A kind of MOF glass and its preparation method and application

Abstract

The application provides a MOF glass as well as a preparation method and application thereof, belongs to the technical field of MOF materials, and provides the preparation method of the MOF glass, which comprises the following steps: S1, mixing a solvent, a soluble metal salt and a first ligand to form a first solution; S2, adding a second ligand into the first solution to form a precursor solution after mixing; S3, using the precursor solution to dip coat a carrier, and then heating the dip-coated carrier at 50-200 DEG C for 10-60 min to prepare a MOF glass film; or, directly heating the precursor solution at 50-200 DEG C for 10-60 min to prepare a MOF glass powder. In the synthesis process of the MOF glass, the halogenated imidazole ligand is introduced, so that the glass transition temperature of the MOF is greatly reduced, and finally the MOF glass is prepared by one-step method, and the method has the advantages of simple film forming condition, low preparation cost and excellent product performance.

Description

Technical Field

[0001] This invention relates to the field of MOF material technology, and more specifically, to a MOF glass, its preparation method, and its application. Background Technology

[0002] MOF glass films are important derivatives of MOF materials, possessing advantages such as absence of intergranular defects, permanent porosity, and ease of processing. Currently, MOF glass films are mainly prepared through melt-quenching methods. For example, Chinese invention patent application CN110975648A discloses a method for preparing a metal-organic framework glass film by heating a crystalline metal-organic framework material to its melting temperature at a rate of 1~15℃ / min and then allowing it to cool naturally. Chinese invention patent application CN117225211A discloses a method for preparing a metal-organic framework glass film by melt-quenching a crystalline film, followed by heating and cooling. The principle of the above preparation methods is that after the polycrystalline film melts at a high temperature, a glass film is formed during the cooling process. However, the preparation of the above glass films requires heating the polycrystalline film to a molten state, which consumes a large amount of energy. Therefore, how to reduce the energy cost required for glass film preparation has become a new technical problem.

[0003] Currently, there are related technologies used to reduce the energy cost of MOF glass membranes. For example, Chinese invention patent application CN119015912A discloses a fluorinated modified MOF glass membrane, which is prepared by contacting the MOF membrane with fluorine-containing ligand vapor. The preparation temperature of the MOF glass membrane in this process is only 60~100℃, which can greatly reduce the energy cost of the glass membrane. However, the film formation time of this method is long, usually more than 24 hours, and the final MOF glass membrane is an amorphous structure membrane with poor gas selectivity. Summary of the Invention

[0004] The purpose of this invention is to provide a MOF glass with low energy cost and short film formation time.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for preparing MOF glass, comprising the following steps:

[0006] S1: A first solution is formed by mixing a solvent, a soluble metal salt, and a first ligand, wherein the soluble metal salt is a zinc salt and / or a cobalt salt, the first ligand is a halogen-free imidazole ligand, and the solvent is an aqueous solution of N,N-dimethylacetamide.

[0007] S2: Add the second ligand to the first solution, mix and form a precursor solution. The second ligand is a halogenated imidazole ligand.

[0008] S3: After dip-coating the carrier with the precursor liquid, heat the dip-coated carrier at 50~200℃ for 10~60min to obtain MOF glass film; or, directly heat the precursor liquid at 50~200℃ for 10~60min to obtain MOF glass powder.

[0009] This invention provides a highly efficient and energy-saving MOF glass preparation process. MOF glass is prepared by low-temperature heating (50-200℃) to impregnate a carrier or by directly heating the precursor solution, effectively avoiding the high-temperature crystallization step (above 300℃) required in traditional MOF glass production, thus significantly reducing energy consumption and operational complexity. Furthermore, this method eliminates solvent exchange or mechanical pressing steps, achieving one-step synthesis of MOF glass and simplifying the preparation process. MOF glass films prepared using this method ensure continuous and dense film layers, avoiding cracks or defects, and providing a foundation for high uniformity and reliability in subsequent gas separation applications.

[0010] Furthermore, the precursor liquid system provided by this invention optimizes the reaction system. The strong electronegativity of the halogenated imidazole ligand weakens the metal-organic bond energies such as Zn-N and Co-N bonds, lowers the glass transition temperature to below 200°C, and promotes rapid amorphous phase formation. The role of the halogen-free imidazole ligand is to assist in stabilizing the structure.

