Ultra-small silver-copper nanoclusters and preparation and application thereof

Abstract

The application belongs to the technical field of environmental protection, and discloses a kind of ultra-small silver copper nanoclusters and its preparation and application.The preparation method of the ultra-small silver copper nanoclusters includes the following steps: (1) disperse copper salt in organic solvent to obtain copper salt suspension liquid; (2) add alkynyl ligand solution, silver salt solution to the copper salt suspension liquid obtained in step (1) in turn, stir, drop the reducing agent solution, continue to stir, solid-liquid separation, remove the organic solvent of the supernatant, wash, dry to obtain silver copper nanoclusters.The preparation method is simple in operation, and has good industrial application prospect;The particle size of the obtained silver copper nanoclusters is between 1.5-3 nanometers, and excellent catalytic activity and stability are shown in the electric synthesis of oxime reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and in particular relates to an ultra-small silver-copper nanocluster and its preparation and application. Background Art

[0002] Organic nitrogen chemicals are an indispensable component of modern society and are widely used in life sciences, pharmaceutical industry, agriculture, textiles, chemicals and other fields. Oxime compounds, especially cyclohexanone oxime, are an important member of the organic nitrogen chemical family and are essential intermediates for the preparation of nylon-6 and industrial resins. It is estimated that the global production of nylon-6 will reach nearly 9 million tons by 2024, so the production demand for cyclohexanone oxime will increase accordingly. Currently, 90% of the world's cyclohexanone oxime is produced through cyclohexanone (C6H 10 Cyclohexanone oxime is produced by a nucleophilic addition-elimination reaction between cyclohexanone (NH2O2) and hydroxylamine (NH2OH). However, the above chemical processes have harsh reaction conditions, high energy consumption, and serious environmental pollution. At the same time, they also face a series of safety hazards. In particular, the production of hydroxylamine requires NH3 (mainly prepared by the Haber process) and excess H2O2, and the reaction is carried out under high temperature and harsh conditions. In addition, hydroxylamine is unstable, and improper storage and use can cause several safety issues (such as explosion). Therefore, it is very necessary to develop a green and safe strategy to achieve the sustainable production of cyclohexanone oxime under mild conditions.

[0003] Electrochemical synthesis is currently emerging as a promising strategy to achieve sustainable production of value-added compounds and chemical raw materials by driving the reaction under mild conditions and utilizing renewable electricity. x ) The reduction reaction can convert NO x Upgrading waste into key chemical raw material NH3 has attracted more and more attention. x During the reduction reaction, the key intermediate *NH2OH (adsorbed hydroxylamine) is produced. Therefore, it is an attractive approach to synthesize cyclohexanone oxime by directly reacting the *NH2OH intermediate generated in situ with cyclohexanone.

[0004] Currently, the development of high-performance electrocatalysts for oxime synthesis focuses on pure copper nanomaterials. While these materials possess high activity, pure copper is susceptible to oxidation or corrosion under ambient conditions, significantly reducing its catalytic activity and stability. Therefore, it is imperative to utilize strategies such as alloying and confinement effects to synthesize highly active and stable copper-based materials. Summary of the Invention

[0005] In order to overcome the above shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing ultra-small silver-copper nanoclusters. + and Cu + Reducibility and Cu + With Ag + Due to the significant difference in the ability to react with alkynes, a large number of silver-copper nanoclusters can be obtained by forming a copper alkyne precursor and then adding silver salt and a mild reducing agent in sequence. The preparation method is simple to operate and has good industrial application prospects.

[0006] Another object of the present invention is to provide ultrasmall silver-copper nanoclusters prepared by the above method. The silver-copper nanoclusters obtained by the present invention have very small and uniform particle sizes ranging from 1.5 to 3 nanometers. The ultrasmall particle size allows for a large number of catalytically active sites on their surface.

[0007] Another object of the present invention is to provide the use of the ultra-small silver-copper nanoclusters in electrocatalytic oxime synthesis. The silver-copper nanoclusters obtained in the present invention have a particle size that exhibits excellent catalytic activity and stability in the electrocatalytic oxime synthesis reaction.

