Chitosan modified MXene electrodialysis membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, in particular to a chitosan modified MXene electrodialysis membrane as well as a preparation method and application thereof. The invention provides a preparation method of a chitosan modified MXene electrodialysis membrane. The preparation method comprises the following steps: mixing an MXene nanosheet dispersion liquid and a chitosan solution, carrying out a reaction under inert gas protection, carrying out centrifugal washing on the reacted mixed solution, carrying out suction filtration on the obtained dispersion liquid to form a membrane, and carrying out drying treatment. According to the electrodialysis membrane prepared through the method, chitosan molecules are limited between MXene nanosheet layers, a two-dimensional confinement channel structure is formed, the channel regulates and controls the ion migration behavior through the space size and the chemical environment, migration of divalent magnesium ions under the effect of a direct-current electric field is blocked, meanwhile, monovalent lithium ions can migrate preferentially, and the effect of the monovalent lithium ions on the surface of the membrane is improved. Therefore, selective separation of Li < + > / Mg < 2 + > is realized.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a chitosan-modified MXene electrodialysis membrane, its preparation method, and its application. Background Technology

[0002] Under the premise that the global energy transition is driving the explosive growth of lithium demand and highlighting the strategic attributes of lithium resources, coupled with the supply and demand contradiction in China, where "resource endowment is mainly based on salt lakes but with a high degree of dependence on foreign sources," as well as technological breakthroughs and policy-driven initiatives, lithium extraction from salt lakes has moved from technological breakthroughs to large-scale industrial applications, becoming a core path to ensure the independent control of lithium resources, reduce costs and increase efficiency, and achieve green and low-carbon development.

[0003] Current lithium extraction technologies from salt lakes primarily rely on salt field concentration and precipitation, adsorption, membrane separation, and extraction. Among these, membrane separation is widely used due to its high separation efficiency, lack of chemical additives, environmental friendliness, and automated controllability. In recent years, the two-dimensional material MXene has been widely applied in membrane separation due to its unique layered structure and excellent ion transport properties. However, existing membrane materials still face several unresolved technical challenges in meeting the practical requirements of electrodialysis separation systems during lithium extraction from salt lakes. Firstly, in neutral or weakly alkaline brine environments, Li... + With Mg 2+ With coexistence and similar migration characteristics, existing electrodialysis membranes have difficulty treating Mg under a DC electric field. 2+ The migration of ions is effectively suppressed, thus limiting further improvements in lithium-magnesium separation efficiency. Secondly, salt lake brines typically have high salinity and complex ionic compositions. During electrodialysis operation, the membrane material needs to be exposed to a combined environment of DC electric field and high ionic strength for extended periods. The structural stability and applicability of existing MXene-based membrane materials under these conditions still require further improvement. Furthermore, existing MXene membrane preparation methods primarily target diffusion dialysis or pressure-driven separation processes, without systematically designing the matching relationship between electric field strength, ion migration paths, and membrane structural parameters under electrodialysis conditions, making it difficult to balance separation efficiency and operational stability.

[0004] CN118371133A discloses a method for preparing a composite membrane by positively modifying MXene with polyethyleneimine (PEI) and using vacuum filtration. This composite membrane is mainly based on the principle of diffusion dialysis to achieve H+ in acidic systems. + Separation from metal ions. It should be noted that this type of technology primarily relies on a concentration gradient-driven diffusion dialysis mechanism. Its separation process differs significantly from electrodialysis driven by a DC electric field in terms of ion transport methods and operating conditions. Furthermore, the membrane's structural design and application scenarios are mainly geared towards acidic separation systems, and not specifically designed for Li-containing separation systems in neutral or weakly alkaline brine environments with high salinity and high magnesium-to-lithium ratios. +With Mg 2+ The design was optimized to address the issue of coexistence and similar migration characteristics of monovalent and divalent cations. Furthermore, there is limited research on the long-term operational stability of the aforementioned composite membrane under DC electric field conditions, and its applicability in electrodialysis requires further investigation.

