Preparation and characterization of novel alkali-resistant nanofiltration membranes with enhanced permeation and antifouling properties: the effects of functionalized graphene nanosheets

In this study, novel alkali-resistant nanocomposite nanofiltration (NF) membranes were prepared via phase inversion by immersion precipitation combined with the addition of two kinds of functionalized graphene nanosheets. The effects of the functional groups and the concentrations of the graphene-based nanosheets on the microstructures and performances of nanocomposite membranes were systematically investigated. Compared with the pure polyethersulfone (PES) membrane, incorporation of a small amount of sulfonated graphene (SG) or graphene oxide (GO) into the PES matrix did not change the membrane morphology. However, the hydrophilicity, permeability and antifouling capabilities were remarkably enhanced without obvious reduction in membrane rejection. Particularly, the water fluxes of optimized PES–SG and PES–GO NF membranes at 0.1 wt% were improved by 119.7% and 71.3%, respectively. Moreover, the PES–SG series membranes exhibited better hydrophilicity and membrane separation performance than the PES–GO series membranes, which was attributed to the different ionisable functional groups from the SG and GO nanosheets. Both the optimized PES–SG and PES–GO NF membranes exhibited long-term stability during a seven-day test in alkaline solution, but PES–SG demonstrated greater promise as a novel alkali-resistant NF membrane due to its superior permeability and antifouling performance.