Method for producing a negatively charged polytetrafluoroethylene membrane, negatively charged polytetrafluoroethylene membrane and use thereof

Abstract

The application provides a preparation method of a negatively charged polytetrafluoroethylene membrane, the negatively charged polytetrafluoroethylene membrane and application thereof, and relates to the technical field of membrane materials. The preparation method of the negatively charged polytetrafluoroethylene membrane comprises the following steps: placing a polytetrafluoroethylene membrane in an alcohol solution containing a siloxane coupling agent for first soaking treatment; placing the treated polytetrafluoroethylene membrane in an acidic aqueous solution for second soaking treatment to complete initial hydrolysis and dehydration condensation; drying the treated polytetrafluoroethylene membrane to complete deep dehydration condensation; and then performing atom transfer radical polymerization reaction on the surface of the polytetrafluoroethylene membrane with the initiation site through electron transfer activation and regeneration catalyst atom transfer radical polymerization reaction to graft a negatively charged hydrophilic monomer on the surface of the polytetrafluoroethylene membrane with the initiation site, so that the negatively charged polytetrafluoroethylene membrane is obtained. The negatively charged polytetrafluoroethylene membrane has excellent hydrophilicity and long-term chargeability.

Description

Technical Field

[0001] This invention relates to the technical field of membrane materials for water treatment, specifically to a method for preparing a negatively charged polytetrafluoroethylene (PTFE) membrane, the negatively charged PTFE membrane and its application, and particularly to a hydrophilic and durable negatively charged PTFE membrane, its preparation method and application. Background Technology

[0002] Polytetrafluoroethylene (PTFE) membranes are microporous materials produced through a special stretching process of PTFE resin. PTFE's inherent hydrophobicity forms the basis of its excellent waterproof and antifouling properties, but this characteristic also limits its application in aquatic systems. Despite the low surface energy of PTFE membranes, their inherent strong hydrophobicity still makes them susceptible to organic fouling. Therefore, constructing a robust hydrophilic coating on the PTFE surface remains a challenge. After hydrophilic modification, the water flux of PTFE membranes increases significantly, operating energy consumption decreases, and resistance to membrane fouling is enhanced, thus making the application of PTFE membranes in aquatic environments possible.

[0003] Typically, hydrophilic modification methods for PTFE membranes include etching modification, grafting modification, and physical modification. Etching modification involves chemical oxidation or high-energy beam treatment to break the C–F or C–C bonds on the PTFE surface. This process introduces polar functional groups (such as amino, carboxyl, and hydroxyl groups) into the PTFE molecular chain, thereby achieving hydrophilic modification. Etching modification often serves as the basis for grafting modification, providing anchoring sites for the subsequent introduction of hydrophilic components. However, chemical oxidation often degrades the nodular-fiber structure of PTFE, adversely affecting the membrane's macroscopic morphology and mechanical properties. Furthermore, chemical oxidation faces challenges in large-scale implementation due to its reliance on hazardous chemicals and the generation of difficult-to-recover wastewater. While high-energy beam treatment offers advantages in terms of safety and reliability, effectively introducing polar functional groups onto the PTFE membrane surface, it faces challenges such as expensive and complex equipment, making continuous large-scale production or batch processing difficult. More importantly, this method typically only modifies the surface and struggles to achieve hydrophilication of the internal pore structure. Therefore, simply enhancing surface hydrophilicity has limited effect on reducing membrane permeation resistance.

[0004] In-situ polymerization is also an effective method to improve the wettability and permeability of PTFE membrane surfaces. Although polymerization occurs during the modification process, the modified layer does not form chemical bonds with the PTFE bulk structure. Therefore, in-situ polymerization is still classified as a form of physical modification and is widely used in large-scale production due to its simplicity and mild reaction conditions. Although the small-molecule modifiers used in in-situ polymerization easily penetrate the membrane pores, their relatively low polymerization efficiency still limits the effective coating of PTFE fibers by the hydrophilic network. Although in-situ polymerization is a mild and environmentally friendly technology, simpler and easier to operate than surface grafting modification, it still has some limitations. These limitations include insufficient hydrophilicity of the membrane due to incomplete hydrophilic polymer coverage and pore blockage caused by imprecise control of the modification process.

