Synergy of surface fluorine and oxygen vacancy of TiO2 nanosheets for O2 activation in selective photocatalytic organic transformations

Abstract

Surface fluorinated TiO₂ has received extensive attention in recent years due to the improved photocatalytic reactivity compared with that of pure TiO₂. However, the synergy of surface fluorine (F_S) and oxygen vacancy (V_O) is not clear and needs further study. Here we systematically studied the effect of F_S, V_O and acidic sites of TiO₂ nanosheets on the selective photocatalytic oxidation of benzylamine to imine. The photocatalytic activity first increased and then decreased as the content of F_S decreased and V_O increased. The photocatalytic activity reached a summit with the imine yield of 92.1% over TiO₂-B-6 h, which is mainly due to the synergy between F_S and adjacent V_O, forming the frustrated Lewis pair that boosts the activation of O₂. The varied contents of F_S and V_O not only cause an evident change in the amount of acidic sites, but also affect the band structure and separation efficiency of charge carriers. The experimental and calculation results demonstrate that the coexistence of F_S and V_O boosted the separation efficiency, density and mobility of photogenerated charge carriers, resulting in the improved photocatalytic activity. The improved photocatalytic activity can be attributed to the combined effects of F_S, V_O and acidic sites. This work provides a strategy for the explicit regulation of surface species on TiO₂ nanosheets for improved photocatalytic activity.