Probability of Two-Step Photoexcitation of Electron from Valence Band to Conduction Band through Doping Level in TiO2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2017-08, Vol.121 (32), p.5991-5997
• Main Authors: Nishikawa, Masami, Shiroishi, Wataru, Honghao, Hou, Suizu, Hiroshi, Nagai, Hideyuki, Saito, Nobuo
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.7b05214

For an Ir-doped TiO2 (Ir:TiO2) photocatalyst, we examined the most dominant electron-transfer path for the visible-light-driven photocatalytic performance. The Ir:TiO2 photocatalyst showed a much higher photocatalytic activity under visible-light irradiation than nondoped TiO2 after grafting with the cocatalyst of Fe3+. For the Ir:TiO2 photocatalyst, the two-step photoexcitation of an electron from the valence band to the conduction band through the Ir doping level occurred upon visible-light irradiation, as observed by electron spin resonance spectroscopy. The two-step photoexcitation through the doping level was found to be a more stable process with a lower recombination rate of hole–electron pairs than the two-step photoexcitation process through an oxygen vacancy. Once electrons are photoexcited to the conduction band by the two-step excitation, the electrons can easily transfer to the surface because the conduction band is a continuous electron path, whereas the electrons photoexcited at only the doping level could not easily transfer to the surface because of the discontinuity of this path. The observed two-step photoexcitation from the valence band to the conduction band through the doping level significantly contributes to the enhancement of the photocatalytic performance.