Oxidation and oriented attachment growth of colloidal nanoparticles during electrophoretic deposition

Abstract

• The electrophoretic deposition can be a chemical oxidization and oriented attachment process. • The charge type of the Ag nanoparticles changes during electrophoretic deposition. • Ag 2 O 2 nanocubes are assembled from Ag 2 O 2 nanoparticles oxidized from Ag nanoparticles. Electrophoretic deposition (EPD) has been widely used to assemble nanoparticles into dense nanoparticle films. Here, we discovered that the EPD might be not necessarily the widely accepted physical pile-up process, but a chemical oxidization and oriented attachment growth process. During EPD of silver colloids prepared by laser ablation of a piece of silver plate in pure water without any chemicals introduced, we observed formation of sub-microscale well-defined silver peroxide (Ag 2 O 2 ) cuboids on the anode electrode surface. The Ag 2 O 2 nanoparticles were oxidized from the Ag nanoparticles during EPD. Fusion between neighbouring Ag 2 O 2 nanoparticles through oriented attachment and Ostwald ripening process rendered the formation of the Ag 2 O 2 cuboids. This study revealed a new growth mechanism during EPD, strengthening the capability of EPD during designing micro/nanostructures.