[0008] The purpose of the present invention is achieved through the following solutions:

[0009] A method for preparing silver-copper nanoclusters comprises the following steps:

[0010] (1) dispersing a copper salt in an organic solvent to obtain a copper salt suspension;

[0011] (2) adding an alkynyl ligand solution and a silver salt solution to the copper salt suspension obtained in step (1) in sequence, stirring, adding a reducing agent solution dropwise, continuing stirring, and performing solid-liquid separation. The organic solvent of the obtained supernatant is removed, and the mixture is washed and dried to obtain silver-copper nanoclusters.

[0012] The copper salt in step (1) is at least one of cuprous acetate, cuprous chloride, cuprous bromide, cuprous iodide, cuprous trifluoroacetate, tetraacetonitrile copper tetrafluoroborate, and cuprous trifluoromethanesulfonate; preferably at least one of cuprous acetate and cuprous chloride.

[0013] The organic solvent in step (1) is at least one of toluene, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, tetrahydrofuran and ethyl acetate.

[0014] The amount of the organic solvent in step (1) is such that the concentration of the copper salt in the copper salt suspension is 0.01 to 0.5 mmol / mL.

[0015] The temperature for dispersing the copper salt in the organic solvent in step (1) is -10 to 5°C; preferably -10 to 3°C.

[0016] The alkynyl ligand in step (2) is at least one of phenylacetylene, 1-ethynylcyclopentane, and 1-ethynylcyclohexane.

[0017] The silver salt in step (2) is at least one of silver acetate, silver trifluoroacetate, silver nitrate, and silver tetrafluoroborate; preferably at least one of silver acetate, silver nitrate, and silver tetrafluoroborate.

[0018] The solvent of the alkynyl ligand solution and the silver salt solution in step (2) is at least one of methanol, ethanol, acetonitrile, tetrahydrofuran, N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

[0019] The reducing agent in step (2) is at least one of sodium cyanoborohydride, tert-butylamine borane complex, and diphenylsilane.

[0020] The solvent of the reducing agent solution in step (2) is at least one of methanol, ethanol and tetrahydrofuran.

[0021] The concentration of the alkynyl ligand in the alkynyl ligand solution in step (2) is 0.01-2 mmol / mL.

[0022] The concentration of silver salt in the silver salt solution in step (2) is 0.1-0.4 mmol / mL.

[0023] The concentration of the reducing agent in the reducing agent solution in step (2) is 0.001-0.25 mmol / mL.

[0024] The molar ratio of the silver salt in step (2) to the copper salt in step (1) is 0.2-4:1.

[0025] The molar ratio of the alkynyl ligand in step (2) to the copper salt in step (1) is 1-4:1; the molar ratio of the reducing agent to the copper salt in step (1) is 0.1-1:1, preferably 0.2-1:1.

[0026] The stirring time in step (2) is 1-4h.

[0027] The rate of the dropwise addition in step (2) is 10-20 mL / h.

[0028] The rotation speed of the continued stirring in step (2) is 1200 rpm or above, preferably 1500-1800 rpm.

[0029] The time for continuing stirring in step (2) is 15h to 24h; the temperature for stirring and continuing stirring in step (2) is -10 to 5°C.

[0030] The solid-liquid separation in step (2) is centrifugation, wherein the centrifugal speed is 6500 rpm or above, preferably 8000-9000 rpm.

[0031] The washing in step (2) is washing the solid with n-hexane at least three times.

[0032] The drying in step (3) is vacuum drying, and the drying temperature is 10-40°C, preferably 30°C.

[0033] The silver-copper nanocluster prepared by the method has a particle size of 1.5-3 nanometers and is uniform.

[0034] Application of the above-mentioned silver-copper nanoclusters in electrocatalytic oxime synthesis.

[0035] The application is specifically to use silver-copper nanoclusters as catalysts in the electrocatalytic reaction of co-reduction of nitrogen oxides and cyclohexanone to cyclohexanone oxime.

