Preparation of cobalt oxide nanoparticles and cobalt powders by solvothermal process and their characterization

Co₃O₄ nanoparticles and cobalt (fcc-Co) powders were successfully synthesized by solvothermal process from a single precursor. The reaction of Co(Ac)₂ with sodium dodecylbenzenesulfonate (SDBS) shows evident-dependent temperature effect. At 180 °C, Co(Ac)₂ reacts with SDBS to produce precursor CoCO₃ plate structures, which are assembled by small nanoparticles. At the temperature of 250 °C, the precursor CoCO₃ can be gradually decomposed to form Co₃O₄ nanoparticles with diameter of ca. 70 nm. While, at 250 °C, the reaction of Co(Ac)₂ with SDBS also produce precursor CoCO₃ nanoparticles/plates, but the CoCO₃ nanoparticles/plates would only decompose to give metal Co. In this process, SDBS acts as not only a surfactant but also a reagent. Magnetic measurements reveal that the as-prepared Co₃O₄ nanoparticles exhibit weak ferromagnetic properties and Co powders show ferromagnetic properties. In addition, a possible formation mechanism was elaborately discussed.