Application Of Graphene Oxide Membranes Research Articles

Graphene Oxide and its Composites: Advanced Membranes for Selective Water Permeation.

Graphene oxide (GO) membranes have gained significant attention as a promising material for separation by selective permeation processes due to their advantageous structural and chemical properties, including high water permeability, chemical resistance, and mechanical strength. In this study, we explore the potential applications of GO membranes in pervaporation to separate liquid mixtures. The layered structure and hydrophilic nature of GO membrane facilitate rapid and selective water transport through angstrom-scale interlayer spacings, resulting in superior performance over conventional polymeric and inorganic membranes. The unique mass transport mechanisms - slip flow and molecular alignment - enable GO membranes to selectively permeate water over organic solvents. For chemical dehydration, GO membranes are the most potential candidates. Furthermore, advancements in composite GO membranes and cross-linking techniques that improve their stability and separation performance are discussed. This study highlights the advantages of GO membranes and their potential to replace or complement existing technologies, by emphasizing their role in advancing membrane-based separation and promoting environmental sustainability. Future research is expected to optimize the fabrication techniques for GO membranes and expand their application scope.

Reduction-enhanced water flux through layered graphene oxide (GO) membranes stabilized with H3O+ and OH- ions.

Graphene oxide (GO) is one of the most promising candidates for next generation of atomically thin membranes. Nevertheless, one of the major issues for real world application of GO membranes is their undesirable swelling in an aqueous environment. Recently, we demonstrated that generation of H3O+ and OH- ions (e.g., with an external electric field) in the interlayer gallery could impart aqueous stability to the layered GO membranes (A. Gogoi, ACS Appl. Mater. Interfaces, 2022, 14, 34946). This, however, compromises the water flux through the membrane. In this study, we report on reducing the GO nanosheets as a solution to this issue. With the reduction of the GO nanosheets, the water flux through the layered GO membrane initially increases and then decreases again beyond a certain degree of reduction. Here, two key factors are at play. Firstly, the instability of the H-bond network between water molecules and the GO nanosheets, which increases the water flux. Secondly, the pore size reduction in the interlayer gallery of the membranes, which decreases the water flux. We also observe a significant improvement in the salt rejection of the membranes, due to the dissociation of water molecules in the interlayer gallery. In particular, for the case of 10% water dissociation, the water flux through the membranes can be enhanced without altering its selectivity. This is an encouraging observation as it breaks the traditional tradeoff between water flux and salt rejection of a membrane.

Cross-flow separation characteristics and piloting of graphene oxide nanofiltration membrane sheets and tubes for kraft black liquor concentration

Dewatering of weak black liquor (WBL) in the kraft cycle by evaporation is highly energy intensive. Membranes are an attractive alternative for energy-efficient dewatering, but existing commercial polymeric or ceramic membranes are either degraded in BL or have high capital costs. Our recent works have demonstrated the engineering of graphene oxide (GO) nanofiltration membranes, their stability and promising performance in BL conditions, and preliminary scale-up into sheets and tubes. Here, we describe in detail the separation characteristics of GO membrane sheets and tubes under real BL conditions and crossflow operation. Recycle-mode piloting of a GO tubular membrane showed average “production flux” of 16 L/m2/h (LMH) and high rejections of lignin (98.3%), total solids (66%), and total organic carbon (83%), with no signs of irreversible fouling identified. A corresponding GO sheet membrane produced an average flux of ~25 LMH and maintained high lignin rejection of ~97% during a slipstream pilot at a kraft mill site using WBL with ~16 wt% total solids (TS). Finally, we piloted a Dow/DuPont XUS1808 polyamide composite reverse osmosis (RO) membrane for last-mile processing of the GO nanofiltration membrane permeate. The RO membrane showed a steady state flux of 19 LMH at 65 bar and produced ~0.02 wt% TS water product, which is highly suitable for reuse in pulp washing operations in the kraft process. The results have strong positive implications for the industrial application of GO membranes in BL concentration and other related applications.

