Generation of Reactive Oxygen Species, Electrons/Holes, and Photocatalytic Degradation of Rhodamine B by Photoexcited CdS and Ag2S Micro-Nano Structures

Identifying the dominantly active species and their reactive behaviors in semiconductor photocatalysis is important for developing a full understanding of their photochemical and photophysical properties. Here we report an effective method for studying the reactive oxygen species (ROS) and charge carriers generated by irradiating single crystalline CdS and Ag2S micro-nano structures (MNS). Our method, based on electron spin resonance spectroscopy (ESR) combined with spin trapping and spin labeling techniques, confirmed the generation of superoxide and charge carriers and their contribution to photocatalytic degradation of rhodamine B elicited by CdS and Ag2S MNS. The electronic band structures determined the reactivity of photogenerated holes/electrons and the generation of reactive oxygen species. Our comparison of CdS and Ag2S MNS showed that, because of the large difference between their band edge positions, these two sulfides differ greatly in ROS production and in the reactivity of photoinduced electrons and holes. Our ESR method not only provides specific mechanistic information, but also can predict the photocatalytic activity for metal sulfide and possible metal oxide micro-nano structures.