[0005] Therefore, in order to meet the actual needs of separating lithium ions and magnesium ions by electrodialysis in the process of lithium extraction from salt lakes, there is still an urgent need to develop a new MXene-based membrane material whose structure and preparation method are suitable for the electrically driven separation process. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for preparing a chitosan-modified MXene electrodialysis membrane.

[0007] The method for preparing the chitosan-modified MXene electrodialysis membrane according to an embodiment of the present invention includes:

[0008] The MXene nanosheet dispersion and chitosan solution were mixed and reacted under inert gas protection. The resulting mixture was centrifuged and washed, and the resulting dispersion was filtered to form a film and then dried.

[0009] The advantages and technical effects of the chitosan-modified MXene electrodialysis membrane preparation method of this invention are as follows: 1. In the method of this invention, chitosan (CS), as a natural polymer material that can be used to construct confined structures, can form a two-dimensional confined ion transport channel after modifying MXene, thereby achieving effective control of ion migration paths; the channel selectively regulates ion migration behavior through the synergistic effect of spatial confinement effect and surface chemical environment, inhibiting the migration of divalent magnesium ions under the action of DC electric field, while allowing monovalent lithium ions to migrate preferentially, thereby achieving Li + / Mg 2+ 1. Highly efficient and selective separation; 2. The electrodialysis membrane prepared by the method of this invention has good long-term operational stability under DC electric field conditions, which is beneficial to reducing the operating cost of lithium extraction from salt lakes and has good prospects for industrial application.

[0010] In some embodiments, the mass ratio of chitosan to MXene nanosheets is (5~15):1; And / or, the concentration of the MXene nanosheet dispersion is 0.1~0.5 mg / mL, and the mass fraction of the chitosan solution is 5~20%.

[0011] In some embodiments, the reaction temperature is 20~25°C, the reaction time is 12~36 h, and the reaction is carried out under magnetic stirring at a speed of 300~800 r / min. And / or, the filtration membrane formation is performed on a nylon substrate using a vacuum-assisted filtration method; And / or, the drying process is carried out at a temperature of 60~120℃ for 8~24 h in a vacuum drying oven.

[0012] In some embodiments, the preparation method of the MXene nanosheet dispersion includes: mixing deionized water, concentrated hydrochloric acid, LiF and MAX and then reacting at a constant temperature; washing the product obtained from the reaction with deionized water and then performing a first centrifugation to obtain a clay-like precipitate; adding deionized water to the clay-like precipitate and then performing ultrasonic exfoliation under inert gas protection and performing a second centrifugation to obtain an MXene nanosheet solution; and then adding deionized water to prepare a nanosheet dispersion of the desired concentration.

[0013] In some embodiments, the ratio of deionized water, concentrated hydrochloric acid, LiF and MAX is (20~40) mL : (80~120) mL : (5~10) g : (3~7) g; And / or, the temperature of the isothermal reaction is 30~70℃, and the isothermal reaction time is 20~40h; And / or, the rotation speed of the first centrifugation treatment is 3000~4000 r / min, and the time of the first centrifugation treatment is 3~5 min; discard the supernatant, add deionized water to wash, and repeat centrifugation-washing to make the pH of the supernatant > 6; And / or, the power of the ultrasonic ablation is 150~300W; the ultrasonic ablation time is 30~60 min; And / or, the second centrifugation is performed at a speed of 5000~6000 r / min for a time of 0.5~2 h; the concentration of the MXene nanosheet solution is 10~20 mg / mL.

[0014] In some embodiments, the chitosan solution is prepared by dissolving chitosan in an aqueous acetic acid solution and stirring until completely homogeneous.

[0015] The present invention also provides a chitosan-modified MXene electrodialysis membrane, which is prepared by the above-described preparation method.

[0016] In some embodiments, the thickness of the electrodialysis membrane is 1~5 μm.

[0017] The present invention also provides the application of the above-mentioned chitosan-modified MXene electrodialysis membrane or the chitosan-modified MXene electrodialysis membrane prepared by the above-mentioned preparation method in the electrodialysis separation of lithium and magnesium in neutral or weakly alkaline salt lake brine.

