Selective Trans-Membrane Transport of Alkali and Alkaline Earth Cations through Graphene Oxide Membranes Based on Cation−π Interactions

Graphene and graphene oxide (G–O) have been demonstrated to be excellent filters for various gases and liquids, showing potential applications in areas such as molecular sieving and water desalination. In this paper, the selective trans-membrane transport properties of alkali and alkaline earth cations through a membrane composed of stacked and overlapped G–O sheets (“G–O membrane”) are investigated. The thermodynamics of the ion transport process reveal that the competition between the generated thermal motions and the interactions of cations with the G–O sheets results in the different penetration behaviors to temperature variations for the considered cations (K⁺, Mg²⁺, Ca²⁺, and Ba²⁺). The interactions between the studied metal atoms and graphene are quantified by first-principles calculations based on the plane-wave-basis-set density functional theory (DFT) approach. The mechanism of the selective ion trans-membrane transportation is discussed further and found to be consistent with the concept of cation−π interactions involved in biological systems. The balance between cation−π interactions of the cations considered with the sp² clusters of G–O membranes and the desolvation effect of the ions is responsible for the selectivity of G–O membranes toward the penetration of different ions. These results help us better understand the ion transport process through G–O membranes, from which the possibility of modeling the ion transport behavior of cellular membrane using G–O can be discussed further. The selectivity toward different ions also makes G–O membrane a promising candidate in areas of membrane separations