Liquid-phase Exfoliation Of Graphite Research Articles

Synergistic reinforcement of poly(vinyl alcohol) nanocomposites with cellulose nanocrystal-stabilized graphene

Abstract Cellulose nanocrystal-stabilized graphene ( GR-CNC ) was produced by liquid phase exfoliation of graphite assisted by cellulose nanocrystals (CNC), a recently reported method that allows stabilization of resulting graphene flakes in aqueous dispersions. Using a simple and environmentally friendly process, GR-CNC was incorporated into poly(vinyl alcohol) (PVA) aqueous solutions to obtain PVA-based nanocomposites ( GR-CNC/PVA ) by a casting method. For comparison purposes, two reference materials were also prepared following the same procedure: CNC/PVA and GR-T/PVA , where graphene was stabilized by an organic surfactant, Triton X-100 (T). At 1wt% nanofiller loading, GR-CNC/PVA exhibited superior mechanical properties (improvements in tensile strength and Young's modulus were about 20% and 50%, respectively, compared with neat PVA) than CNC/PVA (4% increase in tensile strength and 19% in Young's modulus) and GR-T/PVA (where a decrease in mechanical properties was observed), suggesting the synergistic reinforcing effect of CNC and graphene (GR). This significant reinforcement found for GR-CNC/PVA is attributed to the strong interaction between PVA and GR-CNC .

One-pot exfoliation of graphite and synthesis of nanographene/dimesitylporphyrin hybrids.

A simple one-pot process to exfoliate graphite and synthesize nanographene-dimesitylporphyrin hybrids has been developed. Despite the bulky mesityl groups, which are expected to hinder the efficient π–π stacking between the porphyrin core and graphene, the liquid-phase exfoliation of graphite is significantly favored by the presence of the porphyrins. Metallation of the porphyrin further enhances this effect. The resulting graphene/porphyrin hybrids were characterized by spectroscopy (UV-visible, fluorescence, and Raman) and microscopy (STEM, scanning transmission electron microscopy).

Determination of ascorbic acid, dopamine, and uric acid by a novel electrochemical sensor based on pristine graphene

In this article, a novel electrochemical sensor based on pristine graphene (PG) is successfully constructed to detect ascorbic acid (AA), dopamine (DA), and uric acid (UA). The PG is obtained by liquid-phase exfoliation of graphite and characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The sensor based on PG prepared by this method to realize simultaneous determination of AA, DA, and UA is firstly reported. The linear detection ranges for AA, DA, and UA are 9.00–2314μM, 5.00–710μM, and 6.00–1330μM, respectively, with detection limits of 6.45, 2.00, and 4.82μM. This PG based sensor exhibits excellent performance for detection of AA, DA, and UA, which is much better than those electrochemical sensors based on chemical converted graphene.

Defect engineering as a versatile route to estimate various scattering mechanisms in monolayer graphene on solid substrates.

It is known that the experimental conditions and growth methods determine the different carrier scatterings responsible for large variation of carrier mobility in graphene monolayers. Here we present a systematic investigation on various possible scattering mechanisms responsible for limiting the carrier mobility in graphene on a solid substrate, like SiO2. This has been possible by defect engineering in graphene monolayers obtained by liquid phase exfoliation of graphite in polar and non-polar solvents with the dielectric constant varying from 2.5 to 64. Lattice defects in graphene monolayers have been characterized by scanning tunnelling microscopy and Raman spectroscopy. Correlation between the results obtained from electrical measurements and the information obtained from Raman spectra have revealed different scattering mechanisms responsible for deciding the carrier mobility. It has been shown that remote interfacial phonons in SiO2 are responsible for limiting the carrier mobility at room temperature whereas, substrate impurities and Raman active point defects in the graphene lattice are the dominant scatterers for limiting the mobility at low temperatures.

