Photo/electro-catalytic degradation of micro- and nano-plastics by nanomaterials and corresponding degradation mechanism

Micro- and nano-plastics (MPs/NPs) pollution has gained increasing concern worldwide due to its potential threat to human health and ecosystem. Hence it is of great significance to remediate MPs/NPs pollution in the environment. Current reviews in respect to the recent processes of MPs/NPs degradation over nanomaterials (NMs) are still insufficient. Thus this review intends to analyze and discuss various NMs employed in MPs/NPs degradation by adopting photo/electro-catalysis technique. To enhance the performance, the surface modification, element doping and morphology control are performed. Even so, there is still a wide range of catalysts to be further investigated. Additionally, we also review the degradation mechanism regarding the identification of reactive oxygen species (ROS), intermediates and degradation pathways, and density functional theory (DFT) calculations. Basically, ROS play a dominant role during MPs/NPs degradation, causing the scission of polymer chain and the generation of by-products. However, the structure-mechanism-function relationship still needs to be explored by coupling with DFT calculations. Moreover, some recommendations for future directions are presented based on current research gaps. Hence, this review provides a comprehensive reference for future directions with respect to the design of catalysts and the improvements of MPs/NPs degradation efficiency.