Ce-doped nanoparticles of TiO2: Rutile-to-brookite phase transition and evolution of Ce local-structure studied with XRD and XANES

The crystal and electronic structural changes undergone by TiO2 nanoparticles when Ce is introduced were studied using X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES). A small amount of Ce (less than 1% molar concentration) resulted in i/a significant reduction of the average size of the TiO2 nanoparticles and ii/a phase transition in which brookite replaced rutile as the minority phase component (anatase was the majority phase component at all Ce concentrations studied up to 10% molar concentration). The Ce L3 edge XANES revealed changes in the local environment of Ce impurities. As Ce concentration was increased the fraction of Ce that have formal valence of +3 decreased and, for the remaining Ce with valence +4, the 4f orbitals became less-strongly hybridized with the p-orbitals of oxygen neighbors. The results have implications for photocatalytic and gas sensing properties of Ce-doped TiO2. - Highlights: ► Ce-doping: TiO2 nanoparticles shrink and minority phase changes rutile-> brookite. ► XANES reveals phase change for arbitrarily small particles (while XRD fails). ► As Ce added: fraction of Ce+3 dopants falls, hybridization of Ce+4 with O weakens