Cross-linked Graphene Research Articles

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.

Cross-linked and pillared graphene with nonconventional redox benzidine dimethyl ether for high-performance supercapacitors

To hinder Van der Waals-induced agglomeration between graphene sheets to increase specific surface area, and to supplement pseudocapacitance, graphene processing with active molecules is highly effective. Redox polymers and quinones, instead of aromatic ethers, were popular candidates. They were universally blended with graphene sheets through noncovalent modes, leading to issues of electrochemical stability and rate capability, etc. Herein, we broke through stereotype to develop aromatic ethers–benzidine with two remote methoxyls (i.e. 3,3′–dimethoxybenzidine, DMeOBD)–to covalently functionalize graphene, obtaining the cross-linked and pillared graphene electrode material (DMeOBD-rGO). It exhibited redox activity and featured a combination of electrochemical double layer supercapacitor and pseudocapacitor, thus yielded an enhanced specific capacitance of 363 F g−1. When assembled into two-electrode solid-state supercapacitors, the whole devices also delivered an impressive specific capacitance of 263 F g−1, and a high energy density of 13.2 Wh kg−1, along with excellent rate capability and cycling stability.

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.

Nitrogen-Enriched Carbon Aerogels Derived from Polybenzoxazine Cross-Linked Graphene Oxide-Chitosan Hybrid Matrix with Superior CO2 Capture Performance

Nitrogen-Enriched Carbon Aerogels Derived from Polybenzoxazine Cross-Linked Graphene Oxide-Chitosan Hybrid Matrix with Superior CO₂ Capture Performance

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.

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

Highly efficient enzyme less glucose sensor based on cross-linked nitrogen-doped graphene aerogel incorporated with ytterbium oxide and decorated with nickel nitride nanoparticles

Highly efficient enzyme less glucose sensor based on cross-linked nitrogen-doped graphene aerogel incorporated with ytterbium oxide and decorated with nickel nitride nanoparticles

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.

A green cross-linking method for the preparation of renewable three-dimensional graphene sponges for efficient adsorption of Congo red dye

Graphene-based materials possess significant potential for the treatment of dye wastewater due to their exceptional adsorption properties toward stubborn pollutants. However, their utilization is hindered by high preparation costs, low yields, environmental pollution during synthesis, and challenges in regenerating the adsorbent. This study proposes a novel approach to address these limitations by developing nitrogen-doped three-dimensional (3D) polyvinyl alcohol cross-linked graphene sponges (N-PGA) using a cross-linking method with ammonium carbonate. This method offers a relatively mild and environmentally friendly approach. Ammonium carbonate serves as both a reducing and modifying agent, facilitating the formation of the intrinsic structure of N-PGA and acting as a nitrogen source. Meanwhile, polyvinyl alcohol (PVA) is utilized as the cross-linking agent. The results demonstrate that N-PGA exhibits a favorable internal 3D hierarchical porous structure and possesses robust mechanical properties. The measured specific surface area (BET) of N-PGA was as high as 406.538 m2·g–1, which was favorable for its efficient adsorption of Congo red dye molecules. At an initial concentration of 50 mg·L–1, N-PGA achieved an impressive removal rate of 89.6% and an adsorption capacity of 112 mg·g–1 for Congo red (CR) dye. Furthermore, it retained 79% of its initial adsorption capacity after 10 cycles, demonstrating excellent regeneration performance. In summary, the synthesized N-PGA displays remarkable efficacy in the adsorption of CR dye in wastewater, opening up new possibilities for utilizing 3D porous graphene nanomaterials as efficient adsorbents in wastewater treatment.

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.

Hybrid crosslinking for in-situ encapsulation of three-dimensional porous SiOx@rGO as high-performance anodes in lithium-ion batteries

Silicon suboxide (SiOx) anodes have garnered significant attention from both academia and industry due to their superior theoretical capacity compared to graphite, as well as their improved capacity retention in comparison to pure silicon. Nevertheless, SiOx electrodes still confront the challenge of substantial volume expansion (>160 %) during the alloying process, resulting in electrode structural damage or even fragmentation and severely impacting cycling performance. Here, a three-dimensional (3D) conductive network was constructed by ethylenediamine (EDA) cross-linking reduced graphene oxide (rGO), which was encapsulated on the surface of SiOx spheres generated in situ via a magnesium thermal reduction reaction. Accordingly, the SiOx@rGO-EDA anode was prepared successfully with high reversible capacity (892 mAh g−1 after 100 cycles at 1 A g−1) and fascinating rate performance (447 mAh g−1 at 4 A g−1). In full cell, the SiOx@rGO-EDA anode also exhibits outstanding cycling stability (154 mAh g−1 after 100 cycles at 0.1C) and rate capability. The scanning electron microscopy (SEM) images captured from a top-view perspective indicate that the surface of SiOx@rGO-EDA electrode is smooth and dense without any noticeable cracks, and it maintains its structural integrity throughout the cycling process. The cross-sectional thickness of the electrode remains essentially the same. These results illustrate the superior structural stability of the EDA cross-linked graphene conductive network cladding structure, enabling it to adapt to dynamic changes and ensure efficient transport of lithium ions and electrons. The facile and versatile synthesis method of SiOx@rGO-EDA structures by incorporating cross-linking agents provides inspiration for the design of next-generation high-performance anodes.

