| AVS 59th Annual International Symposium and Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+OX-WeM |
| Session: | Synthesis and Characterization of Oxides |
| Presenter: | T.C. Kaspar, Pacific Northwest National Lab |
| Authors: | T.C. Kaspar, Pacific Northwest National Lab A. Ney, Univ. of Duisburg-Essen, Germany A.N. Mangham, Pacific Northwest National Lab S.M. Heald, Advanced Photon Source, Argonne National Lab Y. Joly, Institut Néel, CNRS et Univ. Joseph Fourier, France V. Ney, Univ. of Duisburg-Essen, Germany F. Wilhelm, European Synchrotron Radiation Facility A. Rogalev, European Synchrotron Radiation Facility F. Yakou, European Synchrotron Radiation Facility S.A. Chambers, Pacific Northwest National Lab |
| Correspondent: | Click to Email |
Efficient visible light photocatalysis could revolutionize hydrogen production, chemical synthesis, and pollution mitigation. Binary oxides such as TiO2 have received much attention for these applications since they are stable under aqueous and oxidizing conditions, and show promise as ultraviolet-light photocatalysts. However, to operate in the visible portion of the solar spectrum, the wide bandgap of these oxides (~3 eV for rutile TiO2) must be reduced. Anion doping of anatase TiO2 has been widely explored, and shows some promise. However, in nanoparticles and fine powders, it can be difficult to determine the structural and electronic behavior of N dopants. Homoepitaxial Fe:TiO2 and (Fe,N):TiO2 thin films deposited on rutile TiO2(110) were investigated by x-ray absorption spectroscopy (XAS) and associated theoretical simulations to elucidate the detailed structure of the doped materials. Co-doping with N was found to increase the extent of Fe incorporation into the rutile lattice. X-ray absorption near edge spectroscopy (XANES) spectra were collected at the Ti L-edge, Fe L-edge, O K-edge, N K-edge, and Ti K-edge. No evidence of structural disorder associated with a high concentration of oxygen vacancies was observed. Substitution of Fe for Ti could not be confirmed, although secondary phases such as Fe2O3 and metallic Fe could be ruled out. The similarity of the N K-edge spectra to O, and the presence of a strong x-ray linear dichroism (XLD) signal for the N K-edge, indicates that N is substitutional for O in the rutile lattice, and is not present as a secondary phase such as TiN. Simulations of the XANES spectra qualitatively confirm substitution, although N appears to be present in more than one local environment. Although optical absorption spectra confirm that substitutional N redshifts optical bandgap of Fe-doped rutile into the visible region, the film surfaces are photochemically inert with respect to hole-mediated decomposition of adsorbed trimethyl acetate.