GO Membrane Research Articles

Polydopamine functionalized graphene oxide membrane with the sandwich structure for osmotic energy conversion.

Ion-selective membrane is the key component for osmotic energy conversion. Nanofluid channels based on two-dimensional materials have advantages of facile preparation, tunable channel size, and easy upscaling, which is promising for efficient osmotic energy harvesting. However, further improvement of the output power is hindered by the low ion sensitivity for the limited charge density. Herein, we demonstrate the preparation of a cation-selective polydopamine-coated graphene oxide composite membrane with the sandwich structure by a simple interfacial polymerization technique, which greatly improves the surface charge density and further generates a power density of 3.4W/m2 under river water and seawater. The GO membrane is firstly fabricated to function as the supporting layer and provide the reaction sites. And the ultrathin selective layer of the polydopamine membrane is chemically bonded with the GO layer by the in-situ polymerization on both sides of the GO membrane. The sandwiched nanofluidic membrane with ultrahigh charge density exhibits both high cation selectivity and ionic conductivity, benefiting the performance of osmotic energy conversion. The economic, easy-prepared method of the sandwiched nanofluidic membrane provides a promising strategy for high-performance osmotic energy conversion.

A cation-π interaction confined graphene oxide membrane for separation of light paraffins and olefins.

A supported graphene oxide membrane is endowed with selective function for olefins by a cation intercalation method. The metal-cation fixed GO membrane exhibits a high propane to propylene ideal selectivity of 1817 for single gas and a separation factor of 7.1 for binary mixtures with fast gas permeance in the order of 10-7 mol m-2 s-1 Pa-1 and reliable permeation stability.

Sepiolite@TiO2/Graphene oxide composite membrane for long-term Separation of oily wastewater

Microwave synthesis was taken to synthesis A-SEP@TiO2 which has a steady chemical property. The A-SEP@TiO2 composite materials and GO (with different proportion)were mixed and then pumped on commercial PVDF membranes to filter. Finally, the composite membrane A-SEP@TiO2/GO was obtained Under electrostatic self-assembly. Due to the superhydrophilicity and underwater super hydrophobicity of the surface of A-SEP@TiO2/GO membrane, A-SEP@TiO2/GO composite has shown great potential in the field of oil in water. The separation rates of four different emulsions (petroleum ether, toluene, Mesitylene, n-hexane) are all above 90%. With the steady chemical properties, A-SEP@TiO2/GO composite membrane is able to separate oil from water in harsh environment in long-run. After being immersed in 1 mol/L acid and alkali salt solution for one month respectively, all the sample membranes showed a better stability than commercial PVDF membranes. Also, the oil and water removal flux of A-SEP@TiO2/GO composite membrane only decreased by less than 10%, and that was why the composite membranecan can still maintain good cleaning performance even after ten times’ repetition of experiments,. Moreover, the membrane could efficiently remove dyes and heavy metal ions. Therefore, it has a great application prospect in complex water environment treatment.

Improvement of the chlorine resistance of graphene oxide membranes through siloxane cross-linking

ABSTRACT Nanofiltration membranes exhibit performance deterioration when exposed to highly concentrated chlorinated environments. This is a major challenge of nanofiltration process as chlorine-based chemicals are prevalent within industry for the treatment of organic fouling; thus, making membrane chlorine sensitivity detrimental to sustainable operation. Graphene oxide has an inherent chlorine sensitivity and degrades under exposure to high concentration of chlorine. This work describes a novel nanofiltration membrane fabrication strategy in which Polyethyleneimine and siloxane crosslinking chemistries were used to protect the carboxylic, hydroxyl, and epoxy functional groups of GO nanosheets from the attack of free chlorine. These chemistries were used to improve the chlorine-stability of the GO nanosheets. Polyethyleneimine (PEI) reduces GO and cross-links with oxygenated functional groups preventing their further reaction with chlorine. This chemistry was compared to the chlorine-tolerant siloxane cross-linkers which react with GO’s functional groups to decrease reaction sites. The use of (3-Aminopropyl)triethoxysilane (APTES) and (3-Glycidyloxypropyl)trimethoxysilane (GLYMO) cross-linkers resulted in stable retentions that varied by less than 0.5% following 1,000 ppm chlorine exposure for 1 h. Additionally, GLYMO functionalisation of the GO membrane exhibited exceptional chlorine resistance maintaining a methyl blue retention of 98.0 ± 2.15% following 1 h of exposure 30,000 ppm of chlorine.