[0036] Mechanism of the present invention:

[0037] The present invention selects silver and copper from the same main group, which have good affinity and are easy to form alloy nanomaterials; + and Cu + Reducibility and Cu + With Ag + Significant difference in the ability to react with alkynes, Ag + It is easier to be reduced and become the core of AgCu ultra-small nanoparticles. + The copper has a stronger ability to bind to the alkyne ligand. Copper is more inclined to form a σ bond with the alkyne and is located on the surface of the nanoparticles to become a catalytic active site. Therefore, the copper alkyne precursor is first synthesized by the step-by-step reduction method. The formation of the copper alkyne precursor will make copper difficult to be reduced by the subsequent reducing agent. The addition of the reducing agent will then make the free Ag + It is reduced to zero valence and becomes the core of the nanoparticle, while Cu is located on the surface and connected to the alkynyl ligand, effectively protecting the silver core.

[0038] The alkynyl ligand selected in the present invention has a small radius and has bonding selectivity with silver and copper, thereby preventing the surface of the nanoparticles from being oxidized and agglomerated and not affecting the exposure of the active sites, thereby preparing a highly active and stable electrosynthetic oxime catalyst.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] (1) The preparation method is simple: the present invention adopts a step-by-step reduction method. A large number of silver-copper nanoclusters can be obtained by adding a mild reducing agent to a mixed suspension containing a copper acetylene precursor and a silver salt, so it is easy to scale up for mass production.

[0041] (2) Ultra-small and uniform particle size: The silver-copper nanoclusters synthesized in the present invention have very small and uniform particle sizes, ranging from 1.5 to 3 nanometers. The ultra-small particle size allows them to contain a large number of catalytic active sites on their surface.

[0042] (3) Excellent catalytic performance: It has excellent performance in the co-reduction of NO and cyclohexanone to cyclohexanone oxime at a potential of -0.35 V. The Faradaic efficiency of cyclohexanone oxime can reach 41%. At this potential, the selectivity of cyclohexanone oxime in the product can reach 100%. At the same time, the removal rate of cyclohexanone is as high as 95%. After 8 catalytic cycles, the Faradaic efficiency and yield of cyclohexanone oxime only slightly decay. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 (a)-(c) are transmission electron microscope (TEM) images of the silver-copper nanoclusters obtained in Example 1 at different magnifications.

[0044] Figure 2 The full X-ray photoelectron spectrum of the silver-copper nanoclusters obtained in Example 1 (a), the high-magnification X-ray photoelectron spectrum of the Ag 3d electron orbital (b), and the high-magnification X-ray photoelectron spectrum of the Cu 2p orbital (c).

[0045] Figure 3 Figure 1 shows the Faradaic efficiency and yield (a) of cyclohexanone oxime, product selectivity (b), cyclohexanone removal rate (c), and catalyst stability (d) of the silver-copper nanoclusters obtained in Example 1 in a flow electrolytic cell with an electrolyte of 1 mol / L NaOH solution and a NO gas flow rate of 10 mL / min at different potentials.

[0046] Figure 4 In Example 1, silver-copper nanoclusters are used as catalysts, respectively 14 NO and 15 Mass spectrum of the electrosynthesized oxime product using NO as the nitrogen source.

[0047] Figure 5 The SEM image of the product obtained in Comparative Example 1 and the Faradaic efficiency and yield of the electrosynthesized oxime at different potentials are shown.

[0048] Figure 6 The SEM image of the product obtained in Comparative Example 2 and the Faradaic efficiency and yield of the electrosynthesized oxime at different potentials are shown.

[0049] Figure 7 (a)-(d) are TEM images of the silver-copper nanoclusters obtained in Examples 2, 4, 6, and 8, respectively.

[0050] Figure 8 Graphs showing the Faradaic efficiency and yield of the silver-copper nanoclusters obtained in Examples 2, 4, 6, and 8 at a potential of -0.35 V. DETAILED DESCRIPTION

[0051] The present invention will be described in further detail below with reference to the Examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the Examples, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0052] Unless otherwise specified, all reagents used in the examples can be purchased from the market.

[0053] Example 1

[0054] (1) Disperse 0.3 mmol of cuprous acetate in 10 mL of dichloromethane at 0°C to form a suspension;

[0055] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of diphenylsilane was added to 2 mL of methanol to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of methanol to prepare a ligand solution. 0.3 mmol of silver acetate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 h, the reducing agent was added dropwise at a rate of 12 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 h to obtain a crude product.

