Surface Structure of TiO2P25 Nanoparticles: Infrared Study of Hydroxy Groups on Coordinative Defect Sites

Surface hydroxy groups are known to play a significant role in the photocatalytic behavior of TiO 2 . The molecular or dissociative character of H 2 O adsorption on titania is strongly affected by the local surface structure, but dissociation, producing −OH, should prevail on surface sites with a high degree of coordinative unsaturation. Here we report an IR investigation of hydroxy groups on low coordination sites of TiO 2 P25 (Degussa), a commercial titania powder considered a staple in the field of heterogeneous photocatalysis. The presence of coordinatively defective surface terminations well agrees with the roughness of the border of TiO 2 particles observed by high resolution transmission electron microscopy. Furthermore, IR spectra of adsorbed CO were used to probe the Lewis acidity of surface Ti 4+ ions exposed after the removal of water molecules and hydroxy groups. Evidence for two additional types of surface cationic sites with respect those reported in the literature was found.