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Charge Trapping and Photoadsorption of O 2 on Dehydroxylated TiO 2 Nanocrystals—An Electron Paramagnetic Resonance Study
Author(s) -
Berger Thomas,
Sterrer Martin,
Diwald Oliver,
Knözinger Erich
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200500161
Subject(s) - electron paramagnetic resonance , nanocrystal , electron , atomic physics , trapping , chemistry , resonance (particle physics) , oxygen , spectroscopy , paramagnetism , molecular physics , analytical chemistry (journal) , materials science , nuclear magnetic resonance , condensed matter physics , nanotechnology , physics , ecology , organic chemistry , quantum mechanics , chromatography , biology
The interaction of photogenerated charges with molecular oxygen was investigated on TiO 2 nanocrystals by means of paramagnetic resonance (EPR) spectroscopy. Compared to photoactivation experiments in vacuum at P< 10 − 6 mbar and T =140 K, the presence of O 2 enhances the concentration of persistently trapped electron and hole centres—by a factor of ten—due to the formation of adsorbed O 2 − species. The photoadsorption of oxygen was also tracked quantitatively by pressure measurements, and the number of trapped charges, hole centres and O 2 − was found to correspond to ten electron–hole pairs per TiO 2 nanocrystal. Conversely, in experiments at P< 10 − 6 mbar with one trapped electron–hole pair per particle, charge separation is not persistent and completely reversible with respect to temperature. Heating to 298 K causes the total annihilation of photogenerated and trapped charges.