Basal Plane Of Graphite Research Articles

Light-induced contraction and extension of single macromolecules on a modified graphite surface.

Synthetic rigid-rod polymers incorporating multiple azobenzene photoswitches in the backbone were deposited from solution onto a monolayer of octadecylamine covering the basal plane of graphite. Large contractions and extensions of the single macromolecules on the surface were induced by irradiation with UV and visible light, respectively, as visualized by scanning force microscopy. Upon contraction, the single polymer chains form more compact nanostructures and also may move across the surface, resembling a crawling movement. We attribute the efficiency of these processes to the low mechanical and electronic coupling between the surface and polymers, the high density of azobenzenes in their backbones, and their rigidity, allowing for maximized photodeformations. The visualization of on-surface motions of single macromolecules directly induced by light, as reported herein, could help promote the development of optomechanical nanosystems.

Revisiting oxygen reduction reaction on oxidized and unzipped carbon nanotubes

Carbon-based electrocatalysts without metal or with trace metals are potentially effective in delivering robust and efficient oxygen reduction if the active sites are covalently located on a conductive support. In this report, we demonstrate that active sites on carbon nanotubes are created upon oxidation for efficient oxygen reduction to peroxide, whereas the saturation of oxygen groups at graphitic basal planes leads to the loss of electron conduction thereby deteriorates the electrocatalytic activity. Importantly, oxygen groups at different locations (basal/edge sites) and with different structures (CO, C–OH, COOH, epoxide, etc.) have a significant impact on the oxygen reduction activity. In particular, epoxide bound oxidized carbon shows superior activity among other oxidized carbon nanotubes.

Relationship Between the Trace Elements and Graphite Growth Morphologies in Cast Iron

The graphite morphology transition was studied using various techniques and additives in ultra-pure binary and ternary alloys with hypo- and hypereutectic compositions. Some of the trace elements were observed to stabilize the flake growth morphology of graphite, while others did not. The distance between the graphite basal planes of spheroidal, flake, and undercooled fine graphite was measured and the lattice fringes were studied using high resolution transmission electron microscope, after preparing a thin lamella of graphite using focused ion beam. Latent heat measurement was performed using differential scanning calorimeter on the pure binary alloy with and without sulfur and oxygen additions. The substitution of various elements under study in a monolayer of graphene was analyzed by considering the binding energies of the elements with C and their bonding nature. Simulations were performed using a molecule editor program and visualizer (Avogadro software), which considers various types of interatomic forces to optimize a monolayer of graphene to a minimum energy. The effect of the type of cyclic C-ring structure and energy of the basal plane of graphite with a connection to the addition of trace elements individually in the monolayer of graphene was studied and simulated to understand the resulting bulk graphite growth morphology.

Growth of palladium nanoparticles on nanostructured highly ordered pyrolytic graphite

We report on the growth of palladium nanoparticles on the basal plane of as-cleaved highly oriented pyrolytic graphite (HOPG) samples, and on CO2 ion sputtered nanostructured HOPG surfaces. The morphology of Pd nanostructures grown at room temperature is investigated by scanning tunneling microscopy (STM). The STM observations indicate that the morphology of the Pd films is strongly dependent on the HOPG surface. Stabilized Pd particles only form on the sputtered surface, while ramified Pd particles decorate the clean HOPG terraces. The prestructuring of HOPG surface leads to a selective location of particles at the rim of the nanopits generated by the CO2 ion sputtering and annealing of the surface. The correlation between size, form, density, spatial distribution of the Pd nanoparticles and the quantity of metal added on surface is discussed. We also describe trench channeling of graphite or graphene basal planes by means of Pd nanoparticles in an ambient environment. Copyright (c) 2014 John Wiley & Sons, Ltd.

A comparative study of alkylimidazolium room temperature ionic liquids with FSI and TFSI anions near charged electrodes

Electric double layer (EDL) structure and capacitance generated by the two series of room temperature ionic liquids containing alkylimidazolium Cnmim (n=2,4,6,8) cations and bis(fluorosulfonyl) imide (FSO2)2N−, (FSI) or bis(trifluoromethylsulfonyl) imide (CF3SO2)2N− (TFSI) anions were studied on flat (basal plane graphite) and atomically corrugated (prismatic plane graphite) charged electrode surfaces using atomistic molecular dynamics simulations. On atomically flat surface, generated EDLs in all systems produced a weakly changing differential capacitance (DC) as a function of electrode potential. However, on atomically rough surfaces, ionic liquids with FSI and TFSI anions show substantially different EDL structures and DC dependence. Unlike [Cnmim][TFSI], which generated a camel-shape DC regardless of the cation alkyl tail length, the [Cnmim][FSI] showed a transition from a bell-shape to a camel-shape DC upon increase of the cation alkyl tail length. Analysis of contributions from rearrangement and reorientation of cations and anions indicated that the ability of the FSI anion to respond to changes in electrode potential is the primary driving force for such behavior.

