Activation of Na₂S₂O₈by α-Fe₂O₃/CuS composite oxides for the degradation of Orange II under visible light irradiation

Layered α-Fe2O3/CuS nanoflowers with abundant active sites were synthesized by a hydrothermal method. The heterogeneous composite catalyst of α-Fe2O3/CuS nanoflowers exhibited a remarkable degradation capacity of 97.8% within 25 min for the Orange II (OII) dye under visible light, which was attributed to the synergistic effect of Na2S2O8 to generate SO4- and OH radicals. The initial pH tests revealed that this system showed better adaptability for its application in a wider pH range (pH = 3-9). In addition, the degradation of different azo dyes such as methylene blue (MB), Orange G (OG) and malachite green (MG) was also studied under the same conditions. The catalyst was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) to analyze its size, morphology, valence states of elements and chemical components. α-Fe2O3/CuS was further characterized using a vibrating sample magnetometer (VSM) and diffuse reflectance spectroscopy (DRS) to demonstrate its magnetic properties and light absorption capacity. Moreover, α-Fe2O3/CuS showed good recovery and reuse performance as a catalyst after four repeated cycles. A possible mechanism of degradation was proposed by quenching and ESR experiments, which revealed that the highly active species of SO4-, OH and O2- enhanced the photocatalytic performance of the photocatalytic system.