Synergistic effects of F and Fe in co-doped TiO2 nanoparticles

TiO2 photocatalysts co-doped with F and Fe were synthesized by a sol–gel method. Synergistic effects of F and Fe in the co-doped TiO2 were verified by 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 was analyzed by the simulation based on the density functional theory (DFT). The results from NH3 decomposition confirmed that the cooperation of F and Fe broadened the optical response of TiO2 to visible light region and also enhanced the photocatalytic activity of TiO2 under ultraviolet light. XRD patterns, SEM and HRTEM images showed that the co-doped samples were nanometric anatase with an average particle size of 25 nm. Co-doping with F and Fe inhibited the grain growth of TiO2 from anatase to rutile and resulted in a larger lattice defect. XPS analysis exhibited that the doped F and Fe atoms were into the TiO2 lattice. UV–Vis absorption spectra showed that its optical absorption edge was moved up to approximately 617 nm and its ultraviolet absorption was also enhanced. The DFT results indicated that the cooperation of Fe 3d and O 2p orbits narrowed the band gap of TiO2 and F 2p orbit widened the upper valence bands. The synergistic electron density around F and Fe in co-doped TiO2 was capable to enhance the photo-chemical stability of TiO2.