Cross-Linked Graphene Oxide Membranes Research Articles

Construction of amidinothiourea crosslinked graphene oxide membrane by multilayer self-assembly for efficient removal of heavy metal ions

Abstract Amidinothiourea crosslinked graphene oxide membrane was prepared by a multilayer self-assembly method along with (3-aminopropyl) triethoxysilane modification, while different thicknesses of the membrane layer were obtained by regulating the volume of graphene oxide dispersion. The removal rate of the membrane layer with different thicknesses of heavy metal ions was explored and its removal mechanism was explained. The results show that the membrane can maintain high stability after 90 days of immersion in water. When the volume of graphene oxide dispersant increases from 9 ml to 15 ml, the thickness of the membrane layer enhances from about 120 nm to about 200 nm. After filtration of 140 ml of different nitrate solutions, the water fluxes of different membranes are about 22.6 l m−2 h−1·bar−1, 6.1 l m−2 h−1·bar−1, and 1.4 l m−2 h−1·bar−1, respectively. The removal rates of the preferred membrane for Pb2+, Cd2+, and Cu2+ are 43.3 %, 41.2 %, and 39.7 %, respectively. The ion removal mechanism is mainly due to the Dornan effect.

High-efficiency water-transport channels using the synergistic effect of superhydrophilic PA layer and robust BU cross-linked GO laminates

Graphene oxide (GO) membranes show immense promise in nanofiltration separation for water purification and recycling of water resources. However, pristine GO membranes often suffer from insufficient membrane stability due to swelling and low water permeance under high operation pressure, which severely limits the real-world utilization of GO membranes. Herein, a strategy involving surface modification of GO membrane with superhydrophilic polyamide (PA) layer combined with cross-linking with biurea (BU) amine, is proposed to fabricate highly permeable and robust GO membranes for dye removal from aqueous solution. The PA layer is prepared onto BU cross-linked GO membrane by in-situ interfacial polymerization, which results in superhydrophilic and negative-charged membrane surface. Moreover, the low reactivity of 2,5-diaminobenzenesulfonic acid (DBS) monomer contributes to low cross-linking degree and loose network of PA layer. The BU cross-linked GO laminates possess multi-level interlayer spacings and sufficient covalent interaction between GO interlayer due to crosslinking with BU, which offer large and robust transport channels for water molecules. PA@BU/GO hybrid membrane shows the optimum pure water permeability of 140.2 L·m−2·h−1·bar−1, with water permeance and TB rejection rate of 67.4 L·m−2·h−1·bar−1 and 99.9 %, respectively. Moreover, the membrane exhibits impressive dye/salt selectivity (the dye/NaCl separation factor is up to 873), long-term operation stability and good anti-fouling property, which makes it a potential candidate for the fractionation of dye/salts in textile wastewater. This work provides a promising idea for the development of high-performance 2D membranes with high-efficiency water transport channels using the synergistic effect of superhydrophilic PA Layer and robust BU cross-linked GO laminates.

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

Lamellar graphene oxide (GO) membranes have received significant attention in desalination and water treatment due to their unimpeded permeation of water. Intercalation cross-linking is an effective way of improving the stability and perm-selectivity of GO membranes. This work reports a novel strategy to tune the nanostructure and morphology of GO membrane by combining highly oxidized GO nanosheets with borate cross-linking for desalination by pervaporation. The cross-linking processes covalent bonding of hydroxyl groups of GO membrane with sodium borate as the cross-linker, leading to formation of selective and stable three-dimensional GO-borate framework. The enrichment of hydroxyl groups on GO arising from high oxidation benefits the targeted cross-linking. Meanwhile, higher oxidation level of GO leads to higher content of carboxyl groups and improves the hydrophilicity of membrane. Consequently, the borate cross-linked GO membrane fabricated with fully oxidized GO simultaneously exhibits high water flux and enhanced structural stability. The results reveal that the interlayer spacing and swelling behavior of GO membranes are heavily influenced by the oxidation level and cross-linking, which are critical factors affecting the performance of the membranes in pervaporation desalination applications. The findings hold promise for the development of high-performance and stable GO membranes to address global water scarcity challenges.

