Copper Ion Assisted Reshaping and Etching of Gold Nanorods: Mechanism Studies and Applications

Abstract

This article describes copper ion assisted end-cap morphology transformation and anisotropic etching of gold nanorods (GNRs) under mild conditions. The copper ions are proposed to catalyze the oxidation of the GNRs by dissolved oxygen. We suggest that the surface Au atoms with high surface energy are stabilized by forming Au–O complexes (termed as static adsorbed oxygen). At low concentration of copper ions, the Au–O complexes are removed by oxidative etching, thus leaving a “clean” Au surface. Such a clean surface can relax to a more stable state via surface atom diffusion, leading to the GNR end-cap morphology variation. This is the first time that the existence of adsorbed oxygen species on the surface of the GNRs is probed and demonstrated. At high concentration of copper ions, anisotropic etching of the GNRs is initiated by dissolved oxygen (termed as dynamic adsorbed oxygen) and leads to shorter GNRs. For other etch agents such as H2O2 and Fe3+, addition of copper ions produces a synergistic effect. Due to the high affinity of oxygen to silver and palladium, such synergistic etching is observed in Au@Ag NRs and Au@Pd NRs as well. These interesting findings provide a new way to probe the surface reactivity of noble metal nanocrystals.