[0005] Suspended particles and colloidal substances in mine water typically carry a negative charge, which is a major reason why organic membranes are prone to fouling. Therefore, when treating mine water, especially when selecting membrane processes, it is preferable to choose membrane modules with negatively charged surfaces to effectively mitigate membrane fouling by utilizing electrostatic repulsion.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a negatively charged polytetrafluoroethylene (PTFE) membrane, the negatively charged PTFE membrane itself, and its applications. The negatively charged PTFE membrane prepared by the method described in this invention exhibits excellent hydrophilicity and durability; simultaneously, it can fully utilize the electrostatic repulsion effect to effectively alleviate membrane fouling problems.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] In a first aspect, the present invention provides a method for preparing a negatively charged polytetrafluoroethylene (PTFE) membrane, the method comprising the following steps:

[0010] (1) The polytetrafluoroethylene membrane is placed in an alcohol solution containing a siloxane coupling agent for a first immersion treatment; wherein the siloxane coupling agent is a bifunctional aminosiloxane.

[0011] (2) The polytetrafluoroethylene membrane obtained in step (1) is placed in an acidic aqueous solution for a second immersion treatment to complete the preliminary hydrolysis and dehydration condensation.

[0012] (3) The polytetrafluoroethylene membrane obtained in step (2) is dried to complete the deep dehydration condensation.

[0013] (4) First, react the polytetrafluoroethylene membrane obtained in step (3) with the acyl halide. After bonding the atom transfer radical polymerization initiation sites on the surface of the polytetrafluoroethylene membrane, perform the electron transfer activated regenerating catalyst atom transfer radical polymerization reaction (hereinafter referred to as ARGET ATRP). Graft the negatively charged hydrophilic monomer onto the surface of the polytetrafluoroethylene membrane with initiation sites to obtain the negatively charged polytetrafluoroethylene membrane.

[0014] Further, in step (1), the bifunctional aminosiloxane is selected from bis[3-(trimethoxysilyl)propyl]amine and / or bis[3-(triethoxysilyl)propyl]amine.

[0015] Further, in step (1), the alcohol solution containing siloxane coupling agent comprises, by mass percentage: 0.2-12.5% ​​siloxane coupling agent, with the remainder being alcohol solvent.

[0016] Further, in step (1), the alcohol solvent is selected from ethanol and / or isopropanol.

[0017] Furthermore, in step (1), the temperature of the first soaking treatment is 15~25℃.

[0018] Furthermore, in step (1), the first soaking treatment time is 10~1440 min.

[0019] Furthermore, in step (2), the pH of the acidic aqueous solution is 3.0 to 4.5.

[0020] Furthermore, in step (2), the acidic aqueous solution includes an acidic solute and water.

[0021] Furthermore, in step (2), the acidic solute is selected from any one or a combination of at least two of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0022] Furthermore, in step (2), the temperature of the second soaking treatment is 15~25℃.

[0023] Furthermore, in step (2), the second soaking treatment time is 0.5~24 h.

[0024] Furthermore, in step (3), the drying process is carried out in a drying oven.

[0025] Furthermore, in step (3), the drying temperature is 50~70℃.

[0026] Furthermore, in step (3), the drying process takes 0.5 to 10 hours.

[0027] Further, in step (4), the step of establishing the bonding atom transfer radical polymerization initiation site specifically includes:

[0028] The polytetrafluoroethylene membrane obtained in step (3) is placed in a solution containing acyl halide to carry out a bonding reaction, thereby obtaining a polytetrafluoroethylene membrane with initiation sites.

[0029] Further, in step (4), the acyl halide is selected from 2-bromoisobutyryl bromide and / or 2-bromopropionyl bromide.

[0030] Further, in step (4), the acyl halide-containing solution comprises, by mass percentage: 0.1-5% acyl halide, with the remainder being anhydrous medium.

[0031] Further, in step (4), the anhydrous medium comprises, by mass percentage: 0.1-5% triethylamine, with the remainder being tetrahydrofuran.

[0032] Furthermore, in step (4), the temperature of the bonding reaction is 0~25℃, and the time of the bonding reaction is 0.5~12 h.

[0033] Furthermore, in step (4), the step of grafting negatively charged hydrophilic monomers specifically includes:

[0034] A polytetrafluoroethylene membrane with initiation sites is placed in a solution containing a negatively charged hydrophilic monomer to carry out a grafting reaction, thereby obtaining the negatively charged polytetrafluoroethylene membrane.

[0035] Further, in step (4), the solution containing the negatively charged hydrophilic monomer comprises, by concentration: 1~100 mM of the negatively charged hydrophilic monomer, 0.005~0.5 mM of the reducing agent, 0.01~1 mM of the catalyst, 0.03~3 mM of the ligand, and the remainder is solvent.

[0036] Further, in step (4), the negatively charged hydrophilic monomer is selected from sodium styrene sulfonate and / or acrylamide-2-methylpropanesulfonic acid.

[0037] Further, in step (4), the reducing agent is selected from any one or a combination of at least two of ascorbic acid, stannous isooctanoate or silver powder.

