A nanofiber-reinforced bipolar membrane and its preparation method

Abstract

This invention discloses a nanofiber-reinforced bipolar membrane and its preparation method, relating to the field of bipolar membrane preparation technology. Specifically: S1: Prepare a branched anionic polyacrylamide fiber textile solution; spin it onto a nickel mesh using electrospinning to obtain an intermediate nanofiber membrane; S2: Prepare anionic polyacrylamide fiber textile solution; spin it onto one side of the intermediate nanofiber membrane using electrospinning, immerse it in anhydrous ferric chloride ethanol solution for crosslinking treatment, wash, and dry to form a cationic nanofiber membrane; S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution; spin it onto the other side of the intermediate nanofiber membrane using electrospinning, place it in the vapor of glutaraldehyde aqueous solution for crosslinking treatment, wash, and dry to form an anionic nanofiber membrane, obtaining a nanofiber-reinforced bipolar membrane; the obtained fiber-reinforced bipolar membrane exhibits a low transmembrane voltage and good water dissociation ability.

Description

Technical Field

[0001] This invention relates to the field of bipolar membrane preparation technology, specifically a nanofiber reinforced bipolar membrane and its preparation method. Background Technology

[0002] Bipolar membranes are a special type of ion exchange membrane composed of a cation exchange membrane, an anion exchange membrane, and an intermediate interface layer between them. Under the action of a DC electric field, water molecules in the intermediate interface layer are catalytically dissociated into H+. + and OH - Under the directional migration of the cation exchange membrane and anion exchange membrane, the molecules transfer to both sides of the intermediate membrane, thereby generating acid and base sequentially on both sides of the membrane. In traditional processes, due to the common practice of casting and then hot-pressing, the intermediate interface layer of the bipolar membrane often suffers from problems such as high impedance, resulting in high transmembrane voltage, poor catalytic efficiency, low acid and base production efficiency, and high energy consumption.

[0003] Electrospinning is an important method for preparing nanofibers. By applying a voltage to a polymer solution or melt, charged polymer droplets are stretched under the influence of an electric field, eventually solidifying to form nanofibers and a three-dimensional network structure with a porous structure. This process can significantly reduce transmembrane voltage and improve water dissociation efficiency when used in bipolar membrane preparation. However, in existing electrospinning techniques, the fibers have large diameters and high inhomogeneity, resulting in large pores in the resulting fiber membranes. When used in bipolar membranes, the relatively large and uneven pores make the membrane more prone to swelling. Consequently, it cannot effectively block the transmembrane migration of counterions from the electrolytes on both sides, increasing the transmembrane voltage and reducing water dissociation efficiency.

[0004] In summary, solving the above problems and preparing a nanofiber-reinforced bipolar membrane with low transmembrane voltage and high water dissociation efficiency is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a nanofiber-reinforced bipolar membrane and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for preparing a nanofiber-reinforced bipolar membrane includes the following steps:

[0008] S1: Prepare a branched anionic polyacrylamide fiber textile solution; spin it onto a nickel mesh using a single electrospinning process to obtain an intermediate nanofiber membrane;

[0009] S2: Prepare anionic polyacrylamide fiber textile solution; spin it into a film on one side of the middle nanofiber membrane through a secondary electrospinning process, immerse it in anhydrous ferric chloride ethanol solution for one crosslinking treatment, wash, dry, and form a cationic nanofiber membrane.

[0010] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution; spin it into a film on the other side of the middle nanofiber membrane through a three-stage electrospinning process, place it in the steam of glutaraldehyde aqueous solution for secondary crosslinking treatment, wash, dry, and form an anionic nanofiber membrane to obtain a nanofiber-reinforced bipolar membrane.

[0011] The branched anionic polyacrylamide fiber textile liquid comprises the following raw materials, in parts by weight: 1-3 parts of branched AA-AMA-acrylamide copolymer, 3-5 parts of linear anionic polyacrylamide, 0.3-0.5 parts of modified graphene oxide, and the remainder is 50-60 wt% acetic acid solution.

