Cross-linked Graphene Oxide Research Articles

Cross-Linked Self-Standing Graphene Oxide Membranes: A Pathway to Scalable Applications in Separation Technologies.

The large-scale implementation of 2D material-based membranes is hindered by mechanical stability and mass transport control challenges. This work describes the fabrication, characterisation, and testing of self-standing graphene oxide (GO) membranes cross-linked with oxides such as Fe2O3, Al2O3, CaSO4, Nb2O5, and a carbide, SiC. These cross-linking agents enhance the mechanical stability of the membranes and modulate their mass transport properties. The membranes were prepared by casting aqueous suspensions of GO and SiC or oxide powders onto substrates, followed by drying and detachment to yield self-standing films. This method enabled precise control over membrane thickness and the formation of laminated microstructures with interlayer spacings ranging from 0.8 to 1.2 nm. The resulting self-standing membranes, with areas between 0.002 m2 and 0.090 m2 and thicknesses from 0.6 μm to 20 μm, exhibit excellent flexibility and retain their chemical and physical integrity during prolonged testing in direct contact with ethanol/water and methanol/water mixtures in both liquid and vapour phases, with stability demonstrated over 24 h and up to three months. Gas permeation and chemical characterisation tests evidence their suitability for gas separation applications. The interactions promoted by the oxides and carbide with the functional groups of GO confer great stability and unique mass transport properties-the Nb2O5 cross-linked membranes present distinct performance characteristics-creating the potential for scalable advancements in cross-linked 2D material membranes for separation technologies.

Enhanced selectivity of SPEEK membrane incorporated covalent organic nanosheet crosslinked graphene oxide for vanadium redox flow battery

It is difficult for sulfonated poly(ether ether ketone) (SPEEK) to possess both high proton conduction and vanadium resistance owing to the degree of sulfonation. Herein, the composite membranes (S/GO-TpTG) with cationic covalent organic nanosheet (TpTG) crosslinked graphene oxide (GO-TpTG) are prepared to enhance selectivity by optimizing the ion transport channels. The GO-TpTG can efficiently transport protons utilizing its cationic porous structure and acid-base pairs' interaction with SPEEK. Meanwhile, it can block vanadium ions through the Donnan exclusion and physical blocking effects. The S/GO-TpTG membrane with 3 wt% GO-TpTG exhibits excellent proton conductivity (82.7 mS cm−1) and selectivity (77.9 × 10−7 cm2 min−1). The VRFB with this membrane exhibits excellent energy efficiency (88.6–81.0 % at 100–200 mA cm−2), cycle durability, and self-discharge time (209.8 h). This study confirms the great potential of GO-COF to balance proton conductivity and vanadium resistance, and provides an effective strategy to optimize proton channels.

Different functional groups cross-linked graphene oxide membranes for proton exchange membrane fuel cell

The graphene oxide (GO) membrane treated by ozone, GOL, exhibits a relatively high conductivity, but its mechanical strength cannot be maintained due to severe swelling. To further improve the conductivity while suppressing the swelling, the free-standing GO membrane was subjected to ozone treatment and subsequently modified by crosslinking agents with oxygen functional groups, i.e., glyoxal (GLX) and oxalic acid (OXA). The modified membranes, GLX/GOL and OXA/GOL, successfully reduced the swelling and increased the conductivity to provide an excellent power output of a fuel cell at 30 °C due to the increased oxygen functional groups and the carbon defects. Furthermore, OXA/GOL exhibited a significant stability at elevated temperatures. At 50 °C, the through-plane conductivity and power output increased to 23.5 mS cm−1 and 317 mW cm−2, respectively. This is considered to be due to the relatively high thermal stability of the carboxy group added by the OXA modification.

