Effects of vanadium doping on microstructures and optical properties of TiO2

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 16 nm. 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.