A kind of MOF microsphere and its synthesis method

Abstract

The present invention discloses a MOF microsphere and a synthesis method thereof, relating to the field of material technology. The preparation method of the present invention comprises the following steps: S1, dissolving an inorganic salt with metal ions and an amino acid regulator in a solvent, and ultrasonically dissolving the mixture to form a uniform and transparent mixed solution; S2, dissolving an organic bridging ligand in a solvent, and ultrasonically dissolving the mixture to form a uniform and transparent solution; S3, pouring the solution obtained in the above step S2 into the solution obtained in step S1, mixing, and hydrothermally synthesizing the MOF microspheres. The MOF microspheres prepared by the present invention are formed by self-assembly and stacking of octahedral MOF units, transforming from a 30-80nm octahedral structure to a 0.5-3μm MOF microsphere. The microsphere material has microporous, mesoporous, and macroporous structures. The method involved in preparing the MOF microspheres of the present invention is simple, the process is safe and controllable, the prepared material has a uniform structure, a large specific surface area, good stability in aqueous and acid-base solutions, and combines the advantages of the microstructure and function of the octahedral MOF unit.

Description

Technical Field

[0001] The present invention relates to the technical field of nano and micro materials, and in particular to a method for synthesizing MOF microspheres. Background Art

[0002] Hybrid materials with high complexity have attracted widespread attention due to their open structures and diverse functions. Among them, MOFs are a class of highly crystalline hybrid porous materials with broad application prospects in chemistry and materials science. The construction principle of MOFs is achieved through coordination chemistry, where metal-containing compounds are bonded to organic ligands. Chemical and physical stimuli may affect their crystal structure, thereby providing flexibility for the diversification of MOFs, such as stretching, rotation, "breathing", shearing, interlayer / network movement and combined stacking. To date, structural transformations have mainly been achieved in the case of single crystal to single crystal transformation or self-assembly of two or more MOFs, such as ultrasmall Co-MOF nanocrystals, MOF-on-MOF heterostructures and some hybrid materials. Little attention has been paid to the design process of self-assembly of individual MOFs, and compared with the rich nanocrystal synthesis chemistry, the shape-controlled growth of MOFs has not received enough attention.

[0003] Currently, existing technologies for the self-assembly of MOF microspheres include microwave synthesis and template methods. For example, in a report on the prior art (Sarawade P, Tan H, Anjum D, et al. Size-and shape-controlled synthesis of hexagonal bipyramidal crystals and hollow self-assembled al-mof spheres [J]. ChemSusChem, 2014, 7(2): 529-535.), a method for synthesizing hollow MOF microspheres from hexagonal bipyramidal MOF units was achieved by combining microwave synthesis with solvent replacement. As another example in the prior art report (Shen K, Zhang L, Chen X, et al. Ordered macro-microporous metal-organic framework single crystals [J]. Science, 2018, 359 (6372): 206-210.), a tetradecahedral MOF with uniform size was synthesized by template self-assembly. This strategy benefited from the powerful molding effect of polystyrene nanosphere templates and dual solvent induced heterogeneous nucleation method, synergistically enabling MOFs to grow in situ in ordered voids, so that the single crystal has a directional and ordered macro-microporous structure. There is also a report on an existing technology (Hou C C, Zou L, Xu QA hydrangea-like superstructure of open carbon cages with hierarchical porosity and highly active metal sites [J]. Advanced Materials, 2019, 31 (46): 1904689.), which uses a self-template assembly strategy to induce the growth of Fe-Co nanoalloys by regulating the core-shell structure MOF to generate a carbon cage structure, thereby promoting the growth of carbon nanotubes on the surface of the carbon cage during the carbonization process. These growing carbon nanotubes will gradually connect with adjacent carbon nanoparticles, and finally prepare a class of hydrangea-like superstructure nanomaterials.

