Cooperation between N and Fe in co-doped TiO2 photocatalyst

TiO2 photocatalysts co-doped with N and Fe were synthesized by the sol–gel method. Cooperation of N and Fe in the co-doped TiO2 was studied by monitoring NH3 decomposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis) absorption spectroscopy, and simulation based on density functional theory (DFT). The results from NH3 decomposition revealed that cooperation of N and Fe broadened the range of response of TiO2 to visible light and also enhanced the photocatalytic activity of TiO2 under ultraviolet light. The XRD patterns and SEM and HRTEM images indicated that the co-doped samples prepared were nanometric anatase with an average particle size of 20 nm. Co-doping with N and Fe inhibited grain growth of TiO2 and resulted in larger lattice distortion. XPS analysis showed that the doped N and Fe atoms were replacing lattice oxygen and Ti atoms, respectively. UV–Vis absorption spectra of the co-doped sample showed that the optical absorption edge had been shifted to approximately 675 nm. The DFT results confirmed that cooperation of the Fe3d and N2p orbits reduced the energy gap of TiO2 and thus broadened its range of response to visible light. The synergistic action of the electron density around N and Fe in the co-doped TiO2 enhanced its photochemical stability. In addition, a photocatalytic reaction mechanism for TiO2 co-doped with N and Fe revealed the presence of N2p, Fe3d, and Ti3d orbits as photogenerated hole–electron traps, which enhanced the photocatalytic quantum efficiency.