[0018] In some embodiments, the current density during the electrodialysis process is 1~20 mA·cm⁻¹. -2 ; And / or, during the electrodialysis process, the electrode chambers on both sides contain 100~200 mL of 0.3~0.5 mol·L⁻¹ solution. -1 The raw material chamber contains 100-200 mL of simulated salt lake brine solution with a composition of 0.1 mol·L⁻¹. -1 and 1.0 mol·L -1 A mixed solution of MgCl2, concentrated in a chamber to a volume of 100–200 mL of 0.1 mol·L⁻¹ -1 HCl solution; the flow rate of the solution in each chamber of the membrane stack is 30~70 mL / min. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the electrodialysis lithium-magnesium separation device in Embodiment 1 of the present invention; Figure 2 This is a comparison chart of the performance of electrodialysis membranes prepared by the present invention at different CS to MXene mass ratios during the electrodialysis process; Figure 3 This is a comparison chart of the performance of electrodialysis membranes of different thicknesses in the separation of lithium and magnesium by electrodialysis according to the present invention; Figure 4 The lithium-ion flux of the electrodialysis membrane prepared in Example 1 and the Li under different current densities are compared. + / Mg 2+ A graph showing the relationship between separation selectivity; Figure 5 This is a graph showing the electrodialysis cycle stability test results of the electrodialysis membrane prepared in Example 1 of the present invention. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] The method for preparing the chitosan-modified MXene electrodialysis membrane according to an embodiment of the present invention includes: The MXene nanosheet dispersion and chitosan solution were mixed and reacted under inert gas protection. The resulting mixture was centrifuged and washed, and the resulting dispersion was filtered to form a film and then dried.

[0022] This invention discloses a method for preparing a chitosan-modified MXene electrodialysis membrane. Chitosan (CS), a natural polymer material that can be used to construct confined structures, can form two-dimensional confined ion transport channels after modifying MXene, thereby achieving effective control of ion migration paths. These channels selectively regulate ion migration behavior through the synergistic effect of spatial confinement and surface chemical environment, suppressing the migration of divalent magnesium ions under a DC electric field while preferentially allowing the migration of monovalent lithium ions, thus achieving Li… + / Mg 2+ The method of this invention provides highly efficient and selective separation. The electrodialysis membrane prepared by the method of this invention has good long-term operational stability under DC electric field conditions, which is beneficial to reducing the operating cost of lithium extraction from salt lakes and has good prospects for industrial application.

[0023] In some embodiments, preferably, the mass ratio of chitosan to MXene nanosheets is (5~15):1, for example, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, or 15:1. More preferably, the mass ratio of chitosan to MXene nanosheets is 10:1.

[0024] In this embodiment of the invention, a preferred mass ratio of chitosan (CS) to MXene nanosheets is used to control the density and spatial size of the two-dimensional confined channels, thereby balancing Li + Flux and Mg 2+ The blocking ability enables optimized separation for different brine compositions in salt lakes. If the CS dosage is too low, it can only adsorb onto the MXene surface, resulting in weak interlayer confinement and channel sizes close to the original MXene. Mg 2+ Some of the CS can still enter the interlayer channels, resulting in insufficient inhibition of its migration and limited selective sieving ability of the membrane. If the amount of CS is too high, the interlayer channels are overfilled, forming organic phase enrichment regions. This increases the membrane density but reduces the effective channels, leading to Li... + The migration resistance increases significantly, and the Li in the membrane... + Flux decreased.

[0025] In some embodiments, preferably, the concentration of the MXene nanosheet dispersion is 0.1~0.5 mg / mL, and the mass fraction of the chitosan solution is 5~20%.

[0026] In some embodiments, preferably, the reaction temperature is 20-25°C, and the reaction time is 12-36 h; the reaction is carried out under magnetic stirring at a speed of 300-800 r / min. More preferably, the reaction time is 20-28 h, and the magnetic stirring speed is 500-700 r / min.

