Curious Behaviors of Photogenerated Electrons and Holes at the Defects on Anatase, Rutile, and Brookite TiO2 Powders: A Review

Publication date: Available online 13 December 2018Source: Journal of Photochemistry and Photobiology C: Photochemistry ReviewsAuthor(s): Akira Yamakata, Junie Jhon M. VequizoAbstractPhotocatalytic reactions are governed by photogenerated charge carriers upon band gap excitation. Therefore, for better understanding of the mechanism, the dynamics of photocarriers should be studied. One of the attractive materials is TiO2, which have been extensively investigated in the field of photocatalysis. This review article summarizes our recent works of time-resolved visible to mid-IR absorption measurements to elucidate the difference of anatase, rutile, and brookite TiO2 powders. The distinctive photocatalytic activities of these polymorphs are determined by the electron-trapping processes at the defects on powders. Powders are rich in defects and these defects capture photogenerated electrons. The depth of the trap is crystal phase dependent, and they are estimated to be < 0.1 eV, ~0.4 eV and ~0.9 eV for anatase, brookite, and rutile, respectively. Electron trapping reduces probability to meet with holes and then elongate the lifetime of holes. Therefore, it works negatively for the reaction of electrons but positively works for the reaction of holes. In the steady-state reactions, both electrons and holes should be consumed. Hence, the balance between the positive and negative effects of defects determines the distinctive photocatalytic activities of anatase, rutile, and b...

Source: Journal of Photochemistry and Photobiology C: Photochemistry Reviews - December 14, 2018 Category: Chemistry Source Type: research