MXene Bipolar Membrane, Its Preparation Method and Electrodialysis Device

Abstract

This application relates to the field of electrodialysis technology, and particularly to an MXene bipolar membrane, a preparation method thereof, and an electrodialysis device. The preparation method of the MXene bipolar membrane comprises the following steps: performing a first film-forming treatment on a first casting solution containing polyvinylidene fluoride, a cationic monomer, and a first cross-linking agent to form a cation exchange layer; spraying a suspension containing an MXene material on the cation exchange layer to form an intermediate interface layer; performing a second film-forming treatment on a second casting solution containing polyvinylidene fluoride, an anionic monomer, and a second cross-linking agent to form an anion exchange layer on the intermediate interface layer. The MXene bipolar membrane prepared in this application has the advantages of high hydrolysis dissociation efficiency, excellent electrochemical performance, and good structural stability, and has broad application prospects in the field of electrodialysis.

Description

Technical Field

[0001] This application relates to the technical field of electrodialysis, and particularly to an MXene bipolar membrane, a preparation method thereof, and an electrodialysis device. Background Art

[0002] A bipolar membrane is a novel ion exchange membrane, which is a layered polymer membrane composed of a cation exchange layer, an intermediate interface layer, and an anion exchange layer stacked in sequence. Under the action of an external electric field, water molecules dissociate into H + and OH - in the intermediate interface layer, and migrate to the solutions on both sides of the bipolar membrane through the charged groups on the cation exchange layer and the anion exchange layer, thereby playing the role of producing acid and alkali.

[0003] An efficient bipolar membrane should have characteristics such as high selectivity, high hydrolysis dissociation efficiency, good structural stability, and low energy consumption. However, most traditional bipolar membranes have problems such as low hydrolysis dissociation efficiency, low electrochemical performance, and poor structural stability, which limit the development of bipolar membranes. Summary of the Invention

[0004] Based on this, it is necessary to provide an MXene bipolar membrane, a preparation method thereof, and an electrodialysis device to solve the problems of low hydrolysis dissociation efficiency, low electrochemical performance, and poor structural stability existing in traditional bipolar membranes.

[0005] The above object of this application is achieved through the following technical solutions:

[0006] In the first aspect of this application, a preparation method of an MXene bipolar membrane is provided, including the following steps:

[0007] Perform a first film-forming treatment on a first casting solution containing polyvinylidene fluoride, a cation monomer, and a first cross-linking agent to form a cation exchange layer;

[0008] Spray a suspension containing an MXene material on the cation exchange layer to form an intermediate interface layer;

[0009] Perform a second film-forming treatment on a second casting solution containing polyvinylidene fluoride, an anion monomer, and a second cross-linking agent to form an anion exchange layer on the intermediate interface layer.

[0010] In one embodiment, the cation monomer includes one or more of sodium styrene sulfonate and sodium allyl sulfonate.

[0011] In one embodiment, the anion monomer includes one or more of vinylimidazole and vinylpyridine.

[0012] In one embodiment, in the first casting solution, the mass ratio of polyvinylidene fluoride to the cationic monomer is 1:(0.5 - 1.5).

[0013] In one embodiment, in the second casting solution, the mass ratio of polyvinylidene fluoride to the anionic monomer is 1:(0.5 - 1.5).

[0014] In one embodiment, the first crosslinking agent includes divinylbenzene.

[0015] In one embodiment, the second crosslinking agent includes 1,6 - dibromohexane.

[0016] In one embodiment, the mass ratio of the cationic monomer to the first crosslinking agent is 100:(3 - 15).

[0017] In one embodiment, the mass ratio of the anionic monomer to the second crosslinking agent is 100:(3 - 15).

[0018] In one embodiment, the first casting solution further contains a first initiator, and the second casting solution further contains a second initiator.

[0019] In one embodiment, the first initiator and the second initiator each independently include one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, azodicyanovaleric acid, benzoyl peroxide, and 2,2 - azobis(2 - methylpropylimid) dihydrochloride.

[0020] In one embodiment, the mass ratio of the cationic monomer to the first initiator is 100:(0.5 - 5).

[0021] In one embodiment, the mass ratio of the anionic monomer to the second initiator is 100:(0.5 - 5).

[0022] In one embodiment, the solid content of the first casting solution and the second casting solution is each independently 10% - 30%.

[0023] In one embodiment, the preparation method of the MXene material includes the following steps:

[0024] Etch the MAX precursor in an etching solution containing hydrogen ions and fluoride ions, and perform a purification treatment to prepare the MXene material.

[0025] In one embodiment, the MAX precursor includes one or more of Ti3AlC2, Ti2AlC, Ti3AlCN, Ta4AlC3, V2AlC, V3AlC2, Mo2AlC, and Mo2TiAlC2.

[0026] In one embodiment, the etching solution contains one or more of HF, HCl, and fluoride salts.

[0027] In one embodiment, the etching reaction includes the following steps: etching for 12 h to 48 h at 20°C to 50°C.

[0028] In one embodiment, the mass fraction of the MXene material in the suspension is 0.1% to 5%.

[0029] In one embodiment, the thicknesses of the cation exchange layer and the anion exchange layer are each independently 100 μm to 300 μm.