Study on the Shear Behaviour and Fracture Characteristic of Graphene Kirigami Membranes via Molecular Dynamics Simulation.

In this study, we aimed to provide systematic and critical research to investigate the shear performance and reveal the corresponding structural response and fracture characteristics of the monolayer GK membrane. The results demonstrate that the kirigami structure significant alters the shear performance of graphene-based sheets. Tuning the porosity by controlling the incision size, pore distribution, and incision direction can effectively adjust the shear strength and elastic modulus of GK membranes. The trade-off of the stress and strain of the GK membrane is critical to its shear behaviour. The microstructural damage processes and failure characteristics further reveal that making more carbon atoms on the GK structure sharing the strain energy is the key to reinforcing the shear performance of membranes. Based on this, we found that adding the shear loading in the direction of perpendicular to the incisions on the GK membrane can significantly improve the shear strength and stiffness of the membrane by 26.2–32.1% and 50.2–75.3% compared to applying shear force parallel to GK incisions. This research not only broadens the understanding of shear properties of monolayer GO membrane but also provides more reference on the fracture characteristics of GK membranes for future manufacturing and applications.

Intercalated 2D nanowires network cooperating with its entanglement in tuneable GO membrane nanochannels for ultrafast organic solvent nanofiltration

Organic solvent nanofiltration (OSN) as an emerging membrane separation technology has received substantial attentions recently. However, high permeability and selectivity simultaneously remains a momentous challenge for OSN mainly limited by the trade-off between permeance and selectivity. Here, ultralong and flexible polymeric nanowires (PWs) with positive charge were used to construct highly entangled PWs network fabricating interlayered GO composite membrane for OSN. The membrane exhibits a unique configuration with alternating stacking of highly entangled nanowires network and ultrathin GO layers. Meanwhile, the alternating layers become interlinked closely due to the strong electrostatic interactions between the positively charged nanowires and negatively GO layers. It could endow composite membrane with excellent stability in solvent. Unique membrane separation channels, constructed by close-knit interlaced PWs network and GO interlayer structure, allow a high flux of various solvents through the membrane and excellent rejection for small molecules. Solvent permeance of the optimized membrane could reach 91.3 L/m2·h with rejection of above 90% for Congo Red in methanol. The designed GO composite membrane is promising to practical application in OSN field, and it may also be useful for aqueous applications in separation and precise screening process.

Design lamellar GO membrane based on understanding the effect of functional groups distributed in the port on desalination

The lamellar membranes have been considered as one of the most promising candidates for seawater desalination owing to their well-defined 2D nanochannels for fast water permeation and excellent ions rejection. However, it was difficult to directly determine the influence of different functional groups on the desalination performance through experiments. In this work, the –COOH/–CH3 were introduced to the port of lamellar GO membranes, and the effect of functional group distributed in the port of membranes was investigated via non-equilibrium molecular dynamic simulation (NEMD). It was found that the water flux rate passing through the lamellar GOY-X membranes with –COOH/–CH3 group modified in their port was slightly higher than that in systems without port modification. Some lamellar membranes shown excellent water flux rate and ion rejection ions were designed by taking advantage of functional group distributed in the port of membranes and surfaces of pore channel.

Highly Permeable Sulfonated Graphene-Based Composite Membranes for Electrochemically Enhanced Nanofiltration.