Enhancing electrochemical performance of graphene oxide/polyaniline composite through plasma-assisted chemical cross-linking and surface modification

The composite of graphene oxide (GO) and polyaniline (PANI) is a promising electrode material for supercapacitors. A high loading of PANI can provide large specific capacitance, but it is a pervasive challenge to reconcile long-term cycling stability and high-rate discharge. Herein, we focus on a GO/PANI composite with low PANI content (∼25 wt%), developing a stable network of GO with an even distribution of PANI. Moreover, significantly enhanced electrochemical performance is achieved by utilizing plasma technology. The specific capacitance increases by 99 % to 433 F g−1 at 1.5 A g−1 after Argon (Ar) plasma treatment. Even at 15 A g−1, a capacitance retention rate of 91 % is obtained. After 15,000 cycles, the capacitance retention rate is 93 %, surpassing most previously reported GO/PANI composite electrodes. The further assembled all-solid-state supercapacitors can deliver a high energy density of 13.6 Wh kg−1 and exceptional cycling stability. According to results of characterization, it is demonstrated that Ar plasma imparts GO/PANI better surface morphology and achieves etching, reduction of GO, and cross-linking of GO and PANI, thereby activating the electrochemical activities of GO and PANI while ensuring stability. In this regard, the synergistic effects of cross-linking, reduction, and etching, and the mechanism are theoretically illustrated by dynamic differential equations. This work presents plasma processing unique charm for designing graphene-based materials via a customized strategy, exploiting an effectual approach to drive the applications of graphene-based materials in energy storage.

Anomalous mass transfer behavior of organic molecules in crosslinked graphene oxide membranes induced by intermolecular forces

Membrane-based technology has a wide application for many separation practices, nevertheless, the precise separation of organic molecules using a membrane remains challenging. To get a deeper understanding of the nanoconfined mass transport of the organic molecules, pristine and crosslinked graphene oxide (GO) membranes were synthesized, and their transport properties were systemically studied. With m-phenylenediamine (MPD) crosslinked, the flux of the organics across the GO-MPD membrane was approximately 5-fold lower than that of the pristine GO membrane, though the GO-MPD membrane retains a relatively large pore size. Computational simulations implied the occurrence of strong intermolecular forces between the organics and the GO-MPD membrane, which significantly affected the partitioning and diffusion of the organics. We propose that the synergetic effect of “capacity and strength” needs to be considered when organic transport impacts are examined. By combining a low sorption capacity with strong intermolecular forces between organic molecules and the membrane, the transport of organic molecules across the membrane could be slowed down or inhibited, and vice versa. Our work offers a more comprehensive framework at the nanoscale that deepens the understanding of organic molecule mass transfer, which aids in the designing of high-selective membrane materials for separation practices involving organic molecules.

Enhanced water permeability and antifouling properties of cross-linked graphene oxide composite membranes with tunable d-spacings

Low flux and membrane fouling are major challenges in membrane distillation (MD) for treating concentrated wastewater. This study compared the performance of GO composite membranes with different interlayer distances, by covalently bonding the terminal amine groups of ethylenediamine (EDA) and 1,12-diaminododecane (DADD) with the carboxyl groups present on the GO sheets. The results indicated that the GO-DADD/PTFE membrane, with longer carbon chain cross-linking, achieved the highest flux and antifouling properties. At 70 °C, the pure water flux reached 68.5 kg/m2·h, and the fluxes for treating NaCl, HA containing NaCl, and BSA containing NaCl were 29.8 %, 37.1 %, and 38.5 % higher than the uncrosslinked GO/PTFE, and 95.7 %, 121.2 %, and 146.9 % higher than the PTFE membrane, respectively. Through mathematical models for mass and heat transfer, the study identified the key to this enhancement as the increased d-spacing within the GO layer due to cross-linking, which weakened the Kelvin effect and enhanced the vapor partial pressure on the hot side. The unique surface structure and electrostatic interactions induced by long-chain cross-linking further boosted the antifouling effect. These modifications not only overcome the typical trade-off between retention rates and flux but also offer a scalable and efficient solution for advanced membrane distillation applications.

Transport and separation behaviors of crosslinked GO/PVA sponge with high porosity

