Exfoliation Of Graphite Oxide Research Articles

Strategies for the Synthesis of Graphene, Graphene Nanoribbons, Nanoscrolls and Related Materials

Single-layer graphene (SLG), the 3.4 Å thick two-dimensional sheet of sp(2) carbon atoms, was first prepared in 2004 by mechanical exfoliation of graphite crystals using the scotch tape technique. Since then, SLG has been prepared by other physical methods such as laser irradiation or ultrasonication of graphite in liquid media. Chemical methods of synthesis of SLG are more commonly used; the most popular involves preparation of single-layer graphene oxide followed by reduction with a stable reagent, often assisted by microwave heating. This method yields single-layer reduced graphene oxide. Other methods for preparing SLG include chemical vapour deposition over surfaces of transition metals such as Ni and Cu. Large-area SLG has also been prepared by epitaxial growth over SiC. Few-layer graphene (FLG) is prepared by several methods; arc discharge of graphite in hydrogen atmosphere being the most convenient. Several other methods for preparing FLG include exfoliation of graphite oxide by rapid heating, ultrasonication or laser irradiation of graphite in liquid media, reduction of few-layer graphene oxide, alkali metal intercalation followed by exfoliation. Graphene nanoribbons, which are rectangular strips of graphene, are best prepared by the unzipping of carbon nanotubes by chemical oxidation or laser irradiation. Many graphene analogues of inorganic materials such as MoS(2), MoSe(2) and BN have been prepared by mechanical exfoliation, ultrasonication and by chemical methods involving high-temperature or hydrothermal reactions and intercalation of alkali metals followed by exfoliation. Scrolls of graphene are prepared by potassium intercalation in graphite or by microwave irradiation of graphite immersed in liquid nitrogen.

Ionic liquid-assisted exfoliation of graphite oxide for simultaneous reduction and functionalization to graphenes with improved properties

A novel one-step approach for the pH-triggered electrochemically interacted exfoliation of graphene sheets in graphite oxide and simultaneous reduction and functionalization with the aid of the ionic liquid is reported. The developed method shows significant advantages over the conventional functionalized/chemically reduced graphene. Particularly, for the first time, no additional stabilizer or modifier is needed to stabilize the resulting processible graphene dispersion. The prepared graphene oxide and its functionalized graphene are characterized by SEM, TEM, FTIR, UV-vis, XRD, Raman, XPS, and NMR. The results indicate that, with the aid of the IL during the reaction, the resulting functionalized graphene shows improved organophilicity, good wettability and improved interfacial interactions as well as significant resistance to thermal degradation. The methodology paves a new way for use of the IL as a processing aid and reaction medium to promote chemical functionalization of graphene through the electrochemically interacted exfoliation of graphene sheets and can be expected to provide a new approach with great promise for its organophilic wettability and enhanced interfacial adhesion as well as improved thermal stability. Furthermore, the controlled modifications of graphene nanoreinforcements can also be expected to alter the nature of the interactions between components.

Ultrahigh arsenic sorption using iron oxide-graphene nanocomposite supercapacitor assembly

In response to the increasing water demand, electro-sorption method has shown promise in context of high removal efficiency of metals with less energy consumption. Here, we report for the first time ultrahigh sorption capacity of iron oxide-graphene (Fe3O4-HEG) nanocomposite supercapacitor assembly for both inorganic arsenic species (arsenate and arsenite). Graphene has been synthesized by hydrogen induced exfoliation of graphitic oxide and decorated with iron oxide (Fe3O4) nanocrystals by chemical route. Electrochemical sorption behavior of nanocomposite electrodes for arsenic has been examined by cyclic voltammetry and kinetic studies. Adsorption isotherm models have been tested to calculate the maximum adsorption capacities (using Langmuir isotherm) for arsenate and arsenite and found to be nearly 172.1 and 180.3 mg/g, respectively, using supercapacitor assembly. These values are higher than other adsorbents for arsenic.

