Ionic liquid grafted PVDF membrane incorporating g-C3N4–Fe3O4 for selective cationic dye removal and antibiofouling performance

The development of multifunctional membranes with tunable surface charge, high permeability, and fouling resistance remains a critical challenge in wastewater treatment. In this study, a poly(vinylimidazolium)-functionalized PVDF membrane incorporating g-C ₃ N ₄ –Fe ₃ O ₄ was fabricated via surface activation, composite deposition, and free-radical graft polymerization, followed by hydroxide anion exchange to tailor surface charge characteristics. The engineered membrane exhibited significantly enhanced hydrophilicity and high water permeability (109 L m ^-2 h ^-1 ), representing a 25-fold improvement over pristine PVDF. Owing to its negatively charged surface, the membrane achieved 97% removal of methylene blue and 70% rejection of methyl orange at 20 ppm, demonstrating charge-selective separation behavior. Adsorption kinetics followed a pseudo-second-order model and conformed to the Freundlich isotherm, indicating heterogeneous electrostatic and π–π interactions as the dominant removal mechanism. Compared to photocatalytic degradation, adsorption driven by ionic liquid functionalization played the primary role in dye removal. Furthermore, the membrane showed excellent antibiofouling performance with complete flux recovery over eight filtration cycles. This work highlights the effectiveness of ionic liquid-engineered composite