Theoretical and experimental studies on N, Fe, La co-doped anatase TiO2 band adjustment

Abstract

Based on the plane wave method (PWPP) of densiy functional theory (DFT) we model the N, Fe, La three elements co-doped anatase TiO2 crystal structure and calculate its band structure and density of states with Material Studio. By the sol-gel method, the intrinsic anatase TiO2 and the anatase TiO2 with N, Fe, La three elements co-doping are prepared and investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results indicate that the changes of the N, Fe, La co-doped TiO2 lattice volume and its bond length will result in a decline of the crystal symmetry and the effective separation of the electron-hole pair. Impurity level appearing at the bottom of the conduction band and at the top of valence band leads to the decrease of the TiO2 forbidden band width(1.78 eV to 1.35 eV, reduced by 25%), the red shift of light absorption edge, the increase of density of states as well as, the improve ment of electron transition probability and the photocatalytic efficiency of TiO2. Ion doping makes the particles in doped TiO2 become smaller, i.e. the size of particles in TiO2>N/Fe_TiO2>N/Fe/La_TiO2, the emission peak of the N/Fe/La: TiO2 is 425 nm and its energy gap is smaller than that of the intrinsic TiO2. The measured N/Fe/La: TiO2 photocatalytic ability is stronger than the N/Fe: TiO2, the origin can be due to the increasing number of the electronic states and the impurity energy levels.