Efficient heterogeneous activation of peroxymonosulfate by manganese-doped LaCoO3 perovskites for metronidazole degradation: A mechanistic study and reaction pathways

Abstract

Herein, manganese-doped perovskites LaCo1−xMnxO3 (x = 0, 0.05, 0.1, and 0.2) were synthesized by the so-gel process to dominantly activate PMS for Metronidazole (2-methyl-5-nitroimidazole-1-ethanol (MNZ) degradation. The results revealed that the MNZ degradation rate under the LaCo0.8Mno.2O3/PMS system reached 99.42 % in 30 min with a rate constant of 0.1616 min−1, which is significantly higher than the LaCoO3/PMS system under optimal reaction conditions (LaCo0.8Mn0.2O3 = 0.4 g/L, [PMS] = 0.4 mM, [MNZ] = 15 mg/L, pH = 7, T = 25 ± 2 °C). LaCo0.8Mn0.2O3 has demonstrated a higher surface area (44.35 m2g−1) as compared to pristine LaCoO3 (7.89 m2g−1), suggesting that Mn doping remarkably improves the catalytic activity and provides more active sites to the LaCo0.8Mn0.2O3/PMS to increase MNZ degradation efficiency. Meanwhile, the impact of various influencing factors and associated anions on MNZ degradation was examined. On the surface of LaCo0.8Mn0.2O3, photogenerated electrons and the conversion of Co2+/Mn3+ to Co3+/Mn4+ both played a part in PMS activation for MNZ degradation. The changes in valence states of elements were further corroborated through XPS analysis, which confirmed the potential application of the LaCo0.8Mn0.2O3 catalyst in MNZ degradation process. The generation of SO4•−,HO•, and 1O2 was confirmed through radical quenching studies and further validated by EPR measurements. It is evident from results that SO4•−, contributed significantly towards the degradation of MNZ along with minor role of HO•, and 1O2. This study presents insight into the improvement of new perovskite catalysts for the elimination of organic pollutants in water.