Exfoliated Graphene Nanosheets Research Articles

Morphological and Thermal Characterization of Low-Cost Graphene Produced by Electrochemical Exfoliation Method

The low-cost and mass production of graphene has gained importance in recent years. The electrochemical exfoliation method, one of the graphene production methods, is an efficient technique used to obtain low-cost-effective and large quantities of graphene nanosheets. Exfoliation parameters affect the properties of exfoliated graphene nanosheets. In this study, graphene production is fabricated by the method of exfoliation using electrolyte and voltage parameters. For this, a pen tip was used instead of pure platinum, which is very expensive, at the cathode. The structural research was done by X-ray diffraction spectroscopy (XRD), Raman spectroscopy and Fourier Transform Infrared Spectrometer (F-TIR). Morphological analyses were carried out by Scanning Electron Microscopy (SEM). The number of layers and crystallite of graphene layers were estimated. The obtained results were compared with the results of the other similar studies. Analysis results show that low-cost multilayer graphene can be produced by the electrochemical exfoliation method with the electrical parameters.

High-Throughput and Scalable Exfoliation of Large-Sized Ultrathin 2D Materials by Ball-Milling in Supercritical Carbon Dioxide.

The 2D materials exhibit numerous technological applications, but their scalable production is a core challenge. Herein, ball milling exfoliation in supercritical carbon dioxide (scCO2) and polystyrene (PS) is demonstrated to completely exfoliate hexagonal boron nitride nanosheets (BNNSs), graphene, molybdenum disulfide (MoS2), and tungsten disulfide (WS2). The exfoliation yield of 91%, 93%, 92%, and 92% and average aspect ratios of 743, 565, 564, and 502 for BNNSs, graphene, MoS2, and WS2, respectively, are achieved. Integrating exfoliated BNNSS in the polystyrene matrix, 3768 % thermal conductivity in the axial direction and 316% in the cross-plane direction at 12wt.% loading is increased. Also, the in-plane and cross-plane electrical conductivity of 6.3×10-4Sm-1 and 6.6×10-3Sm-1, respectively, and the electromagnetic interference (EMI) of 63.3 dB is achieved by exfoliated graphene nanosheets based composite. High thermal and electrical conductivities and EMI shielding are attributed to the high aspect ratio and ultrathin morphology of the exfoliated nanosheets, which exert high charge mobility and form better the percolation network in the composite films due to their high surface area. The process demonstrate herein can produce substantial quantities of diverse 2D nanosheets for widespread commercial utilization.

Synthesis of 2D bi-metallic Zn/Cu metal-organic framework integrated graphene nanocomposites for all-solid-state asymmetric supercapacitors

In this work, a novel two-dimensional (2D) bi-metallic metal-organic frameworks (MOFs) consisting of zinc and copper metal centers with 1,3,5-tricarboxylic acid as a chief and efficient organic linker (Zn/Cu-BTC) and its composite with exfoliated graphene nanosheets (EGNSs) have been investigated for supercapacitor applications. The composites were synthesized via facile in-situ solvothermal process. Different spectroscopic, microscopic, and surface analyses confirmed the successful formation of porous electroactive composites, where 2D MOF nanosheets were vertically grown on the EGNS surfaces. In the two-electrode symmetric system, the as-synthesized Zn/Cu-BTC MOF@EGNS electrode achieved an enhanced specific gravimetric capacitance and equivalent volumetric capacitance of 1284.9 F/g and 813.3 F/cm3 at 0.5 A/g. It exhibits high-rate performance and prolonged cycling stability with >90 % retention after 8000 cycles. All-solid-state asymmetric supercapacitor (ASC) device was constructed with Zn/Cu-BTC MOF@EGNS composite and EGNS electrodes, where PVA-KOH membrane served as a separator-cum-electrolyte. The ASC device delivered a satisfactory energy density of 60.55 Wh kg−1 and a maximum power density of 10 kW kg−1 with an admirable cycling stability of 92 % after 10,000 charge-discharge cycles. In the future, this work can encourage manufacturing innovation.

