Preparation method and application of metal-doped hierarchical pore MOF (Metal Organic Framework)

Abstract

The invention discloses a preparation method and application of metal-doped hierarchical-pore MOF, and belongs to the technical field of electrochemical catalyst.The preparation method of the metal-doped hierarchical-pore MOF comprises the following steps that a metal source, a pore forming agent and dimethylimidazole or imidazole are dissolved in a solvent according to a certain proportion, mixing and stirring are conducted, and the metal-doped hierarchical-pore MOF is obtained; the preparation method comprises the following steps: reacting at a specific temperature for a period of time, washing and drying to obtain an internally porous metal-doped MOF material, carbonizing the material at a high temperature to prepare a slurry, and carrying out an electrochemical test to find that the material has good electrocatalytic activity. The metal-doped hierarchical pore MOF is used as a catalyst, the pore forming mode is simple and efficient, and compared with a metal-doped MOF material without a pore forming agent, the hierarchical pore structure improves transmission of substances in the catalytic reaction process, and the catalytic performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical catalysis, and in particular relates to a preparation method and application of a metal-doped multi-level porous MOF. Background Art

[0002] Metal-organic framework materials (MOF) have important uses in water treatment, adsorption and separation, and catalysis due to their advantages of high specific surface area, rich porosity, and adjustable pore size. In MOF materials of different properties, their pore structure, that is, the size, shape, and interconnection of the pores, presents different results in practical applications. Unfortunately, to date, very few MOF materials reported have macropores or mesopores, and most materials are mainly micropores. The active sites of microporous materials are usually confined to the micropores, which severely limits the intrinsic mass transfer rate of microporous materials during the reaction process. In addition, the diffusion rate of gas molecules in micropores is much smaller than that in mesopores, and gas molecules consume more energy to diffuse in micropores than in mesopores, which will seriously affect the gas separation efficiency during the catalytic reaction and increase the desorption energy consumption.

[0003] In the past decade, researchers have been trying to obtain hierarchical MOFs with two or more composite pore sizes, such as micropore-mesopore, micropore-macroporous, and even micropore-mesoporous-macroporous composite pores of different sizes. MOFs are treated by hard template method, soft template method, vapor phase etching method, chemical post-treatment method, etc. However, the current methods for constructing hierarchical MOFs usually have some disadvantages. For example, when using the template method, the template is easily rejected during the crystal growth process; the strategy of directly introducing defects is often difficult to control the pore size and form a wide pore size range; the pores of the post-treatment strategy are uneven, and the formed fragments are easy to block the pores, etc. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing and applying a metal-doped multi-level porous MOF. A pore-forming agent is added during the synthesis process in a one-step method, and the pore-forming method is simple and efficient. Compared with metal-doped MOF materials without pore-forming agents, the multi-level pore structure improves the transmission of substances during the catalytic reaction and enhances the catalytic performance.

[0005] The present invention is achieved through the following technical solutions: A method for preparing a metal-doped multi-level porous MOF comprises the following steps: Step 1, synthesis of MOF: reacting dimethylimidazole or imidazole, a first metal salt, a second metal salt and a pore-forming agent in methanol to obtain a metal-doped hierarchical MOF with a particle size of 30-500 nm; Step 2, carbonization of metal-doped multi-level porous MOF: heating the metal-doped multi-level porous MOF prepared in step 1 at 1-5°C / min under a nitrogen atmosphere, and carbonizing at 900-1100°C for 40-120min to obtain a metal-doped multi-level porous MOF carbon material; Step 3: Evenly disperse the metal-doped multi-level porous MOF carbon material obtained in step 2 in a mixed solution of ethanol, water and Nafion to prepare a slurry.

[0006] Further, in step 1, the mass ratio of the dimethylimidazole or imidazole to the first metal salt is 1:0.5 to 1. Preferably, in step 1, the mass ratio of the dimethylimidazole to the first metal salt is 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.

[0007] Furthermore, in step 1, the mass ratio of the dimethylimidazole or imidazole to the second metal salt is 1:0.05-0.1. Preferably, the mass ratio of the dimethylimidazole to the second metal salt is 1:0.05, 1:0.06, 1:0.07, 1:0.1.

[0008] Furthermore, in step 1, the mass ratio of the dimethylimidazole or imidazole to the pore-forming agent is 1:0.01-0.1. Preferably, the mass ratio of dimethylimidazole to the second metal salt is 1:0.01, 1:0.05, 1:0.07, 1:0.1.

