A high permeability ZIF-67 separation membrane, preparation method and application
By performing steam activation and reverse diffusion on two-dimensional MOF nanosheet stacking layers, the problem of low ZIF-67 crystal nucleus density was solved, and a high-permeability and high-flux ZIF-67 membrane was prepared, achieving efficient separation of H2 and CO2.
Patent Information
- Application Number
- CN202410997969.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-24
- Publication Date
- 2025-10-03
- Estimated Expiration
- 2044-07-24
Smart Images
Figure CN118663095B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of gas separation and relates to a high-permeability ZIF-67 separation membrane, a preparation method and an application thereof. Background Art
[0002] Currently, we still rely heavily on traditional fossil energy, which produces large amounts of greenhouse gases (CO2, CH4, etc.), causing a serious greenhouse effect. The most common method for industrially producing H2 is the water-gas process, where carbon and water react at high temperatures to produce CO2 and H2. Therefore, the separation of hydrogen and carbon dioxide is of great significance. Common methods for gas separation include physical adsorption, chemical absorption, cryogenic separation, and membrane separation. Among them, membrane separation technology has attracted widespread attention in the field of gas separation due to its advantages such as being environmentally friendly, low energy consumption, no phase change, and easy coupling.
[0003] Common microporous materials include zeolite molecular sieves, carbon nanotubes, and metal-organic frameworks (MOFs). MOFs are network structures formed by connecting transition metals with organic ligands, and have advantages such as high porosity, large specific surface area, adjustable pore structure, high gas permeability, and selectivity. Since the kinetic diameter of H2 is 0.289nm, the long diameter of CO2 is 0.55nm, and the short diameter is 0.33nm, ZIF-67, as a MOF material, has a pore diameter of 0.34nm, which is between H2 and CO2. ZIF-67 is also relatively rigid and has no breathing effect. Therefore, ZIF-67 can be used for the separation of H2 and CO2. However, ZIF-67 is prone to homogeneous nucleation, making heterogeneous nucleation difficult, resulting in high film formation difficulty. The counter-diffusion method has the characteristics of self-limiting growth. Its three independent preparation steps (i.e., pre-diffusion, nucleation, and crystallization) make the formation of MOF crystal films more controllable, facilitate heterogeneous nucleation, and reduce intercrystalline defects. However, this method generally suffers from the problem of low crystal nucleus density.
[0004] The secondary growth method is often used to solve the problem of low nucleus density, using seed crystals to provide a metal source, and then provide nucleation sites for the crystals. At present, common seed crystal materials are mainly graphene oxide and porous MOF. However, the airtight structure of graphene oxide will seriously hinder the permeation of gas; using porous MOF as a seed crystal can not only provide sufficient nucleation sites, but also have good gas permeability. However, the deposition of porous MOF seed crystals will undoubtedly increase the membrane thickness and reduce the gas flux. Since two-dimensional MOF nanosheets not only have nanometer-scale thickness, but also have high specific surface area and chemical tunability, they help to achieve MOF membranes with both high selectivity and high permeability. Therefore, two-dimensional MOF nanosheets are selected as seeds.
[0005] Currently, the difficulty of heterogeneous nucleation of ZIF-67 is primarily addressed by the counter-diffusion method. However, this method suffers from a low nucleus density. Therefore, the present invention proposes a method for preparing a high-permeability ZIF-67 separation membrane. This method constructs a two-dimensional MOF stack of a specific thickness and activates the stack using steam activation, providing nucleation sites for subsequent counter-diffusion growth of a ZIF-67 crystal membrane, ultimately forming a continuous, defect-free ZIF-67 separation membrane. Under conditions of a specific seed crystal thickness, the membrane exhibits a uniform honeycomb morphology, which not only ensures the membrane's mechanical strength but also reduces concentration polarization during the separation process. This method achieves excellent gas separation performance and has promising prospects for industrial application. Summary of the Invention
[0006] In response to the problems existing in the prior art, the present invention provides a high-permeability ZIF-67 separation membrane, a preparation method and an application thereof. The method can prepare a high-flux, high-permeability ZIF-67 membrane.
