The oxidative degradation of diclofenac using the activation of peroxymonosulfate by BiFeO3 microspheres-Kinetics, role of visible light and decay pathways

BiFeO3 (BFO) microspheres were synthesized by a microwave-assisted hydrothermal method for the first time. The as-prepared BFO was comprehensively characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Mossbauer spectroscopy. The synthesized BFO was used to activate peroxymonosulfate (PMS) for the decomposition of diclofenac (DCF) in aqueous solution. DCF degradation was found to follow double-exponential decay kinetics in the BFO/PMS system. The effects of several operating parameters such as pH value, BFO dosage and PMS concentration on DCF degradation by BFO/PMS process were investigated in detail. Visible (Vis) light irradiation was observed to promote the DCF degradation by BFO/PMS process by producing additional sulfate and hydroxyl radicals and accelerating the Fe-III-Fe-II-Fe-III redox cycle. Both sulfate radicals (SO4 center dot-) and hydroxyl radicals ((OH)-O-center dot) were detected in the BFO/PMS system by electron spin resonance (ESR). The reusability of as-prepared BFO microspheres was evaluated in both the BFO/PMS and the Vis/BFO/PMS systems. Nine intermediates were identified during DCF degradation in the BFO/PMS system and DCF decay pathways were proposed accordingly.