Efficient degradation of Orange G with persulfate activated by recyclable FeMoO₄

In this study, FeMoO₄ was applied to activate persulfate (PS, S₂O₈^2-) for azo dye Orange G (OG) degradation. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption isotherms. FeMoO₄ showed excellent efficiency in activating PS for OG removal. More than 95% could be removed after 40 min under reaction conditions of 4 mM PS, 0.3 g L^-1 FeMoO₄ and 0.2 mM OG. The effect of different parameters (PS doses, FeMoO₄ doses and pH) were evaluated. The results showed that acid condition provided higher efficiency and overdosing FeMoO₄ and PS presented a scavenging effect. Major intermediates were identified and possible degradation pathway was proposed. Recycle tests presented that FeMoO₄ had excellent recyclable stability in activating PS for OG removal. Sulfate radicals and hydroxyl radicals all occurred in the oxidation reactions and the former came first. The oxidation reaction was involved in the translation of Fe²⁺/Fe³⁺ occurred on the surface layer. This study revealed that the FeMoO₄/PS system is a very promising method for degrading organic contaminants in the environment.