[0004] However, existing methods for synthesizing MOF microspheres through self-assembly are complex, resulting in unsatisfactory roundness, poor pore structure, and product loss and collection difficulties. Furthermore, the performance of MOF microspheres remains to be further improved. Therefore, developing new methods for synthesizing MOF microspheres is crucial for enriching MOF preparation methods and their potential applications. Summary of the Invention

[0005] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the shortcomings of the existing technology and provide a MOF microsphere and a synthesis method thereof, which achieves precise control of morphology and size while maintaining the inorganic-organic skeleton, and realizes the self-assembly synthesis of MOF microspheres spanning orders of magnitude through small-sized nano-octahedral structure MOF units. The synthesized micron-level MOF microspheres, due to their large size, greatly reduce the possibility of product loss during the recovery process. At the same time, the difference from the above-mentioned prior art is that the method used here only requires a simple traditional hydrothermal method, and secondly, the synthesis of MOF microspheres requires the use of a regulator, and the synthesized MOF microspheres are size-controllable hierarchical porous MOF microspheres.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A MOF microsphere is formed by self-assembly and stacking of octahedral MOF units; the average size of the octahedral MOF units is 30-80nm, and the average diameter of the self-assembled MOF microspheres is 0.5-3μm; the MOF microspheres constitute a microsphere material, and have a three-level pore structure of micropores, mesopores and macropores: including micropores with a pore diameter of 0.1-2nm formed between the central atoms of the MOF itself and ligands, mesopores with a pore diameter of 2-10nm formed by the stacking of regular octahedral MOFs, and macropores with a pore diameter of 50-80nm formed by the gaps between adjacent MOF microspheres.

[0008] Preferably, the average diameter of the MOF microspheres formed by self-assembly in the present invention is 0.6-3 μm.

[0009] A method for synthesizing MOF microspheres according to the present invention comprises the following steps:

[0010] Step (1): dissolving the inorganic salt and the amino acid regulator in a solvent, and ultrasonically dissolving them into a uniform and transparent mixed solution for later use;

[0011] Step (2): dissolving the organic bridging ligand in a solvent, and ultrasonically dissolving the ligand to a uniform and transparent solution for later use;

[0012] Step (3): Pour the solution obtained in the above step (2) into the mixed solution obtained in step (1) to mix, to obtain a reactant mixed solution, and synthesize MOF microspheres using a hydrothermal method.

[0013] Preferably, in step (1), the inorganic salt is at least one of copper nitrate trihydrate, ferric oxide, ferric chloride hexahydrate, zirconium tetrachloride, zirconium oxychloride octahydrate, cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt nitrate tetrahydrate, and zinc nitrate tetrahydrate; preferably, the amino acid regulator is at least one of L-glutamic acid, L-threonine, L-proline, serine, lysine, histidine, valine, and tryptophan; wherein, when the amino acid regulator is at least one of L-glutamic acid, serine, histidine, valine, and L-threonine, it is not easily dissolved in the solvent, and hydrochloric acid needs to be added to promote dissolution; preferably, the solvent is at least one of nitrogen-nitrogen dimethylformamide, nitrogen-nitrogen dimethylacetamide, and dimethyl sulfoxide; preferably, the dissolution temperature is 25-40°C, and the ultrasonic mixing time is 5-30 minutes.

[0014] Preferably, in step (2), the organic bridging ligand is at least one of terephthalic acid, biphenyl dicarboxylic acid, 2-aminoterephthalic acid, 2-cyanoterephthalic acid, 1,3,5-benzenetricarboxylic acid, and purine; preferably, the solvent is at least one of nitrogen-nitrogen dimethylformamide, dimethyl sulfoxide, and nitrogen-nitrogen dimethylacetamide; preferably, the dissolution temperature is 25-40°C, and the ultrasonic mixing time is 5-30 minutes.

[0015] Preferably, in step (3), the reactant mixed solution is dissolved and mixed uniformly by ultrasonication, MOF microspheres are synthesized by hydrothermal method, and then the product is obtained by multiple centrifugal separations, and finally self-assembled MOF microspheres are obtained by drying.

