A method for preparing a composite ion exchange membrane with anti-fouling properties

Abstract

This invention relates to the field of membrane separation technology and discloses a method for preparing a composite ion exchange membrane with anti-fouling properties. Using an ion exchange membrane as the base membrane and boron nitride nanosheets as a modifying material, the boron nitride nanosheets are loaded onto the surface of the ion exchange membrane via an electric field. The ion exchange membrane loaded with boron nitride nanosheets is then immersed in an alkaline buffer solution containing dopamine. Utilizing the self-polymerization properties of dopamine under alkaline conditions, a stable functional layer is constructed, achieving a strong bond between the boron nitride nanosheets and the base membrane, thus obtaining the composite ion exchange membrane. This composite ion exchange membrane exhibits excellent anti-fouling and ion separation performance, effectively inhibiting the deposition of inorganic salts on the membrane surface during electrodialysis, reducing the impact of membrane fouling on ion transport and separation performance, lowering membrane cleaning frequency and operating energy consumption, and can be applied in fields such as lithium resource extraction, seawater desalination, and high-salinity wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a method for preparing a composite ion exchange membrane with anti-fouling properties. The prepared composite ion exchange membrane can be used for the selective separation of ions in liquid solutions, and is particularly suitable for ion separation processes in systems such as brine, seawater, and ore leachate. Background Technology

[0002] Electrodialysis is an electrically driven separation technology centered on ion exchange membranes, including conventional electrodialysis, selective electrodialysis, and bipolar membrane electrodialysis. This technology utilizes an electric field to achieve the directional migration and separation of ions, and has broad application prospects in fields such as lithium extraction from salt lake brine, seawater resource utilization, ore leachate treatment, and carbon dioxide resource utilization. However, during long-term operation, ion exchange membranes in electrodialysis systems are susceptible to inorganic fouling. Due to the concentration polarization effect, a high-concentration ion environment easily forms in localized areas on the membrane surface, leading to the precipitation and deposition of sparingly soluble salts such as carbonates, hydroxides, and sulfates on the membrane surface or within the membrane channels, forming an inorganic scale layer. The formation of inorganic scale not only increases membrane resistance and reduces ion transport rates but may also clog membrane channels and affect the membrane surface structure, thereby reducing membrane separation performance and operational stability, and increasing system energy consumption and maintenance costs. Developing ion exchange membranes with high ion selectivity, anti-fouling properties, and operational stability is of great significance for improving the separation efficiency and operational lifespan of the electrodialysis process.

[0003] Boron nitride nanosheets are inorganic nanomaterials with a two-dimensional layered structure and high chemical stability. The dipole moments between their boron-nitrogen bonds closely match those of the oxygen-hydrogen bonds in water molecules, facilitating strong polar interactions between the hexagonal boron nitride nanosheets and water molecules. This results in the formation of a dense hydration layer, inhibiting the formation of inorganic scale. Introducing boron nitride nanosheets onto the surface of ion exchange membranes enhances the hydration capacity of the membrane surface, forming a stable hydration layer that inhibits the deposition of inorganic salts and improves the membrane's ion-selective transport performance. However, commercial ion exchange membranes are all organic and dense membranes, and conventional two-dimensional thin-film preparation methods such as vacuum filtration are not suitable for assembling hexagonal boron nitride nanosheets on the surface of ion exchange membranes. Furthermore, the interfacial bonding between boron nitride nanosheets and the membrane substrate is limited, posing a risk of detachment during long-term operation, thus affecting the membrane's stability and lifespan. Therefore, there is an urgent need to develop a method for stably loading boron nitride nanosheets onto the surface of ion exchange membranes to achieve a synergistic improvement in ion selectivity, anti-scaling performance, and operational stability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a composite ion exchange membrane with anti-fouling properties, so as to solve the problems of poor anti-fouling performance, insufficient operational stability, and easy detachment of boron nitride nanosheets in existing ion exchange membranes.

