Three-dimensional electro-Fenton oxidation of N-heterocyclic compounds with a novel catalytic particle electrode: high activity, wide pH range and catalytic mechanism

Abstract

A novel three-dimensional (3D) heterogeneous electro-Fenton (EF) system with sludge deserved activated carbon from sewage and iron sludge (SAC-Fe) as catalytic particle electrodes (CPEs) was constructed in this study. Its application in degrading nitrogen-heterocyclic compounds (NHCs) exhibited high catalytic efficiency over a wide applicable pH range from 3.0 to 9.0. SAC-Fe worked as both CPEs and a heterogeneous catalyst in this 3D EF system, enhancing oxidation activity. Degradation pathways of the NHCs (indole, quinoline and pyridine) and reasonable reaction mechanisms involved in this 3D EF were proposed. At pH 3.0, hydroxyl radicals were the dominant participant oxidants, following a Haber-Weiss mechanism. The FeII sites catalyzed the decomposition of electro-generated H2O2 to yield and z.rad;OH. At pH 9.0, the oxidants generated from the decomposition of H2O2 were mainly andz.rad;O2-/HO2and z.rad; and to lesser extent were and z.rad;OH. The formation and decomposition of H2O2 complex with catalytic sites (FeII and FeIII) as well as the catalytic decomposition of H2O2 were involved in the catalytic reactions to generate and z.rad;O2-/HO2and z.rad; and and z.rad;OH. A quantitative structure-activity relationship analysis (QSAR) model was developed to describe the relationship between degradation properties of NHCs and their structures by involving quantum descriptors.