An aluminum-based metal-organic framework powder material and its preparation method

Abstract

This invention belongs to the field of materials synthesis technology, specifically relating to an aluminum-based metal-organic framework powder material and its preparation method. The preparation method includes the following steps: mixing organic ligand powder and slightly soluble alkali powder, adding water, stirring and mixing, and ultrasonically dispersing to obtain a uniform emulsion; mixing aluminum salt with water and stirring to obtain an aluminum salt aqueous solution; adding the aluminum salt aqueous solution to the uniform emulsion, stirring and ultrasonicating to obtain a mixed solution; heating the mixed solution under reflux, filtering to remove filter residue, washing with water, washing with alcohol, drying, and vacuum activation to obtain the aluminum-based metal-organic framework powder material. The slightly soluble alkali used in this method can slowly release hydroxyl ions during the heating synthesis of the aluminum-based metal-organic framework powder material, forming a dynamic slightly alkaline environment, slowing down the deprotonation rate of the organic ligands, which is beneficial to improving the crystallinity of the material, forming a material with a regular pore structure, and enhancing the adsorption performance of the material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material synthesis, and particularly relates to an aluminum-based metal-organic framework powder material and a preparation method thereof. BACKGROUND

[0002] Water is an indispensable core strategic resource for human survival and social progress. According to the statistics of the United Nations Environment Programme, more than 50% of the global population experiences water stress for at least one month each year. In the context of the increasing scarcity of fresh water resources, actively exploring new water sources and achieving efficient recycling of wastewater has become an important strategy to address the global water crisis. Among them, the technology of obtaining fresh water from air and converting seawater into fresh water is becoming the most concerned development path to solve the water resource dilemma due to its outstanding advantage of scalable application. Aluminum-based metal-organic frameworks have shown promising potential in atmospheric water harvesting. Its large specific surface area, adjustable pore size and stable crystal structure make it a candidate material to solve the problem of water shortage.

[0003] Deprotonation is a key step for ligand and metal ion bonding. Currently, the synthesis of aluminum-based metal-organic frameworks mainly uses a fully soluble base. The fully soluble base is completely ionized in water, and the produced hydroxyl can completely deprotonate the organic ligand, thereby improving the yield. However, the completely deprotonated carboxylate ligand will quickly and irreversibly react with metal ions, resulting in too fast crystallization speed and generating a large number of defects. A large number of defects will reduce the specific surface area and water adsorption performance of the powder, and also affect the cycle life.

[0004] Slowing down the deprotonation rate of the ligand can effectively reduce the defect density in the crystal and improve the crystallinity of the MOFs. The commonly used method is to use DMF or DEF and other organic solvents through hydrothermal method, and to use the basic organic matter produced by the slow decomposition of these solvents at high temperature and high pressure to achieve slow deprotonation of the ligand. However, this synthesis method is carried out at high pressure and uses a large amount of organic reagents, which is easy to cause safety and environmental problems. Therefore, developing a simple method to control the deprotonation rate of the ligand at normal pressure can effectively improve the crystallinity and adsorption performance of the MOFs, and has important significance for improving the application of MOFs in atmospheric water harvesting and other fields. SUMMARY

[0005] In view of the above problems, the present application uses a slightly soluble base as an important raw material, and controls the deprotonation rate through the dissolution rate of the slightly soluble base, thereby obtaining an aluminum-based metal-organic framework material with regular pore structure and high adsorption performance.

[0006] In order to achieve the above purpose, the embodiment of the present application provides a preparation method of an aluminum-based metal-organic framework powder material, which comprises the following steps: S1, mixing organic ligand powder and slightly soluble base powder, stirring and mixing with water and ultrasonic dispersion to obtain a uniform emulsion, mixing aluminum salt with water to obtain an aluminum salt aqueous solution; S2, adding the aluminum salt aqueous solution to the uniform emulsion, stirring and ultrasonic dispersion to obtain a mixed solution; S3, after heating and refluxing the mixed solution, filtering the residue, washing with water and alcohol, drying and vacuum activation to obtain an aluminum-based metal-organic framework powder material.

[0007] In specific embodiments, the organic ligand is one or more of 3,5-pyrazole dicarboxylic acid monohydrate, 2,5-furan dicarboxylic acid, fumaric acid, terephthalic acid, and isophthalic acid.

[0008] In specific embodiments, the slightly soluble base is one or more of calcium hydroxide, magnesium hydroxide, copper hydroxide, iron hydroxide, ferrous hydroxide, and zinc hydroxide.

