The roles of Li and F ions in Li-F-codoped TiO2 system

An overall comparative study was carried out on Li-doped, F-doped, and Li-F-codoped TiO₂ powders in order to elucidate the roles of Li⁺ and F⁻ ions in photocatalyst. The characteristic data were based on the analysis of XRD, XPS, and PL spectra. The effects of atomic ratio of Li/Ti and F/Ti on the photocatalytic activity were also investigated. As the results, Li doping accelerated the phase formation of rutile in lower temperature while F doping prevented the phase transition from anatase to rutile. Li doping inducted a large amount of O_OH on the surface of TiO₂, while F doping consumed much of O_OH. Li⁺ ions acted as the roles of recombination center of electron-hole pairs while F doping could restrain the recombination of electron-hole pairs on the center of Li⁺ ions. The roles of Li⁺ and F⁻ ions were also confirmed in the experimental section, where the photocatalytic activity of TiO₂ was improved greatly by synergistic reaction of Li⁺ and F⁻ ions.