[0005] The technical solution of this invention is as follows: A method for preparing a composite ion exchange membrane with anti-scaling properties includes the following steps: A. Urea, boron nitride powder and zirconia balls are placed in a zirconia ball mill jar at a certain mass ratio and ball milled. The ball-milled powder is dispersed in deionized water and then subjected to dialysis and centrifugation to obtain a boron nitride nanosheet dispersion. B. Fix the ion exchange membrane in the electric field driven deposition device so that the ion exchange membrane separates the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. C. Electrodes are set on both sides of the electrolytic cell and a DC electric field is applied. The electrode on the side containing the boron nitride nanosheet dispersion is the negative electrode, and the electrode containing the electrolyte solution is the positive electrode, so that the boron nitride nanosheets migrate in a directional manner and are deposited on the surface of the ion exchange membrane to obtain a boron nitride nanosheet modified ion exchange membrane. D. The modified ion exchange membrane is placed in an alkaline buffer solution containing dopamine for surface polymerization reaction to form a composite functional layer containing polydopamine and boron nitride nanosheets on the membrane surface, thereby obtaining a composite ion exchange membrane with both anti-fouling properties and ion selectivity.

[0006] Preferably, the mass ratio of urea, boron nitride, and zirconium oxide balls in step A is 300~10:1:400~800.

[0007] Preferably, the ball milling time in step A is 15-20 hours, and the ball milling speed is 300-500 rpm.

[0008] Preferably, the concentration of the boron nitride nanosheet dispersion in step A is 0.5~10 mg / mL.

[0009] Preferably, the electric field strength applied in step C is 1–3 V / cm, and the electric field-driven deposition time is 10–60 min.

[0010] Preferably, the concentration of dopamine in the alkaline buffer solution in step D is 0–1 mg / mL.

[0011] Preferably, the pH of the alkaline buffer solution in step D is 8.8 to 10.0.

[0012] Preferably, the surface polymerization reaction time in step D is 1 to 60 min.

[0013] Preferably, the alkaline buffer solution in step D is one of Tris-HCl buffer, carbonate-bicarbonate buffer, or phosphate buffer.

[0014] The composite ion exchange membrane of the present invention includes an ion exchange membrane substrate and a composite functional layer formed on its surface; the composite functional layer comprises boron nitride nanosheets and polydopamine, wherein the boron nitride nanosheets are fixed to the surface of the ion exchange membrane substrate by polydopamine. Beneficial effects

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses an electric field driven method to uniformly load boron nitride nanosheets onto the surface of an ion exchange membrane, which promotes the formation of a stable and dense hydration layer on the membrane surface during operation and inhibits the formation of inorganic scale. At the same time, the boron nitride nanosheets can regulate the membrane surface structure and interfacial mass transfer behavior, thereby improving the ion selectivity of the membrane.

[0016] (2) This invention combines electric field driven deposition with in-situ fixation of polydopamine. Through the self-polymerization reaction of dopamine under alkaline conditions, a polydopamine functional layer is constructed on the membrane surface, which overcomes the problems of weak bonding and easy detachment of nanomaterials in traditional physical coating methods, and achieves a firm bond between boron nitride nanosheets and membrane substrate, thereby improving the stability and durability of the functional layer.

[0017] (3) The prepared composite ion exchange membrane has anti-fouling properties, ion selectivity and operational stability. It can be applied to electro-driven membrane processes such as electrodialysis, selective electrodialysis and bipolar membrane electrodialysis. It has application value in fields such as lithium extraction from salt lake brine, seawater desalination, ore leachate treatment and resource utilization of high-salt wastewater. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the electrodeposition apparatus used in Examples 1-7.

[0019] Figure 2 These are surface and cross-sectional SEM images of the commercial ion exchange membrane-cation membrane used in Example 3 and the prepared composite ion exchange membrane-cation membrane.

[0020] Figure 3 These are surface SEM images of the commercial ion exchange membrane-anion membrane used in Example 4 and the prepared composite ion exchange membrane-anion membrane.

[0021] Figure 4 These are surface and cross-sectional SEM images of the composite ion exchange membrane-cation membrane prepared in Example 5.

[0022] Figure 5The changes in the surface morphology of the commercial ion exchange membrane-cation membrane, composite ion exchange membrane-cation membrane, commercial ion exchange membrane-anion membrane, and composite ion exchange membrane-anion membrane in Example 8 after immersion in a saturated lithium carbonate solution are described.

[0023] Figure 6 The infrared spectra are those of the commercial ion exchange membrane-cation membrane used in Example 3, the prepared composite ion exchange membrane-cation membrane, and the commercial ion exchange membrane-anion membrane used in Example 4, and the prepared composite ion exchange membrane-anion membrane.