A sulfophenyl-functionalized reduced graphene oxide (SrGO) membrane is prepared. The SrGO membranes have a high charge density in water and could provide many atomically smooth nanochannels, because of their strong ionized-SO3H groups and low oxygen content. Therefore, the SrGO membranes have an excellent performance in terms of high permeance and high rejection ability. The permeance of SrGO membranes could be up to 118.2 L m−2 h−1 bar−1, which is 7.6 times higher than that of GO membrane (15.5 L m−2 h−1 bar−1). Benefiting from their good electrical conductivity, the SrGO membranes could also function as an electrode and demonstrate a significantly increased rejection toward negatively charged molecules and positively charged heavy metal ions such as Cu2+, Cr3+ and Cd2+, if given an appropriate negative potential. The rejection ratios of these metal ions can be increased from <20% at 0 V to >99% at 2.0 V. This is attributed to the enhanced electrostatic repulsion between the SrGO membrane and the like-charged molecules, and the increased electrostatic adsorption and electrochemical reduction in these heavy metal ions on the membranes. This study is expected to contribute to efficient water treatment and the advance of graphene-based membranes.

Effect of sodium and potassium on polysaccharide fouling on PVDF and graphene oxide modified PVDF membrane surfaces

This study presented the contribution of monovalent cations (Na+ and K+) to the adsorptive sodium alginate (SA) fouling in real-time using a quartz crystal microbalance and dissipation (QCM-D). Polyvinylidene fluoride (PVDF) and graphene oxide modified PVDF membrane (GO-PVDF) were selected as representative membrane materials. Atomic force microscopic (AFM) equipped with probes modified with foulant was used for exploring the adhesion force changes between SA and the membrane. The results showed that both Na+ and K+ can promote the adsorption capacity of SA on the membrane surface. SA fouling in Na+ condition was more severe than that in K+ circumstance due to higher attraction forces under identical ion strength. In addition, the GO-PVDF membrane is more readily/severely fouled than PVDF by SA when Na+ or K+ is present. The difference in the interaction forces was further interpreted using XDLVO theory. The results suggested that the Lewis acid-base adhesion free energy (ΔGflfAB) between SA decreased gradually with increasing Na+ concentration, while in the K+ environment, ΔGflfAB increased instead. Moreover, the increase of the Lifshitz-van der Waals components (γmLW) of the GO membrane, resulted in a higher attractive interaction in the initial phase of the SA fouling. The results of this study provide a microscopic analysis of the possible fouling mechanism of Na+ and K+ on membrane fouling and as well as provide insightful reflections for an appropriate approach (whether GO modified or not) to membrane fouling control.

Bio-inspired graphene oxide-amino acid cross-linked framework membrane trigger high water permeance and high metal ions rejection

As increasing demand for wastewater treatment, membranes with excellent performance are still needed in recent years. Graphene-based membranes are promising candidates by virtue of their outstanding mechanical properties, chemically resistant and atomic thickness. In this work, a kind of membrane with nacre-like structure of the hydrothermal reduction graphene oxide (hrGO) cross-linked by amino acid were fabricated. The hrGO-amino acid membranes exhibited both high water permeance and high metal ions rejection. Typically, when treated FeCl3 solutions, the hrGO membrane cross-linked by tryptophan (Trp) represented 191.0 L m−2 h−1 bar−1 water permeance which is 4.4-fold higher than that of pristine GO membrane, and is superior to other NF membranes while still maintained at 98.2% FeCl3 rejection. Moreover, the hrGO-Trp membrane also exhibited a stable separation performance in a long time. Overall, our work reveals a facile method to realize ultrahigh water permeance of GO-based membranes for wastewater treatment.

High-efficiency graphene oxide membranes intercalated by hollow TiO2 nanospheres and CNS@LDH composite spheres for enhancing dye separation from wastewater

Textile wastewater pollution with dyes has become a major source of water pollution. In the study, GO and composite nanospheres (CNS@LDH and HOTiO2) were used to form the composite materials by electrostatic self-assembly method, and the composite materials vacuum filtration on the surface of CA membrane to prepare the composite membranes for dyes separation. Among them, GO was used as a vertical separation layer in dyes separation, while the hollow structure of HOTiO2 nanosphere with a large specific surface area provided more adsorption sites, and the CNS@LDH nanosphere with core–shell structure played the role of expanding GO sheets and preventing HOTiO2 from collapsing. Compared with the GO membrane, the water flux of three dyes produced by GO/HOTiO2/CNS@LDH composite membrane increased by 18 times with a rejection rate of 99%. In addition, after 10 cycles of experiments, GO/HOTiO2/CNS@LDH composite membrane retained a rejection rate of over 98% with the flux of 79 L∙m−2∙h−1∙bar−1 for MB. GO/HOTiO2/CNS@LDH composite membrane retained a stable rejection rate on three dyes under extreme pH and ionic strength conditions. The composite membrane combined the adsorption and isolation effects of GO, HOTiO2, and CNS@LDH, which significantly enhanced the separation performance of dye wastewater. Accordingly, the GO/HOTiO2/CNS@LDH composite membrane has great potential in practical wastewater treatment.

