Gold nanocluster and application thereof in electro-catalysis of carbon dioxide reaction

Abstract

The invention discloses a gold nanocluster and application thereof in electro-catalysis of carbon dioxide reaction. The synthesis method comprises the following synthesis steps: firstly, adding a gold source into a tetrahydrofuran solution, stirring for five minutes, then adding tetra-n-octyl ammonium bromide, stirring until the solution is dark red, adding cyclohexanol, stirring until the solution is transparent, then adding a reducing agent, stirring overnight, then washing with methanol for multiple times, dissolving a crude product into a small amount of methylbenzene, and drying to obtain a target product. And adding a certain amount of cyclohexanol and 3 (2-furyl) phosphorus again, slowly stirring at 60 DEG C for 12 hours to obtain a crude product, washing with methanol for several times again, and purifying and separating to obtain the gold nanocluster. The gold nanocluster provided by the invention has the characteristics of novel structure, good stability, easy synthesis and high yield, and has excellent catalytic performance in electrocatalytic carbon dioxide reaction.

Description

Technical Field

[0001] The present invention belongs to the fields of nanomaterial synthesis and catalysis, and particularly relates to a gold nanocluster and its application in electrocatalytic carbon dioxide reaction. Background Art

[0002] The size of metal nanoclusters is between that of metal atoms with single valence electrons and large-sized metal nanoparticles with surface plasmon resonance. The number of metal atoms in the cluster ranges from a few to dozens and up to hundreds. These metal atoms are protected by peripheral organic ligands, and the size is between 1 - 3 nm. Clusters have applications in many fields including optical sensing, chemical catalysis, biological applications, and biochemical medical analysis, etc. Their unique optical, electrical, and physical properties are the reasons for their wide applications in various fields.

[0003] Electrocatalytic carbon dioxide reduction reaction (eCO2RR) is the core reaction for realizing the resource utilization of CO2. At present, although the catalyst of noble metal platinum shows high selectivity, its scarcity and high cost further restrict the industrial development. It is found that the catalyst prepared from pure gold nanoclusters shows good catalytic activity in the CO2RR reaction. Inspired by this, it becomes possible to prepare a gold nanocluster catalyst with high catalytic activity. Summary of the Invention

[0004] The present invention provides a gold nanocluster and its application in electrocatalytic carbon dioxide reaction. The gold nanocluster of the present invention has a high yield, good stability, and excellent electrocatalytic carbon dioxide reaction performance. In addition, the synthesis method is simple and easy to implement, and the conditions are mild.

[0005] The gold nanocluster of the present invention has the molecular formula Au 32 (CHT) 20 (TFP), where CHT is cyclohexanethiol and TFP is tris(2-furyl)phosphine.

[0006] The preparation method of the gold nanocluster of the present invention is synthesized by a one-pot method with etching, and includes the following steps:

[0007] Step 1: Place an aqueous solution of chloroauric acid into a tetrahydrofuran solution;

[0008] Step 2: Add tetraoctylammonium bromide to form a dark red color;

[0009] Step 3: Add cyclohexanethiol until the solution becomes transparent;

[0010] Step 4: Add a reducing agent to the system of Step 3 and continue to react for 12 h;

[0011] Step 5: Evaporate the organic solvent under reduced pressure, and wash the crude product with a large amount of methanol;

[0012] Step 6: Dissolve the crude product in toluene solvent, add cyclohexanethiol ligand and tris(2-furyl)phosphine ligand, and slowly stir and etch at 60 °C;

[0013] Step 7: Wash the product of Step 6 with methanol multiple times and purify it through a thin-layer chromatography plate to obtain gold nanoclusters Au 32 (CHT) 20 (TFP).

[0014] In Step 1, the concentration of the chloroauric acid aqueous solution is 0.2 g / mL.

[0015] In Step 2, the molar ratio of chloroauric acid to tetraoctylammonium bromide is 3:4.

[0016] In Step 3, the molar ratio of chloroauric acid to cyclohexanethiol is 1:2. This ratio refers to the ratio of cyclohexanethiol added in Step 3.

[0017] In Step 4, the reducing agent is sodium borohydride, and the molar ratio of chloroauric acid to the reducing agent is 1:7.

[0018] In Step 6, the molar ratio of thiol ligand, phosphine ligand and chloroauric acid is 4:1:1.

[0019] Application of the gold nanoclusters of the present invention in the electrocatalytic carbon dioxide reaction.

[0020] Specifically, it includes the following steps:

[0021] Step 1: Dissolve 2 mg of gold nanoclusters in 495 μL of dichloromethane, and then add 5 μL of 0.05 wt% naphthol;

[0022] Step 2: Drop 20 μL of the above solution on a 1×1 cm 2 carbon fiber paper as the working electrode for electrocatalytic carbon dioxide testing;

[0023] Step 3: Before the test, continuously pump high-purity CO2 gas into the electrolyte for at least 30 minutes or more;

[0024] Step 4: Perform LSV measurement at a scanning rate of 5 mV / s in a CO2-saturated KHCO3 solution;

[0025] Step 5: Use a CHI760E potentiostat to measure the cyclic voltammetry curve of the clusters at multiple potentials from -0.6 to -1.0 V (vs. RHE);

[0026] Step 6: Detect the gas product CO with a GC8860 gas chromatograph.

[0027] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0028] 1. Using chloroauric acid as the gold source, the raw materials are easily available; using organic phosphine and thiol as ligands, the raw material cost is low.

[0029] 2. The gold nanoclusters of the present invention have a definite structure, and the product purity is easy to monitor.

[0030] 3. The synthesis method is simple and feasible, with a high yield and high product stability.

