Hydrothermal synthesis and photocatalytic characterizations of transition metals doped nano TiO2 sols

The TiO2 sols were hydro-thermally synthesized in autoclave from various aqueous TiOCl2 solutions having 1.0 mol.% of transition metal (Ni2+, Cr3+, Fe3+, Nb3+, and V5+) chlorides as starting precursors. All kinds of synthesized TiO2 sols were found to be anatase phase and their particle size was several to 30 nm. Their ζ-potential was measured in the range of −25 to −35 mV and they remained stable for over 6 months. The Cr3+ added TiO2 sols, however had a much lower value of ζ-potential and larger particles comparing with the others. The shape and size of the TiO2 observed in thin films on the porous alumina balls were almost the same as those of the TiO2 sols. In photocatalytic properties, pure TiO2 sol showed the highest optical absorption in ultraviolet light regions, but other TiO2 sols doped with Cr3+, Fe3+ and Ni2+, respectively showed higher optical absorption than pure sol in visible light regions. Consequently, for gas-phase benzene degradation, the pure TiO2 film showed the highest photo-dissociation rate in ultraviolet light regions, but in artificial sunlight the photo-dissociation rate of TiO2 films containing Cr3+, Fe3+ and Ni2+ measured faster due to the increase of optical absorption by doping.