal ion adsorption. While the porous calcium silicate can effectively adsorb heavy metal ions, the resulting filter paper is thick and has a low mass transfer flux, limiting its efficiency in practical water filtration applications. Summary of the Invention

[0004] The purpose of this invention is to provide a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane and its preparation and application, especially a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane with small pore size, high porosity, high filtration flux, and high metal ion adsorption capacity, and its preparation and application.

[0005] The objective of this invention can be achieved through the following technical solution: a method for preparing a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane, comprising the following steps:

[0006] Step (1): Add tetraethyl orthosilicate to water and stir until homogeneous. Slowly add acid reagent to adjust the pH to 2-3 and continue stirring to obtain silica sol.

[0007] Step (2): The PTFE microporous membrane is impregnated in silica sol and then gelled to achieve hydrophilic modification of the PTFE microporous membrane surface;

[0008] Step (3): Functionalize the polymer by grafting functional groups onto the polymer macromolecular chain to provide active sites for metal ion adsorption.

[0009] Step (4): Add the functionalized polymer and surfactant to the solvent and stir until homogeneous to obtain the web-forming solution;

[0010] Step (5): The web-laying solution is uniformly coated on the surface of the hydrophilically modified PTFE microporous membrane. The web-laying solution spontaneously spreads on the hydrophilic surface of the PTFE microporous membrane to form a continuous ultrathin polymer liquid film.

[0011] Step (6): Add non-solvent to the surface of the material obtained in step (5) and perform negative pressure filtration to cause phase separation of the polymer liquid film on the PTFE microporous membrane substrate to form a two-dimensional mesh structure. By changing the filtration speed, the diffusion rates of solvent and non-solvent are controlled to achieve effective control of the two-dimensional mesh structure, thus obtaining a PTFE microporous membrane / two-dimensional nanofiber composite membrane.

[0012] Further, the molar ratio of tetraethyl orthosilicate to water in step (1) is 1:4 to 1:10, the acid reagent includes one or more of phosphoric acid, acetic acid, hydrochloric acid or nitric acid, and the stirring time after adding the acid reagent is 6 to 10 hours.

[0013] Furthermore, the PTFE microporous membrane described in step (2) has a pore size of 1 to 5 μm, a porosity of ≥70%, and a thickness of 10 to 30 μm.

[0014] Furthermore, the immersion time of the PTFE microporous membrane in silica sol in step (2) is 20 to 60 minutes, the gelation treatment temperature is 40 to 60°C, and the time is 10 to 24 hours; the water contact angle of the surface-modified hydrophilic PTFE microporous membrane is ≤40°.

[0015] Further, the polymer mentioned in step (3) includes one or more of cellulose, polyamide-imide, polyether-imide, polyvinylidene fluoride, polyacrylonitrile, polystyrene, polyamide, polyurethane, or polyvinyl alcohol, and the weight-average molecular weight of the polymer is 8 × 10⁻⁶. 3 ~2×10 5g / mol; the functionalization modification method includes one or more of chemical grafting, plasma grafting or radiation grafting; the functional group includes carboxylic acid group, sulfonic acid group, sulfate group, primary amino group, tertiary amino group or secondary amino group.

[0016] Furthermore, the mass fraction of the functionalized polymer in the web-laying solution described in step (4) is 0.1–10 wt%.

[0017] Further, the solvent mentioned in step (4) includes one or more of ethanol, isobutanol, n-propanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, ethyl acetate, acetone or N-methylmorpholine-N-oxide.

[0018] Further, the surfactant mentioned in step (4) includes one or more of the following: cocoyl monoethanolamide, cocoyl diethanolamide, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, potassium lauryl ether phosphate, disodium lauryl sulfosuccinate monoester, monolauryl phosphate, fatty alcohol polyoxyethylene ether ammonium sulfate, or lauramidopropyl betaine, and the mass fraction of the surfactant in the web-laying solution is 0.01 to 5 wt%.

[0019] Furthermore, the coating method of the web-laying solution described in step (5) includes scraping, spin coating, drop coating or spray coating, and the thickness of the polymer liquid film is 1 to 5 μm.

[0020] Further, the non-solvent mentioned in step (6) includes one or more of water, methanol, ethanol, propanol, isobutanol, ethylene glycol, acetone, cresol or cyclohexane; the negative pressure filtration pressure is 0.1 to 1 MPa, the filtration speed is 0.1 to 5 L / min, and the filtration time is 10 to 300 s.

[0021] The second objective of this invention is to provide a PTFE microporous membrane / two-dimensional nanofiber web composite membrane prepared by the above method.

