Gradient frame membrane and separation application thereof

Abstract

The invention discloses a gradient frame membrane and separation application thereof. An integrated gradient membrane material is constructed in a mode of functional group sharing, metal node sharing or skeleton interpenetration, and target molecule recognition sites are designed by utilizing the advantage that a framework material is easy to modify, so that the separation performance is remarkably improved. The gradient film structure comprises a metal organic-metal organic framework gradient film, a metal organic-covalent organic framework gradient film and a covalent organic-metal organic framework gradient film. The invention introduces a new structure of a metal organic framework-covalent organic framework gradient film and a construction strategy thereof in detail. The preparation method comprises the steps of preparing a bottom layer film structure from bottom to top, then preparing a top layer film structure on the bottom layer film structure, performing post-modification and the like. By designing a specific asymmetric porous structure and adsorption sites, the membrane shows excellent ethylene / ethane, propylene / propane, ion screening and organic matter dehydration separation performance under the dual action of adsorption selection and shape-selective screening.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation, specifically relating to a gradient framework membrane and its separation applications. Background Technology

[0002] Separation and purification play a crucial role in modern chemical industrial production. However, traditional separation methods often suffer from high equipment investment, complex processes, and high energy consumption. Membrane separation technology, as a green and environmentally friendly new separation technology, boasts advantages such as low energy consumption, simple operation, and small footprint, making it an important approach to solving my country's energy and environmental problems and promoting green and low-carbon industrial development. It has wide applications in gas separation (low-carbon olefin and alkane separation, hydrogen purification, flue gas capture, natural gas purification, and isomer separation), ion sieving, and organic matter dehydration. Currently, most industrially available membrane materials are polymer-based, but their gas permeation flux and selectivity are very low, making it difficult to overcome the "trade-off" limitation. Therefore, developing new high-performance separation membrane materials is of great significance.

[0003] Porous crystalline framework materials, represented by metal-organic frameworks and covalent organic frameworks, possess advantages such as abundant skeletal structures, regular pore structures, easily modifiable surface chemistry, and high specific surface area and porosity, and are considered among the most promising materials in advanced separation fields. The separation performance of framework membranes typically depends on the precise microstructure of the membrane; however, current technology struggles to achieve integrated design and synergistic effects to promote separation. Furthermore, the challenge of large-scale fabrication of framework membranes also limits their industrial application. Summary of the Invention

[0004] The purpose of this invention is to provide a gradient framework membrane and its separation applications. It constructs an integrated gradient membrane structure by sharing functional groups, sharing metal nodes, or interweaving the framework. It utilizes the advantage of easy modification of the framework structure to design target molecule recognition sites, and conducts gas and liquid separation tests on the obtained ultrathin film to improve its separation performance such as ethylene / ethane, propylene / propane, ion sieving, and organic matter dehydration.

[0005] The gradient framework membrane structure of the present invention comprises two parts: a bottom framework membrane and a top framework membrane. The bottom framework membrane is a metal-organic framework membrane or a covalent organic framework membrane. The top framework membrane is a metal-organic framework membrane or a covalent organic framework membrane. Depending on the type of framework material selected, the gradient framework membrane includes three structures: metal-organic framework-metal-organic framework gradient membrane, metal-organic framework-covalent organic framework gradient membrane, and covalent organic framework-metal-organic framework gradient membrane.

[0006] Based on the above technical solutions, preferably, the metal in the metal-organic framework material is selected from Zn, Cu, Co, Fe, Cr, Mn, Ti, Zr, Cd, Mg, Al, Ni, Ag, Mo, W, Ca, Y, or any combination thereof; the organic ligand of the metal-organic framework material is selected from formic acid, squaric acid, imidazole, benzimidazole, 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, 2,5-di(4'-carboxyphenyl)aniline, terephthalic acid, isophthalic acid, etc. Acids, gallic acid, fumaric acid, triazoles and their derivatives, pyromellitic acid, pyromellitic tetracarboxylic acid, 2,2'-bipyridine-3,3'-dicarboxylic acid, 2-methylimidazole, 2-ethylimidazole, 2,5-dihydroxyterephthalic acid, phthalic acid, 2-methylterephthalic acid, 2-methoxyterephthalic acid, 2-hydroxyterephthalic acid, 5-hydroxyisophthalic acid, 5-bromoisophthalic acid, bis(3,5-dicarboxyphenyl)azo, monosodium 2-sulfonic acid terephthalate, bipyridine, aminopyridine, bromopyridine, methylpyridine, iodopyridine, chloropyridine, nitropyridine, hydroxypyridine, or any combination thereof. Furthermore, the metal-organic framework materials include unfunctionalized metal-organic framework materials and functionalized metal-organic framework materials. Unfunctionalized metal-organic framework materials include UiO-66, UiO-67, MIL-53, MIL-101, MIL-125, ZIFs, CAU-1, CAU-10, UTSA-280, M-gallete (M = Mg, Co, Ni, Cu, or Fe), CuBDC, MOF-74, MIL-88, MOF-303, MOF-808, HKUST-1, ZnBDC, ZnBTC, MIL-68, Ni(BTC)(4,4'- The functional groups of the functionalized metal-organic framework material are amino, carboxyl, hydroxyl, dopamine, etc., and the functionalized metal-organic framework material is preferably UiO-66-NH2, MIL-53-NH2(Al), MIL-88-NH2(Fe), MIL-101-NH2(Cr), MIL-101-SO3H(Cr), MIL-125-NH2, MIL-101-NH2(Fe), MIL-53-NH2(Fe), UiO-66-(COOH)2, UiO-66-OH or any combination thereof.

[0007] Based on the above technical solutions, preferably, the covalent organic framework material monomer is selected from trialdehyde phloroglucinol, 2,5-dihydroxy-terephthalaldehyde, pyromellitic pyrophthalaldehyde, 2-hydroxy-1,3,5-benzenetricaraldehyde, 2,3-dihydroxy-terephthalaldehyde, 2,5-diethoxy-1,4-terephthalaldehyde, 2,5-dipropoxy-1,4-terephthalaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, 5-hydroxy-m-phenylenedialdehyde, p-phenylenediamine, 2-nitro-1,4-phenylenediamine, and 2,5-dibromo-p-phenylenediamine. phenylenediamine, triaminoguanidine hydrochloride, 2,5-diamino-terephthalic acid, 2-methyl-1,4-phenylenediamine, 2-sulfonic-1,4-phenylenediamine, 2-chloro-1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, 2,5-dibromo-1,4-phenylenediamine, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, 5,5'-diamino-2,2'-bipyridine, hydrazine hydrate, ethidium bromide, porphyrin and its derivatives, bipyridine derivatives, or any combination thereof. Furthermore, the covalent organic framework material includes TpPa-1, TpPa-2, TpPa-NO2, TpPa-NH2, TpHz, TpPa-SO3H, TpPa-2SO3H, Tp-Bpy, TpPa-COOH, TGCl, ACOF-1, COF-300, COF-1, COF-5, CTF-1, COF-LZU, TpEBr, TpTTPA, TFP-TTA, and TpBDMe2. Preferably, it is TpPa-1, TpPa-2, TpPa-SO3H, TpPa-2SO3H, Tp-Bpy, or any combination thereof.

