Large-area (100) oriented metal organic framework ZIF-8 film as well as preparation method and application thereof

Abstract

The invention provides a large-area (100) oriented metal organic framework ZIF-8 film as well as a preparation method and application thereof. Specifically, the method comprises the following steps: enabling at least part of the surface of a graphite substrate to be in contact with a ZIF-8 film synthesis solution containing Zn < 2 + > and 2-methylimidazole, enabling the Zn < 2 + > to react with the 2-methylimidazole, and forming the ZIF-8 alignment film on the graphite substrate. The ZIF-8 oriented film prepared by the method disclosed by the invention is uniform and compact, is highly oriented and has high H2 selective separation performance.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation material preparation, specifically relating to a method for synthesizing metal-organic framework membranes widely used in gas separation. In particular, it provides a method for rapidly preparing large-area metal-organic framework ZIF-8 membranes with uniform density, high orientation, and excellent H2 / CO2, H2 / CH4, and H2 / C3H8 separation performance at room temperature by inducing the membrane on a graphite substrate. Background Technology

[0002] Driven by the demand for gas filtration in the chemical and petrochemical industries, the demand for gas separation membranes is constantly increasing due to their high efficiency and low cost. Separating hydrogen from gaseous mixtures or impurities using gas separation membranes is crucial in various chemical processes and production. In the early stages of membrane separation technology development, many polymer materials, such as polyimide, polysulfone, and polycarbonate, were applied to gas separation membranes. However, due to the trade-off effect, a mutual inhibition between gas selectivity and gas permeability often occurs, limiting their application in gas separation. Compared to organic polymer membranes, novel inorganic membranes, such as molecular sieve membranes, typically possess advantages such as higher thermal and chemical stability and higher permeation flux. However, most molecular sieve membranes develop defects in the solution during high-temperature treatment to remove the template agent, affecting their separation performance. Therefore, developing novel, highly efficient hydrogen separation membranes is of great significance.

[0003] Metal-organic framework (MOF) membranes possess advantages such as high porosity, high specific surface area, tunable pore size, and diverse structures, thus holding great potential for hydrogen separation. Zeolite imidazolate framework-8 (ZIF-8) membranes are among the pioneering MOF membranes for gas separation, achieving groundbreaking separation performance exceeding the "Robeson upper limit." ZIF-8 exhibits a sodalite (SOD) topology with a pore size of 0.34 nm. The fabrication of defect-free ZIF-8 membranes is quite challenging due to the poor heterogeneous nucleation of ZIF-8 on the support surface. Furthermore, to reduce intergranular defects, ZIF-8 membranes are typically tens of micrometers thick, resulting in significant resistance to gas permeation. Therefore, the fabrication of dense, defect-free, and highly oriented ultrathin ZIF-8 membranes is crucial for their gas separation performance. Summary of the Invention

[0004] The purpose of this invention is to provide a large-area metal-organic framework (ZIF-8) oriented membrane and its preparation method, aiming to solve the technical problem of separating H2 / CO2, H2 / CH4, and H2 / C3H8 mixed gases. The preparation method utilizes the adsorption effect generated by van der Waals interactions and π-π interactions between 2-methylimidazole and the graphite surface to promote the uniform nucleation of ZIF-8 on the graphite substrate surface. In a high-concentration 2-methylimidazole solution, ZIF-8 crystals grow rapidly along the (100) direction, resulting in a uniform, dense, highly oriented ZIF-8 membrane with high H2 selective separation performance. The separation of H2 / CO2, H2 / CH4, and H2 / C3H8 mixed gases is achieved through the molecular sieving effect of the ZIF-8 membrane.

[0005] In a first aspect, the present invention provides a method for preparing a metal-organic framework (ZIF-8) oriented film, the method comprising the steps of:

[0006] At least a portion of the surface of a graphite substrate is exposed to a Zn-containing substrate. 2+ Contact with the ZIF-8 membrane synthesis solution of 2-methylimidazole, so that Zn 2+ It reacts with 2-methylimidazole to form a ZIF-8 oriented film on the graphite substrate.

[0007] In another preferred embodiment, the solvent of the ZIF-8 membrane synthesis solution is water.

[0008] In another preferred embodiment, the Zn 2+ Salts or their hydrates selected from the group consisting of zinc acetate, zinc nitrate, zinc sulfate, zinc chloride, or combinations thereof.

