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.