An MXene composite membrane, an electrodialysis device, a preparation method thereof and an application thereof

Abstract

The present invention relates to an MXene composite membrane, an electrodialysis device, a preparation method thereof and an application, belonging to the technical field of membrane technology separation and recovery. Aiming at the technical problem that the existing ion exchange membranes are difficult to achieve good separation of co-valent cations, especially divalent cations, the present application provides an MXene composite membrane, which includes an ion exchange base membrane and MXene coated on the surface of the ion exchange base membrane. While improving the selectivity of the ion exchange base membrane for positive and negative ions, it avoids the migration of ions with the same name. The present application also provides a preparation method of the MXene composite membrane, which can obtain MXene composite membranes with different thicknesses. The present application also provides an electrodialysis device, which is applicable to the separation and recovery of cations in high-salt water electrodialysis such as industrial wastewater, mine water, groundwater, seawater desalination, etc., and can be used to separate one or more of potassium, sodium, and lithium in monovalent cations, or one or two of magnesium, strontium, and calcium in divalent cations.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane technology separation and recovery, and specifically relates to an MXene composite membrane, an electrodialysis device, a preparation method thereof, and an application thereof in ion separation. Background Art

[0002] The treatment of high-salt wastewater is one of the technical problems in current water treatment. Industrial wastewater, such as papermaking, printing and dyeing, coal chemical industry, electroplating or pharmaceutical wastewater, etc., has a salt content of more than 3000 mg / L, a high COD concentration, and contains a large number of organic pollutants such as aromatic compounds or hydrocarbon compounds. In addition, the salt content of mine water or groundwater in some areas is also relatively high. With the increasing impact of excessive salts in industrial wastewater on groundwater, surface water and soil, resulting in soil salinization, the separation and recovery of salts is an inevitable requirement for environmental protection, and most industrial wastewater needs to be deeply desalted before it can be discharged and reused.

[0003] Electrodialysis technology is one of the effective treatment means for sewage desalination. Electrodialysis technology is a kind of membrane separation technology driven by electricity. Under a direct current voltage, anions and cations perform counter-ion migration, and through selective membrane pores, salt removal and concentration are achieved. Electrodialysis includes packed bed electrodialysis, reverse electrodialysis, electrodialysis with bipolar membranes, and electrodialysis without partitions. Its core functional component is the ion exchange membrane, which is divided into an anion exchange membrane and a cation exchange membrane. In electrodialysis technology, co-ion migration inevitably exists, that is, some anions migrate into the cation exchange membrane, and some cations migrate into the anion exchange membrane, reducing the selective permeability of ions and affecting the salt separation efficiency.

[0004] In the prior art, many improvements have been made to ion exchange membranes. Surface modification of ion exchange membranes is one of the most commonly used methods. MXene is a two-dimensional material with high conductivity and low resistance. Under the drive of a direct current electric field, rapid charge transfer and migration can be achieved. For example, Chinese Patent Application Publication No. CN114146574A, with an application date of November 26, 2021, and a title of Modified Nb2CTx Nanosheet Membrane and Its Preparation Method, discloses a preparation method that includes adding a modifier to a Nb2CTx MXene suspension and ultrasonically mixing it. Subsequently, it is evenly distributed on the surface of a polyvinylidene fluoride film through vacuum filtration to form a modified Nb2CTx thin layer, which is separated from the polyvinylidene fluoride after drying. The modifier is a functional organic compound that can provide hydroxyl groups and / or carboxyl groups. This solution discusses the basic concept of ion transport behavior and the method of surface modification of two-dimensional nanosheets for ion selective separation. The mixed carboxyl and hydroxyl group modification of the surface brings new ideas for the design of ion selective membranes, further deepens the understanding of the transport of solvated ions in nano-confined two-dimensional channels, and explores its potential applications; this solution is also different from the traditional size exclusion mechanism and the low selectivity understanding of 2D material-based membranes, revealing an interconnected ion-water network within the membrane matrix at high ion concentrations. However, this solution requires the modification of MXene, and the process is relatively complex. Another example is Chinese Patent Application Publication No. CN111167513A, with an application date of December 25, 2019, and a title of A Flexible Electro-Catalytic Membrane for Removing Nitrate from Water, Its Preparation Method and Application. The disclosed inventive method first drops an aramid fiber solution into water to obtain an aramid nanofiber sol, then obtains a conductive aramid nanofiber sol, and finally drops MXene nanosheets ultrasonically pretreated with a tetramethylammonium hydroxide solution into the conductive aramid nanofiber sol to obtain a flexible electro-catalytic membrane. The prepared flexible electro-catalytic membrane has good mechanical strength and flexibility, but it is difficult to achieve good separation for co-valent cations, especially divalent cations. Summary of the Invention