[0008] Based on the above technical solutions, preferably, the method for constructing the film includes one or more of the following methods: two-dimensional nanosheet stacking, in-situ growth, interfacial polymerization, secondary growth, vapor deposition, electrophoretic deposition, sol-gel method, etc.; preferably, two-dimensional nanosheet stacking, interfacial polymerization, secondary growth, and in-situ growth are preferred.

[0009] The significantly improved separation performance of the frame gradient membrane described in this invention stems from the site design or functional molecule loading structure of the top membrane structure, achieving high-precision separation through adsorption, size sieving, or shape selection. The sites include amino, hydroxyl, methyl, methoxy, halogen, sulfonic acid, carboxyl, aldehyde, and metal sites, or any combination thereof. The functional molecules include ionic liquids, metal ions, metal clusters, polyelectrolytes, cellulose, metal salt solutions, cyclodextrin, graphene and its derivatives, polydimethylsiloxane, polyamide, and polyimide, or any combination thereof. Preferably, the sites are amino, hydroxyl, sulfonic acid, or metal sites, or any combination thereof; the functional molecules are preferably ionic liquids, metal clusters, or metal salt solutions, or any combination thereof.

[0010] The method for preparing gradient framework membranes of the present invention includes methods for preparing metal-organic framework-covalent organic framework gradient membranes (the construction strategy includes bottom-up preparation of a bottom layer membrane structure, followed by preparation of a top layer membrane structure thereon, and post-modification steps), metal-organic framework-metal-organic framework gradient membranes, and covalent organic framework-metal-organic framework membranes, specifically including the following steps:

[0011] (I) Preparation of the underlying framework membrane

[0012] The underlying framework membrane is a metal-organic framework membrane or a covalent organic framework membrane.

[0013] (1) The underlying metal-organic framework membrane can be prepared by either method one or method two.

[0014] Method 1 includes the following steps:

[0015] (1.1) Synthesis of precursor metal-organic framework powder by solvothermal method: Metal salt 1, organic ligand, regulator and solvent 1 are mixed and reacted at 40-200 degrees Celsius for 1-100 h to obtain metal-organic framework powder material;

[0016] (1.2) Preparation of nanosheet dispersion: The metal-organic framework powder obtained in step (1.1) is mixed and ground with organic ligands, dispersed in solvent 2, sonicated, and centrifuged to remove organic ligands to obtain metal-organic framework nanosheets; then the metal-organic framework nanosheets are dispersed in solvent 2 to obtain metal-organic framework nanosheet dispersion, and allowed to settle for 1-365 days.

[0017] (1.3) Nanosheet assembly: At room temperature, the metal-organic framework nanosheet dispersion obtained in step (1.2) is mixed with aldehyde monomer. After uniform mixing, a nanosheet dispersion grafted with aldehyde monomer is obtained. The nanosheet dispersion grafted with aldehyde monomer is then assembled onto the surface of a porous carrier and dried to obtain a metal-organic framework nanosheet layer modified with free aldehyde group, i.e. a carrier supporting metal-organic framework membrane.

[0018] Method 2, in-situ growth of metal-organic framework membranes: The porous support is immersed in a mixed solution of metal salt 1, organic ligand, regulator and solvent 1, and reacted at 40-200 degrees Celsius for 1-100 hours to obtain a metal-organic framework membrane, i.e. a support carrying a metal-organic framework membrane.

[0019] (2) Preparation of underlying covalent organic framework membrane

[0020] The surface-modified porous support was immersed in a mixed solution of aldehyde monomer and organic solvent 1 and reacted at 40-200 degrees Celsius for 0.1-100 h to obtain an aldehyde-modified porous support. Then, a mixed solution containing aldehyde monomer, diamine monomer, organic solvent and catalyst was prepared, and the porous support was immersed in the mixed solution containing aldehyde monomer, diamine monomer, organic solvent 1 and catalyst and reacted at 40-200 degrees Celsius for 0.1-100 h. After the reaction was completed, the unreacted monomer on the membrane surface was washed off with solvent 1 and dried to obtain a support supporting a covalent organic framework membrane.

[0021] (II) Preparation of Top Framework Membrane

[0022] The top-layer framework membrane is a top-layer metal-organic framework membrane or a top-layer covalent organic framework membrane;

[0023] (1) Prepare a top metal-organic framework membrane based on the bottom metal-organic framework membrane of step (I) to obtain a metal-organic framework-metal-organic framework gradient membrane, or prepare a top metal-organic framework membrane based on the bottom covalent organic framework membrane of step (I) to obtain a covalent organic framework-metal-organic framework gradient membrane.

[0024] The carrier carrying the metal-organic framework membrane or the carrier carrying the covalent organic framework membrane obtained in step (I) is placed in a reaction solution containing metal salt 1, organic ligand, regulator and solvent 1, and reacted at 40-200 degrees Celsius for 1-100 h to obtain a gradient framework membrane, namely a metal-organic framework-metal-organic framework gradient membrane or a covalent organic framework-metal-organic framework gradient membrane.

[0025] (2) Based on the underlying metal-organic framework membrane of step (1), prepare a covalent organic framework membrane and obtain a metal-organic framework-covalent organic framework gradient membrane.

[0026] The modified porous support (the support carrying the metal-organic framework membrane, including the one obtained by method one or method two) obtained in step (1) is placed in an interfacial polymerization solution containing organic monomer, catalyst, water and organic solvent 2, and reacted at room temperature for 1-200 h. Then the solvent is evaporated, and the membrane is washed with organic solvent 3 and dried to obtain a gradient framework membrane, namely a metal-organic framework-covalent organic framework gradient membrane.

[0027] Based on the above technical solutions, preferably, it also includes: (iii) metal modification of gradient framework membrane: coating the metal salt 2 solution onto the gradient framework membrane material obtained in step (ii), so that the gradient framework membrane material and the metal salt 2 solution are composited, and then dried at room temperature to obtain a metal-modified gradient framework membrane.

[0028] Based on the above technical solution, preferably, in step (1) (1.1), the metal salt 1 used is at least one of anhydrous zirconium chloride, zirconium oxychloride octahydrate, ferric chloride hexahydrate, chromium nitrate nonahydrate, aluminum nitrate nonahydrate, copper nitrate trihydrate, and zinc nitrate hexahydrate; the organic ligand is one or a mixture of several of 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, and 2,5-bis(4'-carboxyphenyl)aniline.

[0029] Based on the above technical solutions, preferably, in step (1.1) of step (1), the solvent 1 used includes one or a mixture of several of the following: water, methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0030] Based on the above technical solutions, preferably, in step (1.1) of step (I), the molar ratio of each raw material is metal:organic ligand:modifier:solvent = 0.01~5:0.01~5:0~1000:0.01~10000, more preferably metal:organic ligand:modifier:solvent = 0.1~2.5:0.1~2.5:10~500:1000~5000.