[0011] The present invention prepares the precursor solution through a two-step method of steps S1 and S2. Step S1 first mixes a solvent, a soluble metal salt and a first ligand. The soluble metal salt and the first ligand can undergo a nucleation reaction to form crystal nuclei. After the crystal nuclei are formed, a second ligand is added. The second ligand can modify the surface of the crystal nuclei and partially replace the first ligand to form a mixed ligand, which can modify the pore size of the film.

[0012] Preferably, the halogen-free imidazole ligand is selected from any one or more of imidazole-2-carboxaldehyde, 2-methylimidazolium, benzimidazole, 2-aminobenzimidazole, 2-nitroimidazolium, and 4-methylimidazolium-5-carboxaldehyde.

[0013] This invention, through the aforementioned halogen-free imidazole ligands, enables flexible control of the chemical environment of MOF glasses. The halogen-free ligands provide steric hindrance and hydrogen bonding capabilities, reducing crystal framework growth, assisting in the induction of amorphous states, and ensuring high density of the film layer during rapid formation at low temperatures. Simultaneously, the halogen-free imidazole ligands can synergistically work with haloimidazole ligands to prevent impurity formation, enhance the thermal stability of MOF glasses, and provide durability assurance for practical industrial applications.

[0014] Preferably, the halogenated imidazole ligand is selected from any one or more of fluorobenzimidazole, difluoromethylimidazolium, difluoromethylbenzimidazole, trifluoromethylimidazolium, trifluoromethylbenzimidazole, 4,5-dichloroimidazolium, 4-chloroimidazolium, 2-bromobenzimidazole, and 4-bromo-1-H-imidazolium.

[0015] Compared with the prior art, the present invention utilizes the strong electronegativity of the above-mentioned halogenated imidazole ligands to weaken the metal-organic bond energy, simultaneously reduce the glass transition temperature and induce the formation of an amorphous phase, so that the precursor solution can be directly converted into a continuous and dense glassy film within 10 to 60 minutes. It has the advantages of simple preparation process, can be synthesized in one step at low temperature in a short time, and the preparation process is simple.

[0016] Taking the preparation of MOF glass films using difluoromethylimidazolium as an example, the difluoromethylimidazolium molecule has a difluoromethyl group, which gives the second ligand a very strong electron-withdrawing ability. In the preparation method provided by this invention, the strong electronegativity of the difluoromethyl group can attract electrons, reduce the electron density on the imidazolium ring, thereby weakening the coordination bond strength between the coordination site in the imidazolium ring and the metal ion. As a result, the weakening of the coordination bond energy reduces the overall stability of the structure, leading to a significant decrease in the glass transition temperature of the MOF. At the same time, through the bond energy weakening effect, difluoromethylimidazolium can destroy the periodicity and order of the MOF lattice, thereby preventing the long-range ordered arrangement of the crystal. Due to the low temperature and short reaction time, the molecules cannot form a stable crystal grid, but can only form a continuous and dense amorphous MOF glass film. In addition, fluorine atoms not only have strong electronegativity, but their atomic size can also enter the MOF channels to act as a "molecular ruler" and thus achieve precise control of the pore size.

[0017] Therefore, the aforementioned halogenated imidazole ligands can effectively suppress the long-range ordered arrangement of crystal frameworks, enabling the crystal frameworks to rapidly transform into amorphous MOF glass membranes below 200℃. Simultaneously, based on the pore size regulation effect of halogen atoms, amorphous MOF glass membranes can achieve precise sub-angstrom-level pore size shrinkage under the influence of halogen atoms, resulting in a smaller pore size and enhanced gas separation performance.

[0018] Preferably, the support is selected from one of α-Al2O3 support, γ-Al2O3 support, anodic aluminum oxide support, TiO2 support, and polymer support.

[0019] Preferably, the zinc salt is selected from any one or more of zinc salts containing acetate, zinc salts containing nitrate, and zinc salts containing sulfate.

[0020] Preferably, the cobalt salt is selected from any one or more of cobalt salts containing acetate, cobalt salts containing nitrate, and cobalt salts containing sulfate.

[0021] Preferably, the molar ratio of the soluble metal salt, the first ligand, water, and N,N-dimethylacetamide in the first solution is 1:(0.2~3.7):(20~200):(10~100).