[0012] Preferably, the anionic polyacrylamide fiber textile solution comprises the following raw materials, based on 100 parts by weight: 2-4 parts linear anionic polyacrylamide, with the remainder being 50-60 wt% acetic acid solution; the polyvinyl alcohol-chitosan fiber textile solution comprises the following raw materials, based on 100 parts by weight: 7-8 parts polyvinyl alcohol, 1-1.5 parts chitosan, with the remainder being 50-60 wt% acetic acid solution.

[0013] A preferred method for preparing the branched AA-AMA-acrylamide copolymer includes the following steps: under a nitrogen atmosphere, acrylamide and a chain transfer agent are added to an acetate buffer solution with a pH of 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; N,N'-methylenebisacrylamide is prepared into a crosslinking agent solution using deionized water; the reactive monomer solution is heated to 55~65℃, ammonium persulfate is added, and the crosslinking agent solution is added dropwise, controlling the dropwise addition time to be 2~2.5h; after completion, anionic monomer is added, and the reaction is stirred at 55~65℃ for 2~3h; the mixture is washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0014] Preferably, the branched AA-AMA-acrylamide copolymer comprises the following raw materials in parts by mass: 8-12 parts acrylamide, 0.05-0.07 parts chain transfer agent, 1.1-1.2 parts N,N'-methylenebisacrylamide, 0.02-0.03 parts ammonium persulfate, and 6-8 parts anionic monomer.

[0015] Preferably, the anionic monomer comprises acrylic acid (AA) and allyl malondiic acid (AMA) in a mass ratio of 8:2~3.

[0016] Preferred method for preparing modified graphene oxide includes the following steps: (1) Adding graphene oxide to deionized water and dispersing it evenly by ultrasonication, adding 2-amino-3-butenoic acid and triethylamine, stirring at 50-60°C for 6-8 hours, centrifuging, washing, and drying to obtain alkenylated graphene oxide; (2) Under a nitrogen atmosphere, adding alkenylated graphene oxide to an acetate buffer solution with pH 5±0.1 and dispersing it evenly by ultrasonication, removing oxygen, and then adding acrylamide and anionic monomer; heating the monomer solution to 55-65°C, adding ammonium persulfate, stirring and reacting for 2-3 hours, washing, purifying, and drying to obtain modified graphene oxide.

[0017] Preferably, the alkenylated graphene oxide comprises the following raw materials, by mass parts: 1-1.5 parts graphene oxide, 2-3 parts 2-amino-3-butenoic acid, and 2-3 parts triethylamine; the modified graphene oxide comprises the following raw materials, by mass parts: 1-1.5 parts alkenylated graphene oxide, 4-6 parts acrylamide, 3-4 parts anionic monomer, and 0.01-0.02 parts ammonium persulfate.

[0018] Preferably, in the first electrospinning process, the voltage is 20-25 kV, the flow rate is 0.3-0.5 mL / h, the distance between the needle and the nickel mesh is 15-20 mm, and the humidity is 50-60%; in the second electrospinning process, the voltage is 15-20 kV, the flow rate is 0.5-1 mL / h, the distance between the needle and the intermediate nanofiber membrane is 10-15 mm, and the humidity is 50-60%; in the third electrospinning process, the voltage is 15-20 kV, the flow rate is 0.5-1 mL / h, the distance between the needle and the intermediate nanofiber membrane is 10-15 mm, and the humidity is 50-60%.

[0019] Preferably, during the primary crosslinking process, the concentration of the anhydrous ferric chloride ethanol solution is 8-10 wt%, and the crosslinking time is 10-12 min; during the secondary crosslinking process, the concentration of the glutaraldehyde aqueous solution is 45-50 wt%, and the crosslinking time is 8-10 min.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention prepares branched AA-AMA-acrylamide copolymer and modified graphene oxide, and formulates them into a spinning solution. An intermediate nanofiber membrane is prepared by electrospinning process, and cationic nanofiber membranes and anionic nanofiber membranes are prepared on both sides of the intermediate nanofiber membrane. The resulting fiber-reinforced bipolar membrane has a low transmembrane voltage and a good water dissociation ability.