[0007] In order to achieve the above object, the technical solution adopted in the present invention is:
[0008] A method for preparing a high-permeability ZIF-67 separation membrane comprises the following steps:
[0009] Step 1: Prepare a stacked layer of Co-containing nanosheets with a total thickness of 100-150 nm on a substrate in the form of a film.
[0010] Step 2: Steam activation of the Co nanosheet stack using a petri dish
[0011] The culture dish used is divided into two parts, the bottom and the lid. The submicron-scale Co-containing nanosheet stacking layer is divided into two sides, the front side is the nanosheet and the back side is the substrate. The prepared submicron-scale Co-containing nanosheet stacking layer is facing up (that is, the substrate layer of the submicron-scale Co-containing nanosheet stacking layer is attached to the inner surface of the culture dish lid) and pasted to the inside of the culture dish lid. The organic ligand 2-methylimidazole is placed at the bottom of the culture dish. The culture dish is transferred to a forced air drying oven at 80-120°C and activated for 0.5-1.5h to obtain a steam-activated submicron-scale Co-containing nanosheet stacking layer. In this step, the high temperature causes the 2-methylimidazole to change from a solid state to a gaseous state, thereby contacting the submicron-scale Co-containing nanosheet stacking layer in the culture dish lid. The nitrogen in the 2-methylimidazole successfully coordinates with the Co in the nanosheet, providing heterogeneous nucleation active sites.
[0012] Step 3: Prepare reaction solution A
[0013] A cobalt source (as a metal ion) was added to a methanol solution and stirred at room temperature until fully dissolved to prepare a methanol solution A containing the metal source.
[0014] Step 4: Prepare reaction solution B
[0015] 2-Methylimidazole was added to the methanol solution and stirred at room temperature until fully dissolved to prepare a methanol solution B containing an organic ligand.
[0016] Step 5: Anti-diffusion
[0017] (1) The submicron-scale Co-containing nanosheet stack layer after the second step of steam activation is placed in the middle of the H-type reactor to assemble the H-type reactor.
[0018] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor, respectively, with the front of the nanosheet stacking layer facing the metal source solution and the back facing the organic ligand solution; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:1 to 1:9.
[0019] (3) After being transferred to a forced air drying oven at 20-80°C and reacting for 3-24 hours, a ZIF-67 membrane is obtained. The reaction process of this step is as follows: the submicron-scale Co-containing nanosheet stacking layer can provide heterogeneous nucleation active sites after steam activation, and the metal source in the reaction solution A preferentially coordinates with the 2-methylimidazole ligand on the surface of the stacking layer. The metal cobalt source and 2-methylimidazole are located on both sides of the nanosheet stacking layer and diffuse in the opposite direction. By regulating the molar ratio of metal ions to organic ligands and their concentration in methanol solution, the reverse diffusion reaches a dynamic equilibrium. Subsequently, ZIF-67 can heterogeneously nucleate and grow at the interface, and finally form a continuous defect-free ZIF-67 membrane.
[0020] (4) After cooling, washing and drying, soak it in methanol solution for 1-12 hours.
[0021] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0022] Furthermore, in the first step, the submicron-scale Co-containing nanosheet stacking layer substrate includes α-Al2O3, PES, PTFE, PVDF, and PP.
[0023] Furthermore, in the second step, the stacking layer is activated by steam activation, and the surface area of the stacking layer is 19.6 cm 2 , add 6.09-36.5 mmol of organic ligand 2-methylimidazole.
[0024] Furthermore, the cobalt source in the third step includes cobalt nitrate hexahydrate, cobalt chloride, and cobalt sulfate.
[0025] Furthermore, in the third step, the concentration of the metal source in the methanol solution A is 0.023 mol / L.
[0026] Furthermore, in the fourth step, 1.1-9.9 mmol of an organic ligand 2-methylimidazole is added to the methanol solution, and the concentration of the organic ligand 2-methylimidazole in the methanol solution B is 0.044-0.396 mol / L.
