Role of reactive oxygen species on the activity of noble metal-doped TiO photocatalysts.

Modified TiO catalysts are of interest in environmental water remediation since they can lead to efficient electron-hole separation and greatly enhance the photocatalytic properties of TiO. Reactive oxygen species (ROS), such as the superoxide radical (O), hydroxyl radical (OH), and positive valence band holes (h), have been reported as the main oxidative species involved in photocatalytic degradation processes. In this work, the role of these species using TiO, TiO/Pt 0.5 wt%, and TiO/Ag 10 wt% has been examined in order to clarify the oxidation pathways. For this purpose, the contribution of the main oxidative species was analyzed in the photocatalytic degradation of dichloroacetic acid (DCA) solutions using specific scavengers (benzoquinone, tert-butyl alcohol, and formic acid). Moreover, the hydroxyl radicals were quantitatively determined in order better understand the results. Regardless of the catalyst used, it is concluded that OH radicals are the major reactive species responsible for DCA degradation and no significant degradation is due to O radicals. Nevertheless, different OH generation pathways were found, depending on the nature of the catalysts. Degradation using TiO was conducted mainly via OH radicals generated in the positive holes, while noble metal-doped TiO catalysts generated OH radicals through the transformation of O radicals.