[0005] 1. Problems to be Solved

[0006] In view of the technical problem that existing ion exchange membranes have difficulty in achieving good separation of isovalent cations, especially divalent cations, the present application provides an MXene composite membrane, which includes an ion exchange base membrane and MXene coated on the surface of the ion exchange base membrane. While improving the selectivity of the ion exchange base membrane for positive and negative ions, it avoids the migration of ions with the same name. The present application also provides a preparation method of the MXene composite membrane, which can obtain MXene composite membranes with different thicknesses. The present application further provides an electrodialysis device, which achieves the separation of isovalent ions through the parallel design of multiple cation exchange membranes and is applicable to the separation and recovery of cations in high-salt water electro-dialysis such as various industrial wastewaters, mine waters, groundwater, and seawater desalination. When applied to ion separation, it can be used to separate one or more of potassium, sodium, and lithium in monovalent cations, or one or two of magnesium, strontium, and calcium in divalent cations.

[0007] 2. Technical Solution

[0008] To achieve the above object, the technical solution provided is as follows:

[0009] An MXene composite membrane of the present application includes an ion exchange base membrane and MXene coated on the surface of the ion exchange base membrane;

[0010] The ion exchange base membrane is composed of an inert polymer support layer and surface monomer polymerization active groups, and the surface monomer polymerization active groups are one or more of sulfonic acid groups, phosphoric acid groups, and carboxylic acid groups;

[0011] The MXene is one or more of Ti3C2Tx, V3C2Tx, and Mo2CTx of the MAX phase, where T is a terminal functional group, oxygen, hydroxide, or fluorine, and x is the number of T.

[0012] Preferably, the polymer support layer base membrane is any one of polysulfone, polyethersulfone, polyamide, polyacrylonitrile, polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene.

[0013] Preferably, one of hydrofluoric acid solution, hydrochloric acid and lithium fluoride solution, sulfuric acid and potassium fluoride solution, and ammonium fluoride aqueous solution is selected, its active ingredient is hydrofluoric acid, and the mass concentration ratio of hydrofluoric acid is 50-100%, and the etching time is 36-72h.

[0014] MXene refers to the carbide or nitride obtained by etching the A layer from the M n+1 AX n phase, where M is a transition metal, including elements such as Ti, V, Mo, Sr, and Zr, A is an element of Group IIIA or IVA, and X represents carbon or nitrogen. N is selected as 1, 2, or 3, namely M2AX, M3AX2, or M4AX3.

[0015] Further, the thickness of the ion exchange base membrane is 50 - 300 μm, and the exchange capacity is 0.2 - 1.5 meq / g.

[0016] Further, the thickness of the etched multi-layer MXene is 5 - 50 μm, and the sheet thickness of the single-layer MXene is 0.5 - 5 nm.

[0017] Further, the thickness of the coated MXene is 20 - 200 μm, the thickness of the MXene composite membrane is 70 - 500 μm, and the exchange capacity is 0.5 - 3 meq / g.

[0018] A method for preparing an MXene composite membrane includes the following steps: dispersing the MXene in a solution and coating it on the ion exchange base membrane by vacuum filtration.

[0019] Preferably, the MXene is ultrasonically dispersed in pure water or absolute ethanol.

