Ultrasonic synthesis and photocatalytic performance of metal-ions doped TiO2 catalysts under solar light irradiation

Eight metal-ions doped TiO2 (M-TiO2) were successfully synthesized by an ultrasonic method, including Fe, Co, Ce, Cr, Mn, Mg, Ni and Ag ions. Among them, the 1% Mg–TiO2 shows the highest photocatalytic efficiency under solar light, which was determined by degrading rhodamine B (RhB) molecules in an aqueous solution. The synthesized M-TiO2 samples were characterized by XRD, BET Surface area, TEM, XPS and diffuse reflectance spectrum. Effects of synthesis conditions and characterized properties on photocatalytic efficiency of the M-TiO2 were investigated comprehensively. A positive correlation between specific surface area and photocatalytic efficiency of the M-TiO2 was found across different synthesis conditions. However, no clear correlation with photocatalytic efficiency was observed for crystal structure and radii of doping ions of the M-TiO2. XPS study indicates the change of oxidation states of Mn ions in Mn–TiO2 during synthesis procedure from the initial Mn2+ to a mixture of Mn3+ and Mn4+ ions. Dye sensitization mechanism was observed during the photocatalytic procedure of the Mg–TiO2, which enhanced the degradation efficiency of the Mg–TiO2 under solar light. Finally, no obvious loss of photocatalytic activity was observed for the Mg–TiO2 after five cycles of RhB degradation.