Synergistic metal–carbon interactions in Fe3O4/N-MWCNT composites for electro-Fenton processes

Abstract

This work investigates the performance of graphitic nitrogen-doped multi-walled carbon nanotubes (N-MWCNT) decorated with Fe₃O₄ nanoparticles for the oxygen reduction reaction (ORR) and their application in the degradation of methyl orange (MO) using a heterogeneous electro-Fenton process. The combination of Fe₃O₄ and N-MWCNT enhances electrocatalytic activity through electronic metal-carbon interactions (EMCI), which promote charge transfer and improve electron mobility. Advanced characterization techniques, including TGA, TEM, XRD, Raman, XPS, UV-Vis, and electrochemical analysis, confirm the synergistic effects of combining graphitic N-MWCNT and Fe₃O₄ during a coprecipitation synthesis. DPR analysis reveals that the Fe₃O₄/N-MWCNT composites (MC1 and MC2) undergo a transition from semiconducting to metalloid behavior (thertherezation), supporting the improved electron transfer properties. Raman and XPS analyses further confirm the structural and electronic contributions of graphitic nitrogen in N-MWCNT and Fe₃O₄, reinforcing the composite's enhanced ORR efficiency. TEM and XRD analysis corroborated the anchorage of Fe₃O₄ in the composite, with crystallite particle sizes of 14.7 nm in MC1 and 16.8 nm in MC2. Electrochemical studies indicate that MC1 exhibits the highest electrochemically active surface area (25.1 cm² mg_Fe3O4⁻¹), mass activity (73.66 mA mg_Fe3O4⁻¹), and turnover frequency (0.1768 s⁻¹), indicating an increased number of active sites. Additionally, when composites are used as cathodic materials deposited by electrophoretic deposition (EPD), they effectively degrade 20 ppm of methyl orange at a neutral pH and a current density of 10 mA cm⁻². MC1 achieved the highest degradation efficiency of 97.0% after 120 minutes in an electrode area of 12 cm². This study provides new insights into how metal–carbon interactions at the nanoscale can be leveraged to engineer multifunctional catalysts for next-generation electrochemical systems.