Preparation method of ligand defect copper-based metal organic framework and application of ligand defect copper-based metal organic framework in preparation of ethylene through electro-catalysis carbon dioxide reduction

Abstract

The invention discloses a preparation method of a ligand defect copper-based metal organic framework and application of the ligand defect copper-based metal organic framework in preparation of ethylene through electro-catalysis carbon dioxide reduction. According to the method, the ligand defect content in the MOFs can be regulated and controlled by controlling different synthesis temperatures, the prepared material with the highest ligand defect content has high ethylene selectivity in the electrocatalytic carbon dioxide reduction reaction, and the regulation and control effect of the ligand defects in the MOFs on the CO2 reduction reaction performance is proved.

Description

Technical Field

[0001] The present invention belongs to the field of metal organic frameworks (MOFs) and electrocatalysis, and specifically relates to a method for preparing a ligand-deficient copper-based metal organic framework and its application in preparing ethylene by electrocatalytic reduction of carbon dioxide. Background Art

[0002] Due to excessive dependence on fossil fuels, a large amount of CO2 has been emitted. The increase in CO2 concentration has caused a series of environmental problems such as global warming and ocean acidification. It is of great significance to find a sustainable CO2 conversion strategy. Electrocatalytic CO2 reduction technology that uses renewable electricity to promote CO2 reduction and produce high-value chemicals is a promising research solution to reduce CO2 emissions. Among the many CO2 reduction products, C2H4 has attracted much attention due to its high volumetric energy density and wide application. However, the electrocatalytic reduction of CO2 to C2H4 is a 12-electron process involving slow carbon-carbon coupling kinetics and multi-step proton-electron transfer steps, which severely limits its activity and selectivity. The surface and interface structure of traditional inorganic copper-based catalysts is unclear, and it is difficult to precisely control them with atomic precision, which poses a major challenge to studying the relationship between their structure and properties. Therefore, it is of great significance to accurately synthesize copper-based catalysts with clear structures for electrocatalytic CO2RR to generate C2H4.

[0003] As a porous crystalline material, MOFs have clear structure and composition, which provides unique advantages for the precise design and preparation of efficient catalysts. Its clear and adjustable structure provides a variety of possibilities for catalyst research. By regulating the number of ligands in MOFs, ligand defects can be introduced to create mesoporous structures and expose more active sites. Therefore, it is of great significance to study its effect on electrocatalytic CO2 reduction. Summary of the invention

[0004] The present invention provides a method for preparing a ligand-defective copper-based metal organic framework and its application in preparing ethylene by electrocatalytic carbon dioxide reduction. The present invention can regulate the ligand defect content in MOFs by controlling different synthesis temperatures. The prepared material with the highest ligand defect content has a higher ethylene selectivity in the electrocatalytic carbon dioxide reduction reaction, proving the regulatory effect of ligand defects in MOFs on the performance of CO2 reduction reactions.

[0005] The method for preparing the ligand-deficient copper-based metal organic framework of the present invention comprises the following steps:

[0006] Step 1: Dissolve the copper salt and the organic ligand in an organic solvent, and heat the reaction to obtain a MOFs precursor coordinated by the solvent and the organic ligand;

[0007] Step 2: Mix the MOFs precursor and the organic ligand, heat and react to obtain a MOFs material containing ligand defects.

[0008] In step 1, the copper salt is copper nitrate trihydrate, and the organic ligand is 1,2,3-triazole; the molar ratio of the copper salt to the organic ligand is 1:3.

[0009] In step 1, the organic solvent is N,N-diethylformamide, and the volume is 10 mL.

[0010] In step 1, the reaction temperature is 80°C and the reaction time is 16 h. After the heating reaction is completed, the temperature is lowered, washed and dried in sequence.

[0011] In step 2, the added mass of the MOF precursor is 300 mg; the organic ligand is 1,2,3-triazole, and the added volume is 3 mL.

[0012] In step 2, the reaction temperature is 120-150° C., such as 120° C., 135° C., and 150° C., the optimal temperature is 120° C., and the reaction time is 16 h. After the heating reaction is completed, the temperature is lowered, washed, and dried in sequence.

