Continuous MOF films with three-dimensional mesh interfaces, their preparation methods and applications

Abstract

This invention belongs to the field of MOF membranes, and particularly relates to a continuous MOF membrane with a three-dimensional mesh interface, its preparation method, and its application. The preparation method includes: diffusing a PVA-cobalt ion aqueous solution from a polydimethylsiloxane layer into a base membrane; diffusing a first ligand solution from a nonwoven fabric layer into the base membrane to coordinate with cobalt ions, forming an α-Co(OH)₂ mesh layer on the surface of the polydimethylsiloxane layer, thus obtaining a membrane with an α-Co(OH)₂ mesh layer; immersing the membrane with the α-Co(OH)₂ mesh layer in a metal salt solution to anchor metal ions in the metal salt solution onto the α-Co(OH)₂ mesh layer; drying the membrane after immersion; and then immersing it in a second ligand solution for reaction, thus obtaining a continuous MOF membrane with a three-dimensional mesh interface. This preparation method solves the problems of difficulty in preparing different types of continuous defect-free MOF membranes on polymer supports and interfacial compatibility issues.

Description

Technical Field

[0001] This invention belongs to the field of MOF membranes, and in particular relates to a continuous MOF membrane with a three-dimensional mesh interface, its preparation method and application. Background Technology

[0002] Membrane separation technology, due to its advantages such as simple operation, low energy consumption, high processing efficiency, and no secondary pollution, as well as its combined separation and purification functions, is widely used in pharmaceuticals, food, biology, energy, seawater desalination, and gas separation, showing great application potential and considered a separation technology with immense potential. In membrane applications, membrane materials with good separation selectivity and high permeation rates are the core of membrane separation technology, determining the selective permeability, process design, membrane stability, and ultimately, the applicable membrane separation system.

[0003] Metal-organic frameworks (MOFs) are crystalline porous materials with a periodic network structure, formed by the self-assembly of inorganic metal centers (metal ions or metal clusters) and bridging organic ligands. Due to their high porosity, large specific surface area, and regular pore size, MOFs play a dominant role in membrane separation processes, making them a preferred material in many application fields.

[0004] Currently, the preparation of most MOF materials requires organic solvents. However, polymer supports exhibit significant swelling in response to organic solvents, leading to the prevalence of existing MOF membrane preparation processes involving loading metal salts or ligands onto the surface of inorganic support layers. The preparation of MOF membranes on low-cost, highly processable polymer supports is extremely rare. Furthermore, even when MOF membranes are successfully prepared on polymer supports, the poor interfacial compatibility between MOFs and polymer supports easily generates defects, resulting in poor separation selectivity of the prepared membranes and significantly limiting the industrial applications of MOF membranes. Summary of the Invention

[0005] To overcome the technical problems in related technologies, such as the difficulty in preparing different types of continuous defect-free MOF films on polymer supports and the interfacial compatibility issues between MOFs and the interface layer, the present invention aims to provide a continuous MOF film with a three-dimensional mesh interface, its preparation method, and its application. This preparation method is simple and significantly solves the problems of difficulty in preparing different types of continuous defect-free MOF films on polymer supports and interfacial compatibility issues, thereby obtaining different types of continuous defect-free metal-organic framework films with a three-dimensional mesh interface.

[0006] In a first aspect, the present invention provides a method for preparing a continuous MOF membrane with a three-dimensional mesh interface, wherein the base membrane of the continuous MOF membrane is formed by bonding a polymer support layer, a polysulfone layer and a nonwoven fabric layer sequentially arranged from top to bottom, wherein the polymer support layer is a polydimethylsiloxane layer, and the preparation method includes the following steps:

[0007] S1. After the PVA-cobalt ion aqueous solution diffuses from the polydimethylsiloxane layer into the base film, the first ligand solution diffuses from the nonwoven fabric layer into the base film in the reverse direction to coordinate with the cobalt ions in the PVA-cobalt ion aqueous solution, forming an α-Co(OH)2 grid layer on the surface of the polydimethylsiloxane layer, thus obtaining a film with an α-Co(OH)2 grid layer.

[0008] S2. The membrane with the α-Co(OH)2 grid layer is immersed in a metal salt solution to fix the metal ions in the metal salt solution onto the α-Co(OH)2 grid layer. After being removed and dried, it is then immersed in a second ligand solution to react and obtain the continuous MOF membrane with the three-dimensional grid interface.

[0009] In some embodiments of the present invention, step S1 specifically involves: suspending and fixing the polydimethylsiloxane layer of the base film with its upper side facing upwards, pouring the PVA-cobalt ion aqueous solution into the polydimethylsiloxane layer and soaking it for 30-50 minutes, then transferring it horizontally into the first ligand solution and soaking it for 10-60 seconds, removing it, washing it, and drying it.

[0010] In some embodiments of the present invention, step S2, specifically the soaking in the second ligand solution, involves immersing the polydimethylsiloxane layer downwards in the second ligand solution for 3-6 hours.

[0011] In some embodiments of the present invention, the solvent of the first ligand solution is methanol or ethanol.

[0012] In some embodiments of the present invention, the ligand of the first ligand solution is 2-methylimidazole.

[0013] In some embodiments of the present invention, the concentration of the first ligand solution is (2.5-3.5) g / mL.

[0014] In some embodiments of the present invention, the metal salt solution is a cobalt salt solution or a zinc salt solution, and the ligand in the second ligand solution is 2-methylimidazole; or, the metal salt solution is a copper salt solution, and the ligand in the second ligand solution is trimesic acid.

[0015] In some embodiments of the present invention, the solvent of the metal salt solution is a mixture of a strongly polar solvent and water, wherein the strongly polar solvent is methanol or ethanol.

[0016] In some embodiments of the present invention, the volume ratio of the strongly polar solvent to water is 1:(1-4).