[0030] In a second aspect of the present application, there is provided an MXene bipolar membrane prepared by using the preparation method of the MXene bipolar membrane as described above.

[0031] In one embodiment, the transmembrane voltage of the MXene bipolar membrane is 0.9 V to 3 V.

[0032] In one embodiment, the current efficiency of the MXene bipolar membrane is 80% to 95%.

[0033] In one embodiment, the energy consumption of the MXene bipolar membrane is 1.1 kWh / kg to 5.3 kWh / kg.

[0034] In a third aspect of the present application, there is provided an electrodialysis device including the MXene bipolar membrane as described above.

[0035] The present application has at least the following beneficial effects:

[0036] This application conducts a blend cross-linking reaction using polyvinylidene fluoride (PVDF), a cationic monomer, and a first cross-linking agent to form a cation exchange membrane with a semi-interpenetrating network structure, and conducts a blend cross-linking reaction using PVDF, an anionic monomer, and a second cross-linking agent to form an anion exchange membrane with a semi-interpenetrating network structure. This can not only keep the bipolar membrane with a high ion exchange capacity but also limit the water absorption rate of the bipolar membrane, avoid the bipolar membrane from swelling due to excessive water absorption, and endow it with good mechanical properties and structural strength. At the same time, the MXene material is selected as the hydrolysis dissociation catalyst for the intermediate interface layer; the MXene material has high hydrophilicity, which can effectively improve the hydrolysis dissociation efficiency of the bipolar membrane; the surface of the MXene material contains rich active groups, which can form intermolecular hydrogen bond interactions with the functional groups on the surfaces of the ion exchange layers on both sides, enhance the interaction between the membrane layers, and improve the structural stability of the bipolar membrane. Therefore, the MXene bipolar membrane prepared in this application has the advantages of high hydrolysis dissociation efficiency, excellent electrochemical performance, and good structural stability, and has broad application prospects in the field of electrodialysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of this application and more completely understand this application and its beneficial effects, the following will briefly introduce the drawings required for use in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of this application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0038] Figure 1 It is a schematic flow chart of the preparation method of the MXene bipolar membrane in one embodiment;

[0039] Figure 2 It is a Raman characterization diagram of the MXene material prepared in Example 1;

[0040] Figure 3 It is an XRD spectrum diagram of the MXene material prepared in Example 1;

[0041] Figure 4 It is a C-V curve diagram of the MXene bipolar membranes of Examples 1 to 3 and the bipolar membranes of Comparative Examples 1 to 2;

[0042] Figure 5 It is a comparison diagram of the current efficiency and energy consumption of the MXene bipolar membranes of Examples 1 to 3 and the bipolar membranes of Comparative Examples 1 to 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] To facilitate the understanding of the present application, the following provides a further detailed description of the present application in conjunction with specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0045] In this application, the meaning of "and / or" includes any and all combinations of one or more of the related listed items. The meaning of "at least one" is more than one, such as one, two or more. The meaning of "multiple" or "several" is at least two, such as two, three, etc., and the meaning of "multiple layers" is at least two layers, such as two layers, three layers, etc., unless otherwise specifically defined. In the description of this application, the meaning of "several" is at least one, such as one, two, etc., unless otherwise specifically defined.

[0046] When a numerical range is disclosed in this application, the above range is considered continuous and includes the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all sub-ranges subsumed therein.

[0047] If there is no special indication, all steps of this application can be carried out sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), indicating that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c) in sequence, or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0048] In this application, "above" or "below" both include the number itself. For example, below 1 includes 1.

[0049] The temperature parameters in this application, unless otherwise specified, are allowed to be either a constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0050] In this application, room temperature refers to indoor temperature, normal temperature, or general temperature. Generally speaking, the range of room temperature can be any one of the following temperature ranges: 23°C ± 2°C, 25°C ± 5°C, or 20°C ± 5°C.

[0051] For bipolar membranes, the hydrolysis dissociation process occurs in the middle interfacial layer. Therefore, the performance of the middle interfacial layer largely determines the performance of the bipolar membrane. By selecting a suitable hydrolysis dissociation catalyst as the middle interfacial layer and adopting appropriate preparation processes and molding materials, bipolar membranes with excellent performance can be obtained. An efficient bipolar membrane should have characteristics such as high selectivity, high hydrolysis dissociation efficiency, good structural stability, and low energy consumption. However, most traditional bipolar membranes have disadvantages such as high production costs and low hydrolysis dissociation efficiency, and the binding between the middle interfacial layer and the cation exchange layer and anion exchange layer on both sides is not tight enough, resulting in reduced electrochemical performance, poor structural stability, and shortened service life of the bipolar membrane, which limits the development of bipolar membranes.

[0052] Based on this, in the first aspect of this application, a preparation method of an MXene bipolar membrane is provided.

[0053] Please refer to Figure 1 , which is a schematic flow diagram of the preparation method of the MXene bipolar membrane in an embodiment.

