Preparation method of zeolite-like imidazole framework ZIF-8

Abstract

The invention provides a preparation method of zeolite-like imidazole framework ZIF-8, which comprises the following steps: mixing a zinc salt aqueous solution with strong acid cation exchange resin, exchanging zinc ions in the zinc salt aqueous solution into the strong acid cation exchange resin, and filtering to obtain resin with the zinc ions. And carrying out solid-phase mixing on the resin with the zinc ions and an imidazole derivative, and carrying out heat treatment on the mixture under a microwave condition, so that the imidazole derivative is diffused into the resin and reacts with the zinc ions, thereby obtaining the resin with the zeolite-like imidazole skeleton ZIF-8. The zeolite-like imidazole framework ZIF-8 in the resin with the zeolite-like imidazole framework ZIF-8 is washed out through a solvent. And then carrying out drying treatment on the eluate, so as to obtain the zeolite-like imidazole framework ZIF-8. According to the method, the influence of anions in the zinc salt on the reaction can be eliminated, and the purity of the zeolite-like imidazole framework ZIF-8 can be improved.

Description

Technical Field

[0001] The present invention relates to the field of preparing ZIF-8 materials, and particularly to a preparation method of zeolitic imidazolate framework ZIF-8. Background Art

[0002] Zeolitic imidazolate framework materials (ZIFs) are a subclass of metal-organic framework materials (MOFs) assembled from transition metal ions and imidazole and its derivatives. Among them, ZIF-8, as one of the most representative ZIFs materials, has characteristics such as a special topological structure, excellent thermal stability, chemical stability, high specific surface area, and abundant active sites, and shows great application potential in many fields such as gas adsorption and separation, catalysis, and sensing.

[0003] At present, there are various synthesis methods for ZIF-8, such as the solvent method, hydrothermal method, microwave synthesis method, ultrasonic / sonochemical method, mechanochemical method, etc. In common synthesis methods, the solvent method usually dissolves metal ions and imidazole ligands in water or organic solvents at room temperature or under heating for reaction; the hydrothermal method heats the precursor solution in a reactor to achieve synthesis under certain pressure and temperature; the microwave method uses the interaction between electromagnetic waves and charged substances to provide energy for the reaction, thereby promoting the formation of ZIF-8; the mechanochemical method obtains the final product by grinding or ball milling the precursor.

[0004] However, these existing synthesis methods have some deficiencies in the actual application process. Taking the solvent method as an example, when using zinc salt as the zinc ion source, anions in the zinc salt (such as nitrate ions, sulfate ions, chloride ions, etc.) may participate in the reaction system and undergo side reactions with the target product ZIF-8, or remain in the product, thus affecting the purity of ZIF-8. And purity is crucial for ZIF-8 in some application scenarios with strict requirements for material performance (such as high-end catalytic reactions, highly sensitive sensing, etc.). Lower purity may lead to a decline in its performance and fail to meet the actual needs.

[0005] Therefore, it is of great practical significance to develop a preparation method that can improve the purity of ZIF-8. Summary of the Invention

[0006] Based on the above problems, the present invention provides a preparation method of zeolitic imidazolate framework ZIF-8, which excludes the influence of anions in zinc salt on the reaction through specific process steps, and significantly improves the purity of zeolitic imidazolate framework ZIF-8.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of zeolitic imidazolate framework ZIF-8, comprising the following steps: Mix an aqueous zinc salt solution with a strongly acidic cation exchange resin, exchange the zinc ions in the aqueous zinc salt solution into the strongly acidic cation exchange resin, filter to obtain a resin with zinc ions; solid-phase mix the resin with zinc ions and an imidazole derivative, and heat-treat the mixture under microwave conditions to allow the imidazole derivative to diffuse into the resin with zinc ions and react with the zinc ions to obtain a resin with zeolitic imidazolate framework ZIF-8; wash out the zeolitic imidazolate framework ZIF-8 in the resin with zeolitic imidazolate framework ZIF-8 through a solvent; then perform a drying treatment on the eluate to obtain zeolitic imidazolate framework ZIF-8.

