A bipolar membrane, its preparation method and use

Abstract

The application provides a bipolar membrane and a preparation method and application thereof. The bipolar membrane comprises a cation exchange layer, an anion exchange layer and an interface catalytic enhancement layer arranged between the cation exchange layer and the anion exchange layer; the cation exchange layer is a cation exchange membrane containing sulfonic acid groups, the anion exchange layer is an anion exchange membrane containing quaternary ammonium groups; the interface catalytic enhancement layer is an interpenetrating polymer network structure containing Cu-ZIF, the interpenetrating polymer network structure is a crosslinked network of epoxy modified polystyrene and acrylate; the cation exchange layer and the interface catalytic enhancement layer are combined through covalent bonds; the anion exchange layer and the interface catalytic enhancement layer are combined through electrostatic adsorption. In the interface catalytic enhancement layer, the stable loading of the catalyst is realized by using Cu-ZIF, and the firm combination between the bipolar membrane layers is realized by using the interpenetrating polymer network structure.

Description

Technical Field

[0001] This invention belongs to the field of bipolar membrane technology, specifically relating to a bipolar membrane, its preparation method, and its application. Background Technology

[0002] Bipolar membranes are composite ion exchange membranes with a special "sandwich" structure, typically consisting of three layers: a cation exchange layer, an intermediate catalyst layer, and an anion exchange layer. Their core function is to efficiently dissociate water molecules into H+ ions through the intermediate catalyst layer under reverse bias. + and OH - This enables in-situ preparation of acids and alkalis, and resource-based treatment of high-salt wastewater.

[0003] However, bipolar membranes suffer from insufficient stability in practical industrial applications, severely limiting their long-term high-efficiency operation. Conventional bipolar membranes often employ simple lamination or coating methods to bond the anion and cation exchange layers and the intermediate catalyst layer, relying solely on physical adhesion. This results in poor interlayer bonding stability, making them prone to delamination and peeling during long-term operation. Furthermore, traditional bipolar membranes commonly use metal oxide catalysts, which are physically adsorbed or simply dispersed and loaded onto the intermediate catalyst layer. During long-term operation, these catalysts are prone to aggregation and detachment, leading to leakage from the intermediate catalyst layer. This catalyst loss directly weakens the water dissociation catalytic performance, affecting the high-efficiency operation of the bipolar membrane. Therefore, there is an urgent need for a bipolar membrane with high stability. Summary of the Invention

[0004] The purpose of this invention is to provide a bipolar membrane and its preparation method. The bipolar membrane provided by this invention maintains high interfacial exfoliation strength and low catalyst loss rate during long-term operation.

[0005] This invention provides a bipolar membrane comprising a cation exchange layer, an anion exchange layer, and an interfacial catalytic enhancement layer disposed between the cation exchange layer and the anion exchange layer; the cation exchange layer is a cation exchange membrane containing sulfonic acid groups, and the anion exchange layer is an anion exchange membrane containing quaternary ammonium groups; the interfacial catalytic enhancement layer is an interpenetrating polymer network structure containing Cu-ZIF, wherein the interpenetrating polymer network structure is a crosslinked network of epoxy-modified polystyrene and acrylate; the cation exchange layer and the interfacial catalytic enhancement layer are bonded by covalent bonds; and the anion exchange layer and the interfacial catalytic enhancement layer are bonded by electrostatic adsorption.

[0006] Preferably, the Cu-ZIF content in the interface catalytic enhancement layer is 5wt%~7wt%; the Cu-ZIF contains Cu 2+ The loading rate is 15wt%~20wt%.

[0007] Preferably, the degree of crosslinking of the epoxy-modified polystyrene and acrylate crosslinking network is 60%~70%.

[0008] Preferably, the cation exchange layer comprises a sulfonic acid polymer and a reinforcing phase distributed in the sulfonic acid polymer; the degree of sulfonation of the sulfonic acid polymer is 50% to 70%.

[0009] Preferably, the anion exchange layer comprises a quaternary ammonium polymer and a conductive phase distributed in the quaternary ammonium polymer; the degree of quaternization of the quaternary ammonium polymer is 50% to 70%.

[0010] Preferably, the bipolar membrane further includes a hydrophilic polymer grafted onto the outside of the cation exchange layer.

[0011] Preferably, the hydrophilic polymer is polyethylene glycol.

[0012] The present invention also provides a method for preparing the bipolar film described in the above technical solution, comprising:

[0013] The Cu-ZIF dispersion was mixed with the prepolymer liquid of the interpenetrating polymer network structure and coated onto the cation exchange layer, and then covered with the anion exchange layer to carry out the cross-linking reaction to obtain the bipolar membrane.

[0014] Alternatively, it may include: mixing Cu-ZIF dispersion with a prepolymer solution of an interpenetrating polymer network structure and coating it onto a cation exchange layer, then covering it with an anion exchange layer for crosslinking reaction, and then grafting a hydrophilic polymer onto the outside of the cation exchange layer to obtain a bipolar membrane;

[0015] The Cu-ZIF dispersion comprises Cu-ZIF and a polar aprotic solvent;

[0016] The prepolymer liquid of the interpenetrating polymer network structure includes epoxy-modified polystyrene, acrylate, initiator, crosslinking agent and polar aprotic solvent.

