Application of Cu5.5Fe1 catalyst from fluidized-bed crystallization reactor for treatment of RB5 azo dye using a Fenton-like system

This work investigates the potential of repurposing a by-product from wastewater treatment as a catalyst in a heterogeneous photo-Fenton-like system for removing a model organic dye. A bimetallic Fe-Cu catalyst was employed to facilitate a heterogeneous Fenton-like reaction under visible light irradiation. Key variables—such as solution pH, catalyst loading, hydrogen peroxide dosage, initial dye concentration, and light exposure—were systematically optimized. The best performance was observed at pH 6.5 with 2 g/L catalyst and 80 % of the theoretical H₂O₂ requirement, resulting in almost complete decolorization of Reactive Black 5 (RB5) within 60 min and a mineralization rate of 96.9 %. Electron spin resonance (ESR) analysis, employing DMPO and TEMP as spin-trapping agents, confirmed the generation of hydroxyl radicals (•OH), superoxide anions (•O₂⁻), and singlet oxygen (¹O₂) during the process. This study highlights the efficiency of a catalyst derived from industrial wastewater containing Fe and Cu, demonstrating superior performance compared to catalysts produced from commercial precursors. The findings support the circular economy concept by turning hazardous waste into a valuable resource for environmental remediation.