[0021] The preparation method of the branched AA-AMA-acrylamide copolymer involves using acrylamide and anionic monomers as reactive monomers, and N,N'-methylenebisacrylamide as a crosslinking agent. The copolymer is prepared by initiation with ammonium persulfate and under the action of a chain transfer agent. The preparation method of modified graphene oxide involves reacting 2-amino-3-butenoic acid with the epoxy groups on the surface of graphene oxide under the catalysis of triethylamine to obtain alkenylated graphene oxide. Further, under the initiation of ammonium persulfate, the double bonds grafted onto the graphene oxide are used as reaction sites to copolymerize with acrylamide and anionic monomers to obtain modified graphene oxide.

[0022] In electrospinning, anionic polyacrylamide has a high viscosity due to its numerous hydrophilic groups, requiring significant solvent dilution for electrospinning. Furthermore, the linear molecules are more prone to entanglement, resulting in larger diameter nanofiber membranes with relatively large and uneven pores, making them more susceptible to swelling. When used in bipolar membranes, this fails to effectively block the transmembrane migration of counterions from the electrolytes on both sides, increasing the transmembrane voltage and reducing water dissociation efficiency. This invention addresses this by adding a prepared branched AA-AMA-acrylamide copolymer. In solution, the more compact branched structure enhances electrostatic repulsion, allowing the branched segments to extend and reducing entanglement between linear polyacrylamide molecular chains. This reduces the solution viscosity, resulting in finer and more uniform fibers during electrospinning. The resulting fiber membrane has smaller pores and a larger specific surface area, thereby reducing the transmembrane voltage and improving hydrolysis efficiency. Simultaneously, acrylic acid and allyl malonic acid with a mass ratio of 8:2~3 are introduced as anionic monomers. On the one hand, their ortho-carboxyl group structure helps to better coordinate with iron ions, reduce the loss of iron ions and improve the stability of the membrane. On the other hand, it can adjust the viscosity and resistivity of the spinning solution, making it easier to stretch and solidify, thereby generating finer fibers, further reducing the transmembrane voltage and improving the hydrolysis efficiency.

[0023] However, the amount of branched AA-AMA-acrylamide copolymer that can be added is limited. Excessive addition can destabilize the system, causing fiber breakage and decreased uniformity during spinning, leading to a sharp increase in the transmembrane voltage of the bipolar membrane. The inventors discovered that by adding graphene oxide, the amount of branched AA-AMA-acrylamide copolymer can be further increased, and the prepared bipolar membrane exhibits even lower transmembrane voltage and better water dissociation performance. This is because graphene oxide, with its nanosheet structure, provides a nanoframework during electrospinning, stabilizing the jet, reducing whiplash instability, lowering the possibility of breakage, and improving uniformity, thereby reducing the transmembrane voltage. Furthermore, graphene oxide itself contains a large number of hydroxyl and carboxyl groups, which can react with water, lowering the activation energy for water dissociation, and effectively fixing iron ions, thus improving the catalytic efficiency of water dissociation. Meanwhile, during the graphene modification process, similar polyacrylamide segments are introduced on its surface through free radical in-situ polymerization, which improves the dispersibility of graphene oxide in the spinning solution, compensates for the defects of nanofibers in electrospinning, improves the stability of the film layer, and makes the fibers more continuous and uniform, thereby reducing the transmembrane voltage and improving the hydrolysis efficiency. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0025] It should be noted that the following quantities are by weight. There are no special restrictions on the manufacturers from which the raw materials involved in this invention can be purchased. Exemplary examples include: Acrylamide (CAS No.: 79-06-1); Chain transfer agent: 3-benzylthioalkylthiocarbonylthioalkyl propionic acid (CAS No.: 497931-76-7); N,N'-methylenebisacrylamide (CAS No.: 110-26-9); Ammonium persulfate (CAS No.: 7727-54-0); Acrylic acid (CAS No.: ). 79-10-7; CAS number of allyl malonic acid: 2583-25-7; Graphene oxide, sheet diameter 0.2~10μm, grade Q-000673, provided by Xi'an Qiyue Biotechnology Co., Ltd.; CAS number of 2-amino-3-butenoic acid: 52773-87-2; Linear anionic polyacrylamide, molecular weight 8 million; Polyvinyl alcohol, average degree of polymerization 1750, degree of alcoholysis ≥99%; Chitosan, molecular weight 500,000, degree of deacetylation ≥99%.

[0026] In the following examples, parts refer to parts by weight, and all raw materials mentioned above and others not mentioned are commercially available.