Rearrangement of GO nanosheets with inner and outer forces under high-speed spin for supercapacitor

The self-standing graphene membranes are considered as ideal electrode materials for supercapacitors. However, maintaining highly regularized and uniform graphene membranes with satisfied electrochemical performance is still a challenge. Herein, with the chelation of metal cation and the radial shear force introduced by high-speed spinning, the uniform interlayer channels and shrunken cracks between adjacent nanosheets can be achieved in the metal-intercalated graphene oxide (GO) membranes, thus realizing regularization both in normal and radial direction. With the promotion in electron transfer and electrolyte penetration, the iron cross-linked GO membrane with spin coating for 40 cycles exhibits a high specific capacitance (427 F g−1 at 1 A g−1) and rate capability (42.6% capacitance retention from 1 to 40 A g−1), as well as excellent cyclic capability (90.5% capacitance retention after 20,000 cycles). Particularly, a 21% increasement in capacitance can be achieved after high-speed spinning treatment. Moreover, the spin regularization strategy can be extended to GO membranes cross-linked by various multi-valence metal cations, the electrochemical performance of metal-cation cross-linked GO membrane electrodes after high-speed spinning treatment can also be improved obviously. Therefore, this paper provides a novel method to fabricate highly ordered GO membranes with promising electrochemical performance, which presents an immense potential application in membrane materials applied in energy storage, separation and catalysis.

Double cross-linked MoS2 intercalation GO membrane: Towards high stability and high permeability

Graphene oxide (GO)-based membrane has shown great potential in water purification due to its unique physicochemical properties and high permeability. However, it is a challenge to pursue highly permeable GO membranes without compromising stability. Here we employed sodium alginate (SA) together with Ca2+ as cross-linkers to double crosslink GO membrane to obtain stable GS membrane. Further, MoS2 nanosheets were inserted between GO nanosheets to obtain GSM membrane with high permeability. The double cross-linked MoS2 intercalation GO membrane, GSM-1:4, showed high removal of multiple dyes (>99%) and enhanced pure water permeance (112.5 L m−2 h−1 bar−1, 1.9 times and 5.8 times of the pure GO membrane and the double cross-linked GS-0.5 membrane, respectively). Meanwhile, the GSM-1:4 membrane demonstrated excellent stability in water and even in acid and alkali solutions. Our work provides new insights into the design of stable and highly efficient GO-based membranes with a two-dimensional layered structure for water treatment.

Enrichment of uranium in seawater by glycine cross-linked graphene oxide membrane

Extraction of uranium from seawater can satisfy the request for uranium in the field of sustainable nuclear power generation. However, direct extraction of uranium from seawater with traditional methods encounters many difficulties with reduced efficiency because of the extremely low uranium concentration. Based on the hydration diameter difference between uranium and the main coexisting ions (K+, Na+, Ca2+ and Mg2+), membrane separation technology is thought as an effective way to enrich uranium in seawater. Here, a new type of glycine (Gly) cross-linked graphene oxide (GO-Gly) membrane was fabricated, whose interlayer spacing (d) is very stable with uniform channel size satisfied the requirement for uranium enrichment. The respectively single ion rejection properties of uranium and the main coexisting ions in seawater revealed that ∼ 100% of uranium was rejected by the GO-Gly membrane. In addition, the excellent uranium rejection property of this membrane can be maintained in continuously filtrating the simulated seawater, only uranium ion was obviously enriched but the concentrations of the main coexisting ions kept nearly constant. The distinct rejection and enrichment properties of uranium ions by GO-Gly membrane made it an ideal candidate for uranium enrichment in seawater.

Dual-site supported graphene oxide membrane with enhanced permeability and selectivity