[0009] In another preferred embodiment, the ZIF-8 membrane synthesis solution contains Zn 2+ The molar concentration is 0.005-0.2 mol / L, preferably 0.008-0.15 mol / L, and even more preferably 0.01-0.1 mol / L, such as 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, 0.035 mol / L, 0.04 mol / L, 0.045 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.8 mol / L, 0.09 mol / L, or 0.1 mol / L.

[0010] In another preferred embodiment, the molar concentration of 2-methylimidazole in the ZIF-8 membrane synthesis solution is 0.1-2 mol / L, more preferably 0.2-1.8 mol / L, and even more preferably 0.3-1.5 mol / L, such as 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, or 1.7 mol / L.

[0011] In another preferred embodiment, the ZIF-8 membrane synthesis solution contains Zn 2+ The molar ratio of 2-methylimidazole to 1:(1-150), preferably 1:(5-120), and even more preferably 1:(10-110)mol / L, such as 1:20, 1:30, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100, or 1:105.

[0012] In another preferred embodiment, the ZIF-8 membrane synthesis solution is a Zn-containing solution. 2+ It is obtained by mixing an aqueous solution and a 2-methylimidazole aqueous solution.

[0013] In another preferred embodiment, the reaction temperature is 4-40°C, more preferably 25±5°C.

[0014] In another preferred embodiment, the reaction time is 30 min to 6 h, more preferably 1 to 4 h, and even more preferably 2 to 3 h.

[0015] In another preferred embodiment, the graphite substrate is washed with deionized water and methanol (e.g., 2-3 times each) before use and then dried (drying at 50-60°C for 6-12 hours).

[0016] In another preferred embodiment, after the reaction is complete, the graphite substrate (and film) is removed and the surface is washed with deionized water and methanol (e.g., 2-3 times each) and dried (e.g., at 50-60°C for 6-24 hours).

[0017] In another preferred embodiment, the thickness of the graphite substrate is 10-100 μm, more preferably 20-80 μm, more preferably 40-60 μm, such as 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm.

[0018] In another preferred embodiment, the ZIF-8 oriented film has a high (100) orientation, or is substantially (100) oriented.

[0019] In another preferred embodiment, the thickness of the ZIF-8 orientation film is 500-1000 nm, more preferably 600-800 nm.

[0020] In another preferred embodiment, the ZIF-8 membrane has a membrane area of ​​100-1000 cm². 2 The ideal height is 400-800cm. 2 500-600cm is even better 2 .

[0021] A second aspect of the present invention provides a metal-organic framework ZIF-8 oriented film prepared as described in the first aspect of the present invention, wherein the metal-organic framework ZIF-8 oriented film is attached to at least a portion of the surface of the graphite substrate.

[0022] In another preferred embodiment, the ZIF-8 oriented film has a high (100) orientation, or is substantially (100) oriented.

[0023] In another preferred embodiment, the thickness of the ZIF-8 orientation film is 500-1000 nm, more preferably 600-800 nm.

[0024] In another preferred embodiment, the ZIF-8 membrane has a membrane area of ​​100-1000 cm². 2 The ideal height is 400-800cm. 2 500-600cm is even better 2 .

[0025] In another preferred embodiment, the thickness of the graphite substrate is 10-100 μm, more preferably 20-80 μm, more preferably 40-60 μm, such as 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm.

[0026] In another preferred embodiment, the area of ​​the graphite substrate is 1-2000 cm². 2 100-1000cm 2 The ideal height is 400-800cm. 2 500-600cm is even better 2 .

[0027] In a third aspect, the present invention provides an application of a metal-organic framework ZIF-8 oriented membrane as described in the second aspect of the present invention, the ZIF-8 oriented membrane being used for the separation of H2 / CO2, H2 / CH4, or H2 / C3H8 mixed gases.

[0028] In another preferred embodiment, the metal-organic framework ZIF-8 oriented film has one or more features selected from the group consisting of:

[0029] At an operating temperature of 100°C, the gas permeation flux of the ZIF-8 oriented membrane to H2 is 1.0-2.0 × 10⁻⁶. - 7 mol m -2 s -1 Pa -1 The preferred value is 1.2-1.8×10. -7 mol m -2 s -1 Pa -1 A more suitable value is 1.3-1.8×10. -7 mol m -2 s - 1 Pa -1 ;

[0030] At an operating temperature of 100℃, the separation coefficient for equimolar H2 / CO2 mixed gases is 15-21, preferably 16-20, and even more preferably 16.4-19.6.

