Large-scale Production Of Graphene Research Articles

A green approach for the reduction of graphene oxide nanosheets using non-aromatic amino acids

A simple and green chemistry approach for the preparation of reduced graphene oxide nanosheets through the reduction of graphene oxide (GO) using non-aromatic and thiol-free amino acids as the reductant was successfully demonstrated. l-Aspartic acid and valine amino acids were used as models to prove that the reduction method is generic to other amino acids. The significance of the proposed method is that it eliminates the use of toxic and harmful chemicals to humans and the environment, which makes it compatible for the large-scale production of graphene. Reduced GO nanosheets showed good stability in aqueous dispersions due to the strong electrostatic repulsion on the graphene surface. Structural studies confirmed the deoxygenation of GO from the loss of hydroxyl, carbonyl and epoxy groups, and preparation of graphene sheets between 20 and 70nm suitable for broad biomedical applications.

Carbon isotope labelling in graphene research.

The large scale production of graphene for any potential application relies on catalytic chemical vapour deposition (CVD). Despite much effort put into the graphene CVD research, there are still many challenges to be solved, not only concerning the growth itself, but also the subsequent treatment, i.e. transfer from the catalyst to a desired substrate. The need for fast progress naturally necessitates easy-to-use, versatile and efficient characterization methods. This perspective reviews the recent advances and potential of probably the most prospective one--Raman spectroscopy in connection with carbon isotope labelling of the CVD grown graphene layers. We discuss its use for the explanation and optimization of the growth process, followed by examples of employing isotope engineering in the studies of fundamental properties of graphene, not only by Raman spectroscopy.

Chemical reduction of graphene oxide: a synthetic chemistry viewpoint

The chemical reduction of graphene oxide is a promising route towards the large scale production of graphene for commercial applications. The current state-of-the-art in graphene oxide reduction, consisting of more than 50 types of reducing agent, will be reviewed from a synthetic chemistry point of view. Emphasis is placed on the techniques, reaction mechanisms and the quality of the produced graphene. The reducing agents are reviewed under two major categories: (i) those which function according to well-supported mechanisms and (ii) those which function according to proposed mechanisms based on knowledge of organic chemistry. This review will serve as a valuable platform to understand the efficiency of these reducing agents for the reduction of graphene oxide.

Reduction of Graphene Oxide in Solution by Radical Treatment

Abstract Reduction of graphene oxide is a promising way for scalable production of graphene. The graphene reduced chemically from graphene oxide, however, retains many defects which were formed in the oxidation process, and thus its crystallinity is rather poor. Here, we report an effective reduction method of graphene oxide by radical treatment in solution. Graphene oxide was reduced more effectively by CH3I or BrC2H4Br than by hydrazine, which is a chemical reagent used for conventional reduction of graphene oxide. This radical reduction would facilitate large-scale production of graphene for various applications.

The Realistic Domain Structure of As-Synthesized Graphene Oxide from Ultrafast Spectroscopy

Graphene oxide (GO) is an attractive alternative for large-scale production of graphene, but its general structure is still under debate due to its complicated nonstoichiometric nature. Here we perform a set of femtosecond pump-probe experiments on as-synthesized GO to extrapolate structural information in situ. Remarkably, it is observed that, in these highly oxidized GO samples, the ultrafast graphene-like dynamics intrinsic to pristine graphene is completely dominant over a wide energy region and can be modified by the localized impurity states and the electron-phonon coupling under certain conditions. These observations, combined with the X-ray photoelectron spectroscopy analysis and control experiments, lead to an important conclusion that GO consists of two types of domain, namely the carbon-rich graphene-like domain and the oxygen-rich domain. This study creates a new understanding of the realistic domain structure and properties of as-synthesized GO, offering useful guidance for future applications based on chemically modified/functionalized graphenes.

