A method for preparing a zeolite-like imidazolate framework ZIF-8

Abstract

The application provides a preparation method of zeolite-like imidazole framework ZIF-8, which comprises the following steps: mixing a zinc salt aqueous solution with a strong acid cation exchange resin, exchanging zinc ions in the zinc salt aqueous solution into the strong acid cation exchange resin, filtering, and obtaining a resin with zinc ions; mixing the resin with zinc ions and an imidazole derivative in solid phase, and performing heat treatment on the mixture under microwave conditions, so that the imidazole derivative diffuses into the resin and reacts with the zinc ions, and the resin with the zeolite-like imidazole framework ZIF-8 is obtained; and washing out the zeolite-like imidazole framework ZIF-8 in the resin with the zeolite-like imidazole framework ZIF-8 through a solvent. Then, the washing liquid is subjected to drying treatment, and the zeolite-like imidazole framework ZIF-8 is obtained. The method can exclude the influence of anions in the zinc salt on the reaction, and is beneficial to improving the purity of the zeolite-like imidazole framework ZIF-8.

Description

Technical Field

[0001] This invention relates to the field of ZIF-8 material preparation, specifically to a method for preparing ZIF-8 with a zeolite-like imidazole framework. Background Technology

[0002] Zeolite-like imidazole frameworks (ZIFs) are a subclass of metal-organic frameworks (MOFs) assembled from transition metal ions and imidazoles and their derivatives. Among them, ZIF-8, as the most representative ZIF material, has unique topological structure, excellent thermal stability, chemical stability, high specific surface area, and abundant active sites, showing great application potential in many fields such as gas adsorption and separation, catalysis, and sensing.

[0003] Currently, there are various methods for synthesizing ZIF-8, such as solvent synthesis, hydrothermal synthesis, microwave synthesis, ultrasonic / sonic chemical synthesis, and mechanochemical synthesis. Among the common synthesis methods, solvent synthesis typically involves dissolving metal ions and imidazole ligands in water or organic solvents at room temperature or under heating conditions; hydrothermal synthesis involves heating the precursor liquid in a reactor under certain pressure and temperature; microwave synthesis utilizes the interaction between electromagnetic waves and charged substances to provide energy for the reaction, thereby promoting the formation of ZIF-8; and mechanochemical synthesis obtains the final product by grinding or ball milling the precursor.

[0004] However, these existing synthesis methods have some shortcomings in practical applications. Taking the solvent method as an example, when using zinc salts as the zinc ion source, the anions in the zinc salts (such as nitrate ions, sulfate ions, chloride ions, etc.) may participate in the reaction system, undergoing side reactions with the target product ZIF-8, or remaining in the product, thus affecting the purity of ZIF-8. Purity is crucial for ZIF-8 in some applications with stringent material performance requirements (such as high-end catalytic reactions and high-sensitivity sensing), and lower purity may lead to performance degradation, failing to meet practical needs.

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

[0006] To address the above issues, this invention provides a method for preparing a zeolite-like imidazole framework ZIF-8. Through specific process steps, the influence of anions in zinc salts on the reaction is eliminated, significantly improving the purity of the zeolite-like imidazole framework ZIF-8.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a zeolite-like imidazole skeleton ZIF-8 includes the following steps: A zinc salt aqueous solution is mixed with a strongly acidic cation exchange resin to exchange zinc ions from the zinc salt aqueous solution into the strongly acidic cation exchange resin. The mixture is then filtered to obtain a resin containing zinc ions. The resin containing zinc ions is then solid-phase mixed with an imidazole derivative, and the mixture is heat-treated under microwave conditions to allow the imidazole derivative to diffuse into the resin containing zinc ions and react with them, resulting in a resin with a zeolite-like imidazole framework ZIF-8. The zeolite-like imidazole framework ZIF-8 in the resin is then eluted with a solvent. The eluent is then dried to obtain the zeolite-like imidazole framework ZIF-8.

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

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

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

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

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

[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 200-500W and the treatment time is 5-15min.

[0015] Optionally, in the step of eluting the ZIF-8 zeolite-like imidazole skeleton from the resin having the ZIF-8 zeolite-like imidazole skeleton with a solvent, the solvent is one or more of methanol, ethanol, and acetone.

[0016] Optionally, the drying temperature is 60-80℃, and the drying time is 2-4 hours.

[0017] Beneficial effects This invention effectively eliminates the interference of zinc salt anions on subsequent reactions by first exchanging zinc ions into a strongly acidic cation exchange resin. In traditional synthesis methods, zinc salt anions may participate in the reaction or remain in the product, reducing the purity of ZIF-8. The method of this invention ensures that only the reaction between zinc ions and imidazole derivatives occurs in the reaction system, greatly reducing side reactions and thus significantly improving the purity of the zeolite-like imidazole skeleton ZIF-8. Detailed Implementation

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

[0019] Understandably, a strongly acidic cation exchange resin can exchange zinc ions from a zinc salt aqueous solution into the resin, while preventing anions from entering. After the zinc salt aqueous solution is mixed with the strongly acidic cation exchange resin, zinc ions enter the resin, while anions remain in the aqueous solution. The solution is then removed by filtration, yielding a resin containing zinc ions.

