Tailoring PVDF membrane performance via graphene oxide–quaternized chitosan composite layer deposition for advanced dye removal

In this study, pristine polyvinylidene fluoride (PVDF) membranes were independently modified with chitosan or its quaternized equivalent and graphene oxide enriched quaternized chitosan (GO-QCS/CS-PVDF) for the rejection of aqueous anionic and cationic dyes. The CS or QCS and GO-QCS layers were deposited on the PVDF support using (i) a combination of immersion and pressure filtration, or (ii) pressure filtration exclusively. The surface of these membranes was characterized using FE-SEM, FTIR, XRD and XPS analyses. Hydrophilicity was investigated using a Contact Angle meter. Additionally, membrane performances were assessed via measurement of water flux, dye rejection and antifouling properties in a crossflow cell setup. The results showed that the membrane flux was significantly decreased even with enhanced hydrophilicity. The decrease in flux is due to increased transport resistance, pore narrowing and obstruction. Consequently, the modified membranes achieved high rejections of RB (98.0%), MB (96.4%), and BSA (97.3%) through combined molecular sieving, adsorption, and electrostatic interactions. Under elevated BSA concentrations, initial flux recovery ratio for GO-QCS layer membranes were >80%, demonstrating excellent fouling resistance. The synergistic interaction of GO, CS and QCS functional groups deposited on the PVDF support enhanced broad-spectrum dye rejection and antifouling properties, providing an efficient and eco-friendly treatment route.