Surfaces of commercially available membrane filters were modified by the dispersion of poly(N-vinylcarbazole) (PVK), graphene (G), poly(N-vinylcarbazole)-graphene (PVK-G), graphene oxide (GO), and poly(Nvinylcarbazole)-graphene oxide (PVK-GO) in order to impart antibacterial properties. The successful coatings of the membranes were demonstrated through scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Investigations carried out on the surface-modified membrane filters using Escherichia coli and Bacillus subtilis showed that the presence of graphene-based nanomaterials significantly improved the antibacterial properties of the membrane filters. One of the mechanisms for this improved antimicrobial property of the filter was attributed to the production of reactive oxygen species by the nanomaterials. Among the nanomaterials used in this study, the PVK-GO-modified membrane filter exhibited the best removal of B. subtilis and E. coli with 4 and 3 log removals, respectively. The different levels of E. coli and B. subtilis removals were attributed to the differences in their cell structures and composition. This study has demonstrated that the use of graphene-based nanomaterials to modify the surfaces of membrane filters is an effective method of imparting antibacterial properties that can find useful application in water and wastewater treatment.

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Nanocomposites containing graphene oxide (GO), polyethyleneimine (PEI), and chitosan (CS) were synthesized for chromium(VI) and copper(II) removal from water. Response surface methodology (RSM) was used for the optimization of the synthesis of the CS-PEI-GO beads to achieve simultaneous maximum Cr(VI) and Cu(II) removals. The RSM experimental design involved investigating different concentrations of PEI (1.0-2.0%), GO (500-1500 ppm), and glutaraldehyde (GLA) (0.5-2.5%), simultaneously. Batch adsorption experiments were performed to obtain responses in terms of percent The optimum bead composition contained 2.0% PEI, 1500 ppm GO, and 2.08% GLA, and allowed Cr (VI) and Cu(II) removals of up to 91.10% and 78.18%, respectively. Finally, characterization of the structure and surface properties of the optimized CS-PEI-GO beads was carried out using X-ray diffraction (XRD), porosity and BET surface area analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), which showed favorable adsorbent characteristics as given by a mesoporous structure with high surface area (358 m 2 g À1 ) and plenty of surface functional groups. Overall, the synthesized CS-PEI-GO beads were proven to be effective in removing both cationic and anionic heavy metal pollutants.