Cogeneration of H2O2 and [rad]OH via a novel Fe3O4/MWCNTs composite cathode in a dual-compartment electro-Fenton membrane reactor

Abstract

A dual-compartment electro-Fenton (EF) membrane reactor coupled with a high-catalytic efficiency gas diffusion electrode (GDE) was developed, which can simultaneously produce H2O2 and OH in situ without any addition of chemicals. The magnetite/multiwalled carbon nanotubes (Fe3O4/MWCNTs) nanocomposites were synthesized by a facile one-step solvothermal reduction method and then mixed with carbon black (CB) and polytetrafluoroethylene (PTFE) to construct a novel GDE. On the gas-liquid-solid interface of the electrode, H2O2 was produced through oxygen reduction reaction due to the presence of CB. Further, OH was generated by heterogeneous Fenton reaction of H2O2 with the active site of ≡Fe(II) on the surface of Fe3O4/MWCNTs. Taking advantage of the high-speed charge channel of MWCNTs, the redox cycling between ≡Fe(II) and ≡Fe(III) could be accelerated; thus, the Fe3O4/MWCNTs-based cathode exhibited a methyl orange (MO) degradation efficiency that was 1.4 times higher than that of Fe3O4. More importantly, a high removal efficiency of 90.3% at pH = 3 and of 52.6% under neutral conditions could be obtained (working conditions CMO = 50 mg/L, I = 80 mA and FO2 = 10 mL/min). These results demonstrated the potential of the Fe3O4/MWCNTs composite cathode for the treatment of wastewater by the heterogeneous EF process over a wide applicable pH range.