Nitrogen-doped graphitic layer confined MOF-based composite cathode for electro-Fenton catalysis with enhanced sustainability

Low H₂O₂ yield and rapid corrosion of cathode are widely regarded as long-standing drawbacks that hamper service life of heterogeneous electro-Fenton (EF) for long-term operation. This study developed a multifunctional cathode based on nitrogen-doped reduced graphene oxide (NrGO) encapsulated iron metal–organic framework (MOF) as a robust and sustainable EF system for removing unwanted water impurities. Among the MOF catalysts, the iron MOF derivative obtained via thermolysis at 400 °C exhibited the best performance in terms of cost-efficiency and durability. Further incorporation of NrGO on the cathode could help improve charge transfer and direct O₂ reduction toward the 2e^- transformation pathway for improved H₂O₂ selectivity (∼80 %). Additionally, NrGO acted as a protection layer to minimize the abrupt leaching of iron catalysts to the solution, thus elongating the lifespan of the EF system. Using tetracycline (TC) as the probe pollutant, the developed EF system maintains the consistent removal performance of TC (∼82.5 %) across at least 8 consecutive cycles. The developed system also proved to be reliable for different types of micropollutants, anions, and natural organic matter (NOM). pH was identified as a critical factor that governs TC removal by the developed EF system. Compared to anodic oxidation (∼30 %), the main degradation mechanism was radical oxidation, which was governed by ·OH, ¹O₂, and ·O₂⁻. Nonetheless, the ·O₂⁻ radical likely serves as an intermediate for maintaining the redox cycle in the EF system rather than directly participating in degradation. Our study sheds a light on the potential application of a novel iron MOF-based EF system aided by NrGO for water treatment with superior stability.