[0024] Figure 7 This is a schematic diagram of the electrodialysis membrane module used in Examples 9 and 10 to test the separation performance of monovalent and divalent cations and the separation performance of monovalent and divalent anions in the composite ion exchange membrane.

[0025] Figure 8 The lithium-magnesium separation performance of the commercial ion exchange membrane-cation membrane, composite ion exchange membrane-cation membrane, commercial ion exchange membrane-anion membrane, and composite ion exchange membrane-anion membrane tested in Examples 9 and 10, as well as the Cl... - SO4 2- Separation performance data graph. Detailed Implementation Example 1

[0026] This example illustrates the preparation of boron nitride nanosheet dispersions via ball milling.

[0027] Urea, boron nitride, and zirconium oxide balls were placed in a ball mill at a mass ratio of 10:1:800 and milled for 20 hours at a speed of 300 rpm. After milling, the resulting boron nitride nanosheets were dispersed in deionized water, and the suspension was then placed in a dialysis bag and dialyzed for 7 days to remove residual urea. The dialysis suspension was then centrifuged at a low speed (4500 rpm for 10 min), and the supernatant was collected and centrifuged at a high speed (8500 rpm for 10 min). The sediment obtained was the boron nitride nanosheets required for the experiment, which were dispersed in deionized water for later use. Example 2

[0028] This example illustrates the preparation of boron nitride nanosheet dispersions via ball milling.

[0029] Urea, boron nitride, and zirconium oxide balls were placed in a ball mill at a mass ratio of 3:1:400 and milled for 15 hours at a speed of 500 rpm. After milling, the resulting boron nitride nanosheets were dispersed in deionized water, and the suspension was then placed in a dialysis bag and dialyzed for 7 days to remove residual urea. The dialysis suspension was centrifuged at low speed (4500 rpm for 10 min), and the supernatant was collected and then centrifuged at high speed (8500 rpm for 10 min). The sediment obtained was the boron nitride nanosheets required for the experiment, which were dispersed in deionized water for later use. Example 3

[0030] This embodiment illustrates the preparation of composite ion exchange membranes using an electric field-driven deposition method.

[0031] Immobilize the commercial ion exchange membrane - cation exchange membrane. Figure 1 In the electrodeposition apparatus shown, the boron nitride nanosheet dispersion obtained in Example 1 was diluted to 0.5 mg / mL, and the commercial ion exchange membrane-cation membrane was used to separate the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. Electrodes were placed on both sides of the electrolytic cell and a DC electric field of 3 V / cm was applied for 60 min. The electrode on the side containing the boron nitride nanosheet dispersion was the negative electrode, and the electrode containing the electrolyte solution was the positive electrode, causing the boron nitride nanosheets to migrate directionally and deposit on the surface of the commercial ion exchange membrane-cation membrane, thus obtaining a boron nitride nanosheet modified ion exchange membrane. The boron nitride nanosheet modified ion exchange membrane was placed in a Tris-HCl buffer solution containing 1 mg / L dopamine and pH=8.8 for a surface polymerization reaction for 30 min, forming a composite functional layer containing polydopamine and boron nitride nanosheets on the membrane surface, thereby obtaining a composite ion exchange membrane with ion selectivity and anti-fouling properties. This membrane is called a composite ion exchange membrane-cation membrane.

[0032] Figure 2 a and Figure 2 c is a surface and cross-sectional SEM image of the commercial ion exchange membrane—the cation exchange membrane—used in this embodiment. Figure 2 b and Figure 2 Image d shows the surface and cross-sectional SEM images of the composite ion exchange membrane-cation membrane prepared in this embodiment. It can be seen that compared with commercial ion exchange membrane-cation membranes, the cross-section of the composite ion exchange membrane-cation membrane has a dense boron nitride modified layer with a thickness of about 10 µm, and the surface of the composite ion exchange membrane-cation membrane also shows the texture of boron nitride nanosheets. Figure 6 These are the infrared spectra of the commercial ion exchange membrane-cation membrane and the composite ion exchange membrane-cation membrane in this embodiment. The composite ion exchange membrane-cation membrane has an infrared spectrum at approximately 1380 cm⁻¹. -1The absorption peak at approximately 780 cm⁻¹ corresponds to the stretching vibration peak of sp² hybridized BN. -1 The interplane transverse optical bending vibration peak corresponding to NBN at this location proves that boron nitride nanosheets have been successfully introduced into the surface of commercial ion exchange membranes - cation exchange membranes. Example 4

[0033] This embodiment illustrates the preparation of composite ion exchange membranes using an electric field-driven deposition method.