[0027] In some embodiments, preferably, the filtration membrane formation is performed on a nylon substrate using a vacuum-assisted filtration method; And / or, the drying process is carried out at a temperature of 60~120℃ for 8~24 h in a vacuum drying oven. More preferably, the drying process is carried out for 10~14 h.

[0028] In some embodiments, preferably, in step (1), the MXene is a type of two-dimensional inorganic compound with the general formula M n+1 X n T x Where M represents a pre-transition metal (such as Ti, V, Nb, etc.), X represents carbon and / or nitrogen, and T represents a carbon-to-nitrogen mixture. x Represents surface terminating groups (such as -O, -OH, -F, etc.). More preferably, the MXene is Ti3C2T. x .

[0029] In some embodiments, preferably, the preparation method of the MXene nanosheet dispersion includes: mixing deionized water, concentrated hydrochloric acid, LiF, and MAX and then reacting at a constant temperature; washing the product obtained from the reaction with deionized water and then performing a first centrifugation to obtain a clay-like precipitate; adding deionized water to the clay-like precipitate and performing ultrasonic exfoliation under inert gas protection, followed by a second centrifugation to obtain an MXene nanosheet solution. The clay-like precipitate is ultrasonically exfoliated to remove MXene flakes; after the second centrifugation, most of the unexfoliated MXene is removed, resulting in a nanosheet solution. Deionized water is then added to prepare a nanosheet dispersion of the desired concentration. MAX materials are a class of ternary layered compounds with the general chemical formula Mx. N+1 AX N Where M is a former transition metal, A is a group A element, and X is carbon or nitrogen.

[0030] In some embodiments, preferably, the ratio of deionized water, concentrated hydrochloric acid, LiF and MAX is (20~40) mL : (80~120) mL : (5~10) g : (3~7) g; And / or, the temperature of the isothermal reaction is 30~70 ℃, and the isothermal reaction time is 20~40 h; And / or, the rotation speed of the first centrifugation treatment is 3000~4000 r / min, and the time of the first centrifugation treatment is 3~5 min; discard the supernatant, add deionized water to wash, and repeat centrifugation-washing to make the pH of the supernatant > 6; And / or, the power of the ultrasonic ablation is 150~300 W; the time of the ultrasonic ablation is 30~60 min; And / or, the second centrifugation is performed at a speed of 5000~6000 r / min for a time of 0.5~2 h; the concentration of the MXene nanosheet solution is 10~20 mg / mL.

[0031] In some embodiments, preferably, the chitosan solution is prepared by dissolving chitosan in an aqueous acetic acid solution and stirring until completely homogeneous.

[0032] The present invention also provides a chitosan-modified MXene electrodialysis membrane, which is prepared by the above-described preparation method.

[0033] In some embodiments, preferably, the thickness of the electrodialysis membrane is 1~5 μm. More preferably, the thickness of the electrodialysis membrane is 3 μm. This thickness range ensures that Li + Enhance Mg flux 2+ Its blocking effect adapts to different current densities and flow rates.

[0034] The present invention also provides the application of the above-mentioned chitosan-modified MXene electrodialysis membrane or the chitosan-modified MXene electrodialysis membrane prepared by the above-mentioned preparation method in the electrodialysis separation of lithium and magnesium in neutral or weakly alkaline salt lake brine.

[0035] In some embodiments, preferably, the current density during the electrodialysis process is 1~20 mA·cm⁻¹. -2 More preferably, the current density is 10 mA·cm⁻¹. -2 .

[0036] In some embodiments, preferably, during the electrodialysis process, the electrode chambers on both sides contain 100-200 mL of 0.3-0.5 mol·L⁻¹ solution. -1 The raw material chamber contains 100-200 mL of simulated salt lake brine solution with a composition of 0.1 mol·L⁻¹. -1 and 1.0 mol·L -1 A mixed solution of MgCl2, concentrated in a chamber to a volume of 100–200 mL of 0.1 mol·L⁻¹ -1HCl solution; the solution flow rate in each chamber of the membrane stack is 30~70 mL / min. Through the combined optimization of the above parameters, Li can be achieved under different brine conditions in salt lakes. + / Mg 2+ Improved separation efficiency; while ensuring the long-term structural stability of the membrane under the action of a DC electric field.