[0008] Optionally, the molar concentration of zinc ions in the aqueous zinc salt solution is 0.1 - 1 mol / L.

[0009] Optionally, the zinc salt in the aqueous zinc salt solution is one or more of zinc nitrate, zinc sulfate, and zinc chloride.

[0010] Optionally, the mass ratio of zinc ions in the aqueous zinc salt solution to the strongly acidic cation exchange resin is 1:(5 - 15).

[0011] Optionally, the strongly acidic cation exchange resin is one or more of styrene-based strongly acidic cation exchange resins and acrylic acid-based strongly acidic cation exchange resins.

[0012] Optionally, the temperature for mixing the aqueous zinc salt solution with the strongly acidic cation exchange resin is 20 - 40 °C, and the mixing time is 1 - 3 h.

[0013] Optionally, the imidazole derivative is one or more of 2-methylimidazole, 2-ethylimidazole, and 2-propylimidazole.

[0014] Optionally, in the heat treatment, the microwave power is 200 - 500 W, and the treatment time is 5 - 15 min.

[0015] Optionally, in the step of washing out the zeolitic imidazolate framework ZIF-8 in the resin with zeolitic imidazolate framework ZIF-8 through a solvent, the solvent is one or more of methanol, ethanol, and acetone.

[0016] Optionally, the temperature of the drying treatment is 60 - 80 °C, and the drying treatment time is 2 - 4 h.

[0017] Beneficial effects In the present invention, zinc ions are first exchanged into a strongly acidic cation exchange resin, effectively eliminating the interference of anions in zinc salts on subsequent reactions. In traditional synthesis methods, the anions in zinc salts may participate in the reaction or remain in the product, reducing the purity of ZIF-8. However, the method of the present invention enables only the reaction between zinc ions and imidazole derivatives to occur in the reaction system, greatly reducing the occurrence of side reactions, thereby significantly improving the purity of zeolitic imidazolate framework ZIF-8. Detailed implementation mode

[0018] An embodiment of the present invention provides a method for preparing zeolitic imidazolate framework ZIF-8, comprising the following steps: mixing an aqueous zinc salt solution with a strongly acidic cation exchange resin, exchanging the zinc ions in the aqueous zinc salt solution into the strongly acidic cation exchange resin, filtering to obtain a resin with zinc ions; performing solid-phase mixing on the resin with zinc ions and an imidazole derivative, and subjecting the mixture to heat treatment under microwave conditions to allow the imidazole derivative to diffuse into the resin with zinc ions and react with the zinc ions to obtain a resin with zeolitic imidazolate framework ZIF-8; washing out the zeolitic imidazolate framework ZIF-8 in the resin with zeolitic imidazolate framework ZIF-8 through a solvent; and then drying the washing solution to obtain zeolitic imidazolate framework ZIF-8.

[0019] It can be understood that the strongly acidic cation exchange resin can exchange the zinc ions in the aqueous zinc salt solution into the strongly acidic cation exchange resin while preventing the anions in the aqueous zinc salt solution from entering. After the aqueous zinc salt solution is mixed with the strongly acidic cation exchange resin, the zinc ions enter the strongly acidic cation exchange resin, and the anions continue to exist in the aqueous solution. Then, through filtration, the aqueous solution can be removed, and thus a resin with zinc ions can be obtained.

[0020] In the above embodiment, by first exchanging zinc ions into a strongly acidic cation exchange resin, the interference of anions in zinc salts on subsequent reactions is effectively eliminated. In traditional synthesis methods, the anions in zinc salts may participate in the reaction or remain in the product, reducing the purity of ZIF-8. However, the method of the present invention enables only the reaction between zinc ions and imidazole derivatives to occur in the reaction system, greatly reducing the occurrence of side reactions, thereby significantly improving the purity of zeolitic imidazolate framework ZIF-8.

