Efficient Degradation of Congo Red by Sodium Persulfate Activated with Zero-Valent Zinc

Zn-0-activated persulfate as a novel and potential approach to the degradation of azo dyes has hardly been reported. In this study, the effects of initial pH, persulfate concentration, Zn-0 dosage, and temperature on the decomposition of Congo red (CR), an azo dye, were investigated. The results demonstrated that Zn-0-activated persulfate could effectively mineralize CR. At the initial pH 5.5 and 25 degrees C, chemical oxygen demand (COD) and total organic carbon (TOC) in the solution with 95 mg/L CR decreased by approximately 87 and 60 %, respectively, within 3 h. The optimum dosages of persulfate and Zn-0 were approximately 95 mg/L and 2 g/L, respectively. The highest decolorization efficiency of CR was realized at the initial pH 5.5. Both center dot OH and SO4-center dot contributed to the degradation of CR, and the spectra of free radicals showed that SO4-center dot was gradually converted to center dot OH with pH increasing from weak acidic to neutral condition.