[0031] At an operating temperature of 100°C, the separation coefficient for equimolar H2 / CH4 gas mixtures is 50-65, preferably 52-62, and even more preferably 56.3-60.5; and / or

[0032] At an operating temperature of 100℃, the separation coefficient for equimolar H2 / C3H8 mixed gases is 90-120, preferably 95-110, and even more preferably 98.5-106.8.

[0033] In a fourth aspect, the present invention provides a mixed gas separation device, which includes the metal-organic framework ZIF-8 oriented membrane of the second aspect of the present invention as a gas separation membrane; and the mixed gas is an H2 / CO2, H2 / CH4 or H2 / C3H8 mixed gas.

[0034] In a fifth aspect, the present invention provides a method for separating mixed gases, comprising the step of using the metal-organic framework ZIF-8 oriented membrane described in the second aspect of the present invention as a gas separation membrane to separate mixed gases; wherein the mixed gas is an H2 / CO2, H2 / CH4, or H2 / C3H8 mixed gas.

[0035] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here. Attached Figure Description

[0036] Figure 1 The XRD diffraction pattern of the ZIF-8 film in Example 1 of this invention;

[0037] Figure 2 This is a SEM image of the ZIF-8 membrane in Example 1 of the present invention;

[0038] Figure 3 The graph shows the permeation performance of the ZIF-8 membrane in Example 1 of this invention for single gases (H2, CO2, CH4, C3H8) and the separation performance of mixed gases H2 / CO2, H2 / CH4 and H2 / C3H8. Detailed Implementation

[0039] Through extensive and in-depth research, including numerous screenings and tests, the inventors have developed a (100) oriented large-area metal-organic framework (ZIF-8) oriented membrane, its preparation method, and its applications. This invention utilizes the van der Waals interactions and π-π interactions between 2-methylimidazole and the graphite surface to achieve adsorption. In a high-concentration 2-methylimidazole solution, ZIF-8 molecules rapidly and uniformly nucleate on the graphite substrate surface, resulting in a uniform, dense, ultrathin, oriented ZIF-8 membrane with high H2 separation performance. The ZIF-8 membrane prepared using this method achieves a gas permeation flux of 1.3-1.8 × 10⁻⁶ for H2 in the separation of H2 / CO2, H2 / CH4, and H2 / C3H8 mixed gases at an operating temperature of 100°C. -7 mol m -2 s -1 Pa -1 The separation coefficients for equimolar H2 / CO2 mixtures are 16.4-19.6, for equimolar H2 / CH4 mixtures are 56.3-60.5, and for equimolar H2 / C3H8 mixtures are 98.5-106.8. Based on these, the present invention was completed.

[0040] the term

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0042] As used herein, the terms “containing” or “including (comprise)” can be open-ended, semi-closed, or closed. In other words, the terms also include “consistently made of” or “composed of”.

[0043] As used herein, the term “room temperature” or “normal temperature” refers to a temperature of 4–40°C, preferably 25 ± 5°C.

[0044] Metal-organic framework (ZIF-8) membranes and their preparation methods

[0045] The metal-organic framework ZIF-8 membrane of the present invention refers to a membrane based on zeolite imidazolium framework-8 (ZIF-8), which is composed of zinc ions (Zn... 2+ It coordinates with 2-methylimidazole to form a porous material with high stability and an ordered pore structure, exhibiting excellent thermal and chemical stability. The pore size is approximately 0.34 nm, which is between the kinetic diameters of H2 and other small molecule gases.

[0046] In particular, the ZIF-8 membrane of the present invention uses graphite as the substrate support material, and ZIF-8 is synthesized and deposited directly on the graphite surface. Surprisingly, large-size, uniform, dense, ultra-thin oriented ((100) oriented) ZIF-8 membranes with excellent H2 separation performance can be prepared using graphite as the substrate.

[0047] One possible reason (but not limiting the present invention) is the adsorption effect produced by the van der Waals interaction and π-π interaction between 2-methylimidazole and the graphite surface. In a high concentration of 2-methylimidazole solution, ZIF-8 is uniformly and rapidly nucleated on the graphite substrate surface, thereby preparing a uniform, dense, ultrathin oriented ZIF-8 membrane with high H2 separation performance.

[0048] Specifically, this invention provides a method for preparing a metal-organic framework (ZIF-8) oriented film, the method comprising the following steps:

[0049] At least a portion of the surface of a graphite substrate is exposed to a Zn-containing substrate. 2+ Contact with the ZIF-8 membrane synthesis solution of 2-methylimidazole, so that Zn 2+ It reacts with 2-methylimidazole to form a ZIF-8 oriented film on the graphite substrate.

