Gradual Transformation of Ag2S to Au2S Nanoparticles by Sequential Cation Exchange Reactions: Binary, Ternary, and Hybrid Compositions

Cation exchange reactions have been exploited in the last years as an efficient tool for the controlled chemical modification of premade nanocrystals. In this work, the gradual transformation of Ag2S nanocrystals into Au2S analogues is performed by sequential cation exchange reactions that allow for a fine control of the chemical composition, delivering also two intermediate ternary sulfides based exclusively on noble metals. The role of two different surfactants in the reaction medium has been studied: while dodecylamine is favoring the heterogeneous nucleation of metallic Au on the surface of the semiconductor domains in detriment of the cation exchange reaction, the use of tetraoctylammonium bromide turns out to be crucial for the enhancement of the exchange in order to reach full cation substitution, if desired. The presence of Br anions in the reaction medium represents an additional tool to modulate the morphology of the final nanocrystals, being either solid or hollow depending on their concentration. The synthetic protocol has been successfully conducted in both spherical and rod-like nanocrystals with identical results, leading to a wide variety of binary, ternary, and/or hybrid nanostructures that have been carefully characterized.