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Chemical vapour deposition of carbon-containing precursors on metal substrates is currently the most promising route for the scalable synthesis of large-area, high-quality graphene films.sup.1. However, there are usually some imperfections present in the resulting films: grain boundaries, regions with additional layers (adlayers), and wrinkles or folds, all of which can degrade the performance of graphene in various applications.sup.2-7. There have been numerous studies on ways to eliminate grain boundaries.sup.8,9 and adlayers.sup.10-12, but graphene folds have been less investigated. Here we explore the wrinkling/folding process for graphene films grown from an ethylene precursor on single-crystal Cu-Ni(111) foils. We identify a critical growth temperature (1,030 kelvin) above which folds will naturally form during the subsequent cooling process. Specifically, the compressive stress that builds up owing to thermal contraction during cooling is released by the abrupt onset of step bunching in the foil at about 1,030 kelvin, triggering the formation of graphene folds perpendicular to the step edge direction. By restricting the initial growth temperature to between 1,000 kelvin and 1,030 kelvin, we can produce large areas of single-crystal monolayer graphene films that are high-quality and fold-free. The resulting films show highly uniform transport properties: field-effect transistors prepared from these films exhibit average room-temperature carrier mobilities of around (7.0 [plus or minus] 1.0) × 10.sup.3 centimetres squared per volt per second for both holes and electrons. The process is also scalable, permitting simultaneous growth of graphene of the same quality on multiple foils stacked in parallel. After electrochemical transfer of the graphene films from the foils, the foils themselves can be reused essentially indefinitely for further graphene growth. Restricting the initial growth temperatures used for chemical vapour deposition of graphene on metal foils produces optimum conditions for growing large areas of fold-free, single-crystal graphene., Author(s): Meihui Wang [sup.1] [sup.2] , Ming Huang [sup.1] [sup.5] , Da Luo [sup.1] , Yunqing Li [sup.1] [sup.3] , Myeonggi Choe [sup.1] [sup.3] , Won Kyung Seong [sup.1] , [...]

Two-dimensional atomic crystals can radically change their properties in response to external influences, such as substrate orientation or strain, forming materials with novel electronic structure.sup.1-5. An example is the creation of weakly dispersive, 'flat' bands in bilayer graphene for certain 'magic' angles of twist between the orientations of the two layers.sup.6. The quenched kinetic energy in these flat bands promotes electron-electron interactions and facilitates the emergence of strongly correlated phases, such as superconductivity and correlated insulators. However, the very accurate fine-tuning required to obtain the magic angle in twisted-bilayer graphene poses challenges to fabrication and scalability. Here we present an alternative route to creating flat bands that does not involve fine-tuning. Using scanning tunnelling microscopy and spectroscopy, together with numerical simulations, we demonstrate that graphene monolayers placed on an atomically flat substrate can be forced to undergo a buckling transition.sup.7-9, resulting in a periodically modulated pseudo-magnetic field.sup.10-14, which in turn creates a 'post-graphene' material with flat electronic bands. When we introduce the Fermi level into these flat bands using electrostatic doping, we observe a pseudogap-like depletion in the density of states, which signals the emergence of a correlated state.sup.15-17. This buckling of two-dimensional crystals offers a strategy for creating other superlattice systems and, in particular, for exploring interaction phenomena characteristic of flat bands. Buckled monolayer graphene superlattices are found to provide an alternative to twisted bilayer graphene for the study of flat bands and correlated states in a carbon-based material., Author(s): Jinhai Mao [sup.1] [sup.2] , Slavisa P. Milovanovic [sup.3] , Misa Andelkovic [sup.3] , Xinyuan Lai [sup.1] , Yang Cao [sup.4] , Kenji Watanabe [sup.5] , Takashi Taniguchi [sup.5] [...]