[0020] Further, the dispersion concentration is 0.1 - 3 wt%, and the vacuum degree is 0.05 - 0.1 Mpa.

[0021] An electrodialysis device includes a positive electrode, an anion exchange membrane, a bipolar membrane, a cation exchange membrane, and a negative electrode arranged in sequence; there are multiple anion exchange membranes and cation exchange membranes, and the numbers are equal; the cation exchange membrane is the above-mentioned MXene composite membrane.

[0022] Preferably, one of a titanium iridium coated electrode, a titanium ruthenium coated electrode, or a silicon carbide antioxidant graphite electrode is selected.

[0023] Further, the number of the anion exchange membranes and the cation exchange membranes is 3 - 10.

[0024] An application of an electrodialysis device in ion separation, applying the electrodialysis device to the separation of isovalent ions.

[0025] Preferably, the electrolyte is lithium chloride, sodium chloride, potassium chloride, strontium sulfate, magnesium chloride, etc.

[0026] Further, the isovalent ions include monovalent cations and divalent cations; the monovalent cations are one or more of potassium, sodium, and lithium; the divalent cations are one or two of magnesium, strontium, and calcium.

[0027] 3. Beneficial effects

[0028] Adopting the technical solution provided by the present invention, compared with the existing well-known technologies, it has the following beneficial effects:

[0029] (1) A MXene composite membrane of the present invention includes an ion exchange base membrane and MXene coated on the surface of the ion exchange base membrane. The ion exchange base membrane consists of an inert polymer support layer and surface monomer polymerization active groups. The surface monomer polymerization active groups are one or more of sulfonic acid groups, phosphoric acid groups, and carboxylic acid groups. MXene is one or more of Ti3C2Tx, V3C2Tx, and Mo2CTx of the MAX phase. The functionalized MXene material is loaded on the surface of the ion exchange base membrane through crosslinking, grafting, and vacuum filtration to form a MXene composite membrane, improving the ion exchange capacity. The surface active groups of the ion exchange base membrane are negatively charged. After loading MXene, the redox potential on one side will be further reduced, the negative charge on the loaded surface will be enhanced, the cation permeability and the anion exclusion effect will be improved, and the selectivity of the ion exchange base membrane for positive and negative ions will be enhanced. By increasing the negative charge amount on the membrane surface, the efficient separation of cations and anions is promoted, the migration of ions of the same name is avoided, the negative impact on the exchange capacity is inhibited, and the membrane separation selectivity is improved.

[0030] (2) A preparation method of a MXene composite membrane of the present invention disperses MXene in a solution and coats it on an ion exchange base membrane through vacuum filtration, and MXene composite membranes with different thicknesses can be obtained, which have strong selectivity for different membrane resistances and different ions.

[0031] (3) An electrodialysis device of the present invention includes a positive electrode, an anion exchange membrane, a bipolar membrane, a cation exchange membrane, and a negative electrode arranged in sequence. The anion exchange membrane and the cation exchange membrane are multiple and equal in number, and the cation exchange membrane is a MXene composite membrane. Through the parallel design of multiple cation exchange membranes, different intensity ion acceleration migration effects are realized in multiple separation chambers, highlighting the difference in migration speed, so as to achieve the separation of ions of the same valence. The problem of impurity pollution of the membrane chamber caused by the migration of ions of the same name is solved. In addition to the surface modification of the ion exchange membrane, the permeation selectivity of the ion exchange membrane can be improved. The operation mode of electrodialysis also has a certain impact on the separation and screening of ions. The traditional anion and cation exchange membranes alternate with each other to form an alternating anion and cation compartment. During the permeation process, it is inevitable that anions will dissociate onto the cation exchange membrane, reducing the active functional groups and thus reducing the exchange capacity. In this application, a new arrangement method of electrodialysis ion exchange membranes is proposed. The anion and cation exchange membranes are arranged in parallel on both sides of the device. First, multiple bipolar membranes are arranged at equal intervals in sequence to achieve the effect of accelerating the migration rate of anions and cations and realizing the separation of anions and cations. Then, the bipolar membrane is placed in the middle of the device. Under the action of the same DC electric field, ions of the same valence pass through multiple chambers separated by ion membranes. Due to the different ion hydration radii, different acceleration intensities are achieved, thus achieving the effect of separating ions of the same valence. It is applicable to the separation and recovery of cations in high-salt water electrodialysis such as various industrial wastewaters, mine waters, groundwaters, and seawater desalination.