[0017] Preferably, the crosslinking reaction is a hot-pressing treatment under ultraviolet irradiation; the temperature of the hot-pressing treatment is 80~90℃, the pressure is 0.5~0.7MPa, and the time of the crosslinking reaction is 25~35min.

[0018] The present invention also provides the application of the bipolar membrane described in the above technical solution or the bipolar membrane prepared according to the preparation method described in the above technical solution in water dissociation.

[0019] This invention provides a bipolar membrane comprising a cation exchange layer, an anion exchange layer, and an interfacial catalytic enhancement layer disposed between the cation exchange layer and the anion exchange layer; the cation exchange layer is a cation exchange membrane containing sulfonic acid groups, and the anion exchange layer is an anion exchange membrane containing quaternary ammonium groups; the interfacial catalytic enhancement layer is an interpenetrating polymer network structure containing Cu-ZIF, wherein the interpenetrating polymer network structure is a crosslinked network of epoxy-modified polystyrene and acrylate; the cation exchange layer and the interfacial catalytic enhancement layer are bonded by covalent bonds; the anion exchange layer and the interfacial catalytic enhancement layer are bonded by electrostatic adsorption. This invention utilizes Cu-ZIF-supported Cu... 2+ Catalyst, whose metal center is Cu 2+ Stable coordination bonds are formed with imidazole ligands, achieving stable catalyst loading and reducing catalyst loss during long-term operation of the bipolar membrane. The interfacial catalytic enhancement layer of this invention utilizes an interpenetrating polymer network (IPN) structure formed by crosslinking epoxy-modified polystyrene and acrylate monomers. The ring-opening epoxy groups in the IPN can form stable sulfonate covalent bonds with the sulfonic acid groups in the cation exchange layer. The IPN deeply penetrates the anion exchange layer containing quaternary ammonium groups. Furthermore, the negatively charged groups on the surface and inside of the IPN can form stable electrostatic interactions with the positively charged quaternary ammonium groups in the anion exchange layer, achieving a strong bond between the intermediate interfacial catalytic enhancement layer and the anion and cation exchange layers, thus improving the interfacial peel strength of the bipolar membrane during long-term operation. Experimental results show that the bipolar membrane provided by this invention has an initial water dissociation rate of 99.8%, which remains as high as 99.4% after 1000 hours of operation; the interfacial peel strength is as high as 28 N / m, decreasing by only 2 N / m after 1000 hours of operation. Detailed Implementation

[0020] This invention provides a bipolar membrane comprising a cation exchange layer, an anion exchange layer, and an interfacial catalytic enhancement layer disposed between the cation exchange layer and the anion exchange layer; the cation exchange layer is a cation exchange membrane containing sulfonic acid groups, and the anion exchange layer is an anion exchange membrane containing quaternary ammonium groups; the interfacial catalytic enhancement layer is an interpenetrating polymer network structure containing Cu-ZIF, wherein the interpenetrating polymer network structure is a crosslinked network of epoxy-modified polystyrene and acrylate; the cation exchange layer and the interfacial catalytic enhancement layer are bonded by covalent bonds; and the anion exchange layer and the interfacial catalytic enhancement layer are bonded by electrostatic adsorption.

[0021] The bipolar membrane provided by this invention includes a cation exchange layer, which is a cation exchange membrane containing sulfonic acid groups. The sulfonic acid groups in the cation exchange layer of this invention are covalently bonded to the interfacial catalytic enhancement layer, achieving a strong bond between the intermediate interfacial catalytic enhancement layer and the cation exchange layer, thereby improving the interfacial peel strength of the bipolar membrane during long-term operation.

[0022] In this invention, the thickness of the cation exchange layer is preferably 30-50 μm; in one embodiment, the thickness of the cation exchange layer can be 30-40 μm or 40-50 μm. By controlling the thickness of the cation exchange layer within the above range, this invention optimizes the interface structure of the bipolar membrane, reduces membrane resistance, improves water dissociation efficiency, avoids interlayer interpenetration and short circuits, and ensures long-term performance.

[0023] In this invention, the exchange capacity of the cation exchange layer is preferably 1.2~1.5 mmol / g; as one embodiment of this invention, the exchange capacity of the cation exchange layer can be 1.3 mmol / g or 1.4 mmol / g.

[0024] In this invention, the cation exchange layer preferably comprises a sulfonic acid polymer and a reinforcing phase distributed within the sulfonic acid polymer. The sulfonic acid polymer is preferably one or more of sulfonated polystyrene, sulfonated polyether ether ketone, sulfonated polyimide, and sulfonated polysulfone. As one embodiment of this invention, the sulfonic acid polymer can be sulfonated polystyrene, sulfonated polyether ether ketone, sulfonated polyimide, or sulfonated polysulfone. The degree of sulfonation of the sulfonic acid polymer is preferably 50% to 70%, more preferably 55% to 65%, and even more preferably 59% to 61%. As one embodiment of this invention, the degree of sulfonation of the sulfonic acid polymer can be 50%, 60%, or 70%. By controlling the degree of sulfonation of the sulfonic acid polymer in the cation exchange layer within the above range, this invention ensures a strong bond between the intermediate interfacial catalytic reinforcement layer and the cation exchange layer.

