Theoretical modeling of photocatalytic active species on illuminated TiO2

P.G. BELELLI; G. F. CABEZA; N. J. CASTELLANI

San Carlos de Bariloche

Conferencia; 13th International Conference on Solid Films and Surfaces; 2006

Recently, the photocatalytic reactions where TiO2 is used as catalyst have been widely investigated as a potential method for decomposing trace contaminants in air and water [1-4]. During the photocatalytic process, this oxide is illuminated with ultraviolet irradiation (UV) and the electrons of the valence band are excited to the conduction band, leaving positive holes in the first of them. The electron-hole pairs such formed and that localize preferentially on the TiO2 surface can interact with H2O and O2 adsorbed molecules, forming OH· radicals and O2 -·superoxide species, respectively. Both have been proposed to be oxidizing agents in the photocatalytic reactions 0. In a previous work, the electronic structure of an activated anatase TiO2 surface due to the electron-hole pair formation was evaluated [6]. The UV irradiation effect on the oxide was simulated assuming that the triplet spin multiplicity of the system (m=3) represents its first excited state. The results indicate that a good description for the spin density distribution is obtained by using of the DFT method and the BHandHLYP functional. By means of the latter, the spin density is localized mainly on the central Ti atom and its O neighbors. For the present study, a theoretical modeling of the active species produced on activated anatase TiO2 was performed. The anatase TiO2 structure was modeled by a stoichiometric cluster of generic formula Ti15O41H22, where the atoms are distributed in two layers. The titania surface considered for this modeling was a exposed (001) plane, chosen from the most experimentally studied planes due to its high stability. The electronic structure and the spin distribution were examined by employing the BHandHLYP functional. The geometries of active species were full optimized, including the cluster relaxation. All the calculations reported in this work were performed by means of the GAUSSIAN 03 code [7].