[0021] Furthermore, in the preparation method of the zeolitic imidazolate framework ZIF-8 of the present invention, the entire preparation process does not require complex equipment and harsh reaction conditions. For example, in the zinc ion exchange step, the exchange can be completed at a conventional temperature (such as 20 - 40°C) and a relatively short time (such as 1 - 3 h); in the microwave heat treatment step, a moderate microwave power (such as 200 - 500 W) and a short treatment time (such as 5 - 15 min) can promote the reaction. This makes the preparation method of the present invention easy to operate and control, which is conducive to large-scale industrial production.

[0022] In addition, in the preparation method of the zeolitic imidazolate framework ZIF-8 of the present invention, the raw materials used, such as strongly acidic cation exchange resins, zinc salts, and imidazole derivatives, etc., are all common chemicals on the market and relatively low in price. At the same time, the simple process steps reduce energy consumption and equipment investment, further reducing production costs and improving economic benefits.

[0023] Optionally, the molar concentration of zinc ions in the zinc salt aqueous solution is 0.1 - 1 mol / L. For example, the molar concentration of zinc ions in the zinc salt aqueous solution can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, etc. It can be understood that the molar concentration of zinc ions in the zinc salt aqueous solution can also make other suitable selections within the range of 0.1 - 1 mol / L.

[0024] Optionally, the zinc salt in the zinc salt aqueous solution is one or more of zinc nitrate, zinc sulfate, and zinc chloride.

[0025] Optionally, the mass ratio of zinc ions to the strongly acidic cation exchange resin in the zinc salt aqueous solution is 1:(5 - 15). At this time, the zinc salt aqueous solution and the strongly acidic cation exchange resin can be better adapted, which is conducive to more fully exchanging zinc ions into the strongly acidic cation exchange resin. Optionally, the mass ratio of zinc ions to the strongly acidic cation exchange resin in the zinc salt aqueous solution can be 1:5, 1:8, 1:10, 1:12, 1:15, etc. It can be understood that the mass ratio of zinc ions to the strongly acidic cation exchange resin in the zinc salt aqueous solution can also make other suitable selections within the range of 1:(5 - 15).

[0026] Optionally, the strongly acidic cation exchange resin is one or more of styrene-based strongly acidic cation exchange resins and acrylic acid-based strongly acidic cation exchange resins.

[0027] Optionally, the zinc salt aqueous solution and the strongly acidic cation exchange resin are mixed by means of stirring and mixing.

[0028] Optionally, the temperature for mixing the zinc salt aqueous solution with the strongly acidic cation exchange resin is 20 - 40°C, and the mixing time is 1 - 3 h. With normal temperature and time, zinc ions can be exchanged into the strongly acidic cation exchange resin, which is beneficial to further reducing the preparation difficulty of zeolitic imidazolate framework ZIF-8 in the present invention. Further optionally, the temperature for mixing the zinc salt aqueous solution with the strongly acidic cation exchange resin can be 20°C, 25°C, 30°C, 35°C, 40°C, etc. The mixing time can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, etc. Further optionally, the mixing can be carried out at room temperature.

[0029] Mix the zinc salt aqueous solution with the strongly acidic cation exchange resin. In this process, zinc ions in the zinc salt aqueous solution will undergo an exchange reaction with the exchangeable cations (usually hydrogen ions) in the strongly acidic cation exchange resin, so that zinc ions are exchanged into the strongly acidic cation exchange resin. After the exchange is completed, through filtration operation, the resin with zinc ions is separated from the remaining solution to obtain the resin with zinc ions. Among them, the zinc salt in the zinc salt aqueous solution can be one or more of zinc nitrate, zinc sulfate, and zinc chloride. The strongly acidic cation exchange resin is preferably a styrene-based strongly acidic cation exchange resin or an acrylic acid-based strongly acidic cation exchange resin. To ensure the efficient progress of the exchange reaction, the temperature for mixing the zinc salt aqueous solution with the strongly acidic cation exchange resin is generally controlled at 20 - 40°C, and the mixing time is 1 - 3 h. Within this temperature and time range, both the exchange rate of zinc ions can be ensured, and the damage to the resin structure caused by too high temperature or too long time can be avoided.

