Interplay of charge composition and nanochannel confinement in ion separation through graphene oxide membranes.

The applicability of layered graphene oxide (GO) membrane for dehydration of acetic acid using forward osmosis (FO) process is investigated with non-equilibrium molecular dynamics (MD) simulations. The performance of layered GO membrane with different pore offset distance (W) and interlayer distance (H) is investigated. The parameter W is a measure of the size of the constituting GO nanosheets. With the increase in W, the water permeance through layered GO membrane decreases and salt rejection increases. On the other hand, as H increases from 8 Å to 12 Å, the water permeance of the layered GO membrane increases and the corresponding salt rejection decreases. But as H increases beyond 12 Å, the water permeance through layered GO membrane decreases and salt rejection increases. The presence of pinhole defects on the GO nanosheets of layered GO membrane provides shorter route to the water molecules for trans-sheet flow which increases the water permeance of the membranes. With the increase in draw solution concentration the water permeance through the membrane increases but the corresponding variation in the draw solute rejection is much less (<2.0%). With the appropriate tuning of sizes of the GO nanosheets and interlayer spacings, layered GO membrane could be a suitable candidate for dehydration of acetic acid using FO process.

Trivalent metal cation cross-linked graphene oxide membranes for NOM removal in water treatment

Cationic stabilized layered graphene oxide (GO) membrane for shale gas wastewater treatment: An atomistic insight

Surface engineering of graphene oxide membranes for selective separation of perfluorooctanoic acids

Tailoring the microstructure of poly(vinyl alcohol)-intercalated graphene oxide membranes for enhanced desalination performance of high-salinity water by pervaporation

Cation-dependent structural instability of graphene oxide membranes and its effect on membrane separation performance

Atomic insight into water and ion transport in 2D interlayer nanochannels of graphene oxide membranes: Implication for desalination

Synthesis and characterization of graphene acid membrane with ultrafast and selective water transport channels

Synthesis of graphene oxide membranes and their behavior in water and isopropanol

Evaluating graphene oxide and holey graphene oxide membrane performance for water purification

Graphene oxide (GO) membranes have shown enormous promise in desalination and molecular/ionic sieving. However, the instability of GO membranes in aqueous solutions seriously hinders their practical applications. Herein, we report a novel and simple strategy to fabricate stable GO membranes in water-based environments through the insertion of various metal cations from metal foils (e.g., copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) foils) and natural deposition. Based on the cation-π, coordination, and electrostatic interaction between metal cations and GO nanosheets, the aqueous stability and mechanical strength of the membranes are significantly improved. The permeation rates for acetone, toluene, and p-xylene molecules across the GO membrane cross-linked by copper ions with a deposition time of 24 h are 0.966, 0.074, and 0.100 mol m-2 h-1, respectively. Moreover, this membrane displays excellent separation performance, and the separation factor of K+/Mg2+ is up to 68.8 in mono-/multivalent metal cation sieving, which indicate the effective molecular/ionic sieving performance. Meanwhile, the ionic sieving of the GO membrane cross-linked by copper ions has excellent repeatability and long-term stability. The versatility of this natural deposition strategy to fabricate GO membranes cross-linked by metal cations is investigated by using Fe foil, Zn foil, and Ni foil as well as other porous substrates such as polyvinylidene fluoride (PVDF), polyethersulfone (PES), and nylon membranes and filter paper. This fabrication strategy also enables low-cost preparation of large-area GO membranes. Therefore, GO membranes cross-linked by metal cations and prepared by this simple metal cation incorporation strategy have large potential application for molecular/ionic sieving in various solution systems.

A graphene oxide (GO) membrane is promising for molecule separation. However, it is still a big challenge to achieve highly stable pristine GO membranes, especially in water. In this work, an ultrathin and robust GO membrane is assembled via the cross-flow method. The as-prepared 12 nm thick GO membrane (GOCF membrane) presents high stability with water permeance of 1505 ± 65 litres per hour per square meter per bar (LHM bar−1) and Evans Blue (EB) rejection of 98.7 ± 0.4%, 21-fold enhancement in water permeance compared with that of a pristine GO membrane (50–70 LHM bar−1) and 100 times higher than that of commercial ultrafiltration membranes (15 LHM.bar−1, GE2540F30, MWCO 1000, GE Co., Ltd) with similar rejection. Attributed to the surface cross-flow, the GO nanosheets will be refolded, crumpled, or wrinkled, resulting in a very strong inter-locking structure among the GO membrane, which significantly enhances the stability and facilitates their separation performance. This cross-flow assembling technique is also easily extended to assemble GO membranes onto other various backing filter supports. Based on the Donnan effect and size sieving mechanism, selective membrane separation of dyes with a similar molecular structure from their mixture (such as Rhodamine B (RhB) and Rose Bengal, and RhB and EB) are achieved with a selectivity of 133 ± 10 and 227 ± 15, respectively. Assembly of this ultrathin GO membrane with high stability and separation performance, via a simple cross-flow method, shows great potential for water purification.

Tuning the oxidation level of GO to construct high performance crosslinked lamellar graphene oxide membrane for pervaporation desalination

The application feasibility of graphene oxide membranes for pressure-driven desalination in a dead-end flow system

Graphene oxide (GO) membrane has gained increasing attention because of its extraordinary physical and chemical properties and high proton conductivity. GO is rich in oxygenated functional groups, which can support proton transportation. However, pristine GO is unstable at high temperatures due to the removal of oxygen functional groups, resulting in a decrease in the interlayer distance of stacked GO nanosheets. Hence, we propose a modification of GO membranes via the intercalation of cations to enhance the proton conductivity. Modified self-standing GO membranes with Al3+ and La3+ were fabricated by a vacuum filtration method. They exhibited a larger distance of the interlayer that serves as proton hopping pathways. Furthermore, the modified GO membrane showed a higher proton conductivity than a pristine GO membrane even at 80 °C, as confirmed by Electrochemical Impedance Spectroscopy. The results demonstrate that intercalating cations in between GO nanosheets is effective in improving the practical feasibility of proton conducting GO membranes.