Biochar derived from soybean residue as an efficient cathode applied in heterogeneous electro-Fenton

This study fabricated an effective cathode (Fe/Zn/BSR@CF), using Fe/Zn co-doped biochar from waste soybean residue (WSR) as the cathodic reactive component. In the electro-Fenton system equipped with the fabricated cathode, the tetracycline (TC) removal efficiency reached 93.86% within 150 min, and total organic carbon (TOC) mineralization efficiency obtained 70.73% within 6 h. The excellent cathodic performance was due to the synergistic strategies, including Fe, N, and P co-doping and specific surface area enhancement via Zn modification of biochar which inherently contained endogenous N and P. The Fe/Zn-doped biochar, characterized by a high specific surface area, facilitated the formation of pyridinic-N and iron phosphide(Fe_xP), thereby endowing the cathode with enhanced H₂O₂ generation and activation capabilities. Electron paramagnetic resonance spectrometer (EPR) test and quenching experiment results showed hydroxyl radicals (OH^•) and superoxide radicals (O₂^•⁻) were identified as the primary oxygen-containing reactive species during the electro-Fenton process. Results also indicated that O₂ was first reduced cathodically to O₂^•⁻ which subsequently combined with a proton to produce H₂O₂. Then, the generated H₂O₂ was activated by the cathodic reactive component (Fe_xP). Furthermore, ecotoxicity evaluation of TC degradation intermediates showed an overall trend toward reduced toxicity. This study presents a biochar-based cathode for the in-situ generation and activation of H₂O₂, offering an approach to improve electro-Fenton efficiency for organic pollutant removal.