[0032] (4) Application of an electrodialysis device of the present invention in ion separation. When the electrodialysis device is applied to the separation of isovalent ions, it can be used to separate monovalent cations and divalent cations, such as one or more of potassium, sodium, and lithium in monovalent cations, or one or two of magnesium, strontium, and calcium in divalent cations. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 SEM image of etched MXene for Example 1.

[0034] Figure 2 Schematic structural diagram of the electrodialysis device for Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0035] To further understand the content of the present invention, the present invention will be described in detail in combination with examples.

[0036] Example 1

[0037] A MXene composite membrane, an electrodialysis device, and a preparation method in this example include the following steps:

[0038] (1) Etching and preparation of MXene: Weigh a total of 2 g of Ti3AlC2 and place it in 40 mL of 50% hydrofluoric acid solution. Ultrasonically disperse for 10 min and react at room temperature for 36 h at a rate of 350 r / min. Take out and centrifuge and rinse with ethanol several times until the hydrofluoric acid is removed. The prepared MXene has a two-dimensional layered structure with a thickness of 30 - 50 μm, and the sheet thickness of a single layer of MXene is 3 - 5 nm. In practice, MXene can also be one or more of V3C2Tx or Mo2CTx, where T is a terminal functional group, oxygen, hydroxide, or fluorine, and x is the number of T.

[0039] (2) Preparation of the MXene composite membrane: Fully disperse the MXene prepared above in pure water or absolute ethanol, ultrasonically disperse evenly, and filter it onto an ion exchange base membrane by vacuum filtration. The loading thickness depends on the loading amount. The dispersion concentration is 0.1 - 3 wt%, the vacuum degree is 0.05 - 0.1 Mpa, and it is loaded onto the surface of a polymer support layer base membrane. The ion exchange base membrane is composed of an inert polymer support layer and a surface monomer polymerization active group. In this example, the inert polymer support layer is polysulfone, and the surface monomer polymerization active group is a sulfonic acid group. The thickness of the ion exchange base membrane is 300 μm, and the exchange capacity is 0.2 meq / g. In practice, the inert polymer support layer can also be any one of polyethersulfone, polyamide, polyacrylonitrile, polypropylene, polyvinylidene fluoride, and polytetrafluoroethylene, and the surface monomer polymerization active group can also be one or more of a phosphoric acid group or a carboxylic acid group.

[0040] The MXene composite membrane prepared in this example has a thickness of 350 μm and an ion exchange capacity of 0.8 meq / g.

[0041] (3) Preparation of the electrodialysis device: A total of 3 prepared composite cation exchange membranes are arranged equidistantly on the right side of the electrodialysis device, and 3 cathode membranes are arranged equidistantly on the left side. A bipolar membrane is placed in the middle to play a role of a strong resistance and separate the left and right sides. In this example, the electrode is a titanium-iridium coated electrode. In practice, the electrode can also be one of a titanium-ruthenium coated electrode or a silicon carbide anti-oxidation graphite electrode.

[0042] (4) Take part of the mine water with a lithium ion concentration of 350 - 500 mg / L and a sodium ion concentration of 1000 - 1500 mg / L. Through the electrodialysis device, the separation of lithium chloride and sodium chloride is achieved, and the separation efficiency is over 99.5%.