Graphene/metal-organic framework nano-sandwiches derived N, P-codoped porous carbon nanosheets as robust material for electrochemical analysis

Construction of novel two-dimensional porous carbon nanosheets with superior electrochemical activity is of great challenge. Here, graphene/ZIF-8 nano-sandwiches derived N, P-codoped porous carbon nanosheets (N, P-codoped PCN) was easily obtained by sequential room temperature self-assembly and high-temperature carbonization method. Relative to the widely used physically exfoliated graphene nanosheets (GN) and graphene/ZIF-8 derived N-doped porous carbon nanosheets (N-doped PCN), N, P-codoped PCN displayed larger active surface, faster electron transport ability and stronger physical adsorption ability, which can be ascribed to the dual doping effect of heteroatoms N and P. As a result, N, P-codoped PCN exhibited remarkable oxidation signal enhancement for tumor marker (8-hydroxy-2′-deoxyguanosine), analgesic and antipyretic drug (acetaminophen) and organic pesticide (benomyl). Besides, the limits of detection were measured as low as 1.58 nM, 7.50 nM and 2.10 nM with sensitivity of 270.00 μA μM−1 cm−2, 757.14 μA μM−1 cm−2 and 272.86 μA μM−1 cm−2 for 8-hydroxy-2′-deoxyguanosine, acetaminophen and benomyl, respectively. Basing on this, a novel and highly sensitive electrochemical sensing platform was developed. It is believed that the reported two-dimensional N, P-codoped PCN with unique structure and composition is highly valuable for the development of carbon-based electrochemical sensors.

Two‐Step Sequential Process for Fabricating Graphene Nanosheets Decorated with Copper Halide Nanocrystals and Their Optoelectronic Applications

AbstractNanocrystals of Cs3Cu2I5, a metal halide with promising potential as a perovskite substitute, are successfully grown on graphene nanosheets. An intermediate stage of physically exfoliated graphene nanosheets, concurrent with the formation of copper‐based seeds on graphene surface, is developed, for the first time, allowing for the subsequent growth of Cs3Cu2I5 nanocrystals (CsNCs) to obtain CsNCs‐decorated graphene nanohybrids (CsGNHs). The morphology and properties of the CsGNHs depend on the input amount of graphene nanosheets during the reaction. The photoluminescence intensity of the CsGNHs decreases with increasing graphene content, indicating that graphene facilitates nonradiative energy transfer from the CsNCs in the CsGNHs. The inherent self‐trapping exciton emission of the CsNCs is also affected by the graphene substrate. As the graphene content increases, the emission peaks of the CsGNHs broaden and diminish. The CsGNHs emit a stable solid‐state luminescence with a large Stokes shift (zero self‐absorption) under a high‐energy ultraviolet (UV) light. Consequently, the CsGNHs can act as optoelectronic transducers and selectively generate a turn‐on photocurrent response under specific‐wavelength UV light. Additionally, a new anticounterfeiting strategy is developed using the CsGNHs as a luminescent black ink to fabricate luminescent quick‐response codes with fake pixels.

Synthesis and electrochemical performance of TiNb2O7 nanoparticles grown on electrochemically prepared graphene as anode materials for Li-ion batteries

In this study, the electrochemically exfoliated graphene nanosheets are used as conductive networks to enhance the electrochemical performance of titanium niobium oxide (TNO) nanoparticles as anode for Li-ion batteries (LIBs). The morphological analyses show that without using graphene, the TNO porous microspheres are formed through the self-assembly mechanism. However, by adding different contents of graphene (1, 3, and 5 wt%), the TNO nanoparticles are distributed on the graphene nanosheets. The distribution of the TNO nanoparticles on graphene nanosheets decreases due to the increase in the number of the graphene layer. Accordingly, the effectiveness of graphene nanosheets in enhancing the electrochemical performance of TNO depends on their content. The TNO/3 wt% graphene has the best electrochemical performance among all samples. At 20C, the capacity value of pure TNO is improved by two orders via the addition of 3.0 wt% graphene nanosheets. The capacity retention of the pure TNO at 1C and after 200 cycles is improved by about 25% by the addition of 3.0 wt% graphene nanosheets due to the buffering effect of graphene. However, the higher contents of graphene nanosheets (5.0 wt%) not only cannot improve the properties of TNO but also reduce its capacity.