Advances and prospects in graphene oxide membranes for seawater salt ion sieving and rejection

Seawater salt ion sieving and rejection achieved through membrane separation is inevitable as the human development to obtain fresh water or pure salt. Recently, graphene oxide (GO) membrane with unique physicochemical properties and adjustable structure has unique advantages in seawater desalination. In this paper, we briefly review the development of the GO membranes for seawater salt ion sieving and rejection including the preparation process, ion sieving mechanism, and physical/chemical functional modification of the GO membranes. We compare the current research status of various membrane separation technologies in different application areas and identify potential future research directions. This article aims to offer researchers ideas for the preparation and application of GO membranes, with a focus on developing green and cost-effective manufacturing processes.

Graphene Oxide Membranes for Ionic/Molecular Filtration: From Self-Assembly to Design

The graphene oxide (GO) membrane holds great promise in desalination and green energy fields due to its naturally occurring nanochannels, which provide significant advantages in gas and ion filtration. In this study, the sizes and distributions of nanopore/channels in GO membranes and the relationship of GO flakes size and membrane thickness are explored by molecular dynamics simulations. Our results demonstrate that the size of GO flakes influences the distribution of nanopore sizes in GO membranes, while it almost has no influence on the total nanopore area in membranes with the same thickness. Additionally, our findings confirm that the total nanopore area of the GO membranes decreases exponentially as the membrane thickness increases, which is consistent with experimental observations. To expand the range of nanopore size regulation, we developed a columnar-array substrate model to create GO membranes customized for specific filtration functions, such as virus filtration. Our findings provide physical insights into the rational design of functional membranes for energy and environmental applications and offer theoretical guidance and technical support for the practical application of GO membranes in separation and filtration.

Electrical, luminescence, and microwave-assisted reduction behaviour of alkali vs. alkaline earth metal ion-modified graphene oxide membranes

Ions are often introduced into graphene oxide (GO) membranes during their preparation and application, which may lead to changes in their properties. In this study, GO membranes regulated by ions were prepared by incorporating alkali and alkaline earth metals. We found that the introduction of different ions led to opposite changes in the electrical properties of the reduced GO (RGO) membranes. The introduction of alkali metal ions improves their conductivity, whereas the introduction of alkaline earth metal ions results in a decrease in their conductivity. Furthermore, we found that the introduction of ions resulted in significantly different changes in the luminescence spectra, which could be used to detect alkali and alkaline earth metal ions. In addition, the introduction of alkali metal and alkaline earth metal ions resulted in significantly different changes in the luminescence spectra and microwave reduction effect of the RGO membranes. The introduction of alkaline earth metal ions was more helpful for the removal of oxygen-containing groups and the restoration of the graphene lattice structure when exposed to microwave irradiation. These results suggest that the properties of GO membranes can be regulated by regulating the introduction of ions, and these findings have potentially important applications in the preparation and application of GO membranes and ion detection.

Swelling Pressures of Graphite Oxide and Graphene Oxide Membranes in Water and Ethanol

AbstractSwelling of graphene oxide (GO) membranes and bulk graphite oxide under confinement conditions is found to produce pressures up to ≈220 bar. Swelling pressure is important to take into account in many applications of GO membranes, but it has not been previously reported. Swelling pressures are typically measured only for bulk materials. However, it is demonstrated that even µm thick GO membranes develop pressures 3–25 bar due to the volume expansion caused by swelling in water. A rather strong difference in kinetics of pressure increase is found for both graphite oxide and GO membranes in water and ethanol despite similar lattice expansion due to swelling. This effect is attributed to slower penetration of ethanol into GO interlayers. Significantly faster saturation of swelling pressure is found for GO membranes (few hours) as compared to bulk graphite oxides (weeks) due to a higher degree of compaction. Swelling pressure is an important factor in applications, which require confinement, encapsulation of GO membranes or using external pressure to limit the lattice expansion. Finally, the swelling pressure can be used as an estimation for the suction pressure developed in pervaporation or vapor permeation applications, which is suggested as a driving force in rapid water permeation across GO membranes.

