Quantum dots/graphene (QDs/GR) composite materials show a distinct synergistic effect between the QDs and graphene, which has aroused vast attention toward their unique characteristics in the last few decades.

Ti–O based materials have attracted great attention recently for their potential applications in clean energy generation and environment remediation. To screen Ti–O based materials for specific applications, the atomic-level understanding of the subtle discrepancy of their properties is of paramount importance. In this regard, the density functional theory computations have been performed to systematically compare the physicochemical properties of three selected Ti–O based materials: anatase titanium dioxides, sodium trititanates and sodium hexatitanates. Due to their structure discrepancy, sodium trititanates show the highest chemical reactivity. However, titanium dioxides are found to be the most photoactive materials. The reactivity and photoactivity of sodium hexatitanates fall between those of titanium dioxide and sodium trititanates. In the meantime, our energetic analysis also confirms that the thermal stabilities of Ti–O based materials are strongly dependent on the acid–base conditions. Titanium dioxides are preferred under acidic conditions, while titanates are more stable in basic solutions.

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.