Using molecular dynamics simulations, we report enhancement in evaporation flux from various ionic solutions (LiCl, NaCl, and KCl) through functionalized nanoporous graphene (FNPG) placed at the liquid-vapor interface. The enhancement with respect to the bare liquid-vapor interface (ξ) depends upon the salt type, concentration, and pore size of the FNPG. Due to cation-π interactions, we found an enhanced density of cations at the surface of FNPG leaving the contact water layer depleted of ions. The propensity of ions to adsorb on the FNPG surface decreases in the order K+ &gt; Na+ &gt; Li+ &gt; Cl-, with, 7.5 &lt; ξ &lt; 11.5. The highest ξ about 11 is observed for the 0.6 M KCl solution. The interaction between edge functional groups at the nanopores and water molecules in the vicinity of the nanopore reduces the number of hydrogen bonds between water molecules increasing the escaping tendency. This increased propensity of water molecules to escape from the liquid-vapor interface is also evident from the higher diffusion coefficient of water molecules. This study illustrates the potential for using nanoporous graphene for desalination applications as well as separation processes with low thermal energy input.

Application of functionalized nanoporous graphene for the selective enhancement of water evaporation from ionic solutions

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