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Charge trapping and photoadsorption of O2 on dehydroxylated TiO2 nanocrystals - An electron paramagnetic resonance study

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Sterrer,  Martin
Chemical Physics, Fritz Haber Institute, Max Planck Society;

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Citation

Berger, T., Sterrer, M., Diwald, O., & Knözinger, E. (2005). Charge trapping and photoadsorption of O2 on dehydroxylated TiO2 nanocrystals - An electron paramagnetic resonance study. ChemPhysChem, 6(10), 2104-2112. doi:10.1002/cphc.200500161.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0011-0754-D
Abstract
The interaction of photogenerated charges with molecular oxygen was investigated on TiO2 nonocrystals by means of paramagnetic resonance (EPR) spectroscopy. Compared to photoactivation experiments in Vacuum at p < 10(-6) mbar and T = 740 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 0,was found to correspond to ten electron-hole pairs per TiO2 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.