[0020] In the above embodiment, by first exchanging zinc ions into a strongly acidic cation exchange resin, the interference of anions in the zinc salt on subsequent reactions is effectively eliminated. In conventional synthesis methods, anions in the zinc salt may participate in the reaction or remain in the product, reducing the purity of ZIF-8. The method of this invention ensures that only the reaction between zinc ions and the imidazole derivative exists in the reaction system, greatly reducing the occurrence of side reactions and thus significantly improving the purity of the zeolite-like imidazole skeleton ZIF-8.

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

[0022] Furthermore, the raw materials used in the preparation method of the zeolite-like imidazole framework ZIF-8 of the present invention, such as strong acid cation exchange resin, zinc salt, and imidazole derivatives, are all commercially available and relatively inexpensive chemicals. At the same time, the simple process steps reduce energy consumption and equipment investment, further lowering production costs and improving economic efficiency.

[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 is understood that other suitable choices can be made within the range of 0.1-1 mol / L for the molar concentration of zinc ions in the zinc salt aqueous solution.

[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). In this case, the zinc salt aqueous solution and the strongly acidic cation exchange resin are better compatible, which facilitates a more complete exchange of zinc ions into the strongly acidic cation exchange resin. Alternatively, 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 is understood that other suitable choices can be made within the range of 1:(5-15) for the mass ratio of zinc ions to the strongly acidic cation exchange resin in the zinc salt aqueous solution.

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

[0027] Optionally, the zinc salt aqueous solution is mixed with a strongly acidic cation exchange resin by stirring.

[0028] Optionally, the zinc salt aqueous solution is mixed with the strongly acidic cation exchange resin at a temperature of 20-40°C for 1-3 hours. By using room temperature and time, zinc ions can be exchanged into the strongly acidic cation exchange resin, which helps to further reduce the difficulty of preparing the zeolite-like imidazole framework ZIF-8 in this invention. Further optionally, the mixing temperature of the zinc salt aqueous solution and the strongly acidic cation exchange resin can be 20°C, 25°C, 30°C, 35°C, 40°C, etc., and the mixing time can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, etc. Further optionally, the mixing can be carried out at room temperature.

[0029] A zinc salt aqueous solution is mixed with a strongly acidic cation exchange resin. During this process, zinc ions in the zinc salt aqueous solution react with exchangeable cations (usually hydrogen ions) in the strongly acidic cation exchange resin, thereby transferring zinc ions into the resin. After the exchange is complete, the resin containing zinc ions is separated from the remaining solution by filtration, yielding a resin containing zinc ions. 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 or acrylic-based strongly acidic cation exchange resin. To ensure efficient exchange, the temperature during mixing of the zinc salt aqueous solution and the strongly acidic cation exchange resin is generally controlled at 20-40℃, and the mixing time is 1-3 hours. Within this temperature and time range, the zinc ion exchange rate is guaranteed while avoiding damage to the resin structure due to excessively high temperature or prolonged time.

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

[0031] Optionally, when the resin containing zinc ions and the imidazole derivative are mixed in a solid phase, the mass ratio of the resin containing zinc ions to the imidazole derivative is 1:(2-5). For example, the mass ratio of the resin containing 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 200-500W, and the treatment time is 5-15 minutes. Optionally, the microwave power can be 200W, 250W, 300W, 350W, 400W, 450W, 500W, etc. The heat treatment time can be 5 minutes, 8 minutes, 10 minutes, 12 minutes, 15 minutes, etc.

[0033] A resin containing zinc ions and an imidazole derivative are mixed in a solid-phase manner. The imidazole derivative can be one or more of 2-methylimidazolium, 2-ethylimidazolium, and 2-propylimidazolium. The mass ratio of the two components during solid-phase mixing is controlled at 1:(2-5). Subsequently, the mixture is subjected to microwave heat treatment. Under microwave irradiation, the imidazole derivative rapidly diffuses into the resin and reacts with the zinc ions in the resin, thereby obtaining a resin with a zeolite-like imidazole framework, ZIF-8. During microwave heat treatment, the microwave power is set to 200-500W, and the treatment time is 5-15 minutes. Appropriate microwave power and treatment time provide sufficient energy to promote the reaction between the imidazole derivative and zinc ions, while avoiding damage to the product structure due to excessive energy or prolonged treatment time.

[0034] Optionally, in the step of eluting the ZIF-8 zeolite-like imidazole skeleton from the resin with a solvent, the solvent is one or more selected from methanol, ethanol, and acetone. These solvents can effectively dissolve and separate ZIF-8 without adversely affecting its structure and properties.

[0035] Optionally, when drying the eluent, the drying temperature is 60-80℃, and the drying time is 2-4 hours. For example, the drying temperature can be 60℃, 65℃, 70℃, 75℃, 80℃, etc. The mixing time can be 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc. Under these temperature and time conditions, the solvent can be fully removed while ensuring the structural stability of ZIF-8, resulting in a high-purity ZIF-8 product.

