Electron shuttling catalytic effect of mellitic acid in zero-valent iron induced oxidative degradation
By Kang, Seung-Hee; Bokare, Alok D.; Park, Yiseul; Choi, Chi Hun; Choi, Wonyong
Published in Catalysis Today
2017
Abstract
Abstract The enhanced oxidation capacity of zero-valent iron (ZVI) using mellitic acid (MA) as an electron shuttle catalyst was investigated using 4-chlorophenol (4-CP) as a model pollutant. In the presence of MA, enhanced electron transfer from {ZVI} surface to molecular oxygen resulted in higher production of hydrogen peroxide (H2O2), which subsequently increased the effective concentration of hydroxyl radical (HO) generated through the Fenton-type reaction. The possible role of {MA} as an efficient electron shuttle was supported by cyclic voltammetric estimation of {MA} reduction potential (E0 = ?0.184 VNHE) and corroborated with photocurrent measurements in the {ZVI} suspension. Control experiments using Fe(II) ions instead of {ZVI} demonstrated that the presence of {MA} in the Fe(II)/H2O2 homogeneous system had no significant effect on the 4-CP oxidation efficiency. This indicates that the formation of a Fe(II)-MA complex does not contribute to the 4-CP oxidation pathway. The primary role of {MA} in the ZVI/O2 system seems to mediate the electron transfer from the {ZVI} surface to dioxygen. It implies that organic species containing multiple carboxylic ligands (species like {MA} or its structural analogues) may function as an electron shuttle in the ZVI/O2 catalytic system.