Roles of the active species involved in the photocatalytic oxidation of benzyl alcohol into benzaldehyde on TiO2 under UV light: Experimental and DFT studies

Active species such as holes, electrons, hydroxyl radicals ( OH), and superoxide radical anions ( O 2 − ) involved in the photocatalytic oxidation of benzyl alcohol (BA) into benzaldehyde (BAD) on TiO 2 under ultraviolet (UV) light were investigated by adding corresponding scavengers. The experimental results show that the oxidation of BA into BAD is driven mainly by the holes and OH radical. The role of dissolved O 2 was studied by bubbling N 2 through the reaction. The results show that the dissolved O 2 is, to some extent, the source of OH. Additional density functional theory (DFT) calculations identified two H-abstraction pathways ( R abs OH and R abs α). The structure of the R abs OH product is less stable and tends to transfer resulting in the R abs α product. The holes are the main driving force for the abstracting of H from BA. The OH radical combines with the H-abstract product to form a precursor of product BAD, detected by LC–MS technique ( m / z 123), which then undergoes an intramolecular dehydration reaction to form BAD. The results will help to select the optimal active species for the photocatalytic oxidation of BA into BAD on TiO 2 under UV light.