A method of preparing a zeolitic imidazolate framework adsorbent

Abstract

This invention relates to a method for preparing a zeolite imidazole framework adsorbent, comprising the following steps: weighing 2-4 grams of cobalt nitrate and dissolving it in 20-40 ml of methanol; then weighing 1-2 grams of 2-methylimidazole and 0.5-1 grams of the secondary ligand 2-aminobenzimidazole and dissolving them in 20-40 ml of methanol; mixing the solutions obtained in steps one and two respectively, stirring with a magnetic stirrer at room temperature (25°C) for 4 hours, centrifuging, rinsing the bottom precipitate three times with anhydrous ethanol after centrifugation, drying in a drying oven at 60°C overnight, and grinding it into powder using a mortar to obtain adsorbent ZIF-67; heating ZIF-67 in a muffle furnace at a calcination temperature of 290°C for 2 hours to remove the secondary ligand, finally forming a hierarchical pore structure zeolite imidazole framework ZIF-67.

Description

Technical Field

[0001] This invention relates to the field of green and environmentally friendly technology, and in particular to the composition of an adsorbent and its preparation method. Background Technology Congo red is an azo anionic dye. Its molecule contains two sulfonic acid groups and has a pKa value of 4.5. It forms a red colloidal solution in water and metabolizes to produce benzidine, a known carcinogen and mutagenizer of aquatic organisms. To date, reported dye removal technologies encompass various methods, including physical, chemical, biological, and physicochemical methods. Among these, physical adsorption techniques are widely recognized as the most promising method for advanced dye wastewater treatment due to their excellent removal capabilities even at low concentrations, simple process, low cost, and environmental friendliness. They are favored over other methods because they not only eliminate pollutants but also allow for recycling and reuse, contributing to the environmental sustainability of industrial processes. However, physical adsorption methods have a significant technical problem. Currently, there is a lack of green synthesis technologies for the preparation of zeolite imidazole framework adsorbents. The preparation process often requires energy-intensive conditions such as heating to 358-423 K or consuming harmful organic solvents such as N,N-dimethylformamide (DMF). Even if harmful organic solvents are avoided, the amount of imidazole organic ligands used increases dramatically. Meanwhile, the microporous structure of the zeolite imidazole framework restricts the adsorption and diffusion of macromolecular organic dyes. Summary of the Invention

[0002] To address the aforementioned problems, this invention provides a green and environmentally friendly zeolite imidazole framework adsorbent with excellent adsorption performance.

[0003] The technical solution of the present invention: Step 1: Weigh 2-4 grams of cobalt nitrate and dissolve it in 20-40 ml of methanol; Step 2: Weigh out 1-2 grams of 2-methylimidazole and 0.5-1 gram of the secondary ligand 2-aminobenzimidazole and dissolve them in 20-40 ml of methanol; Step 3: Mix the solutions obtained in Step 1 and Step 2 separately, stir with a magnetic stirrer at room temperature (25℃) for 4 hours, and then centrifuge. After centrifugation, rinse the bottom precipitate with anhydrous ethanol 3 times, and then dry it overnight in a drying oven at 60℃. Grind it into powder with a mortar and pestle to obtain the adsorbent ZIF-67. Step 4: Heat ZIF-67 in a muffle furnace at 290℃ for 2 hours to remove secondary ligands and finally form a hierarchical pore structure of zeolite imidazole framework ZIF-67.

[0004] In step one, the optimal mass of cobalt nitrate is 2.32 g and the optimal mass of methanol is 30 ml. In step two, the optimal mass of 2-methylimidazole is 1.72 g, the optimal mass of the secondary ligand 2-aminobenzimidazole is 0.9 g, and the optimal mass of methanol is 30 ml.

