Highly visible-light active C- and V-doped TiO2 for degradation of acetaldehyde

C-doped and C- and V-doped TiO2 photocatalysts were prepared by a sol–gel process. Both catalysts showed high activity for the degradation of acetaldehyde under visible irradiation (image). The co-doped TiO2 catalysts also were highly active in the dark; 2.0% V-containing co-doped TiO2 had the highest activity, comparable with the activity under visible light irradiation. The catalysts were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), and N2 adsorption–desorption. The results suggest that vanadium ions were introduced both on the surface and into the bulk of TiO2. A free electron, induced by the formation of V5+ in the sublayers of TiO2 during calcination at 500 °C in air, was delocalized and promoted into the conduction band by thermal energy and further transferred to O2, generating a superoxide radical anion (O⋅−2) that is responsible for degradation of acetaldehyde in the dark. In addition to functioning as a photosensitizer that shifts the optical response of TiO2 from the ultraviolet (UV) to the visible light region, the doped elemental carbon increased the surface area and improved the dispersion of vanadium.