Surface Phases of TiO₂ Nanoparticles Studied by UV Raman Spectroscopy and FT-IR Spectroscopy

Abstract

Surface phases of TiO 2 nanoparticles (30 ∼ 200 nm) were studied by UV Raman spectroscopy and FT-IR spectroscopy with CO and CO 2 as probe molecules. UV Raman spectroscopy can differentiate the surface phase structure of TiO 2 calcined at different temperatures. IR spectra of adsorbed CO and CO 2 on TiO 2 calcined at different temperatures are in good agreement with the results from UV Raman spectra. IR results evidently confirm that UV Raman spectroscopy is a surface-sensitive technique for TiO 2 . Both UV Raman and IR spectra indicate that the crystalline phase of TiO 2 in the surface region is usually different from that in the bulk which is characterized by XRD. CO is weakly adsorbed on Ti 4+ ions of anatase phase but is hardly adsorbed on those of rutile phase at room temperature. Adsorbed CO 2 on anatase phase produces mainly bidentate carbonate, while on rutile phase produces mainly bicarbonate species. These results suggest that the surface Lewis acidity of anatase phase is stronger than that of rutile phase, and the concentration of cus Ti 4+ -O 2- pairs on the surface of anatase phase is much higher than that on rutile phase; however, the basicity of surface OH groups of rutile phase is stronger than that of anatase phase.