Concentration Enhancement of Liquid Phase Exfoliated Graphene with Addition of Organic Salts

Abstract A facile sonochemical route has been proposed in which liquid phase exfoliation of graphite into single and multi-layer graphene is obtained. An organic solvent ortho-dichlorobenzene (ODCB) is used for the graphene exfoliation and the effect of addition of organic salts in ODCB solvent is investigated. The characterization of the as prepared graphene is done using SEM, TEM and UV-Visible spectroscopy. The graphene film was prepared using vacuum filtration method and resistivity measurement was done using Four-Probe method. The application of graphene film in making flexible paper supercapacitor is demonstrated. It is observed that the concentration of graphene synthesized by liquid phase exfoliation method has been found to enhance appreciably with addition of EDTA disodium salt.

A surfactant-free water-processable all-carbon composite and its application to supercapacitor

An easy technique is proposed to prepare a new surfactant-free water-processable supercapacitive material composed of graphene oxide (GO) and pristine graphene (PG). GO and PG are prepared by a modified Hummer's method and direct liquid phase exfoliation of graphite in dimethyl sulfoxide (DMSO) respectively. Water-processable GO/PG composites can be conveniently fabricated by mixing colloidal GO/H2O and PG/DMSO dispersions. The GO/PG composites can be re-dispersed in water to form stable colloidal dispersions. Capacitive behaviors of GO, PG and GO/PG composites were tested by cyclic voltammetry, galvanostatic charge/discharge curves and electrochemical impedance spectroscopy in aqueous electrolyte solutions. GO/PG composites exhibited improved capacitive properties in terms of specific capacitance and cycling stability, compared to those of individual components. The enhanced performances of the GO/PG composites signify the importance of the surface chemical property and conductivity of carbon-based materials for supercapacitor applications.

Electron-accepting phthalocyanine–pyrene conjugates: towards liquid phase exfoliation of graphite and photoactive nanohybrid formation with graphene

Exfoliation of graphite by ultrasonication in the presence of electron-accepting pyrene–phthalocyanines and photophysical characterization of the resulting nanoconjugate are reported.

Effect of Sonication Energy on the Yield of Graphene Nanosheets by Liquid-phase Exfoliation of Graphite

We demonstrate the high concentration exfoliation of graphene nanosheets in dimethyl formamide (DMF) as a solvent from graphite powder. UV-Vis-NIR spectroscopy shows low power bath sonication yields less concentration of graphene nanosheets exfoliation, whereas the high power probe sonication yields high concentration graphene nanosheets exfoliation. The concentration of graphene nanosheets exfoliation depends on amount of energy supplied, and there exists a linear relationship between the concentration of graphene and energy supplied during sonication. TEM micrograph confirms the exfoliation of graphene nanosheets. AFM studies shows; high power sonication for longer time reveals graphene exfoliation with fewer graphene layers. The strategy of bath sonication followed by probe sonication of grapheme solution shows the stable suspension of graphene nanosheets even after one month.

Liquid-phase exfoliation of graphene in organic solvents with addition of naphthalene

We report a facile method for the production of graphene sheets through liquid-phase exfoliation of graphite in organic solvents with addition of naphthalene. The production yield of graphene is significantly increased with the addition of naphthalene in most solvents tested in this work. Naphthalene serves as a “molecular wedge” to intercalate into the edge of graphite, which plays a key role during sonication and significantly improves the production yield of graphene. The graphene concentration of the dispersion in 1-methyl-2-pyrrolidinone is as high as 0.15mg/mL (after sonication for 90min), which allows this method to easily produce films and composites for a range of applications.

Prussian blue-functionalised graphene in the amperometric detection of peroxide and hydrazine

The electrochemical detection of hydrogen peroxide, H 2 O 2, and hydrazine, N 2 H 4, is of considerable interest because of the serious health risks associated with these compounds. The unique zeolite structure of Prussian blue, Fe 4[ Fe ( CN )6]3, endows it with excellent catalytic activity towards these small molecules, but its immobilisation on suitable support materials is limited by its solubility at neutral and basic pH values. Here we report an electroanalytical sensor for peroxide and hydrazine based on composites of Prussian blue and graphene nano-sheets (GNSs). The latter are fabricated using the liquid-phase exfoliation of graphite. When immobilised on graphene, Prussian blue is shown to exhibit higher sensitivity towards these analytes than a number of commercially available graphitic supports, including edge-plane pyrolytic graphite (EPPG) electrodes. The incorporation of graphene into electode systems could lead to great advances in sensor technology for these and many other species of interest.

