Enhanced removal of Ni-EDTA by three-dimensional electro-Fenton process using Fe-N-doped biochar as catalytic particle electrodes

Heavy metal complexes pose a challenge in terms of their resistance to removal due to their stable and intricate structure. In this study, we explored the utilization of Fe and N co-doped biochar derived from rice husk (Fe-N-RHBC) as catalytic particle electrodes in a three-dimensional electro-Fenton (3D-EF) system for the decomplexation and removal of a model pollutant, Ni-EDTA. The characterization analysis and comparison of catalytic activities confirmed the beneficial effects of Fe and N co-doping on various aspects, such as the types of active sites, interfacial electron transfer properties, and H2O2 decomposition capacity. Compared to other investigated oxidation systems, the 3D-EF process demonstrated rapid removal of Ni-EDTA within the initial minute, with a maximum H2O2 utilization of 99.1% after 30 min. The prepared catalytic particle electrodes exhibited high stability and catalytic capacity even after three consecutive cycles. Throughout the reaction, several processes, including anode oxidation, particle electrode polarization, catalysis, and adsorption of Fe-N-RHBC, as well as cathodic electro-deposition, synergistically contributed to the treatment of Ni-EDTA. The surface-bound O2− radicals and 1O2 generated by the Fe-N-RHBC catalytic particle electrode played a crucial role in the decomplexation and removal of Ni-EDTA. Building upon these findings, we further proposed potential mechanisms for the removal of Ni-EDTA in the 3D-EF system using the Fe-N-RHBC catalytic particle electrode.