Oil spill cleanup using graphene

In this article, we study the use of thermally reduced graphene (TRG) for oil spill cleanup. TRG was synthesized by thermal exfoliation of graphite oxide and characterized by X-ray diffusion, Raman spectroscopy, SEM, TEM, elemental analysis, and Brunauer-Emmett-Teller (BET) surface area measurement. Various aspects of the sorption process have been studied including the sorption capacity, the recovery of the adsorbed oil, and the recyclability of TRG. Our results shows that TRG has a higher sorption capacity than any other carbon-based sorbents, with sorption capacity as high as 131 g of oil per gram TRG. With recovery of the sorbed oil via filtration and reuse of TRG for up to six cycles, 1 g of TRG collectively removes approximately 300 g of crude oil. Moreover, the effects of TRG bulk density, pore volume, and carbon/oxygen ratio and the oil viscosity on the sorption process are also discussed.

Effect of synthesis method on solvation and exfoliation of graphite oxide

Graphite oxides (GOs) synthesized by Brodie’s and Hummers’ methods are significantly different with respect to hydration, solvation and exfoliation properties. Hummers GO is more easily intercalated by liquid water and alcohols, exhibiting osmotic type of swelling. In contrast, Brodie GO shows crystalline swelling in alcohol solvents with step-like insertion of methanol or ethanol monolayers. However, the stronger hydration and easier dispersion in water observed for Hummers GO do not correlate with better dispersion of graphene powder obtained by thermal exfoliation. Higher surface area graphene powder was obtained by exfoliation of Brodie GO, while the temperature of its exfoliation is about 75°C higher than that for the studied sample of Hummers GO. It is suggested that higher exfoliation temperature and better crystallinity of GO are important factors for preparation of graphene powder using thermal exfoliation.

X-ray diffraction characterization of polymer intercalated graphite oxide

Graphite oxide (GO) is generated by treating graphite with strong oxidizers. GO retains the structure of graphite, but does so with a larger and irregular basal plane spacing. The oxidation of graphite results in the formation of epoxide groups, as well as C–OH and COOH groups. It is the presence of some of these moieties that allows GO to be dispersed in water, allowing for its use in waterborne formulations. Although GO does not possess the electrical properties of single-sheet graphene, it can be swelled in water, which allows for intercalation of hydrophilic polymer between GO sheets, resulting in a composite that can be coated to produce a continuous film. After coating it may be possible to chemically convert GO to a reduced graphite oxide (r-GO) with improved electrical conductivity. X-ray diffraction (XRD) is ideally suited to evaluate GO–polymer composite samples for evidence of intercalation or exfoliation of GO. Examples of GO–polymer analysis by XRD are presented, along with results that demonstrate the effect of relative humidity (RH) on neat GO. Knowing the ambient RH during XRD data collection was found to be important to correctly assess the extent of polymer intercalation within the GO lattice.

Impact of Ionic Liquids on the Exfoliation of Graphite Oxide

The fabrication of high performance, graphene-based electrochemical energy storage devices, such as ultracapacitors, depends on the reduction of graphite oxide (GO) and its interaction with ionic liquids (ILs), which may be used as the conductive electrolyte. To explore the physical and chemical interactions between ILs and thermally reduced GO (TRG) as a function of annealing temperature, three ILs with ammonium based structures were selected to differentiate the role of their anions and cations in the exfoliation process. Intercalation was accompanied by either covalent or noncovalent bonding, as supported by thermogravimetric analysis (TGA) and infrared (IR) absorption spectroscopy performed in situ during thermal annealing and by X-ray diffraction (XRD) analysis. Upon IL intercalation, covalent bonding between the IL and TRG prevented exfoliation, while noncovalently physisorbed ILs were readily removed and therefore facilitated exfoliation of the reduced GO. The anion and cation moieties of the ILs in GO–IL intercalation compounds investigated were found to affect the decomposition temperature as well as the degree of thermal stabilization. Indeed, the ammonium-based cations bearing long alkyl carbon chains did not functionalize the TRG and therefore promoted both sheet expansion and thermal exfoliation. The solvent-dependency of these properties was also investigated by forming GO–IL intercalation compounds from both deionized (DI) water and propylene carbonate (PC). In contrast to DI water, PC was found to decrease the thermal decomposition temperature of GO by about 100 °C in the presence of intercalated ILs, thus enabling highly efficient oxygen removal in GO–IL intercalation compounds.

