Surface Properties of Reduced and Stoichiometric TiO 2 AsProbed by SO 2 Adsorption

The adsorption and photochemical properties of reduced and stoichiometric anatase TiO2 nanoparticles, prepared by annealing in vacuum and air, respectively, at different temperatures up to 500 °C and 2 days have been investigated. Combined X-ray diffraction and Raman results suggest that vacuum annealing leads to a defective, oxygen vacancy rich surface region with an accompanying decrease of the crystalline core. The surface chemical properties of the reduced and calcined TiO2 nanoparticles were studied by means of SO2 adsorption measured by in situ diffuse reflectance Fourier transform spectroscopy. On pristine TiO2 nanoparticles, SO2 adsorption leads to a broad absorbance band centered at 1140 cm-1. In contrast, SO2 does not adsorb on stoichiometric TiO2 obtained after long-term annealing in air at 500 °C. However, after the same heat treatment in vacuum, SO2 is shown to bind strongly on well-defined adsorption sites associated with a narrow absorbance band at 1150 cm-1. The increased adsorption on red...