Photochemical activities of nitrogen doped rutile and anatase surfaces


Michael A Henderson,, Chemical and Material Sciences Division, Pacific Northwest National Laboratory, PO Box 999, MS K8-87, Richland, WA 99352
TiO2 has been widely used in heterogeneous photocatalysis investigations since the discovery of its utility for the photoelectrolysis of water. One of the major limitations of TiO2 is that it absorbs relatively little of the solar spectrum. Asahi et al. suggest that one way around this problem is by anion doping. Following this suggestion, many groups have undertaken studies involving anion doping of TiO2 for visible-light photochemical activity. Despite intense interest, the origin of visible-light photocatalytic activity in anion doped TiO2 is still controversial. This presentation highlights recent insights into anion doping of TiO2 using single crystals as model materials. The solubility limit of N in the anion sublattice for phase-pure, single crystalline TiO2 is ~2 at. % irrespective of the polymorph. N3- substitutes for lattice O and adds 2p states above the valence band maximum of pure TiO2, thereby reducing the interband optical absorption threshold from 3.0/3.2 eV to ~2.5 eV. The photoactivities of structurally well-defined N-doped TiO2 rutile and anatase films were examine in the UV and visible using trimethyl acetic acid (TMAA) as a photochemical probe molecule sensitive to valence band holes.

This work was supported by the US Department of Energy, Office of Science, Division of Chemical Sciences and performed in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research.