[0037] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0038] Example 1 (1) Preparation of MXene nanosheet dispersion: Weigh 30 mL of deionized water, 100 mL of concentrated hydrochloric acid, 8 g of LiF and 5 g of MAX (Ti3AlC2) and mix them. React at 50 °C for 30 hours. Wash the product with deionized water and centrifuge at 3500 r / min for 5 min. Repeat the centrifugation until the pH of the supernatant is >6 to obtain a clay-like precipitate. Place the clay-like precipitate back into deionized water and perform mild ultrasonic peeling at 200 W for 45 min under inert gas protection. After a second centrifugation at 5500 r / min for 1 hour, most of the unpeeled MXene was removed, and the concentration of the obtained MXene nanosheet solution was 14 mg / mL. Measure 10 mg (dry weight) of the monolayer MXene nanosheet solution and disperse it in 100 mL of deionized water to prepare an MXene nanosheet dispersion with a concentration of 0.1 mg / mL. (2) Preparation of chitosan (CS) solution: Dissolve chitosan in aqueous acetic acid solution and stir until completely homogeneous to obtain a CS solution with a mass fraction of 10%; (3) Add 1 mL of CS solution with a mass fraction of 10% (i.e., the dry weight of CS is 100 mg) to the MXene nanosheet dispersion. The mass ratio of CS to MXene is 10:1. Stir magnetically at 500 r / min for 24 h at room temperature (25 °C) under argon protection. Centrifuge and wash the mixed solution after reaction. Finally, filter the obtained chitosan-modified MXene dispersion on a nylon substrate by vacuum-assisted filtration to form a membrane. Dry it under vacuum at 80 °C for 12 h. The thickness of the obtained electrodialysis membrane is 3 μm.

[0039] Example 2 The preparation method of this embodiment is the same as that of Example 1, except that: the amount of CS solution with a mass fraction of 10% added is 0.5 mL, 0.75 mL, 1.25 mL, and 1.5 mL, respectively, and the mass ratio of CS to MXene is 5:1, 7.5:1, 12.5:1, and 15:1, respectively.

[0040] Example 3 The preparation method of this embodiment is the same as that of Example 1, except that the mass ratio of CS to MXene is 10:1. By changing the amount of MXene, the thickness of the electrodialysis membrane is adjusted to 1μm, 2μm, 4μm and 5μm respectively.

[0041] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 1, except that: 0.25 mL of CS solution with a mass fraction of 10% was added, and the mass ratio of CS to MXene was 2.5:1.

[0042] Comparative Example 2 The preparation method of this comparative example is the same as that of Example 1, except that 2 mL of CS solution with a mass fraction of 10% was added, and the mass ratio of CS to MXene was 20:1.

[0043] Comparative Example 3 The comparative example yielded an electrodialysis membrane of polydiallyldimethylammonium chloride (PDDA) modified MXene.

[0044] The preparation method of this comparative example is the same as that of Example 1, except that CS is replaced with PDDA.

[0045] Comparative Example 4 The comparative example yielded an electrodialysis membrane of polyethyleneimine (PEI) modified MXene.

[0046] The preparation method of this comparative example is the same as that of Example 1, except that PEI is replaced with CS.

[0047] Performance testing (1) Electrodialysis separation experiments were conducted on the membrane samples prepared in Examples 1-3 and Comparative Examples 1-4. The results are shown in Table 1. Figure 2 and Figure 3 As shown: Test methods such as Figure 1 The diagram shows the prepared electrodialysis membrane installed between the feed chamber and the concentration chamber. The electrodialysis operation is as follows: the effective membrane area of ​​the electrodialysis unit is 2 cm². 2 The electrode chamber contains 100 mL of 0.3 mol·L⁻¹ -1 Na₂SO₄ solution, the raw material chamber contains 100 mL of 0.1 mol·L⁻¹ -1 LiCl and 1.0 mol·L -1 A mixed MgCl2 solution, with a concentration of 100 mL (0.1 mol·L⁻¹) in the concentration chamber. - 1 HCl solution, flow rate 50 mL / min, current density 10 mA / cm²2 Temperature: room temperature (25 ± 0.5℃), running time: 1 h. After the run, the solutions from the raw material chamber and the concentration chamber were collected separately.

