Sol–gel-derived VχTi1−χO2 films and their photocatalytic activities under visible light irradiation

VχTi1−χO2 films with various V contents (χ=0–0.1) were prepared on pyrex glass substrates by a sol–gel method. X-ray diffraction (XRD) measurements revealed that all the films crystallized in anatase after heat-treatment at 500 °C for 1 h, and no V-derived peak was detected. V doping resulted in a slight shift of the anatase peak position to higher 2θ value due to the substitution of part of the Ti sites by V. X-ray photoelectron spectroscopic (XPS) measurements showed that vanadium presented in the film mainly in the valence state of V4+ when χ was below 0.075. The absorption spectrum of the VχTi1−χO2 film shifted to longer wavelengths when χ increased. Thus-formed VχTi1−χO2 films were proved to be photocatalytically active not only under ultraviolet (UV) light but also under visible light irradiation, which was confirmed by the decomposition of methylene blue and gaseous acetaldehyde, as well as by the visible light induced change of water contact angle in the film surface. Highest activity was obtained in the film with a V content of 0.01.