Functionalization of Graphene Oxide for the Production of Novel Graphene-Based Polymeric and Colloidal Materials

Graphene oxide (GO) has been long-considered the most convenient route towards the large scale production of graphene. Additionally, the functional groups present within GO permit both covalent and non-covalent chemical functionalization, in particular with polymeric materials. The functionalization of GO therefore enables the development of graphene-based composite materials which possess the properties of both the matrix and the remarkable electrical, thermal and mechanical properties of both GO and graphene. In this review, we discuss the functionalization of GO in two broad settings: macromolecular functionalization of GO, and the use of GO in dispersed/colloidal systems. We review numerous methods for the functionalization of GO with initiators or chain transfer agents to permit controlled/living radical polymerization (CLRP) to take place from the surface of GO; the use of GO as a polymerization initiator, as well as non-covalent polymeric modification is discussed. For applications of GO in dispersed systems, we discuss the incorporation of GO into miniemulsions, emulsions and other dispersed phase polymerization systems, as well as techniques such as layer-by-layer assembly and colloidal templating. The use of GO as a ‘colloidal surfactant’ is also reviewed. These functionalization methods are discussed within the framework of creating materials with enhanced properties for specific applications including electrodes, capsules, polymer particles and composite films.

Influence of the Grain Size of Precursor Graphite on the Synthesis of Graphite Oxide

Graphene is a single sheet of graphite and becomes a widely researched material due to its extraordinary electrical, magnetic, thermal, and mechanical properties [1– 4]. An established route for the large scale production of graphene at low cost is through the graphite oxide (GO) by chemical methods [5]. It is, therefore, important to understand effects of the grain size and type of the precursor graphite on the synthesis of graphite oxide and graphene oxide for the future graphene applications. Two types of graphite, natural and synthetic, exist generally and are distinguished by physical characteristics that are the result of major differences in a geologic origin and occurrence [6,7]. In this paper we considered the influence of the grain size and type of precursor graphite on making graphite oxide. It was found that the smaller size graphite was more oxidized in a same condition and then easily dispersed in the distilled water, indicating that it could produce the single layer of graphene oxide simply. The large size graphite oxides showed higher crystallinity and uniformity after additional sonication treatment. The oxi-

Direct Transformation of Amorphous Silicon Carbide into Graphene under Low Temperature and Ambient Pressure

A large-scale availability of the graphene is critical to the successful application of graphene-based electronic devices. The growth of epitaxial graphene (EG) on insulating silicon carbide (SiC) surfaces has opened a new promising route for large-scale high-quality graphene production. However, two key obstacles to epitaxial growth are extremely high requirements for almost perfectly ordered crystal SiC and harsh process conditions. Here, we report that the amorphous SiC (a-Si1−xCx) nano-shell (nano-film) can be directly transformed into graphene by using chlorination method under very mild reaction conditions of relative low temperature (800°C) and the ambient pressure in chlorine (Cl2) atmosphere. Therefore, our finding, the direct transformation of a-Si1−xCx into graphene under much milder condition, will open a door to apply this new method to the large-scale production of graphene at low costs.

Green chemistry approach for the synthesis of biocompatible graphene.

BackgroundGraphene is a single-atom thick, two-dimensional sheet of hexagonally arranged carbon atoms isolated from its three-dimensional parent material, graphite. One of the most common methods for preparation of graphene is chemical exfoliation of graphite using powerful oxidizing agents. Generally, graphene is synthesized through deoxygenation of graphene oxide (GO) by using hydrazine, which is one of the most widespread and strongest reducing agents. Due to the high toxicity of hydrazine, it is not a promising reducing agent in large-scale production of graphene; therefore, this study focused on a green or sustainable synthesis of graphene and the biocompatibility of graphene in primary mouse embryonic fibroblast cells (PMEFs).MethodsHere, we demonstrated a simple, rapid, and green chemistry approach for the synthesis of reduced GO (rGO) from GO using triethylamine (TEA) as a reducing agent and stabilizing agent. The obtained TEA reduced GO (TEA-rGO) was characterized by ultraviolet (UV)–visible absorption spectroscopy, X-ray diffraction (XRD), particle size dynamic light scattering (DLS), scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM).ResultsThe transition of graphene oxide to graphene was confirmed by UV–visible spectroscopy. XRD and SEM were used to investigate the crystallinity of graphene and the surface morphologies of prepared graphene respectively. The formation of defects further supports the functionalization of graphene as indicated in the Raman spectrum of TEA-rGO. Surface morphology and the thickness of the GO and TEA-rGO were analyzed using AFM. The presented results suggest that TEA-rGO shows significantly more biocompatibility with PMEFs cells than GO.ConclusionThis is the first report about using TEA as a reducing as well as a stabilizing agent for the preparation of biocompatible graphene. The proposed safe and green method offers substitute routes for large-scale production of graphene for several biomedical applications.