Selective Ion Permeation through Stabilized Metal–Phenolic Grafted Graphene Oxide Membranes

AbstractThe structural stability and high permeability of 2D materials‐based membranes are key research interests for separation membranes. However, the instability of their microstructures due to the aqueous‐induced swelling phenomenon affects their performance. It is highly desirable to explore anti‐swelling approaches able to mitigate this challenge as well as develop 2D lamellar membranes with ion selective capabilities beyond the limits based on size exclusion mechanism. Herein, graphene oxide (GO) laminate membranes covalently anchored and intercalated with metal‐phenolic networks display suppressed swelling durability and resist delamination in aqueous media. The resultant Fe@TA‐GO membrane with confined d‐spacing boasts high water fluxes of up to 15.0 L m−2 h−1 under osmotic pressure (2 m sucrose). Furthermore, the permeation tests reveal that the interaction between the metal ions and the immobilized cation–ligand molecules influences the ion permeances through the functionalized GO membranes conducing to fast ion permeation rates with ion diffusion permselectivity as well as effective selective separation of organic contaminants. These results will help advance the applications of GO membranes for challenging ion separations related to sustainable resource recovery and environmental remediation of organic dye and metal ion contaminated wastewaters.

Intercalation of N-doped graphene into graphene oxide-based membranes to improve their overall nanofiltration performance

Due to their tunable nanostructure, graphene oxide membranes (GOMs) have attracted numerous researchers in the water purification fields. However, the practical application of GOMs has been impeded by their low flux and tendency to swell during operation. In this work, we intercalated GOMs with N-doped graphene (NG), which possesses a higher water dispersibility compared to unmodified graphene, to simultaneously improve its stability, water permeability, and water/dye separation ability. The composite GO-NG membrane (GNM) enhanced the water flux to approximately 3 times higher than that of GOM, with higher than 98% rejection for various dyes. GNM remained stable during this purification.

Plastic Forming of Graphene Oxide Membranes into 3D Structures.

Flat, membrane-like materials made of graphene oxide (GO) nanoflakes have extraordinary mechanical properties including high stiffness, high strength, and low weight. However, the forming of complex nonplanar structures from flat GO membranes is difficult because of the intrinsic brittleness of GO. Here we present a simple and low-cost method to plasticize vacuum-filtrated GO membranes using a cellulose additive. Compared with the pure GO membrane, the GO-cellulose membranes had a lower Young's modulus but significantly improved ductility. Using the flat GO-cellulose membrane, we successfully embossed hemispherical caps with high geometrical fidelity, smooth surfaces, and no tearing or other damages to the membrane. The stiffness of the embossed 3D structure was increased further by cross-linking with a borax solution. Hemispherical caps made of 75 wt % GO with 25 wt % cellulose slurry combining borax cross-linking showed the highest stiffness. This study extends the applications of GO membranes and allows the harnessing of their extraordinary properties to nonplanar structures.

Potential application of graphene oxide membranes in high-level liquid waste treatment

The drawbacks of current high-level liquid waste (HLLW) separation processes would bring some adverse effects on the sustainable and clean utilization of nuclear power. In this work, a novel separation method for HLLW treatment based on graphene oxide membranes (GOMs) was investigated. Effects of nitric acid concentration and membrane thickness on the permeation behaviors of typical ions through GOMs were systematically investigated. On the whole, the permeation rates were in the order: hydrogen ion, cesium ion > sodium ion > strontium ion > europium ion, uranyl ion > thorium ion, which could be well explained by size exclusion and chemical interaction. As the nitric acid concentration decreased, strong coordination cations were generally restrained from migrating through GOMs due to cations hydrolysis and deprotonation of graphene oxide sheets. Ions permeation was supposed to be a two-step process which included entrance to the membrane and intramembrane migration. Based on the favorable rejection of f-block elements, GOMs separation showed promising potential in HLLW treatment. Furthermore, a new technical route for HLLW separation was proposed which showed superiority of simplified process, low running cost, less secondary radioactive waste production.

Regulating the Interlayer Spacing of Graphene Oxide Membranes and Enhancing their Stability by Use of PACl.