[0027] A high-permeability and high-flux ZIF-67 membrane, wherein the ZIF-67 membrane material is a composite structure formed by secondary growth of ZIF-67 on a cobalt-containing nanosheet stacking layer, wherein the cobalt-containing nanosheet is an ultra-thin porous submicron-level Co-containing nanosheet stacking layer. The ultra-thin porous submicron-level Co-containing nanosheet stacking layer has an ultra-low mass transfer resistance to gas molecules, ensuring a high gas permeability of the composite membrane and providing nucleation sites for the growth of the ZIF-67 membrane. At the same time, the reverse diffusion method has a self-limiting growth mechanism, which can effectively regulate the growth of ZIF-67, easily achieve heterogeneous nucleation growth, and reduce intercrystalline defects. At the same time, the permeability and selectivity of the membrane are taken into account, and the honeycomb morphology formed not only ensures the mechanical strength of the membrane, but also weakens the concentration polarization phenomenon in the separation process. At the same time, the honeycomb hollow structure reduces the gas transmission resistance, thereby obtaining a high-permeability and high-permeability ZIF-67 membrane, thereby achieving excellent gas separation performance.
[0028] The invention discloses an application of a preparation method of a high-permeability ZIF-67 separation membrane, characterized in that it is used for efficient separation of H2 / CO2.
[0029] The beneficial effects of the present invention are:
[0030] (1) The experimental device of the present invention is an H-type reactor, which is easy to assemble; and the chemicals used in the experimental process are less toxic, which is an environmentally friendly reaction.
[0031] (2) In the method of the present invention, a reverse diffusion method is used to secondary grow ZIF-67 on the stacked layer of cobalt-containing nanosheets to form a composite structure, that is, the secondary growth seed method is combined with the reverse diffusion method. The seed method cleverly solves the problem of low crystal nucleus density existing in the reverse diffusion method.
[0032] (3) The method of the present invention uses cobalt-containing nanosheets as seed crystals, controls the stacking layer thickness to be 100-150 nm, and uses 6.09-36.5 mmol 2-methylimidazole vapor activation to provide a large number of active sites for the reverse diffusion process.
[0033] (4) The method of the present invention not only ensures the continuity of the ZIF-67 membrane and reduces the intercrystalline gap, but also takes into account the permeability and selectivity of the membrane. The honeycomb morphology formed not only ensures the mechanical strength of the membrane, but also weakens the concentration polarization phenomenon during the separation process. At the same time, the honeycomb hollow structure reduces the gas transmission resistance, thereby obtaining a high permeability and high permeability ZIF-67 membrane, thereby achieving excellent gas separation performance. The method has low raw material cost and simple experimental operation. BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Figure 1(a) is a SEM image of a cobalt-containing nanosheet; Figure 1(b) is an AFM image of a cobalt-containing nanosheet; Figure 1(c) is a graph showing the thickness variation of the cobalt-containing nanosheet;
[0035] Figure 2 This is the XRD pattern of the submicron-scale Co nanosheet stacking layer and the steam-activated stacking layer;
[0036] Figure 3(a) is an XPS overall graph of a steam-activated submicron-scale Co-containing nanosheet stacking layer; Figure 3(b) is an XPS graph of Co 2p of a steam-activated submicron-scale Co-containing nanosheet stacking layer; Figure 3(c) is an XPS graph of C1s of a steam-activated submicron-scale Co-containing nanosheet stacking layer; Figure 3(d) is an XPS graph of N1s of a steam-activated submicron-scale Co-containing nanosheet stacking layer;
[0037] Figure 4 Schematic diagram of the H-type reactor for preparing ZIF-67 membrane by counter-diffusion.
[0038] Figure 5 is the FT-IR image of the ZIF-67 membrane prepared by reverse diffusion;
[0039] Figure 6 is the XRD pattern of ZIF-67 membrane prepared by reverse diffusion;
[0040] Figure 7(a) is a surface SEM image of the ZIF-67 membrane prepared by reverse diffusion; Figure 7(b) is a cross-sectional SEM image of the ZIF-67 membrane prepared by reverse diffusion;
[0041] Figure 8 This is a diagram of the permeation flux of H2 and CO2 and the separation performance of H2 / CO2 of ZIF-67 membranes prepared at different temperatures at 0.1 bar. DETAILED DESCRIPTION
[0042] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.