[0054] As Figure 1 shown, the preparation method of the MXene bipolar membrane includes the following steps:

[0055] S100: Perform a first film-forming treatment on a first casting solution containing polyvinylidene fluoride, a cationic monomer, and a first cross-linking agent to form a cation exchange layer;

[0056] S200: Spray a suspension containing MXene material on the cation exchange layer to form a middle interfacial layer;

[0057] S300: Perform a second film-forming treatment on a second casting solution containing polyvinylidene fluoride, an anionic monomer, and a second cross-linking agent to form an anion exchange layer on the middle interfacial layer.

[0058] This application uses polyvinylidene fluoride (PVDF), cationic monomers, and a first crosslinking agent to carry out a blend crosslinking reaction to form a cation exchange membrane with a semi-interpenetrating network structure, and uses PVDF, anionic monomers, and a second crosslinking agent to carry out a blend crosslinking reaction to form an anion exchange membrane with a semi-interpenetrating network structure. This can not only keep the bipolar membrane having a high ion exchange capacity but also limit the water absorption rate of the bipolar membrane, avoid the bipolar membrane from swelling due to excessive water absorption, and endow it with good mechanical properties and structural strength. At the same time, the MXene material is selected as the hydrolysis dissociation catalyst for the intermediate interface layer; the MXene material has high hydrophilicity, which can effectively improve the hydrolysis dissociation efficiency of the bipolar membrane; the surface of the MXene material contains rich active groups, which can form intermolecular hydrogen bond interactions with the functional groups on the surfaces of the ion exchange layers on both sides, enhance the interaction between the membrane layers, and improve the structural stability of the bipolar membrane. Therefore, the MXene bipolar membrane prepared in this application has the advantages of high hydrolysis dissociation efficiency, excellent electrochemical performance, and good structural stability, and has broad application prospects in the field of electrodialysis.

[0059] The preparation method of the MXene bipolar membrane is described in detail below by way of step-by-step description.

[0060] S100: Perform a first film-forming treatment on a first casting solution containing polyvinylidene fluoride, cationic monomers, and a first crosslinking agent to form a cation exchange layer.

[0061] It can be understood that the ion exchange capacity of the cation exchange layer is related to the grafting rate of the cationic monomers. The higher the content of the cationic monomers in the first casting solution, the correspondingly higher the ion exchange capacity of the obtained cation exchange layer. An appropriate water content in the bipolar membrane can promote the migration of ions, but too high a water absorption rate of the bipolar membrane will cause the bipolar membrane to swell, reducing its mechanical properties and structural strength. And this application uses PVDF, cationic monomers, and a first crosslinking agent for blend modification, so that the crosslinked polymer and the non-crosslinked polymer interpenetrate each other to form a semi-interpenetrating network structure, which can limit the water absorption rate of the bipolar membrane while maintaining the high ion exchange amount of the bipolar membrane, thereby endowing the bipolar membrane with good mechanical properties. The function of the anion exchange layer is the same and will not be elaborated.

[0062] Optionally, the cationic monomers include one or more of sodium styrene sulfonate and sodium allyl sulfonate, and further optionally one or more of sodium styrene sulfonate and sodium allyl sulfonate.

[0063] Optionally, in the first casting solution, the mass ratio of polyvinylidene fluoride to the cationic monomer is 1:(0.5 - 1.5). As an example, the mass ratio of PVDF to the cationic monomer can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, and further optionally 1:(0.8 - 1.2).

[0064] Optionally, the first crosslinking agent includes divinylbenzene.

[0065] Optionally, the mass ratio of the cationic monomer to the first crosslinking agent is 100:(3 - 15). As an example, the mass ratio of the cationic monomer to the first crosslinking agent can be 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14 or 100:15, and further optionally 100:(8 - 12).

[0066] Optionally, the first casting solution further contains a first initiator.

[0067] Optionally, the first initiator includes one or more of azobisisobutyronitrile (AIBN), azobisisovaleronitrile (AMBN), azobisisoheptonitrile (ADVN), azodicyanovaleric acid (ACVA), benzoyl peroxide (BPO), and 2,2'-azobis(2-methylpropylimid) dihydrochloride (AAPH), and further optionally azobisisobutyronitrile (AIBN).

[0068] Optionally, the mass ratio of the cationic monomer to the first initiator is 100:(0.5 - 5). As an example, the mass ratio of the cationic monomer to the first initiator can be 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5 or 100:5, and further optionally 100:(1 - 3).

[0069] Optionally, the first casting solution further contains a first organic solvent.

[0070] Optionally, the first organic solvent includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO), and further optionally DMF.

[0071] Optionally, the solid content of the first casting solution is 10% to 30%. Understandably, the solid content in the first casting solution refers to the sum of the mass fractions of PVDF, cationic monomer, first crosslinking agent, and first initiator in the first casting solution. As an example, the solid content of the first casting solution can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30%, and further optionally 10% to 20%.

[0072] Optionally, the preparation method of the first casting solution includes the following steps: Dissolve PVDF, cationic monomer, first crosslinking agent, and first initiator in the first organic solvent, stir evenly, and then carry out a temperature-raising reaction to prepare the first casting solution.

[0073] Optionally, the temperature of the temperature-raising reaction is 40°C to 80°C, and the time is 6h to 24h. As an example, the temperature of the temperature-raising reaction can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C, and the time can be 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h.