Methylammonium Lead Bromide Perovskite Nano-Crystals Grown in a Poly[styrene-co-(2-(dimethylamino)ethyl Methacrylate)] Matrix Immobilized on Exfoliated Graphene Nano-Sheets.

Development of graphene/perovskite heterostructures mediated by polymeric materials may constitute a robust strategy to resolve the environmental instability of metal halide perovskites and provide barrierless charge transport. Herein, a straightforward approach for the growth of perovskite nano-crystals and their electronic communication with graphene is presented. Methylammonium lead bromide (CH3NH3PbBr3) nano-crystals were grown in a poly[styrene-co-(2-(dimethylamino)ethyl methacrylate)], P[St-co-DMAEMA], bi-functional random co-polymer matrix and non-covalently immobilized on graphene. P[St-co-DMAEMA] was selected as a bi-modal polymer capable to stabilize the perovskite nano-crystals via electrostatic interactions between the tri-alkylamine amine sites of the co-polymer and the A-site vacancies of the perovskite and simultaneously enable Van der Waals attractive interactions between the aromatic arene sites of the co-polymer and the surface of graphene. The newly synthesized CH3NH3PbBr3/co-polymer and graphene/CH3NH3PbBr3/co-polymer ensembles were formed by physical mixing of the components in organic media at room temperature. Complementary characterization by dynamic light scattering, microscopy, and energy-dispersive X-ray spectroscopy revealed the formation of uniform spherical perovskite nano-crystals immobilized on the graphene nano-sheets. Complementary photophysical characterization by UV-Vis absorption, steady-state, and time-resolved fluorescence spectroscopy unveiled the photophysical properties of the CH3NH3PbBr3/co-polymer colloid perovskite solution and verified the electronic communication within the graphene/CH3NH3PbBr3/co-polymer ensembles at the ground and excited states.

Ageing-resistant zirconia/graphene-based nanostructures composites for use as biomaterials

This work explores the incorporation of graphene-based two-dimensional nanostructures as moisture barriers to delay hydrothermal ageing of yttria-stabilized zirconia and strengthen its use in biomedical applications. Two sets of highly dense zirconia composites incorporating multilayered graphene with very different lateral dimensions, few layer graphene and exfoliated graphene nanoplatelets, were prepared. The effect of the addition of graphene nanostructures on zirconia ageing was investigated by conducting accelerated hydrothermal degradation experiments in an autoclave. An improved resistance to low-temperature degradation and a high tolerance to damage were achieved in the composites compared to those of monolithic zirconia. The incorporation of 1 vol% multilayered graphene was very effective in restricting the hydrothermal degradation. In particular, the composite incorporating exfoliated graphene nanosheets exhibited outstanding resistance to ageing because of their fine dispersion throughout the matrix, which effectively seemed to restrict grain growth and slow the propagation of the transformation front to the ceramic bulk.

Electrochemically Exfoliated Graphene/Manganese Dioxide Nanowire Composites as Electrode Materials for Flexible Supercapacitors

Flexible supercapacitors are of great significance for the development of intelligent electronic products and wearable devices. Herein, through reasonable design, self-supporting flexible film composites that can be used as supercapacitor electrodes, are synthesised by vacuum filtration. The composites are composed of electrochemically exfoliated graphene nanosheets and MnO2 nanowires, in which the graphene nanosheets mainly play the role of skeleton support, enhance conductivity, and provide electric double-layer capacitance, while the MnO2 nanowires mainly provide pseudocapacitance. Results show that the sample with 20% MnO2 possesses the best electrochemical performance due to the mass ratio which can give full play to the pseudocapacitive properties of MnO2 and the conductivity of graphene. The maximum mass specific capacitance reaches 106.2F g−1 at 0.5A g−1, and the areal specific capacitance is 767.0mF cm−2 at 1mA cm−2. The electrode also maintains 86.7% of the initial capacitance after 10000 cycles, indicating good cyclic stability. Furthermore, an asymmetric solid supercapacitor based on flexible thin films is assembled. The energy density is 20.7Wh kg−1, the power density is 1000W kg−1, and the capacitance remains 84.2% after 3000 cycles at 5.0A g−1. These results suggest that the as-prepared self-supporting material has the potential to be used to construct flexible supercapacitors for wearable equipment.