[0017] In some embodiments of the present invention, the concentration of the ligand in the second ligand solution is (2.5-3.5) g / mL.

[0018] In a second aspect, the present invention provides a continuous MOF membrane with a three-dimensional mesh interface prepared by the above-described preparation method.

[0019] A third aspect of the present invention provides an application of the above-described continuous MOF membrane with a three-dimensional mesh interface in gas separation.

[0020] This invention provides a continuous MOF film with a three-dimensional mesh interface, its preparation method, and its application, which has at least one of the following advantages:

[0021] (1) In this invention, a two-dimensional nanosheet mesh layer is first formed on the polymer support layer of the base membrane. Then, based on the two-dimensional nanosheet mesh layer, metal ions are first anchored on the mesh layer by gradient volume mutual phase diffusion method, and then combined with ligand molecules to successfully prepare a continuous and dense MOF membrane combining two-dimensional and three-dimensional structures. This MOF membrane has excellent separation and selectivity for different gas systems.

[0022] (2) This invention utilizes the instability of MOF in aqueous solution (MOF will decompose into two-dimensional nanosheets in aqueous solution) to form a large-area continuous and defect-free two-dimensional nanosheet mesh layer on the surface of polymer support, thereby avoiding direct contact between organic solvent and polymer support in subsequent steps and solving the swelling problem caused by direct contact between organic solvent and polymer support.

[0023] (3) Since the first ligand solution in this invention binds to metal ions through back diffusion, there are still some metal ions in the grid layer that have not bound to the ligand molecules in the first ligand solution. Therefore, the two-dimensional nanosheet grid layer formed in this invention also plays the role of pre-embedding metal ions. These embedded metal ions and the metal ions anchored to the interface later can bind to the ligand molecules in the second ligand solution, which can solve the problem of uneven anchoring of metal ions later, thereby strengthening the heterogeneous nucleation on the interface layer and enhancing the continuity and compactness of the MOF film.

[0024] (4) Since the technical solution provided by the present invention can effectively solve the swelling problem caused by organic solvents directly contacting the polymer support, it can be applied to the preparation of various MOF membranes. Attached Figure Description

[0025] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0026] Figure 1 The morphological characterization of the α-Co(OH)2-1 grid layer is as follows: (1) SEM image of the α-Co(OH)2-1 grid layer at low magnification; (2) SEM image of the α-Co(OH)2-1 grid layer at high magnification; (3) SEM image of the cross section of the α-Co(OH)2-1 grid layer; (4) AFM image of the α-Co(OH)2-1 grid layer.

[0027] Figure 2 Image of ZIF-67-1 membrane: (The image shows the membrane itself.) Figure 2 -(a) and Figure 2 -(b) shows surface SEM images at different magnifications. Figure 2 -(c) is the cross-sectional SEM image. Figure 2 -(d) is the AFM diagram;

[0028] Figure 3 The morphology and structural characterization diagram of the α-Co(OH)2-2 mesh layer are shown below: Figure 3 -(a) is a morphological diagram of the α-Co(OH)2-2 mesh layer; Figure 3 -(b) shows the XRD patterns of the α-Co(OH)2-2 mesh layer under simulated and experimental conditions; Figure 3 -(c) is the FTIR spectrum of the α-Co(OH)2-2 grid layer. Figure 3 -(d) is the TG analysis spectrum of the α-Co(OH)2-2 grid layer;

[0029] Figure 4 The morphological characterization of the α-Co(OH)2-2 mesh layer is as follows: (1) SEM image of the α-Co(OH)2-2 mesh layer at low magnification; (2) SEM image of the α-Co(OH)2-2 mesh layer at high magnification; (3) SEM image of the cross section of the α-Co(OH)2-2 mesh layer; (4) AFM image of the α-Co(OH)2-2 mesh layer.

[0030] Figure 5 Morphological characterization of the ZIF-67-2 film: (The text abruptly ends here.) Figure 5 -(a) and Figure 5 -(b) shows surface SEM images at different magnifications. Figure 5 -(c) is the cross-sectional SEM image. Figure 5 -(d) is the AFM diagram;

[0031] Figure 6 Structural characterization of the ZIF-67-2 membrane; among which, Figure 6-(a) shows the N2 adsorption-desorption isotherm and specific surface area at 77 K; Figure 6 -(b) shows the CO2 and N2 gas adsorption isotherms of the ZIF-67-2 membrane; Figure 6 -(c) is the CH4 and N2 gas adsorption isotherm of the ZIF-67-2 membrane; Figure 6 -(d) are the adsorption isotherms of C3H6 and C3H8 gases on the ZIF-67-2 membrane;

[0032] Figure 7 Morphological characterization of the α-Co(OH)2-3 mesh layer: where, Figure 7 -(1) is a low-magnification SEM image of the α-Co(OH)2-3 grid layer; Figure 7 -(2) is a high-magnification SEM image of the α-Co(OH)2-3 grid layer; Figure 7 -(3) is a cross-sectional SEM image of the α-Co(OH)2-3 mesh layer; Figure 7 -(4) is the AFM image of the α-Co(OH)2-3 grid layer;

[0033] Figure 8 Morphological characterization of the ZIF-67-3 film: (The text abruptly ends here.) Figure 8 -(a) and Figure 8 -(b) shows surface SEM images at different magnifications. Figure 8 -(c) is the cross-sectional SEM image. Figure 8 -(d) is the AFM diagram;

[0034] Figure 9 Morphological characterization of the ZIF-8 film: (The text abruptly ends here.) Figure 9 -(a) and Figure 9 -(b) shows surface SEM images at different magnifications;

[0035] Figure 10 Morphological characterization of the CuBTC film: where, Figure 10 -(a) and Figure 10 -(b) shows surface SEM images at different magnifications;