[0043] Example 1
[0044] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0045] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0046] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0047] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were used for centrifugation 3 times and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1. (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 hours, the cobalt-containing nanosheets were deposited on the surface of the PES substrate by suction filtration, and allowed to stand for 3 hours. After the membrane was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 100 nm was obtained.
[0048] Step 2: Steam Activation
[0049] The prepared submicron Co-containing nanosheet stacking layer was inverted on the upper surface of the inner part of the culture dish, and 6.09 mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the inner part of the culture dish. After being transferred to an 80°C forced air drying oven and activated for 0.5 h, a steam-activated submicron Co-containing nanosheet stacking layer was obtained.
[0050] Step 3: Prepare reaction solution A
[0051] 0.023 mmol of cobalt chloride was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0052] Step 4: Prepare reaction solution B
[0053] 0.044 mmol of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0054] Step 5: Anti-diffusion
[0055] (1) The steam-activated submicron Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble the H-type reactor.
[0056] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and the methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:1.
[0057] (3) After transferring to room temperature of 20°C and reacting for 3 h, a ZIF-67 membrane was obtained.
[0058] (4) After cooling, washing and drying, soak it in methanol solution for 1 hour.
[0059] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0060] Furthermore, in the fifth step, the concentration of cobalt chloride in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.0018 mol / L.
[0061] The H2 flux of the obtained ZIF-67 membrane was 9×10 -7 mol·m -2 ·s -1 ·Pa -1 , the H2 / CO2 selectivity is 4.7.
[0062] Example 2
[0063] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0064] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0065] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0066] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were centrifuged three times each and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1.
[0067] (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 h, the nanosheets were deposited onto the surface of the PTFE substrate by suction filtration and allowed to stand for 3 h. After the membrane was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 120 nm was obtained.
[0068] Step 2: Steam Activation
[0069] The prepared submicron Co-containing nanosheet stacking layer was inverted on the upper surface of the inner part of the culture dish, and 12.18 mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the inner part of the culture dish. After being transferred to a forced air drying oven at 100°C and activated for 1 hour, a steam-activated submicron Co-containing nanosheet stacking layer was obtained.
[0070] Step 3: Prepare reaction solution A
[0071] 0.165 g of cobalt sulfate was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0072] Step 4: Prepare reaction solution B
[0073] 0.135 g of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0074] Step 5: Anti-diffusion
[0075] (1) The steam-activated submicron Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble the H-type reactor.
[0076] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and the methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:3.
[0077] (3) After transferring to room temperature at 40°C for 10 h, a ZIF-67 membrane was obtained.
[0078] (4) After cooling, washing and drying, soak it in methanol solution for 6 hours.
[0079] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0080] Furthermore, in the fifth step, the concentration of cobalt sulfate in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.066 mol / L.
[0081] The H2 flux of the obtained ZIF-67 membrane was 8.4×10 -7 mol·m -2 ·s -1 ·Pa -1 , the H2 / CO2 selectivity is 5.9.
[0082] Example 3
[0083] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0084] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0085] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0086] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were centrifuged three times each and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1.
[0087] (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 h, they were deposited onto the surface of a PVDF substrate by suction filtration and allowed to stand for 3 h. After the membrane was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 130 nm was obtained.
[0088] Step 2: Steam Activation
[0089] The prepared submicron Co-containing nanosheet stacking layer was inverted on the upper surface of the inner part of the culture dish, and 18.27 mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the inner part of the culture dish. After being transferred to a forced air drying oven at 110°C and activated for 1 hour, a steam-activated submicron Co-containing nanosheet stacking layer was obtained.
[0090] Step 3: Prepare reaction solution A
[0091] 0.165 g of cobalt nitrate hexahydrate was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0092] Step 4: Prepare reaction solution B
[0093] 0.27 g of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0094] Step 5: Anti-diffusion
[0095] (1) The steam-activated submicron Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble the H-type reactor.
