| AVS 55th International Symposium & Exhibition | |
| Surface Science | Friday Sessions |
| Session SS+AS+NC-FrM |
| Session: | Environmental Surfaces and Water Interaction with Oxide Surfaces |
| Presenter: | A. Sandell, Uppsala University, Sweden |
| Authors: | A. Sandell, Uppsala University, Sweden J. Blomquist, Lund University, Sweden L.E. Walle, NTNU, Norway P. Uvdal, Lund University, Sweden A. Borg, NTNU, Norway |
| Correspondent: | Click to Email |
The interaction of water and TiO2 surfaces has been intensely studied since the discovery of photoinduced splitting of water into hydrogen and oxygen on a rutile TiO2 single crystal in 1972.1 However, even though the anatase TiO2 polymorph is more widely used as photocatalyst than rutile studies of the adsorption of water on well-defined anatase TiO2 surfaces are scarce. So far, the efforts have mainly been theoretical. Based on calculations it has been proposed that molecular water adsorption is favored on the (101) surface, whereas water dissociation is favored on the (001) surface.2,3 This implies that the (001) surface may be very important in spite of it being the minority surface termination of anatase crystallites. In this contribution, we present the first study on the coverage dependent adsorption of water on the anatase TiO2(001)-(4x1) surface using core level photoemission spectroscopy. Data with high surface sensitivity were recorded at the MAX-lab synchrotron radiation source. Two types of anatase TiO2(001)-(4x1) surfaces were prepared: One by MOCVD growth on a lattice matched substrate [SrTiO3(001)] and one by cleaning of a natural single crystal. Our results confirm that water dissociate on the anatase TiO2(001)-(4x1) surface. We can define two adsorption phases: Phase 1 consists only of dissociated water, observed as OH-groups. This phase is found at low coverage at low temperature (190 K) and is the only state of adsorbed water above ~230 K. The saturation coverage of phase 1 agrees with the number of four-fold coordinated Ti ridge atoms of the (4x1) surface reconstruction. Phase 2 is found at higher coverage, reached at low temperature. It consists of a mixture of dissociated and molecular water with a ratio of 1:1 at 170 K. The hydroxyl coverage of phase 2 is approximately two times that of phase 1.
1 A. Fujishima and K. Honda, Nature (London) 238, 37 (1972).
2 A. Vittadini, A. Selloni, F. P. Rotzinger, and M. Grätzel, Phys. Rev. Lett. 81, 2954 (1998).
3 X.-Q. Gong and A. Selloni, J. Phys. Chem. B 109, 19560 (2005).