[0022] Preferably, the molar ratio of the first ligand to the second ligand in the precursor solution is (0.2~3.7):(0.3~3.6).

[0023] A second aspect of the present invention provides a MOF glass prepared by the preparation method described in the first aspect.

[0024] A third aspect of the present invention provides an application of the MOF glass described in the second aspect, the application comprising using the MOF glass for the separation of a mixed gas, the mixed gas being selected from any one of a hydrogen-helium mixture, a helium-nitrogen mixture, a helium-methane mixture, a carbon dioxide-methane mixture, a carbon dioxide-nitrogen mixture, and a propylene-propane mixture.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The method for preparing MOF glass provided by the present invention weakens the metal-organic bond energy by using the strong electronegativity of the haloimidazole ligand, thereby reducing the glass transition temperature of MOF glass from 300℃ to 50~200℃. It can also avoid thermal degradation of some carriers during heating, thereby reducing the preparation cost of MOF glass.

[0027] 2. The MOF glass preparation method provided by the present invention has no solvent exchange or mechanical pressing steps, realizing one-step synthesis of MOF glass and simplifying the MOF glass preparation process;

[0028] 3. The method for preparing MOF glass provided by the present invention induces precise shrinkage of sub-angstrom-scale pores through haloimidazole ligands, thereby reducing the pore size of MOF glass and enhancing gas separation performance;

[0029] 4. The method for preparing MOF glass provided by this invention enables the preparation of MOF glass at 50~200℃, is compatible with high-temperature resistant alumina carriers and low-temperature resistant polymer carriers, and can be used for the preparation of self-supporting ultrathin glass films, glass films containing supports and glass powders. It is suitable for the separation of high-value gases such as hydrogen and carbon dioxide, and the prepared MOF glass has broad application prospects. Attached Figure Description

[0030] Figure 1 The XRD characterization results are for product M7 in Embodiment 1 of this invention;

[0031] Figure 2 The above are the SEM characterization results of product M7 in Embodiment 1 of the present invention;

[0032] Figure 3 The results of cross-sectional SEM characterization of product M7 in Embodiment 1 of the present invention;

[0033] Figure 4The XRD characterization results of product G1 in Embodiment 2 of the present invention;

[0034] Figure 5 The results of differential scanning calorimetry testing of product G1 in Embodiment 2 of the present invention;

[0035] Figure 6 The results of SEM characterization of the vitrified bulk material of product G1 in Example 2 of this invention;

[0036] Figure 7 The results of SEM characterization of the vitrified powder of product G1 in Example 2 of this invention;

[0037] Figure 8 The XRD characterization results of product M13 in Embodiment 3 of the present invention;

[0038] Figure 9 The XRD characterization results are for product M15 in Example 4 of this invention. Detailed Implementation

[0039] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0040] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0041] As described in the background section, currently, the preparation of MOF glass films by melt quenching has the drawback of high energy consumption, and existing methods for preparing MOF glass films at low temperatures have long film formation times and still have certain limitations.

[0042] In view of this, the present invention provides a method for preparing MOF glass, comprising the following steps:

[0043] S1: A first solution is formed by mixing a solvent, a soluble metal salt, and a first ligand, wherein the soluble metal salt is a zinc salt and / or a cobalt salt, the first ligand is a halogen-free imidazole ligand, and the solvent is an aqueous solution of N,N-dimethylacetamide.

[0044] S2: Add the second ligand to the first solution, mix and form a precursor solution. The second ligand is a halogenated imidazole ligand.

[0045] S3: After dip-coating the carrier with the precursor liquid, heat the dip-coated carrier at 50~200℃ for 10~60min to obtain MOF glass film; or, directly heat the precursor liquid at 50~200℃ for 10~60min to obtain MOF glass powder.

[0046] In the above embodiments, the halogen-free imidazole ligand is selected from any one or more of imidazole-2-carboxaldehyde, 2-methylimidazolium, benzimidazole, 2-aminobenzimidazole, 2-nitroimidazolium, and 4-methylimidazolium-5-carboxaldehyde.

[0047] In the above embodiments, the halogenated imidazole ligand is selected from any one or more of fluorobenzimidazole, difluoromethylimidazolium, difluoromethylbenzimidazole, trifluoromethylimidazolium, trifluoromethylbenzimidazole, 4,5-dichloroimidazolium, 4-chloroimidazolium, 2-bromobenzimidazole, and 4-bromo-1-H-imidazolium.

