Invited Paper SS+AS+EN-MoM3
Surface and Bulk Properties of Pure and Mixed Titania
Monday, October 19, 2015, 9:00 am, Room 113
Titanium oxide in its different polymorphs remains a model system for structure property relationships in simple oxides. In this talk we address issues related to both the bulk and the surface properties of TiO2. Measuring the photocatalytic activity of anatase- and rutile- epitaxial films we conclude that charge carriers excited deeper in the bulk contribute to the surface photocatalytic activity for anatase compared to rutile [1]. This difference may be an important factor for explaining the generally higher photocatalytic activity of anatase-TiO2. In the second part of the talk, surface properties are presented on the example of rutile TiO2(011). The (011) surface orientation is less frequently studied compared to the (110) surface. Under UHV-conditions the (011) surface reconstructs into a complex 2x1 structure. We investigate the stability of this reconstruction under chemical adsorption. We find that for strongly adsorbing molecules the surface restructures to enable stronger adsorption. We show that this restructuring is strongly anisotropic resulting in quasi-1D adsorbate structures [2]. The instability of the rutile TiO2(011)-2x1 surface may also be exploited for the formation of unique mixed oxide surfaces. This we demonstrate with iron oxide, which forms an ordered mixed TiFeOx surface oxide layer. Such mixed oxide surface may also form by impurity segregation from the bulk and thus may be a common surface structure in Fe-doped TiO2. [1] “Why is anatase a better photocatalyst than rutile? - Model studies on epitaxial TiO2 films” T. Luttrell, S. Halpegamage, J.G. Tao, A. Kramer, E. Sutter, M. Batzill Sci. Rep. 4, 4043 (2014).
[2] “Adsorbate Induced Restructuring of TiO2(011)-(2×1) Leads to One-Dimensional Nanocluster Formation” Q. Cuan, J. Tao, X.Q. Gong, M. Batzill Phys. Rev. Lett. 108, 106105 (2012).