Exceptionally redox-active precursors in the synthesis of gold core-tin oxide shell nanostructures

초록

Core-shell nanostructures are important for applications in sensors, electronics, and fuel cells. We report the synthesis of AuNPs-aryl shell@SnO2 core-shell nanostructure (Au@SnO2) in one-step by green and direct reaction of the redox couples of SnCl(2)(center dot)2H(2)O with aryldiazonium gold(III) salt [HOOC-4-C6H4-N=N]AuCl4 in aqueous solution. The spontaneous reaction occurred simultaneously at room temperature to form a markedly stable structure of Au@SnO2, in which the gold core surface is functionalized with carboxyl groups of -C6H4COOH. The reaction is facilitated by the low reduction potential of diazonium gold salt (aryl/aryl(center dot) and Au3+/Au degrees) and the facile oxidation of tin (Sn2+/Sn4+). From the overall analysis, the presence of the organic shell boosted tailoring the gold core with immobilized, full coverage, and uniform shell of SnO2 Lewis acid. XPS results provided strong supporting evidence for gold in the metallic state and tin in the oxidized state as SnO2 compound. From TEM measurements, the average size of AuNPs increased from 10.4 +/- 4.2 nm to 50.4 +/- 17.9 nm when treated at higher temperatures (i.e., room temperature, 300 degrees C, and 800 degrees C). The average size of SnO2 also increased from 3.0 +/- 0.6 nm to 48.9 +/- 15.8 nm as the heat-treatment temperature increased, besides, the coverage by SnO2 decreased due to an increment of particle sizes of both AuNPs and SnO2. At 800 degrees C, it was difficult to see the coreshell structure. The redox route not only revisits the making of Purple of Cassius but can also be universal and extended to substantial Au@MxOy core-shell structures for catalysis and gas sensors.

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