[0074] Optionally, the first film-forming treatment includes one or more of casting film-forming treatment, knife coating film-forming treatment, spin coating film-forming treatment, and spraying film-forming treatment, and further optionally knife coating film-forming treatment.

[0075] Optionally, after the first film-forming treatment, the following steps are further included: Dry the first liquid film obtained from the first film-forming treatment at 60°C to 120°C for 1h to 12h. As an example, the drying temperature of the first liquid film can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, and the drying time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h.

[0076] Optionally, the thickness of the cation exchange layer is 100μm to 300μm. As an example, the thickness of the cation exchange layer can be 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 260μm, 280μm, or 300μm.

[0077] S200: Spray the suspension containing MXene material on the cation exchange layer to form an intermediate interface layer.

[0078] Among two-dimensional (2D) nanomaterials, MXene materials are a new type of two-dimensional nanolayered materials with good flexibility, high specific surface area, high mechanical strength, and excellent electrical conductivity. Their hydrophilicity and adjustable interlayer space enhance the hydrolysis dissociation efficiency of the prepared bipolar membrane, effectively reducing the transmembrane voltage and the energy consumption of hydrolysis dissociation. The surface of MXene materials contains a large number of active functional groups, such as -OH, -F, or -O, which can form intermolecular hydrogen bond interactions with the functional groups of the ion exchange layers on both sides, making the bipolar membrane have excellent structural stability.

[0079] Optionally, the molecular formula of the MXene material is M n+1 X n T x ;

[0080] where n = 1, 2, 3; M represents a transition metal element, and M includes one or more of Ti, Ta, Mo, V, Sr, and Zr; X represents one or more of carbon and nitrogen elements; T represents a surface active functional group, and T includes one or more of -OH, -F, and -O, and x represents the number of T, and x > 0.

[0081] Optionally, the MXene material includes one or more of Ti3C2T x , Ti2CT x , Ti3CNT x , Ta4C3T x , V2CT x , V3C2T x , Mo2CT x and Mo2TiC2T x .

[0082] Optionally, the MXene material includes one or more of multi-layer MXene materials and single-layer MXene materials. Among them, the thickness of the multi-layer MXene material is 5 μm to 50 μm, and the thickness of the single-layer MXene material is 0.5 nm to 5 nm.

[0083] Optionally, the preparation method of the MXene material includes the following steps: placing the MAX precursor in an etching solution containing hydrogen ions (H + ) and fluoride ions (F - ) for an etching reaction, and performing a purification treatment to prepare the MXene material.

[0084] Optionally, the MAX precursor includes one or more of Ti3AlC2, Ti2AlC, Ti3AlCN, Ta4AlC3, V2AlC, V3AlC2, Mo2AlC, and Mo2TiAlC2.

[0085] Optionally, the etching solution contains one or more of HF, HCl, and fluorinated salts. Among them, the fluorinated salts include one or more of lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), aluminum fluoride (AlF3), and ammonium fluoride (NH4F).

[0086] Optionally, the etching solution is an HF solution, and the concentration of HF is 6 mol / L to 12 mol / L.

[0087] Optionally, the etching solution is a mixed solution containing HCl and fluorinated salts, and the molar ratio of HCl to fluorinated salts is 1:(0.1 - 0.5).

[0088] Optionally, the mass-volume ratio of the MAX precursor to the etching solution is 1 g / 10 mL to 1 g / 20 mL.

[0089] Optionally, the etching reaction includes the following steps: etching at 20°C to 50°C for 12 h to 48 h. As an example, the temperature of the etching reaction can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C, and the time of the etching reaction can be 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h, or 48 h.

[0090] Optionally, the purification treatment includes the following steps: repeatedly centrifuging and washing the reaction solution after the etching reaction with an HCl solution and deionized water until the pH value of the supernatant after centrifugation is ≥6 to obtain a washed product; dispersing the washed product in deionized water and performing ultrasonic treatment in an inert gas atmosphere to obtain a dispersion; then performing high-speed centrifugation and freeze-drying on the dispersion to obtain the MXene material.

[0091] Optionally, the method for preparing the suspension containing the MXene material includes the following steps: dispersing the MXene material in a second organic solvent to obtain a suspension.

[0092] Optionally, the second organic solvent includes one or more of DMF, DMAc, NMP, and DMSO, and further optionally DMF.

[0093] Optionally, the mass fraction of the MXene material in the suspension is 0.1% to 5%. As an example, the mass fraction of the MXene material in the suspension can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, and further optionally 0.5% to 1.5%.

[0094] Optionally, after the step of spraying the suspension containing the MXene material onto the cation exchange layer, the following steps are further included: drying the obtained second liquid film at 50°C to 80°C for 0.5 h to 2 h. As an example, the drying temperature of the second liquid film can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, and the drying time can be 0.5 h, 0.8 h, 1 h, 1.2 h, 1.5 h, 1.8 h or 2 h.

[0095] S300: Perform a second film-forming treatment on the second casting solution containing polyvinylidene fluoride, an anion monomer, and a second cross-linking agent to form an anion exchange layer on the intermediate interface layer.

[0096] Optionally, the anion monomer includes one or more of vinylimidazole and vinylpyridine, and further optionally vinylimidazole.