[0025] In one embodiment of the present invention, the reinforcing phase can be one or both of nano-silica and nano-titanium dioxide; in an embodiment of the present invention, the reinforcing phase is nano-silica. In another embodiment of the present invention, the content of the reinforcing phase can be 5wt%~10wt%, 7wt%~10wt%, or 9wt%~10wt%; in an embodiment of the present invention, the content of the reinforcing phase is 9.09wt%. By introducing the above-mentioned reinforcing phase into the cation exchange layer and controlling its content within the above range, the present invention is beneficial to improving the mechanical strength, dimensional stability, and chemical stability of the cation exchange layer, thereby enhancing the overall performance of the bipolar membrane.

[0026] The bipolar membrane provided by this invention includes an anion exchange layer, which is an anion exchange membrane containing quaternary ammonium groups. The quaternary ammonium groups in the anion exchange layer of this invention are electrostatically adsorbed onto the interfacial catalytic enhancement layer, achieving a strong bond between the intermediate interfacial catalytic enhancement layer and the anion exchange layer, thus improving the interfacial peel strength of the bipolar membrane during long-term operation.

[0027] In this invention, the thickness of the anion exchange layer is preferably 25-40 μm; in one embodiment, the thickness of the anion exchange layer can be 25-35 μm or 35-40 μm. By controlling the thickness of the anion exchange layer within the above range, this invention optimizes the interface structure of the bipolar membrane, reduces membrane resistance, improves water dissociation efficiency, avoids interlayer interpenetration and short circuits, and ensures long-term performance.

[0028] In this invention, the exchange capacity of the anion exchange layer is preferably 1.0~1.3 mmol / g; as one embodiment of this invention, the exchange capacity of the anion exchange layer can be 1.1 mmol / g or 1.2 mmol / g.

[0029] In this invention, the anion exchange layer preferably comprises a quaternary ammonium polymer and a conductive phase distributed within the quaternary ammonium polymer. As one embodiment of this invention, the quaternary ammonium polymer can be one or more of quaternized polystyrene, quaternized polyether ether ketone, quaternized polyimide, and quaternized polysulfone; in an embodiment of this invention, the quaternary ammonium polymer is quaternized polystyrene. As one embodiment of this invention, the degree of quaternization of the quaternary ammonium polymer can be 50%~70%, or 55%~65%; in an embodiment of this invention, the degree of quaternization of the quaternary ammonium polymer is 55%. By controlling the degree of quaternization of the quaternary ammonium polymer in the anion exchange layer within the above range, this invention ensures a strong bond between the intermediate interfacial catalytic enhancement layer and the anion exchange layer.

[0030] In one embodiment of the present invention, the conductive phase may be graphene oxide. In another embodiment, the content of the conductive phase may be 0.5 wt% to 1.0 wt%; in an embodiment of the present invention, the content of the conductive phase is 0.79 wt%. By introducing the aforementioned conductive phase into the anion exchange layer and controlling its content within the above range, the present invention facilitates the construction of continuous and efficient anion transport channels, improves ionic conductivity, reduces membrane resistance, and simultaneously enhances the mechanical strength, dimensional stability, and chemical stability of the anion exchange layer, thereby improving the overall performance of the bipolar membrane.

[0031] The bipolar membrane provided by this invention further includes an interfacial catalytic enhancement layer disposed between the cation exchange layer and the anion exchange layer. The interfacial catalytic enhancement layer is an interpenetrating polymer network structure comprising Cu-ZIF, wherein the interpenetrating polymer network structure is a crosslinked network of epoxy-modified polystyrene and acrylate. This invention utilizes Cu-ZIF-supported Cu... 2+ Catalyst, whose metal center is Cu 2+ The formation of stable coordination bonds with imidazole ligands facilitates stable catalyst loading. This invention utilizes the aforementioned interfacial catalytic enhancement layer. In the interpenetrating polymer network structure of the interfacial catalytic enhancement layer, the epoxy groups of the epoxy-modified polystyrene form ring-opening bonds with the sulfonic acid groups in the cation exchange layer, forming stable sulfonate covalent bonds. The interpenetrating polymer network structure deeply penetrates the anion exchange layer containing quaternary ammonium groups. Furthermore, the interpenetrating polymer network structure can form stable electrostatic interactions with the positively charged quaternary ammonium groups in the anion exchange layer through its surface and internal negatively charged groups, which is beneficial for achieving a strong bond between the intermediate interfacial catalytic enhancement layer and the anion and cation exchange layers.

[0032] In this invention, the thickness of the interfacial catalytic enhancement layer is preferably 8-15 μm; as one embodiment of this invention, the thickness of the interfacial catalytic enhancement layer can be 9 μm, 11 μm, 12 μm, 13 μm, or 15 μm. By controlling the thickness of the interfacial catalytic enhancement layer within the above range, this invention helps to reduce interfacial resistance and energy consumption while ensuring efficient water dissociation catalytic activity, preventing interpenetration and neutralization of anion and cation exchange layers, enhancing interlayer bonding and structural stability, thereby improving the overall service life of the bipolar membrane.

