Water desalination performance of h-BN and optimized charged graphene membranes

CT Nguyen and A Beskok, MICROFLUIDICS AND NANOFLUIDICS, 24, 39 (2020).

DOI: 10.1007/s10404-020-02340-8

Water desalination using pressure-driven flow in hexagonal boron nitride (h-BN) and charged nanoporous graphene membranes are investigated using molecular dynamics (MD) simulations. Nanoporous h-BN membranes with pore diameters of 10.1 angstrom, 12.2 angstrom, and 14.7 angstrom were selected to compare with the desalination performance of uncharged nanoporous graphene membranes with similar pore diameters. Salt rejection efficiency of uncharged graphene membranes is superior to that of h-BN, and the pressure drop for both materials exhibits the same inverse-cubic dependence on the pore diameter, regardless of the hydrophobic versus hydrophilic nature of graphene and h-BN, respectively. Charged graphene membranes with pore diameters of 15.9 angstrom, 18.9 angstrom, and 20.2 angstrom were also considered, and 15.9 angstrom pore diameter with total fixed charge of 12e was found to be the optimum setting for single-layer graphene membrane, resulting in 100% and 98% rejection efficiencies for Na+ and Cl- ions, respectively. The corresponding pressure drop is 51.8% lower than that obtained with 9.9 angstrom pore diameter uncharged graphene with 100% salt rejection. To maintain perfect salt removal, 15.9 angstrom pore diameter charged bilayer graphene membranes with 12e total charge on the first layer, and - 1e on the second one was simulated at different separation distances between the two membranes. The associated pressure drop is 35.7% lower than that obtained in 9.9 angstrom pore diameter uncharged base-line case. These findings confirm the potential application of using charged bilayer nanoporous graphene membranes in improving the performance of reverse osmosis desalination systems.

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