[0056] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0057] Performance structure analysis

[0058] Figure 1 These are transmission electron microscope (TEM) photos of the silver-copper nanoclusters in Example 1 at different magnifications. It can be clearly seen from the TEM images that the particle size of the synthesized silver-copper nanoclusters is very small, basically maintained between 1.5-2 nanometers, and the particle size is very uniform, without silver-copper nanoparticles with too large or too small particle size.

[0059] Figure 2 The X-ray photoelectron energy (XPS) spectrum of the silver-copper nanoclusters of Example 1 shows that the 3d 3 / 2 and 3D 5 / 2 The electron binding energies of the orbitals are 374.53eV and 368.53eV respectively, and their electron binding energies are in the range of Ag. + and Ag 0 Between (Ag + and Ag0 3D 5 / 2 The electron binding energies of the orbitals are 367.3 and 368.68 eV respectively), and the 2p 1 / 2 and 2p 3 / 2 The electron binding energies of the orbitals are 952.83eV and 933.08eV respectively, and their electron binding energies are in the range of Cu + and Cu 0 Between (Cu + and Cu 0 2p 3 / 2 The electron binding energies of the orbitals are 933.3 eV and 932.6 eV, respectively), indicating that the valence states of silver and copper in the synthesized silver-copper nanoclusters are between 0 and +1, which is consistent with the characteristics of ultrasmall nanoparticles. However, the valence state of Cu is almost +1, and the degree of reduction is very small, indicating that silver is almost entirely in the core of the nanoparticles, while Cu is almost entirely connected to the alkynyl ligands on the metal core surface of the nanoparticles. This is very different from traditional silver-copper nanoparticles, which indirectly indicates that the particle size of the obtained clusters is very small, the metal atoms coordinated to the ligands on the surface have a valence of +1, and the metal atoms inside have a valence of 0, which is consistent with the characteristics of the clusters.

[0060] Figure 3 Performance test of the electrosynthesis of cyclohexanone oxime using the silver-copper nanoclusters of Example 1 in a flow electrolytic cell containing a 1 mol / L NaOH solution as the electrolyte and a NO gas flow rate of 10 mL / min. The silver-copper nanoclusters obtained in Example 1 were present at a concentration of 1 mg per square centimeter of electrode surface. (a) The Faradaic efficiency and yield of cyclohexanone oxime electrosynthesized at different potentials are shown in the figure. The figure shows that at a low potential of -0.35 V, the Faradaic efficiency of cyclohexanone oxime reaches a maximum of 41%, and the yield at this potential reaches 2.96 mmol h. -1 cm -2 (b) is the selectivity of the corresponding product. As can be seen from the figure, the selectivity of cyclohexanone oxime reaches 100% in the potential range of -0.15 to -0.55 V. (c) shows the removal rate of cyclohexanone at different potentials. As can be seen from the figure, the removal rate of cyclohexanone reaches a maximum of 95% at -0.35 V. (d) shows that after 8 cycles of catalytic experiments, the silver-copper nanoclusters still have good catalytic activity, and the Faraday efficiency of cyclohexanone oxime is 33%, indicating that this catalyst has good stability.

[0061] Figure 4 The silver-copper nanoclusters of Example 1 were used as catalysts. 14 NO and 15 The mass spectrum of the electrosynthesized oxime product with NO as the nitrogen source shows that when 15 NO, the relative molecular mass of the product increases from 114.09 to 115.09. 15When NO is the nitrogen source, all its products are C6H 10 = 15 N-OH, which means that the nitrogen elements of the oxime in the reduced system all come from the added NO rather than other nitrogen sources in the environment.

[0062] Example 2

[0063] (1) Disperse 0.3 mmol of cuprous chloride in 10 mL of dichloromethane at 0°C to form a suspension;

[0064] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of diphenylsilane was added to 2 mL of methanol to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of methanol to prepare a ligand solution. 0.3 mmol of silver acetate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 h, the reducing agent was added dropwise at a rate of 12 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 h to obtain a crude product.

