Multilayer Graphene Oxide Sheets Research Articles

Large Area, Multilayer Graphene Films as a Flexible Electronic Material.

Chemically reduced graphene oxide possesses unique properties and leads to a secure processing method for many applications. The electrical and optical properties of graphene oxide are strongly dependent on the chemical and atomic structure. In the present work, the reduction of synthesized multilayer graphene oxide sheets by both chemical and thermal methods to use them as a substrate in the field of molecular electronic device fabrication is reported. 1-Dodecanethiol molecules are used to covalently bond on the surface atoms of reduced graphene oxide to constitute molecular electronic devices. The metal–organic molecules–reduced graphene oxide–metal junctions show a significant reduction in current levels and weak diode behavior. The observations confirm the tunneling as the conduction mechanism. The sheets are low cost, highly flexible, and can be used as a substrate to build the molecular electronic junctions.

Interlayer spacing of multilayer graphene oxide: Influences of oxygen-containing group density, thickness, temperature and strain

Multilayer graphene oxide (GO) has shown promising applications in ion sieving, gas separation and water purification. However, accurate control of interlayer spacing is still the bottleneck of practical application. In this paper, molecular dynamic simulations have been conducted to reveal the effects of oxygen-containing group density, thickness, temperature and applied strain on the interlayer spacing of multilayer GO sheets systematically. It is found that the interlayer spacing of multilayer GO is positively correlated with oxygen-containing group density and temperature. The interlayer spacing between the outer layer and the secondary outer layer are smaller than these between the inner layers. The distance between inner layers change little with the thickness. When the oxygen-containing group density is below 20%, the interlayer spacing decreases slightly with the increasing strains, while it reaches 30%, the interlayer space decreases first and then recovers at a turning point with an applied strain of 6% owing to the breakage of C–C bond in epoxy groups. Our results would provide a guidance for interlayer spacing controlling and separation membrane designing.

Effect of alpha particle irradiations on the structural properties of graphene oxide

Graphene has been considered one of the most important materials for many applications due to its unique electronic structure, physical and chemical properties. Graphite flakes are the main source of graphene oxide which can be transformed to graphene after reduction. The effect of irradiation on graphene oxide has been rarely studied, only few studies dealing with the irradiation of graphene oxide with gamma radiation were reported. The effect of irradiation of graphene oxide with gamma ray doses (low linear energy transfer) has been previously studied. It was found that there are no changes in the crystalline structure of graphene oxide after irradiation. Graphene oxide was prepared by modified Hummer’s method. The scanning electron microscopy image of the obtained sample suggests the presence of both single and multilayer graphene oxide sheets. The structural measurements for the graphene oxide samples with high linear energy transfers were carried out after irradiations with different doses of alpha particle (9.30–479.90 Gy). The effect of irradiation on oxygen functional groups of graphene oxide was followed by Fourier transforms infra-red spectrometer. Moreover, the irradiation effect on the lamellar space of graphene oxide layers was measured by X-ray diffraction. It was found that the d-spacing of graphene oxide was decreased after alpha particles irradiation with different doses. The effect of irradiation on dielectric constant and conductivity of graphene oxide samples was measured in the frequency range (200 Hz–1.00 MHz). The dielectric measurements show less dependence on irradiation doses. The graphene oxide sample can be used as radiation dosimeter for [Formula: see text]-particles in the range of the low irradiation doses.

Water Permeation and Ion Rejection in Layer-by-Layer Stacked Graphene Oxide Nanochannels: A Molecular Dynamics Simulation

Layer-by-layer assembled graphene oxide (GO) has been considered as a high-efficiency novel membrane material. However, its performance of water permeation and ion rejection remains largely unresolved. Herein we constructed a model of a GO membrane using laminate nanochannels with aligned flexible multilayered GO sheets, on which functional groups were randomly distributed based on the Lerf–Klinowski model. The water permeation and ion rejection in the flexible GO membranes with various pore widths and surface oxidization degrees were simulated. Our results indicate water flow rate in the GO nanochannels is significantly slowed, which is quantitatively equivalent with the prediction using the no-slip Poiseuille equation. The simulated results suggest the capillary channels within GO stacked laminated membranes might not always work as the major flow route for water to permeate. It is observed that confined water structure becomes more disordered and loose within the corrugated GO nanochannels. The interfa...

