Few-layer Graphene Nanosheets Research Articles

Ultrafast Fabrication of Graphene-Reinforced Nanocomposites via Synergy of Steam Explosion and Alternating Convergent-Divergent Flow.

Producing high-quality graphene and polymer/graphene nanocomposite is facing the problems of complex procedure, low efficiency, and serious resource waste. To explore a new fabrication approach with high efficiency and low cost is crucial for solving these technical issues, which becomes a current research hotspot and also a great challenge. Herein, a one-step melt mixing strategy based on the synergy of steam explosion and alternating convergent-divergent flow, is innovatively developed to fabricate high-density polyethylene (HDPE)/graphene nanocomposites using industrial-grade expanded graphite (EG) without chemical agents and complex procedures. The co-action of the external force derived from elongational melts and the internal force generated by steam explosion make EG ultrafastly exfoliate into few-layer graphene nanosheets (GNS) and simultaneously disperse in melts within 4 min. The as-produced GNS have a lateral size of over 5 µm and a minimum thickness of 1.4 nm, can introduce super heterogeneous nucleation to HDPE macromolecules and greatly increases nanocomposite crystallinity up to 86.5%. Moreover, plentiful HDPE crystallites and well-dispersed GNS jointly form an improved thermally-conductive network, making nanocomposites with a rapid-respond ability in solar-to-thermal conversion and heat dissipation. This facile strategy will facilitate the development of scalable production and wide application of high-performance graphene and highly-filled nanocomposites.

Structure of microwave plasma-torch discharge during graphene synthesis from ethanol

Few-layer graphene nanosheets were synthesised from ethanol using a microwave plasma torch. The stability of the discharge permitted us to directly observe and analyse two distinctive structures—a plasma zone and an assembly zone. Important plasma parameters and insights into the chemical processes taking place in these zones were gained using optical emission spectroscopy and digital imaging for a set of experimental conditions. The results of the plasma diagnostics were then correlated with the synthesised material properties, mainly obtained from electron microscopy and Raman spectroscopy.

A facile method for coal to graphene oxide and its application to a biosensor

The classic methods of synthesis of graphene oxide derived from graphite require harsh oxidation with excessive chemicals (H2SO4, H3PO4, KMnO4, etc.) and multiple processes. In this paper, we present a facile one-pot process using HNO3 to obtain graphene oxide from coal (Coal-GO). Coal has a unique molecular structure comprising of small regions or clusters of graphene-like and aliphatic side chains, for which our process is successfully able to exclude aliphatic compounds while preserving graphene domains during oxidization and subsequent exfoliation. The Coal-GO was converted to reduced graphene oxide (Coal-rGO) by conventional method to produce a few-layered graphene nanosheets in lateral size of 300–700 nm. The surface characteristics of the Coal-GO indicate the persistence of N from the raw coal as well as that introduced in the process. Notably, the Coal-GO shows a considerable amount of COOH compared to the other oxygen groups. Our data indicates that the process is effective in oxidative scissoring of the edges of coal, with minimal effect on swelling of coal towards the c-direction. Lastly, we demonstrate that compared to Graphite-GO, the Coal-GO has superior interaction with single stranded DNA aptamer, which could result in higher sensitivity chemiluminescence resonance energy transfer-based biosensors.

Protein-assisted scalable mechanochemical exfoliation of few-layer biocompatible graphene nanosheets.

A facile method to produce few-layer graphene (FLG) nanosheets is developed using protein-assisted mechanical exfoliation. The predominant shear forces that are generated in a planetary ball mill facilitate the exfoliation of graphene layers from graphite flakes. The process employs a commonly known protein, bovine serum albumin (BSA), which not only acts as an effective exfoliation agent but also provides stability by preventing restacking of the graphene layers. The latter is demonstrated by the excellent long-term dispersibility of exfoliated graphene in an aqueous BSA solution, which exemplifies a common biological medium. The development of such potentially scalable and toxin-free methods is critical for producing cost-effective biocompatible graphene, enabling numerous possible biomedical and biological applications. A methodical study was performed to identify the effect of time and varying concentrations of BSA towards graphene exfoliation. The fabricated product has been characterized using Raman spectroscopy, powder X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The BSA-FLG dispersion was then placed in media containing Astrocyte cells to check for cytotoxicity. It was found that lower concentrations of BSA-FLG dispersion had only minute cytotoxic effects on the Astrocyte cells.