Graphene oxide (GO) is an ideal membrane material for water treatment due to its outstanding physicochemical properties and unique lamellar structure. However, the separation performance and practical application of GO membranes are mainly affected by the interlayer spacing and stability in aqueous solutions. Here, we report a novel and facile approach to fabricating GO membranes with adjustable interlayer spacing and high stability in aqueous solutions through cross-linking with polyaluminum chloride (PACl). With this approach, the lamellar spacing can be adjusted by changing the OH/Al ratios (B values) of the PACl, and the GO nanosheets can be tightly bonded by the strong electrostatic effect that PACl provides between them. The average interlayer spacing of the GO layer could be varied approximately in the range of 0.80-1.09 nm. The PACl-GO membranes demonstrated excellent stability in water and inorganic/organic solutions when the concentration of PACl was 0.1, 1, and 10 mM, remaining unchanged for at least 2 weeks. Moreover, the PACl-GO membranes featured exceptional sieving capabilities for model and natural organic substrates, while it was also observed that increasing the interlayer spacing of the PACl-GO membranes increased both the membrane flux and the separation performance of organic matter.

A freestanding graphene oxide membrane for efficiently harvesting salinity gradient power

Salinity gradient power (SGP) holds great potential for electricity generation. However, the technology scale-up is hindered by the lack of high-performance membranes. Here we initiate the application of freestanding graphene oxide membranes (GOMs) in pressure retarded osmosis (PRO) to generate SGP. The freestanding GOMs have moderate water permeability coefficient and excellent mechanical strength. Due to their ability to minimize internal concentration polarization (ICP), the freestanding GOMs can achieve high water flux in the osmosis systems, especially when the draw solution concentration is high. By combining experimental work and theoretical calculation, we found that the GOMs can have high power density in the PRO system: a power density of 24.62 W/m2 is obtained at a hydraulic pressure of 6.90 bar using 3 M and 0.017 M of NaCl as a draw and a feed solution, respectively. This study provides a new way of designing membranes for PRO system, the results show great potential for application of GOMs in PRO to generate SGP.

Functional graphene oxide membrane preparation for organics/inorganic salts mixture separation aiming at advanced treatment of refractory wastewater

Some refractory organic matters or soluble microbial products remained in the effluents of refractory organic wastewater after biological secondary treatment and need an advanced treatment before final disposal. Graphene oxide (GO) was known to have potential to be the next generation membrane material. The functional organics/inorganic salts separation GO membrane preparation and application in wastewater advanced treatment could reduce energy or chemicals consumption and avoid organics/inorganic salts mixed concentrate waste problems after nanofiltration or reverse osmosis. In this study, we developed a novelty GO membrane aiming at advanced purification of organic matters in the secondary effluents of refractory organic wastewater and avoiding the organics/inorganic salts mixed concentrate waste problem. The influence of preparation conditions including pore size of support membrane, the number of GO layers and the applied pressure was investigated. It was found that for organics/inorganic salts mixture separation membrane preparation, the rejection and flux would achieve balance for the support membrane at a pore size of ~0.1μm and the number of GO layers of has an optimization value (~10 layers). A higher assemble pressure (~10bar) contributed to the acquisition of a higher rejection efficiency and lower roughness membrane. This as prepared GO membrane was applied to practical secondary effluent of a chemical synthesis pharmaceuticals wastewater. A good organic matter rejection efficiency (76%) and limited salt separation (<14%) was finally obtained. These results can promote the practical application of GO membrane and the resourcelized treatment of industrial wastewater.

Application of graphene oxide membranes for removal of natural organic matter from water

Changes in the complexity of natural organic matter (NOM) have impacted the performance of direct filtration plants of water industries, resulting in reduced treatment capacity, and can lead to increased disinfection by-products. Hence, the need to identify new materials in future can be converted into more effective technologies and processes. We report a laboratory scale innovative use of graphene oxide membranes to remove NOMs from water that had been treated and still contained 5 mg/L DOC. Our study shows that graphene oxide based membranes can reject ∼100% of NOM while maintaining high water flux of 65 L m−2 h−1 bar−1 at atmospheric pressure. Our results indicate that it is possible to develop a graphene oxide-based water filtration technology.