Biomimic Heterostructured Graphene Oxide Membranes via Supramolecular-Mediated Intercalation Assembly for Efficient Water Transport.

Two-dimensional (2D) lamellar membranes have attracted increasing attention for efficient water purification. However, the low water-permeability, structural failure in aqua and high production cost have significantly restricted their practical large-scale applications. Inspired by the structures of glomerular filtration barrier (GFB) and nacre, a high-performance biomimic membrane via supramolecular-mediated intercalation assembly is reported, where rod-shaped cyclodextrin (CD) functionalized attapulgite (ATP-CD) is intercalated into CD-modified graphene oxide (GO-CD) lamellar channels, followed by locking adjacent ATP-CD and GO-CD through tannic acid (TA) and CD supramolecular networks. The formed GFB-like heterostructure endows the membrane with excellent water transport capability and the bionic "brick and mortar" nacre configuration boosts its anti-swelling stability simultaneously. The heterostructured GO membranes (≈100nm) fabricated in this way exhibit a good water permeability of 55.6Lm-2 h-1 bar-1 (≈20-fold higher than GO membrane) maintaining excellent dye rejection of >99% during 480h immersion. Given the low-cost materials (ATP, CD, and TA) and the modification generality, this economic strategy can hopefully achieve large-scale membrane fabrication and afford high applicability, which promotes the practical engineering applications of such 2D material membranes.

Mechanically intensified and stabilized MXene membranes via the combination of graphene oxide for highly efficient osmotic power production

Harnessing the osmotic energy from the salt concentration gradient between sea water and river water in nature represents as a promising sustainable power generation pathway that does not generate waste and CO2 emission. However, the current membranes with two-dimensional nano-channels generally have low mechanical strength, poor stability, and low transmission power efficiency, which result into low current and power density (≤1 W m−2) performance. Herein, we use MXene combined with GO (MXene/GO) to synthesize a composite membrane as a high-performance nanofluid permeability generator. The addition of 2D flexible GO membrane enhances the mechanical strength to achieve the required robustness of the composite membrane for practical application. By using river and sea water in the permeability generator, the power density for the MXene/GO composite membrane with 6 wt% GO can reach 3.7 W m−2 at room temperature (298 K). The influences of different GO ratio, pH, temperature, and membrane thickness on power density are also evaluated. At 343 K and pH = 7, the power density of 420 nm-thick MXene/GO composite membrane can achieve 7.88 W m−2, which is higher than most of the state-of-the-art membranes, highlighting the possibility of osmotic power generation. This work reports a new promising membrane for the practical application of osmotic energy conversion.

Graphene oxide membrane regulated by surface charges and interlayer channels for selective transport of monovalent ions over divalent ions

Separation of ions has wide applications both in industry and health care. Among them, the separation of mono-/di-valent ions remains great challenging, even for highly efficient membrane separation technology. The emerging two-dimensional-material (typically, graphene oxide, GO) membranes have shown outstanding molecular separation performance such as for water desalination and gas separation, while unattractive permeance and/or selectivity for separating mono/divalent ions. In this work, we designed a new type of GO membranes to separate mono-/di-valent ions, in which rationally-selected polyelectrolyte coating was introduced to simultaneously tune the surface charge and interlayer channels of assembled GO laminate. The resulting positively-charged membrane surface showed stronger repulsive force towards divalent cations over monovalent cations according to the Coulomb’s law; meanwhile, the regulated interlayer channels rejected divalent cations over monovalent cations with smaller size. The ion transport mechanism was understood by mathematic models of ion diffusion and DLVO theory. By utilizing the synergistic effect of electrostatic interaction and size sieving, the designed GO membrane exhibited excellent separation performance for various mono-/di-valent ion pairs, including K+/Mg2+, Na+/Mg2+, Li+/Mg2+. Especially, the K+ transport rate of ∼ 0.29 mol m−2 h−1 and K+/Mg2+ selectivity of ∼ 116 are demonstrated in single-salt solution test, outperforming the-state-of-the-art 2D-material membranes. In mixed-salt solution test, the K+/Mg2+ selectivity reached 45 and good structural stability was displayed during 80 h continuous operation on the GO membrane. This facile polyelectrolyte coating approach provides a new avenue to develop high-performing 2D-material membranes for efficient separation of mono/divalent ions.

