Method for preparing MOF gas separation membrane by electric field regulation deposition

Abstract

The application belongs to the field of membrane separation technology, and particularly relates to a method for preparing a MOF gas separation membrane by electric field regulation and deposition, which comprises four steps of substrate pretreatment, electric control deposition liquid preparation, multilayer electrodeposition, membrane layer activation and post-treatment, uses a zirconium foil as a counter electrode and a zirconium source, uses Fc(COOH)2 as a ligand, uses dopamine hydrochloride as a polymerization monomer, generates a Zr-Fc MOF composite multilayer membrane in situ under the action of a constant current electric field, and then obtains a finished membrane through PDMS immersion activation. The gas separation membrane prepared by the application has an electric field adjustable pore size, the reversible oxidation and reduction of a ferrocene group can realize real-time regulation of the membrane pore size, and various gas separations such as CO2 / CH4 and He / CH4 can be realized; the rich in-plane micropores of the Zr-Fc MOF give consideration to high permeability and high selectivity, break through the limitation of the traditional 'Trade-off effect', and the CO2 / CH4 selectivity can reach 44-89 under a 0.6V positive potential, and the He / CH4 selectivity can reach 108-201 under a-0.5V negative potential, so the application has a wide application prospect in the field of gas separation.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and particularly relates to a method for preparing MOF gas separation membranes by electric field-controlled deposition. Background Technology

[0002] Gas separation membrane technology originated in the 1980s. After years of development, it has played a vital role in many fields such as air separation, hydrogen purification, helium separation, and carbon dioxide capture, becoming one of the indispensable technologies in modern industrial production.

[0003] However, current gas separation membrane products generally suffer from the following problems: First, a single membrane can typically only be used for one type of gas separation scenario, making it impossible to achieve multi-functionality. When the composition of the feed gas or the separation target changes, the entire membrane module needs to be replaced, resulting in high operating costs and poor adaptability. Second, current gas separation membranes are generally limited by the "trade-off effect," meaning that there is a trade-off relationship between gas permeability and gas selectivity. It is difficult to simultaneously achieve high gas selectivity and high gas permeability, which limits the application of membrane separation technology under more demanding operating conditions.

[0004] Metal-organic frameworks (MOFs) have shown great potential in gas separation due to their designable pore structures, high specific surface area, and abundant functional groups. However, traditional MOF membranes are mostly prepared using solvothermal methods and layer-by-layer self-assembly methods, which suffer from problems such as long film formation cycles, numerous membrane defects, poor adhesion to the substrate, and inability to dynamically control pore size. Therefore, how to prepare gas separation membranes that balance high gas selectivity and high gas permeability while being adaptable to different gas separation scenarios is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] This invention addresses the technical problems of existing gas separation membranes, such as performance limitations due to the "trade-off effect," limited application scenarios, and inability to achieve multifunctionality, by proposing a method for preparing MOF gas separation membranes through electric field-controlled deposition.

[0006] This method uses zirconium foil as the counter electrode and zirconium source, and Fc(COOH)₂ (ferrocene dicarboxylic acid) as the organic ligand to generate Zr-FcMOF in situ under a constant current electric field. Simultaneously, dopamine hydrochloride undergoes oxidative polymerization under the electric field to form a polydopamine framework, which is then combined with Zr-FcMOF to construct a multilayer membrane structure. The prepared gas separation membrane possesses unique electric field-regulated reaction channels. The reversible redox reaction of the ferrocene groups can cause changes in the MOF framework morphology, thereby allowing real-time regulation of the membrane pores through the electric field. This enables the separation and purification of different types of gases, achieving multifunctionality. Furthermore, the unique Zr-FcMOF has abundant in-plane micropores. These pores not only provide additional gas transport paths, but the spatial confinement effect within the pores also enhances the interaction between the gas and the MOF framework, improving gas selectivity and overcoming the limitations of the traditional "trade-off effect."

