Home About us Contact
|
Home About us Contact | ||
|
|
||
Graphene Sheets (graphene + sheet)
Selected AbstractsHydrothermal Route for Cutting Graphene Sheets into Blue-Luminescent Graphene Quantum DotsADVANCED MATERIALS, Issue 6 2010Dengyu Pan Water-soluble graphene quantum dots (GQDs, ca. 10 nm in diameter) that exhibit bright blue photoluminescence (PL) are prepared by hydrothermal (chemical) cutting of oxidized graphene sheets (see figure). The mechanisms of the cutting and luminescence are discussed. This discovery of PL of GQDs may extend the range of application of graphene-based materials to optoelectronics and biological labeling. [source] Expanded Graphite: One-Step Exfoliation Synthesis of Easily Soluble Graphite and Transparent Conducting Graphene Sheets (Adv. Mater.ADVANCED MATERIALS, Issue 43 200943/2009) The inside cover shows an SEM image of easily soluble expanded graphite (ESEG) on a Si substrate. In work by Ji-Beom Yoo and co-workers (p. 4383) the ESEG was prepared from a fluorinated graphite intercalation compound (FGIC),C2F,·,nClF3. The inset scheme shows the fluorinated graphite intercalation compound. Due to the severe expansion state, the ESEG can be dispersed in organic solvents or even water by ultrasonication with common surfactants. [source] One-Step Exfoliation Synthesis of Easily Soluble Graphite and Transparent Conducting Graphene SheetsADVANCED MATERIALS, Issue 43 2009Jong Hak Lee Easily soluble expanded graphite (see figure) is synthesized in a one-step exfoliation process that can be used for the lowcost mass production of graphene for various applications because of the simplicity and speed of the process. The graphene obtained is sufficiently expanded to be dispersed in aqueous solutions with an ordinary surfactant and in organic solvents. [source] Aqueous Stabilization and Self-Assembly of Graphene Sheets into Layered Bio-Nanocomposites using DNAADVANCED MATERIALS, Issue 31 2009Avinash J. Patil Stabilization of aqueous suspensions of graphene single sheets by single-stranded DNA is demonstrated using a range of physical methods. The negatively charged bio-functionalized graphene sheets are spontaneously assembled into layered hybrid nanocomposites containing intercalated DNA molecules, or co-intercalated mixtures of DNA and the redox protein, cytochrome c. Small-molecule reducing agents readily access the intercalated proteins. [source] Dispersion of Graphene Sheets in Organic Solvent Supported by Ionic InteractionsADVANCED MATERIALS, Issue 17 2009Yanyu Liang Organic solution-processable graphene sheets were prepared using a large-scale novel approach based on a transfer process assisted by ionic interactions. Smooth monolayer graphene sheets were easily fabricated on a substrate from organic solution. Such a noncovalent functionalization preserves the extended aromatic conjugation of reduced graphene sheets, giving rise to high-conductivity cast films. [source] A Strategy for Producing Pure Single-Layer Graphene Sheets Based on a Confined Self-Assembly Approach,ANGEWANDTE CHEMIE, Issue 32 2009Weixia Zhang Kohlenstoff-Sandwich: Nach der Polymerisation eines pyrrolhaltigen Tensids zwischen zwei Siliciumoxidschichten (siehe Bild; Pyrrolringe in Rot) und anschließendem Carbonisieren und Entfernen der Siliciumoxidtemplate entstehen ausgedehnte Graphen-Monoschichten. Unter milden Bedingungen sind so ,m-große, reine Graphen-Schichten im Gramm-Maßstab zugänglich. [source] Superhydrophobic to Superhydrophilic Wetting Control in Graphene FilmsADVANCED MATERIALS, Issue 19 2010Javad Rafiee The wetting of graphene films from superhydrophobic (contact angle of ,160°) to superhydrophilic (,0°) is controlled using surface chemistry/roughness effects. Graphene sheets dispersed in water/acetone solvents are deposited on various substrates, where the contact angle of the graphene films could be tuned from superhydrophobic to superhydrophilic by simply controlling the relative proportion of acetone and water in the solvent. [source] Electrochemical Synthesis of CdSe Quantum-Dot Arrays on a Graphene Basal Plane Using Mesoporous Silica Thin-Film TemplatesADVANCED MATERIALS, Issue 4 2010Yong-Tae Kim A mesoporous silica film acts as a template and a potential equalizer between the edge/defect sites and the basal plane of a graphene sheet. Using an electrochemical deposition method of CdSe on these graphene sheets covered with a silica film results in CdSe quantum dots that are evenly distributed in regular hexagonal arrays (see figure). [source] Bridging domain methods for coupled atomistic,continuum models with L2 or H1 couplingsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2009P.