Two-dimensional (2D) graphene oxide (GO) membranes continue to attract interest due to their superior permeation and separation performance, and are regarded as a promising technology for water purification. However, the imperfect interlayer microstructure under the applied hydraulic pressure, and the inferior stability are still considerable challenges to achieve high permeability, selectivity and operability. In this paper, we describe for the first time, the development and testing of a dual-site supported GO membrane (SEN-Mg/GO) by introducing biuret (SEN) and Mg 2+ inside the interlayer structure. SEN can support the GO sheets in the oxide sites based on a condensation reaction between amino and carboxyl groups, while Mg 2+ is fixed in the graphitic sites through a non-covalent cation-π interaction. A synergistic effect of the dual-site crosslinking and support build more favorable nanochannels for the rapid transport of water while also imparting the membrane to maintain a tightly-packed 2D structure, which increases water flux without sacrificing the separation performance. In comparison, SEN-Mg/GO exhibited a water flux 4 times greater than the GO and SEN only cross-linked GO membrane (SEN/GO), with high selectivity towards various model dye molecules (>98%). The SEN-Mg/GO membrane also achieved greater “trade-off” between flux and rejection and significantly improved stability than the Mg 2+ only cross-linked GO membranes (Mg/GO). The optimized nanochannels and the interlayer covalent bond are considered to be the dominant factors in improving the separation performance and stability of the membrane, respectively. The dual-site supporting technique provides a new approach for the fabrication of GO membranes of high performance, and can be used in the design of other 2D lamellar membranes. • Novel SEN-Mg/GO membranes fabricated by dual-site support approach. • Dual-site support approach suppresses shrinkage and collapse of interlayer nanochannels. • SEN-Mg/GO membrane had 4-fold greater water flux and comparable rejection compared with SEN/GO membrane. • SEN-Mg/GO membrane has long term stability over a wide range of pH.

Crosslinked graphene oxide membranes (CGOM) and their asymmetric permeation behaviors

The crosslinked graphene oxide (GO) membranes (CGOM) with reversible pressure-sensitive gating were prepared by a water-soluble polymer (polyvinyl alcohol, PVA) intercalated layered nano-barrier (GO) through layer-by-layer self-assembly technology. The PVA chain cleverly embedded between the GO nanosheets provides an adjustable water channel (membrane pore) in CGOM. The channel controllability of CGOM stems from the conformational change of the flexible PVA chain and the relative layer spacing of the GO nanosheets, which originates from the lifting-up (accompanied by a stretching of PVA chains) and pressing-back (accompanied by a compressing of PVA chains) of GO nanosheets with the change of the fluid direction, and thus the permeability and selectivity could be adjusted by simply adjusting the fluid direction and pressure. When the fluid direction changed from normal filtration mode to reverse filtration mode, the water flux of the same one CGOM was increased by 27 times, and the rejection rate of PEG-20000 was decreased from 73.4% to 2.4%. Thus, the pressure-sensitive CGOM obviously showed asymmetric permeation behavior. The results provide an insight for fabricating smart gating membranes with asymmetric permeation behavior. This membrane has great potential applications in directional fluid transport and substance separation. • Crosslinked graphene oxide membranes (CGOM) were prepared through layer-by-layer self-assembly technology. • The CGOM presented an asymmetric permeation behavior. • The ratio of reverse flux to normal flux for a same CGOM attained to 27.

Synergetic effect of physicochemical and electrostatic strategies on ion sieving for polymer cross-linked graphene oxide membranes

Graphene oxide membranes with polymer-crosslinked structures are designed to simultaneously modify the physicochemical and electrostatic properties of nanochannels for molecular separation.

Amino Acid Cross-Linked Graphene Oxide Membranes for Metal Ions Permeation, Insertion and Antibacterial Properties

Graphene oxide (GO) and its composite membranes have exhibited great potential for application in water purification and desalination. This article reports that a novel graphene oxide membrane (GOM) of ~5 µm thickness was fabricated onto a nylon membrane by vacuum filtration and cross-linked by amino acids (L-alanine, L-phenylalanine, and serine). The GOM cross-linked by amino acids (GOM-A) exhibits excellent stability, high water flux, and high rejection to metal ions. The rejection coefficients to alkali and alkaline earth metal ions through GOM-A were over 94% and 96%, respectively. The rejection coefficients decreased with an increasing H+ concentration. Metal ions (K+, Ca2+, and Fe3+) can be inserted into GOM-A layers, which enlarges the interlayer spacing of GOM-A and neutralizes the electronegativity of the membrane, resulting in the decease in the rejection coefficients to metal ions. Meanwhile, GOM-A showed quite high antibacterial efficiency against E. coli. With the excellent performance as described above, GOM-A could be used to purify and desalt water.

