Highly Stable Silica-Coated Gold Nanoflowers Supported on Alumina

Shape-controlled nanocrystals, such as nanowires and nanoflowers, are attractive because of their potential novel optical and catalytic properties. However, the dispersion and morphological stabilities of shape-controlled nanocrystals are easily destroyed by changing the dispersion solvent and temperature. Methods of support and the silica coating are known to improve the dispersion and morphological stabilities of metal nanocrystals. The silica-coating method often causes morphological changes in shape-controlled nanocrystals because the silica coating is formed in mixed solutions of water and organic solvents such as ethanol, and this results in aggregation due to changes in the dispersion solvent. Furthermore, ligand exchange, designed to improve the dispersion stability in the solvent, often causes morphological changes. This article introduces a method for the preparation of highly stable silica-coated Au nanoflowers (AuNFs) supported on Al₂O₃. The method of support prevents the aggregation and precipitation of AuNFs when the solvent is changed from water to water/ethanol. Through stability improvement, silica coating of AuNFs/Al₂O₃ was conducted in water/ethanol without ligand exchange that causes morphological changes. Furthermore, silica-coated AuNFs/Al₂O₃ exhibit high morphological stability under high-temperature conditions compared to uncoated AuNFs/Al₂O₃. These results are very useful when preparing highly morphologically stable, silica-coated, shape-controlled nanocrystals without ligand exchange.