Environmentally-friendly rGO/Mn nanocomposites for efficient removal of tetracycline and its degradation pathway

Since the widespread use of antibiotics, the residues of antibiotics have frequently been detected in various water sources, making antibiotic pollution an urgent environmental issue. In this paper, one-step green synthetic reduced graphene/manganese nanoparticles (rGO/Mn NPs) composites have been utilized as a novel environmentally-friendly catalyst for tetracycline (TC) removal. The results demonstrated that rGO/Mn NPs exhibit excellent adsorption performance for TC, and can efficiently activate sodium persulfate (PDS) to oxidize and degrade TC. Furthermore, the rGO/Mn NPs adsorption-oxidation system (85.2%) was more effective than the adsorption process (70.9%) in removing TC (50 mg L^-1). Free radical quenching experiments and EPR results elucidated that singlet oxygen (¹O₂) and superoxide radicals (·O₂^-) are the primary reactive species responsible for the degradation of TC in the oxidation system. Based on the characterization results, a mechanism of oxidative degradation of TC by rGO/Mn NPs has been proposed. To further elucidate the degradation pathway of TC, the degradation products were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS). This analysis provides a foundation for understanding how the rGO/Mn NPs composites activate PDS to degrade TC. Additionally, the ecological structure-activity relationship analysis revealed that TC is converted into intermediates with lower toxicity.