Novel strategy for the efficient degradation of organic contaminants using porous graphite electrodes: Synergistic mechanism of anodic and cathodic reactions

Abstract The co-activation of persulfate (PS) using electricity and carbon is a novel method used in sulfate radical-based advanced oxidation processes. However, the full utilisation of the synergistic effects between diverse reactions on both electrodes to achieve high PS activation and efficient removal of contaminants remains challenging. In this study, we designed porous graphite to serve as two electrodes and a continuous-flow reactor; this system resulted in internal PS activation and the degradation of organics within a specified “confined space”. With the enhancement of mass and electron transfer in the reactor, the model contaminant metronidazole (MNZ) was successfully degraded with a removal efficiency of 94.79%. The flow-through design remarkably outperformed the flow-by design, which reflected the stronger restrain of side reactions, larger electrochemical active surface area, higher active-site exposure, lower charge-transfer resistance, and higher diffusion coefficient of porous graphite electrodes. Kinetic experiments, radical scavenging experiments, and electron paramagnetic resonance tests carried out in split cells demonstrated that direct electron transfer, ∙OH oxidation, and non-radical oxidation with active PS* and 1O2 collectively contributed to the degradation of MNZ in the anode; SO4−∙ oxidation played the most significant role in the cathodic cell. Finally, the broad applicability of the reactor was confirmed by the treatment of diverse water matrixes and wastewater containing various persistent organic contaminants, showing great potential for practical applications.