Application of Cobalt-based Metal-Hydrogen Bond-Organic Framework Materials in pH Detection

Abstract

The present invention relates to the field of detection technology, and discloses an application of a cobalt-based metal-hydrogen bond-organic framework material in detecting pH value. The chemical formula of the cobalt-based metal-hydrogen bond-organic framework material is Co(M)6CO3·m(H2O), where M is imidazole and m is 6-9. The range of pH value detected by the cobalt-based metal-hydrogen bond-organic framework material is 2.0-2.4. When the pH value of the solution detected by the cobalt-based metal-hydrogen bond-organic framework material is 2.0-2.4, the color change of the solid precipitate is from pink to purplish red to purple, and its detection accuracy can reach an interval of 0.1 for the pH value.

Description

Technical Field

[0001] The present invention relates to the field of detection technology, and particularly to the application of cobalt-based metal-hydrogen bond-organic framework materials in detecting pH values. Background Art

[0002] The pH value of a material, as an important property of the material, is widely used in various fields such as engineering, agriculture, chemical industry, and medicine. So far, there are three most common methods for detecting the pH value of a liquid environment. The first method is to use a precision pH meter with a glass electrode. A pH meter is a device for precisely measuring the hydrogen ion concentration. However, the price of a pH meter is relatively high, the electrode is easily damaged by a slight impact, and the glass electrode needs to be pre-cleaned before each use, and the operation process is cumbersome. The second method is pH test paper, which is prepared by impregnating filter paper with an indicator. When in use, the approximate pH value of the solution can be found by observing the color change of the test paper and comparing the color of the test paper with a standard colorimetric card. The advantage of this method is that it can simply and quickly test the pH value. However, the pH error range obtained by the pH test paper is about 0.2 - 0.5, the accuracy is poor, and the pH value detection interval of the pH test paper is 1.0, and the detection error is large. The third method is acid-base indicators, which can judge the acidity and alkalinity of the solution by changing the color of the indicator according to the acidity of the solution. The disadvantage of this method is that it can only judge the approximate pH value range of the solution and cannot obtain the specific pH value. In addition, among acid-base indicators, methyl red and methyl orange can be used as acid indicators for detecting pH < 7.0. The pH value range that methyl red can detect is 4.4 - 6.2, and the pH value range that methyl orange can detect is 3.1 - 4.4. The corresponding color changes of these two indicators are all red-orange-yellow, and their colors can only indicate that the pH value of the test solution is in a certain range and cannot measure the specific pH value of the test solution.

[0003] Metal-organic framework materials (MOFs) are porous crystalline materials self-assembled by metal ions or metal clusters and organic ligands through coordination. Hydrogen bond-organic frameworks (HOFs) are a kind of highly ordered new porous crystalline materials. The two materials have advantages such as high porosity, large specific surface area, adjustable material size, diversity of material composition, thermal stability and chemical stability, functionalization modification, and mild synthesis conditions, and have become new porous materials that have attracted wide attention and research. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems such as high cost and complex operation process of traditional pH meters, and large test errors of pH test papers, and provide a cobalt-based metal-hydrogen bond-organic framework material for testing the pH value of a solution.

[0005] To achieve the above object, the present invention provides an application of a cobalt-based metal-hydrogen bond-organic framework material in detecting pH value. The chemical formula of the cobalt-based metal-hydrogen bond-organic framework material is Co(M)6CO3·m(H2O), where M is imidazole and m is 6-9.

[0006] Preferably, the pH value detection range of the cobalt-based metal-hydrogen bond-organic framework material is 2.0-2.4.

[0007] Preferably, the preparation method of the cobalt-based metal-hydrogen bond-organic framework material comprises the following steps:

[0008] (1) Prepare an aqueous solution containing divalent cobalt ions and an aqueous solution containing imidazole and carbonate;

[0009] (2) Mix the aqueous solution containing divalent cobalt ions and the aqueous solution containing imidazole and carbonate to obtain the cobalt-based metal-hydrogen bond-organic framework material.