[0030] Optionally, the imidazole derivative is one or more of 2-methylimidazole, 2-ethylimidazole, and 2-propylimidazole.

[0031] Optionally, when the resin with zinc ions and the imidazole derivative are mixed in solid phase, the mass ratio of the resin with zinc ions to the imidazole derivative is 1:(2 - 5). For example, the mass ratio of the resin with zinc ions to the imidazole derivative can be 1:2, 1:3, 1:4, 1:5, etc.

[0032] Optionally, in the heat treatment, the microwave power is 200 - 500 W, and the treatment time is 5 - 15 min. Optionally, the microwave power can be 200 W, 250 W, 300 W, 350 W, 400 W, 450 W, 500 W, etc. The heat treatment time can be 5 min, 8 min, 10 min, 12 min, 15 min, etc.

[0033] The resin with zinc ions and imidazole derivatives are mixed in solid phase. The imidazole derivatives can be one or more of 2-methylimidazole, 2-ethylimidazole, and 2-propylimidazole. When they are mixed in solid phase, the mass ratio is controlled at 1:(2 - 5). Subsequently, the mixture is placed under microwave conditions for heat treatment. Under the action of microwaves, the imidazole derivatives can rapidly diffuse into the resin and react with the zinc ions in the resin, thereby obtaining a resin with zeolitic imidazolate framework ZIF-8. When performing heat treatment under microwave conditions, the microwave power is set to 200 - 500 W, and the treatment time is 5 - 15 min. Appropriate microwave power and treatment time can provide sufficient energy for the reaction, promote the reaction between the imidazole derivatives and zinc ions, and at the same time avoid the destruction of the product structure due to excessive energy or too long time.

[0034] Optionally, in the step of washing out the zeolitic imidazolate framework ZIF-8 from the resin with zeolitic imidazolate framework ZIF-8 by a solvent, the solvent is one or more of methanol, ethanol, and acetone. These solvents can effectively dissolve and separate ZIF-8 without having an adverse effect on its structure and properties.

[0035] Optionally, when drying the washing solution, the drying temperature is 60 - 80 °C, and the drying time is 2 - 4 h. For example, the drying temperature can be 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, etc. The mixing time can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc. Under these temperature and time conditions, the solvent can be fully removed while ensuring the stability of the ZIF-8 structure, and a high-purity ZIF-8 product can be obtained.

[0036] Example 1 The preparation method of zeolitic imidazolate framework ZIF-8 in this example is as follows: S101: Weigh 10 g of styrene-based strongly acidic cation exchange resin and place it in a 250 ml beaker. Prepare 100 ml of zinc nitrate aqueous solution with a molar concentration of zinc ions of 0.2 mol / L, and slowly add it to the beaker containing the resin. Under the condition of a constant temperature water bath at 25 °C, stir and mix at a speed of 150 r / min for 2 h. Then, filter through a filtering device, and wash the filter residue with deionized water multiple times until no nitrate ions are detected in the filtrate, obtaining a resin with zinc ions.

[0037] S102: Weigh 5 g of the resin with zinc ions and 15 g of 2-methylimidazole, place the two in a mortar and grind them thoroughly and mix evenly. Transfer the mixed material to a microwave reaction vessel, set the microwave power to 300 W, and the treatment time to 10 min, and perform microwave heat treatment. After the reaction, a resin with zeolitic imidazolate framework ZIF-8 is obtained.

[0038] S103: Transfer the resin with zeolitic imidazolate framework ZIF-8 into a 250-ml separatory funnel, add 100 ml of methanol, and shake it vigorously for extraction for 15 min. After standing for layer separation, transfer the lower-layer methanol extract to a clean beaker. Repeat the above extraction operation three times and combine the extracts.

[0039] S104: Place the combined extracts in a vacuum drying oven at 65 °C and dry for 3 h to remove the methanol solvent, obtaining zeolitic imidazolate framework ZIF-8. After testing, the purity of this ZIF-8 is 98.5%.