[0096] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and a methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:6.
[0097] (3) After transferring to room temperature of 80°C and reacting for 16 h, a ZIF-67 membrane was obtained.
[0098] (4) After cooling, washing and drying, soak it in methanol solution for 12 hours.
[0099] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0100] Furthermore, in the fifth step, the concentration of cobalt nitrate hexahydrate in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.132 mol / L.
[0101] The H2 flux of the obtained ZIF-67 membrane was 6.1×10 -7 mol·m -2 ·s -1 ·Pa -1 , H2 / CO2 selectivity is 5.0.
[0102] Example 4
[0103] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0104] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0105] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0106] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were centrifuged three times each and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1.
[0107] (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 h, they were deposited onto the surface of the PP substrate by suction filtration and allowed to stand for 3 h. After the film was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 150 nm was obtained.
[0108] Step 2: Steam Activation
[0109] The prepared submicron Co-containing nanosheet stacking layer was inverted on the upper surface of the inner part of the culture dish, and 36.5 mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the inner part of the culture dish. After being transferred to a forced air drying oven at 120°C and activated for 1.5 hours, a steam-activated submicron Co-containing nanosheet stacking layer was obtained.
[0110] Step 3: Prepare reaction solution A
[0111] 0.165 g of cobalt nitrate hexahydrate was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0112] Step 4: Prepare reaction solution B
[0113] 0.405 g of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0114] Step 5: Anti-diffusion
[0115] (1) The steam-activated submicron Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble the H-type reactor.
[0116] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and the methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:9.
[0117] (3) After transferring to room temperature of 80°C and reacting for 24 h, a ZIF-67 membrane was obtained.
[0118] (4) After cooling, washing and drying, soak it in methanol solution for 12 hours.
[0119] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0120] Furthermore, in the fifth step, the concentration of cobalt nitrate hexahydrate in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.198 mol / L.
[0121] The H2 flux of the obtained ZIF-67 membrane was 9×10 -6 mol·m -2 ·s -1 ·Pa -1 , the H2 / CO2 selectivity is 4.2.
[0122] Example 5
[0123] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0124] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0125] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0126] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were centrifuged three times each and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1.
[0127] As shown in Figure 1(a) and (b), the prepared cobalt-containing nanosheets have an ultra-thin structure. As shown in Figure 1(c), the film thickness is 5 nm and the size is about 350 nm, which is suitable for the preparation of stacked layers.
[0128] (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 h, they were deposited onto the surface of an a-Al2O3 substrate by suction filtration and allowed to stand for 3 h. After the film was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 100 nm was obtained.
[0129] Step 2: Steam Activation
[0130] The prepared 100 nm thick Co-containing nanosheet stacking layer was inverted on the upper surface of the inside of the culture dish, and 18.3 mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the inside of the culture dish. After being transferred to a forced air drying oven at 120°C and activated for 1 hour, a steam-activated submicron Co-containing nanosheet stacking layer was obtained.
[0131] like Figure 2 As shown, it can be seen that the XRD peak position of the obtained Co-containing nanosheets is consistent with the standard peak, and the XRD peak position of the stacking layer after steam activation matches the XRD peak position of the standard ZIF-67, indicating that ZIF-67 seeds are formed on the surface of the stacking layer after steam activation.
[0132] As shown in the full XPS spectrum of Figure 3 (a) (b) (c) (d), compared with the unactivated Co-containing nanosheet stacking layer, the activated Co-containing nanosheet stacking layer has a new N1s characteristic peak. The N1s spectrum shows a Co-N characteristic peak at 400.3 eV, indicating that the Hmim ligand has successfully coordinated with the metallic Co on the surface of the Co-containing nanosheet. Correspondingly, the C1s spectrum of the activated Co-MOF shows a C=N characteristic peak introduced by the Hmim ligand. The above analysis fully proves that during the activation stage of the stacking layer, the coordination effect between water and Co can be destroyed at 120°C, allowing Hmim to form a coordination effect with Co, thereby introducing ZIF-67 seeds on the surface of the Co-containing nanosheet stacking layer, providing the necessary active sites for the subsequent growth of ZIF-67.
