Preparation method of aluminum-based MOF material with high trace benzene adsorption

Abstract

The present invention provides a method for preparing an aluminum-based MOF material with high trace benzene adsorption. The method uses a positive trivalent aluminum salt as a metal source and 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid as an organic ligand. The reactant is dissolved in an organic solvent at a molar ratio of 1:1 to 3:1, and a formic acid / acetic acid regulator is added dropwise, and the reactant is completely dissolved by ultrasonic stirring or the like. The product is prepared by a solvent thermal method, and the product is washed and dried in sequence to obtain a high-purity aluminum-based metal-organic framework material. The aluminum-based metal-organic framework material of the present invention is named ZJU-520(Al), which has a carbon content of 2235.35m 2 / g BET specific surface area, and a rich microporous structure with pores mainly concentrated in #imgabs0#. The material also has good chemical and thermal stability. It has potential applications in the capture, separation, and detection of polluting gases.

Description

Technical Field

[0001] The present invention relates to the field of adsorption separation material research and development, and in particular to a method for preparing an aluminum-based MOF material with high trace benzene adsorption. Background Art

[0002] Volatile Organic Compounds (VOCs), especially benzene and toluene vapors, are widely present in indoor air, and even trace concentrations can cause harm to human health. Therefore, it is very important to develop materials for the adsorption of trace amounts of benzene and toluene gases. The adsorption amount of benzene at a relative pressure of P / P0=0.01 is an objective criterion for evaluating the trace adsorption capacity of adsorption materials (Control of the pore chemistry in metal-organic frameworksfor efficient adsorption of benzene and separation of benzene / cyclohexane, Chem, 2023, 9, 739-754). At present, the metal-organic framework materials used for trace benzene adsorption mainly include ZJU-620(Al), UiO-66(Cu II ) and BUT-54(Zr). For example: at P / P0=0.01 and 298K, ZJU-620(Al) has 1347m 2 / g BET specific surface area (CN202211190864.5), and its adsorption capacity for benzene is 3.80mmol / g; UiO-66 (Cu II ) has 1240m 2 / g BET specific surface area, its adsorption capacity for benzene is 3.92mmol / g; BUT-54(Zr) has 1128m 2 / g BET specific surface area, and its adsorption capacity for benzene is 4.31mmol / g. These excellent materials for trace adsorption have a specific surface area of less than 2000m 2 / g, and its low specific surface area limits its adsorption capacity.

[0003] Metal-organic frameworks (MOFs), a novel adsorption material, are widely used for the adsorption of hazardous gases due to their adjustable pore size and large specific surface area. Aluminum-based MOFs are characterized by their low toxicity due to the abundance of aluminum ions in the Earth's crust. Furthermore, according to Lewis acid-base theory, trivalent aluminum ions are Lewis strong acids, which can react with Lewis strong bases, such as carboxylic acid organic ligands, to form more stable MOFs. 4,6-Di(4-carboxyphenyl)pyrimidine (H2DBP) was selected as a ligand for the aluminum-based MOF. By increasing the length of the benzene ring on the carboxylic acid group, the pore size and specific surface area of the MOF were increased. Furthermore, the pyrimidine nitrogen in the H2DBP ligand exhibits an electron absorption effect, enhancing the strength of the Al-O coordination bond and thus improving the stability of the MOF material. As an organic ligand in the MOF, H2DBP can enhance the adsorption capacity through its C–H…π and C–H…N interactions with benzene molecules. Therefore, the aluminum-based metal-organic framework material synthesized by H2DBP ligand and aluminum ions should have a large specific surface area and a suitable pore size, as well as high stability, and a high adsorption capacity for trace benzene vapor, that is, a high trace benzene adsorption capacity. Summary of the Invention

[0004] This invention provides a method for preparing aluminum-based MOF materials capable of high trace benzene adsorption for metal-organic frameworks (MOFs) in the field of trace pollutant gas adsorption. High trace adsorption refers to the adsorbent's high adsorption capacity for the adsorbate at low pressures. For example, at a relative pressure of 0.01 or less, the adsorption capacity for pollutant gases is 4-10 mmol / g.

[0005] The present invention adopts the following technical solution: a method for preparing an aluminum-based metal organic framework material with high trace benzene adsorption, and the aluminum-based MOF material is named ZJU-520(Al), the method is:

[0006] 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid and trivalent aluminum salt are dissolved in an organic solvent, an acidic regulator is added, and ultrasonication is performed to uniformly disperse the reactants in the organic solvent; an aluminum-based metal-organic framework material is synthesized using a solvothermal method; after the product is cooled, it is washed with a detergent to remove guest molecules in the pores of the metal-organic framework material, and vacuum dried to obtain an aluminum-based metal-organic framework material with high trace benzene adsorption; the molar ratio of the trivalent aluminum salt to 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid is 1:1 to 3:1.

