Insights into the Electron-Transfer Mechanism of Permanganate Activation by Graphite for Enhanced Oxidation of Sulfamethoxazole.

Many reagents as electron sacrificers have been recently investigated to induce decomposition of permanganate (KMnO ₄ ) to produce highly reactive intermediate Mn species toward oxidation of organic contaminants; however, this strategy meanwhile causes low KMnO ₄ utilization efficiency. This study surprisingly found that graphite can mediate direct electron transfer from organics (e.g., sulfamethoxazole (SMX)) to KMnO ₄ , resulting in high KMnO ₄ utilization efficiency, rather than reductive sites of graphite-induced conversion of KMnO ₄ to highly reactive intermediate Mn species. The galvanic oxidation process (GOP) and comparative experiments of different organic contaminants prove that the KMnO ₄ /graphite system mainly extracts electrons from organic contaminants via a one-electron pathway instead of a two-electron pathway. More importantly, the KMnO ₄ /graphite system has superior reusability, graphite can keep a long-lasting reactivity, and the KMnO ₄ utilization efficiency elevates significantly after each cycle of graphite. The transformation of SMX in the KMnO ₄ /graphite system mainly includes self-coupling, hydroxylation, oxidation, and hydrolytic reaction. The work will improve insights into the electron-transfer mechanism and unveil the advantages of efficient KMnO ₄ utilization in the KMnO ₄ -based technologies in environmental remediation.