[0027] Example 1: A method for preparing a nanofiber-reinforced bipolar membrane includes the following steps:

[0028] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 8:2.5) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0029] Step 2: Preparation of modified graphene oxide: (1) Add 1 part of graphene oxide to 100 parts of deionized water and ultrasonically disperse evenly. Add 2.5 parts of 2-amino-3-butenoic acid and 2.5 parts of triethylamine. Stir at 55℃ for 8 hours, centrifuge, wash, and dry to obtain alkenylated graphene oxide; (2) Under a nitrogen atmosphere, add 1 part of alkenylated graphene oxide to an acetate buffer solution with pH 5±0.1 and ultrasonically disperse evenly. After deoxygenation, add 5 parts of acrylamide and 3.5 parts of anionic monomer (including acrylic acid and allyl malonic acid with a mass ratio of 8:2.5); heat the reaction monomer solution to 60℃, add 0.01 parts of ammonium persulfate, stir for 2.5 hours, wash, purify, and dry to obtain modified graphene oxide;

[0030] Step 3: Preparation of nanofiber-reinforced bipolar membranes:

[0031] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 2 parts branched AA-AMA-acrylamide copolymer, 4 parts linear anionic polyacrylamide, 0.5 parts modified graphene oxide, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0032] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0033] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0034] Example 2: A method for preparing a nanofiber-reinforced bipolar film includes the following steps:

[0035] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 8:2.5) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0036] Step 2: Preparation of modified graphene oxide: (1) Add 1 part of graphene oxide to 100 parts of deionized water and ultrasonically disperse evenly. Add 2.5 parts of 2-amino-3-butenoic acid and 2.5 parts of triethylamine. Stir at 55℃ for 8 hours, centrifuge, wash, and dry to obtain alkenylated graphene oxide; (2) Under a nitrogen atmosphere, add 1 part of alkenylated graphene oxide to an acetate buffer solution with pH 5±0.1 and ultrasonically disperse evenly. After deoxygenation, add 5 parts of acrylamide and 3.5 parts of anionic monomer (including acrylic acid and allyl malonic acid with a mass ratio of 8:2.5); heat the reaction monomer solution to 60℃, add 0.01 parts of ammonium persulfate, stir for 2.5 hours, wash, purify, and dry to obtain modified graphene oxide;

[0037] Step 3: Preparation of nanofiber-reinforced bipolar membranes:

[0038] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 1 part branched AA-AMA-acrylamide copolymer, 3 parts linear anionic polyacrylamide, 0.5 parts modified graphene oxide, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0039] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0040] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0041] Example 3: A method for preparing a nanofiber-reinforced bipolar film includes the following steps:

[0042] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 8:2.5) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0043] Step 2: Preparation of modified graphene oxide: (1) Add 1 part of graphene oxide to 100 parts of deionized water and ultrasonically disperse evenly. Add 2.5 parts of 2-amino-3-butenoic acid and 2.5 parts of triethylamine. Stir at 55℃ for 8 hours, centrifuge, wash, and dry to obtain alkenylated graphene oxide; (2) Under a nitrogen atmosphere, add 1 part of alkenylated graphene oxide to an acetate buffer solution with pH 5±0.1 and ultrasonically disperse evenly. After deoxygenation, add 5 parts of acrylamide and 3.5 parts of anionic monomer (including acrylic acid and allyl malonic acid with a mass ratio of 8:2.5); heat the reaction monomer solution to 60℃, add 0.01 parts of ammonium persulfate, stir for 2.5 hours, wash, purify, and dry to obtain modified graphene oxide;

[0044] Step 3: Preparation of nanofiber-reinforced bipolar membranes:

[0045] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 3 parts branched AA-AMA-acrylamide copolymer, 5 parts linear anionic polyacrylamide, 0.5 parts modified graphene oxide, and the remainder being 55wt% acetic acid solution); set the process parameters as follows: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0046] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0047] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0048] Example 4: A method for preparing a nanofiber-reinforced bipolar film includes the following steps:

[0049] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 8:2.5) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0050] Step 2: Preparation of nanofiber-reinforced bipolar membranes:

