Understanding the origin of synergistic catalytic activities for ZnO based sonophotocatalytic degradation of methyl orange

Abstract

Many studies have documented the existence of synergistic catalytic activities for ZnO based sonophotocatalysis, but the role of ultrasonic field during this sonophotocatalytic process is still unclear. In this work, ZnO samples with three different morphologies (rod-like, flower-like and sheet-like) have been synthesized for the sonophotocatalytic degradation of methyl orange (MO). The results indicate that MO degradation efficiency of ZnO based sonophotocatalysis is found to be higher than the sum of ZnO based photocalysis and sonocatalysis, which indicates the existence of synergy in the ZnO based sonophotocatalytic degradation of MO. The mechanistic investigation indicates that reactive oxygen species can be produced by ZnO in the presence of ultrasound. In addition, the presence of ultrasound in the ZnO based sonophotocatalysis is beneficial for the separation of electron-hole pairs of ZnO based photocatalysis, leading to the production of more reactive oxygen species in the ZnO based sonophotocatalysis. Overall, the origin of synergistic catalytic activities for ZnO based sonophotocatalytic degradation of MO has been revealed in this study.