Ionic liquid-grafted PVDF membrane incorporated with g-C₃N₄-Fe₃O₄ for the removal of cationic dye and improved...

The development of multifunctional membranes with tunable surface charge, high permeability, reactive pollutant removal, and bacterial resistance remains a critical challenge in wastewater treatment. Here, a poly(vinylimidazolium)-functionalized PVDF membrane incorporating g-C₃N₄-Fe₃O₄ was fabricated through surface activation, composite deposition, free-radical graft polymerization, and subsequent hydroxide anion exchange to tailor surface physicochemical properties. The engineered membrane exhibited significantly enhanced hydrophilicity and high water permeability (109 L m^- 2 h^- 1 bar ^- 1), corresponding to a 25-fold increase over pristine PVDF. It showed strong removal of methylene blue (97%) but lower removal of methyl orange (30%) at 20 ppm, indicating charge-dependent reactive removal behavior. Methylene blue displayed a strong affinity for the modified surface, enabling effective interfacial adsorption and subsequent photocatalytic degradation under visible light, whereas methyl orange interacted much less effectively. Although most dye-removal experiments were conducted under static conditions to evaluate surface activity, pressure-driven filtration still achieved up to 83% methylene blue removal within the microfiltration pore-size range, confirming that pollutant removal was governed by reactive surface interactions rather than conventional size-exclusion mechanisms. Adsorption kinetics followed pseudo-second-order model and fit the Freundlich isotherm, suggesting heterogeneous interactions between dye molecules and the membrane surface. Interfacial adsorption governed pollutant localization in both dark and illuminated conditions, with photocatalysis providing an additional contribution under light. The membrane also exhibited excellent antibacterial activity, with near-complete flux recovery over eight filtration cycles. Overall, integrating polymeric ionic liquids with carbon nitride-based nanocomposites offers a promising route to low-pressure reactive membranes with enhanced pollutant removal and antibacterial properties for wastewater treatment.