The ionized graphene oxide membranes for water-ethanol separation

Abstract

Nanoporous graphene oxide (GO) membranes have shown great promise in separating water and ethanol with high flux and selectivity. The current design of these membranes focuses on tuning the pore sizes in GO sheets to achieve superior selectivity. In this paper, using molecular dynamics simulations, we study the feasibility of achieving effective water-ethanol separation by tuning the ionization of the functional groups on the periphery of pores in single-layer GO sheets. For pores featuring neutral carboxyl (COOH) groups, the water-to-ethanol selectivity coefficient is ∼7 when the pore diameter is 0.68 nm but decays to ∼1.5 when the pore diameter increases to ∼1.12 nm. However, our simulations suggest that through the ionization (deprotonation) of the COOH groups of the 1.12 nm-wide pores, we can achieve a water-to-ethanol selectivity coefficient of ∼7 in these pores. This improvement is mainly attributed to the enhanced (suppressed) accessibility of water (ethanol) molecules to the pore induced by the ionization of the functional groups.