[0036] Figure 11 Morphological characterization of the ZIF-67-4 film: (The text abruptly ends here.) Figure 11 -(a) and Figure 11 -(b) shows surface SEM images at different magnifications;

[0037] Figure 12 Morphological characterization of the ZIF-67-5 film: (The text abruptly ends here.) Figure 12 -(a) and Figure 12 -(b) shows surface SEM images at different magnifications;

[0038] Figure 13 The gas separation performance of the ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes prepared in Examples 1-3 is as follows: Figure 13 -(a) is the permeation rate of CH4 through ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes under pure gas conditions; Figure 13 -(b) Permeation rates of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes to N2 under pure gas conditions; Figure 13 -(c) Selectivity of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes for CH4 / N2 separation under pure gas conditions;

[0039] Figure 14 The gas separation performance of the ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes prepared in Examples 1-3 is as follows: Figure 14 -(a) is the CO2 permeation rate of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes under pure gas conditions; Figure 14 -(b) Permeation rates of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes to N2 under pure gas conditions; Figure 14 -(c) Selectivity of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes for CO2 / N2 separation under pure gas conditions;

[0040] Figure 15 The gas separation performance of the ZIF-67-2 membrane prepared in Example 2; Figure 15 -(a) Permeation rate of ZIF-67-2 membrane for C3H6 and C3H8 and separation selectivity of C3H6 / C3H8 under pure gas conditions; Figure 15 -(b) Permeation rate of ZIF-67-2 membrane for C3H6 and C3H8 and separation selectivity of C3H6 / C3H8 under mixed gas conditions;

[0041] Figure 16 The gas separation performance of the CuBTC membrane prepared in Example 5; Figure 16 -(a) Permeation rate of CuBTC membrane for CH4 and N2 and CH4 / N2 separation selectivity under pure gas conditions; Figure 16 -(b) Permeation rates of CuBTC membrane for CO2 and N2 and CO2 / N2 separation selectivity under pure gas conditions; Figure 16 -(c) Permeation rate of CuBTC membrane for C3H6 and C3H8 and separation selectivity of C3H6 / C3H8 under pure gas conditions. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.

[0043] The model and manufacturer information of the instruments used for measurement in the various embodiments of this application are as follows:

[0044] Field emission scanning electron microscope (SEM), model DropShapeAnalyzer100, manufactured by Bruker GmbH, Germany;

[0045] Atomic force microscope (AFM), model: TensorII, manufactured by Hitachi, Japan;

[0046] Specific surface area and porosity analyzer (BET), model: Micromeritics, ASAP2020PlusHD88, manufactured by Micromeritics, Inc., USA;

[0047] X-ray diffraction (XRD), model: D2 Discoverdiffractometer, manufactured by Bruker GmbH, Germany;

[0048] Fourier transform infrared spectrometer (FTIR), model: ALPHAII, manufactured by Bruker GmbH, Germany;

[0049] Thermogravimetric analyzer (TG), model: Rigaku, manufactured by Hitachi, Japan;

[0050] Unless otherwise specified below, the specifications and manufacturer information of the various raw materials used in the various embodiments of this application are all commercially available.

[0051] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0052] Polyvinyl alcohol (PVA), purchased from Saen Chemical Technology Co., Ltd.;

[0053] Cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was purchased from Maclean Biochemical Technology Co., Ltd.

[0054] 2-Methylimidazole, 99% purity, purchased from Aladdin Reagent Co., Ltd.

[0055] Anhydrous methanol, all with a specification of 98%, was purchased from Saen Chemical Technology Co., Ltd.

[0056] Polysulfone (PSF) ultrafiltration membrane: average pore size 20-30nm, one side is a non-woven fabric layer, provided by Zhongyi Filter Material Store, Zhouwangmiao Town, Haining City;

[0057] Triamcinolone acetonide (BTC), purchased from Maclean Biotechnology Co., Ltd.

[0058] Polydimethylsiloxane (PDMS), purchased from Saen Chemical Technology Co., Ltd.

[0059] This invention provides a method for preparing a continuous MOF membrane with a three-dimensional mesh interface. The base membrane of the continuous MOF membrane is composed of a polymer support layer, a polysulfone layer, and a nonwoven fabric layer sequentially arranged from top to bottom. The polymer support layer is a polydimethylsiloxane layer. The preparation method includes the following steps:

[0060] S1. After the PVA-cobalt ion aqueous solution diffuses from the polydimethylsiloxane layer into the base film, the first ligand solution diffuses in the reverse direction from the nonwoven fabric layer into the base film to coordinate with the cobalt ions in the PVA-cobalt ion aqueous solution, forming an α-Co(OH)2 grid layer on the surface of the polydimethylsiloxane layer.

[0061] Because cobalt ions in the PVA-cobalt ion aqueous solution are anchored to the PDMS surface under the action of PVA, ligand molecules in the first ligand solution react with the anchored metal when they enter the PVA-cobalt ion aqueous solution, forming MOFs (e.g., ZIF-67) on the surface. However, since there is an aqueous solution above the PDMS, the MOFs decompose into two-dimensional nanosheets in the aqueous solution, forming a large-area continuous and dense two-dimensional nanosheet network layer. This avoids direct contact between the organic solvent and the polymer support in subsequent steps, thus solving the swelling problem caused by direct contact between the organic solvent and the polymer support.

[0062] In addition, since the first ligand solution diffuses backward from the nonwoven fabric layer into the base film to coordinate with the cobalt ions in the PVA-cobalt ion aqueous solution, some metal ions are not bound to the ligand molecules in the first ligand solution and are embedded in the two-dimensional nanosheet mesh layer.

[0063] S2. The base film obtained in step S1 is immersed in a metal salt solution, then removed and dried to anchor metal ions onto the α-Co(OH)2 grid layer.