[0016] Further preferably, the ultrasonic dissolution time is 5 to 30 minutes, the reaction temperature of the hydrothermal method is 120 to 170°C, and the reaction time is 1 to 7 days; then the centrifugal speed for multiple centrifugal separations is 5000 to 10000 rpm, the separation time is 5-30 minutes, the separated product is ultrasonically cleaned with a solution, the centrifugal separation and ultrasonic cleaning are repeated at least twice, and then the separated product is soaked in a solution and centrifuged again. Finally, the separated product is dried to obtain MOF microspheres.

[0017] Further preferably, the solution used for ultrasonic cleaning is at least one of nitrogen-nitrogen dimethylformamide, nitrogen-nitrogen dimethylacetamide, dimethyl sulfoxide, ethanol, and methanol, the ultrasonic time is 5 to 30 minutes, the ultrasonic cleaning is repeated 2 to 6 times, the solution used for soaking is methanol or ethanol, the soaking time is 1 to 7 days, the centrifugal speed used for centrifugal separation is 5000 to 10000 rpm, the separation time is 5-30 minutes, and the drying temperature is 30 to 80°C.

[0018] Preferably, the molar ratio of the inorganic salt to the amino acid regulator used in step (1) is 1:5 to 1:1.

[0019] Preferably, the molar ratio of the inorganic salt used in step (1) to the organic bridging ligand used in step (2) is 1:5 to 1:1.

[0020] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0021] Compared with the prior art, the present invention has the following obvious outstanding substantial features and significant advantages:

[0022] 1. In the hydrothermal synthesis of the material of the present invention, MOF microspheres are formed by self-assembly and stacking of nano-octahedral MOF units through the regulation of a regulator, achieving growth across orders of magnitude in MOF preparation;

[0023] 2. The MOF microspheres prepared by the present invention have good stability in aqueous and acidic and alkaline solutions, while also combining the functional and microstructural advantages of the octahedral MOF unit;

[0024] 3. The method involved in preparing MOF microspheres of the present invention is simple, the process is safe and controllable, and the prepared material has a uniform structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a microscopic photograph of the MOF self-assembled microspheres in Example 1 of the present invention.

[0026] Figure 2 This is a microscopic photograph of the MOF self-assembled microspheres in Example 2 of the present invention.

[0027] Figure 3 This is a microscopic photograph of the MOF self-assembled microspheres in Example 4 of the present invention.

[0028] Figure 4 This is a microscopic photograph of the MOF self-assembled microspheres in Example 5 of the present invention.

[0029] Figure 5 This is a microscopic photograph of the MOF self-assembled microspheres in Example 7 of the present invention. DETAILED DESCRIPTION

[0030] The reagents and raw materials used in the present invention are commercially available.

[0031] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0032] The above solution is further described below with reference to specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0033] Example 1

[0034] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0035] Weigh 0.20 g of zirconium tetrachloride and 0.10 g of L-proline in a molar ratio of 1:1, add them to 12 mL of nitrogen-nitrogen dimethylformamide, dissolve them at 25°C, and ultrasonicate for 10 minutes to dissolve and mix them evenly, which is called solution A;

[0036] Then, 0.20 g of 2-cyanoterephthalic acid was added to 12 mL of nitrogen-nitrogen dimethylformamide in a molar ratio of zirconium tetrachloride to 2-cyanoterephthalic acid of 1:1, and ultrasonicated at 25°C for 10 minutes to dissolve it uniformly, which was called solution B.