[0007] To achieve the above objectives, the present invention employs a method for preparing MOF gas separation membranes by electric field-controlled deposition, comprising the following steps:

[0008] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0009] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to the solvent, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid in sequence while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask and dilute to volume with solvent to obtain the electrostatic deposition solution.

[0010] S3. Multilayer Electrodeposition: Preheat the electro-deposition solution to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electro-deposition solution. Start the electrochemical workstation, apply a constant current, and control the current density to 1~100 mA / cm². 2 The deposition time is 5-100 min; turn off the power, remove the ITO conductive glass, rinse it with solvent at least 3 times, then rinse it with methanol at least 3 times, and dry it with nitrogen; repeat the above steps to perform multilayer deposition, with 1-30 layers. Immerse the deposited membrane in solvent for at least 12 h, then transfer it to methanol for immersion 3 times, each time for at least 8 h, to obtain the nascent gas separation membrane.

[0011] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a certain solid content. Immerse the obtained nascent gas separation membrane in the PDMS solution for a period of time. Then transfer the membrane to a vacuum oven and heat it for a period of time to activate the membrane and solidify the PDMS layer. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited MOF gas separation membrane.

[0012] Preferably, in step S2, the solvent includes, but is not limited to, N,N-dimethylformamide (DMF), γ-valerolactone (GVL), and dihydroglucosenolide.

[0013] Preferably, in step S2, the final concentration of Fc(COOH)2 is 1~100mM, the final concentration of glacial acetic acid is 0.1~5M, the final concentration of nitric acid is 0.01~0.1M, the final concentration of TBAHS is 0.01~1M, and the final concentration of dopamine hydrochloride is 0.1~1mM.

[0014] More preferably, in step S2, the solvent is N,N-dimethylformamide (DMF).

[0015] More preferably, in step S2, the final concentration of Fc(COOH)2 is 5~15mM.

[0016] More preferably, in step S2, the final concentration of the glacial acetic acid is 1~2M.

[0017] More preferably, in step S2, the final concentration of the nitric acid is 0.05~0.08M.

[0018] More preferably, in step S2, the final concentration of the TBAHS is 0.05~0.15M.

[0019] More preferably, in step S2, the final concentration of dopamine hydrochloride is 0.3~0.8mM.

[0020] Preferably, in step S3, the current density is 20~40 mA / cm². 2 .

[0021] Preferably, in step S3, the deposition time is 5 to 60 minutes.

[0022] Preferably, in step S3, the number of multilayer deposition layers is 3 to 20.

[0023] Preferably, in step S4, the solvent of the PDMS solution is one or a mixture of several of petroleum ether, n-hexane, toluene, and xylene.

[0024] Preferably, in step S4, the solid content of the PDMS solution is 1-10%, the impregnation time is 1-60s, the vacuum oven heating temperature is 80-120℃, and the heating time is 1-12h.

[0025] More preferably, in step S4, the solvent of the PDMS solution is petroleum ether.

[0026] More preferably, in step S4, the solid content of the PDMS solution is 3-5%.

[0027] More preferably, in step S4, the immersion time is 10~30s.

[0028] More preferably, in step S4, the heating temperature of the vacuum oven is 90~100℃.

[0029] More preferably, in step S4, the heating time of the vacuum oven is 8~10 hours.

[0030] Compared with existing technologies, the advantages and positive effects of the electric field-controlled deposition method for preparing MOF gas separation membranes provided by this invention are as follows:

[0031] 1. Multifunctionality: The gas separation membrane prepared by this method can adjust the membrane pore size in real time by applying potentials of different directions and magnitudes under the action of electric field-controlled separation channels, thereby realizing the separation of multiple gas systems such as CO2 / CH4 and He / CH4, breaking through the limitation of traditional single membranes that can only correspond to one separation scenario.