Controlled high temperature stability of microwave plasma synthesized graphene nanosheets

High temperature stability of nanomaterials plays an important role for their application in the field of nanocomposites, batteries, and sensors. Few-layer graphene nanosheets prepared by microwave plasma based decomposition of ethanol exhibited high thermal stability in the oxidation atmosphere in dependence on controlled formation of structural disorder. Analysis of differential thermogravimetry (DTG) curve profile showed three temperature regions, around 345 °C, 570 °C and above 700 °C, related to amorphous phase with a carbon–oxygen functional groups, small defective nanostructures and highly crystalline structure of graphene nanosheets, respectively. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) analysis of the nanosheets showed an increase of D/G Raman band ratio as well as increasing of sp3 phase content, from 6.1 at% to 15.2 at%, for highly crystalline and highly disordered structure of the nanosheets. Thermal annealing under synthetic air was used to investigate the variation in D/G and 2D/G Raman band ratio of the samples and to estimate activation energy of oxidation and disintegration process of graphene nanosheets. The highest oxidation resistance exhibited sample with high 2D/G band ratio (1.54) and lowest oxygen content of 1.7 at%. The synthesis process led to stabilization of nanosheet structure by formation of curved edges and elimination of free dangling bonds. The nanosheets prepared in microwave plasma exhibited high surface area, over 350 m2 g−1, and superior thermal stability with defect activation energy in an oxidation atmosphere higher than 2 eV. Heat release rate during the oxidation process was in correlation with the amount of disorder in the samples. Fast and easy to use technique based on high power Raman spectroscopy was developed for assessment of nanomaterial oxidation resistance.

Wear Performance and Nanomechanical Behavior of Sonoelectroplated Cu-Graphene Nanocomposite Thin Films

Few-layer graphene nanosheets (FLGN) and reduced FLGN (rFLGN) have been used as reinforcement with a copper matrix to produce nanocomposite thin film by sonoelectrodeposition method onto Cu substrates. FLGN and rFLGN used in the study were prepared by electrochemical intercalation and exfoliation technique. The phase and structures of FLGN to rFLGN were ratified then after. The prepared composite films were analyzed to confirm the matrix and reinforcement phases, and then the wear behavior has been studied in detail. It was found that all the composite films have better wear properties, i.e., low wear depth, width and rate, low coefficient of friction as compared to pure Cu films. The said improvement is mainly due to the uniform distribution of graphene in the metal matrix and increased hardness (up to 38% higher) and stiffness. Further, the wear mechanism was either abrasive or a combination of abrasive and adhesive types. The Cu-rFLGN composites did show an adhesive type of wear leading to delamination of Cu layers.

Seaweed biomass derived bio solvents for the large scale production of few layered graphene nanosheets from graphite

Large-scale production of graphene sheets by liquid-phase exfoliation of graphite is a challenging task from a sustainability point of view. Certain bio-derived solvents were found to exfoliate graphite to produce single-layered graphene sheets but the high cost of the solvent is always a deterring factor towards upscaling of the process. Herein, Kappaphycus alvarezii, a cultivable red seaweed is demonstrated as a sustainable resource for producing a bio solvent for exfoliation and to produce graphene sheets from graphite. A solvent system consisting of levulinic acid, acetic acid, and γ-valerolactone was prepared from the polysaccharide obtained from the seaweed biomass through acid hydrolysis under pressure and the mixture was found to exfoliate graphite to produce few-layered pristine graphene nanosheets. The process is scalable and cost-effective and the seaweed biomass-derived solvent mixture can be recovered and reused in the subsequent cycles of exfoliation for large-scale production of graphene nanosheets.

Cellulase mimicking nanomaterial-assisted cellulose hydrolysis for enhanced bioethanol fermentation: an emerging sustainable approach

Employment of cellulase mimicking functionalized few-layer graphene (FFG) nanosheets for cellulose hydrolysis to replace enzymes completely/partially could aid in developing a sustainable process for bioethanol fermentation.

Reversible Deposition of Lithium Particles Enabled by Ultraconformal and Stretchable Graphene Film for Lithium Metal Batteries.