[0048] More specifically, the halogenated imidazole ligand is preferably any one or more of 4-trifluoromethylimidazolium, 4-chloroimidazolium, and 4-bromo-1-H-imidazolium.

[0049] In the above embodiments, the support is selected from one of α-Al2O3 support, γ-Al2O3 support, anodic aluminum oxide support, TiO2 support, and polymer support.

[0050] In the above embodiments, the zinc salt is preferably a zinc salt containing acetate and / or a zinc salt containing nitrate and / or a zinc salt containing sulfate, and the cobalt salt is preferably a cobalt salt containing nitrate and / or a cobalt salt containing acetate or / or a cobalt salt containing sulfate.

[0051] In the first solution of the above embodiment, the molar ratio of soluble metal salt, first ligand, water, and N,N-dimethylacetamide is 1:(0.2~3.7):(20~200):(10~100).

[0052] More specifically, the molar ratio of the soluble metal salt, the first ligand, water, and N,N-dimethylacetamide is 1:(0.2~1.7):(40~50):(15~25).

[0053] In the precursor solution of the above embodiments, the molar ratio of the first ligand to the second ligand is (0.2~3.7):(0.3~3.6).

[0054] More specifically, the optimal molar ratio of the first ligand to the second ligand is (0.2~1.7):(0.3~1.8).

[0055] More specifically, the heating method is selected from any one of air heating, vacuum heating, tube furnace N2 / Ar atmosphere heating, and in-vessel heating.

[0056] The MOF glass preparation method provided in the specific embodiments of the present invention weakens the metal-organic bond energy by using the strong electronegativity of haloimidazole ligands, thereby reducing the film-forming temperature of MOF glass from 300℃ to 50~200℃. This can significantly reduce the film-forming temperature of the glass and also avoid thermal degradation of some carriers during heating, thus reducing the preparation cost of MOF glass.

[0057] The MOF glass preparation method provided by this invention eliminates the need for high-temperature crystallization (above 300°C), solvent replacement, and mechanical pressing. The precursor solution can achieve in-situ conversion from liquid precursor to MOF glass within as little as 30 minutes. This technology significantly simplifies the synthesis path of MOF glass, reduces energy consumption, and improves film formation efficiency. Furthermore, the MOF glass film prepared by the above method achieves sub-angstrom-level pore size reduction, resulting in higher selectivity in gas separation.

[0058] The technical solutions of the present invention are further described below through specific embodiments. Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] In some cases, terms with their conventional meaning are defined herein for clarification or ease of reference. Such definitions should not be construed as indicating a significant difference from the conventional understanding in the art. The technical methods described or referenced herein are generally well understood and employed by those skilled in the art through conventional methods. Unless otherwise stated, the use of commercially available reagents and instruments shall be performed according to the manufacturer's instructions and parameters.

[0060] Example 1

[0061] MOF glass membranes were prepared at low temperature (the second ligand was 4-trifluoromethylimidazole).

[0062] In this embodiment, the metal salt in the precursor solution is zinc acetate dihydrate (Zn(OAc)2·2H2O), the first ligand is 2-methylimidazole, the second ligand is 4-trifluoromethylimidazole, and the solvent is an aqueous solution of N,N-dimethylacetamide. The molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and N,N-dimethylacetamide (DMAc) in the precursor solution is 1:(0.2~1.7):(0.3~1.8):45:18.

[0063] The preparation steps of the precursor solution are as follows: First, mix DMAc aqueous solution, zinc acetate dihydrate and 2-methylimidazole, stir for 10 min to obtain the first solution, add 4-trifluoromethylimidazole to the first solution, stir evenly to obtain the precursor solution.

[0064] In this embodiment, the support is α-Al2O3. After the α-Al2O3 support is immersed in the precursor solution, it is reacted in a forced-air oven at 200°C for 15 min to obtain the MOF glass membrane. The MOF glass membranes are numbered M1~M12. To ensure the accuracy of the experimental results, three products were prepared under each condition in this embodiment. Among them, products M1~M3 were prepared from the precursor solution with a molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and DMAc of 1:1.7:0.3:45:18; products M4~M6 were prepared from the precursor solution with a molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and DMAc of 1:1.1:0.9: Products were prepared from a precursor solution with a molar ratio of 45:18; products M7 to M9 were prepared from a precursor solution containing Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O, and DMAc in a molar ratio of 1:0.8:1.2:45:18; products M10 to M12 were prepared from a precursor solution containing Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O, and DMAc in a molar ratio of 1:0.5:1.5:45:18.