[0032] 2. Overcoming the “Trade-off effect”: The Zr-FcMOF membrane formed by electric field-controlled deposition has abundant in-plane micropores, which not only provides additional gas transport paths to ensure high permeability, but also enhances the interaction between gas and framework through the pore space confinement effect to ensure high selectivity, thus taking into account both gas selectivity and permeability.

[0033] 3. Excellent film quality: Multilayer electrodeposition combined with PDMS post-treatment effectively seals micro-defects in the film, improves the film density and adhesion to the substrate, and extends the service life of the film.

[0034] 4. Controllable process: Constant current electrodeposition is adopted, with current density as the core control parameter. The process has good repeatability and a wide parameter adjustment range, which is conducive to large-scale production. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the cross-sectional structure of a MOF gas separation membrane prepared by electric field-controlled deposition. Detailed Implementation

[0037] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0038] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0039] In the following examples, Fc(COOH)2 is ferrocene dicarboxylic acid, TBAHS is tetrabutylammonium hydrogen sulfate, PDMS is polydimethylsiloxane, and DMF is N,N-dimethylformamide. Gas permeation performance was measured using a BONA-GS-17 gas permeation testing device at 25°C and 0.1 MPa. The permeation fluxes of CO2 and CH4 were measured and the CO2 / CH4 selectivity was calculated when a positive potential of 0.6V was applied to the membrane. The permeation fluxes of He and CH4 were measured and the He / CH4 selectivity was calculated when a negative potential of -0.5V was applied to the membrane.

[0040] Example 1, such as Figure 1 As shown, the separation membrane prepared by a method for preparing MOF gas separation membrane by electric field-controlled deposition specifically includes the following steps:

[0041] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for 10 minutes in sequence, and then dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for 10 minutes in sequence, and then dried with dry nitrogen gas.

[0042] S2. Preparation of Electrostatic Deposition Solution: Add Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for 5 min; add TBAHS and stir until completely dissolved; then add dopamine hydrochloride and stir until completely dissolved; transfer the resulting solution to a volumetric flask, and dilute to volume with DMF to control the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0043] S3. Multilayer Electrodeposition: Preheat the electrodeposition solution to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrodeposition solution. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 20 mA / cm². 2 Deposition was carried out for 10 minutes; the power was turned off, the ITO conductive glass was removed, rinsed 3 times with DMF, then rinsed 3 times with methanol, and dried with nitrogen; the above steps were repeated to deposit a total of 3 layers. The deposited membrane was immersed in DMF for 12 hours, and then transferred to methanol for 8 hours each time to obtain the nascent gas separation membrane.

[0044] S4. Membrane activation and post-treatment: Dissolve PDMS in petroleum ether to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain an electric field-controlled deposited MOF gas separation membrane.

[0045] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 512 GPU and a CO2 / CH4 selectivity of 44 at a positive potential of 0.6V; and a He permeation flux of 1280 GPU and a He / CH4 selectivity of 108 at a negative potential of -0.5V.

[0046] Example 2: The only difference between this example and Example 1 is that the current density in step S3 is 30 mA / cm². 2 The remaining steps and parameters are the same as in Example 1.

[0047] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0048] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask, and dilute to volume with DMF, controlling the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0049] S3. Multilayer Electrodeposition: Preheat the electrolyte to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrolyte. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 30 mA / cm². 2 Deposit for 10 minutes; turn off the power, remove the ITO conductive glass, rinse with solvent at least 3 times, then rinse with methanol at least 3 times, and dry with nitrogen; repeat the above steps to deposit a total of 3 layers. Immerse the deposited membrane in solvent for at least 12 hours, then transfer it to methanol for immersion 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane.

[0050] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited gas separation membrane.

[0051] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 401 GPU and a CO2 / CH4 selectivity of 56 at a positive potential of 0.6V; and a He permeation flux of 803 GPU and a He / CH4 selectivity of 122 at a negative potential of -0.5V.

