Advanced oxidation processes (AOPs) based on sulfate radical (SO4•− ) has been widely concerned for past decades, peroxymonosulfate (PMS) which is more cost-effective than peroxydisulfate (PDS) 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, a natural reductant, sinapic acid (SA), was applied in PMS/Fe(III) system for methyl paraben (MEP) degradation. The addition of SA could enhance the transformation of Fe(III) to Fe(II) and maintain a steady Fe(II) concentration, which further promoted PMS activation. Thus, the removal efficiency of MEP was 100% within 90 min in the modified system, which was 7 times higher than in PMS/Fe(II) system. Meanwhile, SA, containing the groups of hydroxl (-OH) and methoxy (-OCH3 ) on the benzene ring, was oxidized to quinone species. Moreover, the results of electron spin resonance (ESR), quenching experiments and chemical probe detection indicated that SO4•− , HO• and Fe(IV) were responsible for MEP degradation, while SO4•− was the dominant radical. In addition, the effect of varied SA concentration was concerned, and the results suggested that the concentration of Fe(II) and total iron, the degradation rate of MEP, the generation of Fe(IV) and the activation efficiency of PMS were all improved with the increasing of SA concentration, whereas the contribution of HO• for MEP degradation was decreased. Finally, the effect of initial pH and common anions were also investigated. For the effect of coexisting anions, HCO3− and SO42− presented inhibition effect on MEP removal, while there was no difference with Cl− and NO3− addition
