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

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 ^[rad]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, ^[rad]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 C_MO = 50 mg/L, I = 80 mA and F_O2 = 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.