Oxygen vacancy induced fast lithium storage and efficient organics photodegradation over ultrathin TiO₂ nanolayers grafted graphene sheets

Highlights: • Oxygen vacancy is tailored by adjusting the treatment conditions. • Unltrathin TiO₂ nanolayers are grafted on the graphene sheets. • Oxygen vacancy is located on the surface of TiO₂/graphene treated by H₂. • Improved lithium storage and organic pollutants removal efficiency. - Abstract: In this work we have developed a unique structure of ultrathin (5 nm) TiO₂ nanolayers grafted graphene nanosheets (TiO₂/G) and integrated oxygen vacancy (V_O) into TiO₂ to enhance its lithium storage and photocatalytic performances. The defective TiO₂/G was synthesized by a solvothermal and subsequent thermal treatment method. When treated in a H₂ atmosphere, the resulting TiO_2-x/G(H₂) has lower crystallinity, smaller crystal size, richer surface V_O, higher surface area, larger pore volume, and lower charge transfer resistance than that reduced by NaBH₄ solid, i.e., TiO_2-x/G(NaBH₄). More importantly, the surface V_O in the TiO_2-x/G(H₂) could remarkably inhibit the recombination of photogenerated electron-hole pairs compared with the bulk Vo in the TiO_2-x/G(NaBH₄). As a result, the combination of all the factors contributed to the superiority of TiO_2-x/G(H₂), which demonstrated not only 70% higher specific capacity, longer cycling performance (1000 cycles) and better rate capability for lithium-ion battery, but also higher photocatalytic activity and 1.5 times faster degradation rate for organic pollutants removal than TiO_2-x/G(NaBH₄). The findings in this work will benefit the fundamental understanding of TiO₂/G surface chemistry and advance the design and preparation of functional materials for energy storage and water treatment.