Separation materials (technology) with high efficiency and high precision is a goal that researchers are relentlessly pursuing. Here, crosslinked graphene oxide and polyvinyl alcohol (GO/PVA) sponges with high porosity are reported, which were constructed by crosslinking a dilute solution of GO/PVA. The structure and transport characteristics of the sponges were investigated. It was found that it took 150 days for 30 mg/L methylene blue (MB) to diffuse from the side of crosslinked GO/PVA sponge (10 mm thickness) to the other side (breakthrough) even though the porosity of sponge was up to 92.9 %, while it needed only 2 days in PVA sponge and 13 days for methyl orange (MO) in the sponge. Hence, the transport and separation behaviors of more substances were explored and it is found that not only a precise separation of more than 99 % was achieved for MB/MO (similar molecular weight) mixed solution due to the extremely wide difference of transport rate, but also a water permeability of (4.3 × 105 L·m−2·h−1·Mpa-1) was reached under 10 cm height of water column pressure (0.01 bar), which is three orders of magnitude higher than that of nanofiltration membrane. The extremely high selectivity and efficiency to MB are attributed to the structural features of the sponge, i.e., the fully dispersed GO nanosheets and their crosslinking structure with PVA. Thus, the adsorption amount, adsorption rate, and adsorption strength to MB were greatly improved due to a synergistic effect of GO and PVA, and the highly efficient, precise, and rapid separation of MB was realized. In addition, the structural characteristics of the sponges favor the slow transport of many substances, which will extend their applications to the controlled release field.

Single-Round Circular Aptamer Discovery Using Bioinspired Magnetosome-Like Magnetic Chain Cross-Linked Graphene Oxide.

Circular aptamers are promising candidates for analytical and therapeutic applications due to their enhanced biological and structural stability. However, the process of circular aptamer selection remains a great challenge, as it requires multiple rounds of binding-separation-amplification that involves issues with nonspecific binding and amplification bias. Here, we develop a highly practical solution for reliable selection of circular aptamers in a single round based on magnetosome-like magnetic chain cross-linked graphene oxide (separation efficiency ≈ 105). High-affinity aptamer candidates can be rapidly selected from a preenriched circular DNA library, while low-affinity candidates are effectively adsorbed and separated by magnetosome-like magnetic chain cross-linked graphene oxide. With lipopolysaccharide as a representative model, the single-round selected lipopolysaccharide circular aptamer has been identified to have a high binding affinity with a Kd value of low to nanomolar range. Using this method, circular aptamers for protein and small-molecule targets were also successfully generated. We envision that this approach will accelerate the discovery of various new circular aptamers and open up a new avenue for analytical and therapeutic studies.

Double cross-linked graphene oxide hydrogel for promoting healing of diabetic ulcers.

This study explores the synthesis and characterization of a novel double cross-linked hydrogel composed of polyvinyl alcohol (PVA), sodium alginate (SA), graphene oxide (GO), and glutathione (GSH), henceforth referred to as PVA/SA/GO/GSH. This innovative hydrogel system incorporates two distinct types of cross-linking networks and is meticulously engineered to exhibit sensitivity to high glucose and/or reactive oxygen species (ROS) environments. A sequential approach was adopted in the hydrogel formation. The initial phase involved the absorption of GSH onto GO, which was subsequently functionalized with boric acid and polyethylene glycol derivatives via a bio-orthogonal click reaction. This stage constituted the formation of the first chemically cross-linked network. Subsequently, freeze-thaw cycles were utilized to induce a secondary cross-linking process involving PVA and SA, thereby forming the second physically cross-linked network. The resultant PVA/SA/GO/GSH hydrogel retained the advantageous hydrogel properties such as superior water retention capacity and elasticity, and additionally exhibited the ability to responsively release GSH under changes in glucose concentration and/or ROS levels. This feature finds particular relevance in the therapeutic management of diabetic ulcers. Preliminary in vitro evaluation affirmed the hydrogel's biocompatibility and its potential to promote cell migration, inhibit apoptosis, and exhibit antibacterial properties. Further in vivo studies demonstrated that the PVA/SA/GO/GSH hydrogel could facilitate the healing of diabetic ulcer sites by mitigating oxidative stress and regulating glucose levels. Thus, the developed PVA/SA/GO/GSH hydrogel emerges as a promising candidate for diabetic ulcer treatment, owing to its specific bio-responsive traits and therapeutic efficacy.

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.

Elimination of Ciprofloxacin from Aqueous Solution by Ultrasonic-Assisted Adsorption Using Chitosan Crosslinked Graphene Oxide Nanoparticles

Elimination of Ciprofloxacin from Aqueous Solution by Ultrasonic-Assisted Adsorption Using Chitosan Crosslinked Graphene Oxide Nanoparticles

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.