[0064] In this step, the solvent for the metal salt solution is a mixture of a highly polar solvent and water, preferably methanol or ethanol. The ratio of the highly polar solvent to water is crucial. If a mixture containing only a highly polar solvent or a high concentration of such a solvent is used to dissolve the ligands, the highly polar solution can easily cause swelling of the interfacial layer, leading to swelling of the pre-grown mesh layer. This, in turn, makes it difficult for metal ions to anchor onto the mesh layer, resulting in uneven metal ion loading or detachment, causing defects in the membrane. If only water is used as the solvent, some ligands will not dissolve, affecting the coordination reaction with the metal and hindering membrane growth.

[0065] S3. The base film obtained in step S2 is immersed in the second ligand solution to coordinate with the metal ions anchored on the two-dimensional nanosheet mesh layer to obtain the continuous MOF film with the three-dimensional mesh interface.

[0066] In this step, the metal ions embedded in the mesh layer and the metal ions anchored to the two-dimensional nanosheet mesh layer both bind to the ligand molecules in the second ligand solution, enhancing the continuity and compactness of the MOF film.

[0067] The above technical implementation schemes will be illustrated by the following examples.

[0068] Preparation of the base membrane: One side of the polysulfone (PSf) ultrafiltration membrane is a non-woven fabric layer, and PDMS is coated on the other side of the polysulfone (PSf) ultrafiltration membrane to obtain the base membrane.

[0069] PVA-cobalt ion aqueous solution: 2.5g of polyvinyl alcohol (PVA) is fully dissolved in 100mL of deionized water, heated to 95℃ and stirred evenly to obtain a PVA aqueous solution; then 3g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) is added to the above solution and stirred evenly to form a PVA-cobalt ion aqueous solution.

[0070] Example 1: Preparation of ZIF-67-1

[0071] Preparation of the first ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0072] Preparation of the second ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0073] S01: Fix the base membrane with the PDMS-coated side facing up on a hollow plastic frame. Measure 50 mL of PVA-cobalt ion aqueous solution and pour it onto the base membrane surface (PDMS side). After soaking for 30 min, move it horizontally into the first ligand solution, allowing the first ligand solution to diffuse from the nonwoven fabric side into the base membrane surface (PDMS side). React for 10 s, remove the membrane and pour off the excess solution. Soak it in clean deionized water, clean it, and place it in a constant temperature and humidity chamber at 30°C and 40°C to dry for 12 h to obtain a membrane with an α-Co(OH)2-1 grid layer.

[0074] The α-Co(OH)2-1 mesh layer was characterized using SEM and AFM, and the results are as follows: Figure 1 As shown in the figure. (1), (2), (3) and (4) are the surface SEM images of the α-Co(OH)2-1 mesh layer at 20 μm, the surface SEM image at 400 nm, the cross-sectional SEM image at 400 nm, and the AFM image, respectively. Analysis of the SEM and AFM images shows that the prepared α-Co(OH)2-1 mesh layer has a shallow mesh structure on the surface, a film thickness of only 50 nm, and a low surface roughness of only 27.7 nm.

[0075] S02: Weigh 3g of Co(NO3)2·6H2O and dissolve it in a solvent with a methanol:water volume ratio of 1:4. Stir thoroughly to form a cobalt metal solution. Then fix the α-Co(OH)2-1 mesh layer of the membrane obtained in step S1 onto a glass plate with the α-Co(OH)2-1 mesh layer facing upwards. Pour the cobalt metal solution onto the membrane and immerse it on the membrane surface for 4 hours. After that, take out the membrane and dry it in an oven at 30°C for 8 hours to form an α-Co(OH)2-1 metal layer.

[0076] S03: Immerse the α-Co(OH)2-1 metal layer of the membrane obtained in step S02 with one side facing down in the second ligand solution. After reacting for 4 hours, take out the membrane and place it in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the ZIF-67-1 membrane.

[0077] The ZIF-67-1 film obtained above was scanned using SEM and AFM. The resulting scanning electron microscope images are shown below. Figure 2 As shown, Figure 2 -(a) and 2-(b) are SEM images of the membrane surface at 2 μm and 400 nm, respectively. Figure 2 -(c) is a cross-sectional SEM image of the membrane at 400 nm; Figure 2 -(d) is the AFM image of the membrane at 2 μm. From Figure 2As can be seen from -(a) and 2-(b), when an α-Co(OH)2-1 mesh layer is used for ZIF-67 membrane growth, the ZIF-67-1 membrane surface is smooth and has a light-colored granular texture. Figure 2 As can be seen from (c), the thickness of the obtained ZIF-67-1 film is 58 nm. Figure 2 As can be seen from (d), the roughness of the obtained ZI F-67-1 film is 48.4 nm. This indicates that the ZI F-67-1 film prepared in Example 1 of the present invention is continuous, dense, and relatively thin.

[0078] Example 2: Preparation of ZIF-67-2

[0079] Preparation of the first ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0080] Preparation of the second ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0081] S01: Fix the base membrane with the PDMS-coated side facing up on a hollow plastic frame. Measure 50 mL of PVA-cobalt ion aqueous solution and pour it onto the base membrane surface (PDMS side). After soaking for 30 min, move it horizontally into the first ligand solution, allowing the first ligand solution to diffuse into the membrane surface from the nonwoven fabric side. React for 30 s, remove the membrane and pour off the excess solution. Soak it in clean deionized water, clean it, and place it in a constant temperature and humidity chamber at 30°C and 40°C to dry for 12 h to obtain a membrane with an α-Co(OH)2-2 mesh layer.

[0082] The above α-Co(OH)2-2 mesh layer was tested using SEM, XRD, BET, and TG, and the results are as follows: Figure 3 and Figure 4 As shown.

