Search

Abstract: V- and N-codoped TiO2 photo-catalyst is synthesized by sol–gel method to sensitize TiO2 to visible light. The concentrations of V and N were varied and optimized to enhance photo-catalytic activity. In order to increase the active surface area, the crystalline powder was ball milled to obtain nanosized particles. The photo-catalysts were characterized by Micro-Raman, TEM, XPS and UV–vis (in diffused reflectance mode) techniques. The co-doped TiO2 photocatalyst displayed narrower band gap (2.3eV) compared to singly doped TiO2 catalyst, namely V (2at.%)-doped (2.42eV), N (4at.%)-doped (2.95eV), and undoped TiO2 (3.13eV). The photocatalytic activity for the degradation of Rhodamine B (an organic dye) under visible light irradiation obtained with co-doped TiO2 photo-catalyst is significantly better as compared to the undoped, V-doped, and N-doped TiO2. The incorporation of V and N in TiO2 lattice induces isolated energy levels near the conduction and valence bands, respectively, causing an effective narrowing of the band gap. In addition, due to the low dopants concentrations, these energy levels can also act as traps for photoexcited holes or electrons thus reducing the recombination between photo-generated charges. Both these effects, namely band narrowing and enhanced charge separation produce synergistic effects to increase the photocatalytic activity of V-N-codoped TiO2. [Copyright &y& Elsevier]

Cu–N-codoped TiO 2 photocatalyst is synthesized by sol–gel method to obtain enhanced optical absorption in the visible region. Optimum concentrations of Cu and N were obtained by maximizing the photocatalytic activity for the monodoped (Cu or N) TiO 2 . These optimized concentrations were used for synthesizing (Cu, N)–codoped TiO 2 . The photocatalysts were characterized using XRD, micro-Raman, SEM, XPS, BET surface area analyzer, UV–vis diffuse reflectance spectroscopy and photoluminescence. XPS study suggests the incorporation of Cu 2+ into TiO 2 lattice, which assists N to substitutionally replace oxygen in codoped TiO 2 , while maintaining the anatase phase even after doping. N-doping creates minor variation in the energy band gap of TiO 2 reducing it upto 3.0 eV, while Cu doping was able to narrow the band gap to 2.2 eV mainly due to the localized levels of Cu-3d states and shifting of Ti-3d states to lower energy (due to oxygen vacancies) in the band-gap as deduced from XPS data and confirmed by the DFT calculation. In (Cu, N)–codoped TiO 2 , visible light absorption is higher than the other TiO 2 samples, a feature that is mainly attributed to the formation of an isolated intermediate band (IB) occurring due to the strong hybridization between Cu 3d and N 2p orbitals. This IB contributes to visible light absorption by two step optical transition with the first transition from valence band (VB) to IB and the second from IB to conduction band (CB). The dopant species may also act to reduce the charge carrier recombination by acting as the trapping sites for photogenerated charges. (Cu, N)–codoped TiO 2 was able to degrade Methylene Blue dye and p -Nitrophenol solution under light irradiation with significantly better rate in comparison to monodoped and undoped TiO 2 . High photocatalytic activity is attributed to the presence of IB in the energy band gap of TiO 2 , which creates the synergic effect by higher visible light absorption and lower recombination of photogenerated charges. [ABSTRACT FROM AUTHOR]