Preparation of Graphene Dispersion: A Review

Graphene has been attracted lots of attention for its unique properties and various applications in transistors, transparent conductors, sensors, etc. Many applications require stable and individual dispersion of graphene sheets in liquid phase. There are two ways to obtain graphene dispersion: 1) to disperse graphene powder in aqueous solution or organic solvents, 2) to exfoliate graphite into monolayer sheets in liquid phase directly. Usually, surfactants are needed to stabilize the dispersion. In this paper, recent work on preparation of graphene dispersion is reviewed, including dispersing, exfoliating, and stabilizing graphene in a variety of liquids. The dispersion of chemically derived graphene and liquidphase exfoliation of graphite are focused. Keywords: Graphene, exfoliation, dispersion, chemically derived, graphene oxide.

Microspherical polyaniline/graphene nanocomposites for high performance supercapacitors

Polyaniline/graphene nanocomposites with microspherical morphology and porous structure are prepared as electrode materials for supercapacitors. Using few-layer graphene obtained by liquid phase exfoliation of graphite as the raw material, porous graphene microspheres are produced by spray drying, and are then employed as the substrates for the growth of polyaniline nanowire arrays by in situ polymerization. In the composite, interconnected graphene sheets with few structural defects constitute a high-efficient conductive network to improve the electrical conductivity of polyaniline. Furthermore, the microspherical architecture prevents restacking of polyaniline/graphene composite nanosheets, thus facilitates fast diffusion of electrolytes. Consequently, the nanocomposite exhibits excellent electrochemical performance. A specific capacitance of 338 F g−1 is reached in 1 M H2SO4 at a scan rate of 20 mV s−1, and a high capacity retention rate of 87.4% after 10,000 cycles at a current density of 3 A g−1 can be achieved, which suggests that the polyaniline/graphene composite with such kind of 3D architecture is a promising electrode material for high-performance supercapacitors.

Lipid Enhanced Exfoliation for Production of Graphene Nanosheets

Liquid-phase exfoliation of graphite is a widely used method to obtain graphene nanosheets, and therefore the development of a simple and efficient exfoliation procedure remains challenging. Here, we present a one-step method of graphene exfoliation in lecithin/chloroform solution. The graphene nanosheets produced by the lecithin assisted exfoliation method were analyzed by microscopy techniques, including statistical analysis of atomic force microscopy (AFM) images and Raman spectroscopy, which both indicate the presence of few-layer graphene nanosheets, including substantial content of three-layer sheets. Molecular dynamics simulations on the time scale of 0.5+ μs suggested that stability of the obtained colloid may originate from formation of lecithin reverse hemimicelles and micelles, which prevents the aggregation of exfoliated graphene flakes by entropic repulsion of the lipid hydrophobic chains.

A mixed-solvent strategy for facile and green preparation of graphene by liquid-phase exfoliation of graphite

A versatile and scalable mixed-solvent strategy, by which two mediocre solvents could be combined into good solvents for exfoliating graphite, is demonstrated for facile and green preparation of graphene by liquid-phase exfoliation of graphite. Mild sonication of crystal graphite powder in a mixture of water and alcohol could yield graphene nanosheets, which formed a highly stable suspension in the mixed solvents. The graphene yield was estimated as *10 wt%. The optimum mass fraction of ethanol in water-ethanol mixtures and isopropanol in water- isopropanol mixtures was experimentally determined as *40 and *55 % respectively, which could be roughly predicted by the theory of Hansen solubility parameters. Statistics based on atomic force micro- scopic analysis show that up to*86 % of the prepared nanosheets were less than 10-layer thick with a monolayer fraction of *8 %. High resolution trans- mission electron microscopy, infrared spectroscopy, X-ray diffraction, and Raman spectrum analysis of the vacuum-filtered films suggest the graphene sheets to be largely free of defects and oxides. The proposed mixed-solvent strategy here extends the scope for liquid-phase processing graphene and gives research- ers great freedom in designing ideal solvent systems for specific applications.