[0083] Figure 3 -(a) is a surface image of the α-Co(OH)2-2 mesh layer. It can be seen from the image that the membrane surface is smooth and without defects. Figure 3 -(b) is the XRD pattern of the α-Co(OH)2-2 grid layer. Compared with the simulated XRD pattern of the α-Co(OH)2-2 grid layer, the α-Co(OH)2-2 grid layer has the same crystal plane at (003) and (006), maintaining a good crystal structure. Figure 3-(c) is the FTIR spectrum of the α-Co(OH)2-2 grid layer. It can be seen from the figure that the prepared α-Co(OH)2-2 grid layer has obvious characteristic peaks. Figure 3 -(d) is the TG spectrum of the α-Co(OH)2-2 grid layer, showing a significant decrease in mass percentage at 260°.

[0084] Figure 4 Morphological characterization of the α-Co(OH)2-2 mesh layer, Figure 4 (1), (2), (3), and (4) are respectively the surface SEM image, surface SEM image, cross-sectional SEM image, and AFM image of the α-Co(OH)2-2 mesh layer at high magnification. Analysis of the SEM and AFM images shows that the mesh layer on the film surface becomes more obvious with increasing reaction time, and the mesh layer thickness increases significantly, reaching 143 nm.

[0085] SO2: Weigh 3g of Co(NO3)2·6H2O and dissolve it in a solvent with a methanol:water volume ratio of 1:4. Stir thoroughly to form a cobalt metal solution. Then fix the dried α-Co(OH)2-2 mesh layer with the top facing up on a glass plate. Pour the cobalt metal solution onto the membrane and immerse the membrane surface for 4 hours. Remove the membrane and dry it in an oven at 30℃ for 8 hours to form an α-Co(OH)2-2 metal layer.

[0086] S03: Immerse the α-Co(OH)2-2 metal layer of the membrane obtained in step S02 with one side facing down in the second ligand solution. After reacting for 4 hours, take out the membrane and place it in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the ZIF-67-2 membrane.

[0087] The ZIF-67-2 film obtained above was scanned using SEM, AFM, BET, and gas adsorption isotherms. The resulting SEM images are shown below. Figure 5 and Figure 6 As shown, Figure 5 -(a) and 5-(b) are SEM images of the membrane surface at 2 μm and 400 nm, respectively. Figure 5 -c is a cross-sectional SEM image of the membrane at 100nm; Figure 5 -d is the AFM image of the membrane at 2 μm. From Figure 5 As can be seen from -(a) and 5-(b), when using an α-Co(OH)2-2 mesh layer for the preparation of ZI F-67-2 membranes, from Figure 5 As can be seen from (c), the thickness of the obtained ZIF-67-2 film is 163 nm. Figure 5As can be seen from (d), the roughness of the obtained ZIF-67-2 film is 11.7 nm. This indicates that the ZIF-67-2 film prepared in Example 2 of the present invention is continuous and dense with obvious granular surface, and the film thickness is significantly increased, but the surface roughness is significantly reduced. Figure 6 Structural characterization of the ZIF-67-2 membrane; among which, Figure 6 -(a) shows the N2 adsorption-desorption isotherm and specific surface area at 77 K; Figure 6 -(b) shows the CO2 and N2 gas adsorption isotherms of the ZIF-67-2 membrane; Figure 6 -(c) is the CH4 and N2 gas adsorption isotherm of the ZIF-67-2 membrane; Figure 6 -(d) is the adsorption isotherm of C3H6 and C3H8 gases on the ZIF-67-2 membrane. From Figure 6 As can be seen from the data, the prepared ZIF-67-2 membrane has a suitable specific surface area of ​​391.02 m². 2 / g, and has significant separation effects on CO2 / N2, CH4 / N2 and C3H6 / C3H8.

[0088] Example 3: Preparation of ZIF-67-3

[0089] Preparation of the first ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0090] Preparation of the second ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0091] S01: Fix the base membrane with the PDMS-coated side facing up on a hollow plastic frame. Measure 50 mL of PVA-cobalt ion aqueous solution and pour it onto the base membrane surface (PDMS side). After soaking for 30 min, move it horizontally into the first ligand solution, allowing the first ligand solution to diffuse from the nonwoven fabric side into the base membrane surface (PDMS side). React for 60 s. Remove the membrane and pour off the excess solution. Soak it in clean deionized water, clean it, and place it in a constant temperature and humidity chamber at 30°C and 40°C to dry for 12 h to obtain a membrane with an α-Co(OH)2-3 mesh layer.

[0092] The α-Co(OH)2-3 mesh layer was characterized using SEM and AFM, and the results are as follows: Figure 7 As shown. In Figure 7In the images, (1), (2), (3), and (4) are SEM images of the α-Co(OH)2-3 mesh layer at 20 μm, 400 nm, 400 nm, and 2 μm, respectively. Analysis of the SEM and AFM images reveals that the mesh structure on the surface of the prepared α-Co(OH)2-3 mesh layer is clearly interconnected, the film thickness is significantly increased to 252 nm, and the surface roughness is significantly increased to 107.4 nm.

[0093] S02: Weigh 3g of Co(NO3)2·6H2O and dissolve it in a solvent with a methanol:water volume ratio of 1:4. Stir thoroughly to form a cobalt metal solution. Then fix the α-Co(OH)2-3 mesh layer of the membrane obtained in step S1 onto a glass plate with the α-Co(OH)2-3 mesh layer facing upwards. Pour the cobalt metal solution onto the membrane and immerse it on the membrane surface for 4 hours. After that, take out the membrane and dry it in an oven at 30°C for 8 hours to form an α-Co(OH)2-3 metal layer.

[0094] S03: Immerse the α-Co(OH)2-3 metal layer of the membrane obtained in step S02 with one side facing down in the second ligand solution. After reacting for 4 hours, take out the membrane and place it in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the ZIF-67-3 membrane.