[0051] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 1 part branched AA-AMA-acrylamide copolymer, 3 parts linear anionic polyacrylamide, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0052] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0053] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0054] Comparative Example 1: Based on Example 4, branched AA-AMA-acrylamide copolymer was not added to the spinning solution of the intermediate nanofiber membrane, and the rest of the process remained unchanged, as follows:

[0055] Step 1: Preparation of nanofiber-reinforced bipolar membranes:

[0056] S1: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 22kV, flow rate is 0.4mL / h, distance between needle and nickel mesh is 16mm, humidity is 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0057] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0058] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0059] Comparative Example 2: Based on Example 4, the ratio of the two components in the anionic monomers was exchanged, while the other processes remained unchanged, as follows:

[0060] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 2.5:8) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0061] Step 2: Preparation of nanofiber-reinforced bipolar membranes:

[0062] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 1 part branched AA-AMA-acrylamide copolymer, 3 parts linear anionic polyacrylamide, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0063] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0064] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0065] Comparative Example 3: Based on Example 1, without the addition of graphene oxide, the remaining processes remain unchanged, as follows:

[0066] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 8:2.5) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0067] Step 2: Preparation of nanofiber-reinforced bipolar membranes:

[0068] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 2 parts branched AA-AMA-acrylamide copolymer, 4 parts linear anionic polyacrylamide, and the remainder is 55wt% acetic acid solution); set the process parameters: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0069] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0070] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0071] Comparative Example 4: Based on Example 1, the graphene oxide was not modified, and the remaining processes remained unchanged, as follows:

[0072] Step 1: Preparation of branched AA-AMA-acrylamide copolymer: Under a nitrogen atmosphere, 10 parts of acrylamide and 0.06 parts of chain transfer agent were added to 30 parts of acetate buffer solution with pH 5±0.1, mixed evenly, and deoxygenated to obtain a reactive monomer solution; 1.1 parts of N,N'-methylenebisacrylamide were prepared into a crosslinking agent solution with 100 parts of deionized water; the reactive monomer solution was heated to 60℃, 0.02 parts of ammonium persulfate were added, and the crosslinking agent solution was added dropwise, controlling the dropwise addition time to 2h. After completion, 7 parts of anionic monomer (including acrylic acid and allyl malonic acid in a mass ratio of 8:2.5) were added, and the reaction was stirred at 60℃ for 2.5h. The mixture was washed, purified, and dried to obtain the branched AA-AMA-acrylamide copolymer.

[0073] Step 2: Preparation of nanofiber-reinforced bipolar membranes:

[0074] S1: Prepare a branched anionic polyacrylamide fiber textile solution (by 100 parts by weight: 2 parts branched AA-AMA-acrylamide copolymer, 4 parts linear anionic polyacrylamide, 0.5 parts graphene oxide, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 22kV, flow rate 0.4mL / h, distance between needle and nickel mesh 16mm, humidity 55%, and spin it onto the nickel mesh in a single electrospinning process to obtain an intermediate nanofiber membrane;

[0075] S2: Prepare anionic polyacrylamide fiber textile solution (3 parts linear anionic polyacrylamide and the remainder is 55wt% acetic acid solution per 100 parts by mass); set the process parameters as follows: voltage is 17kV, flow rate is 0.8mL / h, distance between needle and intermediate nanofiber membrane is 10mm, humidity is 55%, and spin the solution into a film on one side of the intermediate nanofiber membrane through a secondary electrospinning process. Immerse the film in a 10wt% ferric chloride anhydrous ethanol solution for a single crosslinking treatment for 10min, wash, and dry to form a cationic nanofiber membrane.

[0076] S3: Prepare a polyvinyl alcohol-chitosan fiber textile solution (by 100 parts by mass: 7 parts polyvinyl alcohol, 1.5 parts chitosan, and the remainder being a 55wt% acetic acid solution); set the process parameters as follows: voltage 17kV, flow rate 0.6mL / h, distance between the needle and the intermediate nanofiber membrane 10mm, humidity 55%, and spin the solution onto the other side of the intermediate nanofiber membrane through a three-stage electrospinning process. Then, place the solution in a 50wt% glutaraldehyde aqueous solution in steam for a second crosslinking treatment for 10min, wash, and dry to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane.

