Ultrathin Graphene Oxide Membranes Research Articles

Highly permeable PA@GO loose nanofiltration membranes enabled by hierarchical transport channels for efficient dye removal

Graphene oxide (GO) membranes exhibit ultrafast water permeation properties, which have been employed in various membrane-based separations including nanofiltration for dye removal from textile wastewater. However, it’s still a great challenge to achieve precise control over the microstructure of GO membranes and obtain ultrathin GO membranes with exceptional separation efficiency and robust membrane structure. Herein, in-situ confined interfacial polymerization (IP) is proposed for fabricating loose polyamide (PA)@GO hybrid membranes with high permeance and dye rejection as well as robust membrane stability. A new diamine of sulfadiazine (SA) with intrinsic hydrophilic and conjugated sulfonamide groups is employed as cross-linker of GO membranes and monomer of PA in IP process, simultaneously. PA is in-situ synthesized in confined GO interlayer via IP process and intercalated into GO interlayer, which enlarges the interlayer spacing of GO membranes gradiently. The combination of hydrophilic PA nanofiltration layer on GO membrane surface and the PA intercalated GO membrane with varying interlayer spacing creates hierarchical transport channels for water molecules, which contributes to the high water permeance. Moreover, the less reactive SA monomer endows PA@GO selective layer with appropriate negative charge and loose transport channels, which contributes to both of high permeance and dye rejection due to Donnon effect and size exclusion effect. The PA@GO hybrid membrane exhibits high permeance of 75.5 L/(m2·h·bar) with TB dye rejection of 99.8 %, and exhibits low NaCl rejection of 11.6 %. Moreover, PA@GO hybrid membrane shows good fouling resistance and long-term stability as well as stable separation performance under harsh conditions. Both of high permeance and dye rejection of PA@GO hybrid membrane suggests that the integration of PA nanofiltration layer and GO membrane via in-situ confined interfacial polymerization can achieve the delicate control over the interlayer channel structure and the physicochemical properties of the membrane surface of GO membranes, which offers a promising method to break through the trade-off effect between permeability and selectivity of GO membranes.

Development of an Asymmetric Hydrophobic/Hydrophilic Ultrathin Graphene Oxide Membrane as Actuator and Conformable Patch for Heart Repair (Adv. Funct. Mater. 32/2023)

Development of an Asymmetric Hydrophobic/Hydrophilic Ultrathin Graphene Oxide Membrane as Actuator and Conformable Patch for Heart Repair (Adv. Funct. Mater. 32/2023)

Development of an Asymmetric Hydrophobic/Hydrophilic Ultrathin Graphene Oxide Membrane as Actuator and Conformable Patch for Heart Repair

AbstractA conductive engineered cardiac patch (ECP) can reconstruct the biomimetic regenerative microenvironment of an infarcted myocardium. Direct ink writing (DIW) and 3D printing can produce an ECP with precisely controlled microarchitectures. However, developing a printed ECP with high conductivity and flexibility for gapless attachment to conform to epicardial geometry remains a challenge. Herein, an asymmetrical DIW hydrophobic/hydrophilic membrane using heat‐processed graphene oxide (GO) ink is developed. The “Masked spin coating” method is also developed that leads to a microscale GO (hydrophilic)/reduced GO (rGO, hydrophobic) physiological sensor, as well as a macroscale moisture‐driven GO/rGO actuator. Depositing mussel‐inspired polydopamine (PDA) coating on the one side of the DIW rGO , the ultrathin (approximately 500 nm) PDA‐rGO (hydrophilic)/rGO (hydrophobic) microlattice (DrGOM) ECP is bestowed with the flexibility and moisture‐responsive actuation that allows gapless attachment to the curved surface of the epicardium. Conformable DrGOM exhibits a promising therapeutic effect on rats' infarcted hearts through conductive microenvironment reconstruction and improved neovascularization.