Biomimetic scaffold development for bone tissue engineering: Crosslinking graphene with collagen to enhance mechanical strength, conductivity, and porous structure

Biomimetic scaffold development for bone tissue engineering: Crosslinking graphene with collagen to enhance mechanical strength, conductivity, and porous structure

Boosting activity on copper functionalized biomass graphene by coupling nanocrystalline Nb2O5 as impressive rate capability for supercapacitor and outstanding catalytic activity for oxygen reduction

A novel and hierarchical porous but cross-linked copper-doped biomass graphene (Cu@HPBG) combined with Nb2O5 (denoted as Nb2O5/Cu@HPBG) is successfully fabricated on a large-scale using fig peels as biomass carbon and copper as the graphitization catalyst. During the synthesis process, basic copper carbonate serves dual functions of pore-forming agent, as well as homogeneous copper provider, and NH3 is employed as a defect-forming agent and N dopant. Owing to the porous hierarchical structure increased availability of contact interface and pseudo capacitance active sites provided by copper and Nb2O5, the assembled asymmetrical supercapacitor (ASC) employing Nb2O5/Cu@HPBG as positive electrode and HPBG as negative electrode can not only widen the stability window range of 0～1.9 V, but also deliver a maximum gravimetric energy density of 82.8 W h kg−1 at the power density of 950.0 W kg−1 and maintain a remarkable cycling stability of 97.1% after 15,000 cycles. Impressively, due to the synergistic enhancement of Cu@HPBG and Nb2O5, the resulting Nb2O5/Cu@HPBG hybrid displays more positive half wave potential (∼0.85 V) and a long-life stability than Pt/C electrode toward oxygen reduction reaction (ORR). Our research provides a feasible strategy to fabricate renewable biomass graphene electroactive composites for large-scale supercapacitor electrodes and efficient ORR catalysts toward energy applications.

In-situ fabricated copper-holmium co-doped cobalt ferrite nanocomposite with cross-linked graphene as novel electrode material for supercapacitor application

Recently, hybrid electrode materials based on cross-linked carbon analogues have gained significant consideration for their excellent cyclic stability and high specific capacities. This work presents the fabrication of copper and holmium co-doped cobalt ferrite with cross-linked graphene (denoted as CH-CoF/CLG) through one-step hydrothermal route, as novel electrode material for supercapacitor study. The electrochemical performance of CH-CoF/CLG along with its counterparts i.e., CoF, CH-CoF was evaluated through CV, GCD, and EIS analysis using three electrode system. The specific capacitance (Csp) of CoF, CH-CoF, and CH-CoF/CLG nanocomposite at a sweep rate of 5 mV/s is 458 F/g, 762 F/g, and 1258 F/g, respectively, within a potential range of 0.0 to 0.6 V. For CH-CoF/CLG, the calculated slope value (b = 0.84) using power law showed that the energy storage mechanism is based on both capacitive and diffusional processes. The GCD test showed that CH-CoF/CLG exhibited long discharge time (td = 615 s), as compared to CH-CoF (td = 409 s), and CoF (td = 264 s). Moreover, after the fabrication of CH-CoF with CLG, the value of equivalent series resistance (ESR) and charge transfer resistance (Rct) for CH-CoF/CLG were decreased to 0.74 Ω and 0.84 Ω, compared to CoF (1.18 Ω and 1.29 Ω) and CH-CoF (0.88 Ω and 1.0 Ω). When tested for cyclic stability, CH-CoF/CLG displayed insignificant loss in performance up to 3000 cyclic runs. The high supercapacitor performance of CH-CoF/CLG can be assigned to the combined effects arising from the co-doping of transition metal and rare earth metal ions (Cu+2 and Ho+3) into CoF lattice, porous cross-linked structure, high wettability, low intrinsic resistance, and easy accessibility of KOH ions into deep layers of active material. As obtained results deduce that the CH-CoF/CLG nanocomposite is a competent capacitive material for energy storage.

