Synthesis of magnetic Mn/Fe oxides derived from drinking water sludges from a one-pot solvothermal process for the degradation of tetracycline and mixed dyes: synergistic effect and mechanism study

Abstract

The development of low-cost, sustainable, and efficient bimetallic nanocomposites is of remarkable importance but it remains a challenge, particularly as many of these composites tend to be synthesized using multiple steps in time-consuming processes. Herein we present a novel MnO/MnFe2O4 heterostructure loaded onto magnetic drinking water sludge (MF-MDWS) nanocomposite via a simple one-pot solvothermal process and evaluation of its catalytic performance at room temperature for the degradation of tetracycline (TC) and mixed dyes. TC was efficiently mineralized (TOC removal of approx. 49.1%) by PMS/MF-MDWS after 30 min of reaction, with a degradation efficiency of 98.3%. In addition, a synergistic factor and reaction stoichiometric efficiency as high as 73.4% and 4.1%, respectively, under conditions of 0.2 g/L MnO/MnFe2O4/SiO2, 10.0 mg/L TC, and 2.0 mM PMS were obtained over a broad pH range (between 3.1 and 9.0). These findings show that MF-MDWS has a synergistic effect, enhancing the chemical reactivity and stability of the catalyst by restricting the agglomeration of nanoparticles, creating Mn-Fe interactions, and promoting mutual electron transfer between Fe and Mn. It was illustrated that the degrading reaction followed pseudo-first-order kinetics and had a low activation energy of 18.9 kJ/mol. Furthermore, the synergic factor, the reaction stoichiometric efficiency, the specific oxidant efficiency, and the oxidant utilization ratio values for the PMS/MF-MDWS system were 73.4%, 5.7%, 0.03% and 87.5%, respectively. To further investigate the generation of the ROS (1O2> SO4•¯ >•OH) and their decontamination pathways, a series of radical quenching tests and electron paramagnetic resonance (EPR) analysis were carried out. In summary, this study systematically evaluated the performance of the PMS/bimetallic nanocomposite system for TC removal with the aim of treating wastewater as industrial waste, thereby laying a theoretical and practical foundation for the treatment of potential antibiotic/mixed dye wastewater on a large or full scale.