[0031] Based on the above technical solutions, preferably, in step (1.1) of step (1), the reaction temperature is 50-180 degrees Celsius, more preferably 60-150 degrees Celsius, and the reaction time is 2-72 hours, more preferably 4-48 hours.

[0032] Based on the above technical solution, preferably, in step (1) (1.2), the mass ratio of the metal-organic framework powder to the organic ligand is 0.01-1:0.01-1, more preferably 0.01-1:0.1-0.5; the organic ligand is one or a mixture of several of 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, and 2,5-bis(4'-carboxyphenyl)aniline.

[0033] Based on the above technical solutions, preferably, in step (1) (1.2), the mass ratio of the metal-organic framework to the organic monomer is 1:0-10, more preferably 1:0-0.5, and even more preferably 1:0-0.3.

[0034] Based on the above technical solutions, preferably, in step (1) (1.2), the grinding method includes mortar grinding and ball milling.

[0035] Based on the above technical solutions, preferably, in step (1) (1.2), the grinding time in the mortar is 1-60 minutes, more preferably 5-30 minutes.

[0036] Based on the above technical solutions, preferably, in step (1) (1.2), the ball milling time is 1-120 minutes and the rotation speed is 40-100 rpm.

[0037] Based on the above technical solutions, preferably, in step (1) (1.2), the ultrasonic conditions are: power of 1-300W and time of 1-60 minutes; more preferably, power of 200-500W and time of 5-20 minutes.

[0038] Based on the above technical solution, preferably, in step (1) (1.2), the dispersed solvent 2 is one or a mixture of several of the following: water, methanol, ethanol, acetone, tetrahydrofuran, and N,N-dimethylformamide.

[0039] Based on the above technical solution, preferably, in step (1) (1.2), the mass concentration of metal-organic framework nanosheets in the metal-organic framework nanosheet dispersion is 0.0001-10%, more preferably 0.001-1%.

[0040] Based on the above technical solutions, preferably, in step (1) (1.2), the static settling time is more than 7 days and less than 200 days, more preferably 7-100 days.

[0041] Based on the above technical solution, preferably, in step (1) (1.3), the aldehyde monomer is at least one of trialdehyde phloroglucinol, 2,5-dihydroxyterephthalaldehyde, pyromellitic pyrophthalaldehyde, 2-hydroxy-1,3,5-benzenetricaraldehyde, 2,3-dihydroxyterephthalaldehyde, and 2,5-diethoxy-1,4-terephthalaldehyde.

[0042] Based on the above technical solution, preferably, in step (1) (1.3), the mass ratio of metal-organic framework nanosheets to aldehyde monomers in the metal-organic framework nanosheet dispersion is 1:0:~0.01.

[0043] Based on the above technical solutions, preferably, in step (1) (1.3), the method of uniform mixing is ultrasonic dispersion, the ultrasonic power is 1-300W, more preferably 50-150W; the ultrasonic time is 1-60 minutes, more preferably 5-30 minutes.

[0044] Based on the above technical solution, preferably, in step (1.3) of step (I), when preparing the modification layer, the assembly amount of the layered nanosheet dispersion of the grafted aldehyde monomer is 1-100 mL / cm², based on the carrier area per unit area. 2 The carrier is preferably 5–50 mL / cm³. 2 Carrier.

[0045] Based on the above technical solutions, preferably, in step (1) (1.3), the porous carrier (base film) is at least one of porous alumina, anodic alumina, titanium dioxide, silicon nitride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyethersulfone, polyacrylonitrile, nylon, cellulose acetate, polyimide, and stainless steel, preferably one of α-Al2O3 carrier, γ-Al2O3 carrier, polytetrafluoroethylene, polyvinylidene fluoride, and nylon; the pore size of the porous carrier is 5nm-10μm, preferably 5nm-1μm.

[0046] Based on the above technical solutions, preferably, in step (1) (1.3), the porous carrier shape is sheet-like, flat, rolled, fibrous, tubular, etc.

[0047] Based on the above technical solution, preferably, in step (1) (1.3), the drying conditions are: drying temperature 25-80℃, drying time 0.5-18h.

[0048] Based on the above technical solutions, preferably, in step (1) (1.3), the nanosheet assembly method includes at least one of vacuum filtration, hot drop coating, spin coating, dip-coating, scraping coating, and soaking.

[0049] Based on the above technical solutions, preferably, in method two of step (I), the metal salt 1 used is at least one of anhydrous zirconium chloride, zirconium oxychloride octahydrate, ferric chloride hexahydrate, chromium nitrate nonahydrate, aluminum nitrate nonahydrate, copper nitrate trihydrate, and zinc nitrate hexahydrate; the organic ligand is one or a mixture of several of 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, and 2,5-bis(4'-carboxyphenyl)aniline.

[0050] Based on the above technical solutions, preferably, in step (i) of method two, the modifier used includes at least one of formic acid, acetic acid, benzoic acid, hydrochloric acid, and hydrofluoric acid; the solvent 1 used includes one or a mixture of several of water, methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0051] Based on the above technical solutions, preferably, in step (i) of method two, the molar ratio of each raw material in the mixed solution of metal salt 1, organic ligand, regulator and solvent 1 is metal:organic ligand:regulator:solvent = 0.01~5:0.01~5:0~1000:0.01~10000, more preferably metal:organic ligand:regulator:solvent = 0.1~2.5:0.1~2.5:10~500:1000~5000.

[0052] Based on the above technical solutions, preferably, in step (i) of method two, the reaction temperature is 50-180 degrees Celsius, more preferably 60-150 degrees Celsius; the reaction time is 2-72 hours, more preferably 4-48 hours.

[0053] Based on the above technical solutions, preferably, in method two of step (I), the porous carrier (base film) is at least one of porous alumina, anodic alumina, titanium dioxide, silicon nitride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyethersulfone, polyacrylonitrile, nylon, cellulose acetate, polyimide, and stainless steel, preferably one of α-Al2O3 carrier, γ-Al2O3 carrier, polytetrafluoroethylene, polyvinylidene fluoride, and nylon; the pore size of the porous carrier is 5nm-10μm, preferably 5nm-1μm.

[0054] Based on the above technical solutions, preferably, in step (i) of method two, the porous carrier shape is sheet-like, flat-like, rolled, fibrous, tubular, etc.

[0055] Based on the above technical solutions, preferably, in step (i) of method two, the solvent 1 used includes one or a mixture of several of the following: water, methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0056] Based on the above technical solutions, preferably, in step (1) (2), the modification method of the surface functionally modified porous carrier includes carboxyl modification, amino modification, hydroxyl modification, dopamine modification, etc.