Originating from inhomogeneous Li deposition and dissolution, the formation of dendritic and/or dead Li lies as a fundamental barrier to the practical implementation of Li metal anodes for high-energy Li-ion batteries. Here, an ultraconformal and stretchable solid-electrolyte interphase (SEI) composed of parallelly stacked few-layer defect-free graphene nanosheets, which can deform to remain ultraconformal during the expansion and shrinkage of micro-sized Li metal particles is reported. The shape-adaptive graphene protective skin is prepared via a facile mechanical method followed by Li stripping, which enables fast Li-ion diffusion, and inhibits Li dendrites and Li pulverization. The interlayer slips and wrinkles of the graphene film endow the robust protective skin with high stretchability. This work represents a unique strategy of building ultraconformal and stretchable 2D-materials-based protective skins on the surface of Li metal toward high-energy, long-life, and safe Li metal batteries.

Layered mesoporous CoO/reduced graphene oxide with strong interfacial coupling as a high-performance anode for lithium-ion batteries

Composites of few-layer transition metal oxides and graphene nanosheets with strong interfacial connection hold great promise as high-performance anodes for lithium-ion batteries, but it is highly challenging to realize full interfacial properties. Herein, we report an ultra-refined layer-by-layer mesoporous CoO/reduced graphene oxide (CoO/RGO) architecture synthesized via a facile method. The CoO/RGO has stacked interfaces between the CoO nanosheets and the graphene nanosheets via Co–O–C bonds, which has been proposed to have an important role in achieving excellent performance in lithium ion batteries with high initial capacity and good rate capability. It is shown that the CoO/RGO exhibits a high initial discharge capacity of 2189.4 mAh g−1 at a current density of 100 mA g−1. Furthermore, the CoO/RGO exhibits a high reversible capacity retention of 70% after prolonged 300 cycles at a high rate of 2 A g−1. Significantly, it delivers an ultrahigh reversible capacity of 1167 mAh g−1 at 5 A g−1 with an excellent reversible capacity retention of 76% over 40 cycles.

Dual-modal label-free genosensor based on hemoglobin@gold nanocluster stabilized graphene nanosheets for the electrochemical detection of BCR/ABL fusion gene

For the first time, we have successfully synthesized stable graphene nanosheets from graphite powder through sonication in the hemoglobin-capped gold nanoclusters (Hb@AuNCs) solution for biosensing application. This approach, as a simple method for the exfoliation and fragmentation of graphite in a nanocluster solution, enabled us to produce stable aqueous graphene dispersions at low cost and without the need for hazardous chemicals or tedious experimental procedures. In this method, Hb@AuNCs were used not only as stabilizing agent of graphene through non-covalent bonding, but also as dispersing agent of few-layer graphene nanosheets. The Hb@AuNCs stabilized graphene (Hb@AuNCs-G) was characterized by high resolution transmission electron microscopy (HRTEM), zeta-sizer and Raman spectroscopy. Then, the graphene nanosheets were applied as a novel versatile electrochemical platform for ultrasensitive biosensing of short DNA species of chronic myelogenous leukemia (CML) based on the “signal off” and “signal on” strategies. For this purpose, a single strand DNA (ssDNA) was immobilized on the Hb@AuNCs-G/AuNPs modified electrode surface and acted as the biorecognition element. Methylene blue (MB), as the signaling probe, was then intercalated into the ssDNA. The intercalated MB was liberated upon interaction with the synthetic complementary DNA (cDNA, target), thereby resulting in the apparent reduction of MB redox signal. This designed “signal off” sensing system enabled the voltammetric determination of the target cDNA over a dynamic linear range (DLR) of 0.1 fM to 10 pM with a limit of detection (LOD) of 0.037 fM. In the “signal on” strategy, the response to the cDNA was detected by monitoring the change in the electron transfer resistance (Rct) using the ferro/ferricyanide system as a redox probe. The charge transfer resistance of the probe was found to increase linearly with increasing concentration of target cDNA in the range of 0.1 fM–10 pM with a limit of detection of 0.030 fM. Finally, the selectivity and feasibility of genosensor was evaluated by the analysis of derived nucleotides from mismatched sequences and the clinical samples of patients with leukemia as real samples, respectively.