[0048] Li in solution was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). + With Mg 2+ The concentration.

[0049] Table 1. Comparison of lithium-magnesium separation performance of different membrane samples

[0050] Note: J in Table 1 represents ion flux, which is calculated using the following formula:

[0051] Among them, C t C and C0 are the ion concentrations in the concentration chamber at time t and the initial time, respectively, in mol·L⁻¹. -1 ; V is the volume of the solution in the concentration chamber, expressed in liters (L). A m The effective contact area between the membrane and the solution, expressed in m². 2 ; t represents the electrodialysis operation time, in hours (h). P represents ion selectivity, used to measure the membrane's ion selectivity for Li. + Relative to Mg 2+ The selective penetration capability is calculated using the following formula:

[0052] Among them, P Li + / Mg 2+ For Li + and Mg 2+ Selectivity; J Li + and J Mg 2+ Li + and Mg 2+ flux, in units of mol·m -2 ·h -1 ; C Li + and C Mg 2+ These represent the initial concentrations in the desalination chamber, in mol·L⁻¹. -1 .

[0053] (2) To investigate the effect of operating conditions on separation performance and to optimize the electrodialysis operating parameters of the electrodialysis membrane prepared in Example 1 of this invention, a current density optimization experiment was conducted, with current density set at 1 mA / cm². 2 5mA / cm 2 10mA / cm 2 15mA / cm 2 20mA / cm 2 It was run for 1 hour at a constant current density. Performance test results are shown in Table 2 and... Figure 4 As shown.

[0054] Table 2. Performance Comparison of Lithium-Magnesium Separation by Electrodialysis at Different Current Densities

[0055] (3) To examine the long-term operational stability of the membrane described in this invention, the chitosan-modified MXene electrodialysis membrane prepared in Example 1 was subjected to multiple electrodialysis cycle tests.

[0056] Definition of a single cycle: Running for 1 hour under standard conditions (conditions for electrodialysis separation experiments) is recorded as one cycle.

[0057] Loop process: Step 1: Run a loop.

[0058] Step 2: After the operation is completed, collect the solutions from the raw material chamber and the concentration chamber for performance analysis.

[0059] Step 3: Gently rinse the membrane surface and device channels with deionized water to remove adsorbed ions and possible contaminants.

[0060] Step 4: Re-inject fresh feed solution (0.05 M LiCl + 1.0 M MgCl2) and receiving solution (0.1 M HCl).

[0061] Repeat steps 1-4 for a total of 6 cycles.

[0062] Testing and Calculation Methods At the end of each cycle, the lithium-ion flux and Li-ion flux of that cycle were measured and calculated. + / Mg 2+ Separation selectivity.

[0063] Stability assessment: Using the performance data of the first cycle as a baseline (100%), calculate the relative retention rate of the performance data for each subsequent cycle.

[0064] Test results: The results of the cyclic stability performance test are shown in Table 3 and... Figure 5 As shown.

[0065] Table 3. Electrodialysis cycle stability test results of the membrane of the present invention

[0066] As shown in Table 3, during the entire cyclic testing process, the chitosan-modified MXene membrane described in this invention showed an effect on Li... + / Mg 2+ The separation exhibits good stability, and the Li in the membrane... + / Mg 2+ The separation selectivity did not decrease significantly after 6 cycles of testing. + / Mg 2+ The relative retention rate of separation selectivity is still higher than 93.5%.

[0067] After the test, the membrane was observed to be intact, without any damage, cracks or blistering, indicating that it has good mechanical and chemical stability.

[0068] The above results fully demonstrate that the membrane of the present invention not only has excellent initial separation performance, but also excellent long-term operational stability, and can effectively resist the effects of concentration changes, electric field effects and material scouring during operation, thus meeting the basic requirements for membrane material durability in industrial applications.

