Exfoliation Of Graphite Oxide Research Articles

Cytotoxicity of halogenated graphenes

Graphene and its family of derivatives possess unique and remarkable physicochemical properties which make them valuable materials for applications in many areas like electronics, energy storage and biomedicine. In response to the possibility of its large-scale manufacturing as commercial products in the future, an investigation was conducted to determine the cytotoxicity of one particular family of graphene derivatives, the halogenated graphenes, for the first time. Halogenated graphenes were prepared through thermal exfoliation of graphite oxide in gaseous chlorine, bromine or iodine atmospheres to yield chlorine- (TRGO-Cl), bromine- (TRGO-Br) and iodine-doped graphene (TRGO-I) respectively. 24 h exposure of human lung carcinoma epithelial cells (A549) to the three halogenated graphenes and subsequent cell viability assessments using methylthiazolyldiphenyl-tetrazolium bromide (MTT) and water-soluble tetrazolium salt (WST-8) assays revealed that all the halogenated graphenes examined are rather cytotoxic at the concentrations tested (3.125 μg mL(-1) to 200 μg mL(-1)) and the effects are dose-dependent, with TRGO-Cl reducing the cell viability to as low as 25.7% at the maximum concentration of 200 μg mL(-1). Their levels of cytotoxicity can be arranged in the order of TRGO-Cl > TRGO-Br > TRGO-I, and it is suggested that the amount of halogen present in the graphene material is the determining factor for the observed trend. Control experiments were carried out to test for possible nanomaterial-induced interference as a consequence of reaction between the halogenated graphenes and the viability markers (MTT/WST-8 reagent) or binding of the formazan products under cell-free conditions. The data obtained eliminate the probability of significant influence by these interferents as the change in the normalized percentage of formazan formed is relatively small and thorough washings were performed prior to the viability assessments to reduce the amount of halogenated graphenes that could eventually interact with the MTT/WST-8 assays. More studies need to be carried out in the future to complement the results obtained in this initial study in an attempt to develop a better understanding of the health hazards that the halogenated graphenes pose.

Calorimetric study of the low-temperature postradiation polymerization of tetrafluoroethylene in the presence of reduced graphite oxide

Low-temperature postradiation polymerization of tetrafluoroethylene in the presence of carbon material obtained by explosive exfoliation of graphite oxide has been studied by the technique of calorimetry. The process results in tetrafluoroethylene grafting onto modified graphite oxide to form a new composite containing ∼40–65% polytetrafluoroethylene.

Decoration of graphene with nickel nanoparticles: study of the interaction with hydrogen

Graphene obtained from thermal exfoliation of graphite oxide was chemically functionalized with nickel nanoparticles (NPs) without exposing the system to oxidizing agents. Its structural, physical and chemical properties have been studied by means of TEM, X-ray photoelectron and Raman spectroscopies, and SQuID magnetometry. The formation of 17 nm super-paramagnetic (SPM) monodispersed Ni NPs was observed. Nitrogen sorption experiments at 77 K yield a Brunauer–Emmet–Teller specific surface area (BET-SSA) of 505 m2 g−1 and helium adsorption at room temperature gives a skeletal density of 2.1 g cm−3. The interaction with atomic hydrogen was investigated by means of Muon Spin Relaxation (μSR) showing a considerable fraction of captured muonium (∼38%), indicative of strong hydrogen–graphene interactions. Hydrogen adsorption has been measured via pressure concentration isotherms demonstrating a maximum of 1.1 mass% of adsorbed hydrogen at 77 K and thus a 51% increased hydrogen adsorption compared to other common carbon based materials.

Carbon fragments are ripped off from graphite oxide sheets during their thermal reduction

The laser induced thermal exfoliation of graphite oxide with simultaneous TOF-MS analysis of exfoliation products was performed on graphite oxide.

Fluorographenes via thermal exfoliation of graphite oxide in SF6, SF4 and MoF6 atmospheres

Functionalization of graphene with heteroatoms is of paramount interest.