Development of superhydrophillic tannic acid-crosslinked graphene oxide membranes for efficient treatment of oil contaminated water with enhanced stability

In the present age of industrialization, oil contamination in the waste water has become a huge global concern due to its several negative impacts on human health and aquatic ecosystem. In order to address this problem, a novel oleophobic and super-hydrophilic graphene-based membrane has been developed using simple and cost-effective vacuum filtration methodology. Prior developing the membranes, the graphene oxide (GO) sheets were crosslinked with tannic acid (TA) molecules in order to improve their mechanical and surface properties. To obtain the structural and morphological information of the membranes and their constituents, Field Emission Scanning Electron (FE-SEM) microscopy, X-Ray Diffraction (XRD), FTIR spectroscopy and Raman spectroscopy was used. When tested with simulated oilfield effluent samples, these membranes exhibited significant reduction in the values of chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS) and turbidity demonstrating low-oil adhesion and preferable oil rejection rates. Moreover, such crosslinked membranes are highly stable which can withstand the pressure of water filtration. In such a way, TA crosslinked GO membranes present a robust and efficient way to treat oil contaminated water released from various industries which can be reused for numerous further applications.

Impact of monovalent cations on the separation performance of graphene oxide membrane for different organic matters.

Graphene oxide (GO) membrane has become a promising membrane due to its advantages of high flux, good anti-pollution performance, and controllable cost. Since wastewater contains inorganic ions and organic substances, the effect of inorganic ions on the removal of organic matters has attracted attention. This study investigated the impact of monovalent cations (Na+ and K+) on the removal of different organic matters by GO membranes. The results showed that the removal by GO membranes of both macromolecular organic compounds (humic acid, sodium alginate, and bull serum albumin) and small molecular organic substances (new coccine, methyl orange, and methylene blue) were high (>75%). The coexisting Na+ caused the increase in flux and the decrease in removal of small molecular organic matters, while the impact on the removal of macromolecular organic matters was weak. The impact of the coexisting K+ was weaker than Na+. With the crosslinking of ethylenediamine, the structure of GO membrane was more stable. The impacts of Na+ on the flux and separation performance of crosslinked membranes were less than that of non-crosslinked membranes. This suggests that crosslinked GO membrane has more potential for practical wastewater treatment.

Preparation of Cross-Linked Graphene Oxide on Polyethersulfone Membrane for Pharmaceuticals and Personal Care Products Removal.

The unique two-dimensional structure and chemical properties of graphene oxide (GO) provide a convenient method for preparing novel membranes. In this study, GO membranes were prepared through filtration by a pressure-assisted self-assembly method involving the cross-linking of three diamine monomers on a polyethersulfone (PES) support. The different small molecular diamines, ethylenediamine, butanediamine, and p-phenylenediamine, were introduced as cross-linking agents to investigate the effect of diamine on the properties of GO membranes. The hydrophobic substances ibuprofen, gemfibrozil, and triclosan were selected as target pharmaceuticals and personal care products (PPCPs). The adsorption and molecular sieving activities of PPCPs by cross-linked GO membranes at a pH of 3 were investigated. The permeate water was analyzed for dissolved organic carbon, ultraviolet absorption at 254 nm, molecular weight distribution, and fluorescence excitation–emission matrices. The results showed that the removal of hydrophobic PPCPs by GO membranes was mainly due to their adsorption and molecular sieving activities. Adsorption was mainly determined by the hydrophilic and hydrophobic properties of the membranes and PPCPs. The interception effect was mainly determined by the interlayer spacing between the GO membranes and the molecular weight and steric hindrance of the PPCPs. A smaller spacing of the GO membrane layers resulted in greater steric hindrance and a higher removal rate.

Metal-polyphenol dual crosslinked graphene oxide membrane for desalination of textile wastewater

With the fast development of textile industry, the increasing discharge of textile wastewater is posing a grand challenge to the environmental safety. Graphene oxide (GO) nanosheet with excellent physicochemical properties and lamellar structure, is regarded as an ideal membrane material for the rejection of dyes. However, the selectivity and long-term course of GO-based membranes are largely limited due to the narrow interlayer distance as well as poor aqueous solution stability. To address such situations, a series of GO-based membranes (Fe/GO-TAx) were prepared using coordinated tannic acid-functionalized GO (GO-TA) nanosheets with FeIII ions in this study. The results indicated that Fe/GO-TAx membranes exhibited greater interlayer distance and higher hydrophilicity, as well as a decreasing trend of negative surface charge. Furthermore, the Fe/GO-TA20 conferred a superior dye/salt selective sieving mechanism with a high separation factor and a permeability of 61.2 L m−2 h−1 bar−1 (approximately 6-times higher than the pristine GO membrane). Importantly, the fabricated Fe/GO-TA20 membrane exhibited inherent removals for organic dyes, and more than 99% removals were achieved in the test. These findings were expected to provide some simple but practical strategies for the fast fabrication of two-dimensional laminar structure GO separation membranes to achieve excellent sieving of high-salinity textile wastewater.