[0050] In this invention, Zn 2+ There are no particular restrictions on the source of zinc; various salts that can ionize zinc ions can be used, such as (but not limited to): zinc acetate, zinc nitrate, zinc sulfate, zinc chloride, or combinations thereof, which can be used in anhydrous form or in various hydrated forms thereof.

[0051] As described in this invention, "contact" can refer to partial immersion, complete immersion, single surface or multiple surfaces of the graphite substrate in contact with the film synthesis solution, as long as the substrate surface on which the formation of the ZIF-8 oriented film is desired is sufficiently impregnated with the ZIF-8 film synthesis solution and allows the formation of the ZIF-8 oriented film on it. For example, only one surface of the graphite substrate may be in contact with the ZIF-8 film synthesis solution. Preferably, the ZIF-8 film grows on both sides of the graphite substrate.

[0052] In this invention, the shape and size of the graphite substrate can be selected as needed, and preferably it is a graphite film with a horizontal surface.

[0053] In another preferred embodiment, the solvent of the ZIF-8 membrane synthesis solution is an aqueous solution, preferably water, and more preferably deionized water, double-distilled water or ultrapure water.

[0054] In another preferred embodiment, the ZIF-8 membrane synthesis solution is a Zn-containing solution. 2+ It is obtained by mixing an aqueous solution of methylimidazole and an aqueous solution of 2-methylimidazole.

[0055] In another preferred embodiment, the reaction temperature is 4-40°C, more preferably 25±5°C.

[0056] In another preferred embodiment, the reaction time is 30 min to 6 h, more preferably 1 to 4 h, and even more preferably 2 to 3 h.

[0057] In another preferred embodiment, the graphite substrate is washed with deionized water and methanol (e.g., 2-3 times each) before use and then dried (drying at 50-60°C for 6-12 hours).

[0058] In another preferred embodiment, after the reaction is complete, the graphite substrate is removed and its surface is washed with deionized water and methanol (e.g., 2-3 times each), and then dried (e.g., at 50-60°C for 6-24 hours). At this point, the graphite substrate and the ZIF-8 film are not separated, and the final ZIF-8 film includes the graphite substrate.

[0059] In another preferred embodiment, the thickness of the graphite substrate is 10-100 μm, more preferably 20-80 μm, more preferably 40-60 μm, such as 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm or 100 μm.

[0060] According to the electron microscope images, the ZIF-8 oriented film has a high (100) orientation, or is substantially (100) oriented.

[0061] According to the electron microscope images, the thickness of the ZIF-8 oriented film is approximately 500-1000 nm, preferably 600-800 nm. The ZIF-8 film grows on both sides immersed in the reaction solution; the film thickness here refers to the thickness of the ZIF-8 film on one side.

[0062] In this invention, the membrane area of ​​the ZIF-8 membrane can be adjusted as needed, for example, from 100 to 1000 cm². 2 The ideal height is 400-800cm. 2 500-600cm is even better 2 .

[0063] The present invention also provides a metal-organic framework ZIF-8 oriented film prepared by the above method.

[0064] In particular, the ZIF-8 oriented film of the present invention has a high (100) orientation, or is substantially (100) oriented. Herein, a (100) oriented film refers to a thin film crystal structure in which a certain crystal plane is arranged parallel to a certain direction of the substrate, while in the present invention, the ZIF-8 crystal structure is substantially perpendicular to the surface of the graphite substrate.

[0065] In another preferred embodiment, the thickness of the ZIF-8 orientation film is 500-1000 nm, more preferably 600-800 nm.

[0066] In another preferred embodiment, the method of the present invention can prepare large-area films, thus the size of the film can be selected as needed. Typically, the size of the film depends on the size of the graphite substrate. Those skilled in the art will understand that the size and shape of the ZIF-8 oriented film of the present invention can be controlled by adjusting the size and shape of the graphite substrate, particularly the portion of the graphite substrate in contact with the ZIF-8 film synthesis solution. For example, the area of ​​the ZIF-8 film is 100-1000 cm². 2 The ideal height is 400-800cm. 2 500-600cm is even better 2 .

[0067] More specifically, the metal-organic framework (MOR) ZIF-8 oriented film of the present invention comprises the graphite substrate as a carrier of the film. The MORZ-8 oriented film is attached to at least a portion of the surface of the graphite substrate. Preferably, the MORZ-8 oriented film covers both sides of the horizontal graphite substrate.