[0007] Furthermore, the trivalent aluminum salt is aluminum chloride hexahydrate or aluminum nitrate nonahydrate, more preferably aluminum nitrate nonahydrate;

[0008] Furthermore, the molar ratio of the trivalent aluminum salt to 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid is 1:1 to 3:1; more preferably 1.5:1 to 2:1;

[0009] Furthermore, the organic solvent is N,N-dimethylformamide or acetonitrile;

[0010] Furthermore, the volume ratio of the organic solvent to the acidic regulator is 75:1 to 200:1;

[0011] Furthermore, the acidic regulator is formic acid or acetic acid, more preferably formic acid;

[0012] Furthermore, the detergent is one or more of N,N-dimethylformamide or acetone;

[0013] Furthermore, the reaction temperature of the solvothermal method is 120°C to 150°C;

[0014] Furthermore, the reaction time of the solvothermal method is 24 hours to 72 hours;

[0015] Furthermore, the aluminum-based metal organic framework material with ultra-high trace benzene adsorption is used in the adsorption of trace benzene series.

[0016] The present invention has the following beneficial effects:

[0017] (1) The aluminum-based metal organic framework material prepared by the present invention has a 2 / g specific surface area, compared with the previously listed MOFs materials, the BET specific surface area is nearly doubled, and it has a rich microporous structure, and the pore size is mainly concentrated in The kinetic diameter is close to that of benzene and toluene, which makes the material have a good affinity for benzene series. This is mainly attributed to the selection of H2DBP as a ligand for aluminum-based MOF.

[0018] (2) The aluminum-based metal-organic framework material prepared by the present invention can still maintain structural stability after being immersed in water for 5 days, and no obvious mass loss occurs before 550°C, and has good water stability and thermal stability.

[0019] (3) The aluminum-based metal-organic framework material prepared by the present invention has excellent stability due to the presence of pyrimidine in the organic ligand and its strong electron-withdrawing properties, and can be used for the capture, separation and detection of polluting gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a structural diagram of the aluminum-based metal-organic framework material prepared in Example 1 of the present invention;

[0021] Figure 2 The powder X-ray diffraction data of the aluminum-based metal-organic framework material prepared in Example 1 of the present invention before and after being immersed in water;

[0022] Figure 3 is a thermogravimetric curve of the aluminum-based metal-organic framework material prepared in Example 1 of the present invention;

[0023] Figure 4 is a nitrogen adsorption-desorption isotherm diagram of the aluminum-based metal-organic framework material prepared in Example 1 of the present invention;

[0024] Figure 5 is a pore size distribution diagram of the aluminum-based metal organic framework material prepared in Example 1 of the present invention;

[0025] Figure 6 This is a benzene and toluene adsorption isotherm diagram of the aluminum-based metal organic framework material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0027] Example 1 Preparation of aluminum-based MOF materials with high trace benzene adsorption

[0028] Weigh 20 mg of aluminum nitrate nonahydrate and 11.4 mg of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid (molar ratio of 1.5:1) and place them in 1.5 mL of N,N-dimethylformamide organic solution, add 0.01 mL of formic acid dropwise, and ultrasonicate for 30 minutes to completely dissolve the reactants and disperse them evenly. Place the reactants in a reactor and seal it. Set the oven temperature to 130 degrees Celsius and the reaction time to 48 hours. After the reaction is completed, cool the reactor to room temperature, transfer the product to a centrifuge tube, separate it by centrifugation, and pour off the supernatant to obtain the product. Wash with N,N-dimethylformamide and acetone 3 to 4 times in sequence. After washing, place the clean product in a vacuum drying oven and dry it. Finally, a microporous aluminum-based metal-organic framework material with high specific surface area and water stability is obtained, with a BET specific surface area of 2235.35 m 2 / g, pore size range Its adsorption capacity for benzene is 5.98 mmol / g at P / P0=0.01 and 298K.

[0029] Example 2 Preparation of aluminum-based MOF materials with high trace benzene adsorption

[0030] Weigh 20 mg of aluminum nitrate nonahydrate and 11.4 mg of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid (molar ratio of 1.5:1) and place them in 1.5 mL of N,N-dimethylformamide organic solution, add 0.02 mL of formic acid dropwise, and ultrasonicate for 30 minutes to completely dissolve the reactants and disperse them evenly. Place the reactants in a reactor and seal it. Set the oven temperature to 140 degrees Celsius and the reaction time to 72 hours. After the reaction is completed, cool the reactor to room temperature, transfer the product to a centrifuge tube, separate it by centrifugation, and pour off the supernatant to obtain the product. Wash it with N,N-dimethylformamide and acetone 3 to 4 times in sequence. After washing, place the clean product in a vacuum drying oven and dry it. Finally, a microporous aluminum-based metal-organic framework material with high specific surface area and water stability is obtained, with a BET specific surface area of 1532 m 2 / g, and its adsorption capacity for benzene is 2.89mmol / g at P / P0=0.01 and 298K.

