Degradation of aqueous organic pollutants using an Fe₂O₃/WO₃ composite photocatalyst as a magnetically separable peroxymonosulfate activator

Developing a cost-effective method for the separation and recovery of nanomaterials for water treatment is challenging due to the significantly high recovery cost associated with nanomaterial-based water treatment processes. In this study, we synthesized magnetically separable iron oxide/tungsten oxide (Fe₂O₃/WO₃) composites through a chemical co-precipitation method and employed them as peroxymonosulfate (PMS) activators for the degradation of organic pollutants under visible light. Electron spin resonance analysis, chemical quenching, and photoluminescence analysis suggested that hydroxyl radicals, sulfate radicals, and valence band holes contribute to the degradation processes in the Fe₂O₃/WO₃/PMS system under visible light. The results of the degradation and recovery experiments based on the mass ratio of WO₃ to Fe₂O₃ ([WO₃]:[Fe₂O₃]) in the Fe₂O₃/WO₃ composite indicated that the Fe₂O₃/WO₃ composite with [WO₃]:[Fe₂O₃] = 2:1, which can be completely recovered using a magnet (magnetic flux density = 2500 G), is the optimal photocatalyst for PMS activation. The effects of reaction parameters, such as the PMS concentration, Fe₂O₃/WO₃ dosage, solution pH, and background anions (chloride, carbonate, nitrate, and phosphate)/humic acid, on the degradation kinetics were investigated and discussed. Under visible light irradiation, the Fe₂O₃/WO₃/PMS system efficiently degraded various organic pollutants, including 4-chlorophenol, 2-chlorophenol, 4-bromophenol, 4-methylphenol, 2,4-dimethylphenol, bisphenol A, tryptophan, sulfamethoxazole, sulfisoxazole, and furfuryl alcohol. In addition, the complete degradation of 4-chlorophenol in the Fe₂O₃/WO₃/PMS system under visible light was achieved for up to five degradation cycles when Fe₂O₃/WO₃ was reused after recovery using a magnet.