Preparation method of ligand-deficient copper-based metal-organic framework and application thereof in electrocatalytic reduction of carbon dioxide to prepare ethylene

Abstract

The application 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 electrocatalytic carbon dioxide reduction for preparing ethylene. The application can control the content of ligand defects in the MOFs by controlling different synthesis temperatures, and the material with the highest content of ligand defects has higher ethylene selectivity in the electrocatalytic carbon dioxide reduction reaction, which proves the regulation effect of the ligand defects in the MOFs on the CO2 reduction reaction performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of metal organic frameworks (MOFs) and electrocatalysis, and particularly relates to a preparation method of a ligand-defect copper-based metal organic framework and application thereof in electrocatalytic reduction of carbon dioxide to prepare ethylene. BACKGROUND

[0002] Due to excessive dependence on fossil fuels, a large amount of CO2 is emitted, and the increase in CO2 concentration causes a series of environmental problems such as global warming and ocean acidification, so it is of great significance to find a sustainable CO2 conversion strategy. The electrocatalytic CO2 reduction technology for simultaneously producing high-value chemicals by using renewable electricity to drive CO2 reduction is a promising research scheme for reducing CO2 emission. Among numerous CO2 reduction products, C2H4 is concerned 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 seriously limits its activity and selectivity. The surface interface structure of traditional inorganic copper-based catalysts is unclear, and it is difficult to accurately control them at atomic precision, which brings great challenges to the study of the relationship between their structure and properties. Therefore, it is of great significance to accurately synthesize copper-based catalysts with clear structure for electrocatalytic CO2 reduction to generate C2H4.

[0003] As a kind of porous crystal material, MOFs have the characteristics of clear structure and composition, which provides unique advantages for the accurate design and preparation of high-efficiency catalysts. The clear and adjustable structure of MOFs provides multiple possibilities for catalyst research. By regulating the ligand defect content in MOFs, mesoporous structures can be created and more active sites can be exposed, so it is of great significance to study the influence of the ligand defect content on the electrocatalytic CO2 reduction. SUMMARY

[0004] The application provides a preparation method of a ligand-defect copper-based metal organic framework and application thereof in electrocatalytic reduction of carbon dioxide to prepare ethylene. By controlling different synthesis temperatures, the ligand defect content in MOFs can be regulated, and the material with the highest ligand defect content has high ethylene selectivity in the electrocatalytic reduction of carbon dioxide, which proves the regulation effect of the ligand defect in MOFs on the CO2 reduction performance.

[0005] The preparation method of the ligand-defect copper-based metal organic framework comprises the following steps:

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

[0007] Step 2: mix the MOFs precursor and organic ligand, heat the reaction 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-dimethylformamide, and the volume is 10 mL.

[0010] In step 1, the reaction temperature is 80℃, and the reaction time is 16 h. After the heating reaction is completed, sequentially perform cooling, washing, and drying.

[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℃, such as 120℃, 135℃, 150℃, the optimal temperature is 120℃, and the reaction time is 16 h. After the heating reaction is completed, sequentially perform cooling, washing, and drying.

[0013] Application of the ligand-deficient copper-based metal organic framework in electrocatalytic CO2 reduction to prepare ethylene.

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

[0015] The beneficial effects of the present application are reflected in:

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

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

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

[0019] Figure 2The metal copper and 1,2,3-triazole content diagram of the ligand-defective MOFs material prepared in Example 1. From Figure 2 It can be seen from

[0020] Figure 3 The nitrogen adsorption curve diagram of the ligand-defective MOFs material prepared in Example 1 at 77K. From Figure 3 It can be seen from

[0021] Figure 4 The pore size distribution diagram of the ligand-defective MOFs material prepared in Example 1. From Figure 4 It can be seen from

[0022] Figure 5 The ethylene faradic efficiency diagram of the MOFs in Example 2 under the test potential of the electrocatalytic CO2 reduction. From Figure 5 It can be seen from

[0023] Figure 6 The ethylene partial current density diagram of the MOFs in Example 2 under the test potential of the electrocatalytic CO2 reduction. From Figure 6 It can be seen from 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 ultrasonic to ensure complete dissolution; then, 207 mg 1,2,3-triazole was added and mixed uniformly by ultrasonic, and then the vial was sealed and placed in an oven at 80°C for 16 hours; after the reaction was completed, it was cooled to room temperature, washed with DEF and methanol for 3 times respectively, and dried at 80°C for 12 hours to obtain the product Cu-MOF.

