Sol–gel auto-igniting synthesis and structural property of cerium-doped titanium dioxide nanosized powders

Anatase-type TiO2 (titania) doped with cerium up to 5 mol% was directly formed as nanometer-sized particles from TiO(NO3)2–Ce(NO3)2–NH4NO3–citric acid complex compound system by sol–gel auto-igniting synthesis process. The precursor gel was characterized by infrared spectroscopy and TG/DSC analysis. The XPS measurement showed that Ce(III) was easily oxidized to Ce(IV) at 550 °C and above. The XRD data, XPS spectra, and TEM selected-area diffraction patterns confirmed that cerium(IV) formed a solid solution in the anatase-type TiO2 powders. Doping of CeO2 into TiO2 shifted the phase transformation from anatase- to rutile-type structure to a high temperature. On the other hand, CeO2 was segregated on the surface of TiO2 and the rutile formation was accelerated during phase transformation from anatase to rutile at elevated temperature. When the cerium content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV-light region and in the visible-light region over 400–500 nm clearly appeared in the diffuse reflectance spectra of the as-prepared Ce-doped TiO2.