[0097] Optionally, in the second casting solution, the mass ratio of polyvinylidene fluoride to the anion monomer is 1:(0.5 - 1.5). As an example, the mass ratio of PVDF to the anion monomer can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, and further optionally 1:(0.8 - 1.2).

[0098] Optionally, the second cross-linking agent includes one or more of 1,6-dibromohexane and 1-bromo-n-hexane, and further optionally 1,6-dibromohexane.

[0099] Optionally, the mass ratio of the anion monomer to the second cross-linking agent is 100:(3 - 15). As an example, the mass ratio of the anion monomer to the second cross-linking agent can be 100:³, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14 or 100:15, and further optionally 100:(8 - 12).

[0100] Optionally, the second casting solution further contains a second initiator.

[0101] Optionally, the second initiator includes one or more of azobisisobutyronitrile (AIBN), azobisisovaleronitrile (AMBN), azobisisoheptonitrile (ADVN), azodicyanovaleric acid (ACVA), benzoyl peroxide (BPO), and 2,2'-azobis(2-methylpropylimid) dihydrochloride (AAPH), and further optionally azobisisobutyronitrile (AIBN).

[0102] Optionally, the mass ratio of the anionic monomer to the second initiator is 100:(0.5 - 5). As an example, the mass ratio of the anionic monomer to the second initiator can be 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5 or 100:5, and is further optionally 100:(1 - 3).

[0103] Optionally, the second casting solution further contains a third organic solvent.

[0104] Optionally, the second organic solvent includes one or more of DMF, DMAc, NMP and DMSO, and is further optionally DMF.

[0105] Optionally, the solid content of the second casting solution is 10% - 30%. It can be understood that the solid content in the second casting solution refers to the sum of the mass fractions of PVDF, anionic monomer, second crosslinking agent and second initiator in the second casting solution. As an example, the solid content of the second casting solution can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%, and is further optionally 10% - 20%.

[0106] Optionally, the preparation method of the second casting solution includes the following steps: dissolving PVDF, anionic monomer, second crosslinking agent and second initiator in a third organic solvent, stirring evenly and then carrying out a temperature-raising reaction to prepare the second casting solution.

[0107] Optionally, the temperature of the temperature-raising reaction is 40°C - 80°C, and the time is 6h - 24h. As an example, the temperature of the temperature-raising reaction can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, and the time can be 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0108] Optionally, the second film-forming treatment includes one or more of casting film-forming treatment, knife coating film-forming treatment, spin coating film-forming treatment and spraying film-forming treatment, and is further optionally knife coating film-forming treatment.

[0109] Optionally, after the second film-forming treatment, the following steps are further included: drying the third liquid film obtained by the second film-forming treatment at 60°C - 120°C for 1h - 12h. As an example, the drying temperature of the third liquid film can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, and the drying time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0110] Optionally, the thickness of the anion exchange layer is 100 μm to 300 μm. As an example, the thickness of the anion exchange layer can be 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, or 300 μm.

[0111] In the second aspect of the present application, a MXene bipolar membrane is provided, which is prepared by the preparation method of the MXene bipolar membrane described above.

[0112] Optionally, the MXene bipolar membrane includes a cation exchange layer, an intermediate interface layer, and an anion exchange layer stacked in sequence.

[0113] Optionally, the transmembrane voltage of the MXene bipolar membrane is 0.9 V to 3 V. As an example, the transmembrane voltage of the MXene bipolar membrane can be 0.9 V, 1 V, 1.2 V, 1.4 V, 1.6 V, 1.8 V, 2 V, 2.2 V, 2.4 V, 2.6 V, 2.8 V, or 3 V.

[0114] Optionally, the current efficiency of the MXene bipolar membrane is 80% to 95%. As an example, the current efficiency of the MXene bipolar membrane can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, or 95%.

[0115] Optionally, the energy consumption of the MXene bipolar membrane is 1.1 kWh / kg to 5.3 kWh / kg. As an example, the energy consumption of the MXene bipolar membrane can be 1.1 kWh / kg, 1.5 kWh / kg, 2 kWh / kg, 2.5 kWh / kg, 3 kWh / kg, 3.5 kWh / kg, 4 kWh / kg, 4.5 kWh / kg, 5 kWh / kg, or 5.3 kWh / kg.

[0116] It can be understood that the energy consumption of the MXene bipolar membrane is also one of the indicators of the water dissociation efficiency. The higher the water dissociation efficiency, the smaller the transmembrane voltage, and the lower the energy consumption of water dissociation. The MXene bipolar membrane prepared in the present application uses the MXene material as a water dissociation catalyst, and its high hydrophilicity can greatly promote the dissociation of water, reduce the transmembrane voltage, and thus reduce the energy consumption.

[0117] In the third aspect of the present application, an electrodialysis device is provided, which includes the MXene bipolar membrane described above.

[0118] Optionally, the electrodialysis device includes a positive electrode, a MXene bipolar membrane, an anion exchange membrane, a cation exchange membrane, a MXene bipolar membrane, and a negative electrode arranged in sequence.

[0119] Optionally, the electrodialysis device includes an electrode chamber and an acid-base chamber. Among them, the circulating liquid in the electrode chamber is a Na2SO4 solution with a concentration of 0.3M, and the circulating liquid in the acid-base chamber is a NaCl solution with a concentration of 0.5M.