Most bulk-scale graphene is produced by a top-down approach, exfoliating graphite, which often requires large amounts of solvent with high-energy mixing, shearing, sonication or electrochemical treatment.sup.1-3. Although chemical oxidation of graphite to graphene oxide promotes exfoliation, it requires harsh oxidants and leaves the graphene with a defective perforated structure after the subsequent reduction step.sup.3,4. Bottom-up synthesis of high-quality graphene is often restricted to ultrasmall amounts if performed by chemical vapour deposition or advanced synthetic organic methods, or it provides a defect-ridden structure if carried out in bulk solution.sup.4-6. Here we show that flash Joule heating of inexpensive carbon sources--such as coal, petroleum coke, biochar, carbon black, discarded food, rubber tyres and mixed plastic waste--can afford gram-scale quantities of graphene in less than one second. The product, named flash graphene (FG) after the process used to produce it, shows turbostratic arrangement (that is, little order) between the stacked graphene layers. FG synthesis uses no furnace and no solvents or reactive gases. Yields depend on the carbon content of the source; when using a high-carbon source, such as carbon black, anthracitic coal or calcined coke, yields can range from 80 to 90 per cent with carbon purity greater than 99 per cent. No purification steps are necessary. Raman spectroscopy analysis shows a low-intensity or absent D band for FG, indicating that FG has among the lowest defect concentrations reported so far for graphene, and confirms the turbostratic stacking of FG, which is clearly distinguished from turbostratic graphite. The disordered orientation of FG layers facilitates its rapid exfoliation upon mixing during composite formation. The electric energy cost for FG synthesis is only about 7.2 kilojoules per gram, which could render FG suitable for use in bulk composites of plastic, metals, plywood, concrete and other building materials. Flash Joule heating of inexpensive carbon sources is used to produce gram-scale quantities of high-quality graphene in under a second, without the need for a furnace, solvents or reactive gases., Author(s): Duy X. Luong [sup.1] [sup.2] , Ksenia V. Bets [sup.3] , Wala Ali Algozeeb [sup.2] , Michael G. Stanford [sup.2] , Carter Kittrell [sup.2] , Weiyin Chen [sup.2] , [...]

Superconductivity can occur under conditions approaching broken-symmetry parent states.sup.1. In bilayer graphene, the twisting of one layer with respect to the other at 'magic' twist angles of around 1 degree leads to the emergence of ultra-flat moiré superlattice minibands. Such bands are a rich and highly tunable source of strong-correlation physics.sup.2-5, notably superconductivity, which emerges close to interaction-induced insulating states.sup.6,7. Here we report the fabrication of magic-angle twisted bilayer graphene devices with highly uniform twist angles. The reduction in twist-angle disorder reveals the presence of insulating states at all integer occupancies of the fourfold spin-valley degenerate flat conduction and valence bands--that is, at moiré band filling factors [nu] = 0, [plus or minus]1, [plus or minus]2, [plus or minus]3. At [nu] [almost equal to] -2, superconductivity is observed below critical temperatures of up to 3 kelvin. We also observe three new superconducting domes at much lower temperatures, close to the [nu] = 0 and [nu] = [plus or minus]1 insulating states. Notably, at [nu] = [plus or minus] 1 we find states with non-zero Chern numbers. For [nu] = -1 the insulating state exhibits a sharp hysteretic resistance enhancement when a perpendicular magnetic field greater than 3.6 tesla is applied, which is consistent with a field-driven phase transition. Our study shows that broken-symmetry states, interaction-driven insulators, orbital magnets, states with non-zero Chern numbers and superconducting domes occur frequently across a wide range of moiré flat band fillings, including close to charge neutrality. This study provides a more detailed view of the phenomenology of magic-angle twisted bilayer graphene, adding to our evolving understanding of its emergent properties. The fabrication of magic-angle twisted bilayer graphene devices with highly uniform twist angles enables the observation of new superconducting domes, orbital magnets and Chern insulating states., Author(s): Xiaobo Lu [sup.1] , Petr Stepanov [sup.1] , Wei Yang [sup.1] , Ming Xie [sup.2] , Mohammed Ali Aamir [sup.1] , Ipsita Das [sup.1] , Carles Urgell [sup.1] , [...]

Graphene oxide was functionalized with chitosan for palladium immobilization (GO-Chit-Pd), which was used as an efficient catalyst for the reduction of aromatic nitro compounds using sodium borohydride in water. To achieve the best catalytic efficacy, various parameters such as temperature, solvent, mole ratio of hydrogen sources, and the amount of catalyst were optimized. The method has been applied to the reduction of a broad range of nitroarenes with different properties. The easy purification, convenient operation, environmental friendliness, and high product yields render this method viable for use. The nanocatalyst can be easily separated and efficiently recovered and reused for multiple cycles without appreciable loss in its catalytic activity. Key words: graphene oxide, reduction of nitroarene, Pd nanoparticles, chitosan. Nous avons fonctionnalise de l'oxyde de graphene avec du chitosane en vue d'y fixer du palladium (GO-Chit-Pd). Nous avons utilise ce catalyseur pour effectuer la reduction de composes nitroaromatiques a l'aide du borohydrure de sodium dans l'eau. Afin de maximiser l'efficacite catalytique, nous avons optimise divers parametres tels que la temperature, le solvant, le rapport molaire des sources d'hydrogene et la quantite de catalyseur. Nous avons ensuite applique notre methode a la reduction d'une grande variete de nitroarenes aux proprietes diverses. Sa simplicite d'execution et son faible impact environnemental, ainsi que la facilite de purification et les rendements eleves des produits, en font une methode viable pour diverses applications. Le nanocatalyseur peut etre facilement separe et recupere en rendements eleves, puis reutilise plusieurs fois sans perte notable d'activite catalytique. [Traduit par la Redaction] Mots-cles : oxyde de graphene, reduction de nitroarene, nanoparticules de Pd, chitosane., Introduction In the past decades, controlled assembly of nanomaterials received special consideration. Well-known metal nanoparticles with various supports utilized for organic reactions have received considerable attention by material scientists and [...]