[0043] Example 2

[0044] This example is basically the same as Example 1, except that: A total of 2 g of Ti3AlC2 is weighed and placed in 40 mL of 100% hydrofluoric acid solution, ultrasonically dispersed for 60 min, and reacted at room temperature for 72 h at a rate of 350 r / min. The prepared MXene has a thickness of 5 - 20 μm, the sheet thickness of single-layer MXene is 0.5 - 2 nm, and the MXene coating thickness is 50 μm. In this case, the ion exchange base membrane is selected as phosphorylated polyethersulfone, the thickness of the ion exchange base membrane is 50 μm, and the exchange capacity is 1.0 meq / g.

[0045] The MXene composite membrane prepared in this example has a thickness of 100 μm, and the ion exchange capacity of the coated MXene composite membrane is 3 meq / g.

[0046] For the electrodialysis device of this example, a total of 10 prepared composite cation exchange membranes are arranged equidistantly on the right side of the electrodialysis device, and 10 cathode membranes are arranged equidistantly on the left side. A bipolar membrane is placed in the middle to play a role of a strong resistance and separate the left and right sides. In this example, the electrode is a titanium-iridium coated electrode. In practice, the electrode can also be one of a titanium-ruthenium coated electrode or a silicon carbide anti-oxidation graphite electrode.

[0047] The electrodialysis device of this example is used for the separation of magnesium ions and strontium ions in mine water with a magnesium ion concentration of 250 - 350 mg / L and a strontium ion concentration of 1200 - 1500 mg / L. Through the electrodialysis device, the separation of magnesium chloride and strontium chloride is achieved, and the separation efficiency is over 99.9%.

[0048] Example 3

[0049] This example is basically the same as Example 1, except that: A total of 2 g of Ti3AlC2 was weighed and placed in 40 mL of 75% hydrofluoric acid solution, ultrasonically dispersed for 30 min, and reacted at room temperature for 48 h at a rate of 350 r / min. The prepared MXene has a thickness of 10 - 30 μm, and the thickness of the single-layer MXene flakes is 1 - 3 nm.

[0050] In this case, the ion-exchange base membrane is carboxylated polyvinylidene fluoride, the thickness of the base membrane is 100 μm, and the exchange capacity is 0.8 meq / g. The MXene composite membrane prepared in this example has a thickness of 130 μm and an exchange capacity of 1.5 meq / g.

[0051] For the electrodialysis device of this example, a total of 6 prepared composite ion-exchange cation membranes are arranged equidistantly on the right side of the electrodialysis device, 6 cathode membranes are arranged equidistantly on the left side, and a bipolar membrane is placed in the middle to play a role of a strong resistance to separate the left and right sides. In this example, the electrode is a titanium-iridium coated electrode. In practice, the electrode can also be one of a titanium-ruthenium coated electrode or a silicon carbide antioxidant graphite electrode.

[0052] The electrodialysis device of this example is used for the separation of calcium ions and magnesium ions. Take part of the groundwater with a calcium ion concentration of 150 - 250 mg / L and a magnesium ion concentration of 200 - 300 mg / L. Through the electrodialysis device, the separation of calcium chloride and magnesium chloride is achieved, and the separation efficiency is more than 99.8%.

[0053] Comparative Example 1

[0054] This comparative example is basically the same as Example 3, except that: The MXene is Ti2AlN of the MAX phase.

[0055] The MXene composite membrane prepared in the same way in this comparative example has a thickness of 750 μm and an exchange capacity of 0.3 meq / g.

[0056] For the electrodialysis device of this comparative example, a total of 10 prepared composite ion-exchange cation membranes are arranged equidistantly on the right side of the electrodialysis device, 10 cathode membranes are arranged equidistantly on the left side, and a bipolar membrane is placed in the middle for the separation of calcium ions and magnesium ions. The separation efficiency is only 85%. It can be seen that the performance of the ion-exchange composite membrane modified by Ti2AlN is poor. Due to the increase in the thickness of the MXene layer and the reduction of active functional groups, it is difficult to improve the exchange capacity, and the separation effect on divalent homologous cations is not obvious.

[0057] Comparative Example 2

[0058] This comparative example is basically the same as Example 3, except that: The MXene is Zr3C2Tx of the non-MAX phase.