Confining NiCo2O4 nanoparticles in nitrogen doped carbon nanotubes embedded in 3D porous graphene aerogels for superior lithium storage

The huge volume expansion and poor electrical conductivity have seriously hindered the further development of redox-based electrode materials such as NiCo2O4 (NCO). Herein, we designed a novel NiCo2O4@nitrogen-doped carbon nanotube@3D graphene (NCO@CT@3DG) aerogel through hydrothermal assembly and high-temperature carbonization. In this aerogel, graphene nanosheets constructed the framework of the aerogel and NCO nanoparticles were deposited on the surface of nitrogen-doped carbon nanotubes which served as active materials for Lithium-ion batteries. The NCO decorated carbon nanotubes connecting the graphene sheets served as the scaffold to support the 3D cross-linked graphene network. As anode material of lithium-ion batteries, the optimized NCO@CT@3DG exhibited excellent electrochemical properties with high capacity as well as superior cycle and rate performance, which could maintain the discharge specific capacity of 810.3 mAh/g at the current density of 1.0 A/g after 500 cycles. The excellent properties are ascribed to the synergistic effect of each individual component and the unique graphene aerogels hybrid structure. This study demonstrates the great application prospects of 3DG aerogel hybrid structure in improving electrochemical properties of active materials with high volume expansion and poor conductivity.

Construction of core-shell heterostructure containing sandwich-like nanoarray for high-performance supercapacitors

Designing and constructing an ideal architecture is an effective approach to realize high-performance energy storage system. Core-shell heterostructure materials have attracted much attention due to their excellent performance in energy storage applications. Whereas, core-shell heterostructure containing sandwich-like nanoarray materials have rarely been reported by far. Herein, sandwich-like NiCo-PPy-layered double hydroxide (NiCo-PPy-LDH) nanosheets with polypyrrole (PPy) as the intercalation agent were vertically anchored on 3D cross-linked graphene nanoscroll (GNS) skeleton via a hydrothermal method and subsequent in situ polymerization process. Impressively, the as-prepared NiCo-PPy-LDH@GNS composite delivers a prominent specific capacitance of 2561 F·g−1 (equivalent conversion to 1024.4C·g−1) at 1 A·g−1 with 82 % capacitance retention at 10 A·g−1. The superior electrochemical properties of the NiCo-PPy-LDH@GNS is mainly attributed to its novel heterostructure which enhances the synergistic effect between NiCo-LDHs, GNSs, and PPy. The intercalation of PPy enriches hetero-interface and active sites for the redox reaction, while the GNSs skeleton provides a 3D rigid conductive network for further enhancing charge transportation and preventing the aggregation of LDH nanosheets.

Effective cross-linking strategy for graphene oxide membrane with high structural stability and enhanced separation performance

In order to solve the poor structural stability of graphene oxide (GO) membrane, a facile and effective cross-linking technology was employed to create a high-performance GO membrane. Herein, DL-Tyrosine/amidinothiourea and (3-Aminopropyl) triethoxysilane were used to crosslink GO nanosheets and porous alumina substrate, respectively. The group evolution of GO with different cross-linking agents was detected via Fourier transform infrared spectroscopy. Ultrasonic treatment and soaking experiment were conducted to explore the structural stability of the different membranes. The GO membrane cross-linked with amidinothiourea exhibits exceptional structural stability. Meanwhile, the membrane has superior separation performance, with the pure water flux reaching approximately 109.6 l·m−2·h−1·bar−1. During the treatment of 0.1 g l–1 NaCl solution, its permeation flux and rejection for NaCl are about 86.8 l·m−2·h−1·bar−1 and 50.8%, respectively. The long-term filtration experiment also demonstrates that the membrane exhibits great operational stability. All these indicate the cross-linking graphene oxide membrane has promising potential applications in water treatment.

Cross-Linked and Doped Graphene Oxide Membranes with Excellent Antifouling Capacity for Rejection of Antibiotics and Salts.

Graphene oxide (GO) membranes have suffered from the instability of water permeability and low rejection of pollutant separation. In this paper, a reasonable modification protocol for GO nanosheets at the molecular level was proposed. A molecular cross-linking strategy was adopted to regulate the interlayer spacing of GO nanosheets, and nanofiltration membranes with high water stability and excellent antifouling capacity were prepared, which could effectively reject antibiotics and salts. The GO1-MPD0.5 (the mass ratio of GO nanosheets to MPD is 1:0.5) and GO/GO1-MPD0.5-0.25 (the doping ratio of GO1-MPD0.5 is 25%) membranes had stable water permeability of 4.22 ± 0.06 and 3.65 ± 0.11 L m-2 h-1 bar-1, and the rejection rates for ciprofloxacin (CIP) and ofloxacin (OFX) were 93.35 ± 3.62 and 95.48 ± 2.97 and 85.89 ± 6.52 and 88.21 ± 3.67%, respectively. Molecular dynamics simulations well explained the high water stability of membranes, and the cross-linked hydrophobic benzene ring played a role in the rejection of pollutant molecules. Moreover, the GO1-MPD0.5 membrane showed excellent antifouling capacity and the flux recovery ratio (FRR) was more than 98%. This paper provides a new idea for the design of nanofiltration membranes with high stability and good rejection permeability at the molecular level and provides a prospect for the application of nanofiltration membranes in practical water treatment and water purification.