High efficiency heterogeneous Fenton-like catalyst biochar modified CuS for the degradation of sulfisoxazole: Catalytic performance and mechanism

Background This study focuses on the dual issues of catalyst metal agglomeration and metal ion leaching in heterogeneous Fenton reactions, which lead to catalyst inefficiency and secondary metal ion pollution, particularly resulting in significantly insufficient degradation efficiency for persistent antibiotics such as sulfisoxazole (SIZ). Methods The catalyst of copper sulfide-loaded peanut shell biochar catalyst (CCS) was synthesized using a low-temperature hydrothermal method with biochar as the substrate, which was then assessed for its ability to activate hydrogen peroxide system. Advanced characterizations (XRD, SEM, BET, FTIR, EIS, and XPS) were combined with EPR analysis, and DFT calculations to elucidate the structure–property–activity relationship. Additionally, degradation pathways and the toxicity of transformation products were identified by LC-MS and ECOSAR. Significant Findings The CCS catalyst achieved exceptional sulfisoxazole (SIZ) removal (98.4%) under optimal conditions. This high efficiency persisted across a wide pH range and through five reuse cycles, accompanied by consistently negligible copper leaching, confirming superior activity and stability. Mechanistic analysis identified ·OH and O₂·⁻ as the dominant reactive species driving degradation. Furthermore, identified degradation pathways yielded transformation products exhibiting reduced acute and chronic toxicity. Critically, the carbon substrate effectively mitigates metal agglomeration and leaching, underpinning the catalyst's robust performance.