Supercapacitor electrode based on graphene covalently functionalized with cross-linking inorganic-organic molecule

This work presents the fabrication of a supercapacitor electrode based on covalently cross‐linked graphene structure. It introduces a simple method to fabricate modified graphene oxides with an inorganic and organic cross-linked agent. The supercapacitive performance of this cross-linked graphene oxide structure (C-GO) is approved by conventional electrochemical procedures, such as cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy. The calculated specific capacitance amounts of 231 F/g and 240 F/g was achieved via CV and GCD curves at ѵ= 10 mVs−1 and I = 0.8 A g−1, respectively. This C-GO based-supercapacitor indicates a 9 % reduction in specific capacitance value after measurement of 3000 continuous cycles in the CV.

Design, synthesis, and characterization of thiol-decorated cross-linked graphene oxide framework for high-capacity Hg2+ ion adsorption

A 3D framework was effectively created by cross-linking graphene oxide nanosheets with 2,5-bis(((3-mercaptopropyl)dimethoxysilyl)oxy)terephthalohydrazide as a sulfur-containing linker, resulting in a successful synthesis of a novel chelating adsorbent. The resulting material showed remarkable efficiency in removing Hg2+ ions from polluted water, with a high adsorption capacity of 204.08 mg g−1 at pH 6 and 25 °C. The adsorption process followed a monolayer model described by the Langmuir isotherm, and the kinetics followed a pseudo-second-order model, indicating a chemical adsorption mechanism. The material demonstrated rapid adsorption and desorption, maintaining its performance even after multiple regeneration cycles. Overall, the synthesized 3D GOF stands out as an exceptional adsorbent due to its porous structure, efficient chelating functional groups, and robust efficacy in eliminating Hg2+ ions from contaminated water sources.

Na2.60Fe1.70(SO4)3 particles embedded in cross-linked graphene oxide networks as high-performance dual-electrode for sodium-ion batteries

Sodium iron sulfate materials have been initially applied to sodium ion batteries (SIBs) owing to their high operating voltage and stable electrochemical properties, yet poor conductivity and low theoretical capacity limit its commercial development. Herein, we first prepared Na2.60Fe1.70(SO4)3@graphene oxide (GO) composite via a facile solid-phase ball milling strategy, which are Na2.60Fe1.70(SO4)3 particles embedded in cross-linked GO networks. For the cathode of SIBs, the active particles in the material are wrapped with cross-linked GO networks that increases the electrolyte penetration and ion transport channels as well as improves electronic conductivity, resulting in a high operating voltage of 3.74 V and excellent cycle stability (retains over 70 % of capacity after 500 cycles at 8 C). Notably, the as-prepared material could exhibit a reversible capacity of 100 mAh g−1 after 100 cycles at 0.2 C as anode for SIBs. Furthermore, the material was first used to assemble symmetric sodium-ion full cell, demonstrating excellent electrochemical performance (achieving 60 mAh g−1 at 0.2 C). The Na2.60Fe1.70(SO4)3 particles wrapped with cross-linked GO networks offer a simple and effective approach to enhance the performance of SIBs, making an important contribution towards their practical industrial application.

A colorimetric sensor array based on nanoceria crosslinked and heteroatom-doped graphene oxide nanoribbons for the detection and discrimination of multiple pesticides

Nanozymes have demonstrated high potential in constructing colorimetric sensor array for pesticides. However, rarely array for pesticides constructed without bio-enzyme were reported. Herein, nanoceria crosslinked graphene oxide nanoribbons (Ce-GONRs) and heteroatom-doped graphene oxide nanoribbons (Ce-BGONRs and Ce-NGONRs) were prepared, demonstrating excellent peroxidase-like activities. A colorimetric sensor array was developed based on directly inhibiting the peroxidase-like activities of the above three nanozymes, which realized the discrimination and quantitative analysis of six pesticides. In the presence of pesticides including carbaryl (Car), fluroxypyr-mepthyl (Flu), thiophanate-methyl (Thio), thiram (Thir), diafenthiuron (Dia) and fomesafen (Fom), the peroxidase-like activities of three nanozymes were inhibited to different degrees, resulting in different fingerprint responses. The six pesticides in the concentration range of 0.1–50 μg/mL and two pesticides mixtures at varied ratios could be detected and discriminated, and minimum detection limit for pesticides was 0.022 μg/mL. In addition, this sensor array has been successfully applied for pesticides discrimination in lake water and apple samples. This work provided a new strategy of constructing simple and sensitive colorimetric sensor array for pesticides based on directly inhibiting the catalytic activities of nanozymes.

