Photooxidation of sugar and alcohol on TiO$_{2}$ surfaces: A first-pirnciples study

First-principles studies are carried out on TiO$_{2}$/sugar (alcohol) interfaces under UV illumination. A rapid charge separation takes place at the interfaces through a two-step process: (1) trapping of photo-generated carriers at the gap levels induced by the chemisorbed molecules, and (2) upon the carrier trapping, a structural transformation of the adsorbed molecules, which in turn eliminates the gap levels. The second-step here is necessary to avoid carrier recombination, and hence results in an irreversible charge separation. Such a charge transfer across the semiconductor/molecule interface leads to various oxidation and reduction processes with structural reconfigurations (bond- forming and breaking) of the surface molecules. These results reveal the underlying microscopic mechanism of photo-catalytic reactions on the TiO$_{2}$ surfaces. The mechanism for the observed self-assembly of TiO2/cyclodextrin wires under UV illumination will also be discussed. This work was supported by the U. S. Department of Energy, BES and EERE, under Contract No. DE-AC39-98-GO10337.