[0038] Further, in step (4), the catalyst is selected from divalent copper salts and / or trivalent iron salts.

[0039] Further, in step (4), the ligand is selected from any one or a combination of at least two of N,N,N',N',N''-pentamethyldiethylenetriamine, iminodiacetic acid, tri-(3,6-dioxohepyl)amine, and triphenylphosphine.

[0040] Further, in step (4), the solvent in the solution containing the negatively charged hydrophilic monomer is an aqueous ethanol solution.

[0041] Furthermore, the grafting reaction temperature is 20~25℃, and the grafting reaction time is 0.5~6 h.

[0042] In a second aspect, the present invention provides a negatively charged polytetrafluoroethylene membrane, wherein the negatively charged polytetrafluoroethylene membrane is prepared by the preparation method described in the first aspect;

[0043] Furthermore, the initial contact angle of the negatively charged polytetrafluoroethylene film is 50~60°, and the Zeta potential of the negatively charged polytetrafluoroethylene film is -50~-30 mV.

[0044] Thirdly, the present invention provides the application of the negatively charged polytetrafluoroethylene membrane as described in the first aspect in the preparation of products for mine water treatment.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) In the preparation method of the negatively charged polytetrafluoroethylene membrane of the present invention, a bifunctional aminosiloxane is selected as a coupling agent, and then subjected to hydrolysis, preliminary dehydration condensation and deep dehydration condensation treatment to form a stable modified layer with high crosslinking degree, which provides a guarantee for the long-term stability of hydrophilic properties; and the bifunctional aminosiloxane serves as a pre-modified active site, providing a molecular interface for subsequent regulation of the charge on the surface of the polytetrafluoroethylene membrane.

[0047] (2) In the preparation method of the negatively charged polytetrafluoroethylene membrane described in this invention, ARGET ATRP technology is used to modify the surface of the polytetrafluoroethylene membrane by charging, thereby achieving precise control over the growth of the modified layer, avoiding the risk of membrane pore blockage, and at the same time, the negatively charged functional layer chemically bonded to the membrane surface has higher stability.

[0048] (3) The preparation method of the negatively charged polytetrafluoroethylene membrane described in this invention is simpler and more efficient, and the negatively charged polytetrafluoroethylene membrane prepared therefrom has excellent hydrophilicity and long-lasting charge, which can effectively inhibit the adsorption and accumulation of pollutants, and will present the dual advantages of service life and filtration efficiency. Attached Figure Description

[0049] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0050] Figure 1 The image shows the Si distribution across a cross section of the negatively charged polytetrafluoroethylene membrane of Example 2.

[0051] Figure 2 This is a SEM image of the outer wall of the negatively charged polytetrafluoroethylene membrane in Comparative Example 3. Detailed Implementation

[0052] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0053] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In a first aspect, the present invention provides a method for preparing a negatively charged polytetrafluoroethylene (PTFE) membrane, the method comprising the following steps:

[0055] (1) The polytetrafluoroethylene membrane is placed in an alcohol solution containing a siloxane coupling agent for a first immersion treatment; wherein the siloxane coupling agent is a bifunctional aminosiloxane.

[0056] (2) The polytetrafluoroethylene membrane obtained in step (1) is placed in an acidic aqueous solution for a second immersion treatment to complete the preliminary hydrolysis and dehydration condensation.

[0057] (3) The polytetrafluoroethylene membrane obtained in step (2) is dried to complete the deep dehydration condensation.

[0058] (4) First, react the polytetrafluoroethylene membrane obtained in step (3) with the acyl halide. After bonding the atom transfer radical polymerization initiation site to the surface of the polytetrafluoroethylene membrane, the electron transfer activation and regeneration catalyst atom transfer radical polymerization reaction is carried out. The negatively charged hydrophilic monomer is grafted onto the surface of the polytetrafluoroethylene membrane with the initiation site to obtain the negatively charged polytetrafluoroethylene membrane.

[0059] In this invention, the method for preparing the negatively charged polytetrafluoroethylene membrane includes sequentially performing PTFE membrane adsorption of a small molecule modifier (bifunctional aminosiloxane), PTFE membrane hydrolysis preliminary dehydration condensation, PTFE membrane deep dehydration condensation, and PTFE membrane negatively charged modification.

