Dual roles of biochar redox property in mediating 2,4-dichlorophenol degradation in the presence of Fe3+ and persulfate

Abstract

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 Fe3+ 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 Fe3+ addition increased its sorption. The combination of PS and Fe3+ promoted 2,4-DCP degradation over 2 times higher. Various reactive oxygen species (ROS), including SO4•-, HO•, and O2•-, 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 Fe2+. We thus concluded that EDC-involved structures in biochars could either directly donate electron to 2,4-DCP, or reduce Fe3+ to Fe2+, 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.