Enhancement of peroxymonosulfate activation by sinapic acid accelerating Fe(III)/Fe(II) cycle

Peroxymonosulfate (PMS) is more cost-effective than peroxydisulfate (PDS) and has drawn great attention presently. Low efficiency of Fe(III)/Fe(II) cycle is a great intrinsic drawback of Fenton-like system, which extremely limits its widespread application. In this study, sinapic acid (SA) as a natural and environmental-friendly reductant, was applied to enhance Fe(III)/Fe(II) cycle in PMS/Fe(III) system. The removal efficiency of methyl paraben (MEP) was 98.3% (7.2 × 10 −4 s −1 ) within 90 min in the modified system, and the k obs was 18 times higher than in PMS/Fe(II) system. For the active species identification, SO 4 − , HO and Fe(Ⅳ) were all responsible for MEP degradation, while SO 4 − was the dominant radical. The role of SA in SA/PMS/Fe(III) system was investigated, Fe(III) was reduced to Fe(II) and SA was oxidized to quinone species in this reaction process. The concentration of Fe(II) and the activation efficiency of PMS were all improved with SA concentration increasing from 5 to 20 μM, and the contribution of active species for MEP degradation were estimated. The effect of initial pH and common anions were also investigated. For the effect of anions, HCO 3 − and SO 4 2− presented inhibition effect on MEP removal, and with the HCO 3 − concentration increasing 1–10 mM the inhibition decreased. Low concentration Cl − promoted MEP degradation while Cl − with higher concentration exhibited inhibition. And NO 3 − was almost no effect on MEP degradation.