Efficient and selective oxidation of benzylic alcohol by O2 into corresponding aldehydes on a TiO2 photocatalyst under visible light irradiation: Effect of phenyl-ring substitution on the photocatalytic activity

The highly efficient and selective photocatalytic oxidation of benzyl alcohol and its derivatives substituted with –OCH3, –CH3, –C(CH3)3, –Cl, –CF3 and –NO2 into corresponding aldehydes has been successfully carried out on TiO2 in the presence of O2 under visible light irradiation. The photocatalytic activity for the formation of the aldehyde was evaluated by a pseudo-first-order reaction, and it was found that the activity is enhanced by phenyl-ring substitution with the electron-releasing groups (–OCH3, –CH3, –C(CH3)3) and the electron-withdrawing groups (–Cl, –CF3 and –NO2). The effects of the substituents and their orientation on the photocatalytic performance of selective oxidation reaction are discussed here. It was shown that the photocatalytic activities are influenced not only by the oxidative potentials of the reactants but also by the stability of the resonant structures of the benzylic alcohol radicals formed by oxidation with a hole, leading to further reactions to form corresponding aldehydes.