An Ag@ZIF-8 nanosheet composite material, its preparation method and application

Abstract

This invention discloses an Ag@ZIF-8 nanosheet composite material, its preparation method, and its application. The composite material is composed of a ZIF-8 porous framework and Ag nanoparticles, with the Ag nanoparticles uniformly dispersed on the surface of the Ag@ZIF-8 nanosheets. The preparation method includes the following steps: adding silver salt to a solvent to prepare a silver salt solution, then adding ZIF-8 material to the silver salt solution, and carrying out a composite reaction under stirring at room temperature. Ag induces the ZIF-8 structure to recombine and generate Ag@ZIF-8 nanosheets. After centrifugation, washing, and drying, the Ag@ZIF-8 nanosheet composite material is obtained. This method has mild synthesis conditions, does not require high temperature and high pressure, and can achieve large-scale production. When the prepared composite material is applied to the electrocatalytic reduction of CO2 to CO, it exhibits excellent structural characteristics and electrochemical performance, significantly improving the electrochemical active area.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic materials technology, specifically relating to an Ag@ZIF-8 nanosheet composite material, its preparation method, and its application in the electrocatalytic reduction of CO2 to CO. Background Technology

[0002] Among the many products of CO2 reduction reaction (CO2RR), carbon monoxide (CO) is one of the most industrially valuable. CO is not only an important component of syngas, but it can also be further converted into bulk chemicals such as olefins, alcohols, and liquid fuels through mature processes like Fischer-Tropsch synthesis and methanol synthesis, making it highly compatible with the existing chemical industry chain. Compared to products like formic acid, methane, and ethylene, CO is easier to separate and purify, and its two-electron reaction pathway is more efficient, making it one of the most promising target products for the industrial application of electrocatalytic CO2 reduction.

[0003] Ag is a classic catalyst for the electrocatalytic reduction of CO2 to CO, exhibiting excellent CO selectivity and good hydrogen evolution inhibition due to its moderate COOH binding energy and relatively weak CO adsorption strength. However, Ag-based catalysts face two major bottlenecks: firstly, the high cost of precious metals limits large-scale applications; secondly, the low utilization rate of active sites in bulk Ag results in poor atom economy. Loading Ag nanoparticles onto high specific surface area supports is an effective strategy to improve atom utilization efficiency and reduce the amount of precious metals required.

[0004] Metal-organic frameworks (MOFs), as a class of porous crystalline materials constructed from metal nodes and organic ligands, have shown broad application prospects in gas adsorption, separation, and catalysis due to their advantages such as high specific surface area, tunable pore structure, and designable chemical functions. ZIF-8, as an important member of the MOF family, possesses excellent thermal and chemical stability, and its nitrogen-rich pore environment provides ideal sites for the anchoring of metal nanoparticles. In recent years, ZIF-8 and its derivatives have attracted widespread attention as electrocatalysts or catalyst supports in CO2 reduction and regeneration (CORR). Therefore, developing a composite catalytic material with controllable Ag loading, stable structure, and excellent CO selectivity is of great significance for promoting the practical application of electrocatalytic CO2 reduction to CO. Summary of the Invention

[0005] The purpose of this invention is to provide an Ag@ZIF-8 nanosheet composite material, its preparation method, and its application. The method has mild synthesis conditions, does not require high temperature and high pressure, and can achieve large-scale production. When the prepared composite material is applied to the electrocatalytic reduction of CO2 to CO, it can exhibit excellent structural features and electrochemical performance, and significantly improve the electrochemical active area.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: An Ag@ZIF-8 nanosheet composite material is composed of a ZIF-8 porous framework and Ag nanoparticles, with the Ag nanoparticles uniformly dispersed on the surface of the Ag-ZIF-8 nanosheets.

[0007] Preferably, the Ag nanoparticles have a particle size of 5-10 nm, and the loading of Ag nanoparticles is controlled by adjusting the silver salt concentration and recombination time.

[0008] To achieve the purpose of the invention, the present invention also provides a method for preparing the above-mentioned Ag@ZIF-8 nanosheet composite material, comprising the following steps: adding silver salt to a solvent to prepare a silver salt solution, then adding ZIF-8 material to the silver salt solution, carrying out a composite reaction under stirring conditions at room temperature, Ag inducing ZIF-8 structural recombination to generate Ag@ZIF-8 nanosheets, and obtaining the Ag@ZIF-8 nanosheet composite material by centrifugation, washing and drying.

[0009] Preferably, the mass ratio of ZIF-8 to silver salt is (1-10):1; and the composite reaction time is 0.5-12 h.

[0010] Preferably, the silver salt is silver nitrate or silver acetate, and the concentration of the silver salt solution is 0.1-0.3 M.

[0011] Preferably, the solvent is one or more of methanol, ethanol, and deionized water.

[0012] Preferably, the sample is washed three times with methanol and ethanol and then vacuum dried at 60°C for 12 h.

[0013] This invention also provides the application of the above-mentioned Ag@ZIF-8 nanosheet composite material in the electrocatalytic reduction of CO2 to produce CO.