[0033] In this invention, the content of Cu-ZIF in the interfacial catalytic enhancement layer is preferably 5wt%~7wt%, more preferably 6wt%~7wt%. The particle size of the Cu-ZIF is preferably 50~100nm; as one embodiment of this invention, the particle size of the Cu-ZIF can be 50~80nm, or 80~100nm. In this invention, the Cu in the Cu-ZIF... 2+ The loading amount is preferably 15wt%~20wt%, more preferably 15wt%~19wt%.

[0034] In this invention, the degree of crosslinking of the epoxy-modified polystyrene and acrylate crosslinking network is preferably 60% to 70%. By controlling the degree of crosslinking of the epoxy-modified polystyrene and acrylate crosslinking network within the above range, this invention can both ensure the fixation of Cu-ZIF and enhance the interfacial bonding between the interfacial catalytic enhancement layer and the anion and cation exchange layers.

[0035] The bipolar membrane provided by this invention preferably further includes a hydrophilic polymer grafted onto the outer side of the cation exchange layer. In this invention, the hydrophilic polymer is preferably polyethylene glycol (PEG), more preferably PEG with Mn = 1000-2000, and even more preferably PEG with Mn = 1500-2000. By grafting a hydrophilic polymer onto the surface of the cation exchange layer, this invention improves the hydrophilicity and antifouling ability of the membrane without significantly increasing the membrane resistance, protects the internal ion exchange layer, and is beneficial for improving the long-term operational stability of the bipolar membrane.

[0036] In this invention, the grafting method between the hydrophilic polymer and the cation exchange layer is preferably achieved by adding the isocyanate group of the grafted hydrophilic polymer to the sulfonic acid group of the cation exchange layer. Through this grafting method, the hydrophilic polymer can be firmly grafted onto the sulfonic acid polymer of the cation exchange layer, improving the hydrophilicity and antifouling ability of the membrane without significantly increasing the membrane resistance. By forming a hydrophilic surface (also known as an antifouling surface layer), the adsorption of proteins and colloids is reduced, thereby decreasing the increase in membrane resistance.

[0037] In this invention, the cation exchange layer and the interfacial catalytic enhancement layer are bonded by covalent bonds; the anion exchange layer and the interfacial catalytic enhancement layer are bonded by electrostatic adsorption. The ring-opening epoxy groups in the interfacial catalytic enhancement layer of this invention can form stable sulfonate covalent bonds with the sulfonic acid groups in the cation exchange layer. Furthermore, the interfacial catalytic enhancement layer and the quaternary ammonium groups in the anion exchange layer are bonded by electrostatic adsorption, achieving a strong bond between the intermediate interfacial catalytic enhancement layer and the anion and cation exchange layers, thus improving the interfacial peel strength of the bipolar membrane during long-term operation.

[0038] This invention sets the interfacial catalytic enhancement layer as an interpenetrating polymer network structure containing Cu-ZIF. The Cu-ZIF achieves stable catalyst loading and reduces catalyst loss rate during long-term operation of the bipolar membrane. The interpenetrating polymer network structure is formed by crosslinking epoxy-modified polystyrene and acrylate monomers. It can form stable sulfonate covalent bonds with the sulfonic acid groups in the cation exchange layer and stable electrostatic interactions with the quaternary ammonium groups in the anion exchange layer. This achieves a strong bond between the intermediate interfacial catalytic enhancement layer and the anion and cation exchange layers, improving the interfacial peel strength of the bipolar membrane during long-term operation.

[0039] The present invention also provides a method for preparing the bipolar film described in the above technical solution, comprising:

[0040] The Cu-ZIF dispersion was mixed with the prepolymer liquid of the interpenetrating polymer network structure and coated onto the cation exchange layer, and then covered with the anion exchange layer to carry out the cross-linking reaction to obtain the bipolar membrane.

[0041] Alternatively, it may include: mixing Cu-ZIF dispersion with a prepolymer solution of an interpenetrating polymer network structure and coating it onto a cation exchange layer, then covering it with an anion exchange layer for crosslinking reaction, and then grafting a hydrophilic polymer onto the outside of the cation exchange layer to obtain a bipolar membrane;

[0042] The Cu-ZIF dispersion comprises Cu-ZIF and a polar aprotic solvent;

[0043] The prepolymer liquid of the interpenetrating polymer network structure includes epoxy-modified polystyrene, acrylate, initiator, crosslinking agent and polar aprotic solvent.

[0044] In this invention, a Cu-ZIF dispersion is mixed with a prepolymer liquid of an interpenetrating polymer network structure and coated onto a cation exchange layer, and then covered with an anion exchange layer to carry out a crosslinking reaction to obtain a bipolar membrane.

[0045] In this invention, the Cu-ZIF dispersion comprises Cu-ZIF and a polar aprotic solvent. Preferably, the Cu-ZIF content in the Cu-ZIF dispersion is 2wt% to 6wt%, more preferably 4wt%. The polar aprotic solvent is preferably one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, more preferably N,N-dimethylformamide.

[0046] This invention does not specifically limit the source of the Cu-ZIF; products with the desired composition and particle size can be obtained using preparation methods well known to those skilled in the art. As one embodiment of this invention, the preparation method of the Cu-ZIF may include: mixing an organic ligand, an organic solvent, and a copper source to carry out a coordination reaction, followed by sequential solid-liquid separation and drying to obtain Cu-ZIF.

