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 OOH on the surface of TiO2, while F doping consumed much of OOH. 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.