Reusable catalytic membrane of defect engineered nitrogen-doped expanded graphite as a metal-free peroxydisulfate...

Carbon-based catalysts typically rely on graphitized structures, heteroatom doping, and defect sites as active centers, but are often limited by complex synthesis procedures and high preparation costs. Expanded graphite (EG), a low-cost carbon material with widespread industrial applications, is typically considered to have catalytic inertness, leaving its intrinsic capability for peroxydisulfate (PDS) activation insufficiently explored. Herein, a series of nitrogen-doped expanded graphite catalysts (NGIC-x) were synthesized at 350 °C using different nitrogen precursors for PDS-driven bisphenol A oxidation. Among them, the NGIC-C₃H₆N₆/PDS system achieved complete removal of bisphenol A (BPA, 100%) within 25 min and exhibited robust performance over a wide pH range. The superior activity of NGIC-C₃H₆N₆ is attributed to the abundant defects in the sp² carbon network (I_D/I_G = 1.83), pyridinic and graphitic nitrogen species, and oxygen-containing functional groups (e.g., C=O, C-O, O-C=O), which collectively facilitate PDS adsorption and activation. Radical scavenging experiments and electron paramagnetic resonance (EPR) analysis reveal that ^•O₂^-, SO₄^•-, ^•OH, and ¹O₂, jointly contribute to BPA degradation. Furthermore, integrating NGIC-C₃H₆N₆ into a mixed cellulose ester (MCE)-based catalytic membrane enables continuous BPA removal and affords high catalytic durability over at least four consecutive reuse cycles. This work provides a facile and energy-efficient strategy for constructing defect-engineered N-doped expanded graphite catalysts toward persulfate-based advanced oxidation processes.