Inkjet-Printed Graphene Electronics

We demonstrate inkjet printing as a viable method for large-area fabrication of graphene devices. We produce a graphene-based ink by liquid phase exfoliation of graphite in N-methylpyrrolidone. We use it to print thin-film transistors, with mobilities up to ∼95 cm(2) V(-1) s(-1), as well as transparent and conductive patterns, with ∼80% transmittance and ∼30 kΩ/□ sheet resistance. This paves the way to all-printed, flexible, and transparent graphene devices on arbitrary substrates.

High concentration few-layer graphene sheets obtained by liquid phase exfoliation of graphite in ionic liquid

In the present work, the use of a commercial ionic liquid as a convenient solvent medium for graphite exfoliation in mild and easy conditions without any chemical modification is presented. To confirm the presence of few layer graphene, its dispersion was charachterized by Raman spectroscopy, atomic force miscroscopy and field emission electron microscopy. From the UV-Vis characterization, a graphene concentration as high as 2.543 mg/ml was obtained, which is the highest value reported so far in any solvent.

Direct exfoliation of graphene in methanesulfonic acid and facile synthesis of graphene/polybenzimidazole nanocomposites

The emerging field of graphene(GP)-based polymer nanocomposites has continued to be the focus of considerable interest in recent years because of the unparalleled improvement shown in mechanical, thermal, and electrical properties compared to the neat polymer. However, these improvements largely depend on the synthesis of well-exfoliated and high-quality GP. In this paper, we report a facile method for the production of GP sheets through the liquid-phase exfoliation of graphite in methanesulfonic acid (MSA). Raman, X-ray photoelectron and infrared spectroscopies reveal that the obtained GP has a low-defect density with a low degree of oxidation. Transmission electron microscopy and atomic force microscopy further confirm that the resulting GP is in the well-exfoliated state. Using this GP/MSA solution as a reaction solvent medium, polymer nanocomposites are prepared by in situpolymerization of poly [2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI). Compared to pure OPBI, the resulting OPBI/GP nanocomposites show simultaneously improved Young's modulus, tensile stress, toughness, storage modulus and thermal stability with the addition of extremely small amounts of GP. The high levels of reinforcement are attributed to the good dispersion and effective stress transfer between polymer and GP as evidenced by SEM images of the fracture surfaces, and the excellent intrinsic properties of the high-quality GP. All these features make this simple procedure a potential route for the fabrication of low-cost and high-performance polymer nanocomposites.

Direct exfoliation of graphene in organic solvents with addition of NaOH

We report a facile method for the production of graphene sheets through the liquid-phase exfoliation of graphite in organic solvents with addition of NaOH. NaOH was found to be intercalated into the interplanar spaces of graphite, and greatly improves exfoliation efficiency up to 20 times.

Field Emission from Few-Layer Graphene Nanosheets Produced by Liquid Phase Exfoliation of Graphite

Graphene nanosheets have been synthesized from commercial expandable graphite by heating in a microwave oven and dispersing in ethanol by ultrasonication. Scanning and transmission electron microscopy and electron energy-loss spectroscopy and atomic force microscope showed that the nanosheets were about 2 nm in thickness and 10 microm in diameter. The field emission of the graphene sheets has been investigated. An emission current density of 1 mA/cm2 has been achieved at an electric field of 3.7 V/microm with a turn-on field of 1.7 V/microm at 0.01 mA/cm2. The annealing of the samples at 400 degrees C in vacuum greatly improved the field emission performance.

Liquid‐Phase Exfoliation of Nanotubes and Graphene

AbstractMany applications of carbon nanotubes require the exfoliation of the nanotubes to give individual tubes in the liquid phase. This requires the dispersion, exfoliation, and stabilization of nanotubes in a variety of liquids. In this paper recent work in this area is reviewed, focusing on results from the author's group. It begins by reviewing stabilization mechanisms before exploring research into the exfoliation of nanotubes in solvents, by using surfactants or biomolecules and by covalent attachment of molecules. The concentration dependence of the degree of exfoliation in each case will be highlighted. In addition research into the dispersion mechanism for each dispersant type is discussed. Most importantly, dispersion quality metrics for all dispersants are compared. From this analysis, it is concluded that functionalized nanotubes can be exfoliated to the greatest degree. Finally, the extension of this work to the liquid phase exfoliation of graphite to give graphene is reviewed.