[0009] Furthermore, in step 1, the mass ratio of the dimethylimidazole or imidazole to the sum of the first metal salt and the second metal salt is 1:1, 1:4, 1:8, 1:16, and the MOF particle sizes synthesized by different ratios of dimethylimidazole or imidazole and metal salt (i.e., the sum of the first metal salt and the second metal salt) are different. The smaller the ratio, the smaller the synthesized MOF particle size.

[0010] Further, in step 1, the particle size of the metal-doped multi-level porous MOF in step 1 is 30-300 nm. Preferably, the particle size of the metal-doped multi-level porous MOF is 30 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 450 nm or 500 nm.

[0011] Furthermore, in step 1, the first metal salt is zinc nitrate or cobalt nitrate, and the second metal salt is one or more of iron salts such as ferric nitrate, ferric acetate, ferrous sulfate, and ferric chloride, or nickel salts such as nickel nitrate, nickel sulfate, and nickel acetate, or cobalt salts such as cobalt nitrate, cobalt acetate, and cobalt chloride.

[0012] Furthermore, in step 2, the metal-doped multi-level porous MOF carbon material is one or more of ZIF-8, ZIF-67, iron-doped ZIF-8, nickel-doped ZIF-8, iron-cobalt-doped ZIF-8, and iron-nickel-doped ZIF-8.

[0013] The invention also discloses the application of a metal-doped multi-level porous MOF as an electrocatalyst in hydrogen production or carbon dioxide reduction.

[0014] Beneficial effects: The present invention discloses a preparation method and application of a metal-doped multi-level porous MOF. The present invention can achieve the effect that the metal-doped multi-level porous MOF is used as a catalyst, and the pore-forming method is simple and efficient. Compared with the metal-doped MOF material without a pore-forming agent, the multi-level pore structure improves the transmission of substances in the catalytic reaction process and improves the catalytic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a transmission electron microscope image of the metal-doped multi-level porous MOF in Example 1; Figure 2 This is a transmission electron microscopy image of the metal-doped MOF without adding a pore-forming agent in Example 1; Figure 3 This is a comparison diagram of the pore size distribution of the metal-doped multi-level porous MOF and the metal-doped MOF in Example 1; Figure 4 This is a comparison chart of the electrocatalytic hydrogen evolution performance of the metal-doped multi-level porous MOF and the metal-doped MOF in Example 1; Figure 5 This is a transmission electron microscopy image of the metal-doped multi-level porous MOF in Example 2; Figure 6 This is a comparison chart of the electrocatalytic carbon dioxide reduction performance of the metal-doped multi-level porous MOF in Example 2 and the metal-doped MOF. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0018] Example 1 A simple method for preparing metal-doped multi-level porous MOF, the steps are as follows: Step 1: Weigh 1.2 g of dimethylimidazole, 1 g of cobalt nitrate, 0.05 g of ferric nitrate, and 0.01 g of glucose in 300 ml of methanol, react for 4 h, wash by centrifugation, and dry in a vacuum oven at 70°C overnight to obtain iron-doped hierarchical ZIF-67 with a particle size of 200 nm, which is recorded as GFe-ZIF-67.

[0019] Step 2: Weigh 0.2 g of Fe-doped hierarchical ZIF-67 and pyrolyze it at 1000 °C in a nitrogen atmosphere for 2 h to obtain carbonized Fe-doped hierarchical ZIF-67, denoted as GH-FeCoNC. Figure 1 The same method was used to synthesize FeCoNC without adding glucose, as shown in Figure 2 shown.

[0020] The pore size distributions of GH-FeCoNC and FeCoNC shown in step 2 are as follows Figure 3 As shown in Figure 3, the mesopores and macropores of the GH-FeCoNC material with added pore formers are significantly higher than those of the FeCoNC material without added pore formers.

[0021] Step 3: Prepare GH-FeCoNC into catalyst slurry for oxygen reduction electrochemical test.

[0022] The electrochemical test performance of hydrogen evolution shown in step 3 is as follows Figure 4 As shown, the GH-FeCoNC catalyst has mesopores and macropores inside, which reduces the gas transmission resistance and significantly improves the hydrogen evolution performance.

