New insight into reactive oxidation species (ROS) for bismuth-based photocatalysis in phenol removal

Bismuth-based semiconductors (BBS) are a group of promising candidates applied to visible light-induced photocatalysis. With deep positions of valence bands (2.34-4.04 eV), BBS exhibited excellent activity in oxidation processes. Fundamental studies on the reactive oxidation species primarily focused on TiO₂ under ultraviolet, and it was recognized that OH radicals were effective reactive oxidative species in photocatalytic oxidation processes. This verdict may not be applicable for all other photocatalytic systems. In this study, the reactive oxidation species for BBS in the photocatalytic decomposition of phenol were explored. BBS were prepared with Hierarchical structures and high crystallinity. It was found that OH radicals and superoxide radicals were negligibly produced in most BBS photocatalytic systems. Instead, separated holes on the valence band may directly react with adsorbed species including organics, and acted as the primary ROS. One of the possible explanations of this phenomenon may be due to the shorter lifetime of photogenerated charge carriers on most BBS (212.3-415.7 ms) compared to that of TiO₂ (1193.8 ms). Photocatalytic reaction pathways of degradation of phenol were also different between BBS and TiO₂, which were proposed. This work shed light on the significance of addressing and clarifying the reactive oxidation species in BBS photocatalysis.