[0010] Preferably, in step (1), the aqueous solution containing imidazole and carbonate is obtained by mixing N'N-carbonyldiimidazole with water, or by mixing imidazole, a substance providing carbonate, and water.

[0011] Preferably, in step (2), the mixing temperature is 50-100°C, preferably 60-80°C.

[0012] Preferably, the divalent cobalt ions are provided by cobalt chloride, cobalt nitrate, cobalt sulfate or cobalt acetate.

[0013] Preferably, the molar concentration of divalent cobalt ions in the aqueous solution containing divalent cobalt ions is 0.1-0.8 mol / L.

[0014] Preferably, the substance providing carbonate is selected from one of sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate.

[0015] Preferably, the molar ratio of divalent cobalt ions in the divalent cobalt ion aqueous solution to imidazole in the aqueous solution containing imidazole and carbonate is (0.5-2):(5-10), preferably 0.5:5-8.

[0016] Preferably, the mixing method of the two solutions in step (2) includes direct mixing, ultrasonic mixing or magnetic stirring mixing.

[0017] Through the above technical solution, the cobalt-based metal-hydrogen bond-organic framework material of the present invention combines the bonding principle of MOFs. A coordination bond is formed between the metal and the organic ligand, and then it is connected to the hydrogen bond-organic framework (HOFs) by hydrogen bonds to finally obtain the cobalt-based metal-hydrogen bond-organic framework material. This material has a simple preparation process, easily available raw materials, and mild preparation conditions, which is convenient for large-scale production. When the cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O) is used to detect the pH of a solution, due to the presence of carbonate ions in the structure of the cobalt-based metal-hydrogen bond-organic framework material, the crystal has a high sensitivity to acidic solutions. Relying on the coordination color change principle of cobalt ions, it is possible to very simply and quickly determine the solution with a pH value in the range of 2.0 - 2.4, and obtain the pH value of the solution to be measured, and the test result has high accuracy.

[0018] When the cobalt-based metal-hydrogen bond-organic framework is placed in a strong acid solution, it can be observed that when the pH value of the solution is 2.0, the solid precipitate is pink and the supernatant is pink; when the pH value of the solution is 2.4, the solid precipitate is purple and the supernatant is purple; when the pH value of the solution is 2.2, the solid precipitate is magenta and the supernatant is reddish. Thus, strong acidic solutions with pH values in the range of 2.0 - 2.4 can be accurately distinguished by the obvious visible light color change phenomenon of the solution to be measured. The pH value of the solution to be measured with a pH value in the range of 2.0 - 2.4 can also be obtained according to the color change of the cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O), and the pH values of various strong acids and mixed acids can be measured. The specific test accuracy can reach a pH value interval of 0.1. This test accuracy is much higher than that of pH test papers, but the overall test cost is lower than that of pH meters. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a diagram showing the color changes of the solid precipitate and the supernatant when the cobalt-based metal-hydrogen bond-organic framework material prepared in Example 1 is used to detect the pH value of the H2SO4 solution. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0021] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0022] To achieve the above object, the present invention provides an application of a cobalt-based metal-hydrogen bond-organic framework material in pH value detection. The chemical formula of the cobalt-based metal-hydrogen bond-organic framework material is Co(M)6CO3·m(H2O), where M is imidazole and m is 6-9.

[0023] Specifically, in the chemical formula Co(M)6CO3·m(H2O) of the cobalt-based metal-hydrogen bond-organic framework material, m is 6, 7, 8, or 9.

[0024] Preferably, the pH value range detected by the cobalt-based metal-hydrogen bond-organic framework material is 2.0-2.4. Specifically, the pH value can be 2.0, 2.1, 2.2, 2.3, or 2.4.

[0025] In a preferred embodiment, the solution detected by the cobalt-based metal-hydrogen bond-organic framework material is a common strong acid solution, including hydrochloric acid, sulfuric acid, or nitric acid.

