An asymmetric two-dimensional metal-organic framework film and its preparation and separation applications

Abstract

The application discloses an asymmetric two-dimensional metal organic framework film and a preparation method and separation application thereof. By controllable adjustment of an organic ligand, different functional groups are introduced to improve the separation performance of hydrogen / carbon dioxide and ethanol dehydration. The preparation method comprises the following steps: synthesizing precursor nanosheets by a solvothermal method, obtaining a two-dimensional nanosheet dispersion liquid by delamination, assembling the nanosheets on the surface of a porous carrier, and microwave-assisted secondary growth to form a film. The two-dimensional metal organic framework micro-area asymmetric film prepared by the functional group gradient regulation strategy has excellent gas screening and liquid phase separation performance, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of membrane separation and relates to an asymmetric two-dimensional metal organic framework membrane and its preparation and separation application. Background Art

[0002] Separation is an indispensable process in modern chemical industry. Membrane separation technology, with its advantages of low energy consumption, continuous operation, and environmental friendliness, has been widely used in gas separation, water resource treatment, catalysis, sensing, and other fields. The rapid development and widespread application of membrane separation technology has important practical implications for my country's achievement of its "carbon peak and carbon neutrality" goals. Membrane materials are the foundation and core of membrane separation technology. Metal-organic frameworks (MOFs) are porous crystalline structures composed of metal ions or metal clusters and organic ligands connected by coordination bonds. They possess advantages such as a rich skeleton structure, ultra-high relative surface area and porosity, and a rich pore structure and surface chemical properties. The high separation performance of MOFs after membrane formation often depends on the precise microstructure of the membrane. However, existing strategies for regulating membrane structure often face the challenge of achieving fine-grained control of the structure of a specific region, and the introduction of new phases can lead to poor interfacial compatibility. Therefore, to address the problem of microscale phase interfaces in most membrane structures currently studied, the preparation of high-quality two-dimensional MOF microdomain asymmetric membranes, leveraging their excellent selectivity and permeability, is expected to achieve precise and efficient separations for large-scale applications. Summary of the Invention

[0003] The purpose of the present invention is to provide an asymmetric two-dimensional metal-organic framework membrane and its preparation method and application. It is a method for controllably modifying the chemical properties of the membrane material by controllably adjusting the organic ligands and introducing different functional groups. The obtained ultra-thin micro-area asymmetric membrane material is subjected to gas separation and liquid phase separation performance tests to improve its hydrogen / carbon dioxide and ethanol dehydration separation performance.

[0004] A method for preparing an asymmetric two-dimensional metal-organic framework membrane comprises solvothermal synthesis of precursor metal-organic framework nanosheets, ultrasonic dispersion to obtain a nanosheet suspension, and subsequent assembly onto a porous support. Microwave-assisted secondary growth is then performed to obtain a two-dimensional metal-organic framework microdomain asymmetric membrane. The specific preparation process includes the following steps:

[0005] (1) Solvothermal synthesis of sheet precursor materials: trivalent aluminum salt is selected as the metal source, and trivalent aluminum salt, organic ligand, hexadecyltrimethylammonium bromide, tetramethylammonium hydroxide and water are mixed and reacted at 30-200°C for 0.1-48h to obtain a two-dimensional sheet metal organic framework precursor;

[0006] Among them, the molar ratio of each raw material is Al 3+: Organic ligand: hexadecyltrimethylammonium bromide: tetramethylammonium hydroxide: water = 0.01-5: 0.01-5: 0.01-5: 1-10: 1-10000;

[0007] (2) Preparation of a two-dimensional layered nanosheet dispersion: mixing the two-dimensional sheet-like metal organic framework precursor obtained in step (1) with a solvent, exfoliating the mixture to obtain a two-dimensional nanosheet dispersion, and allowing the mixture to settle for 1-300 days;

[0008] The peeling method includes grinding, ultrasonic dispersion, ball milling, freeze-thaw and other methods; the mass concentration of the two-dimensional nanosheets in the obtained nanosheet dispersion is 0.001-1%;

[0009] (3) 2D nanosheet assembly: assembling the nanosheet dispersion obtained in step (2) onto the surface of a porous support at room temperature and drying the dispersion to obtain a porous support carrying a 2D metal organic framework nanosheet seed layer;

