Photocatalytic reduction of oxygen molecules at the (1Â 0Â 0) TiO2 anatase surface

The adsorption, photoreduction and chemical activity of oxygen molecules on the (1 0 0) anatase surface have been investigated here together with the effects that surface oxygen vacancies (VO) can have on these O2-related processes. We use an original approach by treating molecules on the TiO2 surface like surface defects in the same framework successfully used for defects in semiconductors. The achieved results: (i) give the first theoretical evidence of an acceptor behaviour of an adsorbed O2 molecule, which is at the origin of its photoreduction; (ii) show that the VO donor character is strongly affected by the interaction with O2; and (iii) suggest that the release of O2-1 radicals as well as the formation of O2-related radicals may be favoured by photogenerated electrons in presence of surface VO's.