Anticoagulation and endothelial cell behaviors of heparin-loaded graphene oxide coating on titanium surface

Owing to its unique physical and chemical properties, graphene oxide (GO) has attracted tremendous interest in many fields including biomaterials and biomedicine. The purpose of the present study is to investigate the endothelial cell behaviors and anticoagulation of heparin-loaded GO coating on the titanium surface. To this end, the titanium surface was firstly covered by the polydopamine coating followed by the deposition of the GO coating. Heparin was finally loaded on the GO coating to improve the blood compatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated that the heparin-loaded GO coating was successfully created on the titanium surface. The scanning electron microscopy (SEM) images indicated that a relative uniform GO coating consisting of multilayer GO sheets was formed on the substrate. The hydrophilicity of the titanium surface was enhanced after the deposition of GO and further improved significantly by the loading heparin. The GO coating can enhance the endothelial cell adhesion and proliferation as compared with polydopamine coating and the blank titanium. Loading heparin on the GO coating can significantly reduce the platelet adhesion and prolong the activated partial thromboplastin time (APTT) while not influence the endothelial cell adhesion and proliferation. Therefore, the heparin-loaded GO coating can simultaneously enhance the cytocompatibility to endothelial cells and blood compatibility of biomaterials. Because the polydopamine coating can be easily prepared on most of biomaterials including polymer, ceramics and metal, thus the approach of the present study may open up a new window of promising an effective and efficient way to promote endothelialization and improve the blood compatibility of blood-contact biomedical devices such as intravascular stents.

Rolled graphene oxide foams as three-dimensional scaffolds for growth of neural fibers using electrical stimulation of stem cells

Graphene oxide foam (GOF) layers with thicknesses of ∼15–50μm and density of ∼10 graphene oxide (GO) sheets/μm were fabricated by precipitation of chemically exfoliated GO sheets in an aqueous suspension at ∼80°C under UV irradiation. Then, rolled GOFs with desirable scales were developed as electrically conductive 3D-scaffolds and applied in directional growth of neural fibers, through differentiation of human neural stem cells (hNSCs) into neurons under an electrical stimulation. X-ray photoelectron spectroscopy indicated that the UV irradiation resulted in partial deoxygenation of the layers. Scanning electron microscopy and Raman spectroscopy confirmed the presence of multilayer GO sheets in the foam structure. The electrical sheet resistance of the GOFs was found low enough to produce the electrical stimulation currents used in differentiation of the neural cells, under low voltages. Rolling the GOFs (with hydrophilic surfaces) resulted in formation of cross-sections with superhydrophilic characteristics, inducing effective proliferation and differentiation of the hNSCs throughout the pores and interfaces of the scaffold. The electrical stimulation induced more proliferation of the cells and acceleration of the differentiation into neurons (rather than glia). These results suggest the GOFs as flexible and conductive scaffolds for regeneration of nervous systems and tissue engineering.

A Novel Method of Fabricating Flexible Transparent Conductive Large Area Graphene Film**Supported by the Basic Research Program of Nanjing University of Posts and Telecommunications under Grant No NY212002, the Innovative Research Team in University under Grant No IRT1148, and the 2014 Shuangchuang Program of Jiangsu Province.

We fabricate flexible conductive and transparent graphene films on position-emission-tomography substrates and prepare large area graphene films by graphite oxide sheets with the new technical process. The multi-layer graphene oxide sheets can be chemically reduced by HNO3 and HI to form a highly conductive graphene film on a substrate at lower temperature. The reduced graphene oxide sheets show a high conductivity sheet with resistance of 476 Ω/sq and transmittance of 76% at 550 nm (6 layers). The technique used to produce the transparent conductive graphene thin film is facile, inexpensive, and can be tunable for a large area production applied for electronics or touch screens.

Graphene oxide nano-sheets wrapped Cu2O microspheres as improved performance anode materials for lithium ion batteries

Cu2O microspheres were successfully encapsulated by graphene oxide (GO) nano-sheets and used directly as the anode material for lithium ion batteries. The core–shell structured Cu2O@GO composite delivered a reversible capacity of 458mAhg−1 at a current density of 100mAg−1 after 50 cycles. Even at a high charge–discharge rate of 1000mAg−1, Cu2O@GO still demonstrated a reversible capacity of 240mAhg−1 after 200 cycles, significantly higher than those of the bare Cu2O microspheres (37mAhg−1) and GO nano-sheets (11mAhg−1). The rate capability evaluated by the ratio of capacity at 100mAg−1/1000mAg−1 current density was 49%, 25% and 9.8% for Cu2O@GO, bare Cu2O and GO, respectively. The greatly enhanced performance for GO nano-sheets wrapped Cu2O microspheres composite mainly resulted from the synergistic effect of Cu2O microspheres and GO nano-sheets core–shell composite: the flexible in-situ electrochemically reduced GO nano-sheet coating layer functioning as an efficient three dimensional (3D) conductive network and lithium storage active material; the Cu2O microsphere core functioning as a skeleton to support multilayer GO sheets and avoid GO nano-sheets aggregation.