Highly stable graphene oxide/nylon membrane for molecular separation

Graphene oxide (GO), due to its one-atom-thick structure and enriched oxygenated functionalities, is a promising candidate material to develop nanofiltration membranes to tackle the current worldwide water shortage. However, the stability of the GO membrane in an aqueous environment and its long-term operation remains unresolved. These issues greatly affect the mass transfer in the GO membrane. Here, we fabricate an ultrathin GO membrane on a nylon substrate within 5 min with the help of vacuum filtration for molecular separation. Thus, GO/nylon membranes dried in an oven at temperatures of 70 °C show greater aqueous solution stability than those dried at room temperature. To validate the stability, both GO membranes were immersed in DI water for 20 d. As a result, the GO/nylon membrane dried at room temperature was completely detached from the substrate within 12 h, whereas the GO/nylon membrane that dried at 70 °C remained stable for more than 20 d without any physical damage. We suppose the enhanced stability is due to the thermally induced balance in electrostatic repulsion resulting in stabilizing of the GO membrane. This method improves the GO membrane’s operating time, selectivity, and permeability. Therefore, the optimized GO/nylon membrane shows higher rejection of organic dyes (∼100%) and good selectivity for sulfate salts such as Na2SO4 and MgSO4 (>80%). The membrane continuously operates for more than 60 h with only a 30% water permeability decline and 100% rejection of dyes. We believe that the drying of GO/nylon membranes at a moderate temperature is important for enhanced separation performance and stability. This drying technique can be applied to other applications.

Ultra‐Permeable Dual‐Mechanism‐Driven Graphene Oxide Framework Membranes for Precision Ion Separations

AbstractTwo‐dimensional graphene oxide (GO) membranes are gaining popularity as a promising means to address global water scarcity. However, current GO membranes fail to sufficiently exclude angstrom‐sized ions from solution. Herein, a de novo “posterior” interfacial polymerization (p‐IP) strategy is reported to construct a tailor‐made polyamide (PA) network in situ in an ultrathin GO membrane to strengthen size exclusion while imparting a positively charged membrane surface to repel metal ions. The electrostatic repulsion toward metal ions, coupled with the reinforced size exclusion, synergistically drives the high‐efficiency metal ion separation through the synthesized positively charged GO framework (PC‐GOF) membrane. This dual‐mechanism‐driven PC‐GOF membrane exhibits superior metal ion rejection, anti‐fouling ability, good operational stability, and ultra‐high permeance (five times that of pristine GO membranes), enabling a sound step towards a sustainable water‐energy‐food nexus.

Ultra-Permeable Dual-Mechanism-Driven Graphene Oxide Framework Membranes for Precision Ion Separations.

Two-dimensional graphene oxide (GO) membranes are gaining popularity as a promising means to address global water scarcity. However, current GO membranes fail to sufficiently exclude angstrom-sized ions from solution. Herein, a de novo "posterior" interfacial polymerization (p-IP) strategy is reported to construct a tailor-made polyamide (PA) network in situ in an ultrathin GO membrane to strengthen size exclusion while imparting a positively charged membrane surface to repel metal ions. The electrostatic repulsion toward metal ions, coupled with the reinforced size exclusion, synergistically drives the high-efficiency metal ion separation through the synthesized positively charged GO framework (PC-GOF) membrane. This dual-mechanism-driven PC-GOF membrane exhibits superior metal ion rejection, anti-fouling ability, good operational stability, and ultra-high permeance (five times that of pristine GO membranes), enabling a sound step towards a sustainable water-energy-food nexus.

Constructing 2D ultrathin graphene oxide membranes with supramolecular-assembled nano-adhesives for enhancing water stability

Constructing 2D ultrathin graphene oxide membranes with supramolecular-assembled nano-adhesives for enhancing water stability