[0026] Preferably, the preparation method of the cobalt-based metal-hydrogen bond-organic framework material includes the following steps:

[0027] (1) Prepare an aqueous solution containing divalent cobalt ions and an aqueous solution containing imidazole and carbonate ions;

[0028] (2) Mix the aqueous solution containing divalent cobalt ions and the aqueous solution containing imidazole and carbonate ions to obtain the cobalt-based metal-hydrogen bond-organic framework material.

[0029] Preferably, in step (1), the aqueous solution containing imidazole and carbonate ions is obtained by mixing N'N-carbonyldiimidazole with water, or by mixing imidazole, a substance providing carbonate ions, and water.

[0030] Preferably, in step (2), the mixing temperature is 50-100°C, preferably 60-80°C. Specifically, the mixing temperature can be 60°C, 70°C, or 80°C.

[0031] Preferably, the divalent cobalt ions are provided by cobalt chloride, cobalt nitrate, cobalt sulfate, or cobalt acetate.

[0032] Preferably, the molar concentration of divalent cobalt ions in the aqueous solution containing divalent cobalt ions is 0.1-0.8 mol / L. Specifically, the molar concentration of divalent cobalt ions in the aqueous solution containing divalent cobalt ions 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, or 0.8 mol / L.

[0033] Preferably, the substance providing carbonate is selected from one of sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate.

[0034] Preferably, the molar ratio of divalent cobalt ions in the divalent cobalt ion aqueous solution to imidazole in the aqueous solution containing imidazole and carbonate is (0.5 - 2):(5 - 10), preferably 0.5:5 - 8. Specifically, the molar ratio of divalent cobalt ions in the divalent cobalt ion aqueous solution to imidazole in the aqueous solution containing imidazole and carbonate can be 0.5:5, 0.5:6, 0.5:7, 0.5:8.

[0035] Preferably, the mixing method of the two solutions in step (2) includes direct mixing, ultrasonic mixing or magnetic stirring mixing.

[0036] The second aspect of the present invention provides a component for testing the pH value of a solution. The component includes a cobalt-based metal-hydrogen bond-organic framework material and a substrate loaded with the cobalt-based metal-hydrogen bond-organic framework material. The preparation method of the substrate loaded with the cobalt-based metal-hydrogen bond-organic framework material includes the following steps:

[0037] (1) Prepare an aqueous solution containing divalent cobalt ions and an aqueous solution containing imidazole and carbonate;

[0038] (2) Immerse the substrate material in the aqueous solution of divalent cobalt ions;

[0039] (3) Mix the aqueous solution of divalent cobalt ions in which the substrate material is immersed and the aqueous solution containing imidazole and carbonate to obtain a component for testing the pH value of the solution.

[0040] Preferably, the substrate material in step (2) can be a glass sheet, a plastic sheet, a silicon wafer, a base paper or a fabric.

[0041] The object of the present invention is to provide a cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O) for detecting the pH value of materials, which mainly utilizes the coordination color change principle of cobalt ions. The cobalt-based metal-hydrogen bond-organic framework material has the advantages of simple synthesis method, short synthesis time, high yield and low cost. Moreover, the material can distinguish strong acidic solutions with acidity less than 2.0 or greater than 2.4 through obvious visible light color change phenomena, and can accurately distinguish strong acidic solutions with pH values between 2.0 - 2.4 relying on the color change phenomenon of the cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O). The detection accuracy is 0.1 interval and the test results are accurate.

[0042] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto.

[0043] Example 1

[0044] This example is used to illustrate the preparation method of the cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O) of the present invention.

