Galvanic replacement reactions in transition metal oxide nanoparticles

Abstract

In this work, a synthetic method to prepare octahedron-shaped cobalt oxide nanoparticles has been followed. The synthesis is based on the thermodecomposition of cobalt(II) acetate used as the precursor. The nanoparticles were additionally coated with silica (SiO2), by means of a reverse microemulsion method. CoO is an antiferromagnetic material with a consequent characteristic magnetic response. Accordingly, the magnetic properties of the CoO and CoO@SiO2 nanoparticles were recorded in order to distinguish between the intrinsic properties of the nanoparticles and their collective behaviour. Alternatively, the CoO nanoparticles were also coated with shells of transition metal ferrites (MFe2O4, metal M: Mn, Co). The core-shell morphology attained implies an interface between CoO and MFe2O4 that promotes diffusion and galvanic replacement reactions, ultimately favouring the formation of hollow structures. Both types of octahedra, the CoO and the CoO@MFe2O4 nanoparticles, permit the comparison of the thermodynamic and chemicallycontrolled galvanic reaction and the kinetically-driven Kirkendall effect