Preparation, characterization and photocatalytic activity of TiO2 codoped with yttrium and nitrogen

Nanocrystalline photocatalysts of TiO2 codoped with yttrium and nitrogen were prepared by the sol-gel method and investigated by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) surface area measurement, X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), respectively. Slight red-shifts of the Raman peak at 144 cm-1 were observed in the doped samples after the incorporation of Y3+ and N3- into the lattice of TiO2. The N doping caused the improvement of visible light absorption because of the formation of the N 2p states isolated above the valence band maximum of TiO2. Whereas, the absorption property of the pure or N doped TiO2 was depressed after the introduction of Y. The photocatalytic activities of the samples were evaluated by monitoring the degradation of methylene blue (MB) solution. The codoped sample with N and 0.05 at.% Y exhibited an enhanced photocatalytic efficiency. It is suggested that the charge trapping due to the Y doping and the visible light response due to the N doping are responsible for the enhanced photocatalytic performance in this sample. However, the photocatalytic activity of the codoped TiO2 was suppressed step by step as the Y doping level increased, which could be attributed to the formation of photogenerated charge carriers recombination centers at the Y substituting sites.