A method for synthesizing thiol-protected copper metal nanocluster crystals by secondary reduction self-assembly

Abstract

The invention discloses a method for synthesizing thiol-protected copper metal nanocluster crystals by secondary reduction self-assembly, and belongs to the technical field of metal nanoclusters. The invention comprises the following steps: mixing an alcohol solution with a copper precursor, adding a coordination agent, adding a thiol ligand, and then adding a NaBH4 alcohol solution for reduction, heating the mixed product after a period of reaction, and then adding a certain amount of NaBH4 alcohol solution for secondary reduction, volatilizing the alcohol solution in the product by rotary evaporation, then adding an organic reagent to wash the mixture, extracting the product with toluene or dichloromethane, and finally cultivating crystals by a volatilization method or a diffusion method to obtain copper nanocluster crystals. The synthesis method of the invention can obtain high-stability copper metal clusters protected by thiol with a special spatial structure, and solves the problems of unstable products and difficult crystallization in the synthesis of thiol-protected copper metal nanoclusters.

Description

Technical Field

[0001] The invention belongs to the technical field of metal nanoclusters, and in particular relates to a method for synthesizing thiol-protected copper metal nanocluster crystals through secondary reduction self-assembly. Background Art

[0002] Metal nanoclusters refer to nanomolecules composed of dozens of metal atoms. They are metal particles with sizes ranging from subnanometers to 2 nanometers and exhibit properties different from bulk and nanoparticles. Due to their high specific surface area, quantum size effect, special photophysical properties and surface geometry effects, metal nanoclusters have good application prospects in catalysis, biology, electronics, etc. At the same time, due to their clear fine structure, the "structure-effect" relationship can be constructed through theoretical calculations, thereby accurately regulating and designing the synthesis of metal clusters with different properties and developing future applications of metal clusters.

[0003] The analysis of the morphology of copper metal clusters has always been a research hotspot in basic science because it can provide answers to many fundamental questions, including the formation of copper metal bonds, the evolution of electronic and magnetic properties, new assembled structures, and many other new phenomena. However, the synthesis of copper metal clusters is relatively difficult. Compared with the widely reported gold, silver and their alloy nanoclusters, copper nanoclusters are unstable due to their high reactivity and low standard reduction potential. They are easily oxidized during the synthesis process, and it is difficult to accurately control the number of atoms and are not easy to crystallize. As a result, it is difficult to obtain more novel copper nanoclusters. Summary of the invention

[0004] Based on the above-mentioned urgent need for the synthesis of copper metal clusters and the problems existing in the synthesis process, the purpose of the present invention is to provide a method for synthesizing thiol-protected copper metal nanocluster crystals by secondary reduction self-assembly, aiming to solve the defects in the existing copper nanocluster preparation process and solve the key problems of stability and crystallinity of current copper metal nanoclusters.

[0005] The technical solution of the present invention is specifically as follows:

[0006] A method for synthesizing thiol-protected copper metal nanocluster crystals by secondary reduction self-assembly, the method comprising the following steps:

[0007] (1) Preparation of copper-sulfur complex: adding copper precursor to alcohol solution to dissolve, then adding coordination agent and thiol ligand, and reacting for a period of time;

[0008] (2) Reduction of the copper-sulfur complex: adding an alcohol solution containing a reducing agent to the solution obtained in step (1) and reacting for a period of time;

[0009] (3) Secondary reduction of copper metal nanoclusters: heating the solution obtained in step (2) to a certain temperature, adding an alcohol solution containing a reducing agent, maintaining the temperature for a certain period of time, then cooling and reacting for a period of time;

[0010] (4) Purification of copper metal nanoclusters: evaporating the solvent in the mixed solution obtained in step (3), then adding an alcohol solution for washing, and finally extracting with an organic reagent;

[0011] (5) Crystallization of copper metal nanoclusters: Copper nanocluster crystals are obtained by growing crystals through a volatilization method or a diffusion method.

[0012] Based on the above technical scheme, preferably, the copper precursor in step (1) is at least one of CuSO4, Cu(NO3)2, CuCO3, CuCl2, and (CH3COO)2Cu; the ligand is at least one of tetramethylammonium chloride, tetramethylammonium iodide, tetra-n-octylammonium bromide, benzyltriethylammonium chloride (TEBA), tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate (TBAB), and trioctylmethylammonium chloride; and the thiol ligand is at least one of benzyl mercaptan, phenylethyl mercaptan, p-tert-butyl mercaptan, and p-isopropyl mercaptan.

[0013] Based on the above technical solution, preferably, the molar ratio of the copper precursor, the ligand and the thiol ligand in step (1) is 1:0.1-10:0.1-10, and more preferably 1:1-10:1-10.