[0005] Using the above-mentioned technical solution, the adsorption of Congo red on the hierarchical porous zeolite imidazole framework ZIF-67 was demonstrated: Congo red dye exhibited a rapid initial adsorption rate on the hierarchical porous ZIF-67 and reached adsorption equilibrium within 30 min. At room temperature (25℃), the adsorption removal rate of Congo red reached 94.77%, with a maximum adsorption capacity of 471 mg / g. The hierarchical porous ZIF-67 is stable in aqueous solution, exhibiting a large adsorption capacity, rapid adsorption rate, and short adsorption equilibrium time. Therefore, it can be considered an effective and promising zeolite imidazole framework adsorbent for removing dyes from aqueous solutions. Green and environmentally friendly methods, optimized synthesis, and secondary ligand removal technology will be important development directions for the future preparation of ZIFs, which will further promote their sustainable application. Detailed Implementation

[0006] A rapid, room-temperature synthesis of zeolite imidazole framework ZIF-67 was achieved using a conventional solvent method, reducing the molar ratio of the organic ligand 2-methylimidazolium to metal ions to 4:1. Simultaneously, the synthesis was conducted in a minimal alcoholic system. This green synthesis method enabled the adsorption of the azo dye Congo red, achieving not only low energy costs but also minimizing environmental impact and carbon footprint. Furthermore, the hierarchical porous zeolite imidazole framework ZIF-67 was prepared using a secondary ligand removal technique, leveraging the tunable pore structure of the zeolite imidazole framework.

[0007] (1) Green synthesis of zeolite imidazole framework ZIF-67: 2.32 g of cobalt nitrate was dissolved in 30 ml of methanol, and 1.72 g of 2-methylimidazole and 0.9 g of the secondary ligand 2-aminobenzimidazole were dissolved in 30 ml of methanol. The two solutions were mixed and stirred with a magnetic stirrer at room temperature (25 °C) for 4 h. After centrifugation, the bottom precipitate was washed three times with anhydrous ethanol and then dried overnight at 60 °C in a drying oven. Finally, it was ground into powder using a mortar and pestle to obtain the adsorbent ZIF-67.

[0008] (2) Preparation of hierarchical pore zeolite imidazole framework ZIF-67: ZIF-67 was heated in a muffle furnace at a calcination temperature of 290℃ for 2 hours to remove secondary ligands and form a hierarchical pore structure.

[0009] (3) Adsorption of Congo red on hierarchical zeolite imidazole framework ZIF-67: Congo red dye showed a rapid initial adsorption rate on hierarchical ZIF-67 and reached adsorption equilibrium at 30 min. The adsorption removal rate of Congo red at room temperature (25℃) was 94.77%, and the maximum adsorption capacity was 471 mg / g.

[0010] Hierarchical ZIF-67 is stable in aqueous solution, exhibiting high adsorption capacity, rapid adsorption rate, and short adsorption equilibrium time. Therefore, it can serve as an effective and promising zeolite imidazole framework adsorbent for dye removal from aqueous solutions. Green and environmentally friendly methods, optimized synthesis, and secondary ligand removal technologies will be important development directions for the future preparation of ZIFs, further promoting their sustainable applications.

[0011]

[0012]

Claims

1. A method for preparing a zeolite imidazole framework adsorbent, characterized in that: Includes the following steps: Step 1: Weigh 2-4 grams of cobalt nitrate and dissolve it in 20-40 ml of methanol; Step 2: Weigh out 1-2 grams of 2-methylimidazole and 0.5-1 gram of the secondary ligand 2-aminobenzimidazole and dissolve them in 20-40 ml of methanol; Step 3: Mix the solutions obtained in Step 1 and Step 2 separately, stir with a magnetic stirrer at room temperature (25℃) for 4 hours, and then centrifuge. After centrifugation, rinse the bottom precipitate with anhydrous ethanol 3 times, and then dry it overnight in a drying oven at 60℃. Grind it into powder with a mortar and pestle to obtain the adsorbent ZIF-67. Step 4: Heat ZIF-67 in a muffle furnace at 290℃ for 2 hours to remove secondary ligands and finally form a hierarchical pore structure of zeolite imidazole framework ZIF-67.

2. The method for preparing a zeolite imidazole framework adsorbent according to claim 1, characterized in that: In step one, the optimal mass of cobalt nitrate is 2.32 g and the optimal mass of methanol is 30 ml. In step two, the optimal mass of 2-methylimidazole is 1.72 g, the optimal mass of the secondary ligand 2-aminobenzimidazole is 0.9 g, and the optimal mass of methanol is 30 ml.

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