Electrosorption enhanced electro-Fenton process for efficient mineralization of imidacloprid based on mixed-valence iron oxide composite cathode at neutral pH

Abstract

A novel electrosorption enhanced electro-Fenton (ES-EF) method for wastewater treatment was proposed. Mixed-valence iron oxide grown on bulk activated carbon aerogel (FeOx/ACA) was successfully developed as a bifunctional integrated cathode for ES-EF process to purify wastewater. The FeOx/ACA, was prepared firstly by activating carbon aerogel substrate to develop surface area and then controlling Fe(III) reduction to forming the mixed-crystal of Fe2O3 and Fe3O4. The FeOx/ACA was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) techniques. When the composite cathode was applied in an ES-EF system at neutral pH for removing high concentration imidacloprid (237mgL−1), 93% TOC removal was achieved in 150min and the energy consumption removal per unit TOC was only 31% of that in the traditional electro-Fenton with graphite cathode. Results showed that the FeOx/ACA was not only a good electro-Fenton catalyst but also an excellent electrosorption electrode due to its high specific surface area. The electrosorptive ability promoted pollutants mass transfer and H2O2 electrogeneration. The mechanism of synergistic ES-EF degradation was also proposed. Furthermore, it is noteworthy that FeOx/ACA was quite stable and it could be reused without obvious decrease in catalytic activity within 900min, suggesting its potential application for wastewater treatment.