[0022] Furthermore, the diameter of the two-dimensional nanofiber mesh is 10–40 nm, and the pore size is 0.5–1 μm; the porosity of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane is ≥90%, the filtration efficiency for metal ions is ≥90%, and the mass transfer flux is ≥500 L / m. 2 ·h.

[0023] The third objective of this invention is to provide an application of a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane, which is used in liquid filtration. Specifically, the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane adsorbs metal ions through functionalized functional groups grafted onto the polymer macromolecular chain, and forms a stable complex colloid with the metal ions through complexation, thereby achieving the adsorption and deposition of metal ions in the liquid during liquid filtration.

[0024] The technical principle of this invention is as follows: a functionalized polymer web-laying solution is coated on the surface of a PTFE microporous membrane after hydrophilic modification by silica sol, and then the phase is separated into a web by non-solvent negative pressure filtration to obtain a PTFE microporous membrane / two-dimensional nanofiber web composite membrane. First, tetraethyl orthosilicate (TEO) is hydrolyzed using silicon as the silicon source. By adjusting the molar ratio of silicon to water, TEO is fully hydrolyzed, resulting in a large polymer chain with sufficient hydroxyl groups, thus achieving high hydrophilicity. Next, functional groups are grafted onto the polymer chain through functionalization modification, allowing it to complex with metal ions to form a stable colloid complex, achieving adsorption and deposition of metal ions. Then, using a PTFE microporous membrane modified in silica sol as the substrate, a functionalized polymer web solution is coated onto its surface, spreading on the hydrophilic surface to form a continuous, ultrathin polymer liquid film. Then, a non-solvent negative pressure filtration method is used to allow dual diffusion of solvent and non-solvent in the liquid film, causing phase separation and forming a two-dimensional mesh structure. The two-dimensional mesh structure is effectively controlled by changing the filtration speed, ultimately obtaining a PTFE microporous membrane / two-dimensional nanofiber web composite membrane with high metal ion adsorption and high filtration flux.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The two-dimensional nanofiber mesh of the present invention has a fine diameter, small pore size and high specific surface area. Functionalized functional groups are grafted onto the polymer macromolecular chains that form the two-dimensional nanofiber mesh, which can effectively improve the adsorption efficiency of metal ions. At the same time, the thickness of the two-dimensional nanofiber mesh is extremely small, which makes the composite membrane have high filtration flux.

[0027] 2. The PTFE microporous membrane and the two-dimensional nanofiber network of the present invention are connected by a large number of hydrogen bonds between the hydrophilically modified layers to form a tight composite structure. The composite membrane has strong interlayer bonding force, which is beneficial to maintaining the original structure in practical applications and can meet its performance requirements in various application scenarios. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0029] All reagents used in the following examples are commercially available. All equipment used in the following examples is commercially available.

[0030] Example 1

[0031] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0032] 1) Add 100g of tetraethyl orthosilicate to 50g of water and stir continuously. Slowly add 5g of phosphoric acid and continue stirring for 8 hours to obtain silica sol.

[0033] 2) Select a PTFE microporous membrane with a pore size of 1μm, a porosity of 90%, and a thickness of 10μm. Immerse it in silica sol for 20min and then gel at 40℃ for 10h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0034] 3) By chemical grafting, the polypropylene macromolecular chain contains carboxylic acid groups. 10g of functionalized polypropylene is dissolved in 1000g of N,N-dimethylacetamide, and 1g of sodium dodecylbenzenesulfonate is added. The mixture is stirred evenly to obtain a web-forming solution.

[0035] 4) The web-coating solution was coated onto the hydrophilically modified PTFE microporous membrane by a scraping method, and the coating thickness was 1 μm;

[0036] 5) Water was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 0.5 MPa, the filtration speed was 0.5 L / min, and the filtration time was 200 s. The resulting two-dimensional nanofiber network had a diameter of 10 nm and a pore size of 0.5 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber network composite membrane was 92%. The composite membrane was then tested at 0.1 MPa to filter wastewater containing 2 mg / L of metal ions. The metal ion concentration in the filtered water sample decreased to 0.1 mg / L. The filtration efficiency of the composite membrane for metal ions was 95%, and the mass transfer flux was 600 L / m³. 2 ·h.

[0037] Example 2

[0038] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0039] 1) Add 120g of tetraethyl orthosilicate to 50g of water and stir continuously. Slowly add 5g of phosphoric acid and continue stirring for 10 hours to obtain silica sol.

