Insights into the Removal of Organic Contaminants\nby Co-CeO<sub>2</sub> Nanocatalysts via CaCO<sub>3</sub> Activation:\nPerformance, Kinetic, and Mechanism

The\nadvanced oxidation process based on S(IV) has garnered increasing\nattention, owing to its efficiency in degrading contaminants. Here,\na cobalt-doped cerium oxide catalyst (Co-CeO<sub>2</sub>) was employed\nto activate calcium sulfite (CaSO<sub>3</sub>) for imidacloprid degradation.\nThe Co-CeO<sub>2</sub> catalyst was characterized by using SEM, BET,\nXRD, and XPS techniques to analyze its structural and chemical properties.\nXPS analysis revealed the presence of Co<sup>0</sup>, Co<sup>2+</sup>, and Co<sup>3+</sup> species in the Co-CeO<sub>2</sub> catalyst.\nCompared to the CeO<sub>2</sub>/CaSO<sub>3</sub> system, the Co-CeO<sub>2</sub>/CaSO<sub>3</sub> system significantly enhanced the degradation\nrate of imidacloprid from 5.00% to 94.01%. Scavenging experiments,\nin conjunction with electron paramagnetic resonance spectroscopy,\nidentified hydroxyl radicals (<sup>•</sup>OH), sulfate radicals\n(SO<sub>4</sub><sup>•–</sup>), superoxide radicals (O<sub>2</sub><sup>•–</sup>), sulfite radicals (SO<sub>3</sub><sup>•–</sup>), and singlet oxygen (<sup>1</sup>O<sub>2</sub>) as the primary reactive species responsible for the degradation\nof imidacloprid within the Co-CeO<sub>2</sub>/CaSO<sub>3</sub> system.\nDensity functional theory calculation analysis was employed to investigate\nthe specific sites of imidacloprid attacked by reactive oxygen species,\nproposing four potential degradation pathways. Furthermore, the Ecological\nStructure Activity Relationships (ECOSAR) program predicted a significant\ndiminution in the toxicity of intermediate products compared to imidacloprid.\nEven after five cycles, Co-CeO<sub>2</sub> maintained an excellent\nremoval efficiency of 86.35%.