Nanofiltration membrane based on graphene oxide crosslinked with zwitterion-functionalized polydopamine for improved performances

Graphene oxide (GO)-based membranes have received increasing attention recently in liquid separation field. However, the abundant hydrophilic groups of GO nanosheets would cause instability of GO-based membranes under hydrated conditions. In addition, GO-based membranes often suffer from severe membrane fouling in practical application. In this study, polydopamine (PDA) crosslinked GO was synthesized by simply immersing GO into the dopamine alkaline solution and used to prepare GO@PDA/PES composite membranes. Then, a zwitterionic polymer, synthesized by quaterisation reaction of polyethyleneimine (PEI) and sodium chloroacetate, was grafted on the surface of PDA crosslinked GO membrane via Michael addition reaction between amino groups of PEI and quinone groups of PDA. The bonding between GO nanosheets reinforced the structural stability, resulting in the formation of water stable membranes. The grafted zwitterionic polymer coating could improve the membrane surface hydrophilicity, endowing the membranes promising anti-fouling ability. The resulting membrane achieved a flux of 49.5 L m−2 h−1 bar−1 with relatively high rejection of about 100%, 82% and 67% for Congo Red, Orange G and Methyl Orange respectively. The membrane exhibited good anti-fouling properties as well as structural stability under alcohol environments, showing considerable potential in water treatment.

Cross-linked GO membranes assembled with GO nanosheets of differently sized lateral dimensions for organic dye and chromium separation

Membrane microstructure and separation performance largely depend on the property of building units and its subsequent patterning. In this work, three differently sized graphene oxide (GO) nanosheets were prepared by a simple centrifugation method. Supported GO membranes were then fabricated based on these separated GO nanosheets. GO nanosheets of different lateral sizes show varied degree of oxidation and distribution of oxygenated groups at both edge and in-plane areas, which leads to different membrane microstructure and separation performance. The swelling and long-term stability of GO membrane were addressed by a pre-crosslinking process with ethylenediamine (EDA). The ultimate separation performance of these GO/EDA membranes was affected by several factors such as cross-linking density, d-spacing, and microstructure like wrinkles all relating to the lateral size of GO nanosheets. Specifically, compared to smaller GO nanosheets, larger GO sheets have more surface groups and thus higher cross-linking density. In terms of microstructure, larger sheets tend to form more surface wrinkles which could sacrifice the membrane separation performance. GO membranes were tested in different pH conditions for separating methylene blue (MB), methyl orange (MO) and chromium (VI). Overall, exceptional rejection rates of higher than 99.0% were achieved at optimal separation conditions. MB separation performance has been found closely related to GO lateral size at specific pH environments.

Scalable fabrication of graphene-based laminate membranes for liquid and gas separations by crosslinking-induced gelation and doctor-blade casting

Graphene-based laminate membranes have recently demonstrated unique advantages over the traditional separation membranes made of polymers or ceramics. For both gas and liquid separations, various designs of crosslinker-stabilized graphene oxide (GO) membranes have been reported. However, the preparation methods used for those are poorly scalable for industrial applications. Herein, we report the fabrication of large-area (1333 cm2) GO-based membranes via doctor-blade casting of gel-like slurries prepared by incorporating calcium ions (Ca2+), ferric ions (Fe3+), polyethylene oxide (PEO), or polyethyleneimine (PEI) as crosslinkers. We found that all crosslinkers tested are suitable for the gelation of dilute GO dispersions (1–5 mg/mL) for doctor-blade casting. Besides, all crosslinked-GO membranes demonstrated outstanding stability under sonication compared to a GO-only membrane prepared via vacuum-assisted filtration. In aqueous nanofiltration tests, Fe3+-crosslinked GO membranes achieved virtually complete rejection of different organic dyes. PEO-crosslinked GO membranes, on the other hand, exhibited an outstanding performance for the separation of carbon dioxide (CO2) and nitrogen (N2) gases with a CO2/N2 selectivity of 52. Given the scaleup potential of doctor-blade casting and the practicality of crosslinking-based gelation approach, the proposed approach is promising to increase the industrial relevance of GO-based laminate membranes.