[0133] Step 3: Prepare reaction solution A
[0134] 0.165 g of cobalt nitrate hexahydrate was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0135] Step 4: Prepare reaction solution B
[0136] 0.27 g of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0137] Step 5: Anti-diffusion
[0138] (1) The steam-activated submicron-scale Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble an H-type reactor, such as Figure 4 shown.
[0139] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and a methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:6.
[0140] (3) After transferring to a forced air drying oven at 50°C for 10 h, a ZIF-67 membrane was obtained.
[0141] (4) After cooling, washing and drying, soak it in methanol solution for 12 hours.
[0142] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane, as shown in Figure 7(a)(b). The FT-IR spectrum ( Figure 5 ) and XRD spectra ( Figure 6 ) confirmed that the honeycomb morphology crystal membrane was ZIF-67 membrane.
[0143] Furthermore, in the fifth step, the concentration of cobalt nitrate hexahydrate in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.132 mol / L.
[0144] The H2 flux of the obtained ZIF-67 membrane was 1.6×10 -7 mol·m -2 ·s -1 ·Pa -1 , H2 / CO2 selectivity is 17.
[0145] like Figure 8 As shown in the figure, it can be found that the ZIF-67 membrane prepared at 50 °C has the best gas separation performance, with stable flux and separation selectivity.
[0146] Comparison of the stacking layer thickness between Comparative Example 1 and Example 5
[0147] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0148] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0149] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0150] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were centrifuged three times each and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1.
[0151] (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 h, they were deposited onto the surface of an a-Al2O3 substrate by suction filtration and allowed to stand for 3 h. After the film was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 200 nm was obtained.
[0152] Step 2: Steam Activation
[0153] The prepared 200 nm thick Co-containing nanosheet stacking layer was inverted on the upper surface of the inside of the culture dish, and 18.3 mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the inside of the culture dish. After being transferred to a forced air drying oven at 120°C and activated for 1 hour, a steam-activated submicron Co-containing nanosheet stacking layer was obtained.
[0154] Step 3: Prepare reaction solution A
[0155] 0.165 g of cobalt nitrate hexahydrate was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0156] Step 4: Prepare reaction solution B
[0157] 0.27 g of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0158] Step 5: Anti-diffusion
[0159] (1) The steam-activated submicron Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble the H-type reactor.
[0160] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and a methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:6.
[0161] (3) After transferring to a forced air drying oven at 50°C for 10 h, a ZIF-67 membrane was obtained.
[0162] (4) After cooling, washing and drying, soak it in methanol solution for 12 hours.
[0163] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0164] Furthermore, in the fifth step, the concentration of cobalt nitrate hexahydrate in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.132 mol / L.
[0165] The H2 flux of the obtained ZIF-67 membrane was 3.6×10 -8 mol·m -2 ·s -1 ·Pa -1 , H2 / CO2 selectivity is 10.
[0166] Under the condition of a 200 nm thick Co nanosheet stacking layer, the membrane thickness was increased by prolonging the growth time to compensate for the non-selective defects, but the permeation flux was greatly reduced and the gas selectivity was also reduced.
[0167] Comparative Example 2 is compared with Example 5 regarding the amount of 2-methylimidazole used in steam activation
[0168] Step 1: Preparation of submicron-scale Co-containing nanosheet stacks
[0169] (1) Cobalt nitrate was added to N,N-dimethylformamide (DMF) solution and stirred at room temperature until fully dissolved to prepare reaction solution 1. 0.26 mmol of cobalt nitrate hexahydrate was added to every 10 mL of N,N-dimethylformamide (DMF) solution.
[0170] (2) Add terephthalic acid, water, ethanol, and triethylamine to an N,N-dimethylformamide (DMF) solution and stir at room temperature until fully dissolved to prepare reaction solution 2. 0.29 mmol of terephthalic acid, 2 mL each of water, ethanol, and triethylamine were added to every 10 mL of the N,N-dimethylformamide (DMF) solution.
