Insight into enhanced azo dye removal and degradation by biochar-supported Co-Fe bimetallic catalysts: Performance evaluation, mechanism, and ecotoxicity assessment.

The treatment of wastewater containing refractory azo dyes remains a serious challenge, urgently calling for the development of efficient and sustainable advanced oxidation processes (AOPs). This study fabricated a magnetically separable catalyst by anchoring CoFe2O4 onto peanut shell-derived biochar (PBC), which was used to activate peroxymonosulfate (PMS) for azo dye degradation. Comprehensive characterizations (XRD, SEM, BET, VSM, XPS) confirmed the successful synthesis of CoFe2O4@100-PBC, revealing the coexistence of a crystalline spinel phase and amorphous carbon, along with a highly dispersed morphology, strong ferromagnetism (47.5 emu/g), and redox-active species (Co2+/Co3+, Fe2+/Fe3+). The CoFe2O4@100-PBC/PMS system exhibited exceptional performance, achieving complete degradation of Congo red (CR, 100 mg/L) within 20 min. Its observed rate constant (Kobs) was 2.01 and 12.18 times higher than those of the CoFe2O4/PMS and PBC/PMS systems, respectively. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed a synergistic degradation mechanism involving both free-radical (SO4•- and •OH) and non-free-radical (1O2) pathways. The potential degradation pathway of CR, as well as the ecotoxicity of CR and its degradation intermediates, were systematically analyzed via HPLC-MS and ecological structure-activity relationship (ECOSAR) software. The results demonstrated that this method not only effectively degraded CR but also reduced its ecotoxicity and bioaccumulation potential. Furthermore, the excellent recyclability and stability of the catalyst were confirmed, as evidenced by a maintained efficiency of 76.8 % after seven cycles. This work provides a sustainable strategy for converting agricultural waste into high-performance catalysts for environmental remediation.