Preparation and characterization of cerium oxide doped TiO₂ nanoparticles

A mixed oxide consisting of TiO₂ as the major phase and CeO _2-y (0<y<0.5) as the dopant phase was prepared via the sol-gel reaction of Ti(i-OC₃H₇)₃ in an aqueous solution of Ce(NO₃)₃. The resulting oxide powders with different CeO_2-y contents were all composed of nano-sized spheres. The CeO_2-y phase was identified to have retarding effect on the phase transition from anatase TiO₂ to rutile TiO₂ at calcinations temperature as high as 800°C, which would otherwise be a thorough conversion. The CeO_2-y-TiO₂ powders could apparently shift the UV-absorption band of TiO₂ toward visible range, and there was an optimal CeO_2-y content in association with the maximum absorbance. This effect is interpreted as the existence of an n-type impurity band, due to the substitution of Ti⁴⁺ for Ce ^3+/4+ at the interface between the two oxides, in the gap of TiO ₂. According to X-ray photoelectron spectroscopy (XPS) investigation, the Ti element mainly existed as the chemical state of Ti⁴⁺ and the Ce oxide doping did not affect the peak position of Ti 2p. The Ce 3d spectrum of CeO_2-y-doped TiO₂ sample basically denotes a mixture of Ce^3+/4+ oxidation states giving rise to a myriad of peaks.