[0171] (3) The reaction solution 1 was slowly dripped into the reaction solution 2, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, N, N-dimethylformamide and anhydrous ethanol were centrifuged three times each and then dried (the centrifuge speed was 10000 r / min, the centrifugation time was 10 minutes, the drying temperature was 60 ° C, and the drying time was 12 hours to obtain cobalt-containing nanosheets. The volume ratio of the reaction solution A to the reaction solution B was 1:1.
[0172] (4) The prepared cobalt-containing nanosheets were dispersed in a n-propanol solution, wherein 0.2 mg of cobalt-containing nanosheets were added to every 30 mL of n-propanol solution; after ultrasonic dispersion for 6 h, they were deposited onto the surface of an a-Al2O3 substrate by suction filtration and allowed to stand for 3 h. After the film was dried, a submicron-scale Co-containing nanosheet stacking layer with a thickness of 100 nm was obtained.
[0173] Step 2: Steam Activation
[0174] The prepared 100nm thick Co nanosheet stack was placed upside down on the upper surface of the culture dish, and 0mmol of the organic ligand 2-methylimidazole was placed on the lower surface of the culture dish. After being transferred to a 120℃ forced air drying oven for activation for 1h, a steam-activated submicron Co nanosheet stack was obtained. Step 3: Prepare reaction solution A
[0175] 0.165 g of cobalt nitrate hexahydrate was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution A.
[0176] Step 4: Prepare reaction solution B
[0177] 0.27 g of 2-methylimidazole was added to 25 mL of methanol solution and stirred at room temperature until fully dissolved to prepare reaction solution B.
[0178] Step 5: Anti-diffusion
[0179] (1) The steam-activated submicron Co-containing nanosheet stack is placed in the middle of an H-type reactor to assemble the H-type reactor.
[0180] (2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-type reactor respectively, and a methanol solution A containing a metal source Co is placed on the stacking layer side; wherein the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source to the organic ligand is 1:6.
[0181] (3) After transferring to a forced air drying oven at 50°C for 10 h, a ZIF-67 membrane was obtained.
[0182] (4) After cooling, washing and drying, soak it in methanol solution for 12 hours.
[0183] (5) The ZIF-67 membrane is then taken out and dried to obtain a continuous, defect-free ZIF-67 membrane.
[0184] Furthermore, in the fifth step, the concentration of cobalt nitrate hexahydrate in the methanol solution A is 0.023 mol / L; the concentration of 2-methylimidazole in the methanol solution B is 0.132 mol / L.
[0185] The H2 flux of the obtained ZIF-67 membrane was 2.1×10 -6 mol·m -2 ·s -1 ·Pa -1 , the H2 / CO2 selectivity is 5.3.
[0186] Under the condition of unactivated submicron-sized Co nanosheet stacking layers, the membrane thickness was increased by prolonging the growth time to compensate for the non-selective defects, but the permeation flux increased significantly and the gas selectivity decreased.
[0187] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.
Claims
1. A method for preparing a high permeability ZIF-67 separation membrane, characterized in that: The method controls the thickness of the stacked layer of Co-containing nanosheets to be submicron-level, and then prepares a honeycomb ZIF-67 crystal film through a "steam activation-reverse diffusion" coupling process. The steps are as follows: The first step is to prepare a stacked layer of Co-containing nanosheets on a substrate in a film-like form to obtain a submicron-scale stacked layer of Co-containing nanosheets; Step 2: Steam activation of the Co-containing nanosheet stacking layer at an activation temperature of 80-120°C. The high temperature causes 2-methylimidazole to change from solid to gaseous state and contact the submicron-sized Co-containing nanosheet stacking layer to obtain a steam-activated submicron-sized Co-containing nanosheet stacking layer. Step 3: preparing a methanol solution A containing a metal source; Step 4: preparing a methanol solution B containing an organic ligand; Step 5: Counter-diffusion. The methanol solution A containing the metal source and the methanol solution B containing the organic ligand are located on both sides of the nanosheet stacking layer and diffuse in the opposite direction. ZIF-67 heterogeneously nucleates and grows at the interface to obtain a ZIF-67 film.