[0068] application

[0069] The metal-organic framework ZIF-8 oriented membrane of the present invention exhibits high selectivity and high permeability for H2, and therefore can be used to separate mixtures of H2 and other gases, such as H2 with CO2, or mixtures of lower hydrocarbons. More preferably, it can be used to separate H2 / CO2, H2 / CH4, or H2 / C3H8 mixtures.

[0070] Experiments have shown that, at an operating temperature of 100℃, the gas permeation flux of the ZIF-8 oriented membrane to H2 is 1.3-1.8 × 10⁻⁶. -7 mol m -2 s -1 Pa -1 The separation coefficients for equimolar H2 / CO2 mixtures are 16.4-19.6, for equimolar H2 / CH4 mixtures are 56.3-60.5, and for equimolar H2 / C3H8 mixtures are 98.5-106.8.

[0071] This demonstrates that the ZIF-8 oriented membrane of the present invention has excellent separation performance for H2 / CO2, H2 / CH4 and H2 / C3H8 mixed gases.

[0072] Gas separation methods and apparatus

[0073] The present invention also provides a mixed gas separation device, characterized in that it includes the metal-organic framework ZIF-8 oriented membrane described in the present invention as a gas separation membrane. Preferably, the mixed gas is an H2 / CO2, H2 / CH4, or H2 / C3H8 mixed gas.

[0074] The membrane of this invention is applicable to general gas separation apparatuses conforming to the Wicke-Kallenbach method. Typically, the gas separation membrane module of such an apparatus mainly includes a gas separation membrane and an upstream gas inlet, a choke point, and a downstream gas purge and permeate port on the module.

[0075] Furthermore, the present invention also provides a method for separating mixed gases, comprising the step of using the metal-organic framework ZIF-8 oriented membrane described in this invention as a gas separation membrane or gas separation device to separate the mixed gas. Preferably, the mixed gas is a mixture of H2 / CO2, H2 / CH4, and H2 / C3H8.

[0076] The main advantages of this invention include:

[0077] The method of this invention can rapidly prepare large-area ZIF-8 membranes that are uniform, dense, highly oriented, and exhibit high H2 selective separation performance at room temperature. Furthermore, the molecular sieving effect of the ZIF-8 membranes prepared by the method of this invention enables efficient separation of H2 / CO2, H2 / CH4, and H2 / C3H8 gas mixtures, thus providing a new approach for separating H2 from mixed gases.

[0078] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Percentages and parts are by weight unless otherwise stated.

[0079] Example 1

[0080] ZIF-8 membranes are prepared as follows.

[0081] Step 1: Wash the surface of the 50μm thick graphite substrate three times each with deionized water and methanol, and dry it at 60℃ for 12h.

[0082] Step 2: Dissolve 5.5g of zinc acetate dihydrate in 300mL of deionized water and sonicate until clear; dissolve 123.0g of 2-methylimidazole in 1500mL of deionized water and sonicate until clear; mix the two solutions to obtain the synthesis solution of ZIF-8 membrane.

[0083] Step 3: Immerse the graphite substrate in the ZIF-8 membrane synthesis solution and react at room temperature for 2 hours. After the reaction is complete, remove the graphite substrate, wash the surface of the graphite substrate three times each with deionized water and methanol, and then dry it at room temperature for 24 hours.

[0084] Example 2

[0085] ZIF-8 membranes are prepared as follows.

[0086] Step 1: Same as Step 1 in Example 1.

[0087] Step 2: Dissolve 5.5g of zinc acetate dihydrate in 600mL of deionized water and sonicate until clear; dissolve 123.0g of 2-methylimidazole in 1200mL of deionized water and sonicate until clear; mix the two solutions to obtain the synthesis solution of ZIF-8 membrane.

[0088] Step 3: Immerse the graphite substrate in the ZIF-8 membrane synthesis solution and react at room temperature for 2 hours. After the reaction is complete, remove the graphite substrate, wash the surface of the graphite substrate three times each with deionized water and methanol, and then dry it at room temperature for 24 hours.

[0089] Example 3

[0090] ZIF-8 membranes are prepared as follows.

[0091] Step 1: Same as Step 1 in Example 1.

[0092] Step 2: Dissolve 1.1g of zinc acetate dihydrate in 60mL of deionized water and sonicate until clear; dissolve 24.6g of 2-methylimidazole in 300mL of deionized water and sonicate until clear; mix the two solutions to obtain the synthesis solution of ZIF-8 membrane.