Effect of Microwave Irradiation on Exfoliation of Graphene Oxide

Graphene oxide has been synthesized by microwave-assisted exfoliation of graphite oxide prepared by modified Hummers method. Graphite was oxidized in a solution of <TEX>$H_2O_2$</TEX> and <TEX>$KMnO_4$</TEX> at <TEX>$65{\sim}80^{\circ}C$</TEX>, followed by 10 % <TEX>$H_2O_2$</TEX> solution treatment at <TEX>$80{\sim}90^{\circ}C$</TEX>. The graphite oxide was exfoliated under microwave irradiation of 1 kW and was reduced to graphene effectively by hydrazine hydrate (<TEX>$H_4N_2{\cdot}H_2O$</TEX>) treatment. The exfoliation of graphene oxide was significantly affected by the microwave irradiation on (heating)/off (cooling) period. An on/off period of 10 s/20 s resulted in much more effective exfoliation than that of 5 s/10 s with the same total treatment time of 10 min. This can be explained by the higher exfoliation temperature of 10 s/20 s. Repetition of the graphite oxidation and exfoliation processes also enhanced the exfoliation of graphene oxide. The thickness of the final graphene products was estimated to be several layers. The D band peaks of the Raman spectra of the final graphene products were quite low, suggesting a high crystal quality.

A comparative study of graphene materials formed by thermal exfoliation of graphite oxide and chlorine trifluoride-intercalated graphite

Graphene 3D materials GM1 and GM2 obtained by explosive exfoliation of graphite oxide and graphite intercalated with chlorine trifluoride, respectively, have been studied by elemental analysis, X-ray photoelectron spectroscopy, mass spectrometry, infrared and Raman spectroscopy, and scanning electron microscopy. The specific surface area, the pore size, and electrical conductivity of the materials have been measured. A comparative study has shown that the gas mixture produced during the preparation of GM1 is less hazardous than that in the case of GM2. However, GM2 exhibits a higher conductivity and a larger size of graphene crystallites. The feasibility of isolation of a suspension of graphene nanosheets from the test 3D materials has been demonstrated. Possible applications of these materials are discussed.

Grafting of self assembled polyaniline nanorods on reduced graphene oxide for nonlinear optical application

Polyaniline self assembled from nanorods synthesized by a novel inverse microemulsion polymerization technique, is covalently grafted to reduced graphene oxide layers. Amide linkages formed between polyaniline and reduced graphene oxide is confirmed with Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The formation mechanism of the cube-like nanostructures self assembled from nanorods, proposed is in good agreement with the experimental results. The cube-like morphology of polyaniline is disturbed during grafting due to the weakening of π–π stacking and H-bonding interactions between the nanorods by the introduction of graphene layers. Experimental results prove significant reduction and exfoliation of graphite oxide during grafting with polyaniline. At the same linear transmittance, the polyaniline–reduced graphene oxide hybrid (20cm/GW) shows increased nonlinear absorption coefficient compared to the individual components, namely polyaniline (9.5cm/GW) and graphite oxide (5.5cm/GW). The saturation intensity of the hybrid is also decreased considerably with respect to pristine polyaniline and GO. The hybrid with good nonlinear absorption coefficient and low limiting threshold opens up the way to use the material as a good optoelectronic material.

Cover Picture: Highly Hydrogenated Graphene through Microwave Exfoliation of Graphite Oxide in Hydrogen Plasma: Towards Electrochemical Applications (Chem. Eur. J. 46/2013)

Cover Picture: Highly Hydrogenated Graphene through Microwave Exfoliation of Graphite Oxide in Hydrogen Plasma: Towards Electrochemical Applications (Chem. Eur. J. 46/2013)

Boron-Doped Graphene: Scalable and Tunable p-Type Carrier Concentration Doping

Precisely engineered changes in Fermi levels of graphene-based materials are of high importance for their applications in electronic and electrochemical devices. Such applications include photoelectrochemical reactions or enhanced electrochemical performance toward reduction of oxygen. Here we describe a method for scalable and tunable boron doping of graphene via thermal exfoliation of graphite oxide in BF3 atmosphere at different temperatures. The temperature and atmospheric composition during exfoliation influences the kinetics of decomposition of the reactants and levels of doping, which range from 23 to 590 ppm. The resulting materials were characterized by prompt γ-ray analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning electron microscopy. Recent claims on enhanced catalytic properties of boron-doped graphenes toward the reduction of oxygen were addressed, as well as similar claims on enhanced capacitance.