[0065] Products M1 to M12 were characterized by XRD and SEM, and their gas separation and permeability were measured. The XRD characterization results for product M7 are as follows: Figure 1 As shown, by Figure 1 As can be seen, after heating, the topological structure of the precursor is transformed into an amorphous MOF glass structure.

[0066] The SEM characterization results of product M7 are as follows: Figure 2 As shown. By Figure 2 As can be seen, the MOF glass film prepared by the low-temperature preparation method of this embodiment is a continuously spread glass film with a good morphology.

[0067] The cross-sectional SEM characterization results of product M7 are as follows: Figure 3 As shown, by Figure 3 As can be seen, the MOF glass film prepared by the low-temperature preparation method of this embodiment has a thin thickness of only 692.2 nm.

[0068] According to 1H NMR spectroscopy, the molar ratio of 2-methylimidazole to 4-trifluoromethylimidazole in product M1 is 1.7:0.3, in product M4 it is 1.1:0.9, in product M7 it is 0.8:1.2, and in product M10 it is 0.2:1.8. The molar ratio of 2-methylimidazole to 4-trifluoromethylimidazole in the four products is approximately the same as that in the precursor solution.

[0069] The results of carbon dioxide permeability and carbon dioxide-nitrogen selectivity measurements for products M1~M12 are shown in Table 1. As can be seen from Table 1, when the molar ratio of 2-methylimidazole and 4-trifluoromethylimidazole in the driving solution is 1.1:0.9, the MOF glass membrane prepared in this example has extremely excellent carbon dioxide / nitrogen separation performance.

[0070] Table 1

[0071]

[0072] Example 2

[0073] MOF glass powder was prepared at low temperature (the second ligand was 4-trifluoromethylimidazole).

[0074] In this embodiment, the metal salt in the precursor solution is zinc acetate dihydrate (Zn(OAc)2·2H2O), the first ligand is 2-methylimidazole, the second ligand is 4-trifluoromethylimidazole, and the solvent is an aqueous solution of N,N-dimethylacetamide. The molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and DMAc in the precursor solution is 1:0.8:1.2:45:18.

[0075] The preparation steps of the precursor solution are as follows: First, mix DMAc aqueous solution, zinc acetate dihydrate and 2-methylimidazole, stir for 10 min to obtain the first solution, add 4-trifluoromethylimidazole to the first solution, stir evenly to obtain the precursor solution.

[0076] The above precursor solution was placed in a forced-air drying oven at 200°C and reacted for 30 minutes to obtain MOF glass powder. To ensure the accuracy of the experimental results, three products were prepared under the same conditions in this embodiment, and the products were denoted as G1~G3.

[0077] XRD characterization was performed on products G1 to G3 respectively. The XRD characterization results of product G1 are as follows: Figure 4 As shown, by Figure 4 It is evident that the incorporation of 4-trifluoromethylimidazole transforms the product into an amorphous MOF glass.

[0078] Differential scanning calorimetry (DSC) was performed on product G1, and the results are as follows: Figure 5 As shown, by Figure 5 It is evident that the glass transition temperature of product G1 is 167℃, which proves that 4-trifluoromethylimidazole can act as a modifier to cause a change in the glass transition temperature, enabling it to rapidly transform into an amorphous MOF glass film below 200℃.

[0079] Product G1 was characterized by SEM, and the characterization results are as follows: Figure 6 and Figure 7 As shown, by Figure 6 and Figure 7 As can be seen, the product obtained in this embodiment is a vitrified block or vitrified powder. ¹H NMR spectroscopy analysis showed that the molar ratio of 2-methylimidazole to 4-trifluoromethylimidazole in product G1 was 0.8:1.2, which is the same as the molar ratio of 2-methylimidazole to 4-trifluoromethylimidazole in the precursor solution.

[0080] Example 3

[0081] MOF glass membranes were prepared at low temperature (the second ligand was 2-difluoromethyl-benzimidazole).