Green and eco-friendly chemical exfoliation of two-dimensional nanosheets in the C2H4O3-based system under the assistance of microwave irradiation

Eco-friendly exfoliation of two-dimensional nanosheets from their layered bulks is very attracting but still remains a big challenge. Here, we report a novel preparation route of two-dimensional nanosheets through soaking the bulk layered material in the C2H4O3-based chemical exfoliation system followed by microwave irradiation. This route has demonstrated the effective exfoliation of two-dimensional nanosheets (graphene nanosheets, BNNS and MoS2NS) from their layered bulks in a green and eco-friendly way. The average layer-number of the obtained graphene nanosheets, BNNS and MoS2NS is 4, 6 and 5, respectively, behaving a few-layer feature. Interestingly, when the graphene paper is prepared from the exfoliated graphene nanosheets by simple vacuum filtration and mechanical pressing, its average electrical conductivity is up to 7.36 × 105 S/m and the EMI SE value reaches to 61 dB, both among the highest for the graphene papers reported previously. Since there exists no serious fragmentation of layered materials during the whole exfoliation, the present exfoliation strategy is more competent in preparing the large-sized two-dimensional nanosheets over those conventional green routes.

Flexible and high-energy-density Zn/MnO2 batteries enabled by electrochemically exfoliated graphene nanosheets

Electrochemically exfoliated graphene nanosheets were proposed for flexible and high-performance Zn–MnO2 batteries without polymer binder and metal current collectors.

Enhanced compatibility, morphology, rheological and mechanical properties of carboxylated acrylonitrile butadiene rubber/chloroprene rubber/graphene nanocomposites: effect of compatibilizer and graphene content.

Elastomeric nanocomposites were prepared from carboxylated acrylonitrile butadiene rubber/chloroprene rubber (XNBR/CR), graphene and a glycidyl methacrylate (GMA)-grafted XNBR (XNBR-g-GMA) compatibilizer by using a two-roll mill. The effect of graphene and XNBR-g-GMA compatibilizer on curing characteristics, rheological and mechanical properties and morphology of the nanocomposites was investigated. The curing properties and the morphology of the nanocomposites were studied by rheometry, SEM and TEM, respectively. The results of rheometry showed that by adding the XNBR-g-GMA compatibilizer and increasing the graphene content, the scorch time and optimum curing time decreased, but the torque increased, while the curing time increased with increasing CR percentage in the blend. Also, the results of DMTA tests showed that by adding the XNBR-g-GMA compatibilizer, there was compatibility between CR and XNBR and the dispersion of graphene in the XNBR/CR matrix was improved. This phenomenon was confirmed by direct observation of exfoliated graphene nanosheets by TEM. Also, the addition of XNBR-g-GMA and the increase of graphene content in the XNBR/CR matrix caused the fracture surface of the samples to be roughened and the size of dispersed phase (CR) in the XNBR matrix becomes smaller. The results of mechanical properties showed that the addition of the XNBR-g-GMA and increasing the graphene content resulted in increased hardness, fatigue strength, tensile strength, modulus and elongation-at-break.

Multi-role p-styrene sulfonate assisted electrochemical preparation of functionalized graphene nanosheets for improving fire safety and mechanical property of polystyrene composites

Polystyrene sulfonate functionalized graphene nanosheets (PSS@GNS) with high quality (ID/IG = 0.17) were fabricated through electrochemical exfoliation of bulk graphite followed by simple free radical polymerization in water solution, which is a promising strategy for mass production of polymer functionalized graphene. P-styrene sulfonate anions were used to intercalate into the bulk graphite under voltage and also as monomers of the macromolecule modification agents for the exfoliated graphene nanosheets. Besides, benzene rings and carbon double bonds are considered to be able to capture hydroxyl free radicals which produce defects on graphene sheets during electrochemical exfoliation process, thus improve the quality of the exfoliated graphene nanosheets. Then the graphene nanosheets were incorporated into polystyrene (PS) through a solution blending method to reduce the fire hazards and improve mechanical properties of PS resin. According to the results of cone calorimeter, the introduction of functionalized graphene nanosheets into PS reduces heat release rate (decreased by 40%), total heat release (decreased by 35%) and increases the amount of char residues. The flame retardant improvement is attributed to the barrier effect of well-dispersed graphene nanosheets, limiting the mass transfer of the volatile compounds and forming char layers which blocked polymers from heat and oxygen. Meanwhile, the introduction of PSS@GNS into PS also contributed to increase its strength and elongation rate thanks to the pristine properties of graphene nanosheets and their interfacial interaction with the PS matrix.

