Photo-catalytic degradation of Rhodamine B on C-, S-, N-, and Fe-doped TiO2 under visible-light irradiation

C-, S-, N-, and Fe-doped TiO2 photocatalysts were synthesized by a facile sol–gel method. The structure and properties of catalysts were characterized by N2 desorption–adsorption, X-ray diffraction (XRD), UV–vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Results revealed that the surface area of the multi-doped TiO2 was significantly increased and the crystallite size was smaller than the pure TiO2 obtained by a similar route. Compared with TiO2, the peak position in doped-TiO2 XRD patterns was slightly shifted, which could be attributed to the distortion by the substitution of carbon, nitrogen, and sulfur dopants for some oxygen atoms and Fe3+ for Ti4+ in the lattice of TiO2. These substitutions were confirmed by XPS. In addition, these dopants were responsible for narrowing the band gap of TiO2 and shifting its optical response from ultraviolet (UV) to the visible-light region. The photocatalytic reactivities of these multi-doped TiO2 catalysts were investigated by degrading Rhodamine B (RB) in aqueous solution under visible-light irradiation (λ>420nm). It was found out that the reactivity was significantly enhanced and the catalyst doped with nitrogen, carbon, sulfur, and 0.3wt% iron had the highest photocatalytic activity.