[0077] Performance testing: (1) Bipolar membrane IV curve test: Set up four compartments: cathode compartment, anode compartment, acid compartment, and alkali compartment. Place the bipolar membrane samples prepared in each example and comparative example between the acid compartment and the alkali compartment. The cathode compartment and anode compartment are filled with 0.5 mol / L sodium sulfate aqueous solution, and the acid compartment and alkali compartment are filled with 0.5 mol / L sodium chloride solution. Start the peristaltic pump and set the speed to 60 rpm. After the multimeter voltage shows 0V, turn on the DC regulated power supply, adjust the current and record the voltage value. Increase by 10 mA / cm each time. 2 up to 150 mA / cm 2 (2) Water dissociation performance test: Set up four compartments: cathode compartment, anode compartment, acid compartment, and alkali compartment. Set up bipolar membrane samples prepared in each example and comparative example between the acid compartment and the alkali compartment. The cathode compartment and anode compartment are 0.5 mol / L sodium sulfate aqueous solution, and the acid compartment and alkali compartment are 0.5 mol / L sodium chloride solution. Start the peristaltic pump, set the speed to 60 rpm, turn on the DC regulated power supply, and adjust the current to 50 mA / cm. 2 Samples were taken from the acid chamber and the alkali chamber at 15-minute intervals to determine the acid and alkali content. The total test time was 60 minutes, and the acid and alkali production rates were calculated. The experimental data are shown in the table below.

[0078]

[0079] Conclusion: As shown in the table, this invention prepares branched AA-AMA-acrylamide copolymer and modified graphene oxide, formulates them into a spinning solution, and prepares an intermediate nanofiber membrane by electrospinning. Cationic nanofiber membranes and anionic nanofiber membranes are then prepared on both sides of the intermediate nanofiber membrane. The resulting fiber-reinforced bipolar membrane has a low transmembrane voltage and good water dissociation ability.

[0080] In Comparative Example 1, the spinning solution of the intermediate nanofiber membrane did not contain branched AA-AMA-acrylamide copolymer. The linear polyacrylamide molecular chains were more prone to entanglement, resulting in a larger fiber diameter, a significantly increased transmembrane voltage, and a decreased water dissociation efficiency. In Comparative Example 2, the ratio of the two anionic monomers in the exchanged anionic monomers increased the fiber diameter, reduced uniformity, increased transmembrane voltage, and decreased water dissociation efficiency. In Comparative Example 3, without the addition of graphene oxide, the high content of branched AA-AMA-acrylamide copolymer failed to provide a nanostructure, leading to an unstable spinning system, a significantly increased transmembrane voltage, and a decreased water dissociation efficiency in the prepared bipolar membrane. In Comparative Example 4, the graphene oxide was not modified, resulting in decreased dispersibility, increased transmembrane voltage, and a similarly decreased hydrolysis efficiency.

[0081] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nanofiber-reinforced bipolar membrane, characterized in that: Includes the following steps: S1: Prepare branched anionic polyacrylamide fiber textile solution; The intermediate nanofiber membrane was obtained by electrospinning it onto a nickel mesh in a single electrospinning process. S2: Preparation of anionic polyacrylamide fiber textile solution; The nanofiber membrane was spun into a film on one side of the middle nanofiber membrane through a secondary electrospinning process, then immersed in an anhydrous ferric chloride ethanol solution for a single crosslinking treatment, washed, and dried to form a cationic nanofiber membrane. S3: Prepare polyvinyl alcohol-chitosan fiber textile solution; The nanofiber membrane was spun into a film on the other side of the middle nanofiber membrane through a three-stage electrospinning process. It was then subjected to a second cross-linking treatment in the vapor of glutaraldehyde aqueous solution, washed, and dried to form an anionic nanofiber membrane, thus obtaining a nanofiber-reinforced bipolar membrane. The branched anionic polyacrylamide fiber textile liquid comprises the following raw materials, in parts by weight: 1-3 parts branched anionic polyacrylamide, 3-5 parts linear anionic polyacrylamide, 0.3-0.5 parts modified graphene oxide, and the remainder is 50-60 wt% acetic acid solution. The preparation method of the modified graphene oxide includes the following steps: (1) Adding graphene oxide to deionized water and ultrasonically dispersing it evenly, adding 2-amino-3-butenoic acid and triethylamine, stirring at 50~60℃ for 6~8h, centrifuging, washing, and drying to obtain alkenylated graphene oxide; (2) Under a nitrogen atmosphere, adding alkenylated graphene oxide to an acetate buffer solution with pH 5±0.1 and ultrasonically dispersing it evenly, removing oxygen and adding acrylamide and anionic monomer; heating the reaction monomer solution to 55~65℃, adding ammonium persulfate, stirring and reacting for 2~3h, washing, purifying, and drying to obtain modified graphene oxide; The alkenylated graphene oxide comprises the following raw materials, by mass parts: 1-1.5 parts graphene oxide, 2-3 parts 2-amino-3-butenoic acid, and 2-3 parts triethylamine; the modified graphene oxide comprises the following raw materials, by mass parts: 1-1.5 parts alkenylated graphene oxide, 4-6 parts acrylamide, 3-4 parts anionic monomer, and 0.01-0.02 parts ammonium persulfate.