2. The method for preparing a high permeability ZIF-67 separation membrane according to claim 1, wherein The following steps are involved: The first step is to prepare a Co-containing nanosheet stacking layer with a total thickness of 100-150 nm on a substrate in a film-like state, thereby obtaining a submicron-scale Co-containing nanosheet stacking layer; Step 2: Steam-activating the Co-containing nanosheet stacking layer to obtain a steam-activated submicron Co-containing nanosheet stacking layer; The submicron-sized Co-containing nanosheet stacking layer has two sides, the front side being the nanosheets and the back side being the substrate. The submicron-sized Co-containing nanosheet stacking layer is affixed face-up to the inside of a Petri dish lid. The organic ligand 2-methylimidazole is placed at the bottom of the Petri dish. The Petri dish is then transferred to a forced air drying oven for activation, yielding a steam-activated submicron-sized Co-containing nanosheet stacking layer. Step 3: Add the cobalt source to the methanol solution and stir until fully dissolved to obtain a methanol solution A containing the metal source; Step 4: Add 2-methylimidazole to the methanol solution and stir until fully dissolved to obtain a methanol solution B containing an organic ligand; Step 5: Anti-phase diffusion; (5.1) The submicron-sized Co-containing nanosheet stack after the second step of steam activation is placed in the middle of the H-type reactor to assemble the H-type reactor; (5.2) A methanol solution A containing a metal source and a methanol solution B containing an organic ligand are placed at the two ends of an H-shaped reactor, with the front side of the nanosheet stack facing the metal source solution and the back side facing the organic ligand solution. (5.3) After transferring to a forced air drying oven for reaction, a ZIF-67 membrane was obtained; (5.4) After cooling, washing and drying, it is immersed in a methanol solution to obtain a continuous and defect-free ZIF-67 membrane.
3. The method for preparing a high permeability ZIF-67 separation membrane according to claim 2, wherein In the first step, the substrate of the submicron-scale Co-containing nanosheet stacking layer is α-Al2O3, PES, PTFE, PVDF or PP.
4. The method for preparing a high permeability ZIF-67 separation membrane according to claim 2, wherein In the second step, the culture dish is transferred to a forced air drying oven at 80-120°C for activation for 0.5-1.5h; in the second step, the stacking layer is activated by steam activation, and the surface area of the stacking layer is 19.6 cm 2 , add 6.09-36.5 mmol of organic ligand 2-methylimidazole.
5. The method for preparing a high permeability ZIF-67 separation membrane according to claim 2, wherein In the third step, the cobalt source is cobalt nitrate hexahydrate, cobalt chloride, or cobalt sulfate; in the third step, the concentration of the metal source in the methanol solution A is 0.023 mol / L; in the fourth step, the concentration of the organic ligand 2-methylimidazole in the methanol solution B is 0.044-0.396 mol / L.
6. The method for preparing a high permeability ZIF-67 separation membrane according to claim 2, wherein: In the fifth step: In the above (5.2), the volume ratio of methanol solution A to methanol solution B is 1:1, and the molar ratio of the metal source in methanol solution A to the organic ligand in methanol solution B is 1:1 to 1:9; In the above (5.3), the mixture is transferred to a forced air drying oven at 20-80°C and reacted for 3-24 hours to obtain a ZIF-67 membrane; In the above (5.4), the soaking time is 1-12 h.
7. A high permeability ZIF-67 separation membrane, characterized in that The high permeability ZIF-67 separation membrane is prepared by the preparation method described in any one of claims 1 to 6.
8. A high permeability ZIF-67 separation membrane according to claim 7, characterized in that, The ZIF-67 membrane material is a composite structure formed by secondary growth of ZIF-67 on a cobalt-containing nanosheet stacking layer, wherein the cobalt-containing nanosheet is an ultra-thin porous submicron-scale Co-containing nanosheet stacking layer.
9. The use of a high permeability ZIF-67 separation membrane according to claim 7, characterized in that: It is used for H2 / CO2 separation.