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 Mn2+ has a smaller effect on the crystallisation time in comparison with Fe3+. The as-synthesised M-TG materials were used directly as single-source precursors for the preparation of metal-doped titania (M-TiO2) 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-TiO2 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 TiO2 material. In addition, it was noted that in comparison with Mn-TiO2, Fe-TiO2 shows higher photocatalytic 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.