[0031] Example 3 Preparation of microporous aluminum-based MOF materials with high trace benzene adsorption

[0032] Weigh 53 mg of aluminum nitrate nonahydrate and 30 mg of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid (molar ratio of 1.5:1) and place them in 1.5 mL of N,N-dimethylformamide organic solution, add 0.02 mL of formic acid dropwise, and ultrasonicate for 30 minutes to completely dissolve the reactants and disperse them evenly. Place the reactants in a reactor and seal it. Set the oven temperature to 130 degrees Celsius and the reaction time to 48 hours. After the reaction is completed, cool the reactor to room temperature, transfer the product to a centrifuge tube, separate it by centrifugation, and pour off the supernatant to obtain the product. Wash with N,N-dimethylformamide and acetone 3 to 4 times in sequence. After washing, place the clean product in a vacuum drying oven and dry it, and finally obtain a microporous aluminum-based metal-organic framework material with high specific surface area and water stability, with a BET specific surface area of 1446 m 2 / g, and its adsorption capacity for benzene is 2.58mmol / g when P / P0=0.01 and 298K.

[0033] Example 4 Structural Characterization of Aluminum-Based Metal-Organic Framework Materials Without Guest Molecules

[0034] The aluminum-based metal-organic framework material was scanned and structurally analyzed using a Brucker D8 Venture single crystal X-ray diffractometer. The collected data were analyzed and corrected using the least squares method, and the crystal structure of the product was finally obtained. Figure 1 .

[0035] Example 5 Characterization of the Chemical Stability of the Metal-Organic Framework Material Obtained in Example 1

[0036] The metal organic framework material was immersed in water for 72 hours, and the powder X-ray diffraction data before and after immersion did not change significantly. Figure 2 It can be seen that the metal organic framework material of the present invention can maintain structural stability in water without structural collapse.

[0037] Example 6 Characterization of thermal stability of the metal organic framework material obtained in Example 1

[0038] The metal organic framework material was placed in a nitrogen atmosphere and analyzed by thermogravimetric analysis instrument. The obtained thermogravimetric curve is shown in Figure 3 .

[0039] Example 7 N2 adsorption-desorption isotherms of the metal organic framework material obtained in Example 1

[0040] The prepared metal organic framework material was subjected to vacuum heating desorption at 303K to remove impurities in the pores. The N2 adsorption-desorption isotherm of the prepared metal organic framework material was measured at 77K. Figure 4 and pore size distribution, see Figure 5 .

[0041] Example 8 Adsorption effect of trace benzene and toluene on the metal organic framework material obtained in Example 1

[0042] The prepared metal organic framework material was placed in a vapor adsorption instrument to measure the adsorption amount of benzene and toluene. Figure 6 .

[0043] Comparative Example 1

[0044] Weigh 30 mg of aluminum nitrate nonahydrate and 51.2 mg of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid (molar ratio of 0.5:1) and place them in 1.5 mL of N,N-dimethylformamide organic solution, add 0.2 mL of formic acid dropwise, and ultrasonicate for 30 minutes to completely dissolve the reactants and disperse them evenly. Place the reactants in a reactor and seal it. Set the oven temperature to 130 degrees Celsius and the reaction time to 48 hours. After the reaction is completed, the reactor is cooled to room temperature, the product is transferred to a centrifuge tube, centrifuged, and the supernatant is poured out to obtain the product. Wash with N,N-dimethylformamide and acetone 3 to 4 times in sequence. The washed product is placed in a vacuum drying oven and dried to finally obtain a microporous aluminum-based metal-organic framework material with a high specific surface area and water stability. The BET specific surface area is only 127 m 2 / g, and its adsorption capacity for benzene is only 0.50mmol / g when P / P0=0.01 and 298K.

[0045] Comparative Example 2

[0046] Weigh 20 mg of aluminum nitrate nonahydrate and 11.4 mg of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid (molar ratio of 1.5:1) and place them in 1.5 mL of N,N-dimethylformamide organic solution. Add 2 mL of formic acid dropwise and ultrasonicate for 30 minutes to completely dissolve the reactants and disperse them evenly. Place the reactants in a reactor and seal it. Set the oven temperature to 130 degrees Celsius and the reaction time to 48 hours. After the reaction is completed, the reactor is cooled to room temperature, the reactor is clear, and no product is obtained.