[0040] 2) Select a PTFE microporous membrane with a pore size of 2.5 μm, a porosity of 75%, and a thickness of 15 μm. Immerse it in silica sol for 30 min, and then gel it at 40 °C for 12 h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0041] 3) The polyurethane macromolecular chain is made to contain amino groups by chemical grafting, and 15g of functionalized polyurethane is dissolved in 800g of N,N-dimethylformamide, 1.5g of monolauryl phosphate is added, and the mixture is stirred evenly to obtain a web-forming solution.

[0042] 4) The coating solution was applied to the hydrophilically modified PTFE microporous membrane by a scraping method, and the coating thickness was 2 μm.

[0043] 5) Water was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 1 MPa, the filtration rate was 0.3 L / min, and the filtration time was 240 s. The resulting two-dimensional nanofiber mesh had a diameter of 30 nm and a pore size of 0.9 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane was 95%. The composite membrane was tested for filtration of wastewater containing 2 mg / L of metal ions under a pressure of 0.1 MPa. The metal ion concentration in the filtered water sample decreased to 0.08 mg / L. The filtration efficiency of the composite membrane for metal ions was 96%, and the mass transfer flux was 500 L / m³. 2 ·h.

[0044] Example 3

[0045] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0046] 1) Add 45g of tetraethyl orthosilicate to 30g of water and stir continuously. Slowly add 4g of acetic acid and continue stirring for 10 hours to obtain silica sol.

[0047] 2) Select a PTFE microporous membrane with a pore size of 5μm, a porosity of 70%, and a thickness of 30μm. Immerse it in silica sol for 60min and then gel at 50℃ for 24h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0048] 3) By chemical grafting, the polyvinylidene fluoride macromolecular chain contains sulfonic acid groups, and 20g of functionalized polyvinylidene fluoride is dissolved in 600g of dimethyl sulfoxide, 2g of potassium lauryl ether phosphate is added, and the mixture is stirred evenly to obtain a web-forming solution.

[0049] 4) The web-coating solution was coated onto the hydrophilically modified PTFE microporous membrane by spin coating, with a coating thickness of 5 μm;

[0050] 5) Ethanol was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 1 MPa, the filtration rate was 0.1 L / min, and the filtration time was 300 s. The final two-dimensional nanofiber network had a diameter of 40 nm and a pore size of 1 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber network composite membrane was 94%. The composite membrane was tested for filtration of wastewater containing 2 mg / L of metal ions under a pressure of 0.1 MPa. The concentration of metal ions in the filtered water sample decreased to 0.16 mg / L. The filtration efficiency of the composite membrane for metal ions was 92%, and the mass transfer flux was 750 L / m³. 2 ·h.

[0051] Example 4

[0052] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0053] 1) Add 80g of tetraethyl orthosilicate to 40g of water and stir continuously. Slowly add 4g of acetic acid and continue stirring for 10 hours to obtain silica sol.

[0054] 2) Select a PTFE microporous membrane with a pore size of 3μm, a porosity of 75%, and a thickness of 20μm. Immerse it in silica sol for 50min and then gel at 60℃ for 12h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0055] 3) By chemical grafting, amino groups are added to the polyvinyl alcohol macromolecular chain. 10g of functionalized polyvinyl alcohol is dissolved in 500g of ethanol, and 1g of potassium lauryl ether phosphate is added. The mixture is stirred evenly to obtain a web-coated solution.

[0056] 4) The web-coating solution was applied to the hydrophilically modified PTFE microporous membrane by spin coating, with a coating thickness of 5 μm;

[0057] 5) Water was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 0.5 MPa, the filtration rate was 5 L / min, and the filtration time was 180 s. The resulting two-dimensional nanofiber mesh had a diameter of 25 nm and a pore size of 0.7 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane was 95%. The composite membrane was tested at a pressure of 0.1 MPa to filter wastewater containing a metal ion concentration of 2 mg / L. The metal ion concentration in the filtered water sample was reduced to 0.1 mg / L. The filtration efficiency of the composite membrane for metal ions was 95%, and the mass transfer flux was 650 L / m³. 2 ·h.

[0058] Example 5

[0059] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0060] 1) Add 130g of tetraethyl orthosilicate to 50g of water and stir continuously. Slowly add 5g of hydrochloric acid and continue stirring for 10 hours to obtain silica sol.