[0040] Example 2 Compared with Example 1, the difference in this example is that the styrene-based strongly acidic cation exchange resin is replaced with an equal mass of acrylic acid-based strongly acidic cation exchange resin. Other steps are the same as those in Example 1. After testing, the purity of the prepared ZIF-8 is 97.6%.

[0041] Comparative Example 1 The traditional solvent method is used to prepare zeolitic imidazolate framework ZIF-8. The preparation method is as follows: Dissolve the same mass of zinc nitrate (3.78 g) as in the zinc nitrate aqueous solution in Example 1 in 100 mL of methanol. Dissolve 15 g of 2-methylimidazole in methanol. Mix the two solutions at room temperature and stir for reaction for 3 h. After the reaction is completed, obtain the solid product by centrifugal separation, wash it with methanol multiple times, and then dry it in a vacuum drying oven at 65 °C for 3 h to remove the methanol solvent, obtaining zeolitic imidazolate framework ZIF-8. After testing, the purity of this ZIF-8 is 85.7%.

[0042] It can be seen from the examples and comparative examples that the preparation method of the present invention can effectively improve the purity of zeolitic imidazolate framework ZIF-8.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0044] For those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A preparation method of zeolitic imidazolate framework ZIF-8, characterized in that, It includes the following steps: Mix an aqueous zinc salt solution with a strongly acidic cation exchange resin, exchange the zinc ions in the aqueous zinc salt solution onto the strongly acidic cation exchange resin, filter to obtain a resin with zinc ions; perform solid-phase mixing on the resin with zinc ions and an imidazole derivative, and heat-treat the mixture under microwave conditions to allow the imidazole derivative to diffuse into the resin with zinc ions and react with the zinc ions to obtain a resin with zeolitic imidazolate framework ZIF-8; wash out the zeolitic imidazolate framework ZIF-8 in the resin with zeolitic imidazolate framework ZIF-8 through a solvent; then perform a drying treatment on the eluate to obtain zeolitic imidazolate framework ZIF-8.

2. The preparation method of zeolitic imidazolate framework ZIF-8 according to claim 1, characterized in that, The molar concentration of zinc ions in the aqueous zinc salt solution is 0.1 - 1 mol / L.

3. The preparation method of zeolitic imidazolate framework ZIF-8 according to claim 1, characterized in that, The zinc salt in the aqueous zinc salt solution is one or more of zinc nitrate, zinc sulfate, and zinc chloride.

4. The preparation method of zeolitic imidazolate framework ZIF-8 according to claim 1, characterized in that, The mass ratio of zinc ions in the aqueous zinc salt solution to the strongly acidic cation exchange resin is 1:(5 - 15).

5. The preparation method of zeolitic imidazolate framework ZIF-8 according to claim 1, characterized in that, The strongly acidic cation exchange resin is one or more of styrene-based strongly acidic cation exchange resins and acrylic acid-based strongly acidic cation exchange resins.

6. The preparation method of zeolitic imidazolate framework ZIF-8 according to claim 1, wherein, The temperature for mixing the aqueous zinc salt solution with the strongly acidic cation exchange resin is 20 - 40 °C, and the mixing time is 1 - 3 h.

7. The preparation method of zeolitic imidazolate framework ZIF-8 according to claim 1, characterized in that, The imidazole derivative is one or more of 2-methylimidazole, 2-ethylimidazole, and 2-propylimidazole.

8. The preparation method of zeolitic imidazolate framework ZIF-8 according to any one of claims 1-7, characterized in that, In the heat treatment, the microwave power is 200 - 500 W, and the treatment time is 5 - 15 min.

9. The preparation method of zeolitic imidazolate framework ZIF-8 according to any one of claims 1-7, characterized in that, In the step of washing out the zeolitic imidazolate framework ZIF-8 in the resin with zeolitic imidazolate framework ZIF-8 through a solvent, the solvent is one or more of methanol, ethanol, and acetone.

10. The preparation method of zeolitic imidazolate framework ZIF-8 according to any one of claims 1-7, characterized in that, The temperature of the drying treatment is 60 - 80 °C, and the drying treatment time is 2 - 4 h.