[0036] Example 1 In this embodiment, the preparation method of the zeolite imidazole skeleton ZIF-8 is as follows: S101: Weigh 10g of styrene-based strong acid cation exchange resin and place it in a 250ml beaker. Prepare 100ml of a zinc nitrate aqueous solution with a zinc ion molar concentration of 0.2mol / L, and slowly add it to the beaker containing the resin. Mix the resin by stirring at 150r / min for 2 hours under a constant temperature water bath at 25℃. Afterward, filter the solution using a filtration device, and wash the filter residue multiple times with deionized water until no nitrate ions are detected in the filtrate, thus obtaining resin containing zinc ions.

[0037] S102: Weigh 5g of resin containing zinc ions and 15g of 2-methylimidazole, and grind them thoroughly in a mortar until homogeneous. Transfer the mixture to a microwave reaction vessel, set the microwave power to 300W, and the treatment time to 10min for microwave heat treatment. After the reaction is complete, a resin with a zeolite-like imidazole skeleton ZIF-8 is obtained.

[0038] S103: Transfer the resin with the zeolite-like imidazole skeleton ZIF-8 to a 250 ml separatory funnel, add 100 ml of methanol, and extract thoroughly by shaking for 15 min. After standing and separating the layers, transfer the lower methanol extract to a clean beaker. Repeat the above extraction operation 3 times and combine the extracts.

[0039] S104: The combined extracts were dried in a vacuum drying oven at 65°C for 3 hours to remove the methanol solvent, yielding ZIF-8, a zeolite-like imidazole skeleton. The purity of this ZIF-8 was determined to be 98.5%.

[0040] Example 2 Compared to Example 1, the difference in this example is that the styrene-based strong acid cation exchange resin is replaced with an equal mass of acrylic-based strong acid cation exchange resin. All other steps are the same as in Example 1. The purity of the ZIF-8 prepared in this example was tested to be 97.6%.

[0041] Comparative Example 1 The zeolite-like imidazole framework ZIF-8 was prepared using a conventional solvent method. The preparation method was as follows: Zinc nitrate (3.78 g), the same mass as in the zinc nitrate aqueous solution in Example 1, was dissolved in 100 mL of methanol. 15 g of 2-methylimidazole was dissolved in methanol. The two solutions were mixed at room temperature and stirred for 3 h. After the reaction was complete, the solid product was obtained by centrifugation, washed repeatedly with methanol, and dried in a vacuum drying oven at 65 °C for 3 h to remove the methanol solvent, yielding the zeolite-like imidazole framework ZIF-8. The purity of this ZIF-8 was determined to be 85.7%.

[0042] As can be seen from the examples and comparative examples, the preparation method of the present invention can effectively improve the purity of the zeolite-like imidazole skeleton ZIF-8.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0044] For those skilled in the art, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for preparing a zeolite-like imidazole framework ZIF-8, characterized in that, The process includes the following steps: mixing a zinc salt aqueous solution with a strong acid cation exchange resin, exchanging zinc ions from the zinc salt aqueous solution into the strong acid cation exchange resin, filtering to obtain a resin containing zinc ions, wherein the mass ratio of zinc ions in the zinc salt aqueous solution to the strong acid cation exchange resin is 1:(5-15), and the strong acid cation exchange resin is one or more of styrene-based strong acid cation exchange resin and acrylic-based strong acid cation exchange resin; the mixing temperature of the zinc salt aqueous solution and the strong acid cation exchange resin is 20-40℃, and the mixing time is 1-3 hours; the resin containing zinc ions and... Imidazole derivatives are solid-phase mixed and the mixture is heat-treated under microwave conditions to allow the imidazole derivatives to diffuse into the resin containing zinc ions and react with the zinc ions, thereby obtaining a resin with a zeolite-like imidazole skeleton ZIF-8. During the heat treatment, the microwave power is 200-500W and the treatment time is 5-15 minutes. The zeolite-like imidazole skeleton ZIF-8 in the resin is then eluted with a solvent. The elution solution is then dried to obtain the zeolite-like imidazole skeleton ZIF-8. The drying temperature is 60-80℃ and the drying time is 2-4 hours.

2. The method for preparing the zeolite-like imidazole framework ZIF-8 as described in claim 1, characterized in that, The molar concentration of zinc ions in the zinc salt aqueous solution is 0.1-1 mol / L.

3. The method for preparing the zeolite-like imidazole framework ZIF-8 as described in claim 1, characterized in that, The zinc salt in the zinc salt aqueous solution is one or more of zinc nitrate, zinc sulfate, and zinc chloride.

4. The method for preparing the zeolite-like imidazole framework ZIF-8 as described in claim 1, characterized in that, The imidazole derivative is one or more of 2-methylimidazolium, 2-ethylimidazolium, and 2-propylimidazolium.

5. The method for preparing ZIF-8, a zeolite-like imidazole framework as described in any one of claims 1-4, is characterized in that, In the step of eluting the ZIF-8 zeolite-like imidazole skeleton from the resin with the ZIF-8 zeolite-like imidazole skeleton using a solvent, the solvent is one or more of methanol, ethanol, and acetone.