Mechanism of contaminants degradation in aqueous solution by persulfate in different Fe(II)-based synergistic activation environments: Taking chlorinated organic compounds and benzene series as the targets

Abstract

In this study, trichloroethene (TCE) removal was remarkably enhanced with the addition of Fe(II)/CA (citric acid), Fe(II)/nZVI (nano zero-valent iron) and Fe(II)/S-nZVI (sulfidated nano zero-valent iron), respectively, as synergistic activated catalysts in persulfate environment. Among them, the better performance of TCE removal followed the order of PS/Fe(II)/S-nZVI > PS/Fe(II)/nZVI > PS/Fe(II)/CA ≫ PS/Fe(II), and the majority of TCE was declorinated to Cl−. The scavenger and EPR tests indicated that HO and SO4− were responsible for TCE degradation. Further study was conducted through the calculation of reaction rate constants, demonstrating HO produced from SO4− was of greater significance than SO4− itself. With the presence of CA, the concentration of Fe(II) was maintained at a desired level to proceed the catalytic activity. Meanwhile, S-nZVI and nZVI had ability to convert Fe(III) to Fe(II), and sulfur species, especially S(-II) in S-nZVI acted as an reductant to a certain extent. Sufficient Fe(II) in solution activated PS to produce adequate HO for TCE degradation. Furthermore, the broad-spectrum reactivity in different systems were investigated, and the results indicated that most of the chloroalkenes and benzene series frequently detected in contaminated sites could also be removed at the desired chemicals ratio. In conclusion, this research revealed the superiority of synergistic activated catalysts and provided theoretical bases for the remediation of TCE and other pollutants in actual contaminated groundwater.