Fe–Mn bimetallic catalyst to activate peroxymonosulfate (PMS) for efficient degradation of tetracycline: Mechanism insights and application for pharmaceutical wastewater

The conventional treatment of pharmaceutical wastewater exhibits expensive costs and inefficiency. In this paper, novel Fe–Mn bimetallic catalysts were synthesized by Mn doped different precursors of morphologies α-Fe2O3 with one pot hydrothermal method, and then activated peroxymonosulfate (PMS) to degrade tetracycline (TC), as a model of medicaments in the water environment. Meanwhile, density functional theory (DFT) calculations confirmed the Fe–Mn bimetallic catalyst was favored for activating PMS. Notably, the treatment rate of TC was 90.7% within 60 min in the FMDS-3 + PMS system. Besides, the FMDS-3 bimetallic catalyst presented excellent repeatability, and its system treatment rate achieved 75% after repeated use nine times. Subsequently, the adsorption energy reached −6.857 eV as FMDS-3 adsorbed PMS, and differential charge density also clearly indicated that electron transfer was more active in the FMDS-3 + PMS system. In further research on the density of states, the electron spin of the FMDS-3 bimetallic catalyst made its characteristic peak closer to the Fermi level, which promoted the adsorption of PMS on its catalyst. The degradation mechanism revealed that SO4•-, •OH, O2•-, 1O2, and e− were involved in the degradation of TC. Then liquid chromatography-mass spectrometry (LC-MS) and toxicity assessment software tools (TEST) confirmed that intermediate product toxicity during TC degradation was much lower than that of TC. Finally, the removal rates of NH3−N, TOC and COD within 100 min in the FMDS-3 + PMS system were 78.5%, 40.5% and 80.4% respectively in the actual pharmaceutical wastewater. The study can provide support for the effective treatment of pharmaceutical wastewater.