[0060] First, in step (1) of this invention, a bifunctional aminosiloxane is selected as the coupling agent / small molecule modifier. This molecule undergoes hydrolytic condensation through the trialkoxysilyl groups on both sides. Therefore, after the preliminary dehydration condensation and deep dehydration condensation treatments in steps (2) to (3), a hydrophilic functional layer (a highly cross-linked stable modified layer) can be generated on the surface and inside the pores of the PTFE membrane, thereby obtaining a PTFE membrane with durable and stable hydrophilicity. This structure can firmly coat the surface of the PTFE fiber, providing a guarantee for the long-term stability of the hydrophilic properties. This is a significant advantage of this invention compared to the prior art. In addition, the secondary amine group in the silane coupling agent selected in this invention not only participates in hydrophilic modification but also serves as a pre-modified active site, providing a molecular interface for the subsequent regulation of the charge on the PTFE membrane surface.

[0061] Furthermore, in step (4) of this invention, the PTFE membrane is first reacted with an acyl halide in an anhydrous medium for a certain period of time to bond the atom transfer radical polymerization (ATRP) initiation sites to the PTFE membrane surface. Then, the AREGT ATRP technique, which generates catalysts by electron transfer, is used to graft negatively charged hydrophilic monomers onto the PTFE membrane surface, resulting in a hydrophilic and durable negatively charged PTFE membrane. The advantage of using this ARGET ATRP technique to modify the surface charge of the PTFE membrane is that it allows for precise control of the growth of the modified layer, effectively avoiding the risk of membrane pore blockage that easily occurs in traditional methods. Simultaneously, the stability of the negatively charged functional layer chemically bonded to the membrane surface is higher. Therefore, the PTFE membrane prepared by this invention exhibits excellent hydrophilicity and long-lasting charge. This is attributed to the stable hydrophilicity and charge characteristics simultaneously achieved on its surface and within the membrane pores, which effectively inhibits the adsorption and accumulation of pollutants, presenting a dual advantage in terms of service life and filtration efficiency.

[0062] As an optional implementation, in step (1), the bifunctional aminosiloxane is selected from bis[3-(trimethoxysilyl)propyl]amine and / or bis[3-(triethoxysilyl)propyl]amine.

[0063] As an optional implementation, in step (1), the alcohol solution containing siloxane coupling agent comprises, by mass percentage: 0.2-12.5% ​​siloxane coupling agent, with the remainder being alcohol solvent.

[0064] As an optional implementation, based on the mass of the alcohol solution containing the siloxane coupling agent as 100%, the mass percentage of the siloxane coupling agent is 0.2% to 12.5%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 12.5%, etc.

[0065] As a preferred embodiment, the mass percentage of the alcohol solution containing the siloxane coupling agent is 5-10%, with the mass percentage of the siloxane coupling agent being 100%.

[0066] As an optional implementation, in step (1), the alcohol solvent is selected from ethanol and / or isopropanol.

[0067] As an optional implementation, in step (1), the temperature of the first soaking treatment is 15~25℃, for example, it can be 15℃, 16℃, 18℃, 20℃, 22℃, 24℃, 25℃, etc.

[0068] As an optional implementation, in step (1), the time for the first soaking treatment is 10 to 1440 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 100 min, 120 min, 150 min, 200 min, 240 min, 300 min, 400 min, 500 min, 600 min, 700 min, 800 min, 900 min, 1000 min, 1100 min, 1200 min, 1300 min, 1400 min, 1440 min, etc.

[0069] In a preferred embodiment, the first soaking treatment in step (1) takes 60 to 600 minutes.

[0070] In a preferred embodiment, step (1) further includes a step of drying after the first soaking treatment.

[0071] In a preferred embodiment, the drying in step (1) is air drying at room temperature.

[0072] As an optional implementation, in step (2), the pH of the acidic aqueous solution is 3.0 to 4.5, for example, it can be 3.0, 3.2, 3.4, 3.5, 3.6, 3.8, 4.0, 4.2, 4.4, 4.5, etc.

[0073] As an optional implementation, in step (2), the acidic aqueous solution includes an acidic solute and water.

[0074] As an optional implementation, in step (2), the acidic solute is selected from any one or a combination of at least two of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0075] As an optional implementation, in step (2), the temperature of the second soaking treatment is 15~25℃, for example, it can be 15℃, 16℃, 18℃, 20℃, 22℃, 24℃, 25℃, etc.

[0076] As an optional implementation, in step (2), the second soaking treatment time is 0.5~24 h, for example, it can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h, etc.

[0077] In a preferred embodiment, the second soaking treatment in step (2) takes 3 to 24 hours.

[0078] As an optional implementation, step (2) further includes a step of removing the sample after the second soaking treatment.

[0079] As an optional implementation, in step (3), the drying process is carried out in a drying oven.

[0080] As an optional implementation, in step (3), the drying temperature is 50~70℃, for example, it can be 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 68℃, 70℃, etc.

