An EPR study of thermally and photochemically generated oxygen radicals on hydrated and dehydrated titania surfaces

An EPR study of thermally and photochemically generated oxygen radicals on hydrated and... The formation of a series of oxygen-centred radicals on different TiO2 samples (P25 and two different rutile materials) under various conditions was investigated using X-band c.w. Electron Paramagnetic Resonance (EPR) spectroscopy. The radicals were formed either on thermally-reduced TiO2, or by UV irradiation of the oxide under an oxygen atmosphere. The nature and stability of the radicals was also explored as a function of surface hydration. On thermally reduced TiO2, containing surface and bulk Ti3+ centres, oxygen adsorption at 300 K results in the preferential formation and stabilisation of O2 - anions on the P25 surface, but O- and O3 - anions are generated on the rutile surfaces. Superoxide anions (O-) and trapped holes (O2 -) were also identified after photo-irradiation of the thoroughly dehydrated TiO2 samples under oxygen. The O- anions were only visible at low temperatures under continuous irradiation, while the O2 - anions were stable for days at 300 K. By comparison, on fully hydrated surfaces, no stable oxygen centred radicals could be detected on P25, while O2 - anions were easily observed on the rutile surfaces. On partially hydrated P25, the O-, O2 - and HO2 anions were detected after UV irradiation at 77 K; all radicals decayed upon warming to 298 K. On partially hydrated rutile, the O- and O2 - anions were detected and, unlike the case for P25, were found to be stable for days under the same conditions. The results illustrate the varied formation and stability of the oxygen centred radicals on TiO2 surfaces depending on the pretreatment conditions. Research on Chemical Intermediates Springer Journals

An EPR study of thermally and photochemically generated oxygen radicals on hydrated and dehydrated titania surfaces

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Brill Academic Publishers
Copyright © 2003 by VSP 2003
Chemistry; Inorganic Chemistry; Physical Chemistry
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