-A. Guidault Abstract A bridging domain method for coupled atomistic,continuum models is proposed that enables to compare various coupling terms. The approach does not require the finite element mesh to match the lattice spacing of the atomic model. It is based on an overlapping domain decomposition method that makes use of Lagrange multipliers and weight functions in the coupling zone in order to distribute the energy between the two competing models. Two couplings are investigated. The L2 coupling enforces the continuity of displacements between the two models directly. The H1 coupling involves the definition of a strain measure. For this purpose, a moving least-square interpolant of the atomic displacement is defined. The choice of the weight functions is studied. Patch tests and a graphene sheet with a crack are studied. It is shown that both continuous and discontinuous weight functions can be used with the H1 coupling whereas the L2 coupling requires continuous weight functions. For the examples developed herein, the L2 coupling produces less error in the zone of interest. The flexibility of the H1 coupling with constant weight function may be beneficial but the results may be affected depending on the topology of the bridging zone. Copyright © 2008 John Wiley & Sons, Ltd. [source] Density functional study of graphene overlayers on SiCPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2008Alexander Mattausch Abstract Despite the ongoing "graphene boom" of the last three years our understanding of epitaxial graphene grown on SiC substrate is only beginning to emerge. Along with experimental methods such as low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES), ab initio calculations help to uncover the geometric and electronic structure of the graphene/SiC interface. In this chapter we describe the density-functional calculations we performed for single and double graphene layers on Si- and C-terminated 6H-SiC surfaces. Experimental data reveal a pronounced difference between the two surface terminations. On a Si-terminated surface the interface adopts a 6,3 × 6,3 unit cell whereas the C-face supports misoriented (turbostratic) graphene layers. It has been recently realized that, on the Si-face, the large commensurate cell is subdivided into patches of coherently matching to the substrate carbon atoms. In our calculations we assumed the "coherent match" geometry for the whole interface plane. This reduces the periodic unit to the ,3 × ,3R 30° cell but requires a substantial stretching of the graphene sheet. Although simplified, the model provides a qualitative picture of the bonding and of the interface electron energy spectrum. We find that the covalent bonding between the carbon layer and the substrate destroys the massless "relativistic" electron energy spectrum, the hallmark of a freestanding graphene. Hence the first carbon layer cannot be responsible for the graphene-type electron spectrum observed by ARPES and rather plays a role of a buffer between the substrate and the subsequent carbon sheets. The "true" graphene spectrum appears with the second carbon layer which exhibits a weak van der Waals bonding to the underlying structure. For Si-terminated substrate, we find that the Fermi level is pinned by the interface state at 0.45 eV above the graphene Dirac point, in agreement with experimental data. This renders the interface metallic. On the contrary, for a C-face the "coherent match" model predicts the Fermi level exactly at the Dirac point. However, this does not necessarily apply to the turbostratic graphene layers that normally grow on the C-terminated substrate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Morphological and physical properties of a thermoplastic polyurethane reinforced with functionalized graphene sheetPOLYMER INTERNATIONAL, Issue 4 2009Duc Anh Nguyen Abstract BACKGROUND: Functionalized graphene sheet (FGS) was recently introduced as a new nano-sized conductive filler, but little work has yet examined the possibility of using FGS as a nanofiller in the preparation of polymer nanocomposites. In particular, there are currently no published papers that evaluate polyurethane/FGS nanocomposites. The purpose of this study was to prepare a polyurethane/FGS nanocomposite and examine the morphological and physical properties of the material. RESULTS: A cast nanocomposite film was prepared from a mixture of thermoplastic polyurethane (TPU) solution and FGS suspended in methyl ethyl ketone. The FGS dispersed on the nanoscale throughout the TPU matrix and effectively enhanced the conductivity. A nanocomposite containing 2 parts of FGS per 100 parts of TPU had an electrical conductivity of 10,4 S cm,1, a 107 times increase over that of pristine TPU. The dynamic mechanical properties showed that the FGS efficiently reinforced the TPU matrix, particularly in the temperature region above the soft segment melt. CONCLUSION: Our results show that FGS has a high affinity for TPU, and it could therefore be used effectively in the preparation of TPU/FGS nanocomposites without any further chemical surface treatment. This indicates that FGS is an effective and convenient new material that could be used for the modification of polyurethane. It could also be used in place of other nano-sized conductive fillers, such as carbon nanotubes. Copyright © 2009 Society of Chemical Industry [source] Self-Assembled Graphene,Enzyme Hierarchical Nanostructures for Electrochemical BiosensingADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Qiong Zeng Abstract The self-assembly of sodium