[0093] Step 3: Immerse the graphite substrate in the ZIF-8 membrane synthesis solution and react at room temperature for 3 hours. After the reaction is complete, remove the graphite substrate, wash the surface of the graphite substrate three times each with deionized water and methanol, and then dry it at room temperature for 24 hours.

[0094] Example 4

[0095] ZIF-8 membranes are prepared as follows.

[0096] Step 1: Same as Step 1 in Example 1.

[0097] Step 2: Dissolve 1.5g of zinc nitrate hexahydrate in 60mL of deionized water and sonicate until clear; dissolve 24.6g of 2-methylimidazole in 300mL of deionized water and sonicate until clear; mix the two solutions to obtain the synthesis solution of ZIF-8 membrane.

[0098] Step 3: Immerse the graphite substrate in the ZIF-8 membrane synthesis solution and react at room temperature for 2 hours. After the reaction is complete, remove the graphite substrate, wash the surface of the graphite substrate three times each with deionized water and methanol, and then dry it at room temperature for 24 hours.

[0099] Example 5

[0100] ZIF-8 membranes are prepared as follows.

[0101] Step 1: Same as Step 1 in Example 1.

[0102] Step 2: Dissolve 0.7g of anhydrous zinc chloride in 60mL of deionized water and sonicate until clear; dissolve 24.6g of 2-methylimidazole in 300mL of deionized water and sonicate until clear; mix the two solutions to obtain the synthesis solution of ZIF-8 membrane.

[0103] Step 3: Immerse the graphite substrate in the ZIF-8 membrane synthesis solution and react at room temperature for 2 hours. After the reaction is complete, remove the graphite substrate, wash the surface of the graphite substrate three times each with deionized water and methanol, and then dry it at room temperature for 24 hours.

[0104] Example 6

[0105] ZIF-8 membranes are prepared as follows.

[0106] Step 1: Same as Step 1 in Example 1.

[0107] Step 2: Dissolve 1.1g of zinc acetate dihydrate in 60mL of deionized water and sonicate until clear; dissolve 41.0g of 2-methylimidazole in 300mL of deionized water and sonicate until clear; mix the two solutions to obtain the synthesis solution of ZIF-8 membrane.

[0108] Step 3: Immerse the graphite substrate in the ZIF-8 membrane synthesis solution and react at room temperature for 3 hours. After the reaction is complete, remove the graphite substrate, wash the surface of the graphite substrate three times each with deionized water and methanol, and then dry it at room temperature for 24 hours.

[0109] Example 7:

[0110] Characterization of ZIF-8 film

[0111] The crystal structure of the ZIF-8 film was analyzed using X-ray diffraction (XRD, Bruker D8 ADVANCE).

[0112] Figure 1 XRD pattern of the ZIF-8 film prepared according to the present invention; compared with the XRD pattern of the simulated ZIF-8 crystal, the ZIF-8 film prepared according to the present invention has a high (100) orientation. All ZIF-8 films prepared in Examples 1-6 have similar results, and the obtained ZIF-8 films all exhibit strong diffraction peaks only on the (100) crystal plane.

[0113] The microstructure of the ZIF-8 film was characterized using cold field emission scanning electron microscopy (SEM, S-4800).

[0114] Figure 2 SEM image of the ZIF-8 membrane prepared in this invention; by Figure 2 As can be seen, the ZIF-8 film is uniform and dense, with a thickness of approximately 620 nm. The ZIF-8 films prepared in Examples 1-6 all exhibit similar morphologies.

[0115] Example 8: Gas separation performance test of ZIF-8 membrane

[0116] The gas separation performance of the ZIF-8 membrane was evaluated as follows: The prepared ZIF-8 membrane was placed on a porous alumina support and sealed in a permeation cell. The Wicke-Kallenbach method was used to investigate the separation performance of the ZIF-8 membrane for single gases (H2, CO2, CH4, C3H8) and mixed gases (H2 / CO2, H2 / CH4, H2 / C3H8). Feed gases (H2, CO2, CH4, C3H8) and purge gases (N2) were introduced from the upstream feed side and downstream permeation side of the ZIF-8 membrane, respectively, with each gas flow rate maintained at 50 mL / min. -1The concentrations of each permeate gas component were monitored using a mass flow controller. A calibrated gas chromatograph (Agilent 7820A) was used to detect the concentrations of each permeate gas component. Purge gas N2 was used to provide the driving force for the downstream permeate-side gas to enter the gas chromatograph for detection. The mixed gas separation performance of the ZIF-8 membrane was evaluated by the H2 flux and the H2 / CO2, H2 / CH4, and H2 / C3H8 mixed gas separation coefficients. The binary mixed gas separation coefficient (α) is calculated by dividing the molar ratio of the permeate components (i, j) by the molar ratio of the retained components (i, j), expressed as α. i / j The separation factor, y, represents the permeation of a binary gas mixture. i,Perm Let y be the amount of substance of the permeating component i gas. j,Perm Let y be the amount of substance of the permeating component j gas. i,Ret To determine the amount of substance of component i gas to be retained, y j,Ret The amount of substance of component j gas that is retained.