Impacts of mono/divalent cations on the lamellar structure of cross-linked GO layers and membrane filtration performance for different DOM fractions

This study evaluated the effects of co-existing cations (Na+ or Ca2+) on the lamellar structure of cross-linked graphene oxide (GO) layers and GO modified membrane performance in terms of their fouling behaviours and retention for single-model organic matter, namely, bull serum albumin (BSA), sodium alginate (SA), humic acid (HA) and tannic acid (TA). In the absence of co-existing cations, the GO layers mitigated membrane fouling for large molecules (SA, BSA, and HA) but led to severer pore blocking for small molecules (TA) compared with pristine membrane. Na+ and Ca2+ altered the performance impacts of the GO modified membrane due to different interactions with the cross-linked GO layers. Low concentrations of Na+ (<0.4 mM) enlarged interlayer spacing of the GO layers and caused a decrease in flux after physical cleaning, but the GO layers maintained the uniform lamellar structure. High concentrations of Na+ (>0.4 mM) promoted the aggregation of cross-linked GO layers through charge shielding and reduced the uniformity of lamellar structure, which weakened the antifouling performance for large molecules and promoted the passage of small molecules through the membrane. However, Ca2+ complexed with GO sheets and reinforced the uniform lamellar structure of the GO layers, leading to a better antifouling performance for the filtration of large molecules than the pristine membrane but aggravated TA fouling.

Preparation of novel cross-linked graphene oxide membrane for desalination applications using (EDC and NHS)-activated graphene oxide and PEI

A novel cross-linked graphene oxide (GO) membrane was prepared by vacuum filtration using a two-step method, including activation of GO carboxyl groups by a mixture of 1-Ethyl-3- (3-dimethylaminopropyl) carbodiimide (EDC) and N -Hydroxysuccinimide (NHS) and then cross-linking with polyethyleneimine (PEI). In the cross-linking process, the activated carboxyl groups of GO react with amine groups of PEI through a simple and efficient method. GO cross-linking with PEI significantly improves membrane dimensional stability and salt rejection. The rejection of the cross-linked GO membrane was evaluated by NaCl, Na2SO4 and MgCl2 solutions, and the obtained results followed the order of R (MgCl2) > R (NaCl) > R (Na2SO4). The prepared cross-linked GO membrane was characterized by FTIR, XRD, SEM, FESEM, EDS, WCA, AFM and BET analysis. Also, the effects of operating parameters such as N2 pressure, feed temperature and pH on the cross-linked GO membrane performance were investigated.

Enhanced covalent p-phenylenediamine crosslinked graphene oxide membranes: Towards superior contaminant removal from wastewaters and improved membrane reusability.

The increasing depletion of freshwater necessitates the re-use and purification of wastewaters. Among the existing separation membrane materials, graphene oxide (GO) is a promising candidate, owing to its tunable physicochemical properties. However, the widening of GO membranes pore gap in aqueous environments is a major limitation. Crosslinking agents can be incorporated to alleviate this problem. This study describes a comparative analysis of uncrosslinked and p-Phenylenediamine (PPD) crosslinked GO membranes' water purification performance. Dip-coating and dip-assisted layer-by-layer methods were used to fabricate the uncrosslinked and crosslinked membranes respectively. The covalent interaction between GO and PPD was confirmed by Fourier Transform Infra-Red and X-ray Photoelectron Spectroscopy. The excellent membrane topographical continuity and intactness was assessed by means of Scanning Electron Microscopy, while water contact angle measurements were undertaken to evaluate and confirm membrane hydrophilicity. The improvement impact of the crosslinker was manifested on the enhancement of the stability and performance of the membranes during nanofiltration tests of aqueous solutions of methylene blue in a homemade nanofiltration cell operated at 1 bar.