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    Correlating Interlayer Spacing and Separation Capability of Graphene Oxide Membranes in Organic Solvents

    Year: 2020

    Journal: ACS Nano, Volume 14, MAY 26, page 6013–6023

    Authors: Zheng, Sunxiang; Tu, Qingsong; Wang, Monong; Urban, Jeffrey J.; Mi, Baoxia

    Organizations: U.S. National Science Foundation (NSF)National Science Foundation (NSF) [CBET-1565452, CBET-1706059]; U.S. Department of EnergyUnited States Department of Energy (DOE) [DE-IA0000018]; Office of Science, Office of Basic Energy Sciences, of the U.S. Department of EnergyUnited States Department of Energy (DOE) [DE-AC02-05CH11231]

    Keywords: graphene oxide; membrane; interlayer spacing; swelling; solubility distance; organic solvent nanofiltration

    Membranes synthesized by stacking two-dimensional graphene oxide (GO) hold great promise for applications in organic solvent nanofiltration. However, the performance of a layer-stacked GO membrane in organic solvent nanofiltration can be significantly affected by its swelling and interlayer spacing, which have not been systematically characterized. In this study, the interlayer spacing of the layer-stacked GO membrane in different organic solvents was experimentally characterized by liquid-phase ellipsometry. To understand the swelling mechanism, the solubility parameters of GO were experimentally determined and used to mathematically predict the Hansen solubility distance between GO and solvents, which is found to be a good predictor for GO swelling and interlayer spacing. Solvents with a small solubility distance (e.g., dimethylformamide, N-methyl-2-pyrrolidone) tend to cause significant GO swelling, resulting in an interlayer spacing of up to 2.7 nm. Solvents with a solubility distance larger than 9.5 (e.g., ethanol, acetone, hexane, and toluene) only cause minor swelling and are thus able to maintain an interlayer spacing of around 1 nm. Correspondingly, GO membranes in solvents with a large solubility distance exhibit good separation performance, for example, rejection of more than 90% of the small organic dye molecules (e.g., rhodamine B and methylene blue) in ethanol and acetone. Additionally, solvents with a large solubility distance result in a high slip velocity in GO channels and thus high solvent flux through the GO membrane. In summary, the GO membrane performs better in solvents that are unlike GO, i.e., solvents with large solubility distance.
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