[0045] (1) Dissolve 118 mg of cobalt acetate hexahydrate in 1 mL of water to obtain an aqueous solution containing divalent cobalt ions, where the molar concentration of cobalt ions is 0.5 mol / L; dissolve 811 mg of N'N-carbonyldiimidazole (CDI) in 4 mL of water to obtain an aqueous solution containing imidazole and carbonate ions, where the molar concentration of imidazole is 1.25 mol / L;

[0046] (2) Mix the aqueous solution of cobalt nitrate hexahydrate in step (1) with the aqueous solution containing imidazole and carbonate ions at 80 °C. After standing for 3 minutes, perform sedimentation, solid-liquid separation, and drying operations in sequence to obtain the cobalt-based metal-hydrogen bond-organic framework material with the chemical formula Co(M)6CO3·8(H2O).

[0047] Example 2

[0048] This example is used to illustrate the preparation method of the cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O) of the present invention.

[0049] (1) Dissolve 117 mg of cobalt chloride hexahydrate in 1 mL of water to obtain an aqueous solution containing divalent cobalt ions, where the molar concentration of cobalt ions is 0.5 mol / L; dissolve 972 mg of N'N-carbonyldiimidazole (CDI) in 4 mL of water to obtain an aqueous solution containing imidazole and carbonate ions, where the molar concentration of imidazole is 1.5 mol / L;

[0050] (2) Mix the aqueous solution of cobalt chloride hexahydrate in step (1) with the aqueous solution containing imidazole and carbonate ions at 70 °C. After standing for 3 minutes, perform sedimentation, solid-liquid separation, and drying operations in sequence to obtain the cobalt-based metal-hydrogen bond-organic framework material with the chemical formula Co(M)6CO3·8(H2O).

[0051] Example 3

[0052] This example is used to illustrate the preparation method of the cobalt-based metal-hydrogen bond-organic framework material Co(M)6CO3·m(H2O) of the present invention.

[0053] (1) Dissolve 118 mg of cobalt acetate hexahydrate in 1 mL of water to obtain an aqueous solution containing divalent cobalt ions, where the molar concentration of cobalt ions is 0.5 mol / L; dissolve 680 mg of imidazole and 100 mg of sodium bicarbonate in 4 mL of water to obtain an aqueous solution containing imidazole and carbonate ions, where the molar concentration of imidazole is 1.25 mol / L;

[0054] (2) Mix the aqueous solution of cobalt(II) acetate hexahydrate in step (1) with the aqueous solution containing imidazole and carbonate at 80 °C. After standing for 3 minutes, perform sedimentation, solid-liquid separation, and drying operations in sequence to obtain a cobalt-based metal-hydrogen bond-organic framework material with the chemical formula Co(M)6CO3·8(H2O).

[0055] Example 4

[0056] This example is used to illustrate the preparation method of the test solution pH value component of the present invention.

[0057] (1) Dissolve 118 mg of cobalt(II) acetate hexahydrate in 1 mL of water to obtain an aqueous solution containing divalent cobalt ions, where the molar concentration of cobalt ions is 0.5 mol / L; dissolve 811 mg of N'N-carbonyldiimidazole (CDI) in 4 mL of water to obtain an aqueous solution containing imidazole and carbonate, where the molar concentration of imidazole is 1.25 mol / L.

[0058] (2) Immerse a cloth with a size of 1*1 cm 2 in the prepared aqueous solution of cobalt(II) acetate hexahydrate for 10 - 15 min;

[0059] (3) Mix the aqueous solution containing imidazole and carbonate in step (1) with the aqueous solution of cobalt(II) acetate hexahydrate in which the cloth is immersed in step (2) at 80 °C. After standing for 30 minutes, take out the cloth, rinse it with water, and dry it to obtain the test solution pH value component.

[0060] Test Example

[0061] Test Example 1

[0062] This test example is to test the color change of the cobalt-based metal-hydrogen bond-organic framework material prepared in Example 1 when detecting H2SO4 solution. The specific test results are as Figure 1 shown.

[0063] (1) Prepare H2SO4 solutions with pH values of 1.0, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 4.0 in advance;

[0064] (2) Weigh 30 mg of the Co(M)6CO3·8(H2O) crystals obtained in step (2) of Example 1 and place them in a 5 mL centrifuge tube. Then add 2 mL of the HCl solutions with the respective pH values prepared in step (1) to the centrifuge tube. After shaking and standing for 1 min, observe the color changes of the solid precipitate and the supernatant in the mixed solution, and record the color changes of the supernatant and the solid precipitate in the mixed solution after the test.

