Curious behaviors of photogenerated electrons and holes at the defects on anatase,rutile, and brookite TiO2 powders: A review |
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| Institution: | 1. Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya, 468-8511, Japan;2. Cooperative Research Fellow, Institute for Catalysis, Hokkaido University, Hokkaido, 001-0021, Japan;1. Institute of New Catalytic Materials Science and MOE Key Laboratory of Advanced Energy Materials Chemistry, School of Materials Science and Engineering, National Institute of Advanced Materials, Nankai University, Tianjin 300350, People’s Republic of China;2. MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, People’s Republic of China;3. Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, People’s Republic of China;1. Institute of Solid State Chemistry, Ural Branch of RAS, GSP, 620990 Ekaterinburg, Russia;2. Institute of Metal Physics, Ural Branch of RAS, 620990 Ekaterinburg, Russia;1. Department of Solid State Physics, Faculty of Physics, National and Kapodistrian University of Athens, Panepistimioupolis, GR-157 84 Athens, Greece;2. CIDIA-FEAM Universidad de Las Palmas de Gran Canaria, Edificio del Parque Científico Tecnológico de la ULPGC, Campus de Tafira, 35017 Las Palmas de Gran Canaria, Spain;3. Environmental Engineering and Science Program, University of Cincinnati, Cincinnati, OH 45221-0071, USA;4. Institute of Nanoscience and Nanotechnology, NCSR Demokritos, 153 10, Agia Paraskevi Attikis, Athens, Greece |
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| Abstract: | Photocatalytic 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 has 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 brookite TiO2 powders. |
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| Keywords: | Photodynamics Recombination Defects Charge trapping |
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