High energy density supercapacitor based on N/B co-doped graphene nanoarchitectures and ionic liquid electrolyte

Boron-nitrogen co-doped graphene nanoarchitectures were synthesized by annealing a freeze-dried precursor containing exfoliated graphene oxide (GO) nanosheets, ammonium borate, and polyvinyl alcohol (PVA). The microstructures and composition of nanocomposites were optimized and characterized systemically. Effects of a doping element on the electrochemical performances and interface compatibility were evaluated. The restacking of exfoliated graphene nanosheets was hindered effectively by the ultra-fine carbon clusters formed via the thermal decomposition of PVA. Such a three-dimensional structure favors the fast mobility of electrolyte ions. In addition, the co-doping of N and B elements not only increases interface compatibility between ionic liquid electrolyte and graphene but also supplies extra pseudocapacitance. Benefiting from the integrated merits, the optimized nanocomposites could deliver a specific capacitance of 35.4 F g−1 at 1 A g−1 and present a maximum energy density of 78.7 Wh kg−1 with a power density of 2043 W kg−1. Due to the formation of more decoupled ions in ionic liquid electrolyte at elevated temperature, the symmetric supercapacitors based on the as-formed nanocomposite exhibit a maximum energy density of 134.6 Wh kg−1 at 60 °C.

Activated carbon felts with exfoliated graphene nanosheets for flexible all-solid-state supercapacitors

The recent development of portable electronics promotes the growing demand for flexible energy storage devices. Supercapacitors are promising candidates due to their high power density. Therefore, flexible supercapacitors are desired. Here, the porous activated carbon felts (ACFs) with exfoliated graphene nanosheets and rich oxygen-containing groups were fabricated by a facile thermal treatment strategy. Such ACFs can act as the flexible electrodes of all-solid-state supercapacitors directly without the use of binder and conductive materials. They exhibit excellent electrochemical properties, such as high specific areal capacitance, superior rate ability and long-term cycling stability. Moreover, the fabricated flexible all-solid-state supercapacitors based on ACFs deliver stable electrochemical performance under different bending states.

In Situ Synthesis of a Sandwich-like Graphene@ZIF-67 Heterostructure for Highly Sensitive Nonenzymatic Glucose Sensing in Human Serums.

Metal-organic frameworks (MOFs) have been extensively studied in recent years due to their tunable porosity, huge specific area, and controllable structure. The rich metal centers and large specific area have endowed MOFs with excellent electrochemical activity due to the multiple valence states, but the poor electronic conductivity of MOFs seriously impedes their electrocatalytic performance. Here, a polyhedral Co-based zeolite imidazole frame [Co(mim)2] n (denoted as ZIF-67, mim = 2-methylimidazole) is in situ loaded on the two sides of physically exfoliated graphene nanosheets (GSs) at room temperature, and sandwich-like GS@ZIF-67 hybrids with an ordered nanostructure are easily obtained. Compared with each individual component, the as-synthesized GS@ZIF-67 hybrids exhibit higher electrochemical activity toward glucose oxidation. Besides, the hierarchical nanocomposites also show better electrocatalytic performance compared with the same ratio of a physical mixture of GSs and ZIF-67, further demonstrating the synergistic effect between ZIF-67 and GSs. Thus, a highly sensitive nonenzymatic glucose electrochemical sensor is proposed with a linear range of 1-805.5 μM, sensitivity of 1521.1 μA Mm-1 cm-2, detection limit of 0.36 μM (S/N = 3), and excellent stability and selectivity. More importantly, the newly fabricated sensor is also successfully applied for glucose determination in human serums with satisfactory results, suggesting its promising potential toward glucose detection in real samples.