[0014] Based on the above technical solution, preferably, the alcohol solution in steps (1)-(4) is at least one of methanol, ethanol, propanol, isopropanol and n-butanol.

[0015] Based on the above technical solution, preferably, the reaction time in step (1) is 10 to 240 minutes; and the reaction time in steps (2)-(3) is 1 to 24 hours.

[0016] Based on the above technical solution, preferably, in steps (2)-(3), the reducing agent includes sodium borohydride, and the molar ratio of the copper precursor to the reducing agent is 1:0.1-100, more preferably 1:1-100.

[0017] Based on the above technical solution, preferably, in step (3), the heating temperature is 50-100° C. and the holding time is 5-40 min.

[0018] Based on the above technical solution, preferably, the organic reagent in step (4) is at least one of toluene, dichloromethane, acetonitrile, acetone and n-hexane.

[0019] Based on the above technical scheme, preferably, the diffusion method in step (5) includes toluene-methanol diffusion method, dichloromethane-methanol diffusion method, acetonitrile-methanol diffusion method, acetone-methanol diffusion method and n-hexane-methanol diffusion method.

[0020] The beneficial effects achieved by the present invention are as follows:

[0021] (1) The copper nanoclusters synthesized by the method of the present invention for synthesizing thiol-protected copper metal nanocluster crystals through secondary reduction self-assembly are generally divalent and have a very wide size distribution, which can greatly expand the understanding of the structure of nanomaterials.

[0022] (2) The copper metal nanoclusters synthesized in the present invention are protected by organic ligands. The sulfur, carbon and other elements contained in the organic ligands can change the electronic structure and spatial structure of the copper nanoclusters, thereby improving the stability and activity of the copper nanoclusters, providing a new solution for understanding the properties of nanomaterials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0024] Figure 1 Fourier transform electrospray ionization mass spectrometry (ESI-MS) of the copper metal nanoclusters prepared in Example 1;

[0025] Figure 2 This is an optical microscope photograph of the crystallized copper metal nanoclusters obtained in Example 2;

[0026] Figure 3 Fourier transform electrospray ionization mass spectrometry (ESI-MS) of the product obtained in Comparative Example 1;

[0027] Figure 4 The figure is a comparison of the catalytic results of the copper nanoclusters in Example 2 (a) and the copper nanomaterials in Comparative Example 1 (b). DETAILED DESCRIPTION

[0028] The following is further described in conjunction with specific examples to make the advantages and features of the present invention more easily understood by those skilled in the art. Unless otherwise specified, the raw materials used in the following examples are all commercially available conventional raw materials.

[0029] Example 1

[0030] 27 mg CuSO4 was dissolved in 20 mL methanol solution, 26 mg ligand (tetramethylammonium chloride) was added, 90 mg benzyl mercaptan ligand was added, and the reaction was stirred for 60 min, and then the reducing agent NaBH4 methanol solution (38 mg NaBH4) was added. After reacting for 12 h, a mixture was obtained. The solution was heated to 50 ° C and maintained for 10 min, then cooled to room temperature, and then reacted for another 24 h. The methanol solution in the product was first volatilized by rotary evaporation, and then the organic reagent ethanol was added to wash the mixture. Finally, the product was extracted with the organic reagent toluene, and the crystals of copper nanoclusters were obtained using the toluene-methanol diffusion method.

[0031] Example 2

[0032] 24 mg of Cu(NO3)2 was dissolved in 20 mL of ethanol solution, 58 mg of ligand (tetramethylammonium iodide) was added, 120 μL of phenylethanethiol ligand was added, and the reaction was stirred for 120 min. Then, the reducing agent NaBH4 ethanol solution (76 mg NaBH4) was added. After reacting for 18 h, a mixture was obtained. The solution was heated to 60 °C and maintained for 20 min, then cooled to room temperature, and then reacted for another 16 h. The ethanol solution in the product was first volatilized by rotary evaporation, and then the organic reagent methanol was added to wash the mixture. Finally, the product was extracted with an organic reagent dichloromethane, and the crystals of copper nanoclusters were obtained using the dichloromethane volatilization method.

[0033] Example 3

[0034] 17 mg (CH3COO)2Cu was dissolved in 20 mL isopropanol solution, 110 mg of ligand (benzyltriethylammonium chloride) was added, 140 mg of adamantane thiol ligand was added, and the reaction was stirred for 60 min, and then the reducing agent NaBH4 isopropanol solution (57 mgNaBH4) was added. After reacting for 8 h, a mixture was obtained. The solution was heated to 70 ° C and maintained for 30 min, then cooled to room temperature, and then reacted for another 12 h. The isopropanol solution in the product was first volatilized by rotary evaporation, and then the organic reagent ethanol was added to wash the mixture. Finally, the product was extracted with an organic reagent dichloromethane, and the crystals of copper nanoclusters were obtained using the dichloromethane volatilization method.

