Investigation of manganese-iron oxide nanocomposite immobilized on powdered activated carbon as an efficient activator of peroxymonosulfate for antibiotics degradation: Conjunction of adsorption, radical and nonradical processes

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have gained considerable attention for their efficient oxidation of persistent pollutants. A two-step chemical co-precipitation method was used to prepare a bimetallic nanocomposite (MnOx@Fe3O4) consisting of manganese oxides and ferroferric oxides, supported by powdered activated carbon (PAC). The synthesis of MnOx@Fe3O4-PAC (MFP) was aimed to enhance the degradation efficiency of oxytetracycline (OTC) via the simultaneous adsorption and oxidation processes on the solid-liquid interface. The OTC degradation process in the MFP/PMS system could be well described by pseudo-first-order kinetics. A wide pH range (3-6) was acceptable for MFP to degrade OTC via PMS activation with the highest removal efficiency reaching up to 85.6% (OTC0 = 150 mg/L), while a 60.8% removal efficiency of total organic carbon (TOC) was also attained simultaneously. SO4•- and 1O2, which were bound to the surface, played a crucial role as reactive oxygen species in the degradation of OTC. The combination of PAC, Fe3O4, and MnOx of MFP could enhance the degradation efficiency of OTC and fetch up their defects of separate application. The deduced OTC degradation pathway relied on the findings from UPLC-MS analysis and density functional theory (DFT) calculations. Noteworthy, MFP maintained efficient catalysis performance in the five cycles of stability experiment with neglectable loss of manganese and iron. These results provide valuable understanding of the conjunction of adsorption, radical, and nonradical processes driven by MFP for OTC degradation.