Chemical modification of reduced graphene oxide membranes: Enhanced desalination performance and structural properties for forward osmosis

Graphene oxide (GO) nanosheets can offer a breakthrough into the development of novel and efficient laminated forward osmosis membranes, with high hydrophilicity and outstanding desalination performance. However, fabrication of desirable GO-based nanocomposite membrane which can overcome the on-going trade-off between forward osmosis (FO) performance and chemical/mechanical stability, remains to be challenging in practical application. In this study, polyethyleneimine (PEI) was used to reduce GO (rGO) and crosslink and surface modify membrane's GO sheets for the performance enhancement. The crosslinked rGO was then deposited on a hydrophilic nylon support layer (modified by polydopamine, pDA, for structural stability) using vacuum filtration method. The resulting PEI:rGO/pDA membrane showed excellent water flux (25.5 LMH), high sodium chloride (NaCl) salt rejection (98.9%), and low reverse solute flux (0.91 gMH) in lab-scale tests. The combination of crosslinking GO with PEI and modifying the support layer with polydopamine (pDA) enhanced the membranes hydrophilicity and structural stability. The incorporation of PEI into GO resulted in compacted nanochannels, improving molecular/ions separation. Moreover, the pDA coating enhanced desalination performance and reduced internal concentration polarisation effects, further improving the membrane durability and integrity through the formation of numerous binding sites for firmly anchoring with the PEI:rGO nanocomposite structure.

Improving permeability and fouling resistance of GO hydrophilic/hydrophobic Janus membrane by polyether amine crosslinking for membrane distillation of dye wastewater

Graphene oxide (GO) modification is promising to increase vapor flux and antifouling properties of hydrophobic membranes in membrane distillation for wastewater treatment. However, the acid bonding of GO with dyes impedes its wide application in dye wastewater treatment. In this study, polyether amine D400 was used to modify hydrophilic GO layer of Janus membrane. The GD3/PTFE composite membrane (GO and D400 mass ratio of 1:2) demonstrated the best water flux and antifouling performance for methyl orange (MO) containing 3.5 wt% NaCl. The flux was increased by 170.3%− 228.9% compared to PTFE pristine membrane and the flux decline due to fouling was decreased by 41.3%− 60.8% to GO/PTFE membrane. The observed increase in the longitudinal thermal conductivity of the cross-linked GO layer suggests that the enhanced permeability is attributed to improved heat transfer resulting from the higher density of GO nanosheets. Acid bonding of GO layer with dye molecular is weakened and electrostatic repulsion is also increased, leading to the excellent antifouling performance. This study indicate that polyether amine crosslinking is promising method for modification of GO composite membrane for dye wastewater treatment.

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.

High resistivity free-standing crosslinked graphene oxide substrates: hopping conduction mechanism and application to recyclable electronics

Graphene oxide (GO) is an oxidized derivative of graphene that can be formed into free-standing wafers by aqueous processing methods. We propose GO as a potential alternative printed electronic substrate material to mitigate the waste electronic and electrical equipment problem. By dissolving these substrates in water, GO permits the mechanical separation and recovery of discrete components from defunct circuits, thus closing the life cycle of printed circuits. In this work we measure the anisotropic, frequency dependent resistivity of free-standing GO wafers under DC and AC (f = 0.1 Hz–500 kHz) excitation and in varying relative humidity (RH) conditions. Unmodified GO and GO crosslinked with calcium ions, borate ions, and glutaraldehyde were characterized. AC resistivity measurements reveal charge transport in free-standing GO occurs by several distinct hopping conduction mechanisms that are sensitive to the crosslinking formulation. GO crosslinked with calcium ions exhibits the highest DC resistivity, 4.6 × 105 Ωm and 2.6 × 104 Ωm, for out-of-plane and in-plane directions, respectively, at 17% RH. Both AC and DC resistivities decrease with increasing RH. We demonstrate that GO wafers can be used as dielectric substrates in the construction of simple electronic circuits with discrete electronic components. Finally, we present a proof-of-concept for electrical trace and component recovery via disassembly of GO wafers in water.