[0013] The invention discloses an application of the ligand-deficient copper-based metal organic framework in the preparation of ethylene by electrocatalytic CO2 reduction.

[0014] Furthermore, in the electrocatalytic CO2 reduction process, a three-electrode system was used, with the ligand-deficient copper-based metal organic framework as the working electrode, the Pt sheet electrode as the counter electrode, Ag / AgCl (3M KCl) as the reference electrode, and the electrolyte being a CO2-saturated 0.1M KHCO3 solution.

[0015] The beneficial effects of the present invention are embodied in:

[0016] 1. The present invention synthesizes a series of copper-based metal organic frameworks with different ligand defects by simply controlling the synthesis temperature.

[0017] 2. The ligand-defective copper-based MOFs prepared by the present invention have high crystallinity and good porosity, and the high-defect MOFs show excellent ethylene selectivity in electrocatalytic CO2 reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the powder X-ray diffraction pattern of the ligand-deficient MOFs material prepared in Example 1. Figure 1 It can be seen that the three groups of materials have high crystallinity and similar topological structures.

[0019] Figure 2Figure 1 is a graph showing the content of metallic copper and 1,2,3-triazole in the ligand-deficient MOFs material prepared in Example 1. Figure 2 It can be seen that HD-MOF contains less 1,2,3-triazole and LD-MOF contains more, that is, the ligand defect amount HD-MOF>MD-MOF>LD-MOF.

[0020] Figure 3 : is the nitrogen adsorption curve of the ligand-deficient MOFs material prepared in Example 1 at 77K. Figure 3 It can be seen that the three groups of materials are all porous structures and all of them are micropores.

[0021] Figure 4 is the pore size distribution diagram of the ligand-deficient MOFs material prepared in Example 1. Figure 4 It can be seen that HD-MOF contains larger pores, which also indicates that it has more ligand defects.

[0022] Figure 5 This is the Faraday efficiency diagram of ethylene at the electrocatalytic CO2 reduction test potential of MOFs in Example 2. Figure 5 It can be seen that at each test potential, HD-MOF has the highest ethylene Faraday efficiency, while LD-MOF has a lower efficiency, indicating that the more ligand defects there are, the more conducive it is to the production of ethylene.

[0023] Figure 6 This is the ethylene current density diagram at the potential of the electrocatalytic CO2 reduction test of MOFs in Example 2. Figure 6 It can be seen that at each test potential, HD-MOF has the highest ethylene partial current density, and LD-MOF is lower, which also shows that the more ligand defects there are, the more conducive it is to the production of ethylene. DETAILED DESCRIPTION

[0024] Example 1: Preparation of Metal-Organic Frameworks (MOFs) with Different Ligand Defect Contents

[0025] 1. Preparation of MOFs precursor (Cu-MOF)

[0026] 242 mg Cu(NO3)2·3H2O was dissolved in 10 mL DEF by ultrasonication to ensure complete dissolution; then, 207 mg 1,2,3-triazole was added and mixed evenly by ultrasonication, and then the vial was sealed and placed in an oven at 80°C for 16 hours; after the reaction, it was cooled to room temperature, washed with DEF and methanol three times each, and dried at 80°C for 12 hours to obtain the product Cu-MOF.

[0027] 2. Preparation of Highly Defective Metal-Organic Frameworks (HD-MOFs)

[0028] 300 mg of Cu-MOF was placed in a 20 mL glass vial, 3 mL of 1,2,3-triazole was added, and ultrasonic dispersion was performed at room temperature for 10 min. The vial was then sealed and heated at 120 °C for 16 h. After cooling to room temperature, it was washed three times with methanol and dried at 80 °C for 12 h. Finally, the obtained solid was Soxhlet extracted with methanol for 24 h to ensure that 1,2,3-triazole was completely removed from the pores of the material to obtain HD-MOF.

[0029] 3. Preparation of medium defect metal-organic frameworks (MD-MOFs)

[0030] The preparation method is similar to step 2, except that the heating temperature is 135°C.

[0031] 4. Preparation of Low-Defect Metal-Organic Frameworks (LD-MOFs)

[0032] The preparation method is similar to step 2, except that the heating temperature is 150°C.