[0037] Then pour B into A, ultrasonicate for 30 minutes to obtain a uniformly mixed solution, heat to 120℃ in an oil bath, react for 1 day and cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 10000rpm, 30min; then ultrasonicate with nitrogen-nitrogen dimethylformamide 3 times, 20mL each time; then ultrasonicate with ethanol 3 times, 20mL each time; after washing, soak the solid product obtained by centrifugation in ethanol at 60℃ for 12 hours, cool to room temperature and centrifuge again, dry the obtained solid sample in a drying oven at 30℃ for 12 hours to obtain self-assembled MOF microspheres with a smooth surface and a diameter of 0.6μm; there are 0.1nm micropores between the central atom and the ligand, 2nm mesopores between the stacked octahedral MOF units, and 50nm macroporous structures between the microspheres, such as Figure 1 shown.

[0038] Example 2

[0039] This embodiment is basically the same as the first embodiment, except that:

[0040] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0041] Weigh 0.20 g of ferric chloride hexahydrate and 0.27 g of lysine in a molar ratio of 2:5, add them to 12 mL of nitrogen-nitrogen dimethylacetamide, dissolve them at 30°C and ultrasonicate for 5 minutes to dissolve and mix them evenly, and then call it solution A;

[0042] Then, 0.30 g of terephthalic acid was added to 12 mL of nitrogen-nitrogen dimethylacetamide at a molar ratio of ferric chloride hexahydrate to terephthalic acid of 2:5, dissolved at 30°C and ultrasonicated for 5 minutes to make it uniformly dissolved, which was called solution B.

[0043] Then pour B into A, ultrasonicate for 25 minutes to obtain a uniformly mixed solution, heat to 130℃ in an oil bath, react for 2 days and cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 9000rpm, 5min; then ultrasonically clean it once with nitrogen-nitrogen dimethylacetamide, 20mL each time. Then ultrasonically clean it once with methanol, 20mL each time; after completion, soak the solid product obtained by centrifugation in methanol at 60℃ for 12 hours, cool to room temperature and centrifuge again, dry the obtained solid sample in a drying oven at 35℃ for 12 hours, and obtain self-assembled MOF microspheres with a smooth surface and a diameter of 1.7μm, and there are 0.5nm micropores between the central atom and the ligand, and 5nm mesopores between the stacked octahedral MOF units, such as Figure 2 shown.

[0044] Example 3

[0045] This embodiment is basically the same as the previous embodiment, with the following special features:

[0046] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0047] Weigh 0.20 g of cobalt nitrate hexahydrate and 0.23 g of tryptophan in a molar ratio of 3:5, add them to 12 mL of dimethyl sulfoxide, dissolve them at 35°C, and ultrasonicate them for 15 minutes to dissolve and mix them evenly, which is called solution A;

[0048] Then, 0.28 g of biphenyl dicarboxylic acid was added to 12 mL of dimethyl sulfoxide in a molar ratio of cobalt nitrate hexahydrate to biphenyl dicarboxylic acid of 3:5, dissolved at 35°C and ultrasonicated for 15 minutes to achieve uniform dissolution, which was called solution B.

[0049] Then, B was poured into A and sonicated for 20 minutes to obtain a homogeneous solution. The solution was heated to 140°C in an oil bath, allowed to react for 3 days, and then cooled to room temperature. The solid product was collected by centrifugation at 8000 rpm for 10 minutes. The solution was then ultrasonically cleaned twice with dimethyl sulfoxide (20 mL each time) and twice with ethanol (20 mL each time). The resulting solid product was then soaked in ethanol at 60°C for 12 hours, cooled to room temperature, and centrifuged again. The resulting solid sample was dried in a 40°C oven for 12 hours to obtain smooth, self-assembled MOF microspheres with a diameter of 1.7 μm.

