The effect of infrared light on visible light photocatalytic activity: An intensive contrast between Pt-doped TiO2 and N-doped TiO2

Pt-doped TiO2 and N-doped TiO2 were prepared, using nanotubular titanic acid as precursor, by wet impregnation and NH3-heating method, respectively. Both Pt-doped and N-doped TiO2 show an apparent photocatalytic oxidation of propylene under visible light irradiation. The origin of visible light sensitization was ascribed to the intra-band contributed by the formation of single-electron-trapped oxygen vacancies, while dopants platinum or nitrogen play a role not only in suppressing the recombination of photoinduced electrons and holes but also in increasing the ability of visible light absorption of TiO2. The visible light photocatalytic activity of Pt-doped TiO2 can be greatly improved by additional infrared light irradiation, while visible-light-active N-doped TiO2 has no such phenomenon. Infrared light per se is unable to excite Pt-doped TiO2 catalyst to initiate photocatalytic reaction, but the strong interaction between platinum and oxygen vacancies resulted in absorption peaks at 800-900 nm, resulting in a giant enhancement in visible light photocatalytic activity of Pt-doped TiO2 in the presence of infrared light irradiation because the formed heterojunctions between dopants Pt and TiO2 may function as thermal catalytic sites. The influences of reaction temperatures on visible light photoactivity of both Pt-doped and N-doped TiO2 were studied. It was found that both C3H6 removal and CO2 selectivity over Pt-doped TiO2 were increased with increasing the reaction temperature, while it was inert for N-doped TiO2. (C) 2011 Elsevier B.V. All rights reserved.