Ultrathin Graphene Oxide Research Articles

Formation of graphene oxide films at the liquid/liquid interface

A strategy of employing graphene oxide (GO) nanosheets to prepare large-area GO films is proposed in this work. The films are prepared by injecting GO suspension in a mixture of water and ethanol (H2O + EtOH) at the liquid/liquid (hexane/water, C6H14/H2O) interface and forming the GO films at the interface. After evaporation of C6H14, GO films at the air/(H2O + EtOH) interface are transferred onto solid substrates by the horizontal lifting deposition, and large area (2.5 cm × 2.5 cm) of homogeneous GO films with the thickness of 5.4 nm and the roughness of 3.6 nm is obtained. The formation scheme of the GO films at the C6H14/(H2O + EtOH) interface is discussed considering the density difference between the C6H14, (H2O + EtOH), and H2O, as well as the interaction between the GO nanosheets. This facile strategy paves a new path for preparation of large ultrathin GO films from GO nanosheets, which is of great importance for the preparation of GO-based materials to be used in supercapacitor electrodes, transparent conductive films and field-effect transistors.

Synthesis and luminescence of graphene-nano calcium sulphide composite

Graphene-nanocrystalline calcium sulphide has been synthesized using in-situ reduction of calcium salt and graphene oxide. Graphene oxide was prepared using Hummer's method.Surface morphology and crystal structure of samples were observed by transmission electron microscopy (TEM) and X-Ray diffraction (XRD). Ultra thin graphene and graphene oxide sheets with size ranging between tens to several hundreds of square nanometers are observed in TEM images. The TEM micrographs of G-CaS show that CaS particles are embedded in graphene sheets and the average particle size of CaS particles in the composite is less than 50 nm. The reduction in the intensity of various functional groups in FTIR spectrum also confirms the formation of graphene. The UV-Visible spectra of CaS shows absorption peak at 220 nm with a small shoulder at 250 nm whereas in G-CaS 220 nm absorption peak has reduced intensity and the shoulder at 250 nm has now shifted to 270 nm due to modification in the defect structure of CaS by graphene. CaS and G-CaS shows photoluminescence emission at 470 nm (λexc. = 375 nm) and 440 nm (λexc. = 350 nm) respectively, however emission intensity of G-CaS is relatively lower than CaS. Although the emission intensity is found to be lower than CaS, addition of CaS to graphene in G-CaS complex has made graphene luminescent. XPS spectra also indicate reduction of various oxygen containing functional groups in highly reduced graphene oxide and G-CaS.

Controllable fabrication of ultrathin free-standing graphene films

Graphene free-standing film-like or paper-like materials have attracted great attention due to their intriguing electronic, optical and mechanical properties and potential application in chemical filters, molecular storage and supercapacitors. Although significant progress has been made in fabricating graphene films or paper, there is still no effective method targeting ultrathin free-standing graphene films (UFGFs). Here, we present a modified filtration assembly method to prepare these ultrathin films. With this approach, we have fabricated a series of ultrathin free-standing graphene oxide films and UFGFs, up to 40 mm in diameter, with controllable thickness from micrometre to nanoscale (approx. 40 nm) dimensions. This method can be easily scaled up and the films display excellent optical, electrical and electrochemical properties. The ability to produce UFGFs from graphene oxide with a scalable, low-cost approach should take us a step closer to real-world applications of graphene.

Three-Dimensional Porous Supramolecular Architecture from Ultrathin g-C3N4 Nanosheets and Reduced Graphene Oxide: Solution Self-Assembly Construction and Application as a Highly Efficient Metal-Free Electrocatalyst for Oxygen Reduction Reaction

Direct mixing of aqueous dispersions of ultrathin g-C3N4 nanosheets and graphene oxide (GO) under ultrasonication leads to three-dimensional (3D) porous supramolecular architecture. Photoreduction of GO yields conductive porous g-C3N4/rGO hybrid. The resulting 3D architecture possesses high surface area, multilevel porous structure, good electrical conductivity, efficient electron transport network, and fast charge transfer kinetics at g-C3N4/rGO interfaces, which facilitate the diffusion of O2, electrolyte, and electrons in the porous frameworks during oxygen reduction reaction (ORR). Ultrathin g-C3N4 nanosheet also causes effective electron tunneling through g-C3N4 barrier, leading to rich electrode-electrolyte-gas three-phase boundaries, and shortens the electron diffusion distance from rGO to O2. As a novel ORR catalyst, such 3D hybrid exhibits remarkable catalytic performance, outperformed other g-C3N4/rGO composites, and exhibits excellent durability.

Thermoluminescence properties of graphene–nano ZnS composite

This work describes the thermoluminescence (TL) of graphene oxide (GO), reduced graphene oxide (RGO) and graphene–nano ZnS composite. Graphene oxide was synthesized using Hummer's method and then reduced to graphene by hydrazine hydrate. G–ZnS was synthesized via in-situ reduction of graphene oxide (GO) and zinc nitrate [Zn(NO3)2] by sodium sulfide (Na2S). The structures of samples were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). XRD pattern confirmed the formation of graphene oxide, reduced graphene oxide and G–ZnS lattice. The p-XRD spectrum of G–ZnS shows peaks of ZnS superimposed on those of graphene and the particle size of ZnS in the complex is less than 10nm. Ultra thin graphene and graphene oxide sheets with size ranging between tens to several hundreds of square nanometers are observed in TEM images. The TEM micrographs of G–ZnS show that ZnS particles are embedded in graphene sheets and the average particle size of ZnS particles in the composite is less than 10nm. Samples of RGO, GO and G–ZnS were exposed to different doses of γ-rays in the range of 1Gy to 50kGy. The reduced graphene oxide (RGO) did not show any thermoluminescence emission. The thermoluminescence glow curve of GO has a single broad peak whose peak position varied between 500 and 550K with an absorbed dose increasing from 1Gy to 5000Gy. GO shows most intense TL peak, positioned at 523.6K for a dose of 10kGy. The glow curves of G–ZnS over the entire range of irradiation have single peak positioned between 492 and 527K with variation in dose from 1Gy to 50kGy. G–ZnS shows the most intense TL glow curve for a dose of 50kGy. The TL response curve of G–ZnS is found to be linear over a larger dose range from 1Gy to 50kGy whereas the response curve of GO shows linearity only at low doses up to 100Gy.