[0027] 2. Preparation of high-defect metal organic framework (HD-MOF)

[0028] 300 mg of Cu-MOF was placed in a 20 mL glass vial, and 3 mL of 1,2,3-triazole was added. The vial was ultrasonically dispersed at room temperature for 10 min, then sealed and heated at 120 °C for 16 h. After cooling to room temperature, the vial was washed three times with methanol and dried at 80 °C for 12 h. Finally, the obtained solid was subjected to Soxhlet extraction with methanol for 24 h to ensure complete removal of 1,2,3-triazole from the pores of the material, thus obtaining HD-MOF.

[0029] 3. Preparation of moderately defective metal-organic frameworks (MD-MOFs)

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

[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℃.

[0033] Metal-organic framework materials HD-MOF, MD-MOF, and LD-MOF were characterized by X-ray diffraction (XRD) patterns, such as... Figure 1 As shown. By Figure 1 As can be seen, the three sets of materials are in high agreement with the simulation data, proving their high crystallinity and similar topological structure.

[0034] The metal content of the material was determined by ICP. 1 The 1,2,3-triazole content in the materials was determined by ¹H NMR, thereby obtaining the ligand-to-metal ratio in the three groups of materials, and further determining the amount of ligand defects. The measurement results are as follows: Figure 2 As shown in the figure, the results indicate 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 testing. Figure 3 The nitrogen adsorption-desorption curves for the three materials at 77 K are shown. Figure 4 For the corresponding aperture distribution, by Figure 4 It is evident that HD-MOF contains larger pores, which also demonstrates its greater ligand defects.

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

[0037] Take 4 mg of HD-MOF (or MD-MOF, LD-MOF) in Example 1, disperse in 200 μL of absolute ethanol, then add 20 μL of 5 wt% Nafion solution, ultrasonic dispersion at room temperature for 30 min to obtain a uniformly dispersed catalyst dispersant; then the above catalyst dispersant is coated on a 1.0 x 1.0 cm 2 carbon fiber paper electrode as a working electrode. All electrochemical tests were performed using a CHI 760E electrochemical workstation. The H-type electrolytic cell separated by a proton exchange membrane was used as the electrolytic cell for the electrocatalytic CO2 reduction performance test. The three-electrode system was composed of a Pt sheet electrode as the counter electrode, an 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 was a CO2-saturated 0.1M KHCO3 solution. The gaseous product was detected by gas chromatography (GC), and the liquid product was detected by 1 H NMR with DMSO as the internal standard. The test results are shown in Figure 5 and Figure 6 . The results show that the HD-MOF with the highest content of ligand defects has the optimal ethylene Faraday efficiency and partial current density at all test potentials, proving that the introduction of ligand defects can promote the generation of ethylene.

Claims

1. A method for preparing a ligand-deficient copper-based metal-organic framework, characterized in that... Includes the following steps: Step 1: Dissolve copper salt and organic ligand in organic solvent, heat and react to obtain MOF precursor coordinated by solvent and organic ligand; Step 2: Mix the MOF precursor and organic ligand, and heat to react, to obtain MOF material containing ligand defects; The organic ligand is 1,2,3-triazole; In step 1, the reaction temperature is 80℃ and the reaction time is 16 h; In step 2, the reaction temperature is 120-150℃ and the reaction time is 16 h.

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 2, the added mass of the MOF precursor is 300 mg, and the added volume of the organic ligand is 3 mL.

6. The preparation method according to claim 1, characterized in that: In step 2, the reaction temperature is 120℃.

7. The application of the ligand-defect copper-based metal-organic framework prepared by any one of the preparation methods of claims 1-6 in the electrocatalytic reduction of CO2 to ethylene.

8. The application according to claim 7, characterized in that: In the electrocatalytic CO2 reduction process, a three-electrode system is used. The working electrode is prepared with the copper-based metal-organic framework with ligand defects, the Pt sheet electrode is used as the counter electrode, and Ag / AgCl is used as the reference electrode. The electrolyte is a CO2-saturated KHCO3 solution.

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