[0120] The following is a further description in combination with specific examples and comparative examples. For the raw materials involved in the following specific examples and comparative examples, unless otherwise specified, they can all be obtained commercially. For the instruments used, unless otherwise specified, they can all be obtained commercially. For the processes involved, unless otherwise specified, they are all conventional selections of those skilled in the art.

[0121] Example 1

[0122] This example provides a method for preparing an MXene bipolar membrane, and the specific steps are as follows:

[0123] (1) Preparation of the cation exchange layer: Add 3 g of polyvinylidene fluoride, 2.5 g of sodium styrenesulfonate, 0.25 g of divinylbenzene, and 25 mL of N,N-dimethylformamide into a 100 mL round-bottom flask. After stirring and dissolving thoroughly, add 0.05 g of initiator benzoyl peroxide, raise the temperature to 70 °C and react for 8 h. After cooling, let it stand to remove bubbles to obtain the first casting solution; Pour the first casting solution onto a clean glass plate, use a 300 μm doctor blade to scrape and form a film, and then put the film into an oven at 60 °C and dry it for 5 h to obtain a cation exchange layer with a thickness of 300 μm.

[0124] (2) Preparation of the MXene material: Add 3 g of LiF to 60 mL of a 9M HCl solution, stir until completely dissolved to obtain an etching solution; Then slowly add 3 g of the MAX precursor to the etching solution, react at 35 °C for 24 h to obtain a reaction solution; Centrifuge the reaction solution and pour off the supernatant, wash the centrifuged product with a 1M HCl solution, and then repeatedly perform centrifugal washing with deionized water until the pH of the supernatant after centrifugation is ≥ 6 to obtain a washed product; Disperse the washed product in 30 mL of deionized water, and ultrasonicate it for 1 h under a N2 atmosphere to obtain a dispersion; Centrifuge the dispersion at a speed of 3500 rpm and freeze-dry the centrifuged product to obtain the MXene material; Among them, the MAX precursor is Ti3AlC2, and the etched MXene material is Ti3C2T x nanomaterial.

[0125] (3) Preparation of the intermediate interface layer: Ultrasonically disperse the MXene material in N,N-dimethylformamide to prepare a suspension with a mass fraction of 0.5%; Use a spray gun to evenly spray the suspension on the cation exchange layer and dry it at 60 °C for 30 min to obtain the intermediate interface layer.

[0126] (4) Preparation of the anion exchange layer: Add 3 g of polyvinylidene fluoride, 3 g of vinylimidazole, 0.3 g of 1,6-dibromohexane, and 25 mL of N,N-dimethylformamide into a 100 mL round-bottom flask. After fully stirring and dissolving, add 0.05 g of initiator benzoyl peroxide, heat up to 70 °C and react for 8 h. After cooling, let it stand for defoaming to obtain the second casting solution; Cast the second casting solution on the intermediate interface layer, use a 300 μm doctor blade to scrape and form a film, and then place the film in an oven at 60 °C for drying for 5 h to obtain an anion exchange layer with a thickness of 300 μm, thus obtaining the MXene bipolar membrane.

[0127] Example 2

[0128] This example provides a method for preparing an MXene bipolar membrane, and the specific steps are as follows:

[0129] (1) Preparation of the cation exchange layer: Add 2.5 g of polyvinylidene fluoride, 2.5 g of sodium styrenesulfonate, 0.25 g of divinylbenzene, and 25 mL of N,N-dimethylformamide into a 100 mL round-bottom flask. After fully stirring and dissolving, add 0.05 g of initiator benzoyl peroxide, heat up to 70 °C and react for 8 h. After cooling, let it stand for defoaming to obtain the first casting solution; Cast the first casting solution on a clean glass plate, use a 200 μm doctor blade to scrape and form a film, and then place the film in an oven at 60 °C for drying for 5 h to obtain a cation exchange layer with a thickness of 200 μm.

[0130] (2) Preparation of the MXene material: The same as step (2) of Example 1.

[0131] (3) Preparation of the intermediate interface layer: The same as step (3) of Example 1.

[0132] (4) Preparation of the anion exchange layer: Add 2.5 g of polyvinylidene fluoride, 3 g of vinylimidazole, 0.3 g of 1,6-dibromohexane, and 25 mL of N,N-dimethylformamide into a 100 mL round-bottom flask. After fully stirring and dissolving, add 0.05 g of initiator benzoyl peroxide, heat up to 70 °C and react for 8 h. After cooling, let it stand for defoaming to obtain the second casting solution; Cast the second casting solution on the intermediate interface layer, use a 200 μm doctor blade to scrape and form a film, and then place the film in an oven at 60 °C for drying for 5 h to obtain an anion exchange layer with a thickness of 200 μm, thus obtaining the MXene bipolar membrane.