[0031] 4. Excellent electrocatalytic carbon dioxide performance, with FE CO reaching 97.7% at -0.8 V. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the structural diagram of the gold nanoclusters of the present invention. Figure 1 is the Au 32 (CHT) 20 (TFP) after crystallization and tested by single crystal X-ray diffraction, and the structural diagram of the Au 32 (CHT) 20 (TFP) nanoclusters after parsing and refinement of the test results.

[0033] Figure 2 is the schematic diagram of the synthesis route of the gold nanoclusters of the present invention.

[0034] Figure 3 is the ultraviolet-visible light absorption spectrum of the Au 32 (CHT) 20 (TFP) nanoclusters of the present invention.

[0035] Figure 4 is the linear voltammetry scan curve of the Au 32 (CHT) 20 (TFP) nanocluster catalyst at different voltages.

[0036] Figure 5 is the FE 32 (CHT) 20 (TFP) nanocluster catalyst of the present invention at different potentials CO Figure. DETAILED IMPLEMENTATION METHODS

[0038] The technical solution of the present invention will be further analyzed and described below through specific embodiments.

[0039] Example 1: Synthesis of Au 32 (CHT) 20 (TFP) clusters

[0040] First, dissolve 400 μl of chloroauric acid aqueous solution (0.2 mg / ml) in 15 mL of tetrahydrofuran solution in a beaker. Stir it under a magnetic stirrer at 1500 rmp until fully mixed. Then add 100 mg of tetraoctylammonium bromide and let it react for half an hour. After the solution turns red, add 150 μL of cyclohexanethiol. After observing that the solution gradually changes from dark red to light yellow, slowly add 30 mg of sodium borohydride aqueous solution (dissolved in 5 mL of ice water) drop by drop into the beaker. After observing that the solution changes from light yellow to black, stop adding the solution. After the reaction proceeds for 12 hours, spin the obtained solution using a rotary evaporator and wash it once with methanol to remove the reducing agent and some thiol ligand impurities. Then dissolve the obtained product in 5 mL of toluene solution, add 200 μL of cyclohexanethiol and 10 mg of tris(2-furyl)phosphine at the same time, and react at 60 °C for one day. After centrifuging to remove impurities, wash the crude product with methanol several times again. Purify the crude product using thin-layer chromatography, with dichloromethane and n-hexane (DCM:n-Hex = 1:2, v:v) as the developing agent, and finally obtain pure Au 32 (CHT) 20 (TFP).

[0041] Example 2: Au 32 (CHT) 20 (TFP) Electrochemical Catalytic Carbon Dioxide Reaction Performance Test

[0042] Dissolve 2 mg of the nanoclusters in 495 μL of dichloromethane, and then add 5 μL of 0.05 wt% naphthol. Drop 20 μL of the above solution on a 1×1 cm 2 carbon fiber paper as the working electrode for the electrochemical catalytic carbon dioxide test. Before the test, continuously pump high-purity CO2 gas into the electrolyte for at least 30 minutes or more to ensure that the electrolyte is filled with CO2. In a CO2-saturated KHCO3 solution, LSV measurements were performed at a scanning rate of 5 mV / s. At room temperature, using a CHI760E potentiostat, cyclic voltammetry curves of the clusters were measured at multiple potentials from -0.6 to -1.0 V (vs. RHE). The gas product CO was detected using a GC8860 gas chromatograph.

[0043] In the present invention, the sulfur atom of cyclohexanethiol forms a strong Au-S bond with the surface of the gold core. The steric hindrance generated by its rigid cyclohexyl group and the electron transfer of the thiol group act synergistically to stabilize the geometric configuration of the gold core. The tris(2-furyl)phosphine ligand selectively exposes specific gold atom sites through the three-dimensional steric hindrance of the furan ring to form a high-density catalytic active center, while retaining the necessary binding strength between the ligand and the inner core, achieving a balance between catalytic activity and structural stability.

Claims

1. A gold nanocluster, characterized in that: The molecular formula of the gold nanocluster is Au 32 (CHT) 20 (TFP), wherein CHT is cyclohexanethiol and TFP is tri(2-furyl)phosphine.

2. The method for preparing the gold nanoclusters according to claim 1, characterized in that The steps include: Step 1: placing an aqueous solution of chloroauric acid into a tetrahydrofuran solution; Step 2: Add tetra-n-octylammonium bromide to produce a deep red color; Step 3: Add cyclohexanethiol until the solution becomes transparent; Step 4: Add the reducing agent to the system of step 3 and continue the reaction for 12 hours; Step 5: Evaporate the organic solvent under reduced pressure and wash the crude product with a large amount of methanol; Step 6: dissolving the crude product in toluene solvent, adding cyclohexanethiol ligand and tri(2-furyl)phosphine ligand, and slowly stirring and etching at 60° C.; Step 7: Wash the product of step 6 several times with methanol and purify it by thin layer chromatography to obtain gold nanoclusters Au. 32 (CHT) 20 (TFP).

3. The preparation method according to claim 2, characterized in that: In step 2, the molar ratio of chloroauric acid to tetra-n-octylammonium bromide is 3:

4.

4. The preparation method according to claim 2, characterized in that: In step 3, the molar ratio of chloroauric acid to cyclohexyl mercaptan is 1:

2.

5. The preparation method according to claim 2, characterized in that: In step 4, the reducing agent is sodium borohydride, and the molar ratio of the chloroauric acid to the reducing agent is 1:

7.

6. The preparation method according to claim 2, characterized in that: In step 6, the molar ratio of the thiol ligand, the phosphine ligand and the chloroauric acid is 4:1:

1.

7. Use of the gold nanoclusters according to claim 1 in electrocatalytic carbon dioxide reaction.

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