[0014] Furthermore, the specific application process is as follows: the Ag@ZIF-8 nanosheet composite material described in claim 1 or 2 is coated on the electrode surface as a working electrode, and CO is obtained by constant potential electrolysis in a CO2-saturated electrolyte.

[0015] Preferably, the concentration of the electrolyte is 0.05-1.0 mol / L, and the electrolyte is an aqueous solution of KHCO3, NaHCO3, or KOH.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The Ag2@ZIF-8 prepared in this invention has a CO Faradaic efficiency of 82% at a potential of -1.3 V (vs. RHE) and the hydrogen evolution reaction is effectively suppressed to 18%, which is significantly better than pure ZIF-8 (about 45%), Ag1@ZIF-8 (63%), and Ag3@ZIF-8 (70%), showing the best structural characteristics and electrochemical performance, and significantly improving the electrochemical active area; (2) The present invention confirms through structural characterization that Ag nanoparticles are still uniformly dispersed in the ZIF-8 framework, the interplanar spacing of 0.23 nm corresponds to the integrity of the Ag(111) crystal plane, the Zn-N coordination structure of ZIF-8 remains intact, and it exhibits excellent structural stability, providing a structural basis for continuous high-efficiency activity; (3) The present invention adopts a room temperature stirring method, which has mild synthesis conditions and controllable process, and does not require high temperature and high pressure, which is conducive to large-scale preparation. Attached Figure Description

[0017] Figure 1 These are the XRD spectra of Ag1@ZIF-8, Ag2@ZIF-8, and Ag3@ZIF-8 prepared in Examples 1-3, respectively; Figure 2 This is a SEM image of the ZIF-8 material in this invention; Figure 3 These are SEM images of Ag1@ZIF-8 (a), Ag2@ZIF-8 (b), and Ag3@ZIF-8 (c) prepared in Examples 1-3, respectively; Figure 4 These are TEM images and elemental distribution maps of Ag2@ZIF-8 prepared in Example 2; Figure 5 These are the linear sweep voltammetry (LSV) curves of ZIF-8 material (a) and Ag2@ZIF-8 (b) prepared in Example 2 in this invention; Figure 6 The Faraday efficiency (FE) of CO and H2 at different potentials for ZIF-8 material (a) and Ag1@ZIF-8 (a), Ag2@ZIF-8 (b), and Ag3@ZIF-8 (c) prepared in Examples 1-3 of this invention (a), respectively. Figure 7 The image shows the X-ray photoelectron spectroscopy (XPS) spectra of Ag2@ZIF-8 prepared in Example 2 before and after the reaction. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0019] A method for preparing Ag1@ZIF-8 nanosheet composite material includes the following steps: AgNO3 is added to 20 mL of deionized water to prepare a 0.1 M silver salt solution, then 100 mg of ZIF-8 material is added to the silver salt solution, ultrasonically dispersed, and then subjected to a composite reaction at room temperature with stirring for 1 h. Ag induces ZIF-8 structural recombination to generate Ag1@ZIF-8 nanosheets. The obtained product is separated by centrifugation, washed three times with methanol and ethanol in sequence, and finally vacuum dried at 60 °C for 12 h to obtain Ag1@ZIF-8 nanosheet composite material. Example 2

[0020] A method for preparing Ag2@ZIF-8 nanosheet composite material includes the following steps: AgNO3 is added to 20 mL of methanol to prepare a 0.2 M silver salt solution, then 100 mg of ZIF-8 material is added to the silver salt solution, ultrasonically dispersed, and then subjected to a composite reaction at room temperature with stirring for 1 h. Ag induces ZIF-8 structural recombination to generate Ag2@ZIF-8 nanosheets. The obtained product is separated by centrifugation, washed three times with methanol and ethanol in sequence, and finally dried under vacuum at 60 °C for 12 h to obtain Ag2@ZIF-8 nanosheet composite material. Example 3

[0021] A method for preparing Ag3@ZIF-8 nanosheet composite material includes the following steps: silver acetate is added to 20 mL of ethanol to prepare a 0.3 M silver salt solution, then 100 mg of ZIF-8 material is added to the silver salt solution, ultrasonically dispersed, and then subjected to a composite reaction at room temperature with stirring for 1 h. Ag induces ZIF-8 structural recombination to generate Ag3@ZIF-8 nanosheets. The obtained product is separated by centrifugation, washed three times with methanol and ethanol in sequence, and finally vacuum dried at 60 °C for 12 h to obtain Ag3@ZIF-8 nanosheet composite material.

[0022] Application Examples Electrode preparation: 0.5 mg of Ag1@ZIF-8, Ag2@ZIF-8, and Ag3@ZIF-8 prepared in Examples 1-3 were uniformly dispersed with 700 μL of ethanol, 250 μL of pure water, and 50 μL of 5% Nafion perfluorinated resin solution by ultrasonication for 30 min to form ink; then, the catalyst slurry was drop-coated onto carbon paper with an area of ​​1 cm × 1 cm using a pipette; the coated carbon paper was placed in a vacuum drying oven at 60℃ for drying; after complete drying, it was taken out as the working electrode.