[0065] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0066] Example 3

[0067] (1) Disperse 0.3 mmol of cuprous acetate in 10 mL of dichloromethane at 0°C to form a suspension;

[0068] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution. 0.6 mmol of phenylacetylene ligand was added to 3 mL of methanol to prepare a ligand solution. 0.3 mmol of silver acetate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 h, the reducing agent was added dropwise at a rate of 12 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 h to obtain a crude product.

[0069] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0070] Example 4

[0071] (1) Disperse 0.3 mmol of cuprous acetate in 10 mL of toluene at 0°C to form a suspension;

[0072] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of diphenylsilane was added to 2 mL of acetonitrile to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of acetonitrile to prepare a ligand solution. 0.3 mmol of silver acetate was added to 3 mL of acetonitrile to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 h, the reducing agent was added dropwise at a rate of 12 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 h to obtain a crude product.

[0073] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0074] Example 5

[0075] (1) Dissolve 0.3 mmol of cuprous acetate in 10 mL of dichloromethane at 0°C to form a suspension;

[0076] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of diphenylsilane was added to 2 mL of ethanol to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of methanol to prepare a ligand solution. 0.3 mmol of silver nitrate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver nitrate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 h, the reducing agent was added dropwise at a rate of 20 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 h to obtain a crude product.

[0077] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0078] Example 6

[0079] (1) Dissolve 0.3 mmol of cuprous acetate in 10 mL of dichloromethane at 0°C to form a suspension;

[0080] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of diphenylsilane was added to 2 mL of methanol to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of methanol to prepare a ligand solution. 1.2 mmol of silver tetrafluoroborate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 hours, the reducing agent was added dropwise at a rate of 12 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 hours to obtain a crude product.

[0081] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0082] Example 7

[0083] (1) Dissolve 0.3 mmol of cuprous acetate in 10 mL of dichloromethane at 0°C to form a suspension;

[0084] (2) The obtained stable solution was stirred at 0°C, and 0.3 mmol of diphenylsilane was added to 2 mL of methanol to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of methanol to prepare a ligand solution. 0.3 mmol of silver acetate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 2 h, the reducing agent was added dropwise at a rate of 12 mL / h. During the addition process, the rotation speed was maintained at 1500 rpm. After the addition was completed, the reaction was continued for 20 h to obtain a crude product.

[0085] (3) The product obtained in step (2) was centrifuged at 8000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (30° C.) to obtain the final product.

[0086] Example 8

[0087] (1) Dissolve 0.3 mmol of cuprous acetate in 10 mL of dichloromethane at 0°C to form a suspension;

[0088] (2) The obtained stable solution was stirred at 0°C, and 0.12 mmol of diphenylsilane was added to 2 mL of methanol to prepare a reducing agent solution. 0.6 mmol of 1-ethynylcyclohexane ligand was added to 3 mL of methanol to prepare a ligand solution. 0.3 mmol of silver acetate was added to 3 mL of methanol to prepare a silver salt solution. The ligand solution and the silver acetate solution were added to the dichloromethane suspension of the copper salt in sequence. After stirring for 4 hours, the reducing agent was added dropwise at a rate of 15 mL / h. During the addition process, the rotation speed was maintained at 1600 rpm. After the addition was completed, the reaction was continued for 20 hours to obtain a crude product.

[0089] (3) The product obtained in step (2) was centrifuged at 9000 rpm or above to obtain a supernatant, and the organic solvent was removed by vacuum evaporation to obtain a solid. The solid was washed three times with 20 mL of n-hexane to remove by-products, and the solid was vacuum dried (20° C.) to obtain the final product.

[0090] Comparative Example 1

[0091] Comparative Example 1 is substantially the same as Example 1, except that in step (2), the silver salt solution is added before the ligand solution is added to the Cu salt suspension.

