Impact of Ti Incorporation on Hydroxylation and Wetting of Fe3O4

5 years ago

Impact of Ti Incorporation on Hydroxylation and Wetting of Fe3O4

Kevin M. Rosso, Andrey Shavorskiy, Timothy C. Droubay, Carolyn I. Pearce, Kelsey A. Stoerzinger, Vaithiyalingam Shutthanandan, Hendrik Bluhm

Understanding the interaction of water with compositionally tuned metal oxides is central to exploiting their unique catalytic and magnetic properties. However, processes such as hydroxylation, wetting, and resulting changes in electronic structure at ambient conditions are challenging to probe in situ. Here, we examine the hydroxylation and wetting of Fe_(3–x)Ti_xO₄ (001)-oriented epitaxial films directly using ambient pressure X-ray photoelectron spectroscopy under controlled relative humidity. Fe²⁺ formation promoted by Ti⁴⁺ substitution for Fe³⁺ increases with hydroxylation, commensurate with a decrease in the surface work function or change in the surface dipole. The incorporation of small amounts of Ti (x = 0.25) as a bulk dopant dramatically impacts hydroxylation, in part due to surface segregation, leading to coverages closer to that of TiO₂ than Fe₃O₄. However, the Fe_(3–x)Ti_xO₄ compositional series shows a similar affinity for water physisorption, which begins at notably lower relative humidity than on TiO₂. The findings suggest that relative humidity rather than surface hydroxyl density controls wettability. Studies of this kind directly relate to rational design of doped magnetite into more active catalysts for UV/Fenton degradation, the adsorption of contaminants, and the development of spin filters.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06258

DOI: 10.1021/acs.jpcc.7b06258