[0009] In specific embodiments, the molar ratio of the organic ligand to the slightly soluble base is 1:0.2 to 1:1.75.

[0010] In specific embodiments, the aluminum salt is one or more of aluminum chloride hexahydrate, anhydrous aluminum chloride, aluminum sulfate octadecahydrate, aluminum sulfate hydrate, aluminum sulfate, aluminum nitrate nonahydrate, aluminum nitrate hydrate, aluminum isopropylate, and sodium metaaluminate.

[0011] In specific embodiments, the molar ratio of the organic ligand to the aluminum salt in the mixed solution is 1:0.5 to 1:3.

[0012] In specific embodiments, the concentration of the aluminum salt in the mixed solution is 0.01 to 0.1 mol / L. In specific embodiments, in step S3, the reaction temperature during the heating and refluxing process is 40-150℃, and the reaction time is 0.5-24h.

[0013] In specific embodiments, in step S3, the drying temperature is 50-150℃, and the vacuum activation temperature is 100-150℃.

[0014] The embodiments of the present application also provide an aluminum-based metal-organic framework powder material obtained by the above preparation method, wherein the aluminum-based metal-organic framework powder material is a polycrystalline particle.

[0015] Compared with the prior art, the technical scheme of the present application has the following beneficial effects: (1) The synthesis method is simple. The raw materials are directly mixed and heated at room temperature. There is no need to control the order and rate of material addition. (2) The synthesis method is green and safe. The green reflux method is adopted. Deionized water is used as a solvent under normal pressure for synthesis. Compared with the synthesis under hydrothermal conditions using organic solvents, it is greener and safer. (3) The crystallinity and adsorption performance of the obtained aluminum-based metal-organic framework powder are greatly improved. Slightly soluble alkali is used as the reaction raw material. The slow release of hydroxide ions by slightly soluble alkali slows down the deprotonation rate of organic ligands, so that MOFs are assembled more regularly to obtain a more regular pore structure and higher adsorption performance. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A process flow diagram of the preparation method of aluminum-based metal-organic framework powder material provided by the present invention; Figure 2 The XRD pattern of the aluminum-based metal-organic framework powder material provided in Example 1 of this invention; Figure 3 The SEM image of the aluminum-based metal-organic framework powder material provided in Example 1 of this invention; Figure 4 The XRD pattern of the aluminum-based metal-organic framework powder material provided in Example 2 of this invention; Figure 5 The SEM image of the aluminum-based metal-organic framework powder material provided in Example 2 of this invention; Figure 6 XRD patterns of aluminum-based metal-organic framework powder materials provided as comparative examples of this invention; Figure 7 SEM images of aluminum-based metal-organic framework powder materials provided as comparative examples of this invention; Figure 8 The nitrogen adsorption isotherm spectra of the aluminum-based metal-organic framework powder materials provided in Example 1 and the comparative example of the present invention are shown. Detailed Implementation

[0018] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0019] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0020] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0021] like Figure 1 As shown, this embodiment of the invention provides a method for preparing an aluminum-based metal-organic framework powder material, the method comprising the following steps: S1. Mix the organic ligand powder and the slightly soluble alkali powder in a molar ratio of 1:0.2 to 1:1.75, add water, stir and mix, and ultrasonically disperse to obtain a uniform emulsion A. Mix the aluminum salt with water and stir to obtain an aluminum salt aqueous solution B. The organic ligand is one or more of 3,5-pyrazole dicarboxylic acid monohydrate, 2,5-furandicarboxylic acid, fumaric acid, terephthalic acid, and isophthalic acid. The slightly soluble alkali is one or more of calcium hydroxide, magnesium hydroxide, copper hydroxide, iron hydroxide, ferrous hydroxide, and zinc hydroxide. The aluminum salt is one or more of anolyl aluminum chloride hexahydrate, anhydrous aluminum chloride, aluminum sulfate octadecylhydrate, hydrated aluminum sulfate, aluminum sulfate, aluminum nitrate nonahydrate, hydrated aluminum nitrate, aluminum isopropoxide, and sodium aluminate.