[0035] Example 4

[0036] 170 mg (CH3COO)2Cu was dissolved in 20 mL of n-butanol solution, 190 mg of ligand (tetra-n-octylammonium bromide) was added, 100 μL of p-tert-butyl mercaptan ligand was added, and the reaction was stirred for 90 min. Then, a reducing agent NaBH4 n-butanol solution (114 mg NaBH4) was added. After reacting for 10 h, a mixture was obtained. The mixture was heated to 80 °C and maintained for 30 min, then cooled to room temperature, and then reacted for another 6 h. The n-butanol solution in the product was first volatilized by rotary evaporation, and then the organic reagent ethanol was added to wash the mixture. Finally, the product was extracted with an organic reagent toluene, and the crystals of copper nanoclusters were obtained using a toluene-methanol diffusion method.

[0037] Comparative Example 1

[0038] 170 mg (CH3COO)2Cu was dissolved in 20 mL ethanol solution, 100 μL p-tert-butyl mercaptan ligand was added, and the reaction was stirred for 90 min. Then, a reducing agent NaBH4 ethanol solution (38 mg NaBH4) was added. After the reaction for 10 h, the ethanol solution in the product was first volatilized by rotary evaporation, and then an organic reagent acetone was added to wash the mixture. Finally, the product was extracted with an organic reagent toluene to obtain the target product. The target product could not be obtained by crystallization, that is, there was no obvious cluster feature (such as Figure 3 shown).

[0039] In order to further compare the performance differences of the target products prepared in the examples and comparative examples, the hydrogenation of furfural to furfuryl alcohol reaction was selected as a model reaction for catalytic testing. 10 mg of the copper nanoclusters prepared in Example 2 (labeled as CuX) and 10 mg of the target product in Comparative Example 1 (labeled as CuY) were weighed and catalytic tests were performed respectively. 10 mL of ethanol and 150 mg of furfural were added to a stainless steel reactor and catalytic tests were performed at 120°C and 2 MPa of hydrogen to obtain the target product. Figure 4 From the catalytic results, it can be clearly found that the copper metal nanoclusters obtained by the preparation method of the present invention have higher catalytic activity and selectivity.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synthesizing thiol-protected copper metal nanocluster crystals by secondary reduction self-assembly, characterized in that: The method comprises the following steps: (1) Add the copper precursor to an alcohol solution to dissolve it, then add the ligand and the thiol ligand and react for a period of time; (2) adding an alcohol solution containing a reducing agent to the solution obtained in step (1) and reacting for a period of time; (3) heating the solution obtained in step (2) to a certain temperature, adding an alcohol solution containing a reducing agent, maintaining the temperature for a certain period of time, then cooling and reacting for a period of time; (4) evaporating the solvent in the mixed solution obtained in step (3), then adding an alcohol solution for washing, and finally extracting with an organic reagent; (5) Cultivating crystals by volatilization or diffusion to obtain copper nanocluster crystals; The copper precursor in step (1) is at least one of CuSO4, Cu (NO3)2, CuCO3, CuCl2, and (CH3COO)2Cu; the ligand is at least one of tetramethylammonium chloride, tetramethylammonium iodide, tetra-n-octylammonium bromide, benzyltriethylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, and trioctylmethylammonium chloride; the thiol ligand is at least one of benzyl mercaptan, phenylethyl mercaptan, p-tert-butyl mercaptan, and p-isopropyl mercaptan; The molar ratio of the copper precursor, the ligand and the thiol ligand in step (1) is 1:0.1-10:0.1-10; The reaction time in step (1) is 10 to 240 minutes; the reaction time in steps (2) to (3) is 1 to 24 hours; In steps (2)-(3), the reducing agent includes sodium borohydride, and the molar ratio of the copper precursor to the reducing agent is 1:0.1-100; In step (3), the heating temperature is 50-100°C and the holding time is 5-40 minutes.

2. The method according to claim 1, characterized in that: The alcohol solution in steps (1) to (4) is at least one of methanol, ethanol, propanol, isopropanol and n-butanol.

3. The method according to claim 1, characterized in that The organic reagent in step (4) is at least one of toluene, dichloromethane, acetonitrile, acetone and n-hexane.

4. The method according to claim 1, characterized in that: The diffusion method in step (5) includes toluene-methanol diffusion method, dichloromethane-methanol diffusion method, acetonitrile-methanol diffusion method, acetone-methanol diffusion method and n-hexane-methanol diffusion method.

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