| Noble metals especially gold as a souvenir jewelry and currency since ancient times because of its extremely stable physical and chemical properties and the value of eternal fortune, which is human being’s favor and pursuit. The research and study of gold nanoparticles has been already for more than one hundred and fifty years, and the golden-nanoclusters in nanoscale show different physicochemical properties with that big bulk-gold that our naked eye can see under the condition of the nature. Moreover this kind of gold nanoparticles on the biological sensor and catalytic application also shows a great potential value. In 1994, Brust created The Bottom-up method to prepare the gold nanoparticles. From then on such size-focus synthetic methods of gold nanoclusters developed, and the atomically precise gold nanoclusters synthesized through various ways and through a varity of characterization later. More importantly, with the development of the synthesis methods and the rapid development of modern single-crystal diffraction technique, the scientists synthesized all kinds of precise atomic gold nanoclusters, which provides a powerful guarantee of gold nanoparticles in-depth study. Accurate gold nanoclusters with the ordinary gold nanoparticles compared or gold nanocrystals, because of their structure, so can help people to explore gold nanoclusters of the relationship between structure and properties. Au25(SR)18 nanoclusters represented the organic monolayer protected-gold nanoclusters, whose properties’ study has been the hot issue even till now. However, this clusters have failed to be fully understood until now due to its complexity, so it’s driving us to use the metal exchange method to study this 25 - atoms system and the effects of doping into the clusters as well. After a single extraneous metal atom doping into a homo-gold nanoclusters, we can see the new alloy nanoclusters may show the different physical and chemical properties as a result.On the basis of predecessors’ lots of research work of phenyl ethyl mercaptan-capped gold nanoclusters Au25(SR)18, taking advantage of the method of metal exchange, we finally attained the single-scattered with high pure precise Cd1Au24(SR)18 alloy nanoclusters. Further more, compared with the Au25(SR)18, we identified and characterized its related properties such as optical properties and oxidation stability properties, electrochemical properties. In addition, we also observed its application in catalytic organic reactions to explore its catalytic activity. This article’s main research content is as follows:1. Different from the conventional synthetic strategy involves reducing a mixture of metal precursors by NaBH4 in the presence of ligands, such as the cases of MxAu25-x(SR)18 (M= Ag or Cu) NCs, I use a relatively new metal exchange synthesis method to get high purity alloy nanoclusters Cd1Au24(SR)18. In this method, we firstly obtained the precursors Au25(SR)18 nanoclusters with phenyl ethyl mercaptan as the ligand, and then used Au25(SR)18 as raw materials mixing with amounts of phenyl ethyl sulphur cadmium Cd(SC2H4Ph) complex to produce the high purity Cd1Au24(SR)18. Experiments show that the yield of this new method is higher, and the purification method is simpler. This creative method unlike the reported synthesis methods, which may shed light on the study of the controllable preparation of alloy nanoclusters.2. The as-obtained cluster product was conformed to be the target product of high purity of nanoclusters Cd1Au24(SR)18 through characterization by UV-visible absorption spectrum (UV), mass spectrometry including both the matrix mass spectrometry and the electrospray ionization time-of-fight mass spectrometry (MALDI-TOF, ESI-TOF), oxidation stability spectroscopy and the differential pulse voltammetry method of electrochemical analysis. The number of metal kernel atoms in alloy nanoclusters Cd1Au2 has not been changed even after doping, which still maintained a 25-atoms metal kernel and 18-ligands outside structure. However, the center atom of a gold atoms in Au25 nanocluster was replaced by an outer metal cadmium atom. By comparing the two types of nanoclusters Cd1Au24 and Au25, we can see their oxidation stability properties, optical properties and electrochemical properties are different. Compared with the inert metal (gold), the active metal (Cd) is much more prone to oxidation, leading to its high oxidation state. In this work, we found that doping the homogold Au25(SR)18 nanocluster with cadmium largely enhances its stability. The differential pulse voltammetry (DPV) analysis suggested that the active metal (Cd) doping raised the high occupied molecular orbital (HOMO) energy of homogold Au25 nanocluster, which led to stronger retention of its valence electrons. Cd1Au24(SR)18 nanocluster also exhibited much higher activity than homogold Au25 nanocluster in aerobic benzyl alcohol oxidation. Therefore, it is of great significance for the synthesis of this kind of new type outer metal doped gold nanoclusters in the future. |
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