[0061] 2) Select a PTFE microporous membrane with a pore size of 4.5 μm, a porosity of 85%, and a thickness of 20 μm. Immerse it in silica sol for 45 min, and then gel it at 40 °C for 20 h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0062] 3) The polystyrene macromolecular chain is made to contain amino groups by chemical grafting, and 15g of functionalized polystyrene is dissolved in 500g of N-methylpyrrolidone, 1.5g of sodium dodecyl sulfate is added, and the mixture is stirred evenly to obtain a web-forming solution.

[0063] 4) The mesh coating solution was applied to the hydrophilically modified PTFE microporous membrane by drop coating, and the coating thickness was 1 μm.

[0064] 5) Water was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 0.6 MPa, the filtration speed was 4.5 L / min, and the filtration time was 120 s. The resulting two-dimensional nanofiber mesh had a diameter of 15 nm and a pore size of 0.5 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane was 96%. The composite membrane was tested at a pressure of 0.1 MPa to filter wastewater containing a metal ion concentration of 2 mg / L. The metal ion concentration in the filtered water sample was reduced to 0.04 mg / L. The filtration efficiency of the composite membrane for metal ions was 98%, and the mass transfer flux was 700 L / m³. 2 ·h.

[0065] Example 6

[0066] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0067] 1) Add 25g of tetraethyl orthosilicate to 20g of water and stir continuously. Slowly add 5g of nitric acid and continue stirring for 6 hours to obtain silica sol.

[0068] 2) Select a PTFE microporous membrane with a pore size of 5μm, a porosity of 75%, and a thickness of 30μm. Immerse it in silica sol for 60min and then gel at 50℃ for 15h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0069] 3) By chemical grafting, sulfonic acid groups were added to the cellulose macromolecular chain. 6g of functionalized cellulose was dissolved in 5000g of N-methylpyrrolidone, and 0.6g of monolauryl phosphate was added. The mixture was stirred evenly to obtain a web-forming solution.

[0070] 4) The mesh coating solution was applied to the hydrophilically modified PTFE microporous membrane by drop coating, and the coating thickness was 1 μm.

[0071] 5) Water was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 0.1 MPa, the filtration speed was 4.5 L / min, and the filtration time was 10 s. The resulting two-dimensional nanofiber mesh had a diameter of 10 nm and a pore size of 0.5 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane was 95%. The composite membrane was tested for filtration of wastewater containing 2 mg / L of metal ions under a pressure of 0.1 MPa. The concentration of metal ions in the filtered water sample decreased to 0.04 mg / L. The filtration efficiency of the composite membrane for metal ions was 98%, and the mass transfer flux was 500 L / m³. 2 ·h.

[0072] Example 7

[0073] The preparation steps of the PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane are as follows:

[0074] 1) Add 46.2g of tetraethyl orthosilicate to 40g of water and stir continuously. Slowly add 5g of acetic acid and continue stirring for 7 hours to obtain silica sol.

[0075] 2) Select a PTFE microporous membrane with a pore size of 4μm, a porosity of 85%, and a thickness of 20μm. Immerse it in silica sol for 50 min, and then gel it at 40℃ for 20 h to obtain a surface-modified hydrophilic PTFE microporous membrane.

[0076] 3) The polyacrylonitrile macromolecular chain is made to contain amino groups by chemical grafting. 45g of functionalized polyacrylonitrile is dissolved in 400g of N-methylpyrrolidone, and 22g of lauramidopropyl betaine is added. The mixture is stirred evenly to obtain a web-forming solution.

[0077] 4) The mesh-coating solution was coated onto the hydrophilically modified PTFE microporous membrane by drop coating, and the coating thickness was 2 μm;

[0078] 5) Water was added to the surface of the above material for negative pressure filtration. The negative pressure filtration pressure was 0.5 MPa, the filtration rate was 5 L / min, and the filtration time was 100 s. The resulting two-dimensional nanofiber mesh had a diameter of 40 nm and a pore size of 1 μm. The porosity of the obtained PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane was 90%. The composite membrane was tested for filtration of wastewater containing 2 mg / L of metal ions under a pressure of 0.1 MPa. The concentration of metal ions in the filtered water sample decreased to 0.18 mg / L. The filtration efficiency of the composite membrane for metal ions was 91%, and the mass transfer flux was 720 L / m³. 2 ·h.

[0079] It can be seen that the main influencing factor on the formation of pores in two-dimensional nanofiber meshes is the phase separation rate, i.e., the dual diffusion rate of solvent and non-solvent. Changing the filtration speed can regulate the dual diffusion rate of solvent and non-solvent. Increasing the filtration speed results in a faster dual diffusion rate of solvent and non-solvent, rapid phase separation, a shorter nucleation and growth time for the solvent-enriched phase, a smaller area formed by the solvent-enriched phase, and a smaller pore size after solvent removal. Conversely, decreasing the filtration speed is beneficial to increasing the pore size.

