Internal-micro-electrolysis-enhanced heterogeneous electro-Fenton process catalyzed by Fe/Fe3C@PC core-shell hybrid for sulfamethazine degradation

Core-shell structured hybrid octahedron, which contained a Fe-based nanoparticle core (Fe/Fe3C) and a graphitized porous carbon (PC) shell (Fe/Fe3C@PC), prepared through one-pot pyrolysis using MIL-101(Fe) as the sacrificial template, was used as a novel catalyst for the degradation of sulfamethazine (SMT) by heterogeneous electro-Fenton (Hetero-EF). Fe/Fe3C@PC outperformed common heterogeneous catalysts such as Fe-0, Fe3O4 and Fe2O3 due to the synergistic effect between Fe/Fe3C nanoparticles and PC. The rate constant for SMT degradation in the Hetero-EF process was 7.17-folds of that in the heterogeneous Fenton (Hetero-F) process. The plausible catalytic mechanism and degradation pathway for mineralization of SMT by this Hetero-EF process were proposed, confirming the main role of surface-bound hydroxyl radical ((OHads)-O-center dot) oxidation. Moreover, internal-micro-electrolysis (IME)-enhanced Hetero-EF reaction was verified by experiments and density functional theory (DFT) calculations. Fe/Fe3C@PC could be easily recycled due to magnetism and well recovered via a simple thermal treatment in H-2 atmosphere. This work enlightened metal-organic frameworks (MOFs) derived core-shell structured hybrids to be ultra-efficient heterogeneous catalysts and their catalytic mechanism promoting promising utilization in the Hetero-EF process for organic pollutants removal.