[0095] The ZIF-67-3 film obtained above was scanned using SEM and AFM. The resulting scanning electron microscope images are shown below. Figure 8 As shown, Figure 8 -(a) and 8-(b) are SEM images of the membrane surface at 2 μm and 400 nm, respectively. Figure 8 -(c) is a cross-sectional SEM image of the membrane at 400 nm; Figure 8 -(d) is the AFM image of the membrane at 2 μm. From Figure 8 As can be seen from -(a) and 8-(b), when an α-Co(OH)2-3 mesh layer is used for ZIF-67 film growth, the ZIF-67-3 film surface is smooth and has granular accumulation. Figure 8 As can be seen from (c), the thickness of the obtained ZIF-67-3 film is 282 nm. Figure 8 As can be seen from (d), the roughness of the obtained ZI F-67-3 film is 15.5 nm. This indicates that the ZI F-67-3 film prepared in Example 3 of the present invention is continuous, dense, and relatively thick.

[0096] Example 4: Preparation of ZIF-8 membrane

[0097] Preparation of the first ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0098] Preparation of the second ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0099] (1) Weigh 3g of Zn(NO3)2·6H2O and dissolve it in a solvent with a volume ratio of methanol to water of 1:4. Stir thoroughly to form a zinc metal solution. Then fix the α-Co(OH)2-2 mesh layer of the membrane obtained in step S1 of Example 2 onto a glass plate with the α-Co(OH)2-2 mesh layer facing upward. Pour the cobalt metal solution onto the membrane and immerse it on the membrane surface for 4 hours. Then take out the membrane and dry it in an oven at 30°C for 8 hours to form an α-Co(OH)2-Zn metal layer.

[0100] (2) The α-Co(OH)2-Zn metal layer of the membrane obtained in step (1) is immersed in the second ligand solution with one side facing down. After reacting for 4 hours, the membrane is taken out and placed in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the ZIF-8 membrane.

[0101] The ZIF-8 film obtained above was scanned using SEM, and the resulting scanning electron microscope images are shown below. Figure 9 As shown, Figure 9 -(a) and 9-(b) are SEM images of the film surface at 10 μm and 300 nm, respectively. From Figure 9 As can be seen from -(a) and 9-(b), through the comparison of Example 1.2.3, the optimal α-Co(OH)2-2 grid layer was finally selected for ZIF-8 film growth. The ZIF-8 film surface is optically dense, continuous and defect-free, proving that the film preparation method has a certain degree of versatility.

[0102] Example 5: Preparation of CuBTC membrane

[0103] Preparation of the first ligand solution: 3.2 g of 2-methylimidazole was dissolved in 100 mL of anhydrous methanol to obtain an anhydrous methanol solution of 2-methylimidazole with a mass fraction of 3.2 wt%.

[0104] Preparation of the second ligand solution: Weigh 3.2g of trimesic acid (BTC) and dissolve it in 100mL of anhydrous methanol reagent. Stir thoroughly to form the second ligand solution.

[0105] (1) Weigh 3g of Cu(NO3)2·3H2O and dissolve it in a solvent with a volume ratio of methanol to water of 1:4. Stir thoroughly to form a copper metal solution. Then fix the α-Co(OH)2-2 mesh layer of the membrane obtained in step S1 of Example 2 with one side facing up on a glass plate. Pour the copper metal solution onto the membrane and immerse it on the membrane surface for 4 hours. Then take out the membrane and dry it in an oven at 30°C for 8 hours to form an α-Co(OH)2-Cu metal layer.

[0106] (2) The α-Co(OH)2-Cu metal layer of the membrane obtained in step (1) is immersed in the second ligand solution with one side facing down. After reacting for 4 hours, the membrane is taken out and placed in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the CuBTC membrane.

[0107] The CuBTC film obtained above was scanned using SEM, and the resulting SEM images are shown below. Figure 10 As shown, Figure 10 -(a) and 10-(b) are SEM images of the film surface at 4 μm and 400 nm, respectively. From Figure 10 As can be seen from -(a) and 10-(b), when the α-Co(OH)2-2 grid layer is used for CuBTC film growth, the CuBTC film also has the characteristics of being dense, continuous and having excellent crystal structure.

[0108] Preparation of Comparative Example 1Z IF-67-4

[0109] (1) Weigh 3g of Co(NO3)2·6H2O and dissolve it in a solvent with a volume ratio of methanol to water of 1:1. Stir thoroughly to form a cobalt metal solution. Then fix the α-Co(OH)2-2 mesh layer of the membrane obtained in step S1 of Example 2 onto a glass plate with the α-Co(OH)2-2 mesh layer facing upward. Pour the cobalt metal solution onto the membrane and immerse it on the membrane surface for 4 hours. Then take out the membrane and dry it in an oven at 30°C for 8 hours to form an α-Co(OH)2-4 metal layer.

[0110] (2) The α-Co(OH)2-4 metal layer of the membrane obtained in step (1) is immersed in the second ligand solution with one side facing down. After reacting for 4 hours, the membrane is taken out and placed in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the ZIF-67-4 membrane.

[0111] The ZIF-67-4 film obtained above was scanned using SEM, and the resulting SEM images are shown below. Figure 11 As shown, Figure 11 -(a) and 11-(b) are SEM images of the film surface at 10 μm and 400 nm, respectively. From Figure 11As can be seen from -(a) and 11-(b), when using the α-Co(OH)2-2 grid layer for ZIF-67-4 membrane growth, the ZIF-67-4 membrane exhibits significant swelling on the membrane surface due to the use of a methanol:water solvent with a volume ratio of 1:1 in the preparation of the α-Co(OH)2-4 metal layer. This leads to a reduction in the anchoring of copper metal ions, which in turn affects the nucleation and growth of MOFs on the membrane surface, resulting in significant defects in the prepared membrane.

