Synthesis of cobalt nanoparticles in supercritical methanol

Cobalt nanoparticles with a face-centered cubic (fcc) structure were synthesized by the reduction of Co(NO₃)₂ in supercritical methanol. The reduction of Co(NO₃)₂ to fcc Co was completed within 15 min at 400 °C and 300 bar. The reduction mechanism was investigated by varying the reaction temperature (200-400 °C) and the reaction time (0.5-15 min). The results suggested that cobalt methoxynitrate formed at an initial stage was converted to CoO, and then reduced to Co. In addition, an introduction of oleic acid as a stabilizer achieved the formation of Co nanoparticles (∼10 nm).