[0080] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a PTFE microporous membrane / two-dimensional nanofiber web composite membrane, characterized in that, Includes the following steps: Step (1): Add tetraethyl orthosilicate to water and stir until homogeneous. Slowly add acid reagent to adjust the pH to 2-3 and continue stirring to obtain silica sol. Step (2): The PTFE microporous membrane is impregnated in silica sol and then gelled to obtain a surface-modified PTFE microporous membrane. Step (3): The polymer is functionalized to obtain a polymer with functionalized functional groups grafted onto the macromolecular chain. The functionalized functional groups include carboxylic acid group, sulfonic acid group, sulfate group, primary amino group, tertiary amino group or secondary amino group. Step (4): Add the functionalized polymer and surfactant to the solvent and stir until homogeneous to obtain the web-forming solution; Step (5): The web-laying solution is uniformly coated on the surface of the hydrophilic modified PTFE microporous membrane to obtain a continuous polymer liquid film; Step (6): Add non-solvent to the surface of the material obtained in step (5) and perform negative pressure filtration to obtain a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane; The coating method for the web-laying solution described in step (5) includes scraping, spin coating, drop coating, or spray coating, and the thickness of the polymer liquid film is 1~5 μm; The non-solvents mentioned in step (6) include one or more of water, methanol, ethanol, propanol, isobutanol, ethylene glycol, acetone, cresol or cyclohexane; the negative pressure filtration pressure is 0.1~1 MPa, the filtration speed is 0.1~5 L / min, and the filtration time is 10~300 s; In the PTFE microporous membrane / two-dimensional nanofiber web composite membrane prepared by the method described above, the diameter of the two-dimensional nanofiber web is 10~40 nm, and the pore size is 0.5~1 μm; the porosity of the PTFE microporous membrane / two-dimensional nanofiber web composite membrane is ≥90%, the filtration efficiency for metal ions is ≥90%, and the mass transfer flux is ≥500 L / m 2 ·h; The PTFE microporous membrane / two-dimensional nanofiber composite membrane is applied in liquid filtration.

2. The method for preparing a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane according to claim 1, characterized in that, The molar ratio of tetraethyl orthosilicate to water in step (1) is 1:4 to 1:10, and the acid reagent includes one or more of phosphoric acid, acetic acid, hydrochloric acid or nitric acid. The stirring time after adding the acid reagent is 6 to 10 h.

3. The method for preparing a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane according to claim 1, characterized in that, The PTFE microporous membrane mentioned in step (2) has a pore size of 1~5 μm, a porosity of ≥70%, and a thickness of 10~30 μm.

4. The method for preparing a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane according to claim 1, characterized in that, The PTFE microporous membrane described in step (2) is immersed in silica sol for 20 to 60 minutes, the gelation treatment temperature is 40 to 60 °C, and the time is 10 to 24 hours; the water contact angle of the surface-modified hydrophilic PTFE microporous membrane is ≤40°.

5. The method for preparing a PTFE microporous membrane / two-dimensional nanofiber mesh composite membrane according to claim 1, characterized in that, The polymer mentioned in step (3) includes one or more of cellulose, polyamide-imide, polyether-imide, polyvinylidene fluoride, polyacrylonitrile, polystyrene, polyamide, polyurethane, or polyvinyl alcohol, and the weight-average molecular weight of the polymer is 8 × 10⁻⁶. 3 ~2×10 5 g / mol; the functionalization modification methods include one or more of chemical grafting, plasma grafting or radiation grafting.

6. The method for preparing a PTFE microporous membrane / two-dimensional nanofiber web composite membrane according to claim 1, characterized in that, The solvents mentioned in step (4) include ethanol, isobutanol, n-propanol, N , N -Dimethylformamide, N , N -Dimethylacetamide, dimethyl sulfoxide, N -Methylpyrrolidone, ethyl acetate, acetone or N -Methylmorpholine- N - One or more of the oxides; The surfactants mentioned include one or more of the following: cocoyl monoethanolamide, cocoyl diethanolamide, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, potassium lauryl ether phosphate, disodium lauryl sulfosuccinate monoester, monolauryl phosphate, fatty alcohol polyoxyethylene ether ammonium sulfate, or lauramidopropyl betaine; the mass fraction of the surfactant in the web-forming solution is 0.01~5 wt%. The mass fraction of the functionalized polymer in the web-laying solution is 0.1~10 wt%.