[0081] In a preferred embodiment, the drying temperature in step (3) is 60~70°C.

[0082] As an optional implementation, in step (3), the drying time is 0.5 to 10 hours, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0083] In a preferred embodiment, the drying process in step (3) takes 3 to 6 hours.

[0084] As an optional implementation, step (4), specifically including the step of transferring the bonding atom to the radical polymerization initiation site, includes:

[0085] The polytetrafluoroethylene membrane obtained in step (3) is placed in a solution containing acyl halide to carry out a bonding reaction, thereby obtaining a polytetrafluoroethylene membrane with initiation sites.

[0086] As an optional implementation, in step (4), the acyl halide is selected from 2-bromoisobutyryl bromide and / or 2-bromopropionyl bromide.

[0087] As an optional implementation, in step (4), the acyl halide-containing solution comprises, by mass percentage, 0.1-5% acyl halide, with the remainder being anhydrous medium.

[0088] As an optional implementation, the content of the acyl halide is 0.1-5% based on the mass of the solution containing the acyl halide as 100%, for example, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0089] As an optional implementation, in step (4), the anhydrous medium comprises, by mass percentage: 0.1-5% triethylamine, with the remainder being tetrahydrofuran (THF).

[0090] As an optional implementation, the content of triethylamine is 0.1-5% based on the mass of the anhydrous medium of 100%, for example, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0091] As an optional implementation, in step (4), the temperature of the bonding reaction is 0~25℃, for example, it can be 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, and the time of the bonding reaction is 0.5~12 h, for example, it can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, etc.

[0092] As an optional implementation, step (4) specifically includes the following steps:

[0093] A polytetrafluoroethylene membrane with initiation sites is placed in a solution containing a negatively charged hydrophilic monomer to carry out a grafting reaction, thereby obtaining the negatively charged polytetrafluoroethylene membrane.

[0094] As an optional implementation, in step (4), the solution containing the negatively charged hydrophilic monomer includes, by concentration: 1~100 mM of the negatively charged hydrophilic monomer, 0.005~0.5 mM of the reducing agent, 0.01~1 mM of the catalyst, 0.03~3 mM of the ligand, and the remainder is solvent.

[0095] As an optional implementation, the concentration of the negatively charged hydrophilic monomer in the solution is 1~100 mM, for example, it can be 1 mM, 10 mM, 15 mM, 20 mM, 25 mM, 30 mM, 35 mM, 40 mM, 45 mM, 50 mM, 55 mM, 60 mM, 65 mM, 70 mM, 75 mM, 80 mM, 85 mM, 90 mM, 95 mM, 100 mM, etc.

[0096] As an optional implementation, the concentration of the reducing agent in the solution containing the negatively charged hydrophilic monomer is 0.005~0.5 mM, for example, it can be 0.005 mM, 0.01 mM, 0.05 mM, 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, 0.5 mM, etc.

[0097] As an optional implementation, the concentration of the catalyst in the solution containing the negatively charged hydrophilic monomer is 0.01~1mM, for example, it can be 0.01 mM, 0.05 mM, 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, 0.5 mM, 0.6 mM, 0.7 mM, 0.8 mM, 0.9 mM, 1 mM, etc.

[0098] As an optional implementation, the concentration of the ligand in the solution containing the negatively charged hydrophilic monomer is 0.03~3 mM, for example, it can be 0.03 mM, 0.05 mM, 0.1 mM, 0.2 mM, 0.4 mM, 0.6 mM, 0.8 mM, 1 mM, 1.5 mM, 2 mM, 2.5 mM, 3 mM, etc.

[0099] As an optional implementation, in step (4), the negatively charged hydrophilic monomer is selected from sodium styrene sulfonate and / or acrylamide-2-methylpropanesulfonic acid.

[0100] As an optional implementation, in step (4), the reducing agent is selected from any one or a combination of at least two of ascorbic acid, stannous isooctanoate or silver powder.

[0101] As an optional implementation, in step (4), the catalyst is selected from divalent copper salts and / or trivalent iron salts.

[0102] As an optional implementation, in step (4), the ligand is selected from any one or a combination of at least two of N,N,N',N',N''-pentamethyldiethylenetriamine (PMDETA), iminodiacetic acid (IDA), tris-(3,6-dioxohepyl)amine (TDA-1), and triphenylphosphine (PPh3).

[0103] As an optional implementation, in step (4), the solvent in the solution containing the negatively charged hydrophilic monomer is an aqueous ethanol solution.

[0104] As an optional implementation, the grafting reaction temperature is 20~25℃, for example, 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, etc., and the grafting reaction time is 0.5~6 h, for example, 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, etc.

