Exploring the electron transfer regime occurring in peroxides activation by graphite: Origin, mechanism and efficiency in complicated water matrices

Electron transfer pathway (ETP) driven by carbon-catalytic peroxides has become appealing strategy for microcontaminants (MCs) removal, whereas the nature of ETP occurring in different peroxides system is ambiguous. This work developed a controllable model for peroxides activation by using graphite (GP) that is characterized as simple configuration and excellent electronic conductivity. Peracetic acid (PAA) and peroxymonosulfate (PMS) could be readily activated by GP with 72.2% and 93.7% removal efficiency of sulfamethoxazole, respectively, but peroxydisulfate (PDS) and hydrogen peroxide (H2O2) showed low reactivity to GP activation. For PAA/GP system, the adjacent transferring type of ETP was the primary oxidation mechanism with formation of metastable surface complexes to extract electrons from MCs; while the electron shuttling was the dominate ETP route in PMS/GP system via conductive GP acting as a bridge, promoting direct electron transport from organics to PMS and accounting for 49% oxidation efficiency at pH 7.0. Hydroxyl groups of GP were proposed to be decisive sites to form PAA-GP* complexes, while sp2-hybridized carbon functioned as the electron shuttler in PMS oxidation. Importantly, ETP process would not be affected by the coexistence of multiple anions and natural organic matter to remove mixed MCs in actual water. Our work dedicates to exploring selection of various peroxides in ETP regimes and presenting the superiority of ETP strategy to treat complicated aquatic environment.