[0117] At an operating temperature of 100°C, the ZIF-8 oriented membrane prepared in the above examples has a gas permeation flux of 1.3-1.8 × 10⁻⁶ for H₂. -7 mol m -2 s -1 Pa -1 The separation coefficients for equimolar H2 / CO2 mixtures are 16.4-19.6, for equimolar H2 / CH4 mixtures are 56.3-60.5, and for equimolar H2 / C3H8 mixtures are 98.5-106.8, which are much higher than the Knudsen diffusion coefficients of the corresponding mixtures, demonstrating excellent H2 selective separation performance.

[0118] Table 1 shows the separation performance of ZIF-8 membrane for H2 / CH4 mixed gases as reported in the literature.

[0119] base [H2 flux] <![CDATA[H2 / CH4 separation factor]]> References ZIF-8 membrane Polysulfone <![CDATA[4.7x 10 -9 ]]> 17.2 [1] ZIF-8 membrane PVDF <![CDATA[1.6x 10 -6 ]]> 12.1 [2] ZIF-8 membrane <![CDATA[Al2O3-ZnO]]> <![CDATA[1.8x 10 -6 ]]> 12.9 [3] ZIF-8 membrane AAO disc <![CDATA[8.3x 10 -6 ]]> 16.2 [4] ZIF-8 membrane <![CDATA[α-Al2O3]]> <![CDATA[1.84x 10 -7 ]]> 21.4 [5] ZIF-8 membrane Alumina <![CDATA[1.0x 10 -7 ]]> 17 [6]

[0120] Taking the separation of H2 / CH4 mixed gases with equal molar ratios as an example, compared with the ZIF-8 membrane reported in the literature, the ZIF-8 oriented membrane prepared in the above embodiment has significant advantages in both the gas permeation flux of H2 and the separation coefficient of H2 / CH4 mixed gases with equal molar ratios.

[0121] References:

[0122] [1]F.Cacho-Bailo,S.Catalán-Aguirre,M.Etxeberría-Benavides,O.Karvan,V.Sebastian,C.Téllez,J.Coronas,Metal-organic framework membranes on theinner-side of a polymeric hollow fiber by microfluidic synthesis,J.Membr.Sci.476(2015)277-285.

[0123] [2]M.R.Abdul Hamid,H.-K.Jeong,Flow synthesis of polycrystalline ZIF-8membranes on polyvinylidene fluoride hollow fibers for recovery of hydrogenand propylene,J.Ind.Eng.Chem.88(2020)319-327.

[0124] [3]X.Wang,M.Sun,B.Meng,X.Tan,J.Liu,S.Wang,S.Liu,Formation ofcontinuous and highly permeable ZIF-8membranes on porous alumina and zincoxide hollow fibers,Chem.Commun.52(2016)13448-13451.

[0125] [4]G.He,M.Dakhchoune,J.Zhao,S.Huang,K.V.Agrawal,ElectrophoreticNuclei Assembly for Crystallization of High-Performance Membranes onUnmodified Supports,Adv.Funct.Mater.28(2018)1707427.

[0126] [5] C. Zhang, J. Yan, T. Ji, D. Du, Y. Sun, L. Liu,

[0127] [6]H.Bux,A.Feldhoff,J.Cravillon,M.Wiebcke,Y.-S.Li,J.Caro,Orientedzeolitic imidazolate framework-8membrane with sharp H2 / C3H8 molecular sieveseparation,Chem.Mater.23(2011)2262-2269.

