Effects of vanadium doping on microstructures and optical properties of TiO2

Abstract

To improve the photocatalytic activity of titanium dioxide (TiO2), the vanadium (V) was selected to modify TiO2. Pure and V-doped TiO2 samples were first synthesized, then effects of the V doping on microstructures and optical properties of TiO2 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 TiO2 samples only contained anatase phase. The V dopant was uniformly dispersed in TiO2 lattices, not affecting the crystal phase structures of TiO2. The crystallite sizes of TiO2 were decreased first and then increased with the increase in V dopant content within the diameter range from 12 to 16nm. The V dopant inhibited the increase in TiO2 crystallite size. Also, the dispersity of TiO2 nanoparticles was improved with the increase in V dopant content. The V doping brought more defects in TiO2 lattices to capture charge carriers, and to decrease the recombination of electron–hole pairs. Additionally, the prepared TiO2 included such elements as Ti, V and oxygen (O). V consisted of two chemical states of V4+ and V5+, which were served as trapping centers of photo-generated electrons to promote the photocatalytic oxidation process. Ti existed in the form of Ti4+, and O presented in the form of such chemical bonds as Ti-O, Ti-OH and Ti-O-V in V-doped TiO2. Finally, the optical absorption edges of V-doped TiO2 show obvious red shift. The optimal V dopant content is 1.0% for pure TiO2 sample. The V dopant could introduce the doping energy level and narrow the band gap of TiO2, extending the absorption spectral range of TiO2. The V doping was an effective method to improve optical absorption properties of TiO2 in visible light region.