Visible-Light Induced High-Yielding Benzyl Alcohol-to-Benzaldehyde Transformation over Mesoporous Crystalline TiO2: A Self-Adjustable Photo-oxidation System with Controllable Hole-Generation

High-yielding benzyl alcohol-to-benzaldehyde (BA-to-BAD) transformation has been achieved over mesoporous crystalline TiO2 at mild conditions under visible-light irradiation with/without molecular oxygen. DFT calculations show that the antibonding pi molecular orbitals (MOs) of BA can hybridize with the O2p atomic orbitals (AOs) of TiO2, leading to the appearance of new energy levels located in the band gap where holes can be generated under visible-light irradiation. However, the oxidative product, BAD, is not stable when adsorbed on TiO2 surface. This fact is supposed to prevent BAD from overoxidation by ceasing the hole formation. As a result, the hole generation becomes controllable in this type of photoreaction system, and a so-labeled self-adjustable photo-oxidation system (denoted as SAPS) can be established. In addition, we also found that lattice oxygen (O-L) and Ti atoms within TiO2 frameworks serve as the efficient reservoir for hydrogen and electrons in anaerobic reaction.