Self-cleaning GO/g-C₃N₄/ZnO composite membrane for dye nanofiltration

Membrane-based approach is a very effective method for water purification, but fouling is still a major obstacle that limits its performance. In this study, a self-cleaning GO/g-C₃N₄/ZnO composite membrane was developed to improve the fouling resistance by utilizing the structural stability of g-C₃N₄ and the photocatalytic properties of ZnO (band gap 3.2 eV). GO was synthesized via a modified Hummer method, while g-C₃N₄ was obtained via a calcination process. The membranes were prepared using vacuum filtration on nylon support with varying ZnO concentrations (5-25%) and maleic anhydride as a cross-linker to enhance the membrane stability. FTIR, XRD, UV-Vis DRS, PL, and SEM-EDX characterizations confirmed the successful synthesis of the composite with homogeneous distribution of C, O, N, and Zn on the membrane surface. The naphthol blue black filtration test showed the separation efficiency up to 99.9%. The GO/g-C₃N₄/17.5.ZnO membrane exhibited the highest permeability in the first cycle at 70.6 L m^-2·h^-1·bar^-1, while the GO/g-C₃N₄/15.ZnO membrane demonstrated the best stability, maintaining a 93% rejection efficiency after four usage cycles. Long-term cross-flow filtration under periodic UV light irradiation further confirmed stable rejection (~ 99%) over 20 h, highlighting the effective self-cleaning capability of the membrane. These results demonstrate that the GO/g-C₃N₄/ZnO composite membrane is a promising candidate for durable, self-cleaning water filtration applications.