[0010] When preparing a porous carrier supporting a two-dimensional metal organic framework nanosheet seed layer, the assembly amount of the two-dimensional layered nanosheet dispersion is 1 to 100 mL / cm 2 carrier;

[0011] (4) Preparation of a two-dimensional metal organic framework microdomain asymmetric membrane: placing the porous carrier (two-dimensional metal organic framework nanosheet seed layer) loaded with seeds obtained in step (3) in a secondary growth solution, reacting the solution at a certain temperature for an appropriate time by microwaves, and then washing and drying the solution to obtain a two-dimensional metal organic framework microdomain asymmetric membrane;

[0012] The secondary growth solution is a mixed solution of trivalent aluminum salt, organic ligand, tetramethylammonium hydroxide and water, and the molar ratio of each raw material is: Al 3+ :Organic ligand:tetramethylammonium hydroxide:water=0.01~10:0.01~10:1~10:1~5000;;

[0013] In step (1) and step (4), the types of organic ligands are different.

[0014] Based on the above technical solution, preferably, in step (1) and step (4), the trivalent aluminum salt is at least one of aluminum sulfate 18hydrate, aluminum chloride hexahydrate, and aluminum nitrate nonahydrate; and the organic ligand is at least one of isophthalic acid, 5-aminoisophthalic acid, 5-bromoisophthalic acid, 5-hydroxyisophthalic acid, and 5-nitroisophthalic acid, or a mixture thereof.

[0015] Based on the above technical solution, preferably, in step (1), the reaction temperature is 60-150 degrees Celsius and the reaction time is 10-36 hours.

[0016] Based on the above technical solution, preferably, in step (1), the raw material ratio is Al 3+ : Organic ligand: hexadecyltrimethylammonium bromide: tetramethylammonium hydroxide: water = 1.5-3.5: 1.5-3.5: 0.5-1: 1-5: 1000-1500.

[0017] Based on the above technical solution, preferably, in step (2), the solvent includes an organic solvent (the organic solvent is one or more mixtures of methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide) and one or more mixtures of water. Based on the above technical solution, preferably, in step (2), the ultrasonic dispersion conditions are ultrasonic 0.1-4h, and the power is 200-500W.

[0018] Based on the above technical solution, preferably, in step (2), the static sedimentation is more than 7 days and less than 300 days.

[0019] Based on the above technical solution, preferably, in step (2), the static sedimentation is more than 14 days and less than 100 days.

[0020] Based on the above technical solution, preferably, in step (3), the porous carrier (base membrane) is at least one of porous alumina, anodized aluminum oxide, silicon nitride, polytetrafluoroethylene, polyvinylidene fluoride, polyethersulfone, polyacrylonitrile, and stainless steel, preferably one of α-Al2O3 carrier, γ-Al2O3 carrier, stainless steel carrier, and polytetrafluoroethylene; the pore size of the porous carrier is 5nm-10μm, preferably 5nm~1μm.

[0021] Based on the above technical solution, preferably, in step (3), the porous carrier is in the shape of a sheet structure, a fiber structure or a tubular structure.

[0022] Based on the above technical solution, preferably, in step (3), the drying conditions are: drying temperature 30-120° C., and drying time 1-24 h.

[0023] Based on the above technical solution, preferably, in step (3), the nanosheet assembly method includes at least one of filtration, hot drop coating, spin coating, and dip-pulling.

[0024] The filtration is a vacuum filtration method, and the vacuum assembly is performed at room temperature of 0 to -0.1 MPa; the hot drop coating method is a hot drop assembly at 100-150°C; and the amount of the nanosheet dispersion used is 1-15 mL per unit area of ​​the carrier.

[0025] Based on the above technical solution, preferably, in step (4), the molar ratio of the raw materials of the secondary growth solution is: Al 3+: Organic ligand: tetramethylammonium hydroxide: water = 1-3: 1-3: 1-5: 1000-1500.

[0026] Based on the above technical solution, preferably, in step (4), the heating rate is 0.5-20°C / min, preferably 1-15°C / min; the power is 1-900 watts, preferably 200-400 watts; the reaction temperature is 30-120°C, preferably 80-120°C; and the reaction time is 1-240 min, preferably 15-180 min.

