Elucidating Visible-Light Photocatalytic Degradation of Organophosphorus Residues Over Reduced Graphene Oxide/Iron-Manganese Mixed Oxides Composite

Abstract

In this work, a ternary Fe₂O₃/Mn₂O₃/reduced graphene oxide (FM/rGO) composite was prepared via a rapid microwave-assisted coprecipitation method. The engineered composite exhibited exceptional visible-light-driven photocatalytic activity as compared to both single Fe₂O₃ and Fe₂O₃/Mn₂O₃ (FM) heterojunction, achieving nearly complete degradation of parathion, a resistant organophosphorus pollutant, within 60 min accompanied by a remarkable mineralization (∼86% TOC removal). Kinetic analysis confirmed that the degradation complies with a pseudo-first-order model with a significant rate of 0.0597 min⁻¹. Comprehensive photoelectrochemical measurements revealed that the Type-I FM heterojunction and the highly conductive rGO network facilitate efficient charge transfer. Interestingly, the coexistence of mixed-valence transition metals (Fe³⁺/Fe²⁺ and Mn³⁺/Mn²⁺) alongside a high density of π bonds in rGO carriers served as dynamic electron traps, effectively accelerating spatial charge separation and suppressing electron-hole recombination. Radical scavenging and GC-MS analyses identified critical roles of hydroxyl radicals (•OH) for the P─O–aryl bond cleavage. Furthermore, the FM/rGO composite demonstrated practical magnetic recoverability and outstanding cyclic stability, providing a robust and highly efficient photocatalytic platform for hazardous pollutant remediation.