Preparation of nickel oxide– and nickel–silica nanocomposites by spray pyrolysis

Nickel oxide–silica and nickel–silica nanocomposites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing nickel nitrate hexahydrate, without and with ethanol, respectively. During pyrolysis, the silica nanoparticles were restructured, losing their identities, while the nickel oxide or nickel particles in the composites grew by coalescence and sintering. Compactness of the composites, higher in nickel–silica composites than their counterpart nickel oxide, increased with the temperature of preparation and the concentration of nickel nitrate. Nickel always formed larger crystallites than its counterpart nickel oxide, due to its higher sintering rate. At 500 °C, the crystallite growths of nickel oxide and nickel were inhibited by the low sintering rate and the formation of nickel intermediates, respectively, while at 1000 °C their phase-pure crystallites continuously grew with the increase in the nitrate concentration.