[0128] All documents mentioned in this invention are incorporated herein by reference as if each document were individually incorporated by reference. Furthermore, it should be understood that after reading the foregoing teachings of this invention, those skilled in the art can make various alterations or modifications to this invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a metal-organic framework (ZIF-8) oriented film, characterized in that, The method includes the following steps: At least a portion of the surface of a graphite substrate is exposed to a Zn-containing substrate. 2+ Contact with the ZIF-8 membrane synthesis solution of 2-methylimidazole, so that Zn 2+ It reacts with 2-methylimidazole to form a ZIF-8 oriented film on the graphite substrate.

2. The method as described in claim 1, characterized in that, The method has one or more technical features selected from the group consisting of: The solvent for the ZIF-8 membrane synthesis solution is water; The Zn 2+ Salts or their hydrates selected from the group consisting of: zinc acetate, zinc nitrate, zinc sulfate, zinc chloride, or combinations thereof; In the ZIF-8 membrane synthesis solution, Zn 2+ The molar concentration is 0.005-0.2 mol / L; In the ZIF-8 membrane synthesis solution, the molar concentration of 2-methylimidazole is 0.1-2 mol / L; In the ZIF-8 membrane synthesis solution, Zn 2+ The molar ratio of 2-methylimidazole is 1:(1-150); and / or The thickness of the graphite substrate is 10-100 μm.

3. The method as described in claim 1, characterized in that, The method has one or more technical features selected from the group consisting of: The ZIF-8 membrane synthesis solution is prepared by using a Zn-containing solution. 2+ It is obtained by mixing an aqueous solution and a 2-methylimidazole aqueous solution; The reaction temperature is 4-40℃; The reaction time is 30 min to 6 h; The graphite substrate was washed with deionized water and methanol respectively before use and then dried. After the reaction was complete, the graphite substrate was removed and its surface was washed with deionized water and methanol, respectively, and then dried.

4. The method as described in claim 1, characterized in that, The method has one or more technical features selected from the group consisting of: The ZIF-8 oriented film is essentially (100) oriented; The thickness of the ZIF-8 alignment film is 500-1000 nm; and / or The ZIF-8 membrane has a membrane area of ​​100-1000 cm². 2 .

5. A metal-organic framework ZIF-8 oriented film prepared as claimed in claim 1, wherein the metal-organic framework ZIF-8 oriented film is attached to at least a portion of the surface of the graphite substrate.

6. The metal-organic framework ZIF-8 oriented film as described in claim 5, characterized in that, The metal-organic framework ZIF-8 oriented film has one or more technical features selected from the group consisting of: The ZIF-8 oriented film is essentially (100) oriented; The thickness of the ZIF-8 orientation film is 500-1000 nm; The ZIF-8 membrane has a membrane area of ​​100-1000 cm². 2 ; and / or The thickness of the graphite substrate is 10-100 μm.

7. The metal-organic framework ZIF-8 oriented film as described in claim 5, characterized in that, The metal-organic framework ZIF-8 oriented film has one or more technical features selected from the group consisting of: At an operating temperature of 100°C, the gas permeation flux of the ZIF-8 oriented membrane to H2 is 1.0-2.0 × 10⁻⁶. -7 mol m - 2 s -1 Pa -1 The preferred value is 1.2-1.8×10. -7 mol m -2 s -1 Pa -1 A more suitable value is 1.3-1.8×10. -7 molm -2 s -1 Pa -1 ; At an operating temperature of 100℃, the separation coefficient for equimolar H2 / CO2 mixed gases is 15-21, preferably 16-20, and even more preferably 16.4-19.

6. At an operating temperature of 100°C, the separation coefficient for equimolar H2 / CH4 gas mixtures is 50-65, preferably 52-62, and even more preferably 56.3-60.5; and / or At an operating temperature of 100℃, the separation coefficient for equimolar H2 / C3H8 mixed gases is 90-120, preferably 95-110, and even more preferably 98.5-106.

8.

8. An application of the metal-organic framework ZIF-8 oriented film according to any one of claims 5-7, characterized in that, The ZIF-8 oriented membrane is used for the separation of H2 / CO2, H2 / CH4, or H2 / C3H8 mixed gases.

9. A mixed gas separation device, characterized in that, It includes the metal-organic framework ZIF-8 oriented membrane of any one of claims 5-7 as a gas separation membrane; and the mixed gas is an H2 / CO2, H2 / CH4 or H2 / C3H8 mixed gas.

10. A method for separating mixed gases, characterized in that, The method includes the step of using the metal-organic framework ZIF-8 oriented membrane of any one of claims 5-7 as a gas separation membrane to separate a mixed gas; and the mixed gas is an H2 / CO2, H2 / CH4 or H2 / C3H8 mixed gas.

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