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 Fe 3 O 4 @Fe 2 O 3 /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   m 2   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 Fe 3 O 4 @Fe 2 O 3 /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 H 2 O 2 to generate hydroxyl radicals ( OH). While at pH 9, it was expected the formation and deactivation of H 2 O 2 complex as well as the catalytic decomposition of H 2 O 2 with surface Fe(III) and Fe(II) sites to produce both superoxide anion ( O 2 − /HO 2 ) and hydroxyl radicals ( OH), involving an in situ recycling of iron oxide (FeO·Fe 2 O 3   →   Fe 2 O 3 ).