High-quality Graphene Nanosheets Research Articles

Efficient strategy of chlorine-assisted liquid-phase exfoliation of graphite

A large-scale, inexpensive, and facile strategy has been successfully developed for preparation of high-quality graphene nanosheets by combining electron-absorbing materials and chorine in N-methyl-2-pyrrolidone. The as-obtained graphene sheets were proven to contain low levels of naturally absorbed oxygen inherited from the starting graphite by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and X-ray diffraction. Meanwhile, the structure of produced graphene sheets was further characterized using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Compared to the previous techniques, this eco-friendly approach demonstrates obvious advantages, such as low cost and simplicity, which could be an alternative method to prepare graphene-based composites for the potential applications in the near future.

Tri-solvent mediated probing of ultrasonic energy towards exfoliation of graphene nanosheets for supercapacitor application

High quality graphene nanosheets were prepared using simple triple solvent system and probe assisted ultrasonication technique for the first time. Structural and morphological evidences confirmed the formation of high quality, hexagonal crystal structured and sheet like architectures of graphene. Electrochemical analysis confirmed the phenomenal capacitor characteristics in 1M H2SO4 electrolyte with better electrochemical stability and with a specific capacitance of 36.26F/g at the sweep rate of 10mV/s that was achieved for the graphene nanosheets. Moreover, the stable electrochemical activity was mainly due to the non-aggregation effects of graphene nanosheets and it is believed that such a nanostructure prepared by this simple approach would be a promising candidate for supercapacitors.

Influence of reducing reagent combination in graphene oxide reduction

Large-scale production of high-quality graphene nanosheets has been considered to be an interesting and significant challenge. A new approach is reported regarding the fabrication of high-quality graphene nanosheets via chemical reduction with the combination of reducing reagents from graphene oxide (GO). High-conducting reduced GO (RGO) was provided with the combination of hydrazine hydrate and hydroiodic acid. RGO was characterised by X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman, thermo gravimetric analysis, atomic force microscopy and four-probe conductivity tester. Characterisation results indicated that oxygenated functional groups were removed from GO, and high graphitisation has occurred in GO reduction process. The electrical conductivity of RGO was considerably improved and the C/O ratio of RGO was higher than that prepared by single reducing reagent. Combination of hydrate hydrazine and hydroiodic acid have showed high reduction efficiency and good synergistic effect in GO reduction process. The findings in this work can promote research on prepared graphene-based nanosheets composites by a quick and effective processing technique.

BioGraphene: Direct Exfoliation of Graphite in a Kitchen Blender for Enzymology Applications.

A high yielding method for the aqueous exfoliation of graphite crystals to produce high quality graphene nanosheets in a kitchen blender is described here. Bovine serum albumin (BSA), β-lactoglobulin, ovalbumin, lysozyme, and hemoglobin as well as calf serum were used for the exfoliation of graphene. Among these, BSA gave the maximum exfoliation efficiency, exceeding 4mgmL(-1)h(-1) of graphene. Quality of graphene produced was examined by Raman spectroscopy, which indicated 3-5 layer graphene of very high quality and very low levels of defects. Transmission electron microscopy indicated an average size of ~0.5μm flakes. The graphene/BSA dispersions were stable over pH 3.0-11, and at 5°C or 50°C, for more than 2 months. Current approach gave higher rates of BSA/graphene (BioGraphene) in better yields than other methods. Calf serum, when used in place of BSA, also gave high yields of good quality BioGraphene and these preparations may be of direct use for cell culture studies. A simple example of BioGraphene preparation is described that can be adapted in most laboratories, and graphene-adsorbed glucose oxidase is nearly as active as the free enzyme. Current approach may facilitate large-scale production of graphene in most laboratories around the world and it may open new opportunities for biological applications of graphene.

Fabrication of high quality graphene nanosheets via a spontaneous electrochemical reaction process

A highly efficient graphene nanosheet (GNS) production process based on spontaneous electrochemical reactions – (i) spontaneous lithiation reaction through the direct contact between graphite powder and Li metal in an electrolyte due to the high electrochemical potential difference; and (ii) reaction of Li inside the lithiated graphite with water – is reported. This process, with the absence of supplied energies, is oxidation-free, very fast, scalable and produces a high quality GNS (C/O: 17.9 by EA, ID/IG: 0.55 by Raman spectroscopy) with a high yield (>95wt.%).