[0047] In embodiments of the present invention, the organic ligand is 2-methylimidazole, the organic solvent is methanol, and the copper source is copper nitrate trihydrate; the mass-to-volume ratio of 2-methylimidazole to methanol is 0.82 g:50 mL, and the mass ratio of 2-methylimidazole to copper nitrate trihydrate is 41:30; the mixing method involves first dissolving the organic ligand in the organic solvent, and then adding the copper source; the coordination reaction is carried out under stirring conditions at 50°C for 2 hours; the solid-liquid separation method is centrifugation at 8000 rpm for 10 minutes; and the drying method is vacuum drying at 60°C for 12 hours. The present invention obtains Cu-ZIF through the above preparation method, which is beneficial for achieving Cu catalyst… 2+ Stable load.

[0048] In this invention, the prepolymer liquid of the interpenetrating polymer network structure includes epoxy-modified polystyrene, acrylate, initiator, crosslinking agent and polar aprotic solvent.

[0049] In embodiments of the present invention, the initiator is azobisisobutyronitrile (AIBN); the crosslinking agent is divinylbenzene (DVB); the polar aprotic solvent is N,N-dimethylformamide; the mass ratio of epoxy-modified polystyrene, acrylate, AIBN, and DVB is 3:1:0.08:0.08, and the mass-to-volume ratio of epoxy-modified polystyrene to N,N-dimethylformamide is 3g:10mL.

[0050] In this invention, the volume ratio of the Cu-ZIF dispersion to the prepolymer of the interpenetrating polymer network structure is preferably 1:1.5 to 3, more preferably 1:2. By limiting the volume ratio of the Cu-ZIF dispersion to the prepolymer of the interpenetrating polymer network structure within the above range, this invention helps to ensure the interfacial bonding force between the interface reinforcement layer and the anion and cation exchange layers.

[0051] As one embodiment of the present invention, the method for preparing the cation exchange layer may include: mixing a sulfonic acid polymer, an organic solvent and a reinforcing phase to obtain a cation exchange layer casting solution; and sequentially subjecting the cation exchange layer casting solution to casting, drying, annealing and peeling to obtain the cation exchange layer.

[0052] In embodiments of the present invention, the sulfonic acid polymer is sulfonated polystyrene; the organic solvent is N,N-dimethylformamide; the reinforcing phase is nano-silica; the mass ratio of sulfonated polystyrene to nano-silica is 10:1; the mass-volume ratio of sulfonated polystyrene to N,N-dimethylformamide is 1g:8mL; the mixing method is to first dissolve the sulfonic acid polymer in the organic solvent and stir until completely dissolved, then add the reinforcing phase and perform ultrasonic dispersion, the ultrasonic dispersion power is 200~300W, and the ultrasonic dispersion time is 30min; the casting is carried out on a 20cm×20cm glass plate; the drying is carried out in a forced-air drying oven at a temperature of 60℃ for 2h; the annealing is carried out in a vacuum at a temperature of 120℃ for 4h.

[0053] In an embodiment of the present invention, the cation exchange layer is a cation exchange layer with a thickness of 40 μm and an exchange capacity of 1.5 mmol / g prepared by the above preparation method.

[0054] In this invention, the coating thickness of the Cu-ZIF dispersion and the prepolymerized liquid of the interpenetrating polymer network structure onto the cation exchange layer is preferably 10-20 μm, more preferably 12-22 μm, and even more preferably 14-16 μm; in an embodiment of this invention, the coating thickness of the Cu-ZIF dispersion and the prepolymerized liquid of the interpenetrating polymer network structure onto the cation exchange layer is 15 μm. By controlling the coating thickness within the above range, this invention helps to ensure the interfacial bonding force between the interface reinforcement layer and the anion and cation exchange layers.

[0055] As one embodiment of the present invention, the preparation method of the anion exchange layer may include: mixing a quaternary ammonium polymer, an organic solvent and a conductive phase to obtain an anion exchange layer casting solution; and sequentially casting, drying and peeling the anion exchange layer casting solution to obtain the anion exchange layer.

[0056] In embodiments of the present invention, the quaternary ammonium polymer is quaternized polystyrene; the organic solvent is N,N-dimethylformamide; the conductive phase is graphene oxide; the mass ratio of quaternized polystyrene to graphene oxide is 5:0.04; the mass-volume ratio of quaternized polystyrene to N,N-dimethylformamide is 1g:6mL; the mixing method is to first dissolve the quaternary ammonium polymer in the organic solvent and stir until completely dissolved, then add the conductive phase and perform ultrasonic dispersion, the ultrasonic dispersion power is 200~300W, and the ultrasonic dispersion time is 30min; the casting is carried out on a 20cm×20cm glass plate; the drying is carried out in a forced-air drying oven, the drying temperature is 60℃, and the drying time is 2h.

[0057] In an embodiment of the present invention, the anion exchange layer is an anion exchange layer with a thickness of 35 μm and an exchange capacity of 1.2 mmol / g prepared by the above preparation method.