[0050] Example 4

[0051] This embodiment is basically the same as the previous embodiment, with the following special features:

[0052] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0053] Weigh 0.20 g of zirconium oxychloride octahydrate and 0.15 g of L-glutamic acid in a molar ratio of 4:5, add them to 12 mL of nitrogen-nitrogen dimethylformamide, and add 0.17 mL of concentrated hydrochloric acid to assist in dissolution. Dissolve at 40°C and ultrasonicate for 20 minutes to dissolve and mix evenly, which is called solution A;

[0054] Then, according to the molar ratio of zirconium oxychloride octahydrate to 2-aminoterephthalic acid of 4:5, 0.14 g of 2-aminoterephthalic acid was added to 12 mL of nitrogen-nitrogen dimethylformamide, dissolved at 40°C and ultrasonicated for 20 minutes to make it uniformly dissolved, which was called solution B;

[0055] Then pour B into A, ultrasonicate for 25 minutes to obtain a uniformly mixed solution, heat to 130℃ in an oil bath, react for 3 days and cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 9000rpm, 10min; then ultrasonically clean it with dimethyl sulfoxide 3 times, 20mL each time. Then ultrasonically clean it with ethanol 3 times, 20mL each time; after completion, soak the solid product obtained by centrifugation in ethanol at 60℃ for 12 hours, cool to room temperature and centrifuge again, dry the obtained solid sample in a drying oven at 40℃ for 12 hours, and obtain self-assembled MOF microspheres with a smooth surface and a diameter of 1.2μm, and there are 2nm micropores between the central atom and the ligand, 10nm mesopores between the stacked octahedral MOF units, and 80nm macroporous structures between the microspheres. Figure 3 shown.

[0056] Example 5

[0057] This embodiment is basically the same as the previous embodiment, with the following special features:

[0058] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0059] Weigh 0.20 g of cobalt nitrate hexahydrate and 0.08 g of L-threonine in a molar ratio of 1:1, add them to 12 mL of nitrogen-nitrogen dimethylformamide, and add 0.11 concentrated hydrochloric acid to assist in dissolution. Dissolve at 30°C and sonicate for 25 minutes to dissolve and mix evenly, which is called solution A;

[0060] Then, 0.08 g of purine was added to 12 mL of nitrogen-nitrogen dimethylformamide at a molar ratio of 1:1 between cobalt nitrate hexahydrate and purine, dissolved at 30°C and ultrasonicated for 25 minutes to make it uniformly dissolved, which was called solution B.

[0061] Then pour B into A, ultrasonicate for 5 minutes to obtain a uniformly mixed solution, heat it in an oil bath to 140°C, react for 4 days and cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 10000rpm, 15min; then ultrasonically clean it twice with nitrogen-nitrogen dimethylformamide, 20mL each time. Then ultrasonically clean it twice with methanol, 20mL each time; after completion, soak the solid product obtained by centrifugation in ethanol at 60°C for 12 hours, cool it to room temperature and centrifuge it again, dry the obtained solid sample in a drying oven at 50°C for 12 hours, and obtain self-assembled MOF microspheres with a smooth surface and a diameter of 2.5μm, and there are 1nm micropores between the central atom and the ligand, 8nm mesopores between the stacked octahedral MOF units, and 60nm macroporous structures between the microspheres. Figure 4 shown.

[0062] Example 6

[0063] This embodiment is basically the same as the previous embodiment, with the following special features:

[0064] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0065] Weigh 0.20 g of ferric oxide and 0.97 g of histidine in a molar ratio of 1:5, add them to 12 mL of nitrogen-nitrogen dimethylformamide, and add 1.50 mL of concentrated hydrochloric acid to assist in dissolution. Dissolve at 25°C and sonicate for 30 minutes to ensure uniform dissolution and mixing, which is called solution A.

[0066] Then, 1.32 g of 1,3,5-benzenetricarboxylic acid was added to 12 mL of nitrogen-nitrogen dimethylformamide in a molar ratio of ferric oxide to 1,3,5-benzenetricarboxylic acid of 1:5, dissolved at 25°C and ultrasonicated for 30 minutes to make it uniformly dissolved, which was called solution B.