Facile Ge/GR nanocubes synthesis and application for Sudan I photodegradation in water

In this work, highly uniform cubic germanium/husk-derived graphene nanocomposites (Ge/GR nanocubes) were synthesized via facile chemical methods. The structure and composition of the prepared Ge/GR nanocubes were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) etc., confirming a homogeneous distribution of Ge nanocubes (30–90 nm in size) on few-layered graphene nanosheets. Further investigations showed that the prepared novel Ge/GR nanocubes could combine both photocatalytical advantages of Ge nanocubes and graphene nanosheets for Sudan I purification with optimal removal efficiency of 98.1% in wide concentration range (0.25–4.0 mg/mL) at mild conditions. The prepared high active photocatalyst can be used for five consecutive runs. By using husk-derived graphite microcrystalline as the starting material of graphene, the cost of the Ge/GR nanocubes was obvious decreased, which fosters it a high active, low cost and durable candidate for azo dye removal in water.

Industrial scale synthesis of few-layer graphene nanosheets (FLGNSs): an exploration of electrochemical exfoliation approach

Industrial scale manufacturing with tunable properties of graphene nano-sheets has been a practical concern in many applications. This study focuses on, a physical electro-chemistry approach for the synthesis of few-layer graphene nano-sheets (FLGNSs) in a scalable manner. The intercalates are bias-driven anions towards the working electrode of bulk pyrolytic graphite sheet followed by their exfoliations as FLGNSs. In-situ electrochemical studies confirm a higher rate of exfoliation with an increase in the concentration of intercalates. Based on colloidal conductivity and particle size analyses, the degree of crystallinity and effect of variation in intercalates is explored. Rate of oxidation, defects, morphological variation, and number of layers with variation of intercalate concentration have been studied by XRD, Raman spectroscopy, FTIR, UV–Vis spectroscopy, XPS, and electron microscope based analyses. Cost-effectiveness of the electrochemical process in producing FLGNSs is assessed by considering cost of raw materials used in this laboratory process. Schematics of Industrial scalable process for manufacturing FLGNSs.

Design and construction of few-layer graphene cathode for ultrafast and high-capacity aluminum-ion batteries

Graphite is a key cathode material for aluminum-ion batteries (AIBs), but appears poor structural stability and cyclability due to the slow kinetics of intercalation and usage of conductive additives. So far, reasonable design and construction of high-conductive, flexible, binder-free graphitic film cathodes with fast kinetics of anion intercalation mechanism still remains challenging for high-power and high-energy AIBs. Herein, we report the reasonable design for facile construction of high-conductive and mechanically flexible film cathode of high-quality few-layer graphene (FLG) nanosheets for high capacity and fast AIBs, thanks to the strong synergy of ionic surface adsorption/desorption of graphene and ionic intercalation/deintercalation of graphite. The FLG nanosheets prepared by electrochemical cathodic exfoliation from graphite, exhibit predominantly 3–5 layers, extremely low ID/IG ratio of <0.05, ultrahigh C/O atom ratio of 43, and excellent solution-processability, which allow for large-area production of highly conducting (1300 ​S ​cm−1), binder-free and densely stacked FLG films as extremely stable cathodes for ultrafast AIBs. It’s worth mentioning that the resulting AIBs exhibit high capacity of 173 mAh g−1 at 1 ​A ​g−1, outstanding rate capability with exceptionally large capacity of 101 mAh g−1 at 10 ​A ​g−1 that outperforms the most reported graphitic materials, long-term cyclability without noticeable capacity loss after 10000 cycles, and good performance at wide range of temperatures. The multiple characterizations and theoretical simulation further confirm that the unique performance is attributed to the synergistic mechanisms of diffusion-controlled intercalation and surface adsorption of FLG film. Therefore, this work will open intriguing opportunities for the development of advanced AIBs.

Anionic Electrochemical Exfoliation of Few-Layer Graphene Nano-Sheets: An Emphasis on Characterization

Graphene, the most unique member of carbon family has fuelled a huge interest across the globe with its superior mechanical, chemical, optical and electronic properties. It has opened enormous avenues for humankind in terms of different applications. Since its discovery in 2004, people have tried various techniques to extract graphene, such as mechanical exfoliation, chemical exfoliation, epitaxial growth, CVD (chemical vapour deposition) etc. However, the above methods are not optimal for mass production, neither are they simple and cost effective. The present work highlights synthesis of graphene through electrochemical approach and its subsequent characterization. Pyrolytic graphite is subjected to intercalation of two different concentrations of HNO3 electrolyte. XRD, FESEM and TEM were utilised to understand the structure and morphology of the obtained few-layer graphene nanosheets (FLGNs). Scanning probe spectroscopy is a useful technique for understanding the morphological structure of a sample at atomic level. Authors have utilised AFM which shows the thickness of the FLGNs to be in the range of 5-6 nm. STM studies of graphene nanosheets revealed atomic scaled periodicity and atomic flatness.

