Recent theoretical1-2 and experimental studies3 report ultrahigh water permeability and salt rejection in nanoporous single-layer graphene. However, creating and controlling the size of nanometer-size pores in single-layer graphene pose significant challenges to application of these membranes for water desalination. Graphyne and hydrogenated-graphyne have tremendous potential as ultra-permeable membranes for desalination and wastewater reclamation due to its chemical and mechanical stability, flexibility, regular pore-distribution and atomic thickness. Using ReaxFF molecular dynamics simulations, we report the desalination performance of graphyne-2,3,4 and hydrogenated graphyne-2,3,4 membranes under realistic reverse-osmosis pressures (&lt; 100 bar) as a function of its pore size, chemical functionalization and applied pressure. We find that adequately sized pores are essential to allow water passage while blocking ions and an increase in water flux with pore-size comes at the expense of reduced salt rejection performance. Hydrogenated graphyne-3 membranes have the best salt rejection performance while allowing water fluxes up to 100 * 10 -6 g m-2 s-1 40 ○C which is 2 orders of magnitude larger than the flux reported in recent experimental studies3 on nanoporous single-layer graphene. Hydrogenated graphyne-4 membranes selectively block positively charged ions (Na+, K+) while allowing negatively charged ions (Cl-) to pass through. Membrane-functionalization can thus be a pragmatic approach to synthesize semipermeable membranes that separate differently charged ions in solution with possible applications in electrochemical cells. In summary, our simulations indicate that graphyne and hydrogenated-graphyne membranes have tremendous potential as water desalination and semipermeable membranes with water permeability that is orders of magnitude higher than nanoporous graphene and conventional reverse osmosis membranes. (1). Cohen-Tanugi, D.; Grossman, J. C., Water Desalination across Nanoporous Graphene. Nano Lett. 2012, 12, 3602-3608. (2). Cohen-Tanugi, D.; Grossman, J. C., Water permeability of nanoporous graphene at realistic pressures for reverse osmosis desalination. J. Chem. Phys. 2014, 141, 074704. (3). Surwade, S. P.; Smirnov, S. N.; Vlassiouk, I. V.; Unocic, R. R.; Veith, G. M.; Dai, S.; Mahurin, S. M., Water desalination using nanoporous single-layer graphene. Nat. Nanotechnol. 2015, 10, 459-464.

Water desalination and selective ion-separation using single-layer graphyne and hydrogenated graphyne membranes at realistic reverse-osmosis pressures

251st National Meeting (2016)

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