ChemInform Abstract: Doubling the Capacity of Lithium Manganese Oxide Spinel by a Flexible Skinny Graphitic Layer.

AbstractThe capacity of nanoparticular LiMn2O4 (LMO) spinel can be improved up to 220 mAh/g at a cutoff voltage of 2.5 V by coating with a few layers of graphitic basal planes.

Insights into electrocatalytic activity of epitaxial graphene on SiC from cyclic voltammetry and ac impedance spectroscopy

Electrocatalytic activity of graphene grown epitaxially on SiC is studied using cyclic voltammetry and electrochemical impedance spectroscopy. AFM images show step-like topography of SiC-graphene. For ferri-/ferrocyanide redox couple, no voltammetric response is observed at the pristine graphene. Basal planes of graphite are electrochemically inactive as well. After electrochemical oxidation, apparent redox peaks appear at both the graphene and graphite electrode. However, more intensive redox peaks are observed at graphene, where simultaneous redox reaction with the adsorbed and the diffused ferri-/ferrocyanide ions occurs. Electrochemical impedance measurements show that the graphene electrode behaves like an array of microelectrodes. We used the partially blocked electrode model to fit impedance data. Using the fitting parameters, a size of microelectrodes was found to be 23.8 ± 2.1 μm and the active surface of graphene was estimated to be 21 %. A value of the standard electron transfer rate constant found for the anodized epitaxial graphene (2.16 ± 0.32) × 10− 3cm ⋅ s− 1) is by one order of magnitude lower than the standard rate constant estimated for the anodized graphite basal planes (∼5 × 10− 2cm ⋅ s− 1). Electrochemical reduction causes total disappearance of electrochemical responses at the graphene electrode, whereas only slight decrease of the peak currents is observed at the reduced graphene. Such behavior proves that different activation mechanisms occur at the graphene and graphite electrodes.

Doubling the Capacity of Lithium Manganese Oxide Spinel by a Flexible Skinny Graphitic Layer

By coating nanoparticular lithium manganese oxide (LMO) spinel with a few layers of graphitic basal planes, the capacity of the material reached up to 220 mA h g(-1) at a cutoff voltage of 2.5 V. The graphitic layers 1) provided a facile electron-transfer highway without hindering ion access and, more interestingly, 2) stabilized the structural distortion at the 3 V region reaction. The gain was won by a simple method in which microsized LMO was ball-milled in the presence of graphite with high energy. Vibratory ball milling pulverized the LMO into the nanoscale, exfoliated graphite of less than 10 layers and combined them together with an extremely intimate contact. Ab initio calculations show that the intrinsically very low electrical conductivity of the tetragonal phase of the LMO is responsible for the poor electrochemical performance in the 3 V region and could be overcome by the graphitic skin strategy proposed.

Doubling the Capacity of Lithium Manganese Oxide Spinel by a Flexible Skinny Graphitic Layer

AbstractBy coating nanoparticular lithium manganese oxide (LMO) spinel with a few layers of graphitic basal planes, the capacity of the material reached up to 220 mA h g−1 at a cutoff voltage of 2.5 V. The graphitic layers 1) provided a facile electron‐transfer highway without hindering ion access and, more interestingly, 2) stabilized the structural distortion at the 3 V region reaction. The gain was won by a simple method in which microsized LMO was ball‐milled in the presence of graphite with high energy. Vibratory ball milling pulverized the LMO into the nanoscale, exfoliated graphite of less than 10 layers and combined them together with an extremely intimate contact. Ab initio calculations show that the intrinsically very low electrical conductivity of the tetragonal phase of the LMO is responsible for the poor electrochemical performance in the 3 V region and could be overcome by the graphitic skin strategy proposed.

Formation of graphite oxide nano-disks by electrochemical oxidation of HOPG

When HOPG (highly oriented pyrolytic graphite) was electrochemically oxidized in alkali solution, STM observation showed that graphite oxide with homo-sized disks 15nm in diameter and 0.5nm in thickness was formed dispersively on the HOPG surface. With an increase in the anodic charge, the number of the disks enhanced, and covered finally the HOPG surface without overlap at the maximum coverage, 70%. The projected area of the disks was proportional to the anodic charge when the charge was small. The disks were hydrophilic. The double layer capacitance of the oxidized HOPG increased slightly with the anodic charge, implying that the disks should be an electrical insulator. The fully disk-coated HOPG did not block the diffusion-controlled current of the redox species. The layer of the disks must be porous for ions or solutions. The formation of the uniform size may be ascribed to the difference between the density of graphite oxide and that of the basal plane of graphite. The formation of nano-disks and their properties are inconsistent with such an image of intercalation that ions are inserted into layers of graphenes of HOPG.