[0059] The MXene composite membrane prepared in this comparative example has a thickness of 800 μm and an exchange capacity of 0.2 meq / g for the MXene composite membrane.

[0060] For the electrodialysis device of this comparative example, a total of 10 pieces of the above-prepared composite cation exchange membranes are arranged at equal intervals on the right side of the electrodialysis device, 10 cathode membranes are arranged at equal intervals on the left side, and bipolar membranes are placed in the middle for the separation of calcium ions and magnesium ions. The separation efficiency is only 83%. It can be seen that the performance of the ion exchange composite membrane modified by non-MAX phase Zr3C2Tx is poor, and it is also difficult to improve the exchange capacity. The separation effect on monovalent homologous cations is not obvious.

[0061] Example 4

[0062] A kind of MXene composite membrane, electrodialysis device and preparation method of this example include the following steps:

[0063] Weigh 10 g of Ti3AlC2 in total, place it in 400 mL of 50% hydrofluoric acid solution, ultrasonically disperse it for 10 min, and react at room temperature for 36 h at a rate of 350 r / min. Take it out and centrifuge and rinse it several times with ethanol until the hydrofluoric acid is removed. The etching and preparation of MXene has a two-dimensional layered structure. Its thickness is 30 - 45 μm, and the layer thickness of a single layer of MXene is 1 - 2 nm. The MXene prepared above is fully dispersed in pure water or absolute ethanol, ultrasonically and uniformly dispersed, and then on the ion exchange base membrane by vacuum filtration. The loading thickness depends on the loading amount. The dispersion concentration is 1 wt%, and it is loaded onto the surface of the sulfonic acid group ion exchange membrane. A MXene composite membrane with a thickness of 250 μm is formed. A total of 5 pieces of the prepared composite cation exchange membranes are arranged at equal intervals on the right side of the electrodialysis device, 5 cathode membranes are arranged at equal intervals on the left side, and bipolar membranes are placed in the middle to play a role of strong resistance, separating the left and right sides. The electrode is a titanium-iridium coated electrode, and the exchange capacity of the MXene composite membrane is 1.5 meq / g. Take part of the mine water with a lithium ion concentration of 350 - 500 mg / L and a sodium ion concentration of 1000 - 1500 mg / L, and through the electrodialysis device, the separation of lithium chloride and sodium chloride is realized, and the separation efficiency is more than 99.5%.

[0064] Example 5

[0065] A kind of MXene composite membrane, electrodialysis device and preparation method of this example include the following steps:

[0066] Weigh a total of 10 g of Mo3AlC2 and place it in a 400 mL mixed solution of lithium chloride and sulfuric acid. Ultrasonically disperse it for 10 min and react at room temperature for 48 h at 350 r / min. Wash it several times with absolute ethanol until the impurities are removed. Under SEM, MXene has a sponge-like layered structure. Its thickness is 30 - 40 μm, and the layer thickness of single-layer MXene is 1 - 3 nm. Disperse the MXene prepared above sufficiently in pure water or absolute ethanol, ultrasonically disperse it evenly, and the dispersion concentration is 2 wt%. Filter it onto an ion exchange base membrane by vacuum filtration. The loading thickness depends on the loading amount. Load it onto the surface of the sulfonic acid group ion exchange membrane to form an MXene composite membrane with a thickness of 300 μm. Arrange 8 prepared composite ion exchange cation membranes equidistantly on the right side of the electrodialysis device, arrange 8 cathode membranes equidistantly on the left side, and place a bipolar membrane in the middle to separate the left and right sides of the device. The electrodes use titanium ruthenium coated electrodes, and the exchange capacity of the composite dry membrane is 2.5 meq / g. Take a part of the groundwater with a calcium ion concentration of 150 - 250 mg / L and a magnesium ion concentration of 200 - 300 mg / L. Through the electrodialysis device, calcium chloride and magnesium chloride are separated with a separation efficiency of over 99.8%.

