Design of Sub‐Nanochannels between Graphene Oxide Sheets via Crown Ether Intercalation to Selectively Regulate Cation Permeation

Abstract

development and human activities, giving rise to the need for a method to obtain clean water resources. Membrane filtration, one of the processes to separate contaminants and salts from water, has attracted much attention as a way to secure clean water in an energy efficient manner. [2,3] As a result, various kinds of membrane materials, especially polymers, [4] have been widely studied for desalination and water purification. [5][6][7][8] However, the availability of polymer membranes in a large-scale process is unsuitable due to a poor mechanical and chemical stability, along with fouling issues. [9] It is crucial to find other potential material candidates to tackle these problems.Graphene derivatives are emerging candidates for efficient water treatment membranes, attributed to their unique nanochannel network [10] as well as the robust chemical and mechanical stability; [11][12][13] these chemical and physical stability are originated from their graphitic structure. [14,15] In particular, graphene oxide (GO) is regarded as a versatile platform for separating ions or contaminants due to its tunability and scalability. Furthermore, the distinctive nanochannel of the GO membranes formed by vacuum-filtration allows the GO membrane not only to block unwanted solutes, but also to achieve a high water permeability. However, it is extremely difficult to maintain the rejection performance of the GO membrane in a long term since the oxygen functional groups interact with water molecule via hydrogen bonding, resulting in membrane swelling in aqueous solution. For instance, Zheng et al. found that the d-spacing of a GO membrane significantly increased in an aqueous solution compared to its dry state-swelling up to 7 nm at equilibrium-while limiting the mobility of water molecules. [16] Additionally, to explain and predict the separation performance of multilayered GO membrane, several research groups have studied the water flow through such graphene-based layers and the influence of the degree of oxidation using molecular simulations. [17][18][19][20][21][22][23] They observed a swelling effect depending on the oxygen functional groups and an irregular structure of water molecules when passing through GO nanochannels.In order to effectively suppress the permeation of ions through the membrane for desalination, it is necessary not only to design the GO nanopathway more precisely, but also to maintain the fine nanochannels over a long period of time.Graphene-based membranes are a promising candidate for separating pollutants and ions. In particular, graphene oxide (GO) membranes are widely studied due to their unique nanochannels. The characteristic nanochannels of GO membranes can be manipulated via intercalation of cations, inhibiting the transport of other ions in the diffusion process. To maintain the tailored nanochannel during a pressure-assisted filtration procedure, it is essential to retain such inserted cations. Here, dibenzo-18-Crown-6 molecules (DB18C6) tightly binding to potassium ions are intercalated into G...

Rational Fabrication of MXene/Graphene Oxide Membrane and Its Voltage-Gated Ion Transport Behavior

“…Recently, graphene (GN) and graphene oxide (GO) membranes have aroused widespread attention owing to their excellent ion sieving performance. − More importantly, researchers have found that more accurate ion sieving can be achieved by controlling the interlayer spacing of graphene-based membranes . Chen et al have achieved precise control of the interlayer spacing in GO membranes through noncovalent cation−π interactions between hydrate cations and the aromatic ring.…”

Facile Fabrication of Defect-Controlled Graphene Oxide Membrane through Shear-Induced Alignment for Regulating Ion Transport

“…The water permeance and ion rejection tests were conducted using a conventional dead-end filtration method. 7 The prepared GO membrane was placed on the bottom of the stirring cell, and the 50 mL of the salt solution was poured in the cell. The permeation test proceeded for 30 min under 1 bar of N 2 conditions, and the solution was agitated at 350 rpm in order to prevent the concentration polarization effect.…”

An ion-selective crown ether covalently grafted onto chemically exfoliated MoS2 as a biological fluid sensor

“…29 Especially for graphene, embedded crown ethers motifs have been studied by means of theoretical approximations and experimental observations, [30][31][32] whereas basal plane functionalized nanosheets with crown ethers have been evaluated for their cation permeation efficiency. 33 In the field of transition metal dichalcogenides, to the best of our knowledge, crown ethers have been only utilized as Li ions-containing intercalants within MoS2 exfoliated nanosheets serving as potential electrochemical switches. 34,35 The selective recognition of cations by tuning the size of the oxygencontaining macrocycles offers the advantage of developing responsive electrochemical platforms based on the host-guest interactions, arising from the stabilization of the cations within the macrocyclic polyether tether.…”