First-principles Characterization of the Interaction between Oxygen-Passivated Porous Graphene and Cations for Sensors and Water Filtration

Porous graphene has been reported as an effective membrane capable of filtering ions in water and a promising platform for gas sensor applications. Here we characterize the interactions between cations and oxygen-passivated graphene pores using the density functional theory (DFT). The coupling between porous graphene and Li, Na, K, Rb, and Cs is studied in terms of pore size and density. We find that the strongest binding occurs when the size of a pore is similar to the van der Waals radius of the ion, maximizing the electrostatic ion-pore interaction and explaining experimental observations. Analysis of the charge distribution stemming from the electron transfer to the sheet shows different behaviors for porous graphene than for pristine graphene. The latter behaves like a perfect metal, in spite of the semimetal character of graphene and its atom thickness. In contrast, charge transfer in the porous case shows oscillations that decay more rapidly than in pristine graphene. We discuss the trends found within this class of ions and their implications to the design of large-scale water desalination membranes and gas sensors.