PH-Dependent Galvanic Replacement of Supported and Colloidal Cu2O Nanocrystals with Gold and Palladium

Abstract

Galvanic replacement reactions (GRRs) on nanoparticles (NPs) are typically performed between two metals, i.e., a solid metal NP and a replacing salt solution of a more noble metal. The solution pH in GRRs is commonly considered an irrelevant parameter. Yet, the solution pH plays a major role in GRRs involving metal oxide NPs. Here, Cu2O nanocrystals (NCs) are studied as galvanic replacement (GR) precursors, undergoing replacement by gold and palladium, with the resulting nanostructures showing a strong dependence on the pH of the replacing metal salt solution. GRRs are reported for the first time on supported (chemically deposited) oxide NCs and the results are compared with those obtained with corresponding colloidal systems. Control of the pH enables production of different nanostructures, from metal-decorated Cu2O NCs to uniformly coated Cu2O-in-metal (Cu2O@Me) core-shell nanoarchitectures. Improved metal nucleation efficiencies at low pHs are attributed to changes in the Cu2O surface charge resulting from protonation of the oxide surface. GR followed by etching of the Cu2O cores provides metal nanocages that collapse upon drying; the latter is prevented using a sol-gel silica overlayer stabilizing the metal nanocages. Metal-replaced Cu2O NCs and their corresponding stabilized nanostructures may be useful as photocatalysts, electrocatalysts, and nanosensors.