[0112] Preparation of Comparative Example 2Z IF-67-5

[0113] (1) Weigh 3g of Co(NO3)2·6H2O and dissolve it in a solvent with a volume ratio of methanol to water of 1:2. Stir thoroughly to form a cobalt metal solution. Then fix the dried α-Co(OH)2-2 mesh layer on a glass plate and immerse the membrane surface in the cobalt metal solution for 4 hours. After that, take out the membrane and put it in an oven at 30°C to dry for 8 hours to form an α-Co(OH)2-5 metal layer.

[0114] (2) The membrane obtained in step (1) was immersed in the second ligand solution with the α-Co(OH)2-5 side facing down. After reacting for 4 hours, the membrane was taken out and placed in a constant temperature and humidity chamber at 30°C and 40°C for 10 hours to dry, thus preparing the ZIF-67-5 membrane.

[0115] The ZIF-67-5 film obtained above was scanned using SEM, and the resulting SEM images are shown below. Figure 12 As shown, Figure 12 -(a) and 12-(b) are SEM images of the film surface at 2 μm and 600 nm, respectively. From Figure 12 As can be seen from -(a) and 12-(b), when using the α-Co(OH)2-2 grid layer for ZIF-67-5 membrane growth, the ZIF-67-5 membrane also exhibits obvious cracks and non-density due to the use of a methanol:water volume ratio of 1:2 as a solvent in the preparation of the α-Co(OH)2-5 metal layer, resulting in a low metal ion content on the membrane surface. Therefore, Comparative Examples 1 and 2 fully demonstrate that when preparing the α-Co(OH)2 metal layer, an excessively high methanol content will seriously affect the anchoring of metal ions, thereby affecting the density and continuity of the membrane.

[0116] Test Case

[0117] For a single gas permeation measurement, the membrane is installed in a stainless steel tank (effective membrane area = 0.25 cm²). 2 The feed gas pressure is maintained at 0.5-2.0 bar (gauge pressure, transmembrane pressure), which is controlled by a precision pressure gauge.

[0118] The permeation gas flux is measured using a soap bubble flow meter, and the gas permeability R (GPU, 1GPU = 1 × 10⁻⁶) is calculated. -6 cm 3 (STP)·cm -2 ·s -1 ·cmHg -1 =3.35×10 -10 mol·s -1 ·m -2 ·Pa -1 From the formula definition.

[0119] In the formula, N i (mols -1 Let A(m) be the molar flow rate of the permeating component i. 2 ) represents the effective membrane area, Δp i (Pa) represents the intermembrane pressure difference. Ideal selectivity α i / j The permeability ratio of gas component i to component j is determined by the formula... calculate.

[0120] The permeability of the mixed gas was measured using a self-made stainless steel instrument in the laboratory. Under conditions of 30℃ and 0.5-2.0 bar, dry C3H6 / C3H8 (50 / 50 volume), CH4 / N2 (50 / 50 volume), and CO2 / N2 (50 / 50 volume) mixed gases were used. The membrane gas permeability was measured using a constant pressure testing device. The total feed gas flow rate was 40 mL / min. -1 The transmembrane pressure is controlled by a back pressure valve on the feed side. Dry helium is used as the downstream scavenging gas (50 mL / min). -1 The permeate gas was introduced into the gas chromatograph. The downstream sweeping gas components were analyzed using a gas chromatograph equipped with a thermal conductivity detector (HP7890, Porapak N). Three different samples were measured for each membrane, and 18 points were selected for each sample to obtain the mean permeate data and its standard deviation.

[0121] The permeation rate and gas separation selectivity of the ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes obtained in Examples 1-3 above were measured under pure gas conditions. The measurement results are as follows: Figure 13 As shown. Among them, Figure 13 -(a) is the permeation rate of CH4 through ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes under pure gas conditions; Figure 13 -(b) Permeation rates of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes to N2 under pure gas conditions; Figure 13-(c) ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes exhibit selectivity for CH4 / N2 separation under pure gas conditions.

[0122] from Figure 13 As can be seen, the ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes of this application separated CH4 and N2 under different pressures. At 2 bar, their CH4 permeation rates were 3515.5 GPU, 2789.27 GPU, and 2581.75 GPU, respectively, and their CH4 / N2 selectivity was 5.76, 8.00, and 8.42, respectively. Performance characterization showed that with increasing 2-methylimidazole immersion time during the preparation of the α-Co(OH)2-2 mesh layer, the permeation rate of the prepared membrane decreased significantly, but the gas separation selectivity increased significantly. This indicates that the gas separation performance of the MOF membrane obtained by the preparation method of this application does not increase with increasing 2-methylimidazole immersion time.

[0123] Based on the good gas separation selectivity of the prepared membrane for CH4 / N2, its CO2 / N2 separation selectivity was further tested, such as... Figure 14 As shown. Among them, Figure 14 -(a) is the CO2 permeation rate of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes under pure gas conditions; Figure 14 -(b) Permeation rates of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes to N2 under pure gas conditions; Figure 14 -(c) Selectivity of ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes for CO2 / N2 separation under pure gas conditions. From Figure 14 It can be seen that the ZIF-67-1, ZIF-67-2, and ZIF-67-3 membranes in this application separated CO2 and N2 under different pressures. At 2 bar, their CO2 permeation rates were 8661 GPU, 8238 GPU, and 7933.5 GPU, respectively, and their CO2 / N2 selectivity were 14.18, 23.68, and 25.88, respectively. Similarly, with the increase of the immersion time of the first ligand solution during the preparation of the α-Co(OH)2-2 mesh layer, the permeation rate of the prepared membrane decreased significantly, but the gas separation selectivity increased significantly. Through comparison of membrane performance, a high permeation rate is required while ensuring high gas separation selectivity. Therefore, the preparation conditions of the ZIF-67-2 membrane were ultimately selected as the optimal conditions.

