Mechanistic insights into the reactive radicals-assisted degradation of sulfamethoxazole via calcium peroxide activation by manganese-incorporated iron oxide–graphene nanocomposite: Formation of radicals and degradation pathway

In this study, fabrication of manganese-incorporated iron oxide-graphene nanocomposite (rGO-FMBO) was reported for the efficient activation of CaO 2 and generation of reactive radicals for the degradation of sulfamethoxazole (SMX). The effects of different systems, catalyst dosage, oxidant dosage, different pH and different reaction time on the degradation of SMX by rGO-APTMS-FMBO/CaO 2 as well as the production of free radicals were also studied. Electron paramagnetic resonance (EPR) technique was used to detect and identify the radical species in this oxidation system and these radicals were further confirmed by scavenging studies with the addition of isopropanol (IPA) and methyl viologen (MV 2+ ). The results indicated that the CaO 2 could be activated by rGO-APTMS-FMBO efficiently for the effective degradation of SMX at neutral pH ( P  ≤ 0.01). The mechanism of the activation of CaO 2 by rGO-APTMS-FMBO was that carbon dioxide radicals (CO 2 − ) generated by rGO-APTMS-FMBO could activate the CaO 2 to produce more hydroxyl radicals (HO ), which favored the SMX degradation. EPR studies showed that three types of free radicals HO , CO 2 − , and CH 3 were generated and the radical intensities were much higher in rGO-APTMS-FMBO/CaO 2 system. Both increased pH and reaction time led to the production of more CO 2 − , which activated the CaO 2 to give more HO to degrade SMX. Transformation products/intermediates of SMX were determined and potential mechanism and degradation pathway were proposed. The findings of this study provide new insights into the mechanism of heterogeneous catalysis based on CaO 2 activated by rGO-APTMS-FMBO and the reactivity of this oxidation system toward environmental contaminants.