[0052] Example 3 differs from Example 1 only in that the current density in step S3 is 35 mA / cm². 2 The remaining steps and parameters are the same as in Example 1.

[0053] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0054] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask, and dilute to volume with DMF, controlling the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0055] S3. Multilayer Electrodeposition: Preheat the electrolyte to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrolyte. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 35 mA / cm². 2 Deposit for 10 minutes; turn off the power, remove the ITO conductive glass, rinse with solvent at least 3 times, then rinse with methanol at least 3 times, and dry with nitrogen; repeat the above steps to deposit a total of 3 layers. Immerse the deposited membrane in solvent for at least 12 hours, then transfer it to methanol for immersion 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane.

[0056] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited gas separation membrane.

[0057] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 357 GPU and a CO2 / CH4 selectivity of 62 at a positive potential of 0.6V; and a He permeation flux of 777 GPU and a He / CH4 selectivity of 131 at a negative potential of -0.5V.

[0058] Example 4: The only difference between this example and Example 1 is that the current density in step S3 is 10 mA / cm². 2 The deposition time was 20 minutes, and the remaining steps and parameters were the same as in Example 1.

[0059] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0060] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask, and dilute to volume with DMF, controlling the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0061] S3. Multilayer Electrodeposition: Preheat the electrolyte to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrolyte. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 10 mA / cm². 2 Deposit for 20 minutes; turn off the power, remove the ITO conductive glass, rinse with solvent at least 3 times, then rinse with methanol at least 3 times, and dry with nitrogen; repeat the above steps to deposit a total of 3 layers. Immerse the deposited membrane in solvent for at least 12 hours, then transfer it to methanol for immersion 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane.

[0062] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited gas separation membrane.

[0063] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 413 GPU and a CO2 / CH4 selectivity of 64 at a positive potential of 0.6V; and a He permeation flux of 871 GPU and a He / CH4 selectivity of 136 at a negative potential of -0.5V.

[0064] Example 5: The only difference between this example and Example 1 is that the deposition time in step S3 is 30 minutes. All other steps and parameters are the same as in Example 1.

[0065] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0066] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask, and dilute to volume with DMF, controlling the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0067] S3. Multilayer Electrodeposition: Preheat the electrolyte to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrolyte. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 20 mA / cm². 2 Deposit for 30 minutes; turn off the power, remove the ITO conductive glass, rinse with solvent at least 3 times, then rinse with methanol at least 3 times, and dry with nitrogen; repeat the above steps to deposit a total of 3 layers. Immerse the deposited membrane in solvent for at least 12 hours, then transfer it to methanol for immersion 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane.

[0068] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited gas separation membrane.

[0069] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 361 GPU and a CO2 / CH4 selectivity of 79 at a positive potential of 0.6V; and a He permeation flux of 666 GPU and a He / CH4 selectivity of 179 at a negative potential of -0.5V.

[0070] Example 6: The only difference between this example and Example 1 is that the number of multilayer deposition layers in step S3 is 10. All other steps and parameters are the same as in Example 1.

[0071] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0072] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask, and dilute to volume with DMF, controlling the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0073] S3. Multilayer Electrodeposition: Preheat the electrolyte to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrolyte. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 20 mA / cm². 2 Deposit for 10 minutes; turn off the power, remove the ITO conductive glass, rinse with solvent at least 3 times, then rinse with methanol at least 3 times, and dry with nitrogen; repeat the above steps to deposit a total of 10 layers. Immerse the deposited membrane in solvent for at least 12 hours, then transfer it to methanol for immersion 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane.

[0074] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited gas separation membrane.

[0075] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 317 GPU and a CO2 / CH4 selectivity of 77 at a positive potential of 0.6V; and a He permeation flux of 691 GPU and a He / CH4 selectivity of 166 at a negative potential of -0.5V.

[0076] Example 7: The only difference between this example and Example 1 is that the number of multilayer deposition layers in step S3 is 20. All other steps and parameters are the same as in Example 1.

