Heterometal alkoxides as precursors for the preparation of porous Fe- and Mn-TiO2 photocatalysts with high efficiencies

Transition-metal-doped titanium glycolates (M-TG, with M=Fe, Mn), which are the first non-stoichiometric heterometal alkoxides, have been synthesised through a solvothermal doping approach. X-ray diffraction, UV/Vis diffuse reflectance and ESR spectroscopy revealed that the dopant ion (Fe(3+) or Mn(2+)) is substituted for Ti(4+) in the TG lattice. Fe(3+) prolongs the crystallisation time of Fe-TG, whereas Mn(2+) has a smaller effect on the crystallisation time in comparison with Fe(3+). The as-synthesised M-TG materials were used directly as single-source precursors for the preparation of metal-doped titania (M-TiO(2)) through a simple thermal treatment process. The as-prepared M-TiO(2) materials maintain the rod-like morphology of the precursors and possess a mesoporous structure with high crystallinity. It has been proved that the dopant ions are incorporated into the TiO(2) lattice at the Ti(4+) positions. The photocatalytic activities of the M-TiO(2) materials obtained were evaluated by testing the degradation of phenol under UV irradiation. From the photocatalytic results, it was concluded that high crystallinity, a large surface area and appropriate transition-metal-doping are all beneficial to the enhancement of the photocatalytic performance of the doped TiO(2) material. In addition, it was noted that in comparison with Mn-TiO(2), Fe-TiO(2) shows higher photocatalytic activity due to the better inhibition effect of Fe(3+) on recombination of photogenerated electron-hole pairs. In contrast to the conventional nanosized TiO(2) photocatalyst, the micrometre-sized M-TiO(2) particles we obtained can be easily separated and recovered after the photocatalytic reactions.