The capacity and mechanisms of various oxidants on regulating the redox function of ZVI

It is well known that zero-valent iron (ZVI) could catalyze the oxidation of various oxidants to realize the rapid oxidation removal of pollutants. However, in this study, we found that the addition of different oxidants could regulate the redox function of ZVI system. In three different co-treatment systems, the effects of different oxidizers (peroxymonosulfate (PMS), persulfate (PDS), hydrogen peroxide (H2O2)) dosages on the ratios of oxidative degradation rate and reductive degradation rate of p-nitrophenol (PNP) were studied. The effect of the H+ released from oxidizers and the generated reactive oxygen species (ROS) in ZVI/PMS, ZVI/PDS, ZVI/H2O2 systems were detailed discussed. Especially, the contribution of generated ROS for reductive degradation of PNP was quantified in the ZVI/H2O2 system. Based on the results of TOC removal, UV-vis absorption spectra, and intermediates concentration curves, it was found that the degradation of PNP changed from reduction to oxidation with the increase of oxidant proportion. When the molar ratio of ZVI to oxidizer equal to 100, PNP was mainly degraded by reduction accompanied by slight oxidation. Combined with the results of SEM-EDS and XPS, it was confirmed that the enhanced degradation of PNP under the addition of oxidant was mainly related to the generated ROS, the additional Fr, and the corrosion products of ZVI. (C) 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

The study revealed that the addition of different oxidants could regulate the redox function of zero-valent iron (ZVI) system, affecting the degradation ratios of oxidative and reductive degradation of p-nitrophenol (PNP). When the molar ratio of ZVI to oxidizer was 100, PNP degradation mainly occurred through reduction, with the generated reactive oxygen species (ROS) playing a key role in the enhancement of degradation.