Influence of ZnO and rGO in PVDF membranes for enhanced photocatalytic activity

In the present report, pristine zinc oxide nanoparticles (ZnO NPs) and zinc oxide-reduced graphene oxide (rGO) nanocomposites (ZnO@rGO NCs) loaded polyvinylidene fluoride (PVDF) membranes were prepared using the ultrasonication technique, and their photodegradation was analyzed against methylene blue (MB) dye. Structural analysis using the X-ray diffraction (XRD) technique revealed that the sol-gel synthesized ZnO NPs possess a hexagonal wurtzite crystal structure. Furthermore, the ZnO@rGO NCs exhibited characteristic diffraction peaks corresponding to hexagonal ZnO along with the appearance of the (002) diffraction peak attributed to rGO, confirming the formation of ZnO@rGO NCs. The functional groups attached to ZnO NPs and ZnO@rGO NCs appeared at 3456 cm −1 and 3421 cm −1 , corresponding to the hydroxyl (-OH) group, and the peaks 568 cm −1 and 468 cm −1 show the Zn-O vibrations. Furthermore, membrane fouling and antifouling behavior were investigated through permeation flux and flux recovery ratio (FRR) analysis. PL spectra confirmed reduced electron–hole recombination in the PVDF/ZnO@rGO membrane. The pristine PVDF membrane exhibited an initial flux of 210 Lm −2 h −1 , which decreased significantly during filtration, whereas the PVDF/ZnO@rGO membrane demonstrated improved flux stability with an FRR value of 89.8%, confirming enhanced antifouling performance. The influence of solution pH, initial MB dye concentration, and dark adsorption behavior on photocatalytic degradation was also systematically examined. The PVDF/ZnO@rGO membrane exhibited a maximum degradation efficiency of nearly 85% at pH = 7 under UV irradiation. PVDF/ZnO@rGO membrane demonstrated faster degradation of MB dye, achieving 85.5% removal efficiency in 100 min of exposure to UV light as compared to 66.24% achieved at 160 min for PVDF/ZnO membrane. The decolorization of membranes after degradation under UV irradiation also showcases the reusable efficacy of the membrane.