Microwave absorbing properties of a thermally reduced graphene oxide/nitrile butadiene rubber composite

Reduced graphene oxide (RGO) with a layered and porous structure was synthesized by thermal exfoliation of graphite oxide. Synthesized RGO is very light weight and flaky. The formation of RGO was studied using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and scanning electron microscopy. Composites were prepared by dispersing 2%, 4% and 10% by weight of the synthesized RGO into nitrile butadiene rubber (NBR) matrix. Microwave absorption properties of RGO/NBR composites were investigated by measuring their complex permittivity and permeability by using waveguide method. Simulation studies show that 10wt.% of graphene oxide in NBR matrix exhibits high values of reflection loss (>10dB) over a wide frequency range 7.5–12GHz and maximum loss is 57dB at 9.6GHz at a thickness of 3mm.

Simultaneous reduction, exfoliation and functionalization of graphite oxide into a graphene-platinum nanoparticle hybrid for methanol oxidation

We developed a single step thermal method to synthesize platinum nanoparticle functionalized graphene sheets (Pt-G) through the thermal treatment of graphite oxide (GO) with platinum acetylacetonate (Pt(acac)2). The loading concentration of platinum nanoparticles (Pt NPs) on graphene is about 22.3 wt%. We investigate the Pt NP functionalization and the reduction effects of GO by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis and Raman spectroscopy. The results lead to insights into the formation of Pt-G starting from GO upon increasing the temperature. XPS and XRD analysis confirm that the platinum nanoparticle deposition is accompanied by the reduction and exfoliation of GO. Electrochemical studies reveal that Pt-G shows excellent activity and stability towards the methanol oxidation reaction.

A facile strategy to prepare functionalized graphene via intercalation, grafting and self-exfoliation of graphite oxide

A facile method of successive intercalation, grafting and exfoliation of graphite oxide in monomers by γ-ray irradiation to obtain functionalized graphene nanosheets was reported. The monolayer percentage of functionalized graphene nanosheets was sharply increased and the agglomeration showed a significant decrease.

Graphene and graphene/polymer nanocomposites

the graphite by Geim and Novoselov group in 2004, graphene triggered a gold rush for exploiting its possible applications. A search with graphene as a key word using the SciFinder shows even a tremendous increase of publication from 3900 (2010) to 9500 (2011) as they were awarded the novel prize in physics in 2010. Graphene is a one-atom thick, two-dimensional sheet composed of sp2 hybridized carbon atoms arranged in a honeycomb structure. It has combined benefits of layered silicates and carbon nanotubes, and is considered as the most promising reinforcing and functional filler of polymers. Large area graphene is typically produced by bottom-up method such as chemical vapor deposition while flake type by top-down method consisting of oxidation of graphite, exfoliation of graphite oxide (GO) by sonication in liquid media, and reduction. Rapid thermal expansion of GO in inert atmosphere gives thermal exfoliation and reduction simultaneously and is suited for economical, large scale production without using any dispersion media. The oxygen groups on the surface remaining upon reduction of GO enable dispersion in solvent and water and provide sites for chemical functionalization which allows covalent bonding with reactive polymer function (Advanced Materials, DOI: 10.1002/adma.201102036). For example, polyure thanes (PUs) are readily blended with graphene, and hydroxyl functions of graphene react with isocyanate termini of PU to form graphene/PU chemical hybrids. It is vital to control the type and amount of reactive sites on the graphene surface and edges. Markets for graphene are opened for i) energy saving electrodes as secondary cells for smartphone, notebook, electric car and solar cell, ii) transparent electrodes for flat panel (LCD, OLED) and touch screen, and iii) semiconductors. If graphene thin layer is properly deposited on glass or polymer surfaces, flexible displays, thin film transistors, and photovoltaic and LCD devices will be made possible (Macromolecules, DOI: 10.1021/ma100572e). Graphene can be used as functional reinforcement for polymer to include packaging, gasketing, automotive, aircraft, ink, painting, sensor etc. When graphene is doped to PU, electrically and infrared light triggered shape memory material is synthesized where graphene provides crosslinks, strain energy storage and light absorption. However, low cost and large production of graphene will only expedite its applications. Otherwise, ‘It is a dream. The prospect is so far beyond the horizon that we cannot even assess it properly’, as Geim says.