[0077] S1. Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas. The zirconium foil is polished clean with 400, 800 and 1200 grit sandpaper in sequence to remove the surface oxide layer. It is then ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence. After removal, it is dried with dry nitrogen gas.

[0078] S2. Preparation of Electrostatic Deposition Solution: Add a certain amount of Fc(COOH)2 to DMF, heat to 40℃ and sonicate until completely dissolved; add a certain amount of glacial acetic acid and nitric acid sequentially while stirring, and continue stirring for at least 5 minutes; add a certain amount of TBAHS and stir until completely dissolved; then add a certain amount of dopamine hydrochloride and stir until completely dissolved; transfer the obtained solution to a volumetric flask, and dilute to volume with DMF, controlling the final concentration of Fc(COOH)2 to 10 mM, the final concentration of glacial acetic acid to 1 M, the final concentration of nitric acid to 0.07 M, the final concentration of TBAHS to 0.1 M, and the final concentration of dopamine hydrochloride to 0.5 mM, thus obtaining the electrostatic deposition solution.

[0079] S3. Multilayer Electrodeposition: Preheat the electrolyte to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other into the electrolyte. Start the electrochemical workstation and apply a constant current to ensure that the current density of the electrodes is 20 mA / cm². 2 Deposit for 10 minutes; turn off the power, remove the ITO conductive glass, rinse with solvent at least 3 times, then rinse with methanol at least 3 times, and dry with nitrogen; repeat the above steps to deposit a total of 20 layers. Immerse the deposited membrane in solvent for at least 12 hours, then transfer it to methanol for immersion 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane.

[0080] S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a solution with a solid content of 3%. Immerse the obtained nascent gas separation membrane in the PDMS solution for 30 seconds. Then transfer the membrane to a vacuum oven and heat it to 100°C for 6 hours to activate it. Allow it to cool naturally to room temperature to obtain the electric field-controlled deposited gas separation membrane.

[0081] Performance testing: The gas separation membrane prepared in this embodiment has a CO2 permeation flux of 206 GPU and a CO2 / CH4 selectivity of 89 at a positive potential of 0.6V; and a He permeation flux of 416 GPU and a He / CH4 selectivity of 201 at a negative potential of -0.5V.

[0082] The gas separation performance of the above embodiments is summarized in Table 1:

[0083] Table 1: Summary of Gas Separation Performance of Each Example

[0084]

