Mesoporous cobalt-manganese layered double hydroxides promote the activation of calcium sulfite for degradation and detoxification of metronidazole

Metronidazole (MNZ), a commonly used antibiotic, poses risks to water bodies and human health due to its potential carcinogenic, mutagenic, and genotoxic effects. In this study, mesoporous cobalt-manganese layered double hydroxides (Co_xMn_y-LDH) with abundant oxygen vacancies (O_v) were successfully synthesized using the co-precipitation method and used to activate calcium sulfite (CaSO₃) with slight soluble in water for MNZ degradation. The characterization results revealed that Co₂Mn-LDH had higher specific areas and exhibited good crystallinity. Co₂Mn-LDH/CaSO₃ exhibited the best catalytic performance under optimal conditions, achieving a remarkable MNZ degradation efficiency of up to 98.1 % in only 8 min. Quenching experiments and electron paramagnetic resonance (EPR) tests showed that SO₄^•- and ¹O₂ played pivotal roles in the MNZ degradation process by activated CaSO₃, while the redox cycles of Co²⁺/Co³⁺ and Mn³⁺/Mn⁴⁺ on the catalyst surface accelerated electron transfer, promoting radical generation. Three MNZ degradation routes were put forward based on the density functional theory (DFT) and liquid chromatography-mass spectrometer (LC-MS) analysis. Meanwhile, the toxicity analysis result demonstrated that the toxicity of intermediates post-catalytic reaction was decreased. Furthermore, the Co₂Mn-LDH/CaSO₃ system displayed excellent stability, reusability, and anti-interference capability, and achieved a comparably high removal efficiency across various organic pollutant water bodies. This study provides valuable insights into the development and optimization of effective heterogeneous catalysts for treating antibiotic-contaminated wastewater.