dodecyl benzene sulphonate (SDBS) functionalized graphene sheets (GSs) and horseradish peroxidase (HRP) by electrostatic attraction into novel hierarchical nanostructures in aqueous solution is reported. Data from scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction demonstrate that the HRP,GSs bionanocomposites feature ordered hierarchical nanostructures with well-dispersed HRP intercalated between the GSs. UV-vis and infrared spectra indicate the native structure of HRP is maintained after the assembly, implying good biocompatibility of SDBS-functionalized GSs. Furthermore, the HRP,GSs composites are utilized for the fabrication of enzyme electrodes (HRP,GSs electrodes). Electrochemical measurements reveal that the resulting HRP,GSs electrodes display high electrocatalytic activity to H2O2 with high sensitivity, wide linear range, low detection limit, and fast amperometric response. These desirable electrochemical performances are attributed to excellent biocompatibility and superb electron transport efficiency of GSs as well as high HRP loading and synergistic catalytic effect of the HRP,GSs bionanocomposites toward H2O2. As graphene can be readily non-covalently functionalized by "designer" aromatic molecules with different electrostatic properties, the proposed self-assembly strategy affords a facile and effective platform for the assembly of various biomolecules into hierarchically ordered bionanocomposites in biosensing and biocatalytic applications. [source] Self-Propagating Domino-like Reactions in Oxidized GraphiteADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Franklin Kim Abstract Graphite oxide (GO) has received extensive interest as a precursor for the bulk production of graphene-based materials. Here, the highly energetic nature of GO, noted from the self-propagating thermal deoxygenating reaction observed in solid state, is explored. Although the resulting graphene product is quite stable against combustion even in a natural gas flame, its thermal stability is significantly reduced when contaminated with potassium salt by-products left from GO synthesis. In particular, the contaminated GO becomes highly flammable. A gentle touch with a hot soldering iron can trigger violent, catastrophic, total combustion of such GO films, which poses a serious fire hazard. This highlights the need for efficient sample purification methods. Typically, purification of GO is hindered by its tendency to gelate as the pH value increases during rinsing. A two-step, acid,acetone washing procedure is found to be effective for suppressing gelation and thus facilitating purification. Salt-induced flammability is alarming for the fire safety of large-scale manufacturing, processing, and storage of GO materials. However, the energy released from the deoxygenation of GO can also be harnessed to drive new reactions for creating graphene-based hybrid materials. Through such domino-like reactions, graphene sheets decorated with metal and metal oxide particles are synthesized using GO as the in situ power source. Enhanced electrochemical capacitance is observed for graphene sheets loaded with RuO2 nanoparticles. [source] Self-Propagating Domino-like Reactions in Oxidized GraphiteADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Franklin Kim Abstract Graphite oxide (GO) has received extensive interest as a precursor for the bulk production of graphene-based materials. Here, the highly energetic nature of GO, noted from the self-propagating thermal deoxygenating reaction observed in solid state, is explored. Although the resulting graphene product is quite stable against combustion even in a natural gas flame, its thermal stability is significantly reduced when contaminated with potassium salt by-products left from GO synthesis. In particular, the contaminated GO becomes highly flammable. A gentle touch with a hot soldering iron can trigger violent, catastrophic, total combustion of such GO films, which poses a serious fire hazard. This highlights the need for efficient sample purification methods. Typically, purification of GO is hindered by its tendency to gelate as the pH value increases during rinsing. A two-step, acid,acetone washing procedure is found to be effective for suppressing gelation and thus facilitating purification. Salt-induced flammability is alarming for the fire safety of large-scale manufacturing, processing, and storage of GO materials. However, the energy released from the deoxygenation of GO can also be harnessed to drive new reactions for creating graphene-based hybrid materials. Through such domino-like reactions, graphene sheets decorated with metal and metal oxide particles are synthesized using GO as the in situ power source. Enhanced electrochemical capacitance is observed for graphene sheets loaded with RuO2 nanoparticles. [source] Graphene-Based Nanoporous Materials Assembled by Mediation of Polyoxometalate NanoparticlesADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Ding Zhou Abstract A kind of graphene-based nanoporous material is prepared through assembling graphene sheets mediated through polyoxometalate