Cooperation among N, F and Fe in tri-doped TiO 2 photocatalyst

TiO 2 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 TiO 2 was verified by monitoring NH 3 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 NH 3 decomposition revealed that the cooperation of N, F and Fe broadened the optical response of TiO 2 to the visible light range and also enhanced the photocatalytic activity of TiO 2 under UV light. The reusability of the tri-doped TiO 2 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 TiO 2 lattice. UV–Vis absorption spectra of the tri-doped TiO 2 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 TiO 2 and the F 2p orbit broadened the upper valence bands. The synergistic electron density around N, F and Fe in tri-doped TiO 2 was capable of enhancing the photochemical stability and reusability of TiO 2 .