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

Abstract

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 (λ > 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. In 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.