[0133] Example 3

[0134] This example provides a method for preparing an MXene bipolar membrane, and the specific steps are as follows:

[0135] (1) Preparation of the cation exchange layer: Add 2.5 g of polyvinylidene fluoride, 2.5 g of sodium allylsulfonate, 0.25 g of divinylbenzene, and 25 mL of N,N-dimethylformamide into a 100 mL round-bottom flask. After stirring well to dissolve, add 0.05 g of initiator benzoyl peroxide, heat up to 70 °C and react for 8 h. After cooling, let it stand for defoaming to obtain the first casting solution; Cast the first casting solution on a clean glass plate, use a 100 μm doctor blade to scrape and form a film, and then place the film in an oven at 60 °C for drying for 5 h to obtain a cation exchange layer with a thickness of 100 μm.

[0136] (2) Preparation of the MXene material: The same as step (2) of Example 1.

[0137] (3) Preparation of the intermediate interface layer: Ultrasonically disperse the MXene material in N,N-dimethylformamide to prepare a suspension with a mass fraction of 1%; Use a spray gun to evenly spray the suspension on the cation exchange layer and dry it at 60 °C for 30 min to obtain the intermediate interface layer.

[0138] (4) Preparation of the anion exchange layer: Add 2.5 g of polyvinylidene fluoride, 3 g of vinylimidazole, 0.3 g of 1,6-dibromohexane, and 25 mL of N,N-dimethylformamide into a 100 mL round-bottom flask. After stirring well to dissolve, add 0.05 g of initiator benzoyl peroxide, heat up to 70 °C and react for 8 h. After cooling, let it stand for defoaming to obtain the second casting solution; Cast the second casting solution on the intermediate interface layer, use a 100 μm doctor blade to scrape and form a film, and then place the film in an oven at 60 °C for drying for 5 h to obtain an anion exchange layer with a thickness of 100 μm, namely the MXene bipolar membrane.

[0139] Comparative Example 1

[0140] This comparative example provides a method for preparing a bipolar membrane, and the specific steps are as follows:

[0141] (1) Preparation of the cation exchange layer: The same as step (1) of Example 1.

[0142] (2) Preparation of the anion exchange layer: The same as step (4) of Example 1.

[0143] The bipolar membrane of this comparative example consists of a cation exchange layer and an anion exchange layer stacked in sequence, and does not contain an intermediate interface layer made of MXene material.

[0144] Comparative Example 2

[0145] This comparative example provides a method for preparing an MXene bipolar membrane, and the specific steps are as follows:

[0146] (1) Preparation of the cation exchange layer: The same as step (1) of Example 1.

[0147] (2) Preparation of the intermediate interface layer: Dissolve polyvinyl alcohol in deionized water to form a solution with a mass fraction of 4%, and spray it evenly on the cation exchange layer using a spray gun, and dry it at 60 °C for 30 min to obtain the intermediate interface layer.

[0148] (3) Preparation of the anion exchange layer: The same as step (4) of Example 1.

[0149] Test Example

[0150] The MXene bipolar membranes of Examples 1 to 3 and the bipolar membranes of Comparative Examples 1 to 2 were tested as follows.

[0151] (1) MXene materials: Raman spectroscopy and XRD tests were performed on the MAX precursor and MXene materials of Example 1, and the results are shown in Figure 2 and Figure 3 respectively. It can be seen from Figures 2 to 3 that the MXene material was successfully prepared in Example 1.

[0152] (2) Current-voltage (C-V) curve test: Before the test, the bipolar membrane was immersed in a 1 M NaCl solution for 24 h, and then the membrane was installed in a four-compartment electrodialysis device for testing; a 0.3 M Na2SO4 solution was used as the circulating liquid in the electrode chamber, and a 0.5 M NaCl solution was used as the circulating liquid in the acid-base chamber. During the test, the applied current was increased every 20 s, and the transmembrane voltage was recorded using a multimeter. The obtained C-V curve is shown in Figure 4 and the transmembrane voltage during the hydrolysis dissociation process is shown in Table 1. It can be seen from Figure 4 and Table 1 that the MXene bipolar membranes prepared in Examples 1 to 3 have a lower transmembrane voltage and a higher hydrolysis dissociation efficiency.

[0153] (3) Electrodialysis test: The hydrolysis dissociation performance of the bipolar membrane was tested by electrodialysis; before the test, the membrane was immersed in a 1 M NaCl solution for 24 h, and then the membrane was installed in the electrodialysis device and installed in the order of "positive electrode - bipolar membrane - commercially available anion exchange membrane - commercially available cation exchange membrane - bipolar membrane - negative electrode"; a 0.3 M Na2SO4 solution was used as the circulating liquid in the electrode chamber, and the acid-base chamber was a 0.5 M NaCl solution, and a constant current was applied for testing. The obtained current efficiency and energy consumption are shown in Figure 5 and the relevant data are shown in Table 1. It can be seen from Figure 5As can be seen from Table 1, the MXene bipolar membranes prepared in Examples 1 to 3 have higher current efficiency and lower energy consumption, which means that the MXene bipolar membranes have advantages such as high hydrolysis dissociation efficiency and excellent electrochemical performance, and have broad application prospects in the field of electrodialysis.