[0092] Figure 5 (a) is a TEM image of the product of Comparative Example 1. It can be seen from the figure that the material is severely agglomerated, and the overall particle size has reached the micron level and is no longer a nanomaterial. The particle size of the silver-copper nanomaterial obtained after the reaction is completed is much larger than 2 mm or will quickly agglomerate and cannot be dispersed again. The reason is: although it is easier to interact with alkynes, the order in which the Cu salt solution, the alkyne ligand and the silver salt solution are added is also very important. The order of addition of Cu salt-alkyne ligand-silver salt solution must be followed to synthesize ultrasmall silver-copper nanoparticles. If the silver salt is added before the alkyne ligand, it will lead to the formation of a silver alkyne precursor and the copper salt being reduced to nuclei, which will eventually lead to the surface ligand interacting with a large amount of silver. The ability of silver to interact with alkynes is weaker than that of copper. Therefore, the silver-copper nanoparticles cannot be completely protected, resulting in irreversible agglomeration, and ultimately the inability to form ultrasmall and uniform silver-copper nanoclusters. (b) is the result of the addition of the silver salt in an electrolyte of 1 mol L -1 NaOH solution, NO gas flow rate was 10 mL min -1 The Faradaic efficiency and yield of cyclohexanone oxime electrosynthesized in a flow electrolytic cell at different potentials, where 1 mg of the product from Comparative Example 1 is contained per square centimeter of electrode surface. The figure shows that within the potential range of -0.15 V to -0.55 V, the Faradaic efficiency is no more than 13%, and the yield is a maximum of 1.08 mmol h -1 mg -1 , which is far lower than the performance of Example 1.

[0093] Comparative Example 2

[0094] Comparative Example 2 is substantially the same as Example 1, except that in step (2), the alkynyl ligand is 3,5-dimethoxyphenylacetylene.

[0095] Figure 6 (a) is a TEM image of the product of comparative example 2. It can be seen from the figure that the particle size of the material exceeds 200nm. The silver-copper nanomaterial obtained after the reaction is completed cannot be effectively dispersed. The reason is: the ligand selection is wrong. Although 3,5-dimethoxyphenylacetylene has a structure similar to phenylacetylene, cyclohexaneacetylene and cyclopentaneacetylene, its steric hindrance is much greater than the above three. Therefore, it cannot effectively protect the surface of the synthesized AgCu nanoparticles, which ultimately leads to excessive and uncontrollable growth of nanoparticles. (b) is the result of the reaction in an electrolyte of 1 mol L -1 NaOH solution, NO gas flow rate was 10 mL min -1 The Faradaic efficiency and yield of cyclohexanone oxime electrosynthesized in a flow electrolytic cell at different potentials, where 1 mg of the product from Comparative Example 2 is contained per square centimeter of electrode surface. The figure shows that the Faradaic efficiency is no more than 9% in the potential range of -0.15 V to -0.55 V, and the yield is a maximum of 0.7 mmol h -1 mg -1 , far lower than the performance of Example 1

[0096] Figure 7 Figures (a) to (d) are TEM images of Examples 2, 4, 6, and 8. As can be seen from the figures, although the experimental conditions of Examples 2, 4, 6, and 8 are different from those of Example 1, the TEM images show that the particle size of the synthesized silver-copper nanoclusters is approximately 1.5-3 nanometers, which is very close to the particle size of Example 1.

[0097] Figure 8 The silver-copper nanoclusters of Examples 2, 4, 6, and 8 were prepared in an electrolyte of 1 mol L -1 NaOH solution, NO gas flow rate was 10 mL min -1 Performance diagram of electrosynthesis of oximes at a potential of -0.35 V in a flow electrolytic cell, where 1 mg of silver-copper nanoclusters were present per square centimeter of electrode surface. The data in the figure show that Examples 2, 4, 6, and 8 have good catalytic performance, with Faradaic efficiencies between 39% and 40% and yields of up to 2.85 mmol h -1 mg -1 -2.96mmol h -1 mg -1 .

