Materials Science and Chemistry

Biography

Biography: Hisayoshi Kobayashi

Abstract

The selective photocatalytic oxidation of benzyl alcohol by O₂ on the TiO₂ surface was theoretically studied by DFT calculations. Experimentally, it is well known that benzyl alcohol is oxidized to benzaldehyde, but cannot be further oxidized to benzoic acid, and TiO₂ surface itself is insensitive for the visible light, but becomes sensitive by benzyl alcohol adsorption. These phenomena were clarified by the plane wave based DFT calculations. Dehydroxylated and partially hydroxylated TiO₂ with an anatase TiO₂ (101) crystal face were modeled with a slab of Ti₁₆O₃₂ and Ti₁₆O₃₂(OH)H, respectively. It was found that the interaction of benzyl alcohol with the hydroxylated TiO₂ surface significantly induces the formation of the alkoxide species, of which the donative orbitals hybridized with the O₂ p orbital in the valence band (VB) of the TiO₂. The visible light response is attributed to the electronic transition from the donor levels created by the alkoxide species to the conduction band (CB). The dissociation of methylene C-H in the alkoxide was assisted by O₂, and this process was confirmed to be the rate-determining step. Furthermore, the hydro-peroxide (OOH) species formed by O₂ reduction can also oxidize another benzyl alcohol into benzaldehyde together with Ti-OH regeneration. It was thus clearly demonstrated that two benzaldehyde molecules were formed from two benzyl alcohols and one O₂ molecule on the TiO₂ photocatalysis.