| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Energy Harvesting & Storage | Wednesday Sessions |
| Session EH-WeM |
| Session: | Characterization of Materials for Energy Applications I |
| Presenter: | Igor Lyubinetsky, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Hindering Effect of Surface Point-Defectsfor Photoreactivity on TiO2(110)
I. Lyubinetsky*
EMSL and Institute for Integrated Catalysis, Pacific Northwest National Laboratory.
e-mail: igor.lyubinetsky@pnnl.gov
While surface point-defects are expected to act as charge trapping and/or recombination centers in photoinduced processes, their direct impact of surface defects on photoreactivity is not well explored. We present the first observation of a suppressing effect of oxygen vacancy (VO) defects on photoreactivity of TiO2(110). Direct scanning tunneling microscopy imaging reveal a pronounced site-selectivity in the hole-mediated photooxidation of trimethyl acetate (TMA) on TiO2(110) upon ultra-violet light irradiation, wherein the reaction readily occurs at regular Ti sites but is completely inhibited at VO defects. Utilizing electron energy loss spectroscopy and density functional theory, we show that the lack of reactivity of TMA groups adsorbed at VO's cannot be attributed to either a less active adsorption conformation or electron transfer from the VO defect. Instead, we propose that the excess unpaired electrons associated with the VO promptly recombine with photoexcited holes approaching the surface, effectively ‘screening’ TMA species at VO site. We also show that this screening effect is spatially short-ranged, being predominately localized at the VO, and only mildly affecting TMA’s at adjacent Ti sites. The direct impact of O vacancies on TMA photoreactivity over TiO2(110) is expected to have similar implications for other hole-mediated (e.g., photooxidation) reactions in which adsorption at or near electronic point-defects is possible. Furthermore, the localized influence of these defects on hole-mediated chemistry offers opportunities for additional study of site-selective photocatalysis on TiO2.
* In collaboration with Z.-T. Wang and M.A. Henderson, PNNL and N.A. Deskins, Worcester Polytechnic Institute. We acknowledge support from the US DOE BES, Division of Chemical Sciences, Geosciences & Biosciences. A portion of this research was funded by the Chemical Imaging Initiative LDRD at PNNL.