[0057] Based on the above technical solutions, preferably, in step (1) (2), the aldehyde monomer includes at least one of trialdehyde phloroglucinol, 2,5-dihydroxyterephthalaldehyde, pyromellitic terephthalaldehyde, 2-hydroxy-1,3,5-benzenetricaraldehyde, 2,3-dihydroxyterephthalaldehyde, 2,5-diethoxy-1,4-terephthalaldehyde, 2,5-dipropoxy-1,4-terephthalaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, and 5-hydroxy-isophthalaldehyde; more preferably, it is at least one of trialdehyde phloroglucinol, 2,5-dihydroxyterephthalaldehyde, and pyromellitic terephthalaldehyde.

[0058] Based on the above technical solutions, preferably, in step (1) (2), the first reaction temperature is 110-160 degrees Celsius and the time is 0.5-3 hours.

[0059] Based on the above technical solution, preferably, in step (1) (2), the organic solvent 1 used for the first time includes one or more of methanol, ethanol, acetone, tetrahydrofuran, mesitylene, and 1,4-dioxane; the concentration of the aldehyde monomer in the mixed solution of the aldehyde monomer and organic solvent 1 is 0.01-0.05 mol / L.

[0060] Based on the above technical solutions, preferably, in step (1) (2), the molar ratio of each raw material in the mixed solution containing aldehyde monomer, diamine monomer, organic solvent 1 and catalyst is aldehyde monomer: diamine monomer: organic solvent 1: catalyst = 0.001~1: 0.001~1: 0.01~1000: 0.01~1000, more preferably aldehyde monomer: diamine monomer: organic solvent 1: catalyst = 0.01~0.2: 0.01~0.4: 0.1~100: 0.1~100.

[0061] Based on the above technical solutions, preferably, in step (i) (2), the diamine monomer includes at least one of p-phenylenediamine, 2-nitro-1,4-phenylenediamine, 2,5-dibromo-p-phenylenediamine, 2,5-diamino-p-phenylenedisulfonic acid, 2-methyl-1,4-phenylenediamine, 2-sulfonic acid-1,4-phenylenediamine, 2-chloro-1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, 2,5-dibromo-1,4-phenylenediamine, hydrazine hydrate, and ethidium bromide; more preferably, it is at least one of ethidium bromide, 2-methyl-1,4-phenylenediamine, 2-sulfonic acid-1,4-phenylenediamine, and 2-chloro-1,4-phenylenediamine.

[0062] Based on the above technical solutions, preferably, in step (1) (2), the organic solvent 1 used for the second time includes one or more of methanol, ethanol, acetone, tetrahydrofuran, mesitylene, and 1,4-dioxane; the catalyst includes at least one of p-toluenesulfonic acid, acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, and formic acid, more preferably at least one of p-toluenesulfonic acid, acetic acid, and trifluoroacetic acid.

[0063] Based on the above technical solutions, preferably, in step (1) (2), the second reaction temperature is 110-160 degrees Celsius and the time is 60-80 hours.

[0064] Based on the above technical solutions, preferably, in step (ii) (1), the molar ratio of each raw material in the reaction solution is preferably metal:organic ligand:modifier:solvent 1 = 0.01~5:0.01~5:0~1000:0.01~10000, more preferably metal:organic ligand:modifier:solvent 1 = 0.1~2.5:0.1~2.5:10~500:1000~4000.

[0065] Based on the above technical solutions, preferably, in step (ii) (1), the metal salt 1 includes at least one of anhydrous zirconium chloride, zirconium oxychloride octahydrate, ferric chloride hexahydrate, chromium nitrate nonahydrate, aluminum nitrate nonahydrate, copper nitrate trihydrate, and zinc nitrate hexahydrate; the organic ligand is one or a mixture of several of 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, 2,5-bis(4'-carboxyphenyl)aniline, and monosodium terephthalate sulfonate.

[0066] Based on the above technical solutions, preferably, in step (ii) (1), the modifier used includes at least one of formic acid, acetic acid, benzoic acid, hydrochloric acid, and hydrofluoric acid; the solvent 1 used includes one or a mixture of several of water, methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0067] Based on the above technical solutions, preferably, in step (ii) (1), the reaction temperature is 40-200 degrees Celsius, more preferably 90-180 degrees Celsius, and the reaction time is 2-72 hours, more preferably 6-60 hours.

[0068] Based on the above technical solutions, preferably, in step (ii) (2), the organic monomer is at least one of p-phenylenediamine, 2-nitro-1,4-phenylenediamine, 2,5-dibromo-p-phenylenediamine, triaminoguanidine hydrochloride, 2,5-diamino-p-phenylenedisulfonic acid, 2-methyl-1,4-phenylenediamine, and 2-sulfonic acid-1,4-phenylenediamine, more preferably at least one of 2,5-diamino-p-phenylenedisulfonic acid, 2-methyl-1,4-phenylenediamine, and 2-sulfonic acid-1,4-phenylenediamine; the catalyst is at least one of p-toluenesulfonic acid, acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, and formic acid, more preferably at least one of p-toluenesulfonic acid, acetic acid, and trifluoroacetic acid; the organic solvent 2 is one or a mixture of acetonitrile, methanol, ethanol, octanoic acid, and N,N-dimethylformamide; the rinsing organic solvent 3 is one or a mixture of methanol, ethanol, acetone, tetrahydrofuran, mesitylene, and 1,4-dioxane.

[0069] Based on the above technical solutions, preferably, in step (ii) (2), the molar ratio of each raw material in the interfacial polymerization solution is organic monomer: catalyst: water: organic solvent 2 = 0.01~5: 0.01~5: 0.01~10000: 0.01~10000, more preferably organic monomer: catalyst: water: organic solvent = 0.01~0.2: 0.01~0.4: 0.1~100: 0.1~100.

[0070] Based on the above technical solutions, preferably, in step (ii) (2), the reaction time is 8-72h, more preferably 24-72h.

[0071] Based on the above technical solutions, preferably, in step (ii) (2), the solvent is evaporated at 60-150℃ for 1-48 hours after the reaction.

[0072] Based on the above technical solutions, preferably, in step (ii) (2), the drying temperature is 60-120 degrees Celsius and the time is 4-18 hours.

[0073] Based on the above technical solutions, preferably, in step (iii), the metal salt 2 in the metal salt 2 solution is at least one of silver nitrate, silver tetrafluoroborate, silver trifluoromethanesulfonate, cuprous chloride, cuprous bromide, cuprous acetate, magnesium nitrate, nickel nitrate, and ferric nitrate; the solvent in the metal salt 2 solution is one or a mixture of several of water, methanol, ethanol, acetone, and tetrahydrofuran.

[0074] Based on the above technical solutions, preferably, in step (iii), the coating method includes at least one of spin coating, dip coating, spray coating and scraping coating.

[0075] Based on the above technical solution, preferably, in step (iii), the concentration of the metal salt 2 solution is 0.01-10 mol / L, more preferably 1-5 mol / L; and the amount of metal salt 2 solution used per unit area of ​​gradient frame membrane material is 0-0.4 mL / cm². 2 Gradient framework membrane materials, more preferably 0.0004–0.2 mL / cm², are preferred. 2 Gradient framework membrane materials.