Preparation Assisted via Thermal Stress and Electrochemical Performance of Graphene Nano-Sheets as Anode Materials for Lithium-Ion Batteries

Via a simple thermal stress assist process, the high-quality graphene was successfully obtained. The microstructure, morphology and the electrochemical performance of the as-prepared products were characterized by x-ray diffraction (XRD), field emission environment scanning electron microscope (SEM), Micro-Raman Spectroscopy System, element analysis system and LAND battery program-control test system respectively. The results show that the as-prepared products are uniform graphene nano-sheets (GNs) with large and smooth surface, and that the GNs, as an anode material for lithium-ion cell, exhibit good cyclic performance, which imply that the lithium ions and GNs have formed a relative stable structure to large degree. A possible form mechanism of the high-quality GNs is proposed.

Fabrication of High Quality Graphene Nanosheets from Camphor

Fabrication of High Quality Graphene Nanosheets from Camphor

Spontaneous intercalation of long-chain alkyl ammonium into edge-selectively oxidized graphite to efficiently produce high-quality graphene

Mass production of high-quality graphene nanosheets (GNs) is essential for practical applications. We report that oxidation of graphite by low concentration KMnO4 at relatively high temperature (60°C) leads to edge-selectively oxidized graphite (EOG) which preserves the high crystalline graphitic structure on its basal planes while the edges are functionalized by oxygen-containing groups. Long-chain tetradecyl-ammonium salt (C14N+) could be spontaneously intercalated into EOG to form intercalated EOG-C14N+ compounds. Gentle and short-time sonication of EOG-C14N+ in toluene can full exfoliate EOG into edge-oxidized graphene nanosheets (EOGNs) with concentration of 0.67 mg/ml, monolayer population up to 90% and lateral size from 1 μm to >100 μm. The EOG and EOGN films show excellent electrical conductance, which is far superior to their graphene oxide (GO) counterparts. Our method provides an efficient way to produce high-quality GNs, and the resultant EOG also can be directly used for production of multifunctional materials and devices.

High-quality production of graphene by liquid-phase exfoliation of expanded graphite

As one of the most promising candidates, graphene exhibits a potential application in post-silicon nanoelectronics. However, it is a key issue to produce high-quality graphene in large scale. Here, a facile method is demonstrated to produce graphene dispersions by exfoliation of expanded graphite in the co-solvent with N,N-dimethylformamide (DMF) and water. We confirm that the optimal ratio of DMF to water for graphene exfoliation is 9:1 (v:v) by means of UV–Vis absorption spectra. This exfoliation results in large flakes ∼2 μm in diameter, which can potentially be improved by adjusting the sonication power. The relatively perfect hexagonal structure of graphene is confirmed by Raman spectroscopy and the as-prepared graphene nanosheet film the as-prepared graphene nanosheet film possesses good electrical conductivity (∼8.3 × 103 S m−1). DC electrical transport phenomena for the deposited film of graphene nanosheets are well described in terms of conduction models for non-crystal semiconductor. This convenient approach provides an extensive route to prepare high-quality graphene nanosheets.

Synthesis of Co(OH)2/graphene/Ni foam nano-electrodes with excellent pseudocapacitive behavior and high cycling stability for supercapacitors

Vertically aligned graphene nanosheets have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition on nickel-foam current collectors and that have been used as substrates for cathodic electrodeposition of cobalt hydroxide nanosheets in Co(NO3)2 aqueous solution. Raman spectrum exhibits that high-quality graphene nanosheets have been synthesized. The composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and galvanostatic charge/discharge. It indicates that hexagonal Co(OH)2 has a network microstructure, consisting of interlaced sheets with the thickness of 12 nm coated on the graphene nanosheets. The binder-free nano-electrode exhibits excellent pseudocapacitive behavior with pseudocapacitances of 693.8 and 506.2 Fg−1 at current density of 2 and 32 Ag−1, respectively, in a potential range of −0.1–0.45 V. The capacitance can retain about 91.9% after 3000 charge–discharge cycles at 40 Ag−1, which is higher than that of Co(OH)2/Ni foam (after 2000 cycles, 75.5% of initial capacitance remains). The introduction of graphene between Co(OH)2 and Ni foam demonstrates an enhancement of electrochemical stability of the nano-electrodes.

