Mechanistic insights into peracetic acid activation by iron-biochar composites prepared at low and high temperature for enhanced contaminant degradation: Selective reactive species generation

Iron-based activation of peracetic acid (PAA) is an environmentally friendly and low-cost technology for degrading contaminants. In this study, iron-biochar (Fe-BC) composites were prepared at low temperature (Fe-BC-300) and high temperature (Fe-BC-800) and used to activate PAA to degrade acetaminophen (ACT). In the Fe-BC-300/PAA process, Fe(IV) was the dominant reactive species responsible for ACT degradation; in contrast, ^•OH and RO^• (e.g., CH₃C(O)O^•) were the dominant reactive species in the Fe-BC-800/PAA system. To elucidate the contributions of each reactive species, a mixed probes strategy designed for heterogeneous PAA activation systems was deployed (for the first time) to simultaneously determine the steady-state concentrations of Fe(IV), ^•OH, and RO^•. The reaction mechanisms were confirmed by treating a suite of organic contaminants with variable ionization potential by the Fe-BC-300/PAA and Fe-BC-800/PAA systems. The experimental results, in combination with density functional theory calculations, confirmed the aforementioned roles of Fe(IV), ^•OH, and RO^• in Fe-BC/PAA processes. Overall, the new mechanistic insights from this study inform preparation of Fe-BC composites for selective generation of specific reactive species upon PAA activation.