Radical induced degradation of acetaminophen with Fe₃O₄ magnetic nanoparticles as heterogeneous activator of peroxymonosulfate

Magnetic nano-scaled particles Fe₃O₄ were studied for the activation of peroxymonosulfate (PMS) to generate active radicals for degradation of acetaminophen (APAP) in water. The Fe₃O₄ MNPs were found to effectively catalyze PMS for removal of APAP, and the reactions well followed a pseudo-first-order kinetics pattern (R²>0.95). Within 120min, approximately 75% of 10ppm APAP was accomplished by 0.2mM PMS in the presence of 0.8g/L Fe₃O₄ MNPs with little Fe³⁺ leaching (<4μg/L). Higher Fe₃O₄ MNP dose, lower initial APAP concentration, neutral pH, and higher reaction temperature favored the APAP degradation. The production of sulfate radicals and hydroxyl radicals was validated through two ways: (1) indirectly from the scavenging tests with scavenging agents, tert-butyl alcohol (TBA) and ethanol (EtOH); (2) directly from the electron paramagnetic resonance (ESR) tests with 0.1M 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO). Plausible mechanisms on the radical generation from Fe₃O₄ MNP activation of PMS are proposed based on the results of radical identification tests and XPS analysis. It appeared that Fe²⁺Fe³⁺ on the catalyst surface was responsible for the radical generation. The results demonstrated that Fe₃O₄ MNPs activated PMS is a promising technology for water pollution caused by contaminants such as pharmaceuticals.