[0076] Based on the above technical solutions, preferably, in step (iii), the drying time is 18-36 hours.

[0077] This invention also relates to the application of the gradient framework membrane described above in gas and liquid separation, particularly ethylene / ethane separation, propylene / propane separation, organic matter dehydration (such as ethanol dehydration, tetrahydrofuran dehydration, ethylene glycol dehydration, ethyl acetate dehydration, isopropanol dehydration, etc.), and ion separation (such as KCl, NaCl, LiCl, CaCl2, and MgCl2 solutions, etc.). By designing specific asymmetric pore structures and adsorption sites, this invention achieves excellent separation performance through the dual effects of adsorption selectivity and pore sieving.

[0078] Beneficial Effects: This invention prepares gradient framework membrane materials with different structures using various methods and applies them to gas and liquid separation. The preparation methods described in this invention are simple and low-cost, and easily scale up the preparation of framework membrane materials. Furthermore, designing chemical sites or confined functional molecules in the gradient membrane structure can greatly improve the membrane's separation performance, solving the problems of poor separation performance of olefins and alkanes and poor long-term operational stability, and has potential application prospects. Attached Figure Description

[0079] This invention appendix Figure 7 The images are:

[0080] Figure 1 The X-ray diffraction pattern of UiO-66-NH2 synthesized in Example 1;

[0081] Figure 2 This is a scanning electron microscope image of UiO-66-NH2 synthesized in Example 1;

[0082] Figure 3 This is a scanning electron microscope image of the UiO-66-NH2 nanosheet dispersion material synthesized in Example 2;

[0083] Figure 4 This is a scanning electron microscope image of the ordered assembly of UiO-66-NH2 nanosheets synthesized in Example 3;

[0084] Figure 5 This is a scanning electron microscope image of the UiO-66-NH2 / TpPa-SO3H@Ag gradient framework membrane synthesized in Example 5;

[0085] Figure 6 Optical photograph of the large-area UiO-66-NH2 / TpPa-SO3H@Ag gradient framework film synthesized in Example 6;

[0086] Figure 7 Stability testing of the UiO-66-NH2 / TpPa-SO3H@Ag gradient framework membrane synthesized in Example 5. Detailed Implementation

[0087] The following embodiments will further illustrate the present invention, but are not intended to limit the invention.

[0088] Example 1: Preparation of UiO-66-NH2

[0089] 0.36 mmol of anhydrous zirconium chloride and 0.36 mmol of 2-aminoterephthalic acid were dissolved in 20 mL of N,N-dimethylformamide, and 2 mL of acetic acid were added. The mixture was sonicated at 100 W for 10 minutes, then transferred to a 100 mL reaction vessel and placed in an oven at 120 °C for 36 hours. After removing the reaction vessel, it was cooled to room temperature. The resulting UiO-66-NH2 was repeatedly washed with N,N-dimethylformamide and methanol, and the product was dried overnight in an oven at 60 °C.

[0090] X-ray diffraction confirmed that the product has a UiO-66-NH2 structure (e.g. Figure 1 This demonstrates the successful synthesis of a three-dimensional framework precursor material. Scanning electron microscopy images show that the product exhibits a distinct polyhedral structure (e.g., Figure 2 ).

[0091] Example 2: Preparation of UiO-66-NH2 nanosheet dispersion

[0092] 100 mg of UiO-66-NH2 powder and 40 mg of 2-aminoterephthalic acid were ground in a mortar for 45 minutes, then dispersed in 60 mL of methanol and sonicated at 100 W for 10 minutes. After removing the organic ligands by repeated centrifugation and washing with methanol, the powder was dispersed in 1000 mL of methanol and allowed to stand for 10 days for later use.

[0093] Scanning electron microscope images show that the product has a distinct sheet-like morphology (e.g. Figure 3 ).

[0094] Example 3 Assembly of UiO-66-NH2 nanosheets

[0095] Take 30 mL of the nanosheet dispersion from Example 2 and add 0.025 mmol of m-trialdehyde pyrogallol. After sonicating at 100 W for 30 minutes, place the α-Al2O3 porous carrier (18 mm in diameter) with a pore size of 70 nm in a vacuum filtration device and assemble it in an orderly manner at -0.05 MPa. Then, dry it overnight in a 60°C oven.

[0096] Scanning electron microscope images show the successful assembly of nanosheets (e.g. Figure 4 ).

[0097] Example 4: Preparation of UiO-66-NH2 / TpPa-SO3H gradient framework membrane

[0098] 10 mg of 2-sulfonic acid-1,4-phenylenediamine and 15 mg of p-toluenesulfonic acid were dissolved in a mixture of 15 mL of water and 15 mL of acetonitrile. The solution was then placed in the porous alumina supporting the nanosheets from Example 3 and reacted at room temperature for 60 hours. After drying at 90°C for 8 hours, the membrane surface was washed with acetone, 1,4-dioxane, methanol and ethanol in sequence to remove unreacted monomers. The membrane was then dried overnight in a 60°C oven.

[0099] Example 5: Preparation of UiO-66-NH2 / TpPa-SO3H@Ag gradient framework membrane

[0100] Prepare a 1 mol / L silver tetrafluoroborate aqueous solution and spin-coat 50 μL onto the gradient film of Example 4 at 3000 rpm, then air-dry at room temperature for 24 hours.

[0101] Scanning electron microscope images show that the product has a dense and continuous morphology (e.g., Figure 5 ).

[0102] Example 6: Large-area preparation of UiO-66-NH2 / TpPa-SO3H@Ag gradient framework membrane

[0103] The preparation method is the same as in Examples 1-5, except that in Example 3, the amount of nanosheet dispersion and meta-trialdehyde pyrogallol is 180 ml and 0.15 mmol respectively, and the carrier is a polyvinylidene fluoride filter membrane with a diameter of 50 mm and a pore size of 50 nm.

[0104] Film optical images such as Figure 6 The polymer carrier has a diameter of 50 mm, and the central orange area is the membrane area.

[0105] Example 7: Preparation of MIL-101-NH2(Cr) / TpPa-SO3H@Ag gradient framework membrane

[0106] The preparation method of MIL-101-NH2(Cr) is as follows: 0.6 g of chromium nitrate nonahydrate, 0.27 g of 2-aminoterephthalic acid, and 0.2 g of sodium hydroxide are dissolved in 10 mL of deionized water. After stirring for 1 hour, the solution is transferred to a 25 mL reaction vessel and placed in an oven at 150°C for 12 hours. After removing the reaction vessel, it is cooled to room temperature. The resulting MIL-101-NH2(Cr) is repeatedly washed with N,N-dimethylformamide and methanol, and the product is dried overnight in an oven at 60°C. Other steps are the same as in Examples 2-5.

