Effects of vanadium doping on microstructures and optical properties of TiO 2

Abstract To improve the photocatalytic activity of titanium dioxide (TiO 2 ), the vanadium (V) was selected to modify TiO 2 . Pure and V-doped TiO 2 samples were first synthesized, then effects of the V doping on microstructures and optical properties of TiO 2 were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible light diffuse reflectance spectra (UV–vis DRS). Results indicated that the prepared TiO 2 samples only contained anatase phase. The V dopant was uniformly dispersed in TiO 2 lattices, not affecting the crystal phase structures of TiO 2 . The crystallite sizes of TiO 2 were decreased first and then increased with the increase in V dopant content within the diameter range from 12 to 16 nm. The V dopant inhibited the increase in TiO 2 crystallite size. Also, the dispersity of TiO 2 nanoparticles was improved with the increase in V dopant content. The V doping brought more defects in TiO 2 lattices to capture charge carriers, and to decrease the recombination of electron–hole pairs. Additionally, the prepared TiO 2 included such elements as Ti, V and oxygen (O). V consisted of two chemical states of V 4+ and V 5+ , which were served as trapping centers of photo-generated electrons to promote the photocatalytic oxidation process. Ti existed in the form of Ti 4+ , and O presented in the form of such chemical bonds as Ti-O, Ti-OH and Ti-O-V in V-doped TiO 2 . Finally, the optical absorption edges of V-doped TiO 2 show obvious red shift. The optimal V dopant content is 1.0% for pure TiO 2 sample. The V dopant could introduce the doping energy level and narrow the band gap of TiO 2 , extending the absorption spectral range of TiO 2 . The V doping was an effective method to improve optical absorption properties of TiO 2 in visible light region.