Degradation mechanism of acid orange II in persulfate/Fe-based metallic glass system

Fe-based metallic glasses (MGs) not only are an industrially produced amorphous zero-valent iron (AZVI) with a promising reductive degradability to azo dyes but also can activate persulfate (PS) with sulfate radicals (SO4 center dot-, Eo = 2.5-3.1V) for wastewater remediation. In this study, acid orange II (AOII) was rapidly and efficiently decolored by Fe78Si8B14 MG/PS system with a 99% degradation rate in 8 min. Based on monitoring the degradation rate and the concentration of Fe2+/Fe3+, a two-step degradation mechanism is proposed, that one is deductive degradation by AZVI with products of small organic molecules and Fe2+, and the other is oxidative degradation, where AZVI and Fe2+ activate PS with products of SO4 center dot- and center dot OH confirmed by the electron spin resonance (ESR) analysis test. The orthogonal experimental design proves that the effects of the experiment operating parameters on the decolorization efficiency from high to low are Fe-based MGs dosage, PS dosage, and reaction temperature. Meanwhile, the high efficiency of the Fe-based MGs/PS system is also illustrated for the mineralization of AOII by an indication of the TOC removal rate as high as 57%. This work gives new insight into Fe-based MGs for activating PS and will accelerate the application of Fe-based MGs as catalysts in the field of wastewater treatment.