Insights into the Removal of Organic Contaminants by Co-CeO₂ Nanocatalysts via CaCO₃ Activation: Performance, Kinetic, and Mechanism

The advanced oxidation process based on S(IV) has garnered increasing attention, owing to its efficiency in degrading contaminants. Here, a cobalt-doped cerium oxide catalyst (Co-CeO₂) was employed to activate calcium sulfite (CaSO₃) for imidacloprid degradation. The Co-CeO₂ catalyst was characterized by using SEM, BET, XRD, and XPS techniques to analyze its structural and chemical properties. XPS analysis revealed the presence of Co⁰, Co²⁺, and Co³⁺ species in the Co-CeO₂ catalyst. Compared to the CeO₂/CaSO₃ system, the Co-CeO₂/CaSO₃ system significantly enhanced the degradation rate of imidacloprid from 5.00% to 94.01%. Scavenging experiments, in conjunction with electron paramagnetic resonance spectroscopy, identified hydroxyl radicals (^•OH), sulfate radicals (SO₄^•-), superoxide radicals (O₂^•-), sulfite radicals (SO₃^•-), and singlet oxygen (¹O₂) as the primary reactive species responsible for the degradation of imidacloprid within the Co-CeO₂/CaSO₃ system. Density functional theory calculation analysis was employed to investigate the specific sites of imidacloprid attacked by reactive oxygen species, proposing four potential degradation pathways. Furthermore, the Ecological Structure Activity Relationships (ECOSAR) program predicted a significant diminution in the toxicity of intermediate products compared to imidacloprid. Even after five cycles, Co-CeO₂ maintained an excellent removal efficiency of 86.35%.