In this work, graphene oxide (GO) with various oxidation degrees were synthesized by adjusting the dosage of oxidation agent based on a modified Hummers' method, and were then used for the fabrication of the styrene-butadiene rubber (SBR)/GO nanocomposites through latex coagulation method, followed by a high-temperature cure process. The vulcanization characteristics, thermal stability, mechanical properties, thermal conductivity as well as solvent resistance of SBR/GO nanocomposites were investigated. The results indicated that various surface structures of GO due to oxidation degrees may lead to different dispersion states of GO in the rubber matrix, and thus greatly influenced the cure rate, mechanical properties as well as thermal conductivity of SBR/GO nanocomposites. The optimal (moderate) oxidation degree of GO was achieved at the oxidation agent (KMn[O.sub.4])/graphite weight ratio 9/5, for which case the tensile strength, tear strength, and thermal conductivity of SBR/GO nanocomposites increased by 271.3%, 112.3%, and 28.6%, respectively, compared with those of neat SBR. In addition, the mentioned nanocomposites also showed the best solvent resistance in toluene. POLYM. ENG. SCI., 58:1409-1418, 2018. [C] 2017 Society of Plastics Engineers, INTRODUCTION As the most widely used synthetic rubber, styrene-butadiene rubber (SBR) has been applied in tire tread, adhesive tape, rubber hose, medical equipment, and so forth. [1] To satisfy the [...]

3-(4'-Amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid, was synthesized and used to construct a modified-graphene oxide nano sheets paste electrode. The electro-oxidation of isoproterenol at the surface of the modified electrode was studied using cyclic voltammetry, chronoamperometry, and square wave voltammetry. Under the optimized conditions, the square wave voltammetric peak currents of isoproterenol increased linearly with isoproterenol concentrations in the range of 2.5 x [10.sup.-8] to 2.0 x [10.sup.-5] M and detection limit of 12 nM was obtained for isoproterenol. Finally this modified electrode was used for determination of isoproterenol in some real samples. Keywords: isoproterenol, graphene oxide nano sheets, chemically modified electrodes, carbon paste electrode, Isoprenaline (INN) or isoproterenol (4-[1hydroxy-2-(isopropylamino)ethyl] benzene-1,2-diol) is a catecholamine medication. It is a non-selective beta-adrenergic agonist structurally similar to adrenaline (epinephrine). The isopropyl amino group in isoproterenol makes it selective [...]

Abstract: Density functional theory (DFT) calculation was used to investigate the mechanism of [Au.sub.3] clusters, separately supported on pure graphene ([Au.sub.3]/graphene) and one graphitic N-doped graphene ([Au.sub.3]/N-graphene). These supported [Au.sub.3] [...]

Graphene platelets were synthesized from pencil flake graphite and commercial graphite by chemical method. The chemical method involved modified Hummer's method to synthesize graphene oxide (GO) and the use of hydrazine monohydrate to reduce GO to reduced graphene oxide (rGO). rGO were further reduced using rapid microwave treatment in presence of little amount of hydrazine monohydrate to graphene platelets. Chemically modified graphene/polypyrrole (PPy) nanofiber composites were prepared by in situ anodic electropolymerization of pyrrole monomer in the presence of graphene on stainless steel substrate. The morphology, composition, and electronic structure of the composites together with PPy fibers, graphene oxide (GO), rGO, and graphene were characterized using X-ray diffraction (XRD), laser-Raman, and scanning electron microscopic (SEM) methods. From SEM, it was observed that chemically modified graphene formed as a uniform nanocomposite with the PPy fibers absorbed on the graphene surface and/or filled between the graphene sheets. Such uniform structure together with the observed high conductivities afforded high specific capacitance and good cycling stability during the charge-discharge process when used as supercapacitor electrodes. A specific capacitance of supercapacitor was as high as 304 F [g.sup.-1] at a current density of 2 mA [cm.sup.-1] was achieved over a PPy-doped graphene composite., INTRODUCTION The research and development of sustainable energy conversion and storage technologies have attracted a great deal of interest. Although the efficiency of energy conversion and storage devices depends on [...]