2. The method for preparing a nanofiber-reinforced bipolar film according to claim 1, characterized in that: The anionic polyacrylamide fiber textile solution comprises the following raw materials, based on 100 parts by weight: 2-4 parts linear anionic polyacrylamide, with the remainder being a 50-60 wt% acetic acid solution; the polyvinyl alcohol-chitosan fiber textile solution comprises the following raw materials, based on 100 parts by weight: 7-8 parts polyvinyl alcohol, 1-1.5 parts chitosan, with the remainder being a 50-60 wt% acetic acid solution.

3. The method for preparing a nanofiber-reinforced bipolar film according to claim 1, characterized in that: The preparation method of the branched anionic polyacrylamide includes the following steps: under a nitrogen atmosphere, acrylamide and chain transfer agent are added to an acetate buffer solution with a pH of 5±0.1, mixed evenly, and deoxygenated to obtain a reaction monomer solution; N,N'-methylenebisacrylamide is prepared into a crosslinking agent solution using deionized water; the reaction monomer solution is heated to 55~65℃, ammonium persulfate is added, and the crosslinking agent solution is added dropwise, controlling the dropwise addition time to be 2~2.5h; after completion, anionic monomer is added, and the reaction is stirred at 55~65℃ for 2~3h; the mixture is washed, purified, and dried to obtain branched anionic polyacrylamide.

4. The method for preparing a nanofiber-reinforced bipolar film according to claim 3, characterized in that: The branched anionic polyacrylamide comprises the following raw materials, by mass parts: 8-12 parts acrylamide, 0.05-0.07 parts chain transfer agent, 1.1-1.2 parts N,N'-methylenebisacrylamide, 0.02-0.03 parts ammonium persulfate, and 6-8 parts anionic monomer.

5. The method for preparing a nanofiber-reinforced bipolar film according to claim 3, characterized in that: The anionic monomer comprises acrylic acid and allyl malondi acid in a mass ratio of 8:2~3.

6. The method for preparing a nanofiber-reinforced bipolar film according to claim 1, characterized in that: During the first electrospinning process, the voltage is 20-25 kV, the flow rate is 0.3-0.5 mL / h, the distance between the needle and the nickel mesh is 15-20 mm, and the humidity is 50-60%. During the second electrospinning process, the voltage is 15-20 kV, the flow rate is 0.5-1 mL / h, the distance between the needle and the intermediate nanofiber membrane is 10-15 mm, and the humidity is 50-60%. During the third electrospinning process, the voltage is 15-20 kV, the flow rate is 0.5-1 mL / h, the distance between the needle and the intermediate nanofiber membrane is 10-15 mm, and the humidity is 50-60%.

7. The method for preparing a nanofiber-reinforced bipolar film according to claim 1, characterized in that: During the first crosslinking process, the concentration of the anhydrous ferric chloride ethanol solution is 8-10 wt%, and the crosslinking time is 10-12 min; during the second crosslinking process, the concentration of the glutaraldehyde aqueous solution is 45-50 wt%, and the crosslinking time is 8-10 min.

8. The nanofiber-reinforced bipolar membrane prepared by the method for preparing a nanofiber-reinforced bipolar membrane according to any one of claims 1 to 7.

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