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

Abstract

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(+), Mg(2+), Ca(2+), and Ba(2+)). 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 sp(2) 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.

Graphene membranes for water desalination

“…Transition-metal cations can also be adsorbed onto the GO sheets through coordination bonds to sp 3 clusters in the oxidized regions of the GO sheets, whereas alkali metal cations can be adsorbed through cation-π interactions with sp 2 clusters in the pristine regions of the GO sheets. 65 The sieving and electrostatic-based separation performance of the multilayer graphene membranes can be optimized by several modifications. For instance, the GO sheet size and membrane thickness can be changed to tune the separation efficiency of the membrane.…”

Highly efficient quasi-static water desalination using monolayer graphene oxide/titania hybrid laminates

“…16 Within the laminate, the sp 2 graphitic clusters are connected together across all the stacking layers to form a network of nanocapillaries through which water can experience an ultrafast and unimpeded transmembrane permeation while other liquids and gases are completely blocked. 16,17 Notably, due to the narrow dimension of the nanocapillaries and the co-existence of sp 2 aromatic channels with various oxygen functionalities, the GO membranes can afford excellent selectivity toward various ions based on the molecular sieving effect 18 and diverse chemical interactions, [19][20][21][22] which is favorable for filtration and separation. However, in regard to water desalination, assynthesized GO membranes cannot perform well at the current state due to rapid ion flows.…”

“…However, in regard to water desalination, assynthesized GO membranes cannot perform well at the current state due to rapid ion flows. [18][19][20] For example, recent studies have revealed that GO-based membranes can only afford a salt rejection of o40% towards NaCl, 23,24 which is fairly poor and far from practical. More recently, Mi 25 has proposed that for applications of GO membranes in water desalination, the GO interlayer spacing within the laminates has to be reduced to less than 0.7 nm to sieve the hydrated Na + ions (hydrated radii: 0.36 nm) from water.…”

Graphene-based membranes for organic solvent nanofiltration

“…Moreover, it was further demonstrated that GO membranes could act as molecular sieves to block all solutes with hydrated radii > 0.45 nm when immersed in water [2], in which size exclusion appears to account for this behavior. For smaller sizefitted solutes that can enter in nanochannels, GO membrane could achieve more accurate ion selectivity via the diverse interactions between ions and sp 2 clusters or oxygen-containing functional groups on GO basal planes [3].The findings mentioned above implicate that GO membranes are extremely promising for a broad spectrum of separation due to their tunability in pore size to remove various target solutes, including expansion by inserting large spacers and decrease by reducing, crosslinking, etc. [4].…”

“…Moreover, it was further demonstrated that GO membranes could act as molecular sieves to block all solutes with hydrated radii > 0.45 nm when immersed in water [2], in which size exclusion appears to account for this behavior. For smaller sizefitted solutes that can enter in nanochannels, GO membrane could achieve more accurate ion selectivity via the diverse interactions between ions and sp 2 clusters or oxygen-containing functional groups on GO basal planes [3].…”