Reducing agents enhanced Fenton-like oxidation (Fe(III)/Peroxydisulfate): Substrate specific reactivity of reactive oxygen species.

Reduction of Fe(III) is the rate-limiting step of iron induced Fenton-like systems, such as the iron/peroxydisulfate system, reducing agents (RAs) were frequently employed as electron donors to directly reduce Fe(III) to further promote the formation of reactive oxygen species (ROS), mainly including hydroxyl radical (•OH), sulfate radical (SO4•-), and ferryl ion (Fe(IV)). However, the intrinsic distinctions among these ROS cause the substrate specific reactivity towards oxidation of diverse organic contaminants. In this study, various RAs (representative solid amorphous boron (A-Boron) and dissolved hydroxylamine (HA)) were added to enhance the Fe(III)/PDS system for investigating the substrate specific reactivity of ROS. It is demonstrated that RAs remarkably boost the Fe(III)/Fe(II) cycles to produce •OH, SO4•-, and Fe(IV) in the RAs/Fe(III)/PDS systems, based on the results of EPR analysis, quenching tests, and chemical probe analysis. Furthermore, the different yields of methyl phenyl sulfone (PMSO2) indicate that the distribution of multiple oxidizing species changed with various factors (i.e., type and dosage of RAs added, solution pH, Fe(III) and PDS dosage). This work provides the possibility for the adjustment of oxidation selectivity of RAs/Fe(III)/PDS systems by regulating contribution of radicals and non-radical for oxidizing organic contaminants due to the substrate specific reactivity of •OH, SO4•-, and Fe(IV), moreover, the comparison of homogeneous and heterogeneous RAs provides assistance in the application of RAs for environmental remediation.