Cogeneration of H2O2 and •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 (OH)-O-center dot 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 polytetra-fluoroethylene (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)-O-center dot was generated by heterogeneous Fenton reaction of H2O2 with the active site of equivalent to Fe(II) on the surface of Fe3O4/MWCNTs. Taking advantage of the high-speed charge channel of MWCNTs, the redox cycling between equivalent to Fe(II) and equivalent to 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.