Applying a novel advanced oxidation process of biochar activated periodate for the efficient degradation of bisphenol A: Two nonradical pathways

Periodate based advanced oxidation processes (PI-AOPs) exhibited promising future for the abatement of emerging contaminants, yet the underlying mechanism of carbon materials for PI activation was still unclear. In this study, a metal-free biochar (BCx, x represents the pyrolysis temperature) catalyzed PI-AOPs system was established and explored for the degradation of bisphenol A (BPA), one of the endocrine disrupting compounds (EDCs) that was ubiquitously detected in natural ecosystems. Biochar catalysts clearly boosted BPA degradation, suggesting a distinct synergistic effect between PI and biochar. Interestingly, BC350 and BC800 exhibited distinct behaviors for PI activation. Specifically, BC350 performed moderate PI activation, which was believed to be a surface hydroxyl group (OH)-induced nonradical pathway. A unique COOIO3 complex was formed and served as the reactive oxidant responsible for the BPA oxidation. On the other hand, BC800 showed a significant PI activation ability, which was preferentially proved to be a carbon-mediated electron-transfer mechanism. A high potential metastable carbon activated PI complexes (C-PI*) was elucidated to be the dominant oxidative species through electrochemical characterizations and galvanic oxidation process (GOP) experiments. The electron-transfer between adsorbed BPA (electron donor) and C-PI* (electron acceptor) was a crucial step in this pathway. Density functional theory (DFT) calculations confirmed that the interaction between PI and carbon surface was probably caused by the van der Waals force and a part of strong attraction between the interface of PI and BCOH. These findings provide new insights into nonradical pathways in biochar catalyzed PI-AOPs and promote the development and application of PI-AOPs in environmental remediation.