Fe-Mn MOF-derived modified carbon felt cathode: Accelerating iron redox cycle for efficient electro-Fenton degradation of nanoplastics.

Micro/nano plastics (M/NPs), as enduring worldwide environmental contaminants, present significant risks to aquatic ecosystems and human health. The electro-Fenton process demonstrates significant application potential; however, traditional electro-Fenton systems are hindered by sluggish Fe3 +/Fe2+ redox cycling, inadequate electrical conductivity, and restricted pH tolerance. This study fabricates a stable Fe/Mn-MOF-derived modified carbon felt (FeMn@CF-600) and employs it as the cathode for heterogeneous electro-Fenton process. Manganese doping endows it with abundant micropores and more exposed active sites, which facilitates the mass‑transfer process. Meanwhile, it can accelerate the electron transfer from carbon atoms in carbon materials to iron elements during calcination, thereby increasing the content of low‑valence iron in the material. High‑temperature calcination is adopted to construct metal oxide‑porous carbon composite materials, improving the conductivity and stability of electrodes. Such bimetallic synergy accelerates Fe3+/Fe2+ and Mn3+/Mn2+ redox cycling, boosting ·OH generation. As a result, Fe/Mn@CF exhibits significantly enhanced catalytic activity in comparison to the Fe@CF. At a pH of 6.8 and a current intensity of 40 mA, the removal efficiency and mineralisation rate of polystyrene nanoplastics (PS NPs) reached 81.5% and 26.45%, respectively. The degradation pathway and reaction mechanism of PS NPs were proposed based on density functional theory (DFT) calculations and the identification of degradation intermediates. Metal leaching tests and cycling experiments verify the outstanding reusability of the electrode, which retains high degradation performance in tap water and lake water. The results indicate that Fe/Mn@CF-600 possesses significant practical applications and shows considerable potential in water treatment.