Boron-doped few-layer graphene nanosheet gas sensor for enhanced ammonia sensing at room temperature

Heteroatom doping in graphene is now a practiced way to alter its electronic and chemical properties to design a highly-efficient gas sensor for practical applications. In this series, here we propose boron-doped few-layer graphene for enhanced ammonia gas sensing, which could be a potential candidate for designing a sensing device. A facile approach has been used for synthesizing boron-doped few-layer graphene (BFLGr) by using a low-pressure chemical vapor deposition (LPCVD) method. Further, Raman spectroscopy has been performed to confirm the formation of graphene and XPS and FESEM characterization were carried out to validate the boron doping in the graphene lattice. To fabricate the gas sensing device, an Si/SiO2 substrate with gold patterned electrodes was used. More remarkably, the BFLGr-based sensor exhibits an extremely quick response for ammonia gas sensing with fast recovery at ambient conditions. Hence, the obtained results for the BFLGr-based gas sensor provide a new platform to design next-generation lightweight and fast gas sensing devices.

Li+/Na+ Co-Assisted Hydrothermal Exfoliation for Graphite into Few-Layer Graphene Nanosheets and Their Excellent Friction-Reducing Performance

We have successfully developed Li+/Na+ co-intercalated exfoliation for graphene nanosheets by a hydrothermal method without the participation of any organic solvents. The effect of the Li+/Na+ rati...

Comparative analysis of nonlinear optical properties of single-layer graphene and few-layer graphene nanosheets

Nonlinear absorption of suspensions of graphene nanosheets with the number of layers from one to three was studied using the Z-scan method with femtosecond excitation at 1030 nm wavelength. A large modulation depth and lower saturation intensity of the suspensions as compared with nonlinear absorption of single-layer graphene were shown. Dynamics of photoexcited carriers for different duration of excitation pulse was considered. The values of the absorption cross section and the density of photoexcited carriers in single-layer graphene were estimated. The presence of two-photon absorption (TPA) in suspensions of graphene nanosheets and the absence of noticeable TPA in single-layer graphene were shown.

Construction of Layered B3N3-Doped Graphene Sheets from an Acetylenic Compound Containing B3N3 by a Semisynthetic Strategy.

The structural modification of graphene at the atomic level is crucial for electrochemical applications. Doping heteroatoms to modify the structure of graphene has widely been adopted. However, the construction and controllable doping of heteroatom-doped graphene remains a challenge. Herein, a novel semisynthetic method is developed to synthesize a borazine (B3N3)-containing acetylenic compound as a precursor, and a series of B3N3-doped few-layered graphene nanosheets are prepared after annealing at different temperatures. To form graphene sheets, the in situ-forming MgBrCl salt is used as an intercalation agent to enlarge the mutual distance between molecules, which can inhibit the unwanted cross-linking reaction. Nanosheets with different thicknesses of 2.5, 3.5, and 4.1 nm can be obtained at annealing temperatures of 1500, 1200, and 1000 °C, respectively. The results demonstrate that the B and N atoms are co-doped in the graphene by the structure of B3N3, and the doping site can be changed with different annealing temperatures. The optical gap of graphene can be successfully opened by doping with B3N3, and the resultant material can be potentially utilized as a catalyst and semiconductor material. Furthermore, this new semisynthetic strategy will offer the opportunity to fabricate more carbon materials via controllable heteroatom doping.

High concentration of few‐layer graphene and MoS 2 nanosheets using carboxyl methyl cellulose as a high‐performance stabiliser

This work report a facile, rapid and efficient approach to prepare high-concentration graphene and MoS2 nanosheets through the liquid phase exfoliation of bulk materials with the method of high-pressure homogenisation assisted by carboxyl methyl cellulose. The few-layer graphene and MoS2 nanosheets dispersions are prepared under 100 MPa for 10 min at high concentrations up to 1.45 and 0.28 mg/ml. The two nanodispersions could be applied to prepare the polyvinyl alcohol composite with well dispersibility and thermal stability.