[0067] Example 6

[0068] A kind of MXene composite membrane, electrodialysis device, and preparation method of this example include the following steps:

[0069] Weigh 10 g of non-MAX phase Zr3AlC5 and place it in a 400 mL solution of 50% ammonium fluoride. Ultrasonically disperse it for 10 min and react at room temperature for 72 h at a rate of 500 r / min. Wash it several times with ethanol until the impurities are removed. The etched Zr3C2T X has an accordion-like layered structure. Its thickness is 10 - 20 μm, and the layer thickness of single-layer MXene is 1 - 3 nm. Ultrasonically disperse the prepared MXene evenly in pure water or absolute ethanol, and the dispersion concentration is 3 wt%. Filter it onto the ion exchange base membrane under a vacuum condition of 0.05 Mpa. The loading thickness depends on the loading amount. Vacuum filter it onto the surface of the phosphoric acid group ion exchange membrane to form an MXene composite membrane with a thickness of 350 μm. Arrange 10 prepared composite cation membranes equidistantly on the right side of the electrodialysis device, arrange 10 cathode membranes equidistantly on the left side, and place a bipolar membrane in the middle to separate the left and right sides of the device. The electrodes use silicon carbide anti-oxidation graphite electrodes, and the exchange capacity of the composite dry membrane is 3 meq / g. Take a part of the ore metal with a magnesium ion concentration of 250 - 350 mg / L and a strontium ion concentration of 1200 - 1500 mg / L. Through the electrodialysis device, magnesium chloride and strontium chloride are separated with a separation efficiency of over 99.9%.

[0070] The above-described embodiments merely represent the preferred embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as limiting the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications, improvements, and substitutions can be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

Claims

1. A MXene composite membrane, characterized in that: It includes an ion exchange base membrane and MXene coated on the surface of the ion exchange base membrane; The ion exchange base membrane is composed of an inert polymer support layer and surface monomer polymerization active groups, and the surface monomer polymerization active groups are one or more of sulfonic acid groups, phosphoric acid groups, and carboxylic acid groups; The MXene is one or more of Ti3C2Tx, V3C2Tx, and Mo2CTx of the MAX phase, where T is a terminal functional group, oxygen, hydroxide, or fluorine, and x is the number of T; The thickness of the ion exchange base membrane is 50 - 300 μm, and the exchange capacity is 0.2 - 1.5 meq / g.

2. The MXene composite film according to claim 1, wherein: The thickness of the etched multi-layer MXene is 5 - 50 μm, and the sheet thickness of the single-layer MXene is 0.5 - 5 nm.

3. The MXene composite film according to any one of claims 1-2, characterized in that: The thickness of the coated MXene is 20 - 200 μm, the thickness of the MXene composite membrane is 70 - 500 μm, and the exchange capacity is 0.5 - 3 meq / g.

4. A method for preparing the MXene composite film according to any one of claims 1-3, characterized in that: Package Including The following steps: Disperse the MXene in a solution and coat it on the ion exchange base membrane by vacuum filtration.

5. The preparation method of an MXene composite film according to claim 4, characterized in that: The dispersion concentration is 0.1 - 3 wt%, and the vacuum degree is 0.05 - 0.1 Mpa.

6. An electrodialysis device, characterized in that: It includes a positive electrode, an anion exchange membrane, a bipolar membrane, a cation exchange membrane, and a negative electrode arranged in sequence; the anion exchange membrane and the cation exchange membrane are multiple and have equal numbers; the cation exchange membrane is the MXene composite membrane according to any one of claims 1 - 3.

7. An electrodialysis device according to claim 6, characterized in that: The anion exchange membrane and the cation exchange membrane are 3 - 10.

8. Use of an electrodialysis device according to any one of claims 6 or 7 in ion separation, characterized in that: The electrodialysis device is applied to the separation of isovalent ions.

9. Use of an electrodialysis device according to claim 8 in ion separation, characterized in that: The isovalent ions include monovalent cations and divalent cations; the monovalent cations are one or more of potassium, sodium, and lithium; the divalent cations are one or two of magnesium, strontium, and calcium.

Images