[0027] Based on the above technical solution, preferably, in step (4), the solvent used for rinsing is at least one of water, methanol, ethanol, and acetone, the drying temperature is 30-120° C., and the drying time is 1-24 h.

[0028] The present invention also relates to an asymmetric two-dimensional metal organic framework film prepared by the method described above.

[0029] The present invention also relates to the application of the asymmetric two-dimensional metal organic framework membrane described above in gas separation and liquid separation, especially hydrogen / carbon dioxide separation and ethanol dehydration separation.

[0030] Beneficial effects: The present invention first synthesizes a sheet-like precursor by a solvent thermal method, then peels off the layers to obtain a two-dimensional nanosheet dispersion, then orderly assembles it on the surface of a porous carrier, and finally obtains a two-dimensional metal organic framework micro-domain asymmetric membrane by microwave-assisted secondary growth. By selecting organic ligands, functional groups with different chemical properties are introduced into the skeleton to gradient-regulate the chemical properties of the membrane material for controllable modification, thereby achieving optimization of the performance of the two-dimensional ultra-thin film. The two-dimensional metal organic framework micro-domain asymmetric membrane prepared by the functional group gradient control strategy of the present invention has excellent gas screening and liquid phase separation performance, and has good application prospects in the fields of gas separation and liquid phase separation, especially the separation of hydrogen / carbon dioxide and ethanol dehydration. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is attached Figure 7 The widths are:

[0032] Figure 1 This is the X-ray diffraction pattern of the CAU-10-H flake precursor material synthesized in Example 1;

[0033] Figure 2 This is a scanning electron microscope photograph of the CAU-10-H flake precursor material synthesized in Example 1;

[0034] Figure 3 This is a scanning electron microscope photograph of the CAU-10-H nanosheet dispersion material synthesized in Example 2;

[0035] Figure 4This is a scanning electron micrograph of the ordered assembly material of CAU-10-H nanosheets synthesized in Example 3;

[0036] Figure 5 This is the X-ray diffraction pattern of the CAU-10-H pure phase membrane material synthesized in Example 4;

[0037] Figure 6 This is a scanning electron microscope photograph of the CAU-10-H pure phase membrane material synthesized in Example 4;

[0038] Figure 7 This is a scanning electron microscope photograph of the CAU-10-H / OH micro-domain asymmetric membrane material synthesized in Example 5. DETAILED DESCRIPTION

[0039] The present invention will be further described in the following examples, but are not intended to limit the present invention.

[0040] Example 1 Preparation of CAU-10-H sheet precursor

[0041] Dissolve 1.1 g of aluminum nitrate nonahydrate and 0.8 g of hexadecyltrimethylammonium bromide in 15 ml of pure water to obtain Mixture 1. Dissolve 0.4 g of isophthalic acid in 4 ml of tetramethylammonium hydroxide and 10 ml of pure water, stir for 5 minutes, and preheat. This mixture is then mixed with Mixture 1 and placed in a 100 ml reactor. The mixture is then placed in an oven at 100°C for 20 hours, removed from the oven, and cooled to room temperature. The resulting CAU-10 flake precursor is then washed repeatedly with water and ethanol and dried in an oven at 100°C overnight.

[0042] X-ray diffraction confirmed that the product had a CAU-10 structure (e.g. Figure 1 ), proving that the flake precursor material was successfully synthesized. Scanning electron microscope images show that the product has a clear flake morphology (such as Figure 2 ).

[0043] Example 2 Preparation of CAU-10-H Nanosheet Dispersion

[0044] 50 mg of the CAU-10 precursor material prepared in Example 1 was dispersed in 500 ml of ethanol, and subjected to ultrasonic peeling at a power of 300 watts for 30 minutes, and allowed to stand for more than 14 days for use.

[0045] Scanning electron microscope images show that the product has a clear flake morphology (such as Figure 3 ).

[0046] Example 3 Assembly of CAU-10-H nanosheets

[0047] A porous α-Al2O3 support (18 mm in diameter) with a pore size of 70 nm was placed in a suction filtration device, and 10 ml of the nanosheet dispersion in Example 2 was taken and assembled in an orderly manner under a pressure of -0.08 MPa, and then placed in a 100°C oven to dry overnight.