Achieving concentrated graphene dispersions in water/acetone mixtures by the strategy of tailoring Hansen solubility parameters

Although exfoliating graphite to give graphene paves a new way for graphene preparation, a general strategy of low-boiling-point solvents and high graphene concentration is still highly required. In this study, using the strategy of tailoring Hansen solubility parameters (HSP), a method based on exfoliation of graphite in water/acetone mixtures is demonstrated to achieve concentrated graphene dispersions. It is found that in the scope of blending two mediocre solvents, tailoring the HSP of water/acetone mixtures to approach the HSP of graphene could yield graphene dispersions at a high concentration of up to 0.21 mg ml−1. The experimentally determined optimum composition of the mixtures occurs at an acetone mass fraction of ∼75%. The trend of concentration varying with mixture compositions could be well predicated by the model, which relates the concentration to the mixing enthalpy within the scope of HSP theory. The resultant dispersion is highly stabilized. Atomic force microscopic statistical analysis shows that up to ∼50% of the prepared nanosheets are less than 1 nm thick after 4 h sonication and 114g centrifugation. Analyses based on diverse characterizations indicate the graphene sheets to be largely free of basal plane defects and oxidation. The filtered films are also investigated in terms of their electrical and optical properties to show reasonable conductivity and transparency. The strategy of tailoring HSP, which can be easily extended to various solvent systems, and water/acetone mixtures here, extends the scope for large-scale production of graphene in low-boiling-point solutions.

Synthesis and characterization of nanocomposites of thermoplastic polyurethane with both graphene and graphene nanoribbon fillers

Thermoplastic polyurethane (TPU) nanocomposites containing graphene and graphene nanoribbons were obtained by polymerizing 1,4-butanediol with two diisocyanates (namely, 1,6-hexane diisocyanate or isophorone diisocyanate), in which the nanofillers were previously dispersed. Raman spectroscopy and Transmission Electron Microscopy demonstrated the formation of few-layer graphene and graphene nanoribbons dispersed in the monomers. At variance to the methods commonly reported in literature, that used in this work consists of the direct exfoliation of graphite without any chemical manipulation. Apart from the obvious cost and ease advantages, the so-obtained graphene does not contain any carboxy or alkoxy groups formed during the exfoliation process, which, at variance, are typically present in the most commonly reported methods. This finding paves the way toward the large-scale production of graphene and its nanoribbons, which are considered even more interesting than graphene itself for many potential applications. The obtained nanocomposites show a peculiar thermal and rheological behavior due to the presence of the nanofillers and to their reinforcing or plasticizing effect exerted on the TPU matrices.

Low-cost preparation of a conductive and catalytic graphene film from chemical reduction with AlI3

AlI3 synthesized by I2 and Al in ethanol was used as reductive agent to directly obtain flexible reductive graphene oxide (RGO) films with high conductivity of 5320S/m from graphene oxide (GO) films at a low temperature of 80°C. This reductive method has provided a low-cost and effective route for large-scale production of graphene with high catalytic activity. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The RGO films served as counter electrode exhibited high electrochemical activity.

Graphene oxide: the mechanisms of oxidation and exfoliation

Graphene oxides (GOs) with large sheets and more perfect aromatic structure were prepared by a novel modified Hummers method. We demonstrated that the graphite did not need to be oxidized to such a deep degree as described in Hummers method because the space distance increased little when the oxidation proceeded to a certain extent and the obtained graphite oxides (GTOs) could be fully exfoliated to single layers with high thermal stability. The oxidation mechanism and chemical structure model of GO were proposed by analyzing the evolution of the functional groups with oxidation proceeded based on thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The layer spacing calculated by molecular dynamics simulations coincided with the X-ray diffraction results. Furthermore, the size distribution and thickness of GOs were also studied. The results confirmed that the GOs prepared by the modified method were fully exfoliated to uniform single layers, and this method may be important for efficient exfoliation of GTO to GO and large-scale production of graphene.

