Size-dependent transformation from Ag templates to Au–Ag nanoshells via galvanic replacement reaction in organic medium

Abstract

The transformation from Ag templates to Au–Ag nanoshells via galvanic replacement reaction with HAuCl4 was systematically studied in an organic medium in the presence of oleylamine. Decahedral (~43 nm in size) and triangular prism (~53 nm in edge length) Ag templates transformed into equiaxed and triangular prismatic Au–Ag nanoshells, respectively. The first step involved structural and morphological changes from Ag templates to Au–Ag nanoshells with an interior cavity. In the second step, the growth of the shells continued through the deposition of Au. The shell thickness increased from ~5 to ~10 nm for the equiaxed Au–Ag nanoshells (~39-nm interior cavity) and ~5 to ~8 nm for the triangular prismatic Au–Ag nanoshells (~52-nm interior edge length). Oleylamine not only served as a surfactant but also removed AgCl precipitates and reduced HAuCl4. For the nanoshells derived from the ~20-nm Ag decahedrons, further reaction in excess HAuCl4 collapsed the nanoshells into Au-rich solid fragments. However, the nanoshells derived from the ~43-nm Ag decahedrons, the nanoshell structure not only persisted in excess HAuCl4, but its shell thickness also increased. The size-dependent transformation of these nanoshells is discussed.