[0082] In this embodiment, the metal salt in the precursor solution is zinc acetate dihydrate (Zn(OAc)2·2H2O), the first ligand is 2-methylimidazole, the second ligand is 2-difluoromethyl-benzimidazole, and the solvent is an aqueous solution of N,N-dimethylacetamide. The molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and DMAc in the precursor solution is 1:1.4:0.6:45:18.

[0083] The preparation steps of the precursor solution are as follows: First, mix DMAc aqueous solution, zinc acetate dihydrate and 2-methylimidazole, stir for 20 min to obtain the first solution, add 2-difluoromethyl-benzimidazole to the first solution, stir evenly to obtain the precursor solution.

[0084] In this embodiment, the support is γ-Al2O3 support. After the γ-Al2O3 support is immersed in the precursor solution, it is reacted in a forced-air oven at 200°C for 15 minutes to obtain the MOF glass film. To ensure the accuracy of the experimental results, two products are prepared under the same conditions in this embodiment, and the product numbers are recorded as M13 and M14.

[0085] XRD characterization was performed on products M13 and M14. The XRD characterization results of product M13 are as follows: Figure 8 As shown, by Figure 8 It is evident that 2-difluoromethyl-benzimidazole, as a second ligand, can also transform a polycrystalline structure into an amorphous MOF glass structure.

[0086] The results of the carbon dioxide-methane selectivity and carbon dioxide permeability measurements for products M13 and M14 are shown in Table 2. As can be seen from Table 2, 2-difluorobenzimidazole can enable the modified MOF glass membrane to separate carbon dioxide-methane mixtures.

[0087] Table 2

[0088]

[0089] Example 4

[0090] MOF glass membranes were prepared at low temperature (the second ligand was 4,5-dichloroimidazole).

[0091] In this embodiment, the metal salt in the precursor solution is zinc acetate dihydrate (Zn(OAc)2·2H2O), the first ligand is 2-methylimidazole, the second ligand is 4,5-dichloroimidazole, and the solvent is an aqueous solution of N,N-dimethylacetamide. The molar ratio of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and DMAc in the precursor solution is 1:1.4:0.6:45:18.

[0092] The preparation steps of the precursor solution are as follows: First, mix DMAc aqueous solution, zinc acetate dihydrate and 2-methylimidazole, stir for 30 min to obtain the first solution, add 4,5-dichloroimidazole to the first solution, stir evenly to obtain the precursor solution.

[0093] In this embodiment, the support is γ-Al2O3 support. After the γ-Al2O3 support is immersed in the precursor solution, it is reacted in a forced-air oven at 200°C for 15 min to obtain MOF glass film. To ensure the accuracy of the experimental results, two products are prepared under the same conditions in this embodiment, and the product numbers are recorded as M15 and M16.

[0094] XRD characterization was performed on products M15 and M16. The XRD characterization results of product M15 are as follows: Figure 9 As shown, by Figure 9 It is evident that 4,5-dichloroimidazole, as a second ligand, can also transform polycrystalline structures into amorphous MOF glass structures.

[0095] The results of the carbon dioxide-methane selectivity and carbon dioxide permeability determination of products M15 and M16 are shown in Table 3. As can be seen from Table 3, 4,5-dichloroimidazole can enable the modified MOF glass membrane to separate carbon dioxide-methane mixtures.

[0096] Table 3

[0097]

[0098] Comparative Example 1

[0099] Comparison with CN119015912A:

[0100] The method for preparing MOF glass films using the preparation method disclosed in Chinese invention patent application CN119015912A includes the following steps:

[0101] Zn(OAc)2·2H2O, 2-methylimidazole, H2O and DMAc were mixed in a molar ratio of 1:1.1:45:18 to prepare a precursor solution. The α-Al2O3 support was immersed in the precursor solution for dip coating, and then heated in a forced-air oven at 200°C for 15 minutes to obtain the ZIF-8 polycrystalline film.

[0102] 0.2 g of 4-trifluoromethylimidazole was placed in a bottle, and the surface of the α-Al₂O₃ membrane was placed upside down on top of the bottle to ensure that the membrane and the ligand did not come into direct contact. The mixture was heated in a forced-air oven at 80°C for 12 hours to allow the fluorine vapor to come into full contact with the MOF membrane, thereby forming a MOF-F glass membrane.

