Water Permeation and Ion Rejection in Layer-by-Layer Stacked Graphene Oxide Nanochannels: A Molecular Dynamics Simulation
HW Dai and ZJ Xu and XN Yang, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 22585-22596 (2016).
Layer-by-layer assembled graphene oxide (GO) has been considered as a high-efficiency novel membrane material. However, its performance of water permeation and ion rejection remains largely unresolved. Herein we constructed a model of a GO membrane using laminate nanochannels with aligned flexible multilayered GO sheets, on which functional groups were randomly distributed based on the Lerf-Klinowski model. The water permeation and ion rejection in the flexible GO membranes with various pore widths and surface oxidization degrees were simulated. Our results indicate water flow rate in the GO nanochannels is significantly slowed, which is quantitatively equivalent with the prediction using the no-slip Poiseuille equation. The simulated results suggest the capillary channels within GO stacked laminated membranes might not always work as the major flow route for water to permeate. It is observed that confined water structure becomes more disordered and loose within the corrugated GO nanochannels. The interfacial friction provides huge corrugation of surface energy landscape for moving water and largely suppresses the water flow. The microscopic mechanism of ion rejection has been ascribed to the size exclusion of ion hydration and the surface interaction from functional groups. Overall, our results provide new physical pictures
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