[0023] Electrochemical performance testing: An H-type electrolytic cell was used, with an Ag / AgCl electrode as the reference electrode and a platinum sheet as the counter electrode. The cathode and anode chambers were separated by a Nafion 117 membrane. The electrolyte was a CO2-saturated 0.1 M KHCO3 solution (pH=6.8). CO2 was bubbled for 30 min before testing, and CO2 was continuously introduced during electrolysis. Constant potential electrolysis was performed using an electrochemical workstation, with a potential range of -1.0 V to -1.5 V (vs. RHE). The gaseous products were analyzed online by gas chromatography.

[0024] The XRD patterns of Ag1@ZIF-8, Ag2@ZIF-8, and Ag3@ZIF-8 prepared in Examples 1-3 are shown below. Figure 1 As shown, the XRD characteristic peak positions and intensities are basically consistent, with no impurity phase formation. As the silver precursor concentration increases from 0.1 M to 0.3 M, the intensity and full width at half maximum (FWHM) of the main diffraction peaks of ZIF-8 show a regular change. The main peak of Ag1@ZIF-8 has the highest intensity and the sharpest peak shape, indicating that ZIF-8 has the best crystallinity and better crystal integrity at low concentrations. SEM images of pure ZIF-8 are shown below. Figure 2 The diagram shows a regular rhombic dodecahedron, but the introduction of Ag induces a structural evolution, resulting in a predominance of regular plate-like crystals. Figure 3 ). Figure 4 TEM and elemental distribution characterization of Ag2@ZIF-8 were performed. TEM images showed that a large number of high-contrast Ag nanoparticles were uniformly distributed on the surface of the rod-shaped ZIF-8 support, with no obvious aggregation. EDS mapping showed that the elemental signals of Ag, Zn, C, and N highly coincided with the support profile and were uniformly distributed, confirming that Ag was successfully and uniformly loaded in the structurally intact ZIF-8 framework. Figure 5 As shown, in a CO2-saturated 0.1 M KHCO3 solution, the CO2 reduction current density is significantly higher than that in a nitrogen-saturated 0.1 M KHCO3 solution, indicating that it possesses CO2 reduction activity. Figure 6 At a potential of -1.3 V (vs. RHE), the CO Faradaic efficiency of Ag2@ZIF-8 reached 82%, and the hydrogen evolution reaction was effectively suppressed to 18%, which is significantly better than that of pure ZIF-8 (approximately 45%), Ag1@ZIF-8 (63%), and Ag3@ZIF-8 (70%). Under continuous electrolysis, the Faradaic efficiency remained above 80%, and the XPS spectrum after the reaction remained basically unchanged. Figure 7 This indicates that the composite material prepared by the present invention has excellent CO selectivity and catalytic durability.

Claims

1. An Ag@ZIF-8 nanosheet composite material, characterized in that, It is composed of a ZIF-8 porous framework and Ag nanoparticles, with the Ag nanoparticles uniformly dispersed on the surface of Ag-ZIF-8 nanosheets.

2. The Ag@ZIF-8 nanosheet composite material according to claim 1, characterized in that, The Ag nanoparticles have a particle size of 5-10 nm, and the loading of Ag nanoparticles is controlled by adjusting the silver salt concentration and recombination time.

3. A method for preparing the Ag@ZIF-8 nanosheet composite material as described in claim 1 or 2, characterized in that, The process includes the following steps: silver salt is added to a solvent to prepare a silver salt solution, then ZIF-8 material is added to the silver salt solution, and a composite reaction is carried out under stirring conditions at room temperature. Ag induces the ZIF-8 structure to recombine and generate Ag@ZIF-8 nanosheets. After centrifugation, washing and drying, Ag@ZIF-8 nanosheet composite material is obtained.

4. The method for preparing an Ag@ZIF-8 nanosheet composite material according to claim 3, characterized in that, The mass ratio of ZIF-8 to silver salt is (1-10):1; the reaction time is 0.5-12 h.

5. A method for preparing an Ag@ZIF-8 nanosheet composite material according to claim 3 or 4, characterized in that, The silver salt is silver nitrate or silver acetate, and the concentration of the silver salt solution is 0.1-0.3 M.

6. A method for preparing an Ag@ZIF-8 nanosheet composite material according to claim 3 or 4, characterized in that, The solvent is one or more of methanol, ethanol, and deionized water.

7. The method for preparing an Ag@ZIF-8 nanosheet composite material according to claim 3 or 4, characterized in that, Washed three times with methanol and ethanol, and then vacuum dried at 60°C for 12 h.

8. The application of the Ag@ZIF-8 nanosheet composite material according to claim 1 or 2 in the electrocatalytic reduction of CO2 to prepare CO.

9. The application according to claim 8, characterized in that, The specific application process is as follows: the Ag@ZIF-8 nanosheet composite material described in claim 1 or 2 is coated on the electrode surface as a working electrode, and CO is obtained by constant potential electrolysis in a CO2-saturated electrolyte.

10. The application according to claim 9, characterized in that, The concentration of the electrolyte is 0.05-1.0 mol / L, and the electrolyte is an aqueous solution of KHCO3, NaHCO3, or KOH.

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