Digestive ripening in the formation of monodisperse silver nanospheres

Abstract

Digestive ripening is a unique process in colloidal synthesis that can enable direct conversion of polydisperse nanoparticles into monodisperse ones. However, such a strategy usually relies on strongly coordinating ligands such as alkylthiols to initiate etching and stabilize the surfaces and thus affords nanoparticles with hydrophobic and passivated surfaces, which greatly limits their applications. In this work, we report that digestive ripening can be achieved by decoupling the etching and surface stabilization functions using two independent chemical agents, allowing the use of considerably weak capping ligands which are hydrophilic and can be replaced later according to the need of the specific applications. As a proof-of-concept, we, for the first time, demonstrate a novel digestive ripening system to synthesize hydrophilic monodisperse Ag nanospheres capped by conveniently removable ligands. With chloride for oxidative etching and diethylamine for effective surface capping, monodisperse Ag nanospheres have been conveniently obtained by starting with a precursor of either a Ag⁺ solution or a AgCl suspension. These monodisperse Ag nanospheres with a clean surface exhibit excellent activity in surface-enhanced Raman scattering (SERS). We believe that this new strategy may significantly broaden the general applicability of digestive ripening for the controlled synthesis of colloidal nanoparticles for a broad range of applications.