Chemical Doping of TiO2 with Nitrogen and Fluorine and Its Support Effect on Catalytic Activity of CO Oxidation

Abstract

We investigated the effect of the support on catalytic activity for CO oxidation using platinum nanoparticles on doped and undoped titanium dioxide (TiO2). As a support, the undoped TiO2 was synthesized via the sol-gel process. The thin films were then chemically doped with non-metal anions, such as nitrogen (N) and fluorine (F). Thin films were prepared using the spin coating technique; characterization techniques including scanning electron microscopy, X-ray diffraction, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) were carried out to examine the morphology of the films, crystal phase, crystallites, optical properties, and elemental composition, respectively. In particular, XPS analysis of the doped TiO2 thin films revealed that the nitrogen sites were interstitial whereas fluorine was doped substitutionally into TiO2 lattice. The Pt/N-, Pt/F-, and Pt/undoped TiO2 catalysts were fabricated by depositing platinum nanoparticles on N-, F-, and undoped TiO2 thin films using the arc plasma deposition technique. CO oxidation was carried out to elucidate the catalytic activity of the Pt nanoparticles. The turnover rates of Pt/N-, and Pt/F-doped TiO2 were a factor of similar to 2.5 higher than that of the Pt/undoped TiO2. We attribute the enhanced catalytic activity to oxygen vacancies formed during the doping process and the facile charge transfer at the metal-oxide interfaces.