Multi-metal synergistic effect and sulfur-mediated electron transfer in Co-δ-FeOOH@Cu₂S activated CaSO₃ system for...

The widespread occurrence of nitroimidazole antibiotics such as ornidazole (ONZ) in aquatic environments poses considerable ecological and environmental risks, necessitating the development of efficient advanced oxidation processes (AOPs). In this study, a novel ternary heterogeneous catalyst, Co-δ-FeOOH@Cu₂S, was successfully synthesized and employed to activate calcium sulfite (CaSO₃) for efficient ONZ degradation. The Co-δ-FeOOH@Cu₂S/CaSO₃ system could achieve over 98% ONZ removal within 30 min, significantly outperforming individual catalysts and conventional Na₂SO₃-based systems. Its outstanding catalytic performance originated from trimetallic Co-Fe-Cu redox network enables rapid electron shuttling across Co(Ⅲ)/Co(Ⅱ), Fe(Ⅲ)/Fe(Ⅱ), and Cu(Ⅱ)/Cu(I) couples, overcoming sluggish single-metal kinetics. Surface S^2- species serve as an electron-transfer bridge to regenerate low-valent metals, while Co-doping-induced oxygen vacancies accelerate interfacial charge transport, collectively enhancing sulfite activation and reactive oxygen species (ROS) generation. Mechanistic investigations based on radical scavenging experiments and electron paramagnetic resonance analysis demonstrated that both radical SO₄^·-, ·OH, and non-radical O₂1 pathways participated in ONZ degradation. Density functional theory (DFT) calculations identified the imidazole ring and nitroso group as preferential reactive sites for ROS, and the adsorption energy of sulfites on the catalyst. Furthermore, the low solubility of CaSO₃ enabled sustained sulfite release for continuous ROS production while mitigating self-consumption. Toxicity assessment revealed that the degradation process effectively reduced the ecological risks associated with ONZ and its intermediates. Moreover, the catalyst exhibited excellent structural stability, low metal leaching, strong anti-interference capability, and satisfactory reusability over five consecutive cycles. Overall, this study provides an efficient and sustainable strategy for antibiotic-contaminated wastewater treatment via sulfite-based AOPs.