[0034] Immobilize commercial ion exchange membranes-anion membranes on Figure 1 In the electrodeposition apparatus shown, the boron nitride nanosheet dispersion obtained in Example 1 was diluted to 0.5 mg / mL, and the commercial ion exchange membrane-anion membrane was used to separate the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. Electrodes were placed on both sides of the electrolytic cell and a DC electric field of 3 V / cm was applied for 60 min. The electrode on the side containing the boron nitride nanosheet dispersion was the negative electrode, and the electrode containing the electrolyte solution was the positive electrode, causing the boron nitride nanosheets to migrate directionally and deposit on the surface of the commercial ion exchange membrane-anion membrane, thus obtaining a boron nitride nanosheet modified commercial ion exchange membrane-anion membrane. The modified commercial ion exchange membrane-anion membrane was placed in a Tris-HCl buffer solution containing 1 mg / L dopamine and pH=8.8 for a surface polymerization reaction for 30 min, forming a composite functional layer containing polydopamine and boron nitride nanosheets on the membrane surface, thereby obtaining a composite ion exchange membrane with ion selectivity and anti-fouling properties. This membrane is called a composite ion exchange membrane-anion membrane.

[0035] Figure 3 a and Figure 3 b shows SEM images of the surface of the commercial ion exchange membrane-anion membrane used in this embodiment and the surface of the prepared composite ion exchange membrane-anion membrane. It can be seen that the surface of the composite ion exchange membrane-anion membrane exhibits a boron nitride nanosheet texture. Figure 6 These are the infrared spectra of the commercial ion exchange membrane-anion membrane and the composite ion exchange membrane-anion membrane in this embodiment. The composite ion exchange membrane-cation membrane has an infrared spectrum at approximately 1380 cm⁻¹. -1 The absorption peak at approximately 780 cm⁻¹ corresponds to the stretching vibration peak of sp² hybridized BN. -1 The interplane transverse optical bending vibration peak corresponding to NBN at this location proves that boron nitride nanosheets have been successfully introduced into the surface of commercial ion exchange membranes - anion membranes. Example 5

[0036] This embodiment illustrates the preparation of composite ion exchange membranes using an electric field-driven deposition method.

[0037] Immobilize the commercial ion exchange membrane - cation exchange membrane. Figure 1In the electrodeposition apparatus shown, the boron nitride nanosheet dispersion obtained in Example 2 was diluted to 10 mg / mL, and the commercial ion exchange membrane-cation membrane was used to separate the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. Electrodes were placed on both sides of the electrolytic cell and a DC electric field of 2.5 V / cm was applied for 20 min. The electrode on the side containing the boron nitride nanosheet dispersion was the negative electrode, and the electrode containing the electrolyte solution was the positive electrode, so that the boron nitride nanosheets migrated and deposited on the surface of the commercial ion exchange membrane-cation membrane. The modified commercial ion exchange membrane-cation membrane was placed in a carbonate-bicarbonate buffer solution at pH=8.8 for a surface polymerization reaction for 1 min, thereby obtaining a composite ion exchange membrane with ion selectivity and anti-fouling properties. This membrane is called composite ion exchange membrane-cation membrane-2.

[0038] Figure 4 a and Figure 4 b shows the surface and cross-sectional SEM images of the composite ion exchange membrane-cation membrane-2 prepared in this embodiment. It can be seen that compared with the commercial ion exchange membrane-cation membrane, the cross-section of the composite ion exchange membrane-cation membrane-2 has a dense boron nitride modified layer with a thickness of about 1.5 µm, and the surface of the composite ion exchange membrane-cation membrane-2 exhibits the texture of boron nitride nanosheets. Example 6

[0039] This embodiment illustrates the preparation of composite ion exchange membranes using an electric field-driven deposition method.

