Electro-Fenton oxidation of pesticides with a novel Fe3O4@Fe2O3/activated carbon aerogel cathode: High activity, wide pH range and catalytic mechanism

A novel electro-Fenton (E-Fenton) system with the Fe3O4@Fe2O3/activated carbon aerogel (ACA) composite cathode was firstly constructed in this study. Its application on degrading imidacloprid exhibited highly catalytic efficiency over a wide applicable pH range from 3 to 9. The removal of imidacloprid and TOC achieved to 90% within 30 and 60 min, respectively. The nature of composite cathode was examined by BJH, XRD, SEM, TEM, XPS and FTIR techniques. ACA with high surface area of 2410 m2 g−1 and multiplicated porosities composed of micropores and mesopores worked not only as cathode but also as Fenton catalyst support, enhancing oxidation activity. We proposed reasonable E-Fenton oxidation mechanisms with Fe3O4@Fe2O3/ACA cathode at acidic and basic conditions. At pH 3, it followed a Haber–Weiss mechanism that the dissolved iron ions and surface Fe(II) sites catalyzed the decomposition of H2O2 to generate hydroxyl radicals (OH). While at pH 9, it was expected the formation and deactivation of H2O2 complex as well as the catalytic decomposition of H2O2 with surface Fe(III) and Fe(II) sites to produce both superoxide anion (O2−/HO2) and hydroxyl radicals (OH), involving an in situ recycling of iron oxide (FeO·Fe2O3 → Fe2O3).