A reduced pressure-assisted vapor penetration of ionic liquid into the laminated graphene oxide membranes for efficient CO2 separation

Tailor-made ultrathin and defect-free supported ionic liquid membranes (SILMs) have great potential for CO2 separation. Herein, we developed a highly perm-selective CO2-philic laminated GO supported ionic liquid membrane (GO-SILM) with a thickness of 100 nm, via a reduced pressure-assisted vapor penetration strategy. Specifically, under reduced pressure condition, the IL 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) vapor can not only seal the possible defects/pores in GO membrane, but also penetrate into the 2D nanochannels of laminated GO membrane. Based on the favorable interaction between IL and GO nanosheets, IL can be confined within the nanochannels of laminated GO membranes, which favors a fast and selective CO2 transport. Besides, the ultrathin selective layer shortens the transport distance extremely. Benefiting from the aforementioned features, the obtained GO-SILMs display a high CO2 permeance of 56.6 GPU with CO2/CH4 selectivity of 53.5, which is superior to other reported SILMs. The groundbreaking membrane fabrication approach through reduced pressure-assisted IL vapor penetration into GO membrane to seal the non-selective defects is facile, effective and IL-saving, which paves a new way for the development of ultrathin and defect-free SILMs for high-efficient CO2 separation.

Facile preparation of a MXene-graphene oxide membrane and its voltage-gated ion transport behavior.

Two-dimensional MXenes have become a crucial topic in the field of ion transportation owing to their excellent electrochemical performance. Herein, a strategy for preparing a layered MXene-graphene oxide (GO) membrane via vacuum filtration is proposed, which endows the delaminated two-dimensional MXene-GO membrane (MGOm) with excellent electrical conductivity and chemical stability, achieving an excellent voltage-gated ion transport behavior. Owing to the presence of charges or dipoles within the membrane's channel, the movement of electrons or dipoles under the influence of membrane potential is possible. By varying the transmembrane potential, the transition between the closed and open states of the voltage-gated ion channel can be adjusted. When a negative potential is applied at osmotic pressure, the force between the charged MGOm sheet and the cation (K+) is enhanced, promoting ion permeation. Conversely, the application of positive potential attenuates electrostatic attraction, resulting in a decrease in ion permeability. In addition, the effects of MXene and GO with different modulation ratios on the voltage-gated ion transport have shown that when the modulation ratio of MXene : GO is 7 : 3, the optimal ion permeation rate is achieved. In conclusion, the conductive film with voltage-gated nanochannels is a promising alternative for ion transportation, opening up new avenues for the further exploration of MXene materials in energy storage devices.

Amyloid-intercalated graphene oxide membranes for enhanced nanofiltration

We report on fast pressure-driven nanofiltration of strong GO membranes intercalated by protein amyloid fibrils. We investigate the effect of protein amyloid fibril loading on membrane properties including the membrane stability, microstructure, reflux rate, permeance, rejection rate and fouling resistance. With increasing amyloid fibrils, the membrane becomes smooth and resilient and can be reused for many times with little disintegration. Microstructure analysis shows that amyloid fibrils enable expansion of the interlayer spacing between GO sheets, leading to around 100% increase in average water permeance of the 100 nm thick membrane (15.6 L⋅m−2⋅hr−1⋅bar−1) compared to the neat GO membrane (8.8 L⋅m−2⋅hr−1⋅bar−1). The hybrid membranes display improved moderate ion rejection (44–51%) of heavy metal salts and high molecular rejection (>97%) of organic dyes. Antifouling performance is evaluated in terms of flux recovery ratio and fouling ratios. The incorporation of amyloid fibrils enable GO membranes to change from irreversible fouling to reversible fouling and the hybrid membrane exhibits significantly enhanced flux recovery (>95%). A possible nanofiltration mechanism is proposed to explain the observations.