[0067] Then pour B into A, ultrasonicate for 10 minutes to obtain a uniformly mixed solution, heat to 150°C in an oil bath, react for 5 days, cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 5000rpm, 20min; then ultrasonicate with nitrogen-nitrogen dimethylacetamide once, 20mL each time; then ultrasonicate with ethanol once, 20mL each time; after completion, soak the solid product obtained by centrifugation in ethanol at 60°C for 12 hours, cool to room temperature and centrifuge again, and dry the obtained solid sample in a drying oven at 60°C for 12 hours to obtain self-assembled MOF microspheres with a smooth surface and a diameter of 2μm.

[0068] Example 7

[0069] This embodiment is basically the same as the previous embodiment, with the following special features:

[0070] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0071] Weigh 0.20 g of copper nitrate trihydrate and 0.22 g of serine in a molar ratio of 2:5, add them to 12 mL of dimethyl sulfoxide, and add 0.36 mL of concentrated hydrochloric acid to assist in dissolution. Dissolve at 35°C and sonicate for 15 minutes to ensure uniform dissolution and mixing, which is called solution A.

[0072] Then, 0.38 g of 2-aminoterephthalic acid was added to 12 mL of dimethyl sulfoxide in a molar ratio of copper nitrate trihydrate to 2-aminoterephthalic acid of 2:5, dissolved at 35°C and ultrasonicated for 15 minutes to achieve uniform dissolution, which was called solution B.

[0073] Then pour B into A, ultrasonicate for 15 minutes to obtain a uniformly mixed solution, heat it to 160℃ in an oil bath, react for 6 days and cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 6000rpm, 25min; then ultrasonicate it with dimethyl sulfoxide 3 times, 20mL each time; then ultrasonicate it with ethanol 3 times, 20mL each time; after completion, soak the solid product obtained by centrifugation in methanol at 60℃ for 12 hours, cool it to room temperature and centrifuge it again, dry the obtained solid sample in a drying oven at 70℃ for 12 hours, and obtain self-assembled MOF microspheres with a smooth surface and a diameter of 2μm, and there are 0.3nm micropores between the central atom and the ligand, 5nm mesopores between the stacked octahedral MOF units, and 50nm macroporous structures between the microspheres, such as Figure 5 shown.

[0074] Example 8

[0075] This embodiment is basically the same as the previous embodiment, with the following special features:

[0076] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0077] Weigh 0.20 g of cobalt acetate tetrahydrate and 0.28 g of L-threonine in a molar ratio of 3:5, add them to 12 mL of nitrogen-nitrogen dimethylacetamide, and add 0.24 mL of concentrated hydrochloric acid to assist in dissolution. Dissolve at 40°C and sonicate for 15 minutes to ensure uniform dissolution and mixing, which is called solution A.

[0078] Then, according to the molar ratio of cobalt acetate tetrahydrate to 2-cyanoterephthalic acid of 3:5, 0.11 g of 2-cyanoterephthalic acid was added to 12 mL of nitrogen-nitrogen dimethylacetamide, dissolved at 40°C and ultrasonicated for 15 minutes to make it uniformly dissolved, which was called solution B;

[0079] Then pour B into A, ultrasonicate for 20 minutes to obtain a uniformly mixed solution, heat to 120°C in an oil bath, react for 5 days, cool to room temperature, collect the solid product by centrifugation, the centrifugation condition is 6000rpm, 30min; then ultrasonically clean it with dimethyl sulfoxide 3 times, 20mL each time; then ultrasonically clean it with ethanol 3 times, 20mL each time; after completion, soak the solid product obtained by centrifugation in ethanol at 60°C for 12 hours, cool to room temperature and centrifuge again, and dry the obtained solid sample in an 80°C drying oven for 12 hours to obtain self-assembled MOF microspheres with a smooth surface and a diameter of 2μm.

[0080] Example 9

[0081] This embodiment is basically the same as the previous embodiment, with the following special features:

[0082] In this embodiment, a method for synthesizing MOF microspheres comprises the following steps:

[0083] Weigh 0.20 g of zinc nitrate tetrahydrate and 0.15 g of valine in a molar ratio of 3:5, add them to 12 mL of nitrogen-nitrogen dimethylacetamide, and add 0.24 mL of concentrated hydrochloric acid to assist in dissolution. Dissolve at 40°C and ultrasonicate for 15 minutes to dissolve and mix evenly, which is called solution A.

