| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS-WeA |
| Session: | Adsorption & Reactions on Oxide Surfaces |
| Presenter: | Junguang Tao, University of South Florida |
| Authors: | J. Tao, University of South Florida T. Luttrell, University of South Florida M. Batzill, University of South Florida |
| Correspondent: | Click to Email |
Using temperature programmed desorption (TPD), scanning tunneling microscopy (STM) and ultraviolet photoemission spectroscopy (UPS), we have observed very different adsorption dynamics for acetic acid on rutile TiO2(110) and (011)-2×1 surfaces at room temperature. While the bidentate adsorption of carboxylic acids on the (110) surface is well-established, we find a monodentate adsorption on the (011)-2×1 surface as the most likely adsorption geometry. On the (011)-2×1 surface, the initial sticking of adsorbed acetic acid is low. It appears that initial adsorption occurs at defects. These adsorbed acetates then act as nucleation sites for further adsorption. This adsorption mechanism results in the formation of quasi-1D acetate clusters running along direction. The role of acetate adsorption in the formation or annihilation of excess charges in TiO2 is also found to be different on these two surfaces. We find that bidentate adsorption of acetate on the (110) surface results in extraction of excess charges from the substrate, while mono-dentate adsorption on the (011)-2×1 surface causes net-charge donation to the substrate. More interestingly, a difference in the binding energy of excess charges, or Ti-3d band gap states, has been observed. On the TiO2(011)-2×1 surface the binding energy is ~0.3 eV higher than on the (110) surface. This difference is explained by the different crystal fields on the reconstructed (011) surface compared to the bulk-truncated (110) surface. At the rutile TiO2(011)-2×1 surface, Ti-ions are located in a distorted square pyramidal coordination environment, which we propose causes the shift in binding energy of excess electrons at the Ti-site. The differences in binding energy of electrons trapped at the surface for the two surfaces may contribute to the face dependent photocatalytic activity of rutile TiO2.
References:
1. J. Tao, T. Luttrell, J. Bylsma, and M. Batzill, J. Phys. Chem. C 2011, 115, 3434
2. J. Tao and M. Batzill, J. Phys. Chem. Lett. 2010, 1, 3200.