Individual graphene oxide platelets through direct molecular exfoliation with globular amphiphilic hyperbranched polymers

In this study, we used a solution process, involving direct molecular exfoliation of graphite oxide (GO) stacked layers, to obtain individual graphene oxide platelets (GOPs) through amphiphilic hyperbranched polymers (HPs). The HPs, based on poly(amic acid) and polyimide with terminal amino functionalities, were obtained through a facile “A2 + B3” synthesis; gel permeation chromatography of the HPs revealed molecular weights of 5000–8200 g mol−1 with a distribution of polydispersity between 2.0 and 4.2. Next, we inserted these globular HPs into the interlayer spaces of GO to prepare a series of GO/HP nanohybrids possessing intercalated and exfoliated morphologies. The intercalation processes featured a critical transition point at which a dramatic enlargement occurred to the interlayer spacing, depending on the content of the bulky embedded HPs. From transmission electron microscopy images, we observed transparent folding of the GOPs; powder X-ray diffraction analysis revealed individual nanosheets with well-defined diffraction patterns. Incorporating the bulky three-dimensional globular structure into the layered GO significantly influenced the solution exfoliation, allowing us to examine the intercalating behavior of GO intergallery. This solution-phase methodology, through direct HP molecular exfoliation, provides the way toward obtaining individual nanosheets, opening up opportunities for platelet-like nanographene oxide materials in many technological applications.

Synthesis of graphene-multiwalled carbon nanotubes hybrid nanostructure by strengthened electrostatic interaction and its lithium ion battery application

We report a novel way of synthesizing graphene-carbon nanotube hybrid nanostructure as an anode for lithium (Li) ion batteries. For this, graphene was prepared by the solar exfoliation of graphite oxide, while multiwalled carbon nanotubes (MWNTs) were prepared by the chemical vapor deposition method. The graphene–MWNT hybrid nanostructure was synthesized by first modifying graphene surface using a cationic polyelectrolyte and MWNT surface with acid functionalization. The hybrid structure was obtained by homogeneous mixing of chemically modified graphene and MWNT constituents. This hybrid nanostructure exhibits higher specific capacity and cyclic stability. The strengthened electrostatic interaction between the positively charged surface of graphene sheets and the negatively charged surface of MWNTs prevents the restacking of graphene sheets that provides a highly accessible area and short diffusion path length for Li-ions. The higher electrical conductivity of MWNTs promotes an easier movement of the electrons within the electrode. The present synthesis scheme recommends a new pathway for large-scale production of novel hybrid carbon nanomaterials for energy storage applications and underlines the importance of preparation routes followed for synthesizing nanomaterials.

Influence of parent graphite particle size on the electrochemistry of thermally reduced graphene oxide

Electrochemical applications of graphene are of very high importance. For electrochemistry, bulk quantities of materials are needed. The most common preparation of bulk quantities of graphene materials is based on oxidation of graphite to graphite oxide and subsequent thermal exfoliation of graphite oxide to thermally reduced graphene oxide (TR-GO). It is important to investigate to which extent a reaction condition, that is, composition of the oxidation mixture and size of graphite materials, influences the properties of the resulting materials. We characterised six graphite materials with a range of particle sizes (0.05, 11, 20, 32, 35 and 41 μm) and the TR-GO products prepared from them by use of scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetric performance of the TR-GO samples was compared using ferro/ferricyanide and ascorbic acid. We observed no correlation between size of initial graphite and properties of the resultant TR-GO such as density of surface defects, amount of oxygen-containing groups, or rate of heterogeneous electron transfer (HET). A positive correspondence between HET rate and high defect density as well as low amounts of oxygen functionalities was noted. Our findings will have profound influence upon practical fabrication of graphene for applications in sensing and energy storage devices.

Nanostructured polyaniline decorated graphene sheets for reversible CO2 capture

The current scientific community is extensively involved in developing novel materials for energy and environmental applications. Capture of CO2 to remove it from the atmosphere is one of the most important applications among them. In the present work, we have demonstrated for the first time, to the best of our knowledge, a polyaniline–graphene nanocomposite as a CO2 capture candidate. Graphene was prepared by hydrogen induced thermal exfoliation of graphite oxide and was further coated with polyaniline using a chemical method. The nanocomposite was characterized by different techniques and the capture capacity was measured using a high pressure Sievert’s apparatus. FTIR spectroscopy was used to confirm the possible CO2 capture mechanism in the nanocomposite. CO2 adsorption capacities at a pressure of 11 bar and different temperatures of 25, 50 and 100 °C were experimentally found to be 75, 47 and 31 mmol g−1, respectively. This nanocomposite shows much higher CO2 capture capacity compared to pure graphene and shows a high degree of recyclability.