[0048] Scanning electron microscope images show the successful assembly of nanosheets (e.g. Figure 4 ).

[0049] Example 4 Preparation of CAU-10-H Pure Phase Membrane

[0050] 0.75 g of aluminum nitrate nonahydrate and 0.25 g of isophthalic acid were added to a mixture of 3 ml of tetramethylammonium hydroxide and 20 ml of water, stirred thoroughly, and then placed into the porous alumina supported by nanosheets from Example 3. The reaction was carried out in a microwave reactor at 100°C (heating rate of 15°C / min to 100°C) for 120 minutes at a power of 400 watts. After cooling to room temperature, the membrane surface was rinsed with water and then methanol, and then dried in a 100°C oven overnight.

[0051] X-ray diffraction confirmed the formation of film structure and its orientation (such as Figure 5 Scanning electron microscopy images show that the product has a dense and continuous morphology (such as Figure 6 ).

[0052] Example 5 Preparation of CAU-10-H / OH Microdomain Asymmetric Membrane

[0053] The isophthalic acid in Example 4 was replaced with an equal molar amount of 5-hydroxyisophthalic acid. The remaining reaction steps were identical. Specifically, aluminum nitrate nonahydrate and 5-hydroxyisophthalic acid were added to a mixture of tetramethylammonium hydroxide and water, stirred evenly, and then the nanosheet-supported porous alumina from Example 3 was added. The reaction was then carried out in a microwave reactor at 100°C (heating to 100°C at a rate of 15°C / min) for 120 minutes at a power of 400 watts. After cooling to room temperature, the membrane surface was rinsed with a mixture of methanol and water and then dried overnight in a 100°C oven.

[0054] Scanning electron microscope images show that the product has a dense and continuous morphology (such as Figure 7 ).

[0055] Example 6 Preparation of CAU-10-H / NH2 Microdomain Asymmetric Membrane

[0056] The isophthalic acid in Example 4 was replaced with an equal mole of 5-aminoisophthalic acid, and the remaining reaction steps were the same.

[0057] Example 7 Preparation of CAU-10-H / Br Micro-Asymmetric Membrane

[0058] The isophthalic acid in Example 4 was replaced with an equal mole of 5-bromoisophthalic acid, and the remaining reaction steps were the same.

[0059] Example 8 Hydrogen / Carbon Dioxide Gas Separation Test of Two-Dimensional Metal-Organic Framework Membrane

[0060] The two membranes prepared in Examples 4-5 were encapsulated in a Wicke-Kallenbach membrane module and tested for separation of a hydrogen / carbon dioxide mixture at room temperature and ΔP = 0 MPa, with argon as the purge gas. (Under standard conditions, 1 GPU = 1 × 10 -6 cm 3 / cm 2 ·s·cmHg). Three membranes of each type were prepared for performance testing in Examples 4-5. The data in the table show that, compared with pure phase membranes, the gas separation performance of the microdomain asymmetric membranes obtained by secondary growth with the introduction of hydroxyl-containing ligands can be improved by chemically modifying the membrane material from the presence to the absence of hydroxyl groups within the microdomains.

[0061] serial number <![CDATA[H2 / CO2 separation coefficient]]> <![CDATA[H2 Permeation (GPU)]]> <![CDATA[CO2 Permeability (GPU)]]> CAU-10-H pure phase membrane 1 98 720 7.35 CAU-10-H pure phase film 2 112 736 6.57 CAU-10-H pure phase membrane 3 106 816 7.70 CAU-10-H / OH micro-domain asymmetric membrane 1 248 642 2.59 CAU-10-H / OH micro-domain asymmetric membrane 2 209 690 3.30 CAU-10-H / OH micro-domain asymmetric membrane 3 256 603 2.36

[0062] Example 9 Alcohol-water liquid phase separation test of two-dimensional metal organic framework membrane

[0063] The separation performance of the two membranes prepared in Examples 4-5 for ethanol dehydration was evaluated during pervaporation. Three membranes of each type were prepared for performance testing. Testing was performed at 65°C using a 90% ethanol-water solution. The measured performance is shown in the following table:

[0064]

[0065]