[0105] In a second aspect, the present invention provides a negatively charged polytetrafluoroethylene membrane, which is prepared by the preparation method described in the first aspect.

[0106] In this invention, the prepared negatively charged polytetrafluoroethylene membrane is a hydrophilic and durable negatively charged polytetrafluoroethylene (PTFE) membrane, specifically a hydrophilic and durable negatively charged PTFE membrane that can be applied to mine water treatment.

[0107] As an optional implementation, the initial contact angle of the negatively charged polytetrafluoroethylene film is 50~60°, for example, it can be 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, etc.

[0108] As an optional implementation, the zeta potential of the negatively charged polytetrafluoroethylene film is -50 to -30 mV, for example, it can be -50 mV, -48 mV, -46 mV, -44 mV, -42 mV, -40 mV, -38 mV, -36 mV, -34 mV, -32 mV, -30 mV, etc.

[0109] As an optional implementation, the negatively charged polytetrafluoroethylene membrane is resistant to cleaning by acids (HCl solution with pH = 2), alkalis (NaOH solution with pH = 12), and oxidants (1000 ppm NaClO solution).

[0110] Thirdly, the present invention provides the application of the negatively charged polytetrafluoroethylene membrane as described in the first aspect in the preparation of products for mine water treatment.

[0111] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0112] Example 1

[0113] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0114] (1) Place the PTFE membrane in a 5 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 15°C for 600 min, and then take it out and air dry at room temperature;

[0115] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of hydrochloric acid with pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0116] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 60°C for 6 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0117] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 0°C for 1.5 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol sodium styrene sulfonate, 0.001 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.005 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0118] Example 2

[0119] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0120] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0121] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of nitric acid at pH 3.0 and soak it at 15°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0122] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 60°C for 6 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0123] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 5°C for 1.5 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol sodium styrene sulfonate, 0.001 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.005 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0124] Figure 1 EDS plot showing the Si distribution across a cross-section of the hydrophilic, durable, negatively charged PTFE membrane of Example 2. Figure 1 As shown, Si is uniformly distributed across the cross-section of the PTFE hollow fiber membrane.

[0125] Example 3

[0126] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0127] (1) Place the PTFE membrane in a 5 wt% solution of bis[3-(triethoxysilyl)propyl]amine in ethanol and isopropanol (v / v=1 / 1), soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0128] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of phosphoric acid at pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0129] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 60°C for 6 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0130] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 15°C for 6 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol sodium styrene sulfonate, 0.001 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.005 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0131] Example 4

[0132] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0133] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0134] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of sulfuric acid at pH 4.5 and soak it at 25°C for 24 hours to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0135] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 60°C for 6 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0136] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 25°C for 1 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol sodium styrene sulfonate, 0.001 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.005 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0137] Example 5

[0138] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0139] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0140] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of hydrochloric acid with pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0141] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 70°C for 3 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0142] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 5°C for 1.5 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol sodium styrene sulfonate, 0.001 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.005 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0143] Example 6

[0144] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0145] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0146] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of sulfuric acid at pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0147] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 70°C for 3 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0148] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 5.0 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 25°C for 0.3 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol sodium styrene sulfonate, 0.001 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.005 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0149] Example 7

[0150] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0151] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0152] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of sulfuric acid at pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0153] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 70°C for 3 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0154] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 5°C for 1.5 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 5 mmol acrylamide-2-methylpropanesulfonic acid, 0.05 mmol FeCl3·6H2O, and 0.5 mmol PPh3 were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.25 mmol stannous isooctanoate was added, the flask was sealed, and the membrane was reacted at room temperature for 2 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0155] Example 8

[0156] This embodiment provides a method for preparing a hydrophilic, durable, negatively charged PTFE membrane, the preparation method specifically including the following steps:

[0157] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0158] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of sulfuric acid at pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0159] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 70°C for 3 h to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0160] (4) The PTFE membrane obtained in step (3) was placed in a THF solution containing 1 wt% 2-bromoisobutyryl bromide and 2 wt% triethylamine and reacted at 10°C for 1.5 h. The membrane was then removed and air-dried at room temperature. The PTFE membrane was then placed in an Erlenmeyer flask and 100 mL of an aqueous solution containing 20 vol% ethanol, 10 mmol sodium styrene sulfonate, 0.002 mmol CuBr2, and 0.01 mmol PMDETA were added sequentially. Argon gas was passed through the system for 10 min to remove most of the air. Then 0.01 mmol ascorbic acid was added, the flask was sealed, and the membrane was reacted at room temperature for 1 h. After the reaction was completed, the membrane fibers were rinsed with pure water and air-dried at room temperature.

