Environmental Performance and Applications of Biochar-Derived Persistent Free Radicals

Persistent free radicals (PFRs) in biochar have emerged as a research focus in environmental remediation due to their high efficiency in pollutant degradation. Biochar serves as an ideal matrix for generating PFRs, showing significant potential for treating industrial wastewater and exhaust gases. This review systematically examines the critical factors influencing PFR generation in biochar, including feedstock type (lignocellulosic vs non-lignocellulosic), pyrolysis temperature range (200–700°C), and hydrothermal carboniza­tion conditions. The mechanisms of PFR-mediated contaminant transformation via generation of reactive oxygen species (ROS) are elucidated, demonstrating effectiveness against diverse pollutants such as organo­chlorides (e.g., polychlorinated biphenyls), variable-valence metals e.g., Cr(VI), As(III), sulfonamide antibiotics (e.g., sulfamethazine), and reduced sulfur compounds (e.g., hydrogen sulfide). To address current challenges like the low concentration of PFRs in typical biochars and incomplete understanding of ROS activation pathways, future research should prioritize the development of targeted strategies to enhance the ROS generation efficiency of biochar-derived PFRs. This review aims to provide a theoretical foundation for the green and high-value application of biochar-based materials.