Surface effect on the self-reinforcing behavior of graphene oxide membranes

Cyclic microbridge tests were applied to investigate the mechanical properties of the 100-to-400-nm-thick graphene oxide membranes. The effective Young’s moduli of different thickness graphene oxide membranes were derived and proved to be size dependent. The self-reinforcing behavior of graphene oxide membranes, which exhibits as an increase in Young’s modulus after cyclic loading, was observed and turned out to be in a relationship with thickness. A theoretical analysis is presented to explain the size dependence of the self-reinforcing Young’s moduli. This work is meaningful for the applications of graphene oxide membranes and the development of basic elements of the micro/nano-electro-mechanical systems.

Ion sieving in graphene oxide membranes via cationic control of interlayer spacing.

Graphene oxide membranes-partially oxidized, stacked sheets of graphene-can provide ultrathin, high-flux and energy-efficient membranes for precise ionic and molecular sieving in aqueous solution. These materials have shown potential in a variety of applications, including water desalination and purification, gas and ion separation, biosensors, proton conductors, lithium-based batteries and super-capacitors. Unlike the pores of carbon nanotube membranes, which have fixed sizes, the pores of graphene oxide membranes-that is, the interlayer spacing between graphene oxide sheets (a sheet is a single flake inside the membrane)-are of variable size. Furthermore, it is difficult to reduce the interlayer spacing sufficiently to exclude small ions and to maintain this spacing against the tendency of graphene oxide membranes to swell when immersed in aqueous solution. These challenges hinder the potential ion filtration applications of graphene oxide membranes. Here we demonstrate cationic control of the interlayer spacing of graphene oxide membranes with ångström precision using K+, Na+, Ca2+, Li+ or Mg2+ ions. Moreover, membrane spacings controlled by one type of cation can efficiently and selectively exclude other cations that have larger hydrated volumes. First-principles calculations and ultraviolet absorption spectroscopy reveal that the location of the most stable cation adsorption is where oxide groups and aromatic rings coexist. Previous density functional theory computations show that other cations (Fe2+, Co2+, Cu2+, Cd2+, Cr2+ and Pb2+) should have a much stronger cation-π interaction with the graphene sheet than Na+ has, suggesting that other ions could be used to produce a wider range of interlayer spacings.

Potential application of graphene oxide membranes for removal of Cs(I) and Sr(II) from high level-liquid waste

Abstract As a new carbon-based membrane material used for ionic and molecular sieving, the graphene oxide (GO) membrane also has potential application in radiochemical separation. In this work, the permeation performances of some typical metallic elements in high level-liquid waste (HLLW) through the ionic sieving 5-μm-thick GO membranes were investigated. It was found that the permeation rates of ions through GO membranes markedly decreased with the increase of hydrated ionic radii. Cs(I) and Sr(II) permeated through GO membranes quickly, whereas lanthanide ions and actinide ions infiltrated much more slowly, thus providing the feasibility of separation according to the difference of hydrated ionic radii. Moreover, the concentrations of initial metal ions and acidity in feed solutions also had influences on the permeation of ions through GO membranes, and higher initial metal ions and feed solution acidity were favorable to the removal of Cs(I) and Sr(II). The barrier separation test indicated that GO membranes had promising ability for the separation of Cs(I) and Sr(II) from lanthanide and actinide ions due to the difference of hydrated ion radius, and the separation factor of Cs(I)/U(VI) and Sr(II)/U(VI) would reach about 10 and 3 in single penetration. The presented results demonstrated that the membrane separation based on GO membrane would be a promising candidate for the removal of Cs(I) and Sr(II) from HLLW.

Graphene Oxide Membrane Fuel Cells: Utilizing of a New Class of Ionic Conductor

The characterization and application of graphene oxide membranes as fuel cell electrolytes is explored and presented. Morphology, chemical composition, mechanical and electrochemical properties of vacuum-filtration prepared graphene oxide membranes and their performance as fuel cell electrolytes are discussed. Our graphene oxide membrane fuel cell (GOMFC) showed a maximum power density of ~ 6 mW/cm2 at 30 °C. Power density exhibited a decrease with increasing temperature and operation time, possibly due to partial loss of oxygen through reduction, and a resulting decrease in water-mediated proton transport.