[0107] Example 8: Preparation of MIL-53-NH2(Al) / TpPa-SO3H@Ag gradient framework membrane

[0108] The preparation method of MIL-53-NH2(Al) is as follows: 0.8 g of aluminum nitrate nonahydrate and 0.4 g of 2-aminoterephthalic acid are dissolved in 30 mL of N,N-dimethylformamide. After sonication for 10 minutes, the solution is transferred to a 100 mL reaction vessel and placed in an oven at 150°C for 60 hours. After removing the reaction vessel, it is cooled to room temperature. The resulting MIL-53-NH2(Al) is repeatedly washed with N,N-dimethylformamide and methanol, and the product is dried overnight in an oven at 60°C. Other steps are the same as in Examples 2-5.

[0109] Example 9: Metal-Organic Framework-Covalent Organic Framework Gradient Membrane Separation Test for Olefins / Alkanes

[0110] The membranes prepared in Examples 4-8 were encapsulated in Wicke-Kallenbach membrane modules, and equimolar ethylene / ethane and propylene / propane mixed gas separation tests were conducted at room temperature and under conditions of ΔP = 0 MPa, with argon as the purge gas. (1 GPU = 1 × 10⁻⁶ under standard conditions) -6 cm 3 / cm 2 (·s·cmHg). The data in the table show that after confining the functional metal, the membrane's olefin / alkanes separation performance is significantly improved under the dual effects of adsorption and pore shape-selective sieving. Furthermore, the membrane material prepared over a large area still exhibits good separation performance and has promising prospects for industrial application.

[0111]

[0112] in, Figure 7 The stability test of the gradient framework membrane prepared in Example 5 shows that the membrane maintained almost no change in permeability and selectivity during the approximately 80-hour stability test.

[0113] Example 10: Preparation of MIL-101-NH2(Cr)-MIL-101-SO3H(Cr)@Ag gradient framework membrane

[0114] The preparation of MIL-101-NH2(Cr) nanosheets was the same as in Example 7. A porous alumina support modified with MIL-101-NH2(Cr) nanosheet seeds was placed in the following solution: 12.5 mmol of monosodium 2-sulfonate terephthalate and 12.5 mmol of chromium nitrate nonahydrate were dissolved in 50 mL of water and 25 mmol of concentrated hydrochloric acid. After reacting at 180°C for 60 hours, the membrane was removed and repeatedly washed with deionized water and methanol, then dried overnight at 60°C. A 0.8 mol / L silver nitrate aqueous solution was prepared and spin-coated 40 μL onto a gradient membrane at 2000 rpm, then air-dried at room temperature for 24 hours.

[0115] Example 11: Preparation of TpEBr-UiO-66-(COOH)2 gradient framework membrane

[0116] A porous alumina support with a pore size of 70 nm (18 mm in diameter) was immersed in a toluene solution containing 33 μL of (3-aminopropyl)ethoxysilane at 80°C for 24 hours. After rinsing with acetone and drying, it was placed in 10 mL of 1,4-dioxane containing 0.18 mmol of trialdehyde-resorcinol and reacted at 150°C for 1 hour, then dried. 0.18 mmol of trialdehyde-resorcinol and 0.3 mmol of ethidium bromide were dissolved in 7.5 mL of mesitylene, 2.5 mL of 1,4-dioxane, and 1 mL of 1.5 M acetic acid. The alumina support was vertically immersed in the solution and reacted at 120°C for 72 hours, then dried to obtain a TpEBr membrane. The TpEBr membrane was then dissolved in 30 mL of water in a solution of 0.6 mmol of zirconium chloride and 1.3 mmol of pyromellitic acid. After reacting at 100 degrees Celsius for 6 hours, the membrane was removed, rinsed with methanol and dried to obtain a TpEBr-UiO-66-(COOH)2 gradient framework membrane.

[0117] Example 12 Ion separation test of TpEBr-UiO-66-(COOH)2 gradient framework membrane

[0118] The gradient framework membrane from Example 11 was packed into an H-type electrolytic cell. 0.1 mol / L solutions of KCl, NaCl, LiCl, CaCl2, and MgCl2 were used as feed solutions, and a voltage of 1 V was applied. Three parallel experiments were performed for each membrane sample. The performance is as follows:

[0119]

Claims

1. A gradient framework membrane, characterized in that: The gradient framework membrane includes a bottom framework membrane and a top framework membrane. The bottom framework membrane is a metal-organic framework membrane or a covalent organic framework membrane. The top framework membrane is a metal-organic framework membrane or a covalent organic framework membrane. Depending on the type of framework material selected, the gradient framework membrane encompasses three structures: metal-organic framework-metal-organic framework gradient membrane, metal-organic framework-covalent organic framework gradient membrane, and covalent organic framework-metal-organic framework gradient membrane.

2. The gradient framework membrane according to claim 1, characterized in that: The metal in the metal-organic framework material is selected from Zn, Cu, Co, Fe, Cr, Mn, Ti, Zr, Cd, Mg, Al, Ni, Ag, Mo, W, Ca, Y, or any combination thereof; the organic ligand of the metal-organic framework material is selected from formic acid, squaric acid, imidazole, benzimidazole, 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, 2,5-di(4'-carboxyphenyl)aniline, terephthalic acid, isophthalic acid, gallic acid, etc. Fumaric acid, triazole and its derivatives, pyromellitic acid, pyromellitic tetroxide, 2,2'-bipyridine-3,3'-dicarboxylic acid, 2-methylimidazole, 2-ethylimidazole, 2,5-dihydroxyterephthalic acid, phthalic acid, 2-methylterephthalic acid, 2-methoxyterephthalic acid, 2-hydroxyterephthalic acid, 5-hydroxyisophthalic acid, 5-bromoisophthalic acid, bis(3,5-dicarboxyphenyl)azo, monosodium 2-sulfonic acid terephthalate, bipyridine, aminopyridine, bromopyridine, methylpyridine, iodopyridine, chloropyridine, nitropyridine, hydroxypyridine, or any combination thereof; The monomers of the covalent organic framework material are selected from trialdehyde phloroglucinol, 2,5-dihydroxyterephthalaldehyde, pyromellitic pyroxenaldehyde, 2-hydroxy-1,3,5-benzenetrialdehyde, 2,3-dihydroxyterephthalaldehyde, 2,5-diethoxy-1,4-terephthalaldehyde, 2,5-dipropoxy-1,4-terephthalaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, 5-hydroxy-m-phenylenedialdehyde, p-phenylenediamine, 2-nitro-1,4-phenylenediamine, 2,5-dibromo-p-phenylenediamine, triammonium chloride, and other similar monomers. The following are considered as well: methylguanidine hydrochloride, 2,5-diamino-terephthalic acid, 2-methyl-1,4-phenylenediamine, 2-sulfonic-1,4-phenylenediamine, 2-chloro-1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, 2,5-dibromo-1,4-phenylenediamine, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, 5,5'-diamino-2,2'-bipyridine, hydrazine hydrate, ethidium bromide, porphyrin and its derivatives, bipyridine derivatives, or any combination thereof.

