Modified auto-combustion synthesis of mixed-oxides TiO2/NiO nanoparticles: Physical properties and photocatalytic performance

TiO2/NiO 50:50 wt % mixed-oxide nanopowders were successfully synthesized by a modified combustion based process. The effects of the synthesis condition, i.e. the pH of the starting solutions and the presence of the hydrogen peroxide (H2O2) as an oxidant, on the physical and structural characteristics of the synthesized nanopowders were evaluated. X-ray diffraction patterns (XRD) indicated that TiO2/NiO 50:50 wt % mixed-oxide nanopowders could be successfully synthesized through the combustion process in both acidic and alkaline conditions. XRD characteristic peaks of the TiO2 phase were intensified when H2O2 was used as the oxidant. The result of the dynamic light scattering (DLS) analysis showed that TiO2 and NiO powders, as well as the mixedoxide samples synthesized at the alkaline condition, had very fine particle size distributions. The result of the scattering electron microscopy (SEM) demonstrated that the morphology of the combusted particles was affected by the molar ratios of TiO2/NiO and the pH of the synthesis process. UV-visible spectroscopy results implied that single-oxide NiO, TiO2, and TiO2/NiO mixed-oxide nanoparticles had narrow band gap values of 1.8, 2.6 and 2.5 eV, respectively. Zeta potential of the combusted mixed oxide nanoparticles was -28 mV. Adsorption-desorption isotherm of the as-prepared powders showed the formation of porous powders with a specific surface area of 19, 22, and 192 m(2)/g for NiO, TiO2, and TiO2/NiO particles, respectively. Results of the photocatalytic experiments under daylight emission using methylene blue (MB) as the dye molecule showed that degradation percentage of MB was more than 90% for all synthesized nanopowders. The small particle size, presence of the residual organics and narrow band gap energy were the leading factors which improved photocatalytic activity of the synthesized nanoparticles.