Ozonated Graphene Oxide Film as a Proton‐Exchange Membrane

AbstractGraphene oxide (GO) contains several chemical functional groups that are attached to the graphite basal plane and can be manipulated to tailor GO for specific applications. It is now revealed that the reaction of GO with ozone results in a high level of oxidation, which leads to significantly improved ionic (protonic) conductivity of the GO. Freestanding ozonated GO films were synthesized and used as efficient polymer electrolyte fuel cell membranes. The increase in protonic conductivity of the ozonated GO originates from enhanced proton hopping, which is due to the higher content of oxygenated functional groups in the basal planes and edges of ozonated GO as well as the morphology changes in GO that are caused by ozonation. The results of this study demonstrate that the modification of dispersed GO presents a powerful opportunity for optimizing a nanoscale material for proton‐exchange membranes.

Ozonated Graphene Oxide Film as a Proton‐Exchange Membrane

Graphene oxide (GO) contains several chemical functional groups that are attached to the graphite basal plane and can be manipulated to tailor GO for specific applications. It is now revealed that the reaction of GO with ozone results in a high level of oxidation, which leads to significantly improved ionic (protonic) conductivity of the GO. Freestanding ozonated GO films were synthesized and used as efficient polymer electrolyte fuel cell membranes. The increase in protonic conductivity of the ozonated GO originates from enhanced proton hopping, which is due to the higher content of oxygenated functional groups in the basal planes and edges of ozonated GO as well as the morphology changes in GO that are caused by ozonation. The results of this study demonstrate that the modification of dispersed GO presents a powerful opportunity for optimizing a nanoscale material for proton-exchange membranes.

Improvement of stacking order in graphite by molten fluoride salt infiltration

The structure of molten fluoride salt infiltrated graphite has been studied by X-ray diffraction and Raman spectroscopy. The full width at half maximum and asymmetry degree of the (002) diffraction peak decrease with the increase of salt weight gain in the infiltration indicates the improvement of the stacking order of the graphite by the molten salt infiltration. The shape of G′ resonance of Raman spectra further indicated the enhancement of the stacking order of graphite by molten salt infiltration. The shift of the (002) diffraction peak position to the higher 2θ angle and the increase of the coefficient of thermal expansion reveal that the improvement of the stacking order is resulted from the compression of the graphite matrix by the infiltrated salt network. The compressive stress induced by the salt network in the graphite matrix could reduce the d-spacing fluctuation between graphite basal planes and close the Mrozowski crack generated by the anisotropy of graphite crystal, thus increase the crystallite size along c-axis.

The structure of deuterated benzene films adsorbed on the graphite (0001) basal plane: what happens below and above the monolayer coverage?

An exact description of the interactions in aromatic carbon systems is a key condition for the design of carbon based nanomaterials. In this paper we investigate the binding and adsorbate structure of the simplest prototype system in this class - the single aromatic ring molecule benzene on graphite. We have collected neutron diffraction data of the ordered phase of deuterated benzene, C6D6, adsorbed on the graphite (0001) basal plane surface. We examined relative coverages from 0.15 up to 1.3 monolayers (ML) in a temperature range of 80 to 250 K. The results confirm the flat lying commensurate (√7 × √7)R19.1° monolayer with lattice constants a = b = 6.5 Å at coverages of less than 1 ML. For this structure we observe a progressive melting well below the desorption temperature. At higher coverages we do neither observe an ordered second layer nor a densification of the structure by upright tilting of first layer molecules, as generally assumed up to now. Instead, we see the formation of clusters with a bulk crystalline structure for coverages only weakly exceeding 1 ML.

Electrochemistry in a drop: a study of the electrochemical behaviour of mechanically exfoliated graphene on photoresist coated silicon substrate

A micro apparatus for electrochemical studies on individual high quality graphene flakes is presented. A microinjection-micromanipulator system has been employed to deposit droplets of aqueous solutions containing redox-active species directly on selected micro-scale areas of mechanically exfoliated graphene layers on polymer coated silicon wafers. This approach allows the clear distinction between the electrochemical activity of pristine basal planes and the edges (defects) or steps to be measured. Voltammetric measurements were performed in a two-electrode configuration, and the standard heterogeneous electron transfer rate (k°) for reduction of hexachloroiridate (IrCl62−) was estimated. The kinetics of electron transfer were evaluated for several types of graphene: mono, bi, and few layer basal planes, and the k° was estimated for an edge/step between two few layer graphene flakes. As a comparison, the kinetic behaviour of graphite basal planes was measured for the deposited aqueous droplets. The appearance of ruptures on the graphene monolayer was observed after deposition of the aqueous solution for the case of graphene on a bare silicon/silicon oxide substrate.