Graphene Oxide Wrapping on Squaraine-Loaded Mesoporous Silica Nanoparticles for Bioimaging

Squaraine dyes were loaded inside mesoporous silica nanoparticles, and the nanoparticle surfaces were then wrapped with ultrathin graphene oxide sheets, leading to the formation of a novel hybrid material. The hybrid exhibits remarkable stability and can efficiently protect the loaded dye from nucleophilic attack. The biocompatible hybrid is noncytotoxic and presents significant potential for application in fluorescence imaging in vitro.

Transparent polyimide/graphene oxide nanocomposite with improved moisture barrier property

Colorless and organo-soluble polyimide (PI) films have been synthesized from an alicyclic dianhydride BCDA and aromatic diamine 3,4′-ODA in the cosolvent of DMAc and GBL via one-step process. The graphene oxide (GO) was mixed with the above PI in DMAc solution to fabricate the PI/GO nanocomposite films. With the addition of only 0.001 wt% of GO in PI matrix, the resultant nanocomposite (PI/GO-0.001) exhibits not only the enhanced resistance to moisture but also retains superior visible light transmission, enhanced mechanical strength, and excellent dimensional stability, simultaneously. The water-vapor-transmission-rate (WVTR) significantly reduced to 30 g mil m−2 day−1 for this nanocomposite compared to 181 g mil m−2 day−1 for pure PI. Notably, the PI/GO-0.001 nanocomposite also exhibits low coefficient of thermal expansion (CTE) of 41 ppm °C−1, which is benefited from the homogeneous distribution of ultrathin GO nanosheets in PI matrix.

Graphene-Based Environmental Barriers

Many environmental technologies rely on containment by engineered barriers that inhibit the release or transport of toxicants. Graphene is a new, atomically thin, two-dimensional sheet material, whose aspect ratio, chemical resistance, flexibility, and impermeability make it a promising candidate for inclusion in a next generation of engineered barriers. Here we show that ultrathin graphene oxide (GO) films can serve as effective barriers for both liquid and vapor permeants. First, GO deposition on porous substrates is shown to block convective flow at much lower mass loadings than other carbon nanomaterials, and can achieve hydraulic conductivities of 5 × 10(-12) cm/s or lower. Second we show that ultrathin GO films of only 20-nm thickness coated on polyethylene films reduce their vapor permeability by 90% using elemental mercury as a model vapor toxicant. The barrier performance of GO in this thin-film configuration is much better than the Nielsen model limit, which describes ideal behavior of flake-like fillers uniformly imbedded in a polymer. The Hg barrier performance of GO films is found to be sensitive to residual water in the films, which is consistent with molecular dynamics (MD) simulations that show lateral diffusion of Hg atoms in graphene interlayer spaces that have been expanded by hydration.

Graphene Based Ultrahin Composite Films Prepared by Layer-by-Layer Electrostatic Assembly and Spinning Coating

Ultra thin graphene oxide (GO)/polyvinyl alcohol and graphene-polyvinyl alcohol/gelatin composite films were fabricated by electrostatic layer-by-layer assembly and spinning coating methods. The assembling and coating process were traced with UV-visible absorption spectroscopy and the morphology of the formed ultra thin films was observed under scanning electron microscopy. The results show that the adsorption value of the GO based composite films linearly increased as the number of layers increased. The ultra thin graphene oxide/polyvinyl alcohol and graphene-polyvinyl alcohol/gelatin composite films have layered structure with high tensile strength because of the incorporation of GO. These strong ultra thin films have potential applications in coating, sensor and electrochemical devices.

Thickness-dependent solar power conversion efficiencies of catalytic graphene oxide films in dye-sensitized solar cells

The catalytic effects of graphene oxide (GO) films were investigated for dye-sensitized solar cell (DSSC). The GO film consisted of a networked structure of two phases of GO with intercalated H 2O and exfoliated GO. A maximum solar power conversion efficiency ( η) of 2.30% was obtained for the ultrathin GO film. This η is higher than that of other reported types of DSSCs (0.84%) and organic solar cells (1.1%) with graphene electrodes. The catalytic effect of the GO film is attributed to the good ion permeability along the interlayer hydrophilic spaces; the electrons present in these spaces on the exfoliated GO were supplied to the iodide ions.

Solution‐processed semitransparent p–n graphene oxide:CNT/ZnO heterojunction diodes for visible‐blind UV sensors

AbstractA high quality transparent p–n heterojunction device comprised of 1D zinc oxide (ZnO) nanorods (NRs) and an ultrathin 2D graphene oxide (GO):carbon nanotube (CNT) hybrid film was fabricated through a solution process. The turn on voltage and ideality factor of the device were 1.5 V and 6.1, respectively. Optical measurements revealed that the UV absorption of the ZnO NRs increased after a GO:CNT hybrid film was spray‐coated onto the NRs. As a result, the device exhibited a high response to UV illumination. The fabricated diode displayed high rectifying characteristics and excellent performance as a visible‐blind UV sensor.