Ultrathin graphene oxide membrane for pilot scale dyehouse effluent treatment

In the past decade, thanks to their ultrafast water transport and excellent molecule sieving properties, researches on graphene oxide (GO) based membranes have developed rapidly. However, the researches were mainly conducted in laboratory scale, and so far, there is no real on-site wastewater treatment experiments using GO-based membranes in pilot-scale reported. Herein, we report an on-site pilot trial study using the ultrathin GO membrane to treat a dyehouse effluent. The performance of the GO membrane was studied to provide insight for the large-scale applications. A long-term pilot trial of 45 days was conducted to investigate the long-term stability of the GO membrane. The rejection of mixed salts in the dyehouse effluent can be maintained at about 77.0%. And most typical organic pollutants in the effluent can be effectively removed. The quality of the produced water fully meets the requirements of the Chinese Industry Standard FZ/T 01107-2011. The results showed that the GO membrane has excellent purification efficiency for the real dyehouse effluent and excellent stability during the long-term trial run. The pilot scale study suggests that the GO membrane is highly feasible to treat the dyehouse effluent in a large industrial scale.

A Facile and Scalable Method of Fabrication of Large-Area Ultrathin Graphene Oxide Nanofiltration Membrane.

With their ultrafast water transport and excellent molecule sieving properties, graphene oxide (GO)-based membranes show great potential in the membrane filtration field for water purification and molecular separation. However, the inability of uniform GO membranes to be produced on an industrial scale and their nonenvironmentally friendly reduction treatment are the bottleneck preventing their industrial applications. Herein, we report a scalable ultrathin uniform GO membrane fabrication technique. Ultrathin GO membranes with a large area of 30 × 80 cm2 and a thickness of a few nanometers were uniformly and facilely fabricated using a continuous process combining Mayer rod-coating and a short-time, high-power UV reduction. The interlayer spacing of the GO membrane could be effectively reduced and regulated to improve the salt rejection rate. The fabricated membrane showed superior water permeability of over 60.0 kg m-2 h-1 and a high separation efficiency of over 96.0% for a sodium sulfate (Na2SO4) solution. It also exhibited excellent mechanical stability under various harsh crossflow conditions. More importantly, the fabrication method developed here can be scaled up using a roll-to-roll industrial production process, which successfully solves the problem currently faced by GO membrane researchers and makes the industrial usage of GO membrane a reality.

Nacre-like ultra-robust supramolecular-functionalized graphene oxide membrane for bifunctional separation

Two-dimensional graphene oxide (GO) membranes exhibit great potential for environmental aqueous separation and purification. However, their viability and performance are greatly limited under cross-flow conditions due to the enlargement of interlayer spacing and peeling of stacked GO laminates in aqueous environments. Herein, inspired by natural nacre structure, we present a dual-functional and ultra-stable β-cyclodextrin (β-CD) -polyacrylic acid (PAA) -GO composite membrane, with a constant d-spacing in both wet and dry states. Nanosheets and chain polymers construct a typical “brick-mortar” structural configuration, which exhibits great anti-swelling property compared with other reported GO membranes. By rationally optimizing and tuning the membrane structures, the ultrathin GO membrane (∼50 nm) exhibits outstanding stability in cross-flow and long-term filtration. Moreover, the designed membrane shows dual functions (high-throughput enantioselectivity and excellent dyes rejection) with the increase of molecular size. This strategy boosts the ongoing research in designing robust lamellar membrane materials for practical engineering applications in aqueous environments.

Ultra-thin graphene oxide membrane deposited on highly porous anodized aluminum oxide surface for heavy metal ions preconcentration

Analyte extraction using graphene oxide (GO) can be challenging owing to the stochastic behavior of the permeation of water molecules and heavy metal ions, imperfect pore structures, and irregular distribution of multi-layer sheets. We prepared a free standing, through-hole graphene oxide membrane deposited on porous anodic aluminum oxide (AAO) substrate. The hydrophilicity of the GO membrane was improved via oxygen plasma treatment. The resulting AAO–GO membrane was used as novel adsorbent for the heavy metal ions preconcentration prior to their determination using inductively coupled plasma optical emission spectroscopy. This sub-micrometer-thick membrane allowed unimpeded permeation of water molecules via two-dimensional capillaries formed across the pores and in between the closely spaced GO sheets. The proposed method shows good detection limit of 1.2 ng L−1, and the co-existing ions did not affect the extraction efficiency of the adsorbent. The accuracy of the method was assessed by analyzing standard reference materials, where the Student’s t-test values were less than the critical Student’s t-value of 4.303 (95% confidence level). Good precision was achieved, as coefficients of variation ranged between 4% and 5%. The developed SPE adsorbent is a promising alternative for bulk adsorbents owing to the wide variety of available 2D materials and deposition methods.

