Cooperation among N, F and Fe in tri-doped TiO2 photocatalyst

Abstract

TiO2 photocatalysts tri-doped with N, F and Fe were synthesized by a sol–gel method. The cooperation of N, F and Fe in tri-doped TiO2 was verified by monitoring NH3 decomposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–Vis) absorption spectroscopy, and by the simulation based on the density functional theory (DFT). The results from NH3 decomposition revealed that the cooperation of N, F and Fe broadened the optical response of TiO2 to the visible light range and also enhanced the photocatalytic activity of TiO2 under UV light. The reusability of the tri-doped TiO2 sample after three cycles under UV and visible light irradiation was very good. XRD patterns and SEM and HRTEM images indicated that the tri-doped sample was nanometric anatase with a small amount of rutile with an average particle size of 18 nm. Tri-doping with N, F and Fe suppressed the phase transition from anatase to rutile and also resulted in some more lattice defects. XPS analysis showed that the N, F and Fe atoms were doped into the TiO2 lattice. UV–Vis absorption spectra of the tri-doped TiO2 showed that its optical absorption edge was moved up to 640 nm and its UV absorption was also enhanced. The DFT results confirmed that the cooperation of Fe 3d and N 2p orbits narrowed the band gap of TiO2 and the F 2p orbit broadened the upper valence bands. The synergistic electron density around N, F and Fe in tri-doped TiO2 was capable of enhancing the photochemical stability and reusability of TiO2.