Effects of Casting Solvents on the Morphologies, Properties, and Performance of Polysulfone Supports and the Resultant Graphene Oxide-Embedded Thin-Film Nanocomposite Nanofiltration Membranes

In this study, the influences of different casting solvents including N-methylpyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF) on the morphologies, properties, and performance of polysulfone (PSU) supports and their resultant graphene oxide (GO)-embedded thin-film nanocomposite (TFN) nanofiltration (NF) membranes were systematically investigated. The influences of casting solvents on the mechanism of immersion precipitation phase-inversion process and the morphology of PSU supports were analyzed by Hansen solubility parameters. The results indicated that the physicochemical properties and performance of both PSU supports and the resultant composite NF membranes were significantly affected by the type of casting solvents. PSU support made from NMP exhibited a small surface pore size that prevented the penetration of poly(piperazine amide) (PPA) into the PSU pores, which contributed to form a defect-free active layer with excellent permeaselectivity regardless of TFC or TFN NF membranes. On the contrary, the surface pore size of PSU support made from DMF was too large to generate a dense and defect-free PPA active layer, which led to inferior rejection of the corresponding TFC or TFN membranes. After introducing an appropriate amount of GO into the aqueous phase, the nanocomposite active layer became thinner and smoother with enhanced hydrophilicity and negative charge. At a GO concentration of 40 ppm, TFN-NMP-GO-40 NF membrane exhibited excellent permeaselectivity, antifouling ability, and chlorine resistance compared with TFC-NMP membrane. Particularly, on the basis of retaining the high salt rejection (>98%) without a loss, the water flux of TFN-NMP-GO-40 membrane significantly increased to 46.9 L.m(-2).h(-1), which was 137.9% of the value for TFC-NMP membrane.