Greener Electrochemical Synthesis of High Quality Graphene Nanosheets Directly from Pencil and its SPR Sensing Application

AbstractA green, simple, and cost effective electrochemical method to synthesize pure graphene oxide (GO) and graphene nanosheets (GNs) using pencil in ionic liquid medium is reported. The morphology and microstructure of prepared GNs and GO are examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X‐ray diffraction (XRD), and Raman spectroscopy; the experiments confirm the formation of high quality graphene. The synthesized GO is used for the real‐time and label‐free surface plasmon resonance (SPR) sensing of the biological warfare agent Salmonella typhi.

Controllable selective exfoliation of high-quality graphene nanosheets and nanodots by ionic liquid assisted grinding

Bulk quantities of graphene nanosheets and nanodots have been selectively fabricated by mechanical grinding exfoliation of natural graphite in a small quantity of ionic liquids. The resulting graphene sheets and dots are solvent free with low levels of naturally absorbed oxygen, inherited from the starting graphite. The sheets are only two to five layers thick. The graphene nanodots have diameters in the range of 9-29 nm and heights in the range of 1-16 nm, which can be controlled by changing the processing time.

Solid-state microwave irradiation synthesis of high quality graphenenanosheets under hydrogen containing atmosphere

High quality graphene nanosheets were fabricated within 1 min by solid-state microwave irradiation of a mixture of graphite oxide and graphene nanosheets under a hydrogen atmosphere. The graphene nanosheets in the mixture acted as an effective microwave susceptor under microwave irradiation synthesis, and could provide sufficiently rapid heating for the effective exfoliation of graphite oxide. A hydrogen containing atmosphere played important roles in improving the quality of the graphene nanosheets by increasing the level of reduction and preventing the formation of defects in the graphene nanosheets. The graphene nanosheets thus obtained exhibited a specific surface area of 586 m2 g−1 and an outstanding carbon/oxygen ratio of 18.5.

Low-temperature rapid synthesis of high-quality pristine or boron-doped graphene via Wurtz-type reductive coupling reaction

High-quality graphene nanosheets are prepared via a rapid Wurtz-type reductive coupling (WRC) reaction without the assistance of any transition metal catalysts. This method involves a nearly stoichiometric reaction of tetrachloromethane (CCl4) and potassium (K) at 150–210 °C for as short as 10 min, which possesses great advantages compared with the solvothermal method. The layer number of the as-prepared graphene is mainly less than five. The formation mechanism of graphene is proposed, which comprises of three steps, stripping off the chlorines from CCl4 by the highly reductive K, the coupling and assembly of –CC– and the layer growth of hexagonal carbon clusters to form graphene. Many important factors determining the quality of graphene, such as the residual chlorines, the reaction temperature and the reductant, are discussed in detail. The low residual chlorine in the reaction favors the improvement of the graphene quality. Furthermore, controllable boron doping can be easily realized by adding an appropriate amount of BBr3. The developed method provides a cost-effective route to prepare high-quality pristine or doped graphene for mass production.

A Green Approach to the Synthesis of Graphene Nanosheets

Graphene can be viewed as an individual atomic plane extracted from graphite, as unrolled single-walled carbon nanotube or as an extended flat fullerene molecule. In this paper, a facile approach to the synthesis of high quality graphene nanosheets in large scale through electrochemical reduction of exfoliated graphite oxide precursor at cathodic potentials (completely reduced potential: -1.5 V) is reported. This method is green and fast, and will not result in contamination of the reduced material. The electrochemically reduced graphene nanosheets have been carefully characterized by spectroscopic and electrochemical techniques in comparison to the chemically reduced graphene-based product. Particularly, FTIR spectra indicate that a variety of the oxygen-containing functional groups have been thoroughly removed from the graphite oxide plane via electrochemical reduction. The chemically converted materials are not expected to exhibit graphene's electronic properties because of residual defects. Indeed, the high quality graphene accelerates the electron transfer rate in dopamine electrochemistry (DeltaE(p) is as small as 44 mV which is much smaller than that on a glassy carbon electrode). This approach opens up the possibility for assembling graphene biocomposites for electrocatalysis and the construction of biosensors.