Functionalized Graphene Nanosheet as a Membrane for Water Desalination Using Applied Electric Fields: Insights from Molecular Dynamics Simulations

Desalination is a favorable method employed to supply clean water in recent years. Various contaminants entering water resources must be removed from water by novel structures like nanostructure membranes. Accordingly, molecular dynamics simulations were performed to study the ion removal from the water using a graphene nanosheet (GNS) based on the permeability and selectivity of graphene. The studied system consisted of two functionalized GNSs immersed in the aqueous ionic solution of NaCl. The GNSs had one pore each, both being approximately of the same size. For the ion removal from water using these GNSs, an external electric field was applied to the system. For the preferential permeation of cation or anion across the graphene, the pore of the GNS was functionalized by passivating each carbon atom at the edge of the pore by fluoride (F-pore), negatively charged, and hydrogen atoms (H-pore), which were positively charged. The results showed that by using the electric field the F-pore and the H-pore of GNS were preferential selective to Na+ and Cl-, respectively; also, the higher the electric field, the faster the movement of the ions from the salty water. The calculations of the potential of mean force for ions showed that sodium and chloride ions encountered an energy barrier, and thus, cation and anion failed to permit across the H-pore and F-pore of the GNS, respectively. Based on the results of this research, the functionalized GNS, as a membrane, can be suggested as a device in the field of water desalination.