[0084] Then, 0.30 g of 2-cyanoterephthalic acid was added to 12 mL of nitrogen-nitrogen dimethylacetamide at a molar ratio of zinc nitrate tetrahydrate to 2-cyanoterephthalic acid of 3:5, dissolved at 40°C and ultrasonicated for 15 minutes to achieve uniform dissolution, which was called solution B.

[0085] B was then poured into A and sonicated for 20 minutes to obtain a homogeneous solution. The solution was then heated to 170°C in an oil bath and allowed to react for 7 days before cooling to room temperature. The solid product was collected by centrifugation at 7000 rpm for 30 minutes. The solution was then ultrasonically cleaned three times with 20 mL of dimethyl sulfoxide (DMSO) and three times with 20 mL of ethanol. The resulting solid was then soaked in ethanol at 60°C for 12 hours, cooled to room temperature, and centrifuged again. The resulting solid sample was dried in an oven at 80°C for 12 hours to obtain smooth, self-assembled MOF microspheres with a diameter of 3 μm.

[0086] In summary, the above-described method for synthesizing MOF microspheres relates to the field of materials technology. The preparation method of the above-described embodiment of the present invention comprises the following steps: S1, dissolving an inorganic salt containing metal ions and an amino acid modifier in a solvent and sonicating until a homogeneous, transparent mixed solution is obtained; S2, dissolving an organic bridging ligand in a solvent and sonicating until a homogeneous, transparent solution is obtained; S3, pouring the solution obtained in step S2 into step S1, mixing, and hydrothermally synthesizing the MOF microspheres. The MOF microspheres prepared in the above-described embodiment of the present invention are formed by the self-assembly and stacking of octahedral MOF units, transforming from 30-80 nm octahedral structures into MOF microspheres of 0.5-3 μm. The microsphere material exhibits a combination of microporous, mesoporous, and macroporous structures. The method for preparing the MOF microspheres in the above-described embodiment of the present invention is simple, safe, and controllable. The resulting material exhibits a uniform structure, a large specific surface area, and excellent stability in aqueous and acidic / alkaline solutions, combining the advantages of the microstructure and functionality of octahedral MOF units.

[0087] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principles of the technical solution of the present invention should be equivalent replacement methods. As long as they comply with the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the scope of protection of the present invention.

Claims

1. A MOF microsphere, characterized in that: The material is formed by the self-assembly and stacking of octahedral MOF units; the average size of the octahedral MOF units is 30-80nm, and the average diameter of the self-assembled MOF microspheres is 0.5-3μm; the MOF microspheres form a microsphere material with a three-level pore structure of micropores, mesopores and macropores: micropores with a pore diameter of 0.1-2nm formed between the central atoms of the MOF itself and the ligands, mesopores with a pore diameter of 2-10nm formed by the stacking of regular octahedral MOFs, and macropores with a pore diameter of 50-80nm formed by the gaps between adjacent MOF microspheres; The MOF microspheres are prepared by the following method, which includes the following steps: Step (1): dissolving the inorganic salt and the amino acid regulator in a solvent, and ultrasonically dissolving them into a uniform and transparent mixed solution for later use; Step (2): dissolving the organic bridging ligand in a solvent and ultrasonically dissolving the ligand to a uniform and transparent solution for later use; Step (3): Pour the solution obtained in the above step (2) into the mixed solution obtained in step (1) and mix them to obtain a reactant mixed solution. The reaction temperature is 120~170℃ to synthesize MOF microspheres.

2. The MOF microspheres according to claim 1, wherein: The average diameter of MOF microspheres formed by self-assembly is 0.6-3 μm.