[0040] Immobilize the commercial ion exchange membrane - cation exchange membrane. Figure 1 In the electrodeposition apparatus shown, the boron nitride nanosheet dispersion obtained in Example 2 was diluted to 10 mg / mL, and the commercial ion exchange membrane-cation membrane was used to separate the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. Electrodes were placed on both sides of the electrolytic cell and a DC electric field of 1 V / cm was applied for 10 min. The electrode on the side containing the boron nitride nanosheet dispersion was the negative electrode, and the electrode containing the electrolyte solution was the positive electrode, causing the boron nitride nanosheets to migrate directionally and deposit on the surface of the commercial ion exchange membrane-cation membrane, thus obtaining a boron nitride nanosheet modified commercial ion exchange membrane-cation membrane. The modified commercial ion exchange membrane-cation membrane was placed in a phosphate buffer solution containing 1 mg / L dopamine at pH=10 for a surface polymerization reaction for 60 min, thereby obtaining a composite ion exchange membrane with ion selectivity and anti-fouling properties. This membrane is called composite ion exchange membrane-cation membrane-3. Example 7

[0041] This embodiment illustrates the preparation of composite ion exchange membranes using an electric field-driven deposition method.

[0042] Immobilize the commercial ion exchange membrane - cation exchange membrane. Figure 1In the electrodeposition apparatus shown, the boron nitride nanosheet dispersion obtained in Example 2 was diluted to 10 mg / mL, and the commercial ion exchange membrane-cation membrane was used to separate the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. Electrodes were placed on both sides of the electrolytic cell and a DC electric field of 1 V / cm was applied for 10 min. The electrode on the side containing the boron nitride nanosheet dispersion was the negative electrode, and the electrode containing the electrolyte solution was the positive electrode, causing the boron nitride nanosheets to migrate directionally and deposit on the surface of the commercial ion exchange membrane-cation membrane, thus obtaining a boron nitride nanosheet modified commercial ion exchange membrane-cation membrane. The modified commercial ion exchange membrane-cation membrane was placed in a carbonate-bicarbonate buffer solution at pH=10 for a surface polymerization reaction for 60 min, thereby obtaining a composite ion exchange membrane with ion selectivity and anti-fouling properties. This membrane is called composite ion exchange membrane-cation membrane-4. Example 8

[0043] This embodiment is used to illustrate the anti-fouling performance test of composite ion exchange membranes.

[0044] First, the commercial ion exchange membranes (cationic membranes), composite ion exchange membranes (cationic membranes), commercial ion exchange membranes (anion membranes), and composite ion exchange membranes (anion membranes) from Examples 3 and 4 were immersed in a saturated lithium carbonate solution for 24 hours. After immersion, the membranes were removed, and the changes in surface morphology of the commercial ion exchange membranes (cationic membranes), composite ion exchange membranes (cationic membranes), commercial ion exchange membranes (anion membranes), and composite ion exchange membranes (anion membranes) after immersion in the saturated lithium carbonate solution were tested.

[0045] Figure 5 The figures show the surface morphology changes of the commercial ion exchange membrane-cation membrane, composite ion exchange membrane-cation membrane, commercial ion exchange membrane-anion membrane, and composite ion exchange membrane-anion membrane in this embodiment after immersion in a saturated lithium carbonate solution. It can be seen from the figures that the composite ion exchange membrane-cation membrane and composite ion exchange membrane-anion membrane have better anti-scaling performance than the commercial ion exchange membrane-cation membrane and commercial ion exchange membrane-anion membrane. Example 9

[0046] This embodiment illustrates the separation performance of monovalent and divalent cations by electrodialysis testing of a composite ion exchange membrane-cation membrane.

[0047] Three solutions, namely 150 mL each of simulated feed solution, pure water, and electrode solution, were successively introduced into the electrodialysis apparatus. The simulated feed solution was a 0.1 mol / L mixed ion solution, a lithium-magnesium mixture: LiCl:MgCl2 = 1:1 (molar ratio). The electrode solution was a 0.1 mol / L KCl solution. The voltage applied to the electrodialysis apparatus was 1.2 V, and all experiments were conducted at room temperature. After 3 hours of electrodialysis testing, the concentrations of lithium and magnesium ions on the pure water side were measured, and the lithium-magnesium selectivity of the composite ion exchange membrane-cation membrane was calculated.

