Nickel and nickel oxide nanoparticles prepared from nickel nitrate hexahydrate by a low pressure spray pyrolysis

Nickel nanoparticles prepared from Ni(NO3)2·6H2O by using a low pressure spray pyrolysis (LPSP) are reported in this paper. Effects of pressure, carrier gas flow rate, concentration of precursor and type of reducing agents on the size, morphology and crystallinity of nickel nanoparticles were investigated. It is found that pressure and carrier gas flow rate play crucial roles in the reduction of NiO to nickel in the LPSP process. A relatively higher solution concentration is suitable for the generation of nanoparticles. Cosolvents such as, formic acid and ethanol, as well as H2, were treated as the reductives in the synthesis of nickel (nanoparticles) in this work. Weak NiO peaks, together with strong nickel peaks, in powder XRD patterns, indicated that nickel nanoparticles are easier to be oxidized compared with the submicron-sized one investigated by conventional spray pyrolysis due to their higher surface potential. Another possible reason may come from the incomplete reduction in very short residence time because of the decrease of H2 amount in some cases. A possible mechanism of nickel nanoparticles formation has been suggested based on the demonstration of our previous research as well.