Activation of K2S2O8 by Ni–Ce composite oxides for the degradation of orange II with visible light assistance

Abstract NiO and CeO2 composite metal oxides (NiO–CeO2) were synthesized by sol-gel method to investigate a degradation system by persulfate (PS) activation with the assistance of visible light (Vis). The phase composition of NiO–CeO2 was detected by X-ray diffraction (XRD), the morphology of NiO–CeO2 was characterized by scanning electron microscope (SEM), and the result of X-ray photoelectron spectroscopy (XPS) proved the element composition and valence state of the NiO–CeO2. In the Vis/PS/NiO–CeO2 system, the degradation rate of Orange II using a concentration of 50 mg/L was as high as 90% in 15 min but it increased to as high as 99% in 60 min. Mechanism studies have shown that the combination of NiO and CeO2 generated more oxygen vacancies, and activated persulfate to generate active oxygen species. Moreover, the effects of visible light, persulfate concentration and pH were evaluated, and the results showed that the participation of visible light and persulfate could significantly increase the degradation efficiency of Orange II, but pH had little effect on the degradation. Quenching experiments and detection by ESR showed that O2‾, •SO4‾, •OH, and 1O2 all contribute to the removal of Orange II. In addition, the recovery and reuse properties of NiO–CeO2 may lead to sustainable treatment of wastewater.