[0161] Comparative Example 1

[0162] This comparative example provides a pristine, unmodified PTFE membrane.

[0163] Comparative Example 2

[0164] This comparative example provides a method for preparing a hydrophilic PTFE membrane, the preparation method specifically including the following steps:

[0165] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0166] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of sulfuric acid at pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out.

[0167] Comparative Example 3

[0168] This comparative example provides a method for preparing a hydrophilic PTFE membrane, the preparation method specifically including the following steps:

[0169] (1) Place the PTFE membrane in a 10 wt% ethanol solution of bis[3-(trimethoxysilyl)propyl]amine, soak it at 25°C for 60 min, and then remove it and air dry at room temperature;

[0170] (2) Place the PTFE membrane obtained in step (1) into an aqueous solution of sulfuric acid at pH 3.0 and soak it at 25°C for 3 h to complete the preliminary hydrolysis, dehydration and condensation, and then take it out;

[0171] (3) Place the PTFE membrane obtained in step (2) in a drying oven at 60°C for 6 hours to perform deep dehydration and condensation, and generate a hydrophilic functional layer on the membrane surface and in the membrane pores. Then remove the membrane.

[0172] Figure 2The image shown is a SEM image of the outer wall of the hydrophilic, durable, negatively charged PTFE membrane in Comparative Example 3. Figure 2 As shown, the pore structure on the outer surface of the PTFE membrane still exists, and the modification process will not cause membrane pore blockage.

[0173] Comparative Example 4

[0174] This comparative example provides a method for preparing a hydrophilic PTFE membrane. The difference from Example 1 is that the bis[3-(trimethoxysilyl)propyl]amine in step (1) is replaced with an equal mass of N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (KH792), while the other steps are the same as in Example 1.

[0175] Comparative Example 5

[0176] This comparative example provides a method for preparing a hydrophilic PTFE membrane. The difference from Example 1 is that the bis[3-(trimethoxysilyl)propyl]amine in step (1) is replaced with an equal mass of vinyltriethoxysilane. The other steps are the same as in Example 1.

[0177] Comparative Example 6

[0178] This comparative example provides a method for preparing a hydrophilic PTFE membrane. The difference from Example 1 is that the bis[3-(trimethoxysilyl)propyl]amine in step (1) is replaced with an equal mass of γ - Glycidyl etheroxypropyltrimethoxysilane, with other steps consistent with Example 1.

[0179] Test Example 1

[0180] Test samples: hydrophilic, durable, negatively charged PTFE membranes provided in Examples 1-8, unmodified PTFE membranes provided in Comparative Example 1, and hydrophilic PTFE membranes provided in Comparative Examples 2-6.

[0181] Test methods: The hydrophilicity, durability, and charge properties of the prepared hydrophilic, durable, and negatively charged PTFE membrane were tested. The PTFE membrane fibers were dried in an oven at 40°C for 24 h, followed by characterization tests, as detailed below:

[0182] (1) Hydrophilicity test: Static contact angle test was used.

[0183] (2) Durability test: The PTFE membrane was immersed in HCl solution with pH = 2, NaOH solution with pH = 12 and NaClO solution with 1000 ppm for 10 days respectively. After washing off the acid, alkali or oxidant with pure water, it was thoroughly dried and the contact angle test was carried out to examine the hydrophilicity of the PTFE membrane.

[0184] (3) Charge potential test: The potential value at pH 7.0 was measured using a Zeta potentiometer.

[0185] The specific test results are shown in Table 1:

[0186] Table 1

[0187]

