Embedding Fe/Fe3O4 Heterojunctions in Nitrogen-Doped Carbon Nanotubes for Efficient Removal of Organic Pollutants via Heterogeneous Electro-Fenton Catalysis

The electro-Fenton process is considered one of the most reliable techniques for eliminating organic pollutants from water. However, its performance is still not up to par with its potential due to the lack of cathodic catalysts with the essential cycling catalytic functionality required for sustained Fenton reactions. Herein, Fe and Fe₃O₄ heterojunctions embedded in N-doped carbon nanotubes stitched on porous nitrogen-doped carbon (denoted Fe/Fe₃O₄@PNC) are fabricated and employed as a bifunctional cathode catalyst for the highly efficient degradation of organic pollutants. The N-doped carbon with rich pyridinic-N sites enables in situ generation of H₂O₂ via a two-electron oxygen reduction reaction (ORR), while Fe/Fe₃O₄ heterojunctions with multivalent states promote the cycling efficiency of Fe³⁺/Fe²⁺ for activating H₂O₂ to produce reactive oxidative species (ROS) of ^•O₂^- and ¹O₂. Benefitting from the synergistic effects between Fe/Fe₃O₄ heterojunctions and N-doped carbon nanotubes, along with abundant mass transfer channels and rapid Fe³⁺/Fe²⁺ cycling, Fe/Fe₃O₄@PNC, as a heterogeneous cathode electrocatalyst, displays superior catalytic activity, achieving a favorable organic pollutant removal efficiency of 98.72% within 1 h. This study provides a feasible way to the rational design of Fe-based heterojunction cathode materials for an efficient electro-Fenton process.