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 (Fe³⁺ or Mn²⁺) is substituted for Ti⁴⁺ in the TG lattice. Fe³⁺ prolongs the crystallisation time of Fe-TG, whereas Mn ²⁺ has a smaller effect on the crystallisation time in comparison with Fe³⁺. The as-synthesised M-TG materials were used directly as singlesource precursors for the preparation of metal-doped titania (M-TiO ₂) through a simple thermal treatment process. The as-prepared M-TiO₂ 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 TiO₂ lattice at the Ti⁴⁺ 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 resuits, it was concluded that high crystal-linity, a large surface area and appropriate transition-metal-doping are all beneficial to the enhancement of the photocatalytic performance of the doped TiO₂ material. In addition, it was noted that in comparison with Mn-TiO₂, Fe-TiO₂ shows higher photo-catalytic activity due to the better inhibition effect of Fe³⁺ on recombination of photogenerated electron-hole pairs. In contrast to the conventional nanosized TiO₂ photocatalyst, the micrometre-sized M-TiO₂ particles we obtained can be easily separated and recovered after the photocatalytic reactions.