Three-dimensional electro-Fenton degradation of Rhodamine B with efficient Fe-Cu/kaolin particle electrodes: Electrodes optimization, kinetics, influencing factors and mechanism

In this study, Fe-Cu/kaolin particle electrodes were prepared and optimized for Rhodamine B (RhB) degradation in 3-dimensional electro-Fenton (3D/EF) system. Various characterizations, including scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD), demonstrated that Fe and Cu elements were existed in the forms of alpha-Fe2O3 and CuO on kaolin surface, forming Fe-Cu/kaolin particle electrodes. The optimized Fe-Cu/kaolin particle electrodes outperformed kaolin and activated carbon, with a kinetic constant of 0.0503 min(-1), owing to that both Fe and Cu could catalyze Fenton-like reaction in the system. The optimized operational conditions for RhB removal were: particle electrodes dosage of 30 g/L, applied voltage of 10 V, pH of 3, and aeration rate of 0.8 L/min. Notably, RhB removal efficiencies of 91.6% and 81.1% were achieved at initial pH of 6.71 and 9, respectively, indicating that Fe-Cu/kaolin particle electrodes hold great potential for practical application over wide pH range. Also, for RhB mineralization, the 3D/EF system held advantage over 2D system. Comparative experiment and trapping experiment results demonstrated that anode oxidation, particle electrodes oxidation, heterogeneous and homogeneous Fenton-like reactions synergistically contributed to RhB degradation in 3D/EF system with Fe-Cu/kaolin particle electrodes, and possible involved reactions were proposed.