Surface Bridge Hydroxyl-Mediated Promotion of Reactive Oxygen Species in Different Particle Size TiO₂ Suspensions

Reactive oxygen species (ROS) play an essential role in TiO2 photocatalysis. They arise from the transfer of light-initiated carriers to the TiO2 surface and react with oxygen or water, in which the TiO2 surface is crucial. However, how the TiO2 surface affects ROS production is unclear. Herein, dynamic generation of ROS in suspensions of TiO2 of different particle sizes was investigated under ultraviolet-light irradiation. It is surprising to find that more ROS were produced more quickly for 100–140 nm TiO2 than for 20–60 nm TiO2. Further research suggested that ROS production was intrinsically correlated with the surface bridging hydroxyls per unit area. More bridging hydroxyls induced lower IEP and more negative charges on the TiO2 surface, which favored the transfer of photogenerated carriers, resulting in the promotion of ROS and photocatalytic activity. This provided insight into designing high-efficiency photocatalysts to solve the problem of small particle sizes causing loss and blockage in wastewater treatment