New insights into the formation and recovery of sublethally injured Escherichia coli O157:H7 induced by lactic acid

Escherichia coli O157:H7 can be injured by the action of lactic acid (LA) and injured cells can be recovered under suitable condition. In this study, RNA sequencing analysis revealed the overall genes change of sublethally injured (4 mM LA, 60 min; SI) and initial recovered (minA, 20 min; R) cells. Compared with untreated samples, 53 up-regulated and 98 down-regulated differentially expressed genes (DEGs; Padj < 0.05, change fold ≥2) were found in SI. Meanwhile, Genes related to carbohydrate transport and metabolic were up-regulated and the addition of carbohydrate increased cells resistance to LA. Genes involved in osmotic stress response and cell membrane integrity were down-regulated and E. coli O157:H7 cells were sensitive to osmotic stress during sublethal injury. Genes related to iron stress response and cation transport were changed and cation may affect sublethal injury formation by influencing production of ROS and cellular processes. In R, 1370 up-regulated and 1110 down-regulated DEGs were subdivided into various GO terms and membrane, biological adhesion, cell projection, oxidation-reduction process and catalytic activity, etc., showed significant enrichment (corrected P < 0.05). Particularly, genes related to fimbrial, flagellum and type III secretion system were up-regulated, which may improve infection ability and virulence property during recovery of injured cells. These findings provide novel insights into formation and recovery of sublethally injured E. coli O157:H7 induced by LA.

Modulation of reduced graphene oxide membrane for low-fouling wastewater filtration: Membrane structure, wastewater property, and DFT calculation

Membrane fouling is a major hurdle impeding real-world application of membranes for advanced wastewater treatment. In this study, a GO membrane and a reduced GO (rGO) membrane were examined in parallel for their anti-fouling propensities and ability to remove pharmaceutical compounds from realistic wastewater effluents. The effects of membrane properties and wastewater characteristics on the two aspects were also assessed by experiments and DFT simulation. The results showed that the transmembrane pressure (TMP) of the rGO membrane increased by 0–3.5 kPa after filtering a secondary wastewater effluent from an activated sludge system (SW), as compared to 201.6–292.1 kPa for the GO membrane. Meanwhile, slightly greater TMP increases were observed for both membranes after filtering a secondary wastewater effluent from a partial nitrification and denitrification system (PND), but the fouling remained low for the rGO membrane. Overall, chemical reduction of GO to rGO led to larger SSA and reduced negative charge, which promoted adsorptive filtration of pharmaceutical compounds. Also, the diminishing of functional groups possessed by the GO membrane mitigated attractive interlayer polar interaction and expanded membrane pore dimension, thus enhancing the permeability and anti-fouling propensity of GO membranes.

The Combination of 2D Layered Graphene Oxide and 3D Porous Cellulose Heterogeneous Membranes for Nanofluidic Osmotic Power Generation.

Salinity gradient energy, as a type of blue energy, is a promising sustainable energy source. Its energy conversion efficiency is significantly determined by the selective membranes. Recently, nanofluidic membrane made by two-dimensional (2D) nanomaterials (e.g., graphene) with densely packed nanochannels has been considered as a high-efficient membrane in the osmotic power generation research field. Herein, the graphene oxide-cellulose acetate (GO–CA) heterogeneous membrane was assembled by combining a porous CA membrane and a layered GO membrane; the combination of 2D nanochannels and 3D porous structures make it show high surface-charge-governed property and excellent ion transport stability, resulting in an efficient osmotic power harvesting. A power density of about 0.13 W/m2 is achieved for the sea–river mimicking system and up to 0.55 W/m2 at a 500-fold salinity gradient. With different functions, the CA and GO membranes served as ion storage layer and ion selection layer, respectively. The GO–CA heterogeneous membrane open a promising avenue for fabrication of porous and layered platform for wide potential applications, such as sustainable power generation, water purification, and seawater desalination.