[0058] In this invention, the crosslinking reaction is preferably carried out under hot pressing under ultraviolet irradiation; the crosslinking reaction time is preferably 25-35 min, more preferably 30-35 min; the hot pressing temperature is preferably 80-90℃, more preferably 80-85℃; the hot pressing pressure is preferably 0.5-0.7 MPa, more preferably 0.5-0.6 MPa; the ultraviolet irradiation wavelength is 360-370 nm, the ultraviolet irradiation power is 100-200 W, and the ultraviolet irradiation distance is 10-15 cm; as one embodiment of this invention, the ultraviolet irradiation wavelength is 365 nm, the ultraviolet irradiation power is 100 W, and the ultraviolet irradiation distance is 10 cm. The conditions described above for the crosslinking reaction are conducive to the ring-opening of the epoxy groups in the interpenetrating polymer network structure of the interfacial catalytic enhancement layer, which react with the sulfonic acid groups of the cation exchange layer to form stable sulfonate covalent bonds. At the same time, the interpenetrating polymer network structure of the interfacial catalytic enhancement layer and the polystyrene segments of the anion exchange layer deeply penetrate each other. Furthermore, the negatively charged groups on the surface and inside of the interpenetrating polymer network structure form a stable electrostatic interaction with the positively charged quaternary ammonium groups in the anion exchange layer to enhance interfacial adhesion. This is beneficial for achieving a strong bond between the intermediate interfacial catalytic enhancement layer and the anion and cation exchange layers, thereby improving the interfacial peel strength of the bipolar film.

[0059] When the bipolar membrane includes a hydrophilic polymer grafted onto the outside of the cation exchange layer, after the crosslinking reaction is completed, the present invention preferably sprays an isocyanate solution of the grafted hydrophilic polymer onto the outside of the cation exchange layer to carry out the grafting reaction, thereby obtaining the bipolar membrane.

[0060] In this invention, the isocyanate solution of the grafted hydrophilic polymer is preferably composed of the isocyanate of the grafted hydrophilic polymer and an organic solvent. The preferred mass-to-volume ratio of the grafted hydrophilic polymer isocyanate to the organic solvent is (0.2~0.4 g):(10~20 mL). The hydrophilic polymer is preferably polyethylene glycol. The grafting rate of the hydrophilic polymer in the grafted hydrophilic polymer isocyanate is preferably 30%~40%. The preferred organic solvent is ethanol.

[0061] In this invention, the coating thickness of the grafted polyethylene glycol isocyanate solution is preferably 10-15 μm.

[0062] In this invention, the grafting reaction temperature is preferably 55-65°C, and the grafting reaction time is preferably 2-3 hours; in an embodiment of this invention, the grafting reaction temperature is 60°C, and the time is 2 hours. These curing conditions facilitate the addition reaction between the isocyanate groups of the grafted polyethylene glycol and the sulfonic acid groups of the cation exchange layer, grafting polyethylene glycol into the sulfonic acid polymer of the cation exchange layer, thereby achieving the grafting of a hydrophilic polymer onto the outside of the cation exchange layer, resulting in a bipolar membrane with antifouling capabilities.

[0063] The bipolar membrane prepared by the above method in this invention can realize the catalyst Cu 2+ It provides a stable load and achieves a strong bond between the bipolar film layers.

[0064] This invention also provides the application of the bipolar membrane described in the above-described technical solution, or the bipolar membrane prepared according to the preparation method described in the above-described technical solution, in water dissociation. This invention does not impose any special limitations on the application; any application method well known to those skilled in the art can be used.

[0065] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0066] Example 1

[0067] The bipolar membrane consists of a cation exchange layer, an anion exchange layer, an interfacial catalytic enhancement layer disposed between the cation and anion exchange layers, and a hydrophilic polymer grafted onto the outside of the cation exchange layer. The cation exchange layer is composed of sulfonated polystyrene (sulfonation degree of 60%) and reinforcing phase nano-silica, with a thickness of 40 μm and an exchange capacity of 1.4 mmol / g. The anion exchange layer is composed of quaternized polystyrene (quaternization degree of 55%) and conductive phase graphene oxide, with a thickness of 35 μm and an exchange capacity of 1.2 mmol / g. The interfacial catalytic enhancement layer is composed of Cu-ZIF and an interpenetrating polymer network structure (Cu-ZIF content in the interfacial catalytic enhancement layer is 6 wt%), the interpenetrating polymer network structure is a cross-linked network of epoxy-modified polystyrene and acrylate (cross-linking degree of 65%), and the thickness of the interfacial catalytic enhancement layer is 12 μm.

[0068] Preparation method of bipolar membrane: Cu-ZIF dispersion and prepolymer liquid of interpenetrating polymer network structure were mixed at a volume ratio of 1:2 and coated onto cation exchange layer with a coating thickness of 15 μm. Then, an anion exchange layer was covered and crosslinking reaction was carried out (hot pressing under UV irradiation for 30 min, UV irradiation wavelength of 365 nm, power of 100 W, distance of 10 cm, hot pressing temperature of 80℃, pressure of 0.5 MPa). A polyethylene glycol grafted isocyanate solution (obtained by dissolving 0.4 g of polyethylene glycol grafted isocyanate (polyethylene glycol grafting rate of 30%, polyethylene glycol Mn=1500) in 10 mL of ethanol organic solvent) was sprayed onto the outside of cation exchange layer with a spray thickness of 10 μm. The grafting reaction was carried out to obtain bipolar membrane (grafting reaction temperature of 60℃, time of 2 h).

