Dual roles of biochar redox property in mediating 2,4-dichlorophenol degradation in the presence of Fe and persulfate.

Recent studies suggested that biochars could mediate the degradation of organic contaminants. The role of biochars in mediating organic contaminant degradation could be amplified in a Fenton-like reaction, and comparing biochars with varied properties may provide insightful information to understand the reaction mechanisms. In this study, biochar was applied in a Fenton-like reaction system with Fe and persulfate (PS) to degrade 2,4-dichlorophenel (2,4-DCP). Biochars with different intensities of persistent free radicals (PFRs), oxygen-containing functional groups (OFGs), and redox properties were investigated regarding their roles in 2,4-DCP removal. Compared to biochar system, PS addition increased 2,4-DCP degradation and Fe addition increased its sorption. The combination of PS and Fe promoted 2,4-DCP degradation over 2 times higher. Various reactive oxygen species (ROS), including SO, HO, and O, were involved in 2,4-DCP degradation, contributing to around 50% of the overall 2,4-DCP degradation. The direct electron transfer between biochar particles and 2,4-DCP contributed to the rest of 2,4-DCP degradation. A significant positive correlation was observed between 2,4-DCP degradation and electron donating capacity (EDC) or Fe. We thus concluded that EDC-involved structures in biochars could either directly donate electron to 2,4-DCP, or reduce Fe to Fe, which activated PS to generate ROS. This dual roles of biochar should be well considered in biochar application and production. This study provided a useful theoretical basis for manipulating biochar redox properties to enhance their application potential in pollution control.