A Comparative Study of Particle Size Distribution of Graphene Nanosheets Synthesized by an Ultrasound-Assisted Method.

Graphene-based materials are highly interesting in virtue of their excellent chemical, physical and mechanical properties that make them extremely useful as privileged materials in different industrial applications. Sonochemical methods allow the production of low-defect graphene materials, which are preferred for certain uses. Graphene nanosheets (GNS) have been prepared by exfoliation of a commercial micrographite (MG) using an ultrasound probe. Both materials were characterized by common techniques such as X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All of them revealed the formation of exfoliated graphene nanosheets with similar surface characteristics to the pristine graphite but with a decreased crystallite size and number of layers. An exhaustive study of the particle size distribution was carried out by different analytical techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and asymmetric flow field flow fractionation (AF4). The results provided by these techniques have been compared. NTA and AF4 gave higher resolution than DLS. AF4 has shown to be a precise analytical technique for the separation of GNS of different sizes.

Exfoliated graphene nanosheets as high-power anodes for lithium-ion batteries

High-quality and solution processable graphene sheets are produced by a simple electrochemical exfoliation method and employed as a high-power anode for lithium-ion batteries (LIBs). The electrochemically exfoliated graphene (EEG) composed of a few layers of graphene sheets, have low oxygen content and high C/O ratio (~ 14.9). The LIBs with EEG anode exhibit ultrafast lithium storage and excellent cycling stability, but low initial efficiency. The excellent rate capability and cycling stability are attributed to the favorable structural and chemical properties of the EEG, but the large irreversibility needs to be overcome for practical applications.

Growth of vanadium dioxide nanostructures on graphene nanosheets

The metal oxide/graphene hybrid nanomaterials have been known as promising functional materials for advanced applications such as high capacitive electrode material of secondary batteries, and high sensitive material of high performance gas sensors. Here, morphology controlled vanadium dioxide (VO2) nanostructures were grown on Si wafer and exfoliated graphene by the vapor transport method using a horizontal furnace system. One-dimensional VO2 nanowires were grown on SiO2(300 nm)/Si substrate under 0.4 kPa condition. On the other hand, thick polycrystalline of VO2 platelets were grown on exfoliated graphene nanosheets under 0.4 kPa condition. In addition, polycrystalline VO2 platelets were only grown on exfoliated graphene nanosheets under 101 kPa (atmospheric pressure) condition. The growth of polycrystalline VO2 platelets on graphene nanosheets in atmospheric pressure condition is attributed to preferential growth on functional group of graphene surface such as carbonyl. The functional group is served as nucleation site of VO2 nanostructures.

Comparison on exfoliated graphene nano-sheets and triturated graphite nano-particles for mode-locking the Erbium-doped fibre lasers

Comparisons on exfoliated graphene nano-sheets and triturated graphite nano-particles for mode-locking the Erbium-doped fiber lasers (EDFLs) are performed. As opposed to the graphite nano-particles obtained by physically triturating the graphite foil, the tri-layer graphene nano-sheets is obtained by electrochemically exfoliating the graphite foil. To precisely control the size dispersion and the layer number of the exfoliated graphene nano-sheet, both the bias of electrochemical exfoliation and the speed of centrifugation are optimized. Under a threshold exfoliation bias of 3 volts and a centrifugation at 1000 rpm, graphene nano-sheets with an average diameter of 100 ± 40 nm can be obtained. The graphene nano-sheets with an area density of 15 #/µm2 are directly imprinted onto the end-face of a single-mode fiber made patchcord connector inside the EDFL cavity. Such electrochemically exfoliated graphene nano-sheets show comparable saturable absorption with standard single-graphene and perform the self-amplitude modulation better than physically triturated graphite nano-particles. The linear transmittance and modulation depth of the inserted graphene nano-sheets are 92.5% and 53%, respectively. Under the operation with a power gain of 21.5 dB, the EDFL can be passively mode-locked to deliver a pulsewidth of 454.5 fs with a spectral linewidth of 5.6 nm. The time-bandwidth product of 0.31 is close to the transform limit. The Kelly sideband frequency spacing of 1.34 THz is used to calculate the chirp coefficient as −0.0015.