Claims

1. A method for preparing an asymmetric two-dimensional metal-organic framework membrane, characterized in that: The steps include: (1) mixing trivalent aluminum salt, organic ligand, hexadecyltrimethylammonium bromide, tetramethylammonium hydroxide and water, and reacting at 30-200° C. for 0.1-48 hours to obtain a two-dimensional sheet-like metal organic framework precursor; Among them, the molar ratio of each raw material is Al 3+ : Organic ligand: hexadecyltrimethylammonium bromide: tetramethylammonium hydroxide: water = 0.01-5: 0.01-5: 0.01-5: 1-10: 1-10000; (2) mixing the precursor of the two-dimensional sheet-like metal organic framework obtained in step (1) with a solvent, peeling the layers to obtain a nanosheet dispersion, and allowing it to settle for 1-300 days; Wherein, the mass concentration of the two-dimensional nanosheets in the nanosheet dispersion is 0.001-1%; (3) assembling the nanosheet dispersion obtained in step (2) onto the surface of a porous carrier at room temperature and drying the nanosheet dispersion to obtain a porous carrier carrying a two-dimensional metal organic framework nanosheet seed layer; When preparing a porous carrier supporting a two-dimensional metal organic framework nanosheet seed layer, the assembly amount of the two-dimensional layered nanosheet dispersion is 1 to 100 mL / cm 2 carrier; (4) placing the porous carrier carrying the two-dimensional metal organic framework nanosheet seed layer obtained in step (3) in a secondary growth solution, reacting it at a certain temperature for a certain time by microwave, and then washing and drying to obtain a two-dimensional metal organic framework micro-domain asymmetric membrane; The secondary growth solution is a mixed solution of trivalent aluminum salt, organic ligand, tetramethylammonium hydroxide and water, and the molar ratio of each raw material is: Al 3+ : Organic ligand: tetramethylammonium hydroxide: water = 0.01-10: 0.01-10: 1-10: 1-5000; In step (1) and step (4), the types of organic ligands are different, and the organic ligand is at least one of unsubstituted isophthalic acid, 5-aminoisophthalic acid, 5-bromoisophthalic acid, 5-hydroxyisophthalic acid, 5-nitroisophthalic acid, 5-methylisophthalic acid, 5-methoxyisophthalic acid, and 5-fluoroisophthalic acid; In step (2), the solvent includes one or a mixture of methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, and water.

2. The preparation method according to claim 1, characterized in that In step (1) and step (4), the trivalent aluminum salt is at least one of aluminum sulfate 18hydrate, aluminum chloride hexahydrate, and aluminum nitrate nonahydrate; and the tetramethylammonium hydroxide is a 25% tetramethylammonium hydroxide aqueous solution.

3. The preparation method according to claim 1, characterized in that In step (2), the peeling method includes at least one of grinding, ultrasonic dispersion, ball milling, and freeze-thawing.

4. The preparation method according to claim 1, characterized in that In step (3), the porous carrier used is at least one of porous alumina, anodized aluminum oxide, silicon nitride, polytetrafluoroethylene, polyvinylidene fluoride, polyethersulfone, polyacrylonitrile, and stainless steel, with a pore size of 5nm-10μm; the porous carrier is in the shape of a sheet, fiber, or tubular structure.

5. The preparation method according to claim 1, characterized in that In step (3), the drying temperature is 30-120° C. and the drying time is 1-24 h.

6. The preparation method according to claim 1, characterized in that In step (3), the nanosheet assembly method includes at least one of filtration, hot drop coating, spin coating, and dip-pulling.

7. The preparation method according to claim 1, characterized in that In step (4), the microwave reaction conditions are: heating rate of 0.5-20°C / min, power of 1-900 watts, reaction temperature of 60-150°C, and reaction time of 1-240 min.

8. The preparation method according to claim 1, characterized in that In step (4), the solvent used for rinsing is at least one of water, methanol, ethanol, and acetone, the drying temperature is 30-120° C., and the drying time is 1-24 hours.

9. An asymmetric two-dimensional metal organic framework membrane prepared by the method according to any one of claims 1 to 8.

10. Use of the asymmetric two-dimensional metal organic framework membrane according to claim 9 in gas separation and liquid separation.

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