[0085] As shown in Table 1 above, with the increase of current density, deposition time, or number of deposition layers, the membrane gradually becomes denser, and the gas permeation flux decreases. However, the selectivity of CO2 / CH4 and He / CH4 is significantly improved, indicating that the present invention can flexibly control the permeability and selectivity by adjusting the electrodeposition process parameters. At the same time, by applying potentials in different directions, the same membrane can achieve efficient separation of CO2 / CH4 and He / CH4 systems respectively, verifying the multifunctional characteristics of the membrane.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing MOF gas separation membranes by electric field-controlled deposition, characterized in that, Includes the following steps: S1. Substrate pretreatment: Substrate pretreatment: The ITO conductive glass is ultrasonically treated in deionized water, acetone and ethanol for at least 10 minutes in sequence, and then dried with dry nitrogen gas. The zirconium foil is polished with 400 grit, 800 grit and 1200 grit sandpaper to remove the surface oxide layer. The zirconium foil is ultrasonically treated in deionized water and ethanol for at least 10 minutes in sequence, and then dried with dry nitrogen gas. S2. Preparation of Electrostatic Deposition Solution: Add Fc(COOH)2 to the solvent, heat to 40℃ and sonicate until completely dissolved; under stirring, add glacial acetic acid and nitric acid sequentially, and continue stirring for at least 5 minutes; then add TBAHS and stir to dissolve, and continue adding dopamine hydrochloride and stirring to dissolve, and bring to a final volume to obtain the electrostatic deposition solution; the solvent is selected from at least one of N,N-dimethylformamide, γ-valerolactone, and dihydroglucoselenone; the final concentration of Fc(COOH)2 is 1~100mM, the final concentration of glacial acetic acid is 0.1~5M, the final concentration of nitric acid is 0.01~0.1M, the final concentration of TBAHS is 0.01~1M, and the final concentration of dopamine hydrochloride is 0.1~1mM; S3. Multilayer Electrodeposition: Preheat the electro-deposition solution to 110°C in an oil bath. Place the pretreated zirconium foil and ITO conductive glass parallel to each other in the electro-deposition solution. Start the electrochemical workstation and apply a constant current with a current density of 1~100 mA / cm². 2 The deposition time for a single deposition is 5 to 100 minutes. After deposition, the ITO conductive glass is removed, rinsed with solvent at least 3 times, rinsed with methanol at least 3 times, and dried with nitrogen. Repeated deposition-rinse-drying process was used to perform multi-layer deposition, with 1 to 30 layers deposited; the resulting membrane was immersed in solvent for at least 12 hours, and then immersed in methanol 3 times, each time for at least 8 hours, to obtain the nascent gas separation membrane; S4. Membrane activation and post-treatment: Dissolve PDMS in a solvent to prepare a PDMS solution with a solid content of 1-10%. Immerse the nascent gas separation membrane in the PDMS solution for 1-60 seconds, then place it in a vacuum oven at 80-120℃ for 1-12 hours for activation and curing. Allow it to cool naturally to room temperature to obtain an electric field-controlled MOF gas separation membrane. The solvent for the PDMS solution is selected from at least one of petroleum ether, n-hexane, toluene, and xylene.

2. The method for preparing MOF gas separation membrane by electric field-controlled deposition according to claim 1, characterized in that, In step S2, the solvent is N,N-dimethylformamide; the final concentration of Fc(COOH)2 is 5~15mM, the final concentration of glacial acetic acid is 1~2M, the final concentration of nitric acid is 0.05~0.08M, the final concentration of TBAHS is 0.05~0.15M, and the final concentration of dopamine hydrochloride is 0.3~0.8mM.

3. The method for preparing MOF gas separation membrane by electric field-controlled deposition according to claim 1, characterized in that, In step S3, the current density is 20~40 mA / cm². 2 The single deposition time is 5-60 minutes, and the number of deposition layers is 3-20.

4. The method for preparing MOF gas separation membrane by electric field-controlled deposition according to claim 1, characterized in that, In step S4, the PDMS solution solvent is petroleum ether, the PDMS solid content is 3-5%, and the impregnation time is 10-30 seconds.

5. The method for preparing MOF gas separation membrane by electric field-controlled deposition according to claim 1, characterized in that, In step S4, the vacuum oven is heated to 90~100℃ for 8~10 hours.

6. The method for preparing MOF gas separation membrane by electric field-controlled deposition according to claim 5, characterized in that, In step S3, ITO conductive glass is used as the working electrode and zirconium foil is used as the counter electrode. The two electrodes are arranged in parallel for electrodeposition.

7. A method for preparing MOF gas separation membranes by electric field-controlled deposition, characterized in that, Prepared by the method described in any one of claims 1-6.

8. The method for preparing MOF gas separation membrane by electric field-controlled deposition according to claim 7, characterized in that, Under test conditions of 25℃ and 0.1MPa, the CO2 / CH4 selectivity of the gas separation membrane was 44~89 when a positive potential of 0.6V was applied. When a negative potential of -0.5V is applied, the selectivity of He / CH4 is 10⁸~20¹.

9. The application of the MOF gas separation membrane prepared by electric field-controlled deposition according to claim 7 or 8 in gas separation, characterized in that, The CO2 / CH4 mixture can be separated by applying a positive potential of 0.6V, or the He / CH4 mixture can be separated by applying a negative potential of -0.5V.

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