Modulation of titanium dioxide surface hydroxyl groups for photocatalytic selective conversion of biopolyols

Photocatalysis has demonstrated considerable potential as a highly efficient approach to the valorization of biomass under mild conditions, while the selectivity control is a long-standing challenge, notably when the targets are complex and reactive biopolyols. In this study, we have successfully achieved selectivity control of photocatalytic biopolyols reforming to formic acid (FA) or CO by modulating the surface hydroxyl groups on TiO2 semiconductor. Photogenerated holes typically localize at bridging oxygen atoms (O2c) on the TiO2 surface, while shifting to terminal hydroxyl groups upon their introduction. The state of holes strongly affects the hole transfer process, which in turn influences the course of the reaction and thus controls the selectivity. By modulating the surface hydroxyl groups, the model substrate glycerol was selectively converted to CO (49% yield) and FA (50% yield). A range of other biopolyols, exemplified by erythritol, have demonstrated the same reaction selectivity. This work provides an effective strategy to manipulate reaction pathways by means of regulating the catalyst surface structure itself.