Nanocomposites obtained by melt mixing commercial graphene in an amorphous polyamide are investigated. No symptoms of percolation are observed, which is attributed to the low aspect ratio (fs = 20) deduced from elastic modulus data. The study of the effect of temperature and pressure on viscosity, carried out combining extrusion rheometry and PVT tests, reveals that the nanocomposites can be extruded and injected under similar conditions to pure polyamide. The time evolution of the dynamic viscoelastic functions are analyzed to investigate the crystallization process, observing that it is considerably accelerated in nanocomposites. The results represent a valuable outcome for practical applications., INTRODUCTION Graphene is an atomically thick, two dimensional sheet, composed of [sp.sup.2] carbon atoms arranged in a honeycomb structure, with extraordinary physical properties. Commercial graphene is currently produced by chemical [...]

This study explores how the presence of nanofillers with different structural and chemical characteristics, specifically silica nanoparticles and exfoliated graphite nanoplatelets (GNP), alters the crystallization behavior and polymorphism of a semicrystalline polymer, such as polypropylene (PP). The main focus of this research is to investigate how silica and GNP affect the nucleation and growth of PP crystals during isothermal crystallization. The nonisothermal crystallization behavior, including crystal structures, crystallization temperature, and rate, is also determined. PP composites with nanomaterial content up to 7 wt% were produced by melt mixing and injection molding. Both silica and graphite were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization, with greater changes observed in case of GNP composites. The effect of filler type and amount on the PP polymorphism and lamella thickness was studied by X-ray diffraction and modulated differential scanning calorimetry. Both silica and graphite were found to be effective nucleating agents for the less common β-phase of PP crystals even at low nanomaterial concentration, α--crystal perfection and the recrystallization of the β-form in the α-form and/ or at the transcrystalline regime were found to be responsible for the recrystallization occurring upon melting in nanocomposites at high silica or medium GNP content. POLYM. ENG. SCI., 55:672-680, 2015. © 2014 Society of Plastics Engineers, INTRODUCTION Isotactic polypropylene (PP) can crystallize in various forms or phases. In particular, depending on the crystallization conditions and molecular characteristics, different packing structures of the PP helices lead to [...]

In this study, we investigated the enrichment ability of exfoliated graphene nanosheets for determination of trace cadmium in water and vegetable samples with flame atomic absorption spectrometry. Various experimental parameters that could affect the extraction efficiency have been investigated. Under the optimum conditions, the enrichment factor of the method for the target analyte was 100. A liner response was achieved in the concentration range of 0.3-28.8 ng [mL.sup.-1]. The detection limit and precision of the method were 0.2 ng [mL.sup.-1] and 0.8%, respectively. The proposed method was applied to determine the cadmium in water, onion, and tomato samples and recoveries of target analyte were in the range 97.6%-98.5%. All of these experimental results indicated that this new procedure could be applied for the determination of trace cadmium in real samples. Key words: exfoliated graphene nanosheets, flame atomic absorption spectrometry, cadmium, water, vegetable. On a etudie la capacite d'enrichissement de nanofeuillets de graphene exfolies pour le dosage de traces de cadmium dans des echantillon d'eau et de legumes par spectrometrie d'absorption atomique de flamme. Divers parametres experimentaux susceptibles d'avoir une incidence sur l'efficacite d'extraction ont ete examines. Dans les conditions optimales, le facteur d'enrichissement de la methode pour l'analyte cible etait egal a 100. Une reponse lineaire a ete obtenue dans la plage de concentrations de 0,3 a 28,8 ng [mL.sup.-1]. La limite de detection et la precision de la methode etaient de 0,2 ng [mL.sup.-1] et 0,8%, respectivement. La methode proposee a ete appliquee pour determiner la concentration de cadmium dans des echantillons d'eau, d'onions et de tomates, avec un taux de recuperation de l'analyte cible variant de 97,6% a 98,5%. Tous ces resultats experimentaux indiquent que la nouvelle procedure pourrait etre appliquee au dosage de traces de cadmium dans des echantillons reels. [Traduit par la Redaction] Mots-cles: nanofeuillets de graphene exfolies, spectrometrie d'absorption atomique de flamme, cadmium, eau, legumes., Introduction Heavy metal levels in food and environmental samples are an important key for environmental pollution. (1,2) The determination of traces of heavy metal ions in environmental samples is restricted [...]