[0069] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0070] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a chitosan-modified MXene electrodialysis membrane, characterized in that, include: The MXene nanosheet dispersion and chitosan solution were mixed and reacted under inert gas protection. The resulting mixture was centrifuged and washed, and the resulting dispersion was filtered to form a film and then dried.

2. The method for preparing the chitosan-modified MXene electrodialysis membrane according to claim 1, characterized in that, The mass ratio of chitosan to MXene nanosheets is (5~15):1; And / or, the concentration of the MXene nanosheet dispersion is 0.1~0.5 mg / mL, and the mass fraction of the chitosan solution is 5~20%.

3. The method for preparing the chitosan-modified MXene electrodialysis membrane according to claim 1 or 2, characterized in that, The reaction temperature is 20~25℃, and the reaction time is 12~36 h; the reaction is carried out under magnetic stirring, and the magnetic stirring speed is 300~800 r / min. And / or, the filtration membrane formation is performed on a nylon substrate using a vacuum-assisted filtration method; And / or, the drying process is carried out at a temperature of 60~120℃ for 8~24 h in a vacuum drying oven.

4. The method for preparing the chitosan-modified MXene electrodialysis membrane according to claim 1, characterized in that, The preparation method of the MXene nanosheet dispersion includes: mixing deionized water, concentrated hydrochloric acid, LiF and MAX and then reacting at a constant temperature; washing the product obtained from the reaction with deionized water and then performing a first centrifugation to obtain a clay-like precipitate; adding deionized water to the clay-like precipitate and then performing ultrasonic exfoliation under inert gas protection and performing a second centrifugation to obtain an MXene nanosheet solution; and then adding deionized water to prepare a nanosheet dispersion of the required concentration.

5. The method for preparing the chitosan-modified MXene electrodialysis membrane according to claim 4, characterized in that, The ratio of deionized water, concentrated hydrochloric acid, LiF and MAX used is (20~40) mL : (80~120) mL : (5~10) g : (3~7) g; And / or, the temperature of the isothermal reaction is 30~70℃, and the isothermal reaction time is 20~40h; And / or, the rotation speed of the first centrifugation treatment is 3000~4000 r / min, and the time of the first centrifugation treatment is 3~5 min; discard the supernatant, add deionized water to wash, and repeat centrifugation-washing to make the pH of the supernatant > 6; And / or, the power of the ultrasonic ablation is 150~300W; the ultrasonic ablation time is 30~60 min; And / or, the second centrifugation is performed at a speed of 5000~6000 r / min for a time of 0.5~2 h; the concentration of the MXene nanosheet solution is 10~20 mg / mL.

6. The method for preparing the chitosan-modified MXene electrodialysis membrane according to claim 1, characterized in that, The chitosan solution is prepared by dissolving chitosan in an aqueous acetic acid solution and stirring until completely homogeneous.

7. A chitosan-modified MXene electrodialysis membrane, characterized in that, It is prepared by any one of claims 1 to 6.

8. The chitosan-modified MXene electrodialysis membrane according to claim 7, characterized in that, The thickness of the electrodialysis membrane is 1~5μm.

9. The application of the chitosan-modified MXene electrodialysis membrane according to claim 7 or 8, or the chitosan-modified MXene electrodialysis membrane prepared by any one of claims 1 to 6, in the electrodialysis separation of lithium and magnesium in neutral or weakly alkaline salt lake brine.

10. The application according to claim 9, characterized in that, The current density during the electrodialysis process is 1~20 mA·cm. -2 ; And / or, during the electrodialysis process, the electrode chambers on both sides contain 100~200 mL of 0.3~0.5 mol·L⁻¹ solution. -1 The raw material chamber contains 100-200 mL of simulated salt lake brine solution with a composition of 0.1 mol·L⁻¹. -1 and 1.0 mol·L -1 A mixed solution of MgCl2, concentrated in a chamber to a volume of 100–200 mL of 0.1 mol·L⁻¹ -1 HCl solution; the flow rate of the solution in each chamber of the membrane stack is 30~70 mL / min.

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