Effect of synergy on the visible light activity of B, N and Fe co-doped TiO2 for the degradation of MO

Single doped, co-doped and tri-doped TiO2 with B, N and Fe are successfully synthesized by using the hydrothermal method. The samples are characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples are evaluated for degradation of methyl-orange (MO, 20 mg L-1) in aqueous solutions under visible light (lambda > 420 nm). The results of XRD suggest that all the catalysts present anatase crystal. All the doping catalysts show higher photoactivities than pure TiO2 under visible light irradiation. In the single nonmetal doped TiO2, the localized dopant levels near the valence band (VB) are responsible for the enhancement of photoactivies. Fe3+ impurity level formed under the conduction band (CB) induces the high photocatalytic activities of iron doped TiO2. wIn the co-doped and tri-doped catalysts, the B 2p and N 2p acceptor states contribute to the band gap narrowing by mixing with O 2p states combined with the overlapping of the conduction band by the iron "d'' orbital, resulting in improvement of the photo-performance under visible light irradiation. Iron co-doped with boron catalyst shows low photoactivity under visible light due to the absence of Fe3+ impurity levels at the bottom of the conduction band. In addition, the XPS results indicate the presence of synergistic effects in co-doped and tri-doped catalysts, which contribute to the enhancement of photocatalytic activities.