Ultrathin graphene oxide membrane with constructed tent-shaped structures for efficient and tunable molecular sieving

Tent-shaped ultrathin GO membrane for tunable molecular sieving.

Operando study of water vapor transport through ultra-thin graphene oxide membranes

The paper reports operando study of ultra-thin (50 nm) graphene oxide membranes by grazing incidence x-ray scattering in air dehumidification experiments. Absorption of water vapors in GO layers follows a modified Kelvin equation revealing condensation in an elastic slit, while desorption of water is limited by a few outer GO layers providing bottleneck restrictions to water transport and resulting in classical H2-type isotherms. GO interlayer distances (d) vary in range from 7.2 Å to 11.5 Å depending on partial water pressures in a feed stream and permeate. The permeance of water vapor through GO decreases steadily with decreasing interlayer distance between GO sheets from ~80 000 l/(m2 · atm · h) to ~30 000 l/(m2 · atm · h) falling down to negligible values below d ≈ 9.2 Å. Water transport in GO is described by Poiseuille equation and hopping diffusion depending on the number of water layers between GO planes, and was modelled with semi-empirical methods. It is shown the performance of thin GO membranes is strongly governed by the interstitial water quantity as dictated by water partial pressure.

Cross-flow-assembled ultrathin and robust graphene oxide membranes for efficient molecule separation

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.

Ultrathin graphene oxide membranes on freestanding carbon nanotube supports for enhanced selective permeation in organic solvents

Among the various factors required for membranes in organic solvent separations, the stability of membrane supports is critical in the preparation of membranes with universal chemical stability, mechanical flexibility, and high flux. In this study, nanoporous freestanding carbon nanotube (CNT) films were fabricated and utilized as supports for enhanced permeation in organic solvents. The excellent chemical stability of the CNT support allowed it to withstand various organic solvents such as toluene, acetone, and dimethylformamide. In addition, the structural stability and high pore density of CNT supports allowed the deposition of an ultrathin selective layer for an enhanced-flux membrane. Membrane performance was demonstrated by depositing a thin graphene oxide (GO) layer on the CNT support; GO was selected because of its high chemical stability. CNT-supported GO membranes effectively blocked molecules with molecular weight larger than ~800 g mol−1 while allowing the fast permeation of small molecules such as naphthalene (permeation was 50 times faster than that through thick GO membranes) and maintaining selective permeation in harsh solvents even after 72 hours of operation. We believe that the developed CNT support can provide fundamental insights in utilizing selective materials toward organic solvent membranes.

Self-Assembly: A Facile Way of Forming Ultrathin, High-Performance Graphene Oxide Membranes for Water Purification.

Single-layer graphene oxide (SLGO) is emerging as a new-generation membrane material for high-flux, high-selectivity water purification, owing to its favorable two-dimensional morphology that allows facile fabrication of ultrathin membranes with subnanometer interlayer channels. However, reliable and precise molecular sieving performance still necessarily depends on thick graphene oxide (GO) deposition that usually leads to low water flux. This trade-off between selectivity and flux significantly impedes the development of ultrathin GO membranes. In this work, we demonstrate that the selectivity/flux trade-off can be broken by self-assembly of SLGO via simple deposition rate control. We find GO membranes, prepared by slow deposition of SLGO flakes, exhibit considerably improved salt rejection, while counterintuitively having 2.5-4 times higher water flux than that of membranes prepared by fast deposition. This finding has extensive implications of designing/tuning interlayer nanostructure of ultrathin GO membranes by simply controlling SLGO deposition rate and thus may greatly facilitate their development for high flux, high selectivity water purification.

Imaging and Analysis of Encapsulated Objects through Self-Assembled Electron and Optically Transparent Graphene Oxide Membranes.