[0022] S2. The aluminum salt aqueous solution is added to the homogeneous emulsion according to the molar ratio of organic ligand to aluminum salt of 1:0.5~1:3, and the mixture is stirred and sonicated to obtain a mixed solution C with an aluminum salt concentration of 0.01~0.1mol / L; S3. The mixture is heated to 40-150℃ under normal pressure, refluxed for 0.5-24 hours, filtered to remove residue, washed with water and alcohol, dried at 50-150℃, and then vacuum activated at 100-150℃ to obtain aluminum-based metal-organic framework powder material.

[0023] In this process, the slightly soluble alkali slowly releases hydroxide ions to control the deprotonation rate: the deprotonation of organic ligands is a prerequisite for their assembly reaction with metal ions to form MOFs. Using slightly soluble alkali as the reaction raw material, when the system reaches the assembly temperature, the organic ligands and metal ions undergo an assembly reaction, consuming hydroxide ions and generating MOF powder. The consumption of hydroxide ions in the solution causes the precipitation-dissolution equilibrium of the slightly soluble alkali to shift towards dissolution. Since the assembly rate of organic ligands and metal ions is very fast, the dissolution process of the slightly soluble alkali is the rate-controlling step of the reaction. This method can effectively slow down the deprotonation rate of organic ligands, thereby slowing down the assembly rate of MOFs, resulting in crystals with a more regular pore structure, higher specific surface area, and better adsorption performance. Taking MOF-303 as an example, the specific surface area of ​​MOF-303-Ca(OH)2 prepared using slightly soluble alkali is 1489.73 m². 2 / g, greater than MOF-303-NaOH (1133.99 m) prepared using soluble alkali. 2 / g).

[0024] The following is a further explanation using specific embodiments.

[0025] Example 1 Preparation of MOF-303-Ca(OH)2: S1. Take a certain amount of 3,5-pyrazole dicarboxylic acid monohydrate and calcium hydroxide, control the ratio of 3,5-pyrazole dicarboxylic acid monohydrate to calcium hydroxide to be 1:1, add deionized water, mix thoroughly by ultrasonication, and prepare an emulsion A with a concentration of 0.05 mol / L of 3,5-pyrazole dicarboxylic acid; take a certain amount of aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution B, and control the aluminum ion concentration to be 0.05 mol / L.

[0026] S2. Mix emulsion A and aqueous solution B to obtain mixture C, and control the molar ratio of aluminum ions and 3,5-pyrazole dicarboxylic acid in the mixture to be 1:1.

[0027] S3. Place the mixture C in an oil bath at 120°C and heat for 6 hours. Filter the reaction product using a centrifuge, and wash the filtrate three times with water and anhydrous ethanol in sequence. Dry it in a forced-air environment at 60°C and activate it under vacuum at 150°C to obtain MOF-303-Ca(OH)2 powder material.

[0028] The aluminum-based metal-organic framework powder material obtained above was tested using X-ray diffraction (XRD), and the resulting diffraction pattern is shown below. Figure 2 As shown in the figure, MOF-303-Ca(OH)2 exhibits high crystallinity. The morphology of the obtained aluminum-based metal-organic framework powder material was observed using scanning electron microscopy (SEM), and the resulting SEM images are shown below. Figure 3As shown in the figure, MOF-303-Ca(OH)2 consists of uniform polycrystalline particles.

[0029] Example 2 Preparation of Al-fumarate-Ca(OH)2: S1. Take a certain amount of fumaric acid powder and calcium hydroxide, controlling the ratio of fumaric acid to calcium hydroxide to be 1:1.15, add deionized water, and mix thoroughly by ultrasonication to prepare an emulsion A with a fumaric acid concentration of 0.1 mol / L. Take a certain amount of aluminum sulfate octadechydrate to prepare an aluminum sulfate aqueous solution B, controlling the aluminum ion concentration to be 0.05 mol / L.

[0030] S2. Mix emulsion A and aqueous solution B to obtain mixture C, and control the molar ratio of aluminum ions and 3,5-pyrazole dicarboxylic acid in the mixture to be 1:2.

[0031] S3. Place the mixture C in an oil bath at 60°C and heat for 9 hours. Filter the reaction product using a centrifuge, and wash the filtrate three times with water and anhydrous ethanol in sequence. Dry it in a forced-air environment at 60°C and activate it under vacuum at 150°C to obtain Al-fumarate-Ca(OH)2 powder material.

