Effect of surfactants on the size and shape of cobalt nanoparticles synthesized by thermal decomposition

Cobalt nanoparticles with various morphologies were synthesized by thermal decomposition of cobalt acetate in the presence of various surfactants at 260°C. A combination of surfactants consisting of sufficient amount of oleic acid together with polyvinylpyrrolidone and oleylamine resulted in well-dispersed cubic cobalt nanoparticles of ∼25nm in average size. When 1,2-dodecanediol was added as a reducing agent to the surfactant mixture, triangular-prism-shaped nanoparticles of ∼50nm in average size were synthesized. Furthermore, an injection of trioctylphosphine into the reactor as an additional surfactant decreased the particle size to ∼10nm. The XRD pattern of the prism-like particles corresponded to hexagonal close-packed crystalline phase of cobalt.