[0033] The metal organic framework materials HD-MOF, MD-MOF, and LD-MOF were characterized by X-ray diffraction patterns (XRD), such as Figure 1 As shown. Figure 1 It can be seen that the three groups of materials are highly consistent with the simulation data, proving their high crystallinity and similar topological structures.

[0034] Determination of metal content in materials by ICP 1 H NMR was used to measure the 1,2,3-triazole content in the materials, thereby obtaining the ratio of ligand to metal in the three groups of materials and further determining the amount of ligand defect. Figure 2 As shown, the results show that the trend of ligand defect content in the three groups of materials is HD-MOF>MD-MOF>LD-MOF.

[0035] The pore size distribution was characterized by nitrogen adsorption test. Figure 3 The nitrogen adsorption-desorption curves of the three groups of materials at 77K are: Figure 4 is the corresponding pore size distribution, given by Figure 4 It can be seen that HD-MOF contains larger pores, which also proves that it has more ligand defects.

[0036] Example 2: Application of ligand-deficient MOFs in electrocatalytic CO2 reduction

[0037] Take 4 mg of the HD-MOF (or MD-MOF, LD-MOF) in Example 1, disperse it in 200 μL of anhydrous ethanol, add 20 μL of 5 wt% Nafion solution, and ultrasonically disperse it at room temperature for 30 min to obtain a uniformly dispersed catalyst dispersant; then coat the above catalyst dispersant on a 1.0×1.0 cm 2 The carbon fiber paper electrode was used as the working electrode. All electrochemical tests were performed using a CHI 760E electrochemical workstation. An H-type electrolytic cell separated by a proton exchange membrane was used as the electrolyzer for the electrocatalytic CO2 reduction performance test. The three-electrode system consists of a Pt sheet electrode as the counter electrode, Ag / AgCl (filled with 3M KCl solution) as the reference electrode, and the above catalyst-coated carbon fiber paper electrode as the working electrode. The electrolyte is a 0.1M KHCO3 solution saturated with CO2. The gas phase products and liquid products are detected by gas chromatograph (GC), and the liquid phase products are detected by 1 H NMR detection, using DMSO as internal standard. The test results are as follows Figure 5 and Figure 6 The results show that the HD-MOF with the highest ligand defect content has the best ethylene Faraday efficiency and partial current density at all tested potentials, proving that the introduction of ligand defects can promote the production of ethylene.

Claims

1. A method for preparing a ligand-deficient copper-based metal organic framework, characterized in that The steps include: Step 1: Dissolve the copper salt and the organic ligand in an organic solvent, and heat the reaction to obtain a MOFs precursor coordinated by the solvent and the organic ligand; Step 2: mixing the MOFs precursor and the organic ligand, heating and reacting to obtain a MOFs material containing ligand defects; The organic ligand is 1,2,3-triazole.

2. The preparation method according to claim 1, characterized in that: In step 1, the copper salt is copper nitrate trihydrate.

3. The preparation method according to claim 2, characterized in that: The molar ratio of the copper salt to the organic ligand is 1:

3.

4. The preparation method according to claim 1, characterized in that: In step 1, the organic solvent is N,N-diethylformamide.

5. The preparation method according to claim 1, characterized in that: In step 1, the reaction temperature is 80°C and the reaction time is 16 h.

6. The preparation method according to claim 1, characterized in that: In step 2, the added mass of the MOF precursor is 300 mg, and the added volume of the organic ligand is 3 mL.

7. The preparation method according to claim 1, characterized in that: In step 2, the reaction temperature is 120-150°C and the reaction time is 16 h.

8. The preparation method according to claim 7, characterized in that: The reaction temperature was 120°C.

9. Use of a ligand-deficient copper-based metal organic framework prepared by the preparation method according to any one of claims 1 to 8 in the electrocatalytic reduction of CO2 to produce ethylene.

10. The use according to claim 9, characterized in that: In the electrocatalytic CO2 reduction process, a three-electrode system is used, the ligand-deficient copper-based metal organic framework is used to prepare the working electrode, the Pt sheet electrode is used as the counter electrode, Ag / AgCl is used as the reference electrode, and the electrolyte is a CO2-saturated KHCO3 solution.

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