nanoparticles. Owing to the strong interaction between graphene and polyoxometalate, 2D graphene sheets with honeycomb-latticed carbon atoms could assemble into a porous structure, in which 3D polyoxometalate nanoparticles serve as the crosslinkers. Nitrogen and hydrogen sorption analysis reveal that the as-prepared graphene-based hybrid material possesses a specific surface area of 680 m2 g,1 and a hydrogen uptake volume of 0.8,1.3 wt%. Infrared spectrometry is used to probe the electron density changes of polyoxometalate particle in the redox-cycle and to verify the interaction between graphene and polyoxometalate. The as-prepared graphene-based materials are further characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. [source] High-Performance Photoresponsive Organic Nanotransistors with Single-Layer Graphenes as Two-Dimensional ElectrodesADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Yang Cao Abstract Graphene behaves as a robust semimetal with the high electrical conductivity stemming from its high-quality tight two-dimensional crystallographic lattice. It is therefore a promising electrode material. Here, a general methodology for making stable photoresponsive field effect transistors, whose device geometries are comparable to traditional macroscopic semiconducting devices at the nanometer scale, using cut graphene sheets as 2D contacts is detailed. These contacts are produced through oxidative cutting of individual 2D planar graphene by electron beam lithography and oxygen plasma etching. Nanoscale organic transistors based on graphene contacts show high-performance FET behavior with bulk-like carrier mobility, high on/off current ratio, and high reproducibility. Due to the presence of photoactive molecules, the devices display reversible changes in current when they are exposed to visible light. The calculated responsivity of the devices is found to be as high as ,8.3,A,W,1. This study forms the basis for making new types of ultrasensitive molecular devices, thus initiating broad research interest in the field of nanoscale/molecular electronics. [source] One-Step Ionic-Liquid-Assisted Electrochemical Synthesis of Ionic-Liquid-Functionalized Graphene Sheets Directly from Graphite,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2008Na Liu Abstract Graphite, inexpensive and available in large quantities, unfortunately does not readily exfoliate to yield individual graphene sheets. Here a mild, one-step electrochemical approach for the preparation of ionic-liquid-functionalized graphite sheets with the assistance of an ionic liquid and water is presented. These ionic-liquid-treated graphite sheets can be exfoliated into functionalized graphene nanosheets that can not only be individuated and homogeneously distributed into polar aprotic solvents, but also need not be further deoxidized. Different types of ionic liquids and different ratios of the ionic liquid to water can influence the properties of the graphene nanosheets. Graphene nanosheet/polystyrene composites synthesized by a liquid-phase blend route exhibit a percolation threshold of 0.1 vol % for room temperature electrical conductivity, and, at only 4.19 vol %, this composite has a conductivity of 13.84,S m,1, which is 3,15 times that of polystyrene composites filled with single-walled carbon nanotubes. [source] Graphene-On-Silicon Schottky Junction Solar CellsADVANCED MATERIALS, Issue 25 2010Xinming Li Highly conductive semitransparent graphene sheets are combined with an n-type silicon (n-Si) wafer to fabricate solar cells with power conversion efficiencies up to 1.5% at AM 1.5 and an illumination intensity of 100 mW cm,2. The Schottky junction solar cells can be extended to other semiconducting materials in which graphene serves multiple functions as active junction layer, charge transport path, and transparent electrode. [source] Hydrothermal Route for Cutting Graphene Sheets into Blue-Luminescent Graphene Quantum DotsADVANCED MATERIALS, Issue 6 2010Dengyu Pan Water-soluble graphene quantum dots (GQDs, ca. 10 nm in diameter) that exhibit bright blue photoluminescence (PL) are prepared by hydrothermal (chemical) cutting of oxidized graphene sheets (see figure). The mechanisms of the cutting and luminescence are discussed. This discovery of PL of GQDs may extend the range of application of graphene-based materials to optoelectronics and biological labeling. [source] Electrochemical Synthesis of CdSe Quantum-Dot Arrays on a Graphene Basal Plane Using Mesoporous Silica Thin-Film TemplatesADVANCED MATERIALS, Issue 4 2010Yong-Tae Kim A mesoporous silica film acts as a template and a potential equalizer between the edge/defect sites and the basal plane of a graphene sheet. Using an electrochemical deposition method of CdSe on these graphene sheets covered with a silica film results in CdSe quantum dots that are evenly distributed in regular hexagonal arrays (see figure). [source] Aqueous Stabilization and Self-Assembly of Graphene Sheets into Layered Bio-Nanocomposites using DNAADVANCED MATERIALS, Issue 31 2009Avinash J. Patil Stabilization of aqueous suspensions of graphene