A hierarchical CoFe-layered double hydroxide modified carbon-felt cathode for heterogeneous electro-Fenton process.

Abstract : Hierarchical CoFe-Layered Double Hydroxide (CoFe-LDH) was grown on carbon felt (CF) as heterogeneous catalyst by insitu solvothermal growth. The CoFe-LDH/CF serves as cathode as well as Fe2+ (catalyst) source in electro-Fenton (EF) process. A combined structural and electrochemical characterization revealed highly ordered and well crystallized CoFeLDH anisotropically grown on CF substrate with highly dense urchin-like structures that were highly stable at circumneutral pH. EF experiments with CoFe-LDH/CF cathode showed excellent mineralization of Acid Orange II (AO7) over a wide pH range (2 – 7.1). The mineralization of AO7 with CoFe-LDH/CF was by both homogeneous and surfaced catalyzed process at low acidic pH, whereas only surface catalyzed process occurs at circumneutral pH due to stability of the LDH as well as precipitation of the catalyst. Higher mineralization was achieved with CoFe-LDH/CF compared to homogeneous EF with raw CF using Fe2+/Co2+ catalyst at all pH studied and the TOC removal with CoFe-LDH/CF cathode was at least 1.7 and 3.5 times higher than homogeneous system with Fe2+/Co2+ at pH 5.83 and 7.1 respectively. The enhanced performance observed with CoFe-LDH/CF was ascribed to (i) surface-catalyzed reaction occurring at the surface of the cathode which can expand the working pH window and avoiding the precipitation of iron sludge as pH increases, (ii) enhanced generation of H2O2 due to improved electroactive surface area of the cathode and (iii) co-catalyst effect of the Co2+ in the LDH that can promote regeneration and additional production of Fe2+ and hydroxyl radical, respectively. The CoFe-LDH/CF cathode exhibited relatively good reusability as the TOC removal after 2 h was still above 60% after 7 cycles of degradation, indicating that the prepared CoFe-LDH/CF is a promising cathode for the removal of organic pollutants by EF technology.