[0032] The aluminum-based metal-organic framework powder material obtained above was tested using X-ray diffraction (XRD), and the resulting diffraction pattern is shown below. Figure 4 As shown in the figure, Al-fumarate-Ca(OH)2 exhibits high crystallinity. The morphology of the obtained aluminum-based metal-organic framework powder material was observed using scanning electron microscopy (SEM), and the resulting SEM images are shown below. Figure 5 As shown in the figure, Al-fumarate-Ca(OH)2 consists of uniform polycrystalline particles.

[0033] Comparative Example Preparation of MOF-303-NaOH: S1. Take a certain amount of 3,5-pyrazole dicarboxylic acid monohydrate and sodium hydroxide, controlling the ratio of 3,5-pyrazole dicarboxylic acid monohydrate to sodium hydroxide to be 1:2, add deionized water, stir, and prepare a clear solution A with a concentration of 0.05 mol / L for 3,5-pyrazole dicarboxylic acid; take a certain amount of aluminum chloride hexahydrate to prepare an aluminum chloride aqueous solution B, controlling the aluminum ion concentration to be 0.05 mol / L.

[0034] S2. Mix the clear solution A and the aqueous solution B to obtain the mixed solution C, controlling the mixing ratio to be 1:1.

[0035] S3. Place the mixture C in an oil bath at 120°C and heat for 6 hours. Filter the reaction product using a centrifuge, and wash the filtrate three times with water and anhydrous ethanol in sequence. Dry it in a forced-air environment at 60°C and activate it under vacuum at 150°C to obtain MOF-303-NaOH powder material.

[0036] The aluminum-based metal-organic framework powder material obtained above was tested using X-ray diffraction (XRD), and the resulting diffraction pattern is shown below. Figure 6 As shown, compared with MOF-303-Ca(OH)2 prepared in Example 1, MOF-303-NaOH has more impurity peaks and a wider half-peak width, indicating that MOF-303-NaOH has poor crystallinity. The morphology of the obtained aluminum-based metal-organic framework powder material was observed using scanning electron microscopy (SEM), and the obtained SEM images are shown below. Figure 7 As shown in the figure, MOF-303-NaOH consists of disordered and irregular polycrystalline particles. Nitrogen adsorption tests are as follows... Figure 8 As shown, comparing MOF-303-Ca(OH)2 prepared in Example 1 with MOF-303-NaOH prepared in the comparative example, it can be seen that MOF-303-Ca(OH)2 has stronger adsorption capacity and higher specific surface area.

[0037] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum-based metal-organic framework powder material, characterized in that, The method includes the following steps: S1. Mix the organic ligand powder and the slightly soluble alkali powder, add water, stir and mix, and ultrasonically disperse to obtain a uniform emulsion. Mix the aluminum salt with water and stir to obtain an aluminum salt aqueous solution. S2. Add the aluminum salt aqueous solution to the homogeneous emulsion, stir and sonicate to obtain a mixture; S3. After heating and refluxing the mixture, filter to remove the residue, and then wash with water, wash with alcohol, dry and activate under vacuum to obtain aluminum-based metal-organic framework powder material.

2. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, The organic ligand is one or more of 3,5-pyrazole dicarboxylic acid monohydrate, 2,5-furandicarboxylic acid, fumaric acid, terephthalic acid, and isophthalic acid.

3. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, The slightly soluble alkali is one or more of calcium hydroxide, magnesium hydroxide, copper hydroxide, iron hydroxide, ferrous hydroxide, and zinc hydroxide.

4. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, The molar ratio of the organic ligand to the slightly soluble base is 1:0.2 to 1:1.

75.

5. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, The aluminum salt is one or more of aluminum chloride hexahydrate, anhydrous aluminum chloride, aluminum sulfate octadechydrate, hydrated aluminum sulfate, aluminum sulfate, aluminum nitrate nonahydrate, hydrated aluminum nitrate, aluminum isopropoxide, and sodium aluminate.

6. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, The molar ratio of organic ligands to aluminum salts in the mixture is 1:0.5 to 1:

3.

7. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, The concentration of aluminum salt in the mixture is 0.01~0.1 mol / L.

8. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, In step S3, during the heating and reflux reaction, the reaction temperature is 40-150℃ and the reaction time is 0.5-24h.

9. The method for preparing aluminum-based metal-organic framework powder material according to claim 1, characterized in that, In step S3, the drying temperature is 50~150℃ and the vacuum activation temperature is 100~150℃.

10. The aluminum-based metal-organic framework powder material obtained by the preparation method according to any one of claims 1 to 9, characterized in that, The aluminum-based metal-organic framework powder material is a polycrystalline particle.

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