Construction of Fe-Mn-La/Ce@biochar electrodes 3D/HEF systems for efficient electro-Fenton degradation of coking wastewater: performance and mechanism insights.

Heterogeneous electro-Fenton (HEF) technology has emerged as a prominent research focus for the efficient degradation of organic pollutants in wastewater. Herein, a novel enhanced heterogeneous electro-Fenton (HEF) system was developed using Fe-Mn-La/Ce tri-metal co-doped biochar electrodes (FML@BC and FMC@BC) to degrade contaminants in coking wastewater. The results demonstrated that the FMC@BC electrode outperformed FML@BC in catalytic degradation, achieving chemical oxygen demand (COD) and total organic carbon (TOC) removal rates of 90.95 % and 95.18 %, respectively, within 120 min under optimized conditions. The superior degradation efficiency of the FMC@BC electrode in the 3D/HEF system arose from biochar-enabled H2O2 generation via selective two-electron oxygen reduction reaction (ORR) and Fe-Mn-Ce-mediated activation through Fenton-type reactions. This synergy facilitated magnetite-like electron transport and multi-valent cycling to boost hydroxyl radicals (•OH) yield for efficient pollutant degradation. Quenching experiments and electron paramagnetic resonance (EPR) analysis confirmed that •OH played the dominant role in the degradation of organic compounds, while superoxide radicals (O2•-) acted as supplementary contributors. Furthermore, the FMC@BC particle electrode exhibited exceptional stability and magnetic properties across 10 cycles, maintaining a COD removal rate of 84.12 %. The 3D/HEF system also demonstrated high energy efficiency and cost-effectiveness, with an energy consumption of 16.25 kWh·kg-1·COD-1. This work provides a promising 3D/HEF catalyst, demonstrating practical potential for the remediation of refractory organic contaminants.