Highly efficient degradation of antibiotic metronidazole by an environmental-friendly metal-free dual-cathode electro-Fenton system

[Display omitted] •A novel, eco-friendly and metal-free dual-cathode electro-Fenton system was developed.•The dual cathodes consisted of KOH-activated GF cathode and B, N co-doped GF cathode.•Excellent performance was achieved for MNZ degradation across a wide pH range.•O2– and 1O2 played primary roles in the degradation of MNZ in this system. The widespread presence of antibiotic metronidazole (MNZ) in the environment and its associated harmful effects require effective treatment methods. In this study, a novel, environmental-friendly and metal-free dual-cathode electro-Fenton system was developed to explore the degradation process of MNZ. KOH-activated graphite felt (AGF) served as one of the double cathodes and was mainly utilized to reduce O2 to generate H2O2, while boron (B) and nitrogen (N) co-doped graphite felt (BN-GF) cathode was mainly utilized to activate the in-situ generated H2O2 to form active species to degrade MNZ. The system exhibited excellent catalytic degradation performance (99.9 %) and extremely high-rate constant (0.12352 min−1) for MNZ removal at a wide pH range under a low current density. The system also had a wide range of environmental adaptability (satisfactory treatment of various antibiotics in various practical water substrates), good stability and reusability, and significant biotoxicity reduction, etc.. Mechanism analysis showed that •O2– and 1O2 played a primary role in the degradation of MNZ in this system. These results suggest that the environmental-friendly and metal-free dual-cathode electro-Fenton system may provide a promising route for the degradation/removal of organic contaminants.