3. The gradient framework membrane according to claim 1, characterized in that: The metal-organic framework materials include unfunctionalized metal-organic framework materials and functionalized metal-organic framework materials. Unfunctionalized metal-organic framework materials include UiO-66, UiO-67, MIL-53, MIL-101, MIL-125, ZIFs, CAU-1, CAU-10, UTSA-280, M-gallete (M = Mg, Co, Ni, Cu, or Fe), CuBDC, MOF-74, MIL-88, MOF-303, MOF-808, HKUST-1, ZnBDC, ZnBTC, MIL-68, Ni(BTC)(4) The functional groups of the functionalized metal-organic framework material are amino, carboxyl, hydroxyl, and dopamine, preferably UiO-66-NH2, MIL-53-NH2(Al), MIL-88-NH2(Fe), MIL-101-NH2(Cr), MIL-101-SO3H(Cr), MIL-125-NH2, MIL-101-NH2(Fe), MIL-53-NH2(Fe), UiO-66-(COOH)2, UiO-66-OH or any combination thereof; The covalent organic framework materials include TpPa-1, TpPa-2, TpPa-NO2, TpPa-NH2, TpHz, TpPa-SO3H, TpPa-2SO3H, Tp-Bpy, TpPa-COOH, TGCl, ACOF-1, COF-300, COF-1, COF-5, CTF-1, COF-LZU, TpEBr, TpTTPA, TFP-TTA, and TpBDMe2.

4. The gradient framework membrane according to claim 1, characterized in that: Methods for constructing membranes include one or more of the following: two-dimensional nanosheet stacking, in-situ growth, interfacial polymerization, secondary growth, vapor deposition, electrophoretic deposition, sol-gel method, and precursor-induced transformation method. The improved separation performance of the membrane originates from the sites or functional molecule loading structures of the top membrane structure, achieving separation through adsorption, size sieving, or shape selection. The sites include amino, hydroxyl, methyl, methoxy, halogen, sulfonic acid, carboxyl, aldehyde, metal sites, or any combination thereof. The functional molecules include ionic liquids, metal ions, metal clusters, polyelectrolytes, cellulose, metal salt solutions, cyclodextrin, graphene and its derivatives, polydimethylsiloxane, polyamide, polyimide, or any combination thereof.

5. The gradient framework membrane according to claim 1, characterized in that, The method for preparing the gradient framework membrane includes the following steps: (I) Preparation of the underlying framework membrane (1) The underlying metal-organic framework membrane can be prepared by either method one or method two. Method 1: Includes the following steps: (1.1) Mix metal salt 1, organic ligand, regulator and solvent 1, and react at 40-200 degrees Celsius for 1-100 h to obtain metal-organic framework powder material; (1.2) After mixing and grinding the metal-organic framework powder obtained in step (1.1) with the organic ligand, disperse it in solvent 2, sonicate, centrifuge and wash to remove the organic ligand, and obtain metal-organic framework nanosheets; then disperse the metal-organic framework nanosheets in solvent 2 to obtain metal-organic framework nanosheet dispersion, and let it stand for 1-365 days to settle. (1.3) At room temperature, the metal-organic framework nanosheet dispersion obtained in step (1.2) is mixed with aldehyde monomer. After uniform mixing, a nanosheet dispersion grafted with aldehyde monomer is obtained. The nanosheet dispersion grafted with aldehyde monomer is then assembled onto the surface of a porous carrier and dried to obtain a carrier carrying a metal-organic framework membrane. Method 2: Immerse the porous support in a mixed solution of metal salt 1, organic ligand, regulator and solvent 1, and react at 40-200 degrees Celsius for 1-100 hours to grow a metal-organic framework membrane in situ, thereby obtaining a support carrying a metal-organic framework membrane. (2) Preparation of underlying covalent organic framework membrane The surface-modified porous support was immersed in a mixed solution of aldehyde monomer and organic solvent 1 and reacted at 40-200 degrees Celsius for 0.1-100 h to obtain an aldehyde-modified porous support. Then, the aldehyde-modified porous support was immersed in a mixed solution containing aldehyde monomer, diamine monomer, organic solvent 1 and catalyst and reacted at 40-200 degrees Celsius for 0.1-100 h. After the reaction was completed, the unreacted monomer on the membrane surface was washed off with solvent 1 and dried to obtain a covalent organic framework membrane. (II) Preparation of Top Framework Membrane (1) Preparation of top metal-organic framework membrane The carrier loaded with metal-organic framework membrane or the carrier loaded with covalent organic framework membrane obtained in step (I) is placed in a reaction solution containing metal salt 1, organic ligand, regulator and solvent 1, and reacted at 40-200 degrees Celsius for 1-100 h to obtain a gradient framework membrane. (2) Preparation of top covalent organic framework membrane The support carrying the metal-organic framework membrane obtained in step (1) is placed in an interfacial polymerization solution containing organic monomers, catalysts, water and organic solvent 2, and reacted at room temperature for 1-200 h. Then the solvent is evaporated, and the membrane is washed and dried with organic solvent 3 to obtain a gradient framework membrane.

6. The gradient framework membrane according to claim 5, characterized in that, Also includes: (III) Metal modification of gradient framework membrane: The metal salt 2 solution is coated onto the gradient framework membrane material obtained in step (II) to make the gradient framework membrane material and the metal salt solution composite, and then dried to obtain the metal-modified gradient framework membrane.