[0124] Based on the above comparison, we conducted a C3H6 / C3H8 separation selectivity performance test on the ZIF-67-2 membrane, and the results are as follows: Figure 15 . Figure 15 -(a) Permeation rate of ZIF-67-2 membrane for C3H6 and C3H8 and separation selectivity of C3H6 / C3H8 under pure gas conditions; Figure 15 (b) Permeation rates of C3H6 and C3H8 and the C3H6 / C3H8 separation selectivity of the ZIF-67-2 membrane under mixed gas conditions. Under pure gas conditions at 2 bar, the C3H6 permeation rate of the ZIF-67-2 membrane was 6778.195 GPU, and the C3H6 / C3H8 separation selectivity was 19.555. Under mixed gas conditions at 2 bar, the C3H6 permeation rate of the ZIF-67-2 membrane was 6602.57 GPU, and the C3H6 / C3H8 separation selectivity was 18.855. The test results for different gas systems show that the membrane preparation method described in this application has excellent gas separation performance.

[0125] Based on this method, we conducted tests on CuBTC membranes, such as... Figure 16 As shown, the CuBTC membrane exhibits excellent gas separation selectivity for CH4 / N2, CO2 / N2, and C3H6 / C3H8. Figure 16 -(a) Permeation rate of CuBTC membrane for CH4 and N2 and CH4 / N2 separation selectivity under pure gas conditions; Figure 16 -(b) Permeation rates of CuBTC membrane for CO2 and N2 and CO2 / N2 separation selectivity under pure gas conditions; Figure 16 -(c) Permeation rates of CuBTC membranes for C3H6 and C3H8 under pure gas conditions and the separation selectivity of C3H6 / C3H8. Specifically, under pure gas conditions of 2 bar, the membrane's CH4 permeation rate was 763.67 GPU, with a CH4 / N2 selectivity of 1.91; the membrane's CO2 permeation rate was 7745.125 GPU, with a CO2 / N2 selectivity of 19.73; and the membrane's C3H6 permeation rate was 7003.665 GPU, with a C3H6 / C3H8 selectivity of 13.16. Characterization tests demonstrate that other types of MOF membranes prepared by this method also exhibit good gas separation selectivity.

[0126] In summary, the method for preparing a continuous MOF membrane with a three-dimensional mesh interface, as described in this application, is carried out entirely at room temperature. First, utilizing the unstable properties of ZIF-67, a large-area, defect-free α-Co(OH)₂ nanosheet mesh layer is formed on the surface of a polymer support. Because the α-Co(OH)₂ mesh layer exhibits hydrophobic properties, a suitable water-to-methanol ratio during preparation can effectively solve the swelling problem of the polymer support, further leveraging the pre-embedded metal effect of the mesh layer to enhance heterogeneous nucleation at the interface layer, enabling the preparation of different types of MOF membranes on the polymer support. Furthermore, based on the two-dimensional α-Co(OH)₂ mesh layer, a three-dimensional MOF membrane is prepared on the two-dimensional structure using a gradient volume mutual phase diffusion method, achieving a continuous and dense MOF membrane combining two-dimensional and three-dimensional structures. Moreover, the prepared membrane exhibits excellent separation selectivity for different gas systems.

[0127] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a continuous MOF membrane with a three-dimensional mesh interface, wherein the base membrane of the continuous MOF membrane is formed by laminating a polymer support layer, a polysulfone layer, and a nonwoven fabric layer arranged sequentially from top to bottom, characterized in that, The polymer support layer is a polydimethylsiloxane layer, and the preparation method includes the following steps: S1. After the PVA-cobalt ion aqueous solution is diffused from the polydimethylsiloxane layer into the base film, the first ligand solution is diffused from the nonwoven fabric layer into the base film to coordinate with the cobalt ions in the PVA-cobalt ion aqueous solution, forming an α-Co(OH)2 grid layer on the surface of the polydimethylsiloxane layer, thus obtaining a film with an α-Co(OH)2 grid layer. S2. The membrane with the α-Co(OH)2 grid layer is immersed in a metal salt solution to fix the metal ions in the metal salt solution onto the α-Co(OH)2 grid layer. After being removed and dried, it is then immersed in a second ligand solution to react and obtain the continuous MOF membrane with the three-dimensional grid interface.

2. The preparation method according to claim 1, characterized in that, Step S1 is as follows: The polydimethylsiloxane layer of the base film is suspended and fixed with the top facing up. The PVA-cobalt ion aqueous solution is poured into the polydimethylsiloxane layer and soaked for 30-50 minutes. Then, it is moved horizontally into the first ligand solution and soaked for 10-60 seconds. After taking it out, it is washed and dried.

3. The preparation method according to claim 1, characterized in that, In step S2, the soaking in the second ligand solution specifically involves immersing the polydimethylsiloxane layer face down in the second ligand solution for 3-6 hours.

4. The preparation method according to claim 1, characterized in that, The solvent for the first ligand solution is methanol or ethanol.

5. The preparation method according to claim 1, characterized in that, The ligand in the first ligand solution is 2-methylimidazole.

6. The preparation method according to claim 1, characterized in that, The metal salt solution is a cobalt salt solution or a zinc salt solution, and the ligand in the second ligand solution is 2-methylimidazole; or, The metal salt solution is a copper salt solution, and the ligand in the second ligand solution is pyromellitic acid.

7. The preparation method according to claim 6, characterized in that, The solvent for the metal salt solution is a mixture of a highly polar solvent and water, wherein the highly polar solvent is methanol or ethanol.

8. The preparation method according to claim 7, characterized in that, The volume ratio of the highly polar solvent to water is 1:(1-4).

9. A continuous MOF membrane with a three-dimensional mesh interface prepared by the preparation method according to any one of claims 1-8.

10. The application of the continuous MOF membrane with a three-dimensional mesh interface as described in claim 9 in gas separation.

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