A layer of carbon atoms preserves a painting's vibrant hues -- and can be applied and removed without damage. A layer of carbon atoms preserves a painting's vibrant hues -- and can be applied and removed without damage., Author Affiliations: After 130 hours of artificial ageing by visible light, the painting Triton and Nereid has lost some of the purple tint to the figures' right, but a graphene [...]

Raman spectroscopy is a sensitive method for monitoring the self-assembly of biological macromolecules. Amyloidogenic peptides have been shown to form peptide nanotubes often with a central diphenylalanine core. In this [...]

This report compares the electroanalytical performances of single- (G-SL), few- (G-FL), and multilayer graphene (G-ML), graphite microparticles, and edge-plane pyrolytic graphite electrodes in terms of sensitivity, linearity, and repeatability. We show that in the case of differential pulse voltammetric (DPV) detection of ascorbic acid, the sensitivity of a G-SL electrode is about 30% greater than that of G-ML and about 40% greater than graphite microparticles. However, in the case of DPV determination of uric acid, sensitivity is practically the same for all (G-SL, G-FL, and G-ML) and, importantly, the graphite microparticles do provide higher sensitivity than graphenes do for this analyte. Graphenes also do not provide a significant advantage in terms of repeatability. We pose the question of whether the efforts leading to the bulk method of producing single-layer graphene are justified for electroanalytical applications. 10.1021/ac101996m

In this paper, we carded out detailed electrochemical studies of epitaxial graphene (EG) using inner-sphere and outer-sphere redox mediators. The EG sample was anodized systematically to investigate the effect of edge plane defects on the heterogeneous charge transfer kinetics and capacitive noise. We found that anodized EG, consisting of oxygen-related defects, is a superior biosensing platform for the detection of nucleic acids, uric acids (UA), dopamine (DA), and ascorbic acids (AA). Mixtures of nucleic acids (A, T, C, G) or biomolecules (AA, UA, DA) can be resolved as individual peaks using differential pulse voltammetry. In fact, an anodized EG voltammetric sensor can realize the simultaneous detection of all four DNA bases in double stranded DNA (dsDNA) without a prehydrolysis step, and it can also differentiate single stranded DNA from dsDNA. Our results show that graphene with high edge plane defects, as opposed to pristine graphene, is the choice platform in high resolution electrochemical sensing. 10.1021/ac101519v

This work develops a novel electrochemical approach for detection of the extracellular oxygen released from human erythrocytes. The sensing is based on the bioelectrocatalytic system of graphene integrated with laccase (Lac) and 2,2-azino-bis(3-ethyibenzothiazoline-6-sulfonic acid) (ABTS) toward the reduction of oxygen. ABTS and laccase are assembled on the surface of graphene, which is synthesized by a chemistry route, utilizing the [pi]--[pi] and electrostatic interactions of these components. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and FT-IR spectroscopy demonstrate that graphene has been successfully synthesized, and ABTS and laccase have been effectively assembled on a graphene surface with the formation of Lac--ABTS--graphene hybrid. The voltammetric results indicate that ABTS can be used as a redox mediator when it is in immobilized form. The hybrid deposited on the glassy carbon (GC) electrode is demonstrated to be a good bioelectrocatalyst for the reduction of oxygen with inherent enzyme activity, accepted stability, high half-wave potential (ca.670 mV vs NHE), and unimpeded electrical communication to the copper redox sites of laccase. Therefore, this study has not only established a novel approach of detection of extracellular oxygen but also provided a general route for fabricating a graphene-based biosensing platform via assembling enzymes/ proteins on a graphene surface. 10.1021/ac100621r

A novel electrochemical immunosensor for sensitive detection of cancer biomarker [alpha]-fetoprotein (AFP) is described that uses a graphene sheet sensor platform and functionalized carbon nanospheres (CNSs) labeled with horseradish peroxidase-secondary antibodies (HRP-Ab2). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the synthesized CNSs yielded a homogeneous and narrow size distribution, which allowed several binding events of HRP-Ab2 on each nanosphere. Enhanced sensitivity was achieved by introducing the multibioconjugates of HRP-Ab2-CNSs onto the electrode surface through 'sandwich' immunoreactions. Second, functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), thus amplifying the detection response. On the basis of the dual signal amplification strategy of graphene sheets and the multienzyme labeling, the developed immunosensot showed a 7-fold increase in detection signal compared to the immunosensor without graphene modification and CNSs labeling. The proposed method could respond to 0.02 ng [mL.sup.-1] AFP with a linear calibration range from 0.05 to 6 ng [mL.sup.-1]. This amplification strategy is a promising platform for clinical screening of cancer biomarkers and point-of-care diagnostics. 10.1021/ac100036p