Surface Chemistry of TiO2 Photocatalysis and LIF Detection of OH Radicals

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Abstract

By means of laser induced fluorescence (LIF) method, OH radicals formed and released from the surface of TiO2 photocatalysts were detected. The effect of heat treatments of TiO2 on the OH radical formation shows that the amount of OH radicals is affected by the states of surface hydroxyl groups but not the crystalline phase. The effects of the surface hydroxyl groups were discussed based on the measurements of the trapped holes with low temperature ESR spectroscopy and adsorbed water with proton NMR spectroscopy. Then, the reaction mechanism of OH radical formation on the TiO2 surface was suggested to be the reduction of adsorbed H2O2 which is accumulated on the surface by photo irradiation. Finally, the previously reported reaction mechanism of the acetic-acid decomposition was reconsidered based on the mechanism of OH radical formation.