Microwave-assisted and liquid oxidation combination techniques for the preparation of nickel oxide nanoparticles

A nickel hydroxide, Ni(OH)2, was prepared by microwave-assisted heating technique from nickel nitrate aqueous solution and sodium hydroxide (assigned as PM). Then, the as-prepared PM was oxidized by liquid oxidation with sodium hypochlorite (assigned as PMO). Further, pure nanocrystalline nickel oxide (NiO) particles were obtained from the as-prepared PMO by calcination at 300, 400, 500, 600, 650 and 700 °C (labeled as C300, C400, C500, C600, C650 and C700, respectively). The as-prepared powders (PM and PMO) and the NiO nanoparticles were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), temperature-programmed reduction (TPR) and scanning electron microscope (SEM). The results indicated that the particle size of nickel oxide was controlled by the calcined temperature. The average crystal size of the NiO nanoparticles ranges from about 5 to 35 nm at 300–700 °C. Mechanism of nickel oxide nanocrystallite growth during thermal treatment was investigated.