7. The gradient framework membrane according to claim 5, characterized in that, In step (1) of step (1), the metal salt 1 is at least one of anhydrous zirconium chloride, zirconium oxychloride octahydrate, ferric chloride hexahydrate, ferric nitrate nonahydrate, ferric oxalate dihydrate, chromium nitrate nonahydrate, aluminum sulfate octahydrate, aluminum chloride hexahydrate, aluminum nitrate nonahydrate, copper nitrate trihydrate, zinc nitrate hexahydrate, and cobalt nitrate hexahydrate; the organic ligand is 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, or 2-amino-4,4'-triazole. The first is selected from biphenyl dicarboxylic acid and 2,5-di(4'-carboxyphenyl)aniline; the second is selected from formic acid, acetic acid, benzoic acid, hydrochloric acid, and hydrofluoric acid; the third is selected from water, methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile, or a mixture thereof; the molar ratio of each raw material is metal:organic ligand:regulator:solvent 1 = 0.01-5:0.01-5:0-1000:0.01-10000; In step (1) (1.2), the grinding method includes mortar grinding and ball milling; the ultrasonic conditions are: power of 1-300W, time of 1-60 minutes; the dispersion solvent is one or a mixture of several of water, methanol, ethanol, acetone, tetrahydrofuran, and N,N-dimethylformamide; the mass concentration of metal-organic framework nanosheets in the metal-organic framework nanosheet dispersion is 0.0001-10%; In step (1) (1.3), the aldehyde monomer is at least one selected from the following: trialdehyde phloroglucinol, 2,5-dihydroxyterephthalaldehyde, pyromellitic pyrophthalaldehyde, 2-hydroxy-1,3,5-benzenetricaraldehyde, 2,3-dihydroxyterephthalaldehyde, 2,5-diethoxy-1,4-terephthalaldehyde, 2,5-dipropoxy-1,4-terephthalaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, and 5-hydroxy-isophthalaldehyde; the mixing method is ultrasonic dispersion, with an ultrasonic power of 1- 300W, ultrasonic time is 1-60 minutes; the porous carrier used is at least one of porous alumina, anodic alumina, titanium dioxide, silicon nitride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyethersulfone, polyacrylonitrile, nylon, cellulose acetate, polyimide, and stainless steel, with a pore size of 5nm-10μm; the porous carrier shape is sheet, plate, roll, fiber, or tubular structure; the nanosheet assembly method includes at least one of vacuum filtration, hot drop coating, spin coating, dip-coating, scraping, and immersion. In step (I) of method two, the metal salt 1 is at least one of anhydrous zirconium chloride, zirconium oxychloride octahydrate, ferric chloride hexahydrate, ferric nitrate nonahydrate, ferric oxalate dihydrate, chromium nitrate nonahydrate, aluminum sulfate octahydrate, aluminum chloride hexahydrate, aluminum nitrate nonahydrate, copper nitrate trihydrate, zinc nitrate hexahydrate, and cobalt nitrate hexahydrate; the organic ligand is one of 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, and 2,5-di(4'-carboxyphenyl)aniline; the regulator includes at least one of formic acid, acetic acid, benzoic acid, hydrochloric acid, and hydrofluoric acid; and the solvent 1 includes water, methanol, and ethanol. The solution contains one or more of the following: acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile; the porous carrier is at least one of the following: porous alumina, anodic alumina, titanium dioxide, silicon nitride, polytetrafluoroethylene, polyvinylidene fluoride, polyamide, polyethersulfone, polyacrylonitrile, nylon, cellulose acetate, polyimide, and stainless steel; the pore size of the porous carrier is 5 nm-10 μm; the shape of the porous carrier is sheet-like, plate-like, rolled, fibrous, or tubular; the molar ratio of each raw material in the mixed solution of metal salt 1, organic ligand, regulator, and solvent 1 is metal:organic ligand:regulator:solvent = 0.01-5:0.01-5:0-1000:0.01-10000; In step (1) (2), the modification method of the surface-functionalized porous carrier includes carboxyl modification, amino modification, hydroxyl modification, or dopamine modification; the aldehyde monomer includes at least one of trialdehyde phloroglucinol, 2,5-dihydroxy-terephthalaldehyde, pyromellitic pyrophthalaldehyde, 2-hydroxy-1,3,5-phenyltricarboxaldehyde, 2,3-dihydroxy-terephthalaldehyde, 2,5-diethoxy-1,4-terephthalaldehyde, 2,5-dipropoxy-1,4-terephthalaldehyde, 2,2'-bipyridine-5,5'-dicarboxaldehyde, and 5-hydroxy-morephthalaldehyde; the diamine monomer includes p-phenylenediamine, 2-nitro-1,4-phenylenediamine, 2,5-dibromo-p-phenylenediamine, 2,5-diamino-terephthalic acid, 2-methyl-1,4-phenylenediamine, 2-sulfonic acid-1,4-phenylenediamine, and 2-chloro- At least one of 1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, 2,5-dibromo-1,4-phenylenediamine, hydrazine hydrate, and ethidium bromide; the organic solvent 1 includes one or more of methanol, ethanol, acetone, tetrahydrofuran, mesitylene, and 1,4-dioxane; the concentration of the aldehyde monomer in the mixed solution of the aldehyde monomer and organic solvent 1 is 0.01-0.05 mol / L; the catalyst includes at least one of p-toluenesulfonic acid, acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, and formic acid; in the mixed solution containing the aldehyde monomer, diamine monomer, organic solvent 1, and catalyst, the molar ratio of each raw material is aldehyde monomer: diamine monomer: organic solvent 1: catalyst = 0.001-1: 0.001-1: 0.01-1000: 0.01-1000.

8. The gradient framework membrane according to claim 5, characterized in that, In step (ii) (1), the metal salt 1 includes at least one of anhydrous zirconium chloride, zirconium oxychloride octahydrate, ferric chloride hexahydrate, chromium nitrate nonahydrate, aluminum nitrate nonahydrate, copper nitrate trihydrate, and zinc nitrate hexahydrate; the organic ligand is 2-aminoterephthalic acid, 5-aminoisophthalic acid, 5-aminobenzimidazole, 3-amino-1,2,4-triazole, 2-amino-4,4'-biphenyldicarboxylic acid, 2,5-di(4'-carboxyphenyl)aniline, and 2-sulfonic acid p-benzene One or a mixture of several sodium dicarboxylate salts; the regulator includes at least one of formic acid, acetic acid, benzoic acid, hydrochloric acid, and hydrofluoric acid; the solvent 1 includes one or a mixture of several of water, methanol, ethanol, acetone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide; in the reaction solution, the preferred molar ratio of each raw material is metal:organic ligand:regulator:solvent 1 = 0.01-5:0.01-5:0-1000:0.01-10000; In step (ii) (2), the organic monomer is at least one of p-phenylenediamine, 2-nitro-1,4-phenylenediamine, 2,5-dibromo-p-phenylenediamine, triaminoguanidine hydrochloride, 2,5-diamino-p-phenylenedisulfonic acid, 2-methyl-1,4-phenylenediamine, 2-sulfonic-1,4-phenylenediamine, 2-chloro-1,4-phenylenediamine, 2,5-dichloro-1,4-phenylenediamine, 2,5-dibromo-1,4-phenylenediamine, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, and 5,5'-diamino-2,2'-bipyridine; The catalyst is at least one of p-toluenesulfonic acid, acetic acid, trifluoroacetic acid, scandium trifluoromethanesulfonate, and formic acid; the organic solvent 2 is one or a mixture of several of acetonitrile, methanol, ethanol, octanoic acid, and N,N-dimethylformamide; the organic solvent 3 is one or more of methanol, ethanol, acetone, tetrahydrofuran, mesitylene, and 1,4-dioxane; in the interfacial polymerization solution, the molar ratio of each raw material is organic monomer: catalyst: water: organic solvent 2 = 0.01~5: 0.01~5: 0.01~10000: 0.01~10000.

9. The gradient framework membrane according to claim 5, characterized in that, In step (iii), the metal salt 2 in the metal salt 2 solution is at least one of silver nitrate, silver tetrafluoroborate, silver trifluoromethanesulfonate, cuprous chloride, cuprous bromide, cuprous acetate, magnesium nitrate, nickel nitrate, and ferric nitrate; the solvent used in the metal salt 2 solution is one or a mixture of several of water, methanol, ethanol, acetone, and tetrahydrofuran; the concentration of the metal salt 2 solution is 0.01-10 mol / L; the coating method includes at least one of spin coating, dip coating, spray coating, and blade coating; after the reaction, the solvent is evaporated at 60-150℃ for 1-48 hours.

10. The application of the gradient frame membrane according to any one of claims 1-9 in gas separation and liquid separation, preferably in ethylene / ethane separation, propylene / propane separation, organic matter dehydration, and ion separation.

Images