Deciphering the Electron Transport Pathway for Graphene Oxide Reduction by Shewanella oneidensis MR-1

We determined that graphene oxide reduction by Shewanella oneidensis MR-1 requires the Mtr respiratory pathway by analyzing a range of mutants lacking these proteins. Electron shuttling compounds increased the graphene oxide reduction rate 3- to 5-fold. These results may help facilitate the use of bacteria for large-scale graphene production.

A method for the catalytic reduction of graphene oxide at temperatures below 150 °C

Anhydrous AlCl 3 was used to increase the reducing ability of sodium borohydride (NaBH 4) for removing oxygen functional groups on graphene oxide (GO) at a reaction temperature below 150 °C, which provided an extendable, mild, and controllable route for large-scale production of graphene. The influences of reducing temperature and reducing time on the electrical conductivity of reduced GO were examined. Structural evolution during the reduction of GO was studied by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, and elemental analysis.

Melatonin as a powerful bio-antioxidant for reduction of graphene oxide

Graphene is usually synthesized through deoxygenation of graphene oxide (GO) by hydrazine as the most common and one of the strongest reducing agents. But, due to the high toxicity of hydrazine, it is not a promising reductant in large-scale production of graphene. Here, for the first time, we used melatonin (MLT), as a powerful antioxidant and a biocompatible competitor of hydrazine in reduction of GO suspension. X-ray photoelectron spectroscopy (XPS), current–voltage and optical characteristics of the sheets indicated that the deoxygenation efficiency of the GO suspensions by MLT and under heating in an alkaline condition for 3 h was comparable with the efficiency obtained by hydrazine in similar conditions for 30 min. Based on the XPS analysis, although the amount of nitrogen detected on the surface of the MLT-reduced GO sheets was higher than that of the hydrazine-reduced ones, smaller C–N bonds were formed on the surface of the former. The higher amount of nitrogen on the MLT-reduced GO sheets was assigned to the π–π adsorption of the oxidized MLT molecules on the reduced sheets, which resulted in more stability of the MLT-reduced GO suspension than the aggregation observed in the hydrazine-reduced one, as also confirmed by Raman spectroscopy. A mechanism describing the chemical reduction of the GO sheets by MLT was also proposed. Our results open up a promising outlook for substitution of hydrazine by a safe, biocompatible and powerful reductant for efficient deoxygenation of GO, especially in large-scale production and bio-applications.

Large-scale production of graphene by microwave synthesis and rapid cooling

Graphene was prepared via carbonization of microwave synthesized metal phthalocyanine, followed by a rapid cooling process. The morphology and structure of the obtained graphene were controlled by the coolants.

Graphene Production With Stirred Media Mills

AbstractSince the discovery of stable graphene sheets by Novoselov und Geim in 2004 the one atom thick carbon material has been attracted great interest because of its outstanding physical, mechanical and chemical properties. Although there had been intensive research to find new ways in the preparation of single-layer graphene sheets in the last few years, especially the large-scale production of graphene still remains challenging. In this paper we present a new approach, which allows the high-yield production of graphene sheets in a simple stirred media milling process. Under mild milling conditions single- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a liquid medium. During the delamination procedure, the graphite particles were stressed between the milling beads. Shear and compressive normal forces can lead under mild milling conditions, i.e. low stress energies, to a continuous mechanical peeling of graphene sheets from the graphite surface. By means of Atomic Force Microscopy a high yield of single- and multilayer graphene sheets was detected. A concentration of exfoliated sheets of 2 wt% starting from a 5 wt% suspension of coarse graphite particles could be determined after a milling time of only 3 h. This concentration is much higher than those, which were reached by most of the known chemical methods. Since stirred media milling can be realized as large-scale process, a high-yield and low-cost production of graphene flakes becomes possible at ambient temperature.

Large-scale graphene production: Worm treatment

Large-scale graphene production: Worm treatment

Large-scale graphene production by RF-cCVD method

In this work, we report a low-cost facile method for the production of few-layer graphene sheets in large quantities through radio-frequency chemical vapor deposition.