single sheets by single-stranded DNA is demonstrated using a range of physical methods. The negatively charged bio-functionalized graphene sheets are spontaneously assembled into layered hybrid nanocomposites containing intercalated DNA molecules, or co-intercalated mixtures of DNA and the redox protein, cytochrome c. Small-molecule reducing agents readily access the intercalated proteins. [source] Composites of Graphene with Large Aromatic MoleculesADVANCED MATERIALS, Issue 31 2009Qi Su A novel approach to functionalize graphene with large aromatic donor and acceptor molecules consisting of nanographene units is presented, producing an unprecedented class of graphene and nanographene composites with tunable electronic properties. The stability of aqueous dispersion of graphene sheets is greatly enhanced, and a large number of monolayer and double-layer graphene sheets could be facilely fabricated on the substrates [source] Fabrication of Graphene,Polymer Nanocomposites With Higher-Order Three-Dimensional ArchitecturesADVANCED MATERIALS, Issue 21 2009Jemma L. Vickery The use of aqueous dispersions of polystyrene sulfonate-stabilized graphene sheets for the fabrication of nanocomposites with higher-order 3D architectures is demonstrated using two examples of template-directed assembly. Macroscopic sponge-like polymer,graphene scaffolds are readily produced by directional freeze casting, while hollow graphene microspheres are prepared by electrostatically induced assembly on positively charged polymer beads. [source] Dispersion of Graphene Sheets in Organic Solvent Supported by Ionic InteractionsADVANCED MATERIALS, Issue 17 2009Yanyu Liang Organic solution-processable graphene sheets were prepared using a large-scale novel approach based on a transfer process assisted by ionic interactions. Smooth monolayer graphene sheets were easily fabricated on a substrate from organic solution. Such a noncovalent functionalization preserves the extended aromatic conjugation of reduced graphene sheets, giving rise to high-conductivity cast films. [source] Initiating electropolymerization on graphene sheets in graphite oxide structureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2010Ali Eftekhari Abstract Because of its special chemical composition, graphite oxide has peculiar influences on electrochemical processes. The existence of various functional groups significantly affects electropolymerization processes and the formation of conductive polymers. Electrochemical synthesis of polyaniline (as a prototype of conductive polymers) on a paste-based substrate of graphite oxide was investigated. In this case, the electropolymerization is significantly different from conventional cases, and the polymer is generated just during the first potential cycle. This can be attributed to the fact that graphite oxide can assist the monomer oxidation. Alternatively, electropolymerization was successfully performed inside the graphite oxide layers via electrochemical treatment of aniline-intercalated graphite oxide in the supporting electrolyte. Although these phenomena are related to the chemical composition of graphite oxide, the graphite prepared by the reduction of graphite oxide also displayed some advantages for the electropolymerization (over natural graphite). There is an emphasis on the morphological investigations throughout this study, because novel morphologies were observed in the system under investigation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2204,2213, 2010 [source] Electrochemistry of graphene: new horizons for sensing and energy storageTHE CHEMICAL RECORD, Issue 4 2009Martin Pumera Abstract Graphene is a new 2D nanomaterial with outstanding material, physical, chemical, and electrochemical properties. In this review, we first discuss the methods of preparing graphene sheets and their chemistry. Following that, the fundamental reasons governing the electrochemistry of graphene are meaningfully described. Graphene is an excellent electrode material with the advantages of conductivity and electrochemistry of sp2 carbon but without the disadvantages related to carbon nanotubes, such as residual metallic impurities. We highlight important applications of graphene and graphene nanoplatelets for sensing, biosensing, and energy storage. © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 211,223; 2009: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.200900008 [source] Fabrication of Cobalt and Cobalt Oxide/Graphene Composites: Towards High-Performance Anode Materials for Lithium Ion BatteriesCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 2 2010Shubin Yang Dr. Pave a way to high-performance anode materials: Organic metal/graphene composites are fabricated through an in,situ assembly of disc-shaped phthalocyanine molecules with graphene sheets during the chemical reduction of graphite oxide, which enables a homogenous dispersion of Co and Co3O4 nanoparticles in the sheets after simple pyrolysis and oxidation. The resulting Co3O4/graphene composites exhibit remarkable lithium storage performance. [source] | ||||||||||||||||||||||||||||