Synthesis of Size and Shape-Controlled Co Nanoparticles from Cobalt Acetate by Thermal Decomposition

摘要

Monodisperse cobalt nanoparticles with relatively high coercivities were synthesized by thermal decomposition of cobalt acetate for the application of ultra-high density magnetic recording media. For thermal decomposition, cobalt carbonyl, Co2(CO)8, has often been used as a precursor to generate the nanoparticles. However, this cobalt carbonyl is strongly toxic and relatively expensive. To avoid these disadvantages, we synthesized Co nanoparticles by thermal decomposition of cobalt acetate tetrahydrate, Co(CH3COO)2·4H2O. The cobalt nanoparticles with various morphologies were synthesized in a high boiling point solvent trioctylamine (TOA). First, Co nanoparticles were prepared using various protecting agents consisting of oleic acid, oleylamine, trioctylphosphine (TOP), and polyvinylpyrrolidone (PVP) in the absence of reducing agents. These Co nanoparticles had average particle sizes of 13.9～21.3 nm, clear face-centered cubic crystalline structure and their coercivity was measured to be 342.0 Oe. The PVP was very effective in controlling the particle growth while hindering agglomeration between the particles. When 1,2-dodecanediol as a reducing agent was added to the reactant, the particle size was decreased down to 10 nm. However, in the case of without TOP, triangular prism-shaped nanoparticles were prepared with the average size of about 86.0 nm and its coercivity is 478.5 Oe. XRD pattern of the prism-like cobalt particles corresponded to a hexagonal close-packed crystalline phase. PVP was effective in controlling particle growth while hindering agglomeration between the particles at high temperature. These as-prepared Co nanoparticles with a moderate coercivity can be used in the application of patterned media.