[0065] Test Example 2

[0066] This test example is to test the color change of the cobalt-based metal-hydrogen bond-organic framework material prepared in Test Example 1 when detecting HCl solution.

[0067] (1) Prepare HCl solutions with pH values of 1.0, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 4.0 in advance;

[0068] (2) Weigh 30 mg of Co(M)6CO3·8(H2O) obtained in Step (2) of Example 1 and place it in a 5 mL centrifuge tube. Then add 2 mL of the HCl solutions with the respective pH values prepared in Step (1) to the centrifuge tube. After shaking well and standing for 1 min, observe the color changes of the solid precipitate and the supernatant in the mixed solution, record the color changes of the supernatant and the solid precipitate in the mixed solution after the test, and compare this color change with the result obtained in Test Example 1.

[0069] Test Example 3

[0070] This test example is to test the color change of the cobalt-based metal-hydrogen bond-organic framework material prepared in Test Example 2 when detecting HNO3 solution.

[0071] (1) Prepare HNO3 solutions with pH values of 1.0, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 4.0 in advance;

[0072] (2) Weigh 30 mg of Co(M)6CO3·8(H2O) obtained in Step (2) of Example 2 and place it in a 5 mL centrifuge tube. Then add 2 mL of the HNO3 solutions with the respective pH values prepared in Step (1) to the centrifuge tube. After shaking well and standing for 1 min, observe the color changes of the solid precipitate and the supernatant in the mixed solution, record the color changes of the supernatant and the solid precipitate in the mixed solution after the test, and compare this color change with the result obtained in Test Example 1.

[0073] Test Example 4

[0074] This test example is to test the color change of the cobalt-based metal-hydrogen bond-organic framework material prepared in Test Example 3 when detecting a mixed solution of H2SO4, HNO3, and HCl.

[0075] (1) Prepare a mixed solution of H2SO4, HNO3, and HCl with pH values of 1.0, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 4.0 in advance;

[0076] (2) Weigh 30 mg of Co(M)6CO3·8(H2O) obtained in step (2) of Example 3 and place it in a 5 mL centrifuge tube. Then add 2 mL of the mixed solution of H2SO4, HNO3, and HCl with various pH values pre-prepared in step (1) into the centrifuge tube. After shaking well and standing for 1 min, observe the color changes of the solid precipitate and the supernatant in the mixed solution, record the color changes of the supernatant and the solid precipitate in the mixed solution after the test, and compare this color change with the result obtained in Test Example 1.

[0077] Test Example 5

[0078] This test example is to detect the color change when the pH value component of the test solution prepared in Example 4 detects H2SO4 solution.

[0079] (1) Pre-prepare H2SO4 solutions with pH values of 1.0, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 4.0.

[0080] (2) Drop the pre-prepared H2SO4 solutions with various pH values in step (1) onto the cloth loaded with cobalt-based metal-hydrogen bond-organic framework material after drying, observe the color change of the cloth, and compare the color change of the cloth after the test with the color of the solid precipitate after the test in Example 1.

[0081] From the results of Test Example 1, it can be seen that after mixing the cobalt-based metal-hydrogen bond-organic framework material with the test solution, it can be observed that when the pH value of the test solution is 2.0, the solid precipitate in the mixed solution is pink and the supernatant is pink. When the pH value of the test solution is 2.2, the solid precipitate in the mixed solution is magenta and the supernatant tends to be red. When the pH value of the test solution is 2.4, the solid precipitate in the mixed solution is purple and the supernatant is purple. From this color change, it can be known that the cobalt-based metal-hydrogen bond-organic framework material can accurately judge the solution with a pH value of 2.0 - 2.4 through the visible light color change phenomenon.