High-pressure hydrogenation of graphene: towards graphane

The conversion of graphene to graphane is of high importance from a technological and scientific point of view. We present here a scalable method for the hydrogenation of graphene based on thermal exfoliation of graphite oxide in a hydrogen atmosphere under high pressure (60-150 bar) and temperature (200-500 °C). This method does not require a plasma source and is able to produce gram quantities of the material. The properties of the resultant hydrogenated graphene were studied by scanning and transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy and combustible elemental analysis techniques. Sheet and specific resistance of the graphene and hydrogenated graphene were measured. This scalable synthesis method has great potential to serve as a pathway towards the mass production of graphane.

Graphene-Based Engine Oil Nanofluids for Tribological Applications

Ultrathin graphene (UG) has been prepared by exfoliation of graphite oxide by a novel technique based on focused solar radiation. Graphene based engine oil nanofluids have been prepared and their frictional characteristics (FC), antiwear (AW), and extreme pressure (EP) properties have been evaluated. The improvement in FC, AW, and EP properties of nanofluids is respectively by 80, 33, and 40% compared with base oil. The enhancement can be attributed to the nanobearing mechanism of graphene in engine oil and ultimate mechanical strength of graphene.

Hydrogen storage in graphene decorated with Pd and Pt nano-particles using an electroless deposition technique

Graphene samples prepared by the exfoliation of graphitic oxide were decorated with platinum (Pt) and palladium (Pd) by an electroless deposition technique. The obtained composites were attempted to be used as hydrogen storage materials. The composites were characterized by transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The porous texture of all graphenes was analyzed using nitrogen adsorption isotherms at 77 K. The hydrogen adsorption was accurately measured by a volumetric adsorption apparatus at 303 K up to 5.7 MPa. The mesopores that originated from the space between exfoliated graphene sheets were observed by nitrogen adsorption isotherms on all graphene samples. Structure investigations reveal that specific surface areas apparently decrease after Pd or Pt decoration. The Pt and Pd nanoparticles of 2–5 nm diameter homogeneously dispersed on the exfoliated graphene sheets and voids of graphene sheets. Experimental results show that Pd or Pt decoration doubles the hydrogen capacity supporting the existence of the hydrogen spillover effect in Pd- or Pt-graphene systems.

Carbon dioxide adsorption in graphene sheets

Control over the CO2 emission via automobiles and industrial exhaust in atmosphere, is one of the major concerns to render environmental friendly milieu. Adsorption can be considered to be one of the more promising methods, offering potential energy savings compared to absorbent systems. Different carbon nanostructures (activated carbon and carbon nanotubes) have attracted attention as CO2 adsorbents due to their unique surface morphology. In the present work, we have demonstrated the CO2 adsorption capacity of graphene, prepared via hydrogen induced exfoliation of graphitic oxide at moderate temperatures. The CO2 adsorption study was performed using high pressure Sieverts apparatus and capacity was calculated by gas equation using van der Waals corrections. Physical adsorption of CO2 molecules in graphene was confirmed by FTIR study. Synthesis of graphene sheets via hydrogen exfoliation is possible at large scale and lower cost and higher adsorption capacity of as prepared graphene compared to other carbon nanostructures suggests its possible use as CO2 adsorbent for industrial application. Maximum adsorption capacity of 21.6 mmole/g was observed at 11 bar pressure and room temperature (25 ºC).

Wrinkled Graphenes: A Study on the Effects of Synthesis Parameters on Exfoliation-Reduction of Graphite Oxide

In the present work, we have systematically investigated the effect of different exfoliation conditions on the synthesis of graphene from graphite oxide (GO). Four different conditions were used to exfoliate GO: Ar @ 1050 °C, vacuum @ 200 °C, H2 + Ar mixture @ 200 °C, and H2 @ 200 °C. Few layered graphenes obtained by these methods were characterized by thermogravimetry, diffractometry, spectroscopy, microscopy, surface, and elemental analysis techniques. New insights obtained upon a detailed analysis of these are presented. Although the morphology and characteristics of these graphenes are similar, differences are observed in the amount of functional groups present, resulting in considerable change in their electrical properties. These results show conclusively that the atmosphere for exfoliation of GO plays a critical role in low temperature syntheses of graphene. It is observed that exfoliation-reduction of GO in pure hydrogen atmosphere at 200 °C results in the highest quality of a few layered graphen...