[0098] In summary, Example 1 has the best catalytic performance, and its structure and performance are the most representative. In terms of structure, the particle size of the silver-copper nanoclusters is uniform and ranges from 1.5 to 2 nanometers. Generally speaking, the smaller the particle size, the more active sites can be exposed, and the better the performance of the nanomaterial. By analyzing the electrosynthesized oxime products at different potentials, we found that it has the best performance for electrosynthesizing oxime at a potential of -0.35V. At this potential, the Faradaic efficiency of the oxime reaches 41%, and the yield can reach 2.96mmol h -1 mg -1 At the same time, the selectivity of oxime reached more than 100%, and the removal rate of cyclohexanone was greater than 95%. At the same time, after 8 cycles of catalytic experiments at this potential, the Faradaic efficiency of oxime only slightly decayed, indicating that the stability of silver-copper nanoclusters is very good, and using them as electrosynthetic oximes has great application prospects and industrial value.

[0099] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing silver-copper nanoclusters, characterized in that: The following steps are involved: (1) dispersing copper salt in an organic solvent to obtain a copper salt suspension; (2) adding an alkynyl ligand solution and a silver salt solution to the copper salt suspension obtained in step (1) in sequence, stirring, adding a reducing agent solution dropwise, continuing stirring, separating the solid and liquid, removing the organic solvent from the obtained supernatant, washing, and drying to obtain silver-copper nanoclusters; The concentration of the alkynyl ligand in the alkynyl ligand solution in step (2) is 0.01-2 mmol / mL; the alkynyl ligand is at least one of phenylacetylene, 1-ethynylcyclopentane, and 1-ethynylcyclohexane; The concentration of the silver salt in the silver salt solution in step (2) is 0.1-0.4 mmol / mL; The concentration of the reducing agent in the reducing agent solution in step (2) is 0.001-0.25 mmol / mL; The molar ratio of the silver salt in step (2) to the copper salt in step (1) is 0.2-4:1; The molar ratio of the alkynyl ligand in step (2) to the copper salt in step (1) is 1-4:1; the molar ratio of the reducing agent to the copper salt in step (1) is 0.1-1:1; The rate of the dropwise addition in step (2) is 10-20 mL / h.

2. The method for preparing silver-copper nanoclusters according to claim 1, wherein: The copper salt in step (1) is at least one of cuprous acetate, cuprous chloride, cuprous bromide, cuprous iodide, cuprous trifluoroacetate, tetraacetonitrile copper tetrafluoroborate, and cuprous trifluoromethanesulfonate; The organic solvent in step (1) is at least one of toluene, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, tetrahydrofuran and ethyl acetate.

3. The method for preparing silver-copper nanoclusters according to claim 1, wherein: The amount of the organic solvent in step (1) is such that the concentration of the copper salt in the copper salt suspension is 0.01 to 0.5 mmol / mL; The temperature of dispersing the copper salt in the organic solvent in step (1) is -10~5°C.

4. The method for preparing silver-copper nanoclusters according to claim 1, wherein: The silver salt in step (2) is at least one of silver acetate, silver trifluoroacetate, silver nitrate, and silver tetrafluoroborate; The solvent of the alkynyl ligand solution and the silver salt solution in step (2) is at least one of methanol, ethanol, acetonitrile, tetrahydrofuran, N, N-dimethylformamide, and dimethyl sulfoxide; The reducing agent in step (2) is at least one of sodium cyanoborohydride, tert-butylamine borane complex, and diphenylsilane; The solvent of the reducing agent solution in step (2) is at least one of methanol, ethanol, and tetrahydrofuran.

5. The method for preparing silver-copper nanoclusters according to claim 1, characterized in that: The molar ratio of the reducing agent in step (2) to the copper salt in step (1) is 0.2-1:

1.

6. The method for preparing silver-copper nanoclusters according to claim 1, characterized in that: The stirring time in step (2) is 1-4 hours; The stirring time in step (2) is 15 h to 24 h; The temperature for stirring and continuing stirring in step (2) is -10 ~ 5 °C.

7. A silver-copper nanocluster prepared by the method according to any one of claims 1 to 6, characterized in that: The particle size is 1.5-3 nanometers.

8. Use of the silver-copper nanoclusters according to claim 7 in electrocatalytic oxime synthesis.

9. The application according to claim 8, characterized in that: Silver-copper nanoclusters were used as catalysts in the electrocatalytic co-reduction of nitrogen oxides and cyclohexanone to cyclohexanone oxime.

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