[0154] Table 1. Performance comparison of bipolar membranes

[0155] Transmembrane voltage (V) Current efficiency (%) Energy consumption (kWh / kg) Example 1 2.3 87.3 3.5 Example 2 1.7 90.4 2.9 Example 3 1.2 91.6 2.1 Comparative Example 1 2.6 85.2 4.2 Comparative Example 2 2.4 86.3 3.9

[0156] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0157] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the protection scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A preparation method of MXene bipolar membrane, characterized in that, Comprising the following steps: Performing a first film-forming treatment on a first casting solution containing polyvinylidene fluoride, a cationic monomer, a first crosslinking agent, and a first initiator to form a cation exchange layer, wherein the cationic monomer includes one or more of sodium styrenesulfonate and sodium allylsulfonate, the first crosslinking agent includes divinylbenzene, the first initiator includes one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, azodicyanovaleric acid, benzoyl peroxide, and 2,2'-azobis(2-methylpropylimid) dihydrochloride, the mass ratio of the polyvinylidene fluoride to the cationic monomer is 1:(0.5 - 1.5), the mass ratio of the cationic monomer to the first crosslinking agent is 100:(3 - 15), and the mass ratio of the cationic monomer to the first initiator is 100:(0.5 - 5); Spraying a suspension containing MXene material onto the cation exchange layer to form an intermediate interface layer; Performing a second film-forming treatment on a second casting solution containing polyvinylidene fluoride, an anionic monomer, a second crosslinking agent, and a second initiator to form an anion exchange layer on the intermediate interface layer, wherein the anionic monomer includes one or more of vinylimidazole and vinylpyridine, the second crosslinking agent includes one or more of 1,6-dibromohexane and 1-bromohexane, the second initiator includes one or more of azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile, azodicyanovaleric acid, benzoyl peroxide, and 2,2'-azobis(2-methylpropylimid) dihydrochloride, the mass ratio of the polyvinylidene fluoride to the anionic monomer is 1:(0.5 - 1.5), the mass ratio of the anionic monomer to the second crosslinking agent is 100:(3 - 15), and the mass ratio of the anionic monomer to the second initiator is 100:(0.5 - 5); The cation exchange layer and the anion exchange layer each independently have a semi-interpenetrating network structure; The thicknesses of the cation exchange layer and the anion exchange layer are each independently 100 μm - 140 μm.

2. The preparation method of the MXene bipolar membrane according to claim 1, characterized in that, The solid contents of the first casting solution and the second casting solution are each independently 10% - 30%.

3. The preparation method of the MXene bipolar membrane according to claim 2, wherein, The preparation method of the first casting solution includes the following steps: Dissolving polyvinylidene fluoride, a cationic monomer, a first crosslinking agent, and a first initiator in a first organic solvent, and performing a temperature-raising reaction after stirring evenly to prepare the first casting solution, wherein the temperature of the temperature-raising reaction is 40°C - 80°C, and the time is 6 h - 24 h.

4. The preparation method of the MXene bipolar membrane according to claim 2, wherein, The preparation method of the second casting solution includes the following steps: Dissolving polyvinylidene fluoride, an anionic monomer, a second crosslinking agent, and a second initiator in a third organic solvent, and performing a temperature-raising reaction after stirring evenly to prepare the second casting solution, wherein the temperature of the temperature-raising reaction is 40°C - 80°C, and the time is 6 h - 24 h.

5. The preparation method of the MXene bipolar membrane according to any one of claims 1 to 4, characterized in that, The first film-forming treatment and the second film-forming treatment each independently include one or more of casting film-forming treatment, knife coating film-forming treatment, spin coating film-forming treatment, and spraying film-forming treatment.

6. The preparation method of the MXene bipolar membrane according to any one of claims 1 to 4, characterized in that, The preparation method of the MXene material includes the following steps: The MAX precursor is placed in an etching solution for an etching reaction and then purified to prepare the MXene material; The etching solution contains one or more of HF, HCl, and fluoride salts.

7. The preparation method of the MXene bipolar membrane according to claim 6, wherein, Meet one or more of the following conditions: (1) The MAX precursor includes one or more of Ti3AlC2, Ti2AlC, Ti3AlCN, Ta4AlC3, V2AlC, V3AlC2, Mo2AlC, and Mo2TiAlC2; (2) The etching reaction includes the following steps: etching at 20°C to 50°C for 12h to 48h; (3) The mass fraction of the MXene material in the suspension is 0.1% to 5%.

8. The preparation method of the MXene bipolar membrane according to claim 7, wherein The MXene material includes Ti3C2Tx x , Ti2CTx x , Ti3CNTx x , Ta4C3Tx x , V2CTx x , V3C2Tx x , Mo2CTx x and Mo2TiC2Tx x , where T includes one or more of -OH, -F, and -O, and x represents the number of T, and x > 0.

9. A MXene bipolar membrane, characterized in that, Prepared by using the method for preparing an MXene bipolar membrane according to any one of claims 1 to 8.

10. The MXene bipolar membrane according to claim 9, characterized in that, Meet one or more of the following conditions: (1) The transmembrane voltage of the MXene bipolar membrane is 0.9V to 3V; (2) The current efficiency of the MXene bipolar membrane is 80% to 95%; (3) The energy consumption of the MXene bipolar membrane is 1.1 kWh / kg to 5.3 kWh / kg.

11. An electrodialysis device, characterized in that, Includes the MXene bipolar membrane according to claim 9 or 10.

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