[0069] Preparation method of Cu-ZIF dispersion: 0.82 g of 2-methylimidazole was dissolved in 50 mL of methanol, and then 0.6 g of copper nitrate trihydrate was added. The mixture was stirred at 50 °C for 2 h, centrifuged at 8000 rpm for 10 min to collect the precipitate, and vacuum dried at 60 °C for 12 h to obtain Cu-ZIF (Cu in Cu-ZIF). 2+ The loading was 18%); Cu-ZIF was dispersed in N,N-dimethylformamide to prepare a Cu-ZIF dispersion with a Cu-ZIF content of 4wt%.

[0070] Preparation method of prepolymer liquid with interpenetrating polymer network structure: Mix 3g epoxy modified polystyrene, 1g acrylate, 0.08g AIBN and 0.08g DVB and dissolve in 10mL N,N-dimethylformamide and stir until homogeneous;

[0071] Preparation method of cation exchange layer: 10g of sulfonated polystyrene with a sulfonation degree of 60% was dissolved in 80mL of N,N-dimethylformamide and stirred until completely dissolved. Then, 1g of nano-silica was added and ultrasonically dispersed for 30min under a power of 280W to obtain cation exchange layer casting solution. The cation exchange layer casting solution was cast in a 20cm×20cm glass plate, dried at 60℃ for 2h, and vacuum annealed at 120℃ for 4h. The cation exchange layer was then peeled off to obtain the cation exchange layer.

[0072] Preparation method of anion exchange layer: 5g of quaternized polystyrene with a degree of quaternization of 55% was dissolved in 30mL of N,N-dimethylformamide and stirred until completely dissolved. Then, 0.04g of graphene oxide was added and ultrasonically dispersed for 30min at a power of 280W to obtain a cation exchange layer casting solution. The cation exchange layer casting solution was cast in a 20cm×20cm glass plate and dried at 60℃ for 2h. The cation exchange layer was then peeled off to obtain the cation exchange layer.

[0073] Comparative Example 1

[0074] It consists of a cation exchange layer, an anion exchange layer, and an intermediate simple catalyst layer; wherein the composition, thickness, and exchange capacity of the cation exchange layer and the anion exchange layer are exactly the same as those in Example 1; the intermediate simple catalyst layer is a simple coating formed by mixing FeSO4 (ferrous catalyst) and polyvinyl alcohol (FeSO4 content is 6wt%), without interpenetrating polymer network structure, and the thickness of the intermediate simple catalyst layer is 12μm.

[0075] Methods for preparing bipolar films:

[0076] Preparation of the catalyst coating solution: Mix 0.6g FeSO4 with 9.4g polyvinyl alcohol, disperse it in 25mL N,N-dimethylformamide, and stir until dissolved to obtain the catalyst coating solution; directly coat the cation exchange layer surface with the catalyst coating solution to a thickness of 15μm, directly cover the anion exchange layer, and dry at 60℃ for 2h (omit the ultraviolet irradiation and hot-press crosslinking steps). There are no covalent bonds or stable electrostatic adsorption bindings, and no hydrophilic polymer grafting is performed to obtain a bipolar membrane.

[0077] The preparation methods for the cation exchange layer and the anion exchange layer are exactly the same as those in Example 1.

[0078] The water dissociation efficiency of the bipolar membrane prepared in Example 1 and the bipolar membrane in Comparative Example 1 was tested. The specific test conditions were as follows: in a three-compartment electrodialysis apparatus, using 0.5 mol / L NaCl as the feed solution, and a current density of 1000 A / m 2 It runs continuously for 1000 hours.

[0079] The bipolar membrane prepared in Example 1 had an initial water dissociation efficiency of 99.8% and a transmembrane voltage of 1.35V. After 1000 hours of continuous operation, the water dissociation efficiency was 99.4% and the transmembrane voltage was 1.46V. The bipolar membrane in Comparative Example 1 had an initial water dissociation efficiency of 98.1% and a transmembrane voltage of 1.63V. After 1000 hours of continuous operation, the water dissociation efficiency was 97.4% and the transmembrane voltage was 2.37V. It can be calculated that the water dissociation efficiency retention rate of the bipolar membrane in Example 1 after 1000 hours of operation was 99.6%, while that of the bipolar membrane in Comparative Example 1 was 99.3%. The transmembrane voltage increase in Example 1 was 8.1%, and that in Comparative Example 1 was 45.4%. This indicates that the stability of the catalyst in the bipolar membrane of this application has been significantly improved.

[0080] The bipolar membrane prepared in Example 1 and the bipolar membrane in Comparative Example 1 were subjected to interfacial peel strength test. The specific test method was as follows: the interfacial peel strength was tested using a universal tensile testing machine (speed 5 mm / min).

[0081] The bipolar membrane prepared in Example 1 exhibited an interfacial peel strength of 28 N / m, which decreased by only 2 N / m after 1000 h (retention rate 92.86%). In contrast, the bipolar membrane in Comparative Example 1 had an interfacial peel strength of 18 N / m, which decreased by 7 N / m after 1000 h (retention rate 61.11%). This demonstrates that the bipolar membrane prepared in Example 1 of this invention achieves strong interlayer bonding and can maintain high interfacial peel strength during long-term operation.