[0103] The steam-treated MOF-F glass membrane was taken out and activated in 10 ml of chloroform for 2 hours. Then, it was vacuum activated at 100°C for 12 hours in a vacuum oven to finally obtain the fluorinated modified MOF glass membrane, which was designated as product number D1.

[0104] The total film formation time, process steps, film structure, and gas selectivity of D1 and product M7 were compared, and the results are shown in Table 4. As can be seen from Table 4, the MOF glass film prepared by the method provided in the specific embodiment of the present invention has a shorter film formation time, a simpler process, and better selectivity of carbon dioxide-nitrogen mixed gas.

[0105] Table 4

[0106]

[0107] Comparative Example 2

[0108] Comparison with CN111841333A:

[0109] The method for preparing MOF glass films using the preparation method disclosed in Chinese invention patent application CN111841333A includes the following steps:

[0110] A solution of Zn(OAc)2·2H2O, 2-methylimidazole, 4-trifluoromethylimidazole, H2O and DMAc in a molar ratio of 1:0.8:1.2:45:18 was directly mixed evenly, dip-coated, and then reacted in a forced-air oven at 200℃ for 15 min to obtain a MOF membrane, which was designated as product number D2.

[0111] The gas selectivity of D2 and product M7 was compared, and the results are shown in Table 5. As can be seen from Table 5, the preparation process of product M7 is simpler and the carbon dioxide-nitrogen selectivity is better.

[0112] Table 5

[0113]

[0114] As can be seen from the above embodiments and comparative examples, the method for preparing MOF glass films at low temperatures provided by the present invention can prepare MOF glass films with simpler steps and lower temperatures, and the prepared MOF glass films have better gas selectivity and have broad application prospects.

[0115] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing MOF glass, characterized in that, Includes the following steps: S1: A first solution is formed by mixing a solvent, a soluble metal salt, and a first ligand, wherein the soluble metal salt is a zinc salt and / or a cobalt salt, and the first ligand is a halogen-free imidazole ligand selected from any one or more of imidazole-2-carboxaldehyde, 2-methylimidazolium, benzimidazole, 2-aminobenzimidazole, 2-nitroimidazolium, and 4-methylimidazolium-5-carboxaldehyde; the solvent is an aqueous solution of N,N-dimethylacetamide; and the molar ratio of the soluble metal salt, the first ligand, water, and N,N-dimethylacetamide in the first solution is 1:(0.2~3.7):(20~200):(10~100). S2: Add a second ligand to the first solution, and mix to form a precursor solution. The second ligand is a halogenated imidazole ligand, which is selected from any one or more of fluorobenzimidazole, difluoromethylimidazolium, difluoromethylbenzimidazole, trifluoromethylimidazolium, trifluoromethylbenzimidazole, 4,5-dichloroimidazolium, 4-chloroimidazolium, 2-bromobenzimidazole, and 4-bromo-1-H-imidazolium. The molar ratio of the first ligand to the second ligand in the precursor solution is (0.2~3.7):(0.3~3.6). S3: After dip-coating the carrier with the precursor liquid, heat the dip-coated carrier at 50~200℃ for 10~60min to obtain MOF glass film; or, directly heat the precursor liquid at 50~200℃ for 10~60min to obtain MOF glass powder.

2. The preparation method according to claim 1, characterized in that, The support is selected from one of the following: α-Al2O3 support, γ-Al2O3 support, anodic aluminum oxide support, TiO2 support, and polymer support.

3. The preparation method according to claim 1, characterized in that, The zinc salt is selected from any one or more of zinc salts containing acetate, zinc salts containing nitrate, and zinc salts containing sulfate.

4. The preparation method according to claim 1, characterized in that, The cobalt salt is selected from any one or more of cobalt salts containing acetate, cobalt salts containing nitrate, and cobalt salts containing sulfate.

5. A MOF glass, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 4.

6. An application of the MOF glass according to claim 5, characterized in that, The application includes using the MOF glass for the separation of mixed gases selected from any one of hydrogen-helium mixtures, helium-nitrogen mixtures, helium-methane mixtures, carbon dioxide-methane mixtures, carbon dioxide-nitrogen mixtures, and propylene-propane mixtures.

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