3. A method for synthesizing MOF microspheres according to claim 1, characterized in that: It includes the following steps: Step (1): dissolving the inorganic salt and the amino acid regulator in a solvent, and ultrasonically dissolving them into a uniform and transparent mixed solution for later use; Step (2): dissolving the organic bridging ligand in a solvent and ultrasonically dissolving the ligand to a uniform and transparent solution for later use; Step (3): Pour the solution obtained in the above step (2) into the mixed solution obtained in step (1) and mix them to obtain a reactant mixed solution to synthesize MOF microspheres.

4. The method for synthesizing MOF microspheres according to claim 3, wherein: In the step (1), the inorganic salt is at least one of copper nitrate trihydrate, ferric oxide, ferric chloride hexahydrate, zirconium tetrachloride, zirconium oxychloride octahydrate, cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt nitrate tetrahydrate, and zinc nitrate tetrahydrate; the amino acid regulator is at least one of L-glutamic acid, L-threonine, L-proline, serine, lysine, histidine, valine, and tryptophan; wherein, when the amino acid regulator is at least one of L-glutamic acid, serine, histidine, valine, and L-threonine, it is not easy to dissolve in the solvent, and hydrochloric acid needs to be added to promote dissolution. The solvent is at least one of nitrogen-nitrogen dimethylformamide, nitrogen-nitrogen dimethylacetamide, and dimethyl sulfoxide. The dissolution temperature is 25-40°C, and the ultrasonic mixing time is 5-30 minutes.

5. The method for synthesizing MOF microspheres according to claim 3, wherein: In the step (2), the organic bridging ligand is at least one of terephthalic acid, biphenyl dicarboxylic acid, 2-aminoterephthalic acid, 2-cyanoterephthalic acid, 1,3,5-benzenetricarboxylic acid, and purine; the solvent is at least one of nitrogen-nitrogen dimethylformamide, dimethyl sulfoxide, and nitrogen-nitrogen dimethylacetamide; the dissolution temperature is 25-40°C; and the ultrasonic mixing time is 5-30 minutes.

6. The method for synthesizing MOF microspheres according to claim 3, wherein: In the step (3), the reactant mixed solution is dissolved and mixed uniformly by ultrasonication to synthesize MOF microspheres, and then the product is obtained by multiple centrifugal separations, and finally the self-assembled MOF microspheres are obtained by drying.

7. The method for synthesizing MOF microspheres according to claim 6, wherein: The ultrasonic dissolution time is 5 to 30 minutes, the reaction temperature is 120 to 170°C, and the reaction time is 1 to 7 days; then the centrifugal speed for multiple centrifugation separations is 5000 to 10000 rpm, the separation time is 5-30 minutes, and the separated product is ultrasonically cleaned with a solution. After the centrifugation and ultrasonic cleaning are repeated at least twice, the separated product is soaked in a solution and centrifuged again. Finally, the separated product is dried to obtain MOF microspheres.

8. The method for synthesizing MOF microspheres according to claim 7, wherein: The solution used for ultrasonic cleaning is at least one of nitrogen-nitrogen dimethylformamide, nitrogen-nitrogen dimethylacetamide, dimethyl sulfoxide, ethanol, and methanol. The ultrasonic time is 5 to 30 minutes, and the ultrasonic cleaning is repeated 2 to 6 times. The solution used for soaking is methanol or ethanol, and the soaking time is 1 to 7 days. The centrifugal speed used for centrifugal separation is 5000 to 10000 rpm, the separation time is 5-30 minutes, and the drying temperature is 30 to 80°C.

9. The method for synthesizing MOF microspheres according to claim 3, wherein: The molar ratio of the inorganic salt to the amino acid regulator used in step (1) is 1:5 to 1:

1.

10. The method for synthesizing MOF microspheres according to claim 3, wherein: The molar ratio of the inorganic salt used in step (1) to the organic bridging ligand used in step (2) is 1:5 to 1:1.

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