Cobalt and Silica Based Core–Shell Structured Nanospheres

Verónica Salgueiriño-Maceira, and Miguel A. Correa-Duarte

J. Mater. Chem., 2006, 16, 3593–3597

This article presents state-of-art strategies for engineering particle structure using colloidal chemistry in such a way that environmentally stable silica-coated cobalt nanoparticles and cobalt-coated silica spheres were prepared combining sodium borohydride reduction in aqueous solution, the Stöber method, and/or the layer-by-layer self-assembly technique. We highlight the synthesis and manipulation of cobalt clusters in aqueous solution producing monodisperse building blocks. Silica-coated cobalt nanoparticles, whose core and shell can be tuned depending on the experimental conditions, were also found to organize into chains when driven by a weak external magnetic field and strong dipole–dipole magnetic interactions are believed to be the driving force for the self-organization. The same cobalt clusters were used for the preparation of cobalt-coated silica spheres taking advantage of the layer-by-layer self-assembly technique. The nanoscale engineering of this type of colloids is expected to extend the spectrum of magnetic effects and functionalities.