[0082] The bipolar membrane prepared in Example 1 and the bipolar membrane in Comparative Example 1 were subjected to antifouling tests. The specific test conditions were as follows: 0.5 mol / L NaCl containing 500 ppm bovine serum albumin (BSA) was used as the feed solution and the mixture was continuously run for 300 h.

[0083] The bipolar film prepared in Example 1 showed an internal resistance of 4.2 Ω·cm after 300 hours. 2 Increased to 4.8Ω·cm 2 The internal resistance of the bipolar film in Comparative Example 1 decreased from 4.0 Ω·cm after 300 hours. 2 Increased to 5.8Ω·cm 2 It can be calculated that the membrane resistance of the bipolar membrane in Example 1 increased by 14.29% after 300 hours of operation, while the membrane resistance of the bipolar membrane in Comparative Example 1 increased by 45% after 300 hours of operation. This indicates that the antifouling performance of the bipolar membrane of this application has been significantly improved. By grafting hydrophilic polymers onto the outside of the cation exchange layer to form a hydrophilic surface, the adsorption of proteins and colloids can be reduced.

[0084] As can be seen from the above embodiments, the bipolar membrane provided by the present invention exhibits good stability during long-term operation. In the interfacial catalytic enhancement layer, stable catalyst loading is achieved through the use of Cu-ZIF, resulting in a low catalyst loss rate. The initial water dissociation efficiency of the bipolar membrane is 99.8%, and after 1000 hours of continuous operation, the hydrolysis efficiency remains at 99.4%, achieving a hydrolysis efficiency retention rate as high as 99.6%. In the bipolar membrane, the interfacial catalytic enhancement layer is firmly bonded to the anion and cation exchange layers, with an interfacial peel strength as high as 28 N / m, decreasing by only 2 N / m after 1000 hours, demonstrating high interfacial peel strength. By grafting hydrophilic polymers onto the outside of the cation exchange layer, the adsorption of proteins and colloids is reduced, and the membrane resistance of the bipolar membrane decreases from 4.2 Ω·cm within 300 hours. 2 Increased to 4.8Ω·cm 2 This resulted in an increase in film resistance as low as 14.29%.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A bipolar membrane, comprising a cation exchange layer, an anion exchange layer, and an interfacial catalytic enhancement layer disposed between the cation exchange layer and the anion exchange layer; wherein the cation exchange layer is a cation exchange membrane containing sulfonic acid groups, and the anion exchange layer is an anion exchange membrane containing quaternary ammonium groups; the interfacial catalytic enhancement layer is an interpenetrating polymer network structure containing Cu-ZIF, wherein the interpenetrating polymer network structure is a crosslinked network of epoxy-modified polystyrene and acrylate; the cation exchange layer and the interfacial catalytic enhancement layer are bonded by covalent bonds; and the anion exchange layer and the interfacial catalytic enhancement layer are bonded by electrostatic adsorption.

2. The bipolar film according to claim 1, characterized in that, The content of Cu-ZIF in the interface catalytic enhancement layer is 5wt%~7wt%; the Cu-ZIF contains Cu 2+ The loading rate is 15wt%~20wt%.

3. The bipolar film according to claim 1, characterized in that, The degree of crosslinking of the epoxy-modified polystyrene and acrylate crosslinking network is 60%~70%.

4. The bipolar film according to claim 1, characterized in that, The cation exchange layer comprises a sulfonic acid polymer and a reinforcing phase distributed in the sulfonic acid polymer; the degree of sulfonation of the sulfonic acid polymer is 50% to 70%.

5. The bipolar film according to claim 1, characterized in that, The anion exchange layer comprises a quaternary ammonium polymer and a conductive phase distributed in the quaternary ammonium polymer; the degree of quaternization of the quaternary ammonium polymer is 50%~70%.

6. The bipolar film according to any one of claims 1 to 5, characterized in that, The bipolar membrane also includes a hydrophilic polymer grafted onto the outside of the cation exchange layer.

7. The bipolar film according to claim 6, characterized in that, The hydrophilic polymer is polyethylene glycol.

8. A method for preparing the bipolar film according to any one of claims 1 to 7, comprising: The Cu-ZIF dispersion was mixed with the prepolymer liquid of the interpenetrating polymer network structure and coated onto the cation exchange layer, and then covered with the anion exchange layer to carry out the cross-linking reaction to obtain the bipolar membrane. Alternatively, it may include: mixing Cu-ZIF dispersion with a prepolymer solution of an interpenetrating polymer network structure and coating it onto a cation exchange layer, then covering it with an anion exchange layer for crosslinking reaction, and then grafting a hydrophilic polymer onto the outside of the cation exchange layer to obtain a bipolar membrane; The Cu-ZIF dispersion comprises Cu-ZIF and a polar aprotic solvent; The prepolymer liquid of the interpenetrating polymer network structure includes epoxy-modified polystyrene, acrylate, initiator, crosslinking agent and polar aprotic solvent.

9. The preparation method according to claim 8, characterized in that, The crosslinking reaction is carried out by hot pressing under ultraviolet irradiation; the temperature of the hot pressing is 80~90℃, the pressure is 0.5~0.7MPa, and the time of the crosslinking reaction is 25~35min.

10. The application of the bipolar membrane according to any one of claims 1 to 7 or the bipolar membrane prepared by the preparation method according to any one of claims 8 to 9 in water dissociation.