Adsorption behavior of Co and C2H2 on the graphite basal surface: A quantum chemistry study

The adsorption of CO and C2H2 molecules on the perfect basal surface of graphite is investigated by adopting cluster models in conjunction with quantum chemical calculations. The noncovalent interaction potential energy curves for three different orientations of CO and C2H2 molecules with respect to the inert basal plane of graphite are calculated via semi-empirical and Moller-Plesset ab initio methods. Then, we have considered the effects of interaction energies on the C≡O and C≡C bond lengths by performing the partial geometry optimization procedure on the CO-graphite and C2H2-graphite systems in various intermolecular distances. The computational analysis of all physical noncovalent potential energy curves reveals that the relative configurations in which CO and C2H2 molecules approach the graphite sheet from out of the plane have stronger interaction energy and so is more favorable from the energetic viewpoint. This means that the graphite layer prefers to increase its thickness via the chemical vapor deposition of CO and C2H2 on the graphite.

Highly selective dopamine electrochemical sensor based on electrochemically pretreated graphite and nafion composite modified screen printed carbon electrode

Herein, we report a highly selective dopamine electrochemical sensor based on electrochemically pretreated graphite/nafion composite modified screen printed carbon (SPC) electrode. Electrochemically activated graphite/nafion composite was prepared by using a simple electrochemical method. Scanning electron microscope (SEM) used to characterize the surface morphology of the fabricated composite electrode. The SEM result clearly indicates that the graphitic basal planes were totally disturbed and leads to the formation of graphite nanosheets. The composite modified electrode showed an enhanced electrocatalytic activity toward the oxidation of DA when compared with either electrochemical pretreated graphite or nafion SPC electrodes. The fabricated composite electrode exhibits a good electrocatalytic oxidation toward DA in the linear response range from 0.5 to 70μM with the detection limit of 0.023μM. The proposed sensor also exhibits very good selectivity and stability, with the appreciable sensitivity. In addition, the proposed sensor showed satisfactory recovery results toward the commercial pharmaceutical DA samples.

Anisotropic friction behaviour of highly oriented pyrolytic graphite

Friction tests on two surfaces of highly oriented pyrolytic graphite that are parallel and perpendicular to the direction of the graphite basal plane were performed under various test conditions. The average friction coefficient value of the perpendicular surface (0.25) is higher than that of the parallel surface (0.1). The friction coefficient of both parallel and perpendicular surfaces decline when the environment is changed from wet air to wet nitrogen and the trend is more pronounced for the perpendicular surface. The perpendicular worn surface has been observed to be much rougher and owns more edge faces than the parallel worn surface. The amount of dangling bonds and chemisorbed oxygen measured on both surfaces after friction is quite different. The influence of atmosphere on the friction of graphite is attributed to the chemical reaction of dangling bonds with gases, which can affect the adhesive force of the two contact surfaces. The amount of dangling bonds generated on the sliding surface is confirmed to impact the sensitivity of graphite to gases during friction.

Direct Electrochemistry of Hemoglobin at a Graphene Gold Nanoparticle Composite Film for Nitric Oxide Biosensing

A simple two-step method was employed for preparing nano-sized gold nanoparticles-graphene composite to construct a GNPs-GR-SDS modified electrode. Hemoglobin (Hb) was successfully immobilized on the surface of a basal plane graphite (BPG) electrode through a simple dropping technique. Direct electrochemistry and electrocatalysis of the hemoglobin-modified electrode was investigated. The as-prepared composites showed an obvious promotion of the direct electro-transfer between hemoglobin and the electrode. A couple of well-defined and quasi-reversible Hb CV peaks can be observed in a phosphate buffer solution (pH 7.0). The separation of anodic and cathodic peak potentials is 81 mV, indicating a fast electron transfer reaction. The experimental results also clarified that the immobilized Hb retained its biological activity for the catalysis toward NO. The biosensor showed high sensitivity and fast response upon the addition of NO, under the conditions of pH 7.0, potential -0.82 V. The time to reach the stable-state current was less than 3 s, and the linear response range of NO was 0.72-7.92 μM, with a correlation coefficient of 0.9991.

On the relative strength of adsorption of gases on carbon surfaces with functional groups: fluid–fluid, fluid–graphite and fluid–functional group interactions

Experiments at several temperatures were carried out for adsorption of non-polar and polar fluids on a highly graphitized carbon black, Carbopack F, which is composed of a basal plane of graphene and functional groups at the edges of the graphene layers. By comparing the experimental Henry constants with the theoretical Henry constants, calculated for adsorption on an ideal basal plane of graphite, we can determine the different relations and mutual influences between the various interactions, fluid–basal plane, fluid–functional group and fluid–fluid interactions, in the initial stages of adsorption.