[0188] The data in Table 1 above show that the surface properties of the PTFE membrane underwent a fundamental transformation after modification using the ARGET ATRP technique: the water contact angle decreased significantly from ~133° of the original membrane to below 60°, and the Zeta potential shifted negatively from ~-15 mV to -35.6~-49.2 mV. This indicates that the hydrophilicity and negative charge of the membrane surface were simultaneously achieved and precisely controlled. More importantly, the examples show that the modified membrane maintained stable performance parameters after 10 days of accelerated aging with acid, alkali, and oxidants. This result fully demonstrates that the functional layer constructed using the method of this invention is extremely firmly bonded to the PTFE fiber substrate, capable of withstanding the harsh chemical cleaning conditions in actual use, and ensuring the durability of its performance.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a negatively charged polytetrafluoroethylene membrane, characterized in that, The method for preparing the negatively charged polytetrafluoroethylene membrane includes the following steps: (1) The polytetrafluoroethylene membrane is placed in an alcohol solution containing a siloxane coupling agent for a first immersion treatment; wherein the siloxane coupling agent is a bifunctional aminosiloxane. (2) The polytetrafluoroethylene membrane obtained in step (1) is placed in an acidic aqueous solution for a second immersion treatment to complete the preliminary hydrolysis and dehydration condensation. (3) The polytetrafluoroethylene membrane obtained in step (2) is dried to complete the deep dehydration condensation. (4) First, react the polytetrafluoroethylene membrane obtained in step (3) with the acyl halide. After bonding the atom transfer radical polymerization initiation site on the surface of the polytetrafluoroethylene membrane, the electron transfer activation and regeneration catalyst atom transfer radical polymerization reaction is carried out. The negatively charged hydrophilic monomer is grafted onto the surface of the polytetrafluoroethylene membrane with the initiation site to obtain the negatively charged polytetrafluoroethylene membrane. The specific steps of grafting negatively charged hydrophilic monomers include: placing a polytetrafluoroethylene membrane with initiation sites in a solution containing negatively charged hydrophilic monomers to carry out a grafting reaction, thereby obtaining the negatively charged polytetrafluoroethylene membrane. The solution containing the negatively charged hydrophilic monomer comprises, by concentration: 1-100 mM of the negatively charged hydrophilic monomer, 0.005-0.5 mM of the reducing agent, 0.01-1 mM of the catalyst, 0.03-3 mM of the ligand, and the balance being the solvent; the negatively charged hydrophilic monomer is selected from sodium styrene sulfonate and / or acrylamido-2-methylpropanesulfonic acid.

2. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (1), the bifunctional aminosiloxane is selected from bis[3-(trimethoxysilyl)propyl]amine and / or bis[3-(triethoxysilyl)propyl]amine; And / or, in step (1), the alcohol solution containing siloxane coupling agent comprises, by mass percentage: 0.2-12.5% ​​siloxane coupling agent, with the remainder being alcohol solvent; And / or, in step (1), the alcohol solvent is selected from ethanol and / or isopropanol.

3. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (1), the temperature of the first soaking treatment is 15~25℃; And / or, in step (1), the first soaking treatment time is 10~1440 min.

4. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (2), the pH of the acidic aqueous solution is 3.0~4.5; And / or, in step (2), the acidic aqueous solution comprises an acidic solute and water; In step (2), the acidic solute is selected from any one or at least a combination of two of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

5. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (2), the temperature of the second soaking treatment is 15~25℃; And / or, in step (2), the second soaking treatment time is 0.5~24 h.

6. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (3), the drying process is carried out in a drying oven; And / or, in step (3), the drying temperature is 50~70℃; And / or, in step (3), the drying process takes 0.5 to 10 hours.

7. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (4), the step of transferring the bonded atom to the radical polymerization initiation site specifically includes: The polytetrafluoroethylene membrane obtained in step (3) is placed in a solution containing acyl halide to carry out a bonding reaction, thereby obtaining a polytetrafluoroethylene membrane with initiation sites. And / or, the acyl halide is selected from 2-bromoisobutyryl bromide and / or 2-bromopropionyl bromide; And / or, the acyl halide-containing solution comprises, by mass percentage: 0.1-5% acyl halide, with the remainder being anhydrous medium; And / or, the anhydrous medium comprises, by mass percentage: 0.1-5% triethylamine, with the balance being tetrahydrofuran; And / or, the bonding reaction is carried out at a temperature of 0~25℃ and for a time of 0.5~12 h.

8. The method for preparing a negatively charged polytetrafluoroethylene membrane according to claim 1, characterized in that, In step (4), the reducing agent is selected from any one or a combination of at least two of ascorbic acid, stannous isooctanoate or silver powder; And / or, the catalyst is selected from divalent copper salts and / or trivalent iron salts; And / or, the ligand is selected from any one or a combination of at least two of N,N,N',N',N''-pentamethyldiethylenetriamine, iminodiacetic acid, tri-(3,6-dioxoheptyl)amine, and triphenylphosphine; And / or, the solvent is an aqueous solution of ethanol; And / or, the grafting reaction temperature is 20~25℃, and the grafting reaction time is 0.5~6 h.

9. A negatively charged polytetrafluoroethylene membrane, characterized in that, The negatively charged polytetrafluoroethylene membrane is prepared by the preparation method according to any one of claims 1 to 8; The initial contact angle of the negatively charged polytetrafluoroethylene film is 50~60°, and the Zeta potential of the negatively charged polytetrafluoroethylene film is -50~-30 mV.

10. The use of a negatively charged polytetrafluoroethylene membrane according to claim 9 in the preparation of products for mine water treatment.

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