[0023] Example 2 A simple method for preparing metal-doped multi-level porous MOF, the steps are as follows: Step 1: Weigh 1.2 g of dimethylimidazole, 0.8 g of zinc nitrate, 0.06 g of nickel nitrate, and 0.02 g of zinc gluconate in 300 ml of methanol, react for 4 h, centrifuge and wash, and dry in a vacuum oven at 70°C overnight to obtain nickel-doped multi-level porous ZIF-8 with a particle size of 200 nm, recorded as GZNi-ZIF-8.

[0024] Step 2: Weigh 0.2 g of nickel-doped hierarchical ZIF-8 and pyrolyze it at 1100 °C in a nitrogen atmosphere for 2 h to obtain carbonized nickel-doped hierarchical ZIF-8, denoted as GH-NiNC. Figure 5 The same method was used to synthesize NiNC without adding zinc gluconate.

[0025] Step 3: Prepare NiNC into catalyst slurry for oxygen reduction electrochemical test.

[0026] The electrochemical test performance of carbon dioxide reduction shown in step 3 is as follows Figure 6 As shown, at 20 mV s -1The linear sweep voltammetry (LSV) curves of GH-NiNC and NiNC were obtained at a scan rate of . The GH-NiNC catalyst has mesopores and macropores inside, which reduces the gas transmission resistance and shows a higher current density in a saturated CO2 atmosphere, indicating that GH-NiNC has better electrocatalytic activity for carbon dioxide reduction reaction (CO2RR).

[0027] The above descriptions are merely embodiments of the present application and are not intended to limit the scope of the present application. Any equivalent structural or equivalent process transformations made using the contents of the specification and drawings of the present application, such as the mutual combination of technical features between the embodiments, or direct or indirect application in other related technical fields, are also included in the protection scope of the present application.

Claims

1. A method for preparing metal-doped multi-level porous MOF, It is characterized in that The steps include: Step 1, synthesis of MOF: reacting dimethylimidazole or imidazole, a first metal salt, a second metal salt and a pore-forming agent in methanol to obtain a metal-doped hierarchical MOF with a particle size of 30-500 nm; Step 2, carbonization of metal-doped multi-level porous MOF: heating the metal-doped multi-level porous MOF prepared in step 1 at 1-5°C / min under a nitrogen atmosphere, and carbonizing at 900-1100°C for 40-120min to obtain a metal-doped multi-level porous MOF carbon material; Step 3: Prepare a slurry by preparing the metal-doped multi-level porous MOF carbon material obtained in step 2.

2. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 1, the mass ratio of the dimethylimidazole or imidazole to the first metal salt is 1:0.5-1.

3. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 1, the mass ratio of the dimethylimidazole or imidazole to the second metal salt is 1:0.05-0.

1.

4. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 1, the mass ratio of the dimethylimidazole or imidazole to the pore-forming agent is 1:0.01-0.

1.

5. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 1, the mass ratio of the dimethylimidazole or imidazole to the sum of the first metal salt and the second metal salt is 1:1, 1:4, 1:8, or 1:

16.

6. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 1, the particle size of the metal-doped multi-level porous MOF in step 1 is 30-300 nm.

7. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 1, the first metal salt is zinc nitrate or cobalt nitrate, and the second metal salt is one or more of ferric nitrate, ferric acetate, ferrous sulfate, ferric chloride, nickel nitrate, nickel sulfate, nickel acetate, cobalt nitrate, cobalt acetate or cobalt chloride.

8. A method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: Step 2 also includes the preparation of a flexible fiber membrane: dissolving a matrix polymer in a solvent, stirring for 6 hours at 30-70°C, then adding the metal-doped multi-level porous MOF carbon material, and receiving the electrospun fiber filaments through an oriented receiver to obtain a flexible fiber membrane; the matrix polymer is one or more of polyvinyl alcohol, polyacrylonitrile or polyvinyl pyrrolidone.

9. The method for preparing a metal-doped multi-level porous MOF according to claim 1, Features: In step 2, the metal-doped multi-level porous MOF carbon material is one or more of ZIF-8, ZIF-67, iron-doped ZIF-8, nickel-doped ZIF-8, iron-cobalt-doped ZIF-8 or iron-nickel-doped ZIF-8.

10. Use of the metal-doped multi-level porous MOF as claimed in any one of claims 1 to 9 as an electrocatalyst in hydrogen evolution or carbon dioxide reduction.

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