Trace catechin enhanced degradation of organic pollutants with activated peroxymonosulfate: Comprehensive identification of working oxidizing species

Abstract

Peroxymonosulfate (PMS), which served as a precursor of Reactive oxygen species (ROS) in the advanced oxidation processes has drawn increasing attention in the past few decades. Iron ions activation method is one of the most popular way for PMS activation. In this study, catechin (CAT), a typical green tea extract polyphenol, was introduced into the PMS/Fe(III) system, and a remarkable enhancement in contaminant removal was observed. The ofloxacin (OFL) degradation rate were 100% and 30% after 60 min reaction with and without CAT. It was principally because CAT was an effective natural antioxidant and chelating agent, which could reduce Fe(III) to Fe(II). The OFL degradation rate was increased by the accelerating activation of PMS by Fe(II). ROS was fully identified. Sulfate radicals (SO4•−) were the predominant ROS, whereas hydroxyl (HO•) and superoxide anion (O2•−) radicals hardly existed at the experiment conditions. Singlet oxygen (1O2) was produced but did not contribute to the degradation of contaminants. The existence of Fe(IV) was also considered, which contributed to the degradation of OFL. The effects of the influencing factors, including concentrations of CAT, Fe(III), PMS, pH and coexisting anions, on OFL degradation in PMS/Fe(III)/CAT system were also investigated. The optimum ratio of CAT to Fe(III) was 1:2, and a circumneutral pH was more favorable for this system. Coexisting anions, such as NO3− and SO42− did not affect the removal of OFL, but the degradation of OFL was totally inhibited by HCO3− and HPO42−.