We demonstrate a technique for facile encapsulation and adhesion of micro- and nano objects on arbitrary substrates, stencils, and micro structured surfaces by ultrathin graphene oxide membranes via a simple drop casting of graphene oxide solution. A self-assembled encapsulating membrane forms during the drying process at the liquid-air and liquid-solid interfaces and consists of a water-permeable quasi-2D network of overlapping graphene oxide flakes. Upon drying and interlocking between the flakes, the encapsulating coating around the object becomes mechanically robust, chemically protective, and yet highly transparent to electrons and photons in a wide energy range, enabling microscopic and spectroscopic access to encapsulated objects. The characteristic encapsulation scenarios were demonstrated on a set of representative inorganic and organic micro and nano-objects and microstructured surfaces. Different coating regimes can be achieved by controlling the pH of the supporting solution, and the hydrophobicity and morphology of interfaces. Several specific phenomena such as compression of encased objects by contracting membranes as well as hierarchical encapsulations were observed. Finally, electron as well as optical microscopy and analysis of encapsulated objects along with the membrane effect on the image contrast formation, and signal attenuation are discussed.

Extended friction elucidates the breakdown of fast water transport in graphene oxide membranes

The understanding of water transport in graphene oxide (GO) membranes stands out as a major theoretical problem in graphene research. Notwithstanding the intense efforts devoted to the subject in the recent years, a consolidated picture of water transport in GO membranes is yet to emerge. By performing mesoscale simulations of water transport in ultrathin GO membranes, we show that even small amounts of oxygen functionalities can lead to a dramatic drop of the GO permeability, in line with experimental findings. The coexistence of bulk viscous dissipation and spatially extended molecular friction results in a major decrease of both slip and bulk flow, thereby suppressing the fast water transport regime observed in pristine graphene nanochannels. Inspection of the flow structure reveals an inverted curvature in the near-wall region, which connects smoothly with a parabolic profile in the bulk region. Such inverted curvature is a distinctive signature of the coexistence between single-particle zero-temperature (noiseless) Langevin friction and collective hydrodynamics. The present mesoscopic model with spatially extended friction may offer a computationally efficient tool for future simulations of water transport in nanomaterials.

Ambivalent Effect of Thermal Reduction in Mass Rejection through Graphene Oxide Membrane.

We report ambivalent rejection behavior of a graphene oxide membrane (GOM) having a reduced interlayer spacing. Ultrathin GOMs having a thickness of 50 nm were fabricated using a vacuum filtration method followed by subjecting the samples to thermal reduction at 162 °C. The interlayer spacing of GOMs was reduced by 1 Å on thermal reduction as compared with that of the natural GOMs. The rejection rate with dye molecules was tested using dyes having three different types of charges in a dead-end filtration instrument. Rejection rate of the reduced GOM with the dyes having an opposite charge was improved up to 99.7%, indicating the dominant effect of the physical sieving diameter. In contrast, in the case of ion permeation of natural GOM, a higher rejection rate for several metal ions was observed as compared with that of GOMs having 1 Å smaller interlayer spacing, indicating the dominant effect of surface charges on the GOM samples.

Ultrathin graphene oxide membranes for the removal of humic acid

In this study, multiple layers of graphene oxide (GO) were coated on a commercially available polyethersulfone ultrafiltration membrane via simple vacuum filtration of a GO suspension. The effect of GO coating on the membrane performance and fouling resistance was examined, in terms of water flux, natural organic matter (NOM) rejection, and flux decline due to NOM fouling. The results showed that the water flux change of the permeate was minimal (less than ±10%), while NOM rejection was improved significantly by the GO coating (31%, 51%, and 67% for the GO-5nm, GO-10nm, and GO-30nm membranes, respectively). The GO-coated membranes also enhanced membrane recovery and antifouling capabilities, due mainly to increased hydrophilicity of the GO-membrane surface. These observations suggest that the GO-coated membrane, prepared by a facile filtration process in the laboratory, facilitates removal of NOM from water and minimizes the associated membrane fouling.