Nature of visible-light responsive fluorinated titanium dioxides

The origin of the visible-light activity of fluorinated TiO₂ has been systematically investigated via comprehensive theoretical studies. The 3-coordinated surface F atoms with higher 1s binding energy are identified to be the origin of the visible light activity of the fluorinated TiO₂ by systematically analysing 1s core-level shifts of various types of F atoms in fluorinated TiO₂. Further analysing the electronic structures of the fluorinated TiO₂ using semi-local density functional theory and non-local hybrid density functional theory calculations demonstrates that the introduction of the 3-coordinated surface F atoms leads to the formation of Ti³⁺ ions in the sub-surface, which is the cause for the bandgap shrinking, increasing the visible-light activity. The results also reveal that the presence of 3-coordinated surface F atoms strengthens the adsorption of hydroxyl groups in their vicinity to enhance the photocatalytic activity. The findings of this work address a long-standing scientific question, providing useful guidance for the design and development of high performance VL photocatalysts.