[0047] Comparative Example 3

[0048] Weigh 30 mg of aluminum nitrate nonahydrate and 5 mg of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid (molar ratio of 5:1) and place them in 1.5 mL of N,N-dimethylformamide organic solution. Add 0.02 mL of formic acid dropwise and ultrasonicate for 30 minutes to completely dissolve the reactants and disperse them evenly. Place the reactants in a reactor and seal it. Set the oven temperature to 130 degrees Celsius and the reaction time to 72 hours. After the reaction is completed, cool the reactor to room temperature, centrifuge the product, wash and dry it, and its specific surface area is 235.23 m 2 / g, and its adsorption capacity for benzene is only 1.02mmol / g when P / P0=0.01 and 298K.

[0049] Figure 1 : is a crystal structure diagram of the metal organic framework material prepared in Example 1, which is a framework material with a periodic structure composed of 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid and helical aluminum clusters through coordination. Figure 2 1 and 2. The PXRD pattern of the metal organic framework material prepared in Example 1 and the measured PXRD pattern after immersion in water for 24 hours, as well as the corresponding theoretical PXRD pattern.

[0050] from Figure 2 It can be seen that the prepared metal-organic framework material has good chemical stability. After being immersed in water for 24 hours, the main diffraction peaks of its PXRD pattern correspond to the theoretical main diffraction peak positions, indicating that its crystal structure has good water stability.

[0051] Figure 3 The thermogravimetric analysis of the prepared material shows good thermal stability, with significant mass loss occurring only at 550°C. The mass loss at 100°C is due to the evaporation of water molecules within the pores. In summary, ZJU-520(Al) exhibits excellent chemical and thermal stability.

[0052] Figure 4The N2 adsorption-desorption isotherm of the prepared material at 77K. The BET specific surface area of ZJU-520(Al) is 2235.35m 2 / g, pore size range Dominated by micropores, mainly concentrated in

[0053] Compared to Comparative Example 1, the excessive amount of formic acid added resulted in a decrease in the product's specific surface area and its adsorption capacity for trace amounts of benzene, failing to produce a material with good performance. Even when the formic acid dosage was excessive, no product was produced, as shown in Comparative Example 2. Compared to Comparative Example 3, the ratio of the metal aluminum salt to the H2DBP ligand was 5:1, and the H2DBP ligand dosage was low, resulting in a decrease in the product's specific surface area and its adsorption capacity for trace amounts of benzene.

[0054] The metal organic framework material ZJU-520 (Al) prepared in Example 1 was subjected to a benzene and toluene vapor adsorption experiment. Figure 6 It can be seen that ZJU-520(Al) has excellent adsorption performance at low pressure. Taking benzene as an example, the prepared ZJU-520(Al) has an adsorption capacity of 5.98 mmol / g for benzene at a relative pressure of P / P0=0.01 and 298K, which is one of the largest trace adsorption capacities reported so far.

[0055] The embodiments of the present invention only express preferred technical solutions and should not be understood as limiting the patent of the present invention. Those skilled in the art can make substitutions and improvements based on the present invention, which fall within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum-based MOF material with high trace benzene adsorption, characterized in that: The method comprises the following steps: A trivalent aluminum salt and 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid are dissolved in an organic solvent, an acidic regulator is added, and ultrasonication is performed to uniformly disperse the reactants in the organic solvent; an aluminum-based metal-organic framework material is synthesized using a solvothermal method; after the product is cooled, it is washed with a detergent to remove guest molecules in the pores of the metal-organic framework material, and vacuum dried to obtain an aluminum-based metal-organic framework material with high trace benzene adsorption; the molar ratio of the trivalent aluminum salt to the 4,4'-(pyrimidine-4,6-diyl)dibenzoic acid is 1:1 to 3:

1.

2. The preparation method according to claim 1, characterized in that The trivalent aluminum salt is aluminum chloride hexahydrate or aluminum nitrate nonahydrate.

3. The preparation method according to claim 1, characterized in that The organic solvent is N,N-dimethylformamide or acetonitrile.

4. The preparation method according to claim 1, characterized in that The acidic regulator is acetic acid or formic acid, and the volume ratio of the organic solvent to the acidic regulator is 75:1 to 200:

1.

5. The preparation method according to claim 1, characterized in that The reaction temperature of the solvent thermal method is 120°C to 150°C.

6. The preparation method according to claim 1, characterized in that The reaction time of the solvent thermal method is 24 hours to 72 hours.

7. The preparation method according to claim 1, characterized in that The detergent is one or more of N,N-dimethylformamide and acetone.

8. An aluminum-based metal-organic framework material with high trace benzene adsorption prepared according to the method according to any one of claims 1 to 7.

9. Use of the aluminum-based metal-organic framework material with high trace benzene adsorption according to claim 8 in the adsorption of trace benzene series.

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