[0048] Figure 7 a is a schematic diagram of the electrodialysis membrane assembly device used in this embodiment. Figure 8 Figure a shows the lithium-magnesium separation performance of the composite ion exchange membrane-cation membrane obtained after electrodialysis testing in this embodiment. As can be seen from the figure, the Li... + / Mg 2+ The separation factor is 1.5, and the Li-ion composite ion exchange membrane-cation membrane has a separation factor of 1.5. + / Mg 2+ The separation factor is around 2, which is the Li of the composite ion exchange membrane-cation membrane. + / Mg 2+ The separation performance is slightly improved compared to commercial ion exchange membranes - cation exchange membranes. Example 10

[0049] This embodiment illustrates the separation performance of monovalent and divalent anions by electrodialysis testing of a composite ion exchange membrane-anion membrane.

[0050] Three solutions, namely 150 mL each of simulated feed solution, pure water, and electrode solution, were successively introduced into the electrodialysis apparatus. The simulated feed solution was a 0.1 mol / L mixed ion solution with a molar ratio of NaCl:Na₂SO₄ = 1:1. The electrode solution was a 0.1 mol / L KOH solution. The voltage applied to the electrodialysis apparatus was 1.2 V, and all experiments were conducted at room temperature. After 3 h of electrodialysis testing, the concentrations of chloride and sulfate ions on the pure water side were measured, and the selectivity of the composite ion exchange membrane-anion membrane for chloride and sulfate ions was calculated.

[0051] Figure 7 b is a schematic diagram of the electrodialysis membrane assembly device used in this embodiment. Figure 8 b is a graph showing the chloride and sulfate ion separation performance of the composite ion exchange membrane-anion membrane obtained after electrodialysis testing in this embodiment. The graph shows that the chloride ion separation performance of the commercial ion exchange membrane-anion membrane is... - SO4 2- The separation factor is 3.5, and the Cl- content of the composite ion exchange membrane-anion membrane is... - SO4 2- The separation factor is around 55, meaning the composite ion exchange membrane-anion membrane exhibits excellent Cl-cosity. - SO4 2- Separation performance.

Claims

1. A method for preparing a composite ion exchange membrane with anti-scaling properties, characterized in that: The specific operating steps are as follows: A. Urea, boron nitride powder and zirconia balls are placed in a zirconia ball mill jar at a certain mass ratio and ball milled. The ball-milled powder is dispersed in deionized water and then subjected to dialysis and centrifugation to obtain a boron nitride nanosheet dispersion. B. Fix the ion exchange membrane in the electrodeposition device so that the ion exchange membrane separates the electrolytic cell containing the boron nitride nanosheet dispersion from the electrolytic cell containing the electrolyte solution. C. Electrodes are set on both sides of the electrolytic cell and a DC electric field is applied to cause boron nitride nanosheets to migrate in a directional manner and deposit on the surface of the ion exchange membrane, thereby obtaining a boron nitride nanosheet modified ion exchange membrane. D. The modified ion exchange membrane is placed in an alkaline buffer solution containing dopamine for surface polymerization to obtain a composite ion exchange membrane with ion selectivity and anti-fouling properties.

2. The method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: In step A, the mass ratio of urea, boron nitride, and zirconium oxide balls is 3~10:1:400~800.

3. The method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: In step A, the ball milling time is 15-20 hours and the ball milling speed is 300-500 rpm.

4. The method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: In step A, the concentration of the boron nitride nanosheet dispersion is 0.5~10 mg / mL.

5. The method for preparing a composite ion exchange membrane with both anti-scaling properties and ion selectivity according to claim 1, characterized in that: The electric field strength applied in step C is 1–3 V / cm, and the electrodeposition time is 10–60 min.

6. A method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: The concentration of dopamine in the alkaline buffer solution in step D is 0–1 mg / mL.

7. The method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: The pH of the alkaline buffer solution in step D is 8.8–10.

0.

8. A method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: The surface polymerization reaction time in step D is 1 to 60 min.

9. The method for preparing a composite ion exchange membrane with anti-scaling properties according to claim 1, characterized in that: The alkaline buffer solution mentioned in step D is one of Tris-HCl buffer, carbonate-bicarbonate buffer, borate buffer, or phosphate buffer.

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