[0082] Observe the color changes in Test Examples 2 - 4. By comparing the color changes of the supernatant and the solid precipitate in this test example with the colors observed in Example 1, it can be seen that although the components of the test solutions used in Test Examples 2 - 4 are different, the color changes of the supernatant and the lower solid in the mixed solution obtained by the test are similar to those in Test Example 1, indicating that the color changes of this cobalt-based metal-hydrogen bond-organic framework material when testing strong acid solutions with different components are consistent, with high accuracy and small error in detecting the pH value.

[0083] Observe the color change in Test Example 5. By comparing the color change of the fabric in the components of the test example with the color observed in Example 1, it can be seen that when the pH value of the solution to be tested is 2.0, the fabric color turns pink. When the pH value of the solution to be tested is 2.2, the fabric color turns purplish red. When the pH value of the solution to be tested is 2.4, the fabric color turns purple. From the results of Test Example 5, it can be known that the color change presented by the component for testing the pH value of the test solution at different pH values is consistent with the color change of the solid precipitate in Test Example 1, indicating that this component has high accuracy when used to test the pH value of strong acidic solutions.

[0084] Using the method described in the present invention to detect the pH value of a solution with a cobalt-based metal-hydrogen bond-organic framework material, the pH value of the solution to be tested can be obtained based on the obvious visible light color change phenomenon of the cobalt-based metal-hydrogen bond-organic framework material. Relying on this phenomenon, the solution to be tested with pH values of 2.0, 2.1, 2.2, 2.3, and 2.4 can be accurately judged, and the detection accuracy can reach a pH value interval of 0.1, and the detection results are accurate.

[0085] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. Application of a cobalt-based metal-hydrogen bond-organic framework material in detecting pH value, characterized in that, The chemical formula of the cobalt-based metal-hydrogen bond-organic framework material is Co(M)6CO3·m(H2O), where M is imidazole and m is 6-9; The pH value range for detecting the cobalt-based metal-hydrogen bond-organic framework material is 2.0-2.

4.

2. The application according to claim 1, characterized in that, The preparation method of the cobalt-based metal-hydrogen bond-organic framework material comprises the following steps: (1) Prepare an aqueous solution of divalent cobalt ions and an aqueous solution containing imidazole and carbonate; (2) Mix the aqueous solution containing divalent cobalt ions and the aqueous solution containing imidazole and carbonate to obtain the cobalt-based metal-hydrogen bond-organic framework material.

3. The application according to claim 2, wherein, In step (1), the aqueous solution containing imidazole and carbonate is obtained by mixing N'N-carbonyldiimidazole with water, or by mixing imidazole, a substance providing carbonate, and water.

4. The application according to claim 2, wherein In step (2), the temperature of the mixing is 50-100°C.

5. The application according to claim 2 or 4, characterized in that, In step (2), the temperature of the mixing is 60-80°C.

6. The application according to claim 2, wherein The divalent cobalt ions are provided by cobalt chloride, cobalt nitrate, cobalt sulfate, or cobalt acetate.

7. The application according to claim 2 or 6, characterized in that, The molar concentration of divalent cobalt ions in the aqueous solution containing divalent cobalt ions is 0.1-0.8 mol / L.

8. The application according to claim 3, wherein The substance providing carbonate is selected from one of sodium carbonate, potassium carbonate, sodium bicarbonate, or potassium bicarbonate.

9. The application according to claim 2, wherein The molar ratio of divalent cobalt ions in the aqueous solution of divalent cobalt ions to imidazole in the aqueous solution containing imidazole and carbonate is (0.5-2):(5-10).

10. The application according to claim 2, wherein The molar ratio of divalent cobalt ions in the aqueous solution of divalent cobalt ions to imidazole in the aqueous solution containing imidazole and carbonate is 0.5:(5-8).

11. The application according to claim 2, wherein The mixing method of the two solutions in step (2) includes direct mixing, ultrasonic mixing, or magnetic stirring mixing.

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