Mechanical characteristics of individual multi-layer graphene-oxide sheets under direct tensile loading

The mechanical characteristics of graphene oxide (GO) play a critical role in its great applications. In this study, based on the experimental fracture data of individual multilayer free-standing GO sheets under tensile load, in combination with finite element analysis and molecular dynamics (MD) simulations, the failure strength, strain, and Young’s modulus are estimated to be 4–5GPa, 8–15%, and 34–77GPa, respectively. MD is used to disclose the effects of the structural characteristics of GO on the mechanical properties and failure mechanisms along both the armchair and zigzag directions. The failure strength and Young’s modulus of GO are found to slowly decrease with the increase in the ratio of hydroxyl and epoxy groups. The reason is that the breakage of sp3 bonds in the epoxy groups occurs prior to the breakage of sp3 bonds in hydroxyl groups. The former can lead to the formation of heptagonal rings that are able to sustain large strain and insignificantly implicate their surrounding bonds, whereas the latter may result in the complete fracture failure of GO. The fracture of multilayer GO sheets is initiated at the surface sheet due to the intrinsic absence of half-cooperative hydrogen bonding, which may lead to structural instability.

Nanocarbon aerogel complexes inspired by the leaf structure

Inspired by the structure of a leaf, which is constituted of veins, midribs and laminas, we report the synthesis of aerogels based on nanocarbon complexes that exhibit good electrical conductivity, large internal surface area and stable structural integrity upon cyclic compression. These materials are prepared as monolithic solids from suspensions of unzipped and partially exfoliated multi-walled carbon nanotubes. Under optimized oxidation conditions, all the walls of the multi-walled carbon nanotubes are unzipped but only the outer tubes are exfoliated, creating nanoscale multi-layered graphene oxide sheets attached to inner trench-like structures. The exfoliated parts provide high surface area and functional groups, while the inner trench-like structures remain relatively intact and thus retain their electrical conductivity and mechanical properties, which facilitates charge transport and structural stability for the aerogel. The hydrophilic functional groups on the graphene oxide nanosheets make these structures highly soluble, and as a result, the density and mechanical properties can be adjusted to a large extent without sacrificing the porosity or cell wall uniformity. These nanocarbon aerogel complexes exhibit high damping capability with no significant change in piezoresistive properties after more than 4500 compressive cycles, and its original shape can be recovered quickly after compression release.

Graphene oxide sheet-polyaniline nanocomposite prepared through in-situ polymerization/deposition method for counter electrode of dye-sensitized solar cell

In this study, graphene oxide sheet-polyaniline (GOS-PANI) nanocomposite was prepared through in-situ polymerization/deposition method for using as the counter electrode of dye-sensitized solar cell (DSSC). The fluorine-doped tin oxide (FTO) coated glass was immersed into the solution of the aniline and graphite oxide (GO) during the polymerization of PANI. The GOS-PANI nanocomposite was in-situ deposited onto the surface of the FTO glass. X-ray diffraction patterns indicate that the multi-layered graphene oxide sheets (GOS) were exfoliated by the chain segments of PANI. The images of scanning electron and atomic-force microscopes confirmed that the GOS were well distributed in the nanorod-type PANI based thin film. The presence of the synergistic effect of PANI and GO led to the higher electrochemical catalytic activity of GOS-PANI nanocomposite than that of GO or PANI. As a result, better PV performance was observed for DSSCs based on the GOS-PANI electrode as compared to that of the DSSC sample based on the PANI electrode. The highest photo-energy conversion efficiency (6.55 %) was obtained for the GOS-PANI electrode based DSSC sample.

Functionalized Exfoliated Graphene Oxide as Supercapacitor Electrodes

Functionalized exfoliated graphene oxide (EGO) for supercapacitor electrodes have been synthesized by simple chemical methods from the exfoliated graphite (EG) as precursor. Structural and morphological characterizations of EGO have been carried out using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), FTIR and Raman spectroscopy. Electrochemical performance of these electrodes has been investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The fabricated supercapacitor gave a specific capacitance of 146 Fg-1 and energy density of 20 Wh·kg-1 for a highly oxidized sample with more functional groups compared to pure, lower level oxidized and reduced samples. The single and multi layered graphene oxide sheets produced by this method have a lower degree of agglomeration. We found that the graphene oxide with functional oxygen groups of quinine type enhances the capacitance compared to other oxygen functional groups.

Good electrical and mechanical properties induced by the multilayer graphene oxide sheets incorporated to amorphous carbon films

Multilayer graphene oxide nanosheets were fabricated using commercially available expanded graphite by simple ultrasonic treatment and then were incorporated into the amorphous carbon matrix as fillers by electrochemical deposition. The electrical conductivity of the films was strongly improved due to the contribution of the multilayer graphene oxide sheets. Moreover, the Young’s modulus, hardness and elastic recovery of the composite films were measured to be about 171.1 GPa, 10.1 GPa and 81.4%, respectively, compared to 137.4 GPa, 5.1 GPa and 44.3% of undoped a-C:H films prepared at the same conditions. Additionally, the friction coefficient was tested to be 0.15 (0.5 N, 2 Hz) and the antiwear life was prolonged to about 200 s while the undoped DLC films obtained at the same condition were easy to be frazzled.