Highly Hydrogenated Graphene through Microwave Exfoliation of Graphite Oxide in Hydrogen Plasma: Towards Electrochemical Applications

Hydrogenated graphenes exhibit a variety of properties with potential applications in devices, ranging from a tunable band gap to fluorescence, ferromagnetism, and the storage of hydrogen. We utilize a one-step microwave-irradiation process in hydrogen plasma to create highly hydrogenated graphene from graphite oxides. The procedure serves the dual purposes of deoxygenation and concurrent hydrogenation of the carbon backbone. The effectiveness of the hydrogenation process is investigated on three different graphite oxides (GOs), which are synthesized by using the Staudenmaier, Hofmann, and Hummers methods. A systematic characterization of our hydrogenated graphenes is performed using UV/Vis spectroscopy, SEM, AFM, Raman spectroscopy, FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), combustible elemental analysis, and electrical conductivity measurements. The highest hydrogenation extent is observed in hydrogenated graphene produced from the Hummers-method GO, with a hydrogen content of 19 atomic % in the final product. In terms of the removal of oxygen groups, microwave exfoliation yields graphenes with very similar oxygen contents despite differences in their parent GOs. In addition, we examine the prospective application of hydrogenated graphenes as electrochemical transducers through a cyclic voltammetry (CV) study. The highly hydrogenated graphenes exhibit fast heterogeneous electron-transfer rates, suggestive of their suitability for electrochemical applications in electrodes, supercapacitors, batteries, and sensors.

Fast and Efficient Removal of Cationic Dye Using Graphite Oxide, Adsorption, and Kinetics Studies

Dye adsorption on graphite oxides, which were prepared by different methods, was compared for the first time. The adsorption process was followed using ultraviolet-visible spectroscopy, while the adsorbents before and after adsorption were characterized using physicochemical and spectroscopic techniques. Surprisingly, we found that higher oxidation degree of graphite oxide resulted in higher adsorption efficiency for methylene blue (MB), while the ultrasonic exfoliation of graphite oxide impaired the adsorption efficiency. Among all samples investigated, graphite oxide prepared by modified Hummers' method (HmGO) before ultrasonic exfoliation exhibited the best adsorption capacity of MB. It is pretty high compared with other reported absorbents for MB. The experiment conditions such as pH, adsorbent dosage, stirring speed and adsorption time on adsorption of MB on graphite oxide, as well as adsorption kinetics and isotherms, were also investigated. The maximum adsorption capacity of graphite oxide is 751.9 mg · g−1 based on the Langmuir model. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Dispersion Science and Technology to view the free supplemental file.]

Spontaneous exfoliation of graphite oxide in polar aprotic solvents as the route to produce graphene oxide – organic solvents liquid crystals

It is highly desirable for many applications including liquid crystal formation to have non-aqueous dispersion of graphene oxide (GO). Here, we report our findings on spontaneous exfoliation of graphite oxide flakes into GO in the general class of polar aprotic solvents, which similar to water, induce chemical transformations in GO. We further proposed solvent exchange method as a complementary step to widen the range of organic dispersing media for GO. Having dispersions of very large GO particles results in lyotropic nematic liquid crystalline phases formation for all those solvents at very low GO concentration (typically 0.1wt%). Suspensions with liquid crystalline phases of GO, provide a basis for fabrication of highly ordered and conductive graphene-based composite materials. For a polymer–graphene composite with layered structure, an exceptionally high electrical conductivity (1050Sm−1) is obtained using liquid crystalline GO dispersion in the polymer solution.

Low-temperature radiation polymerization of tetrafluoroethylene in the presence of the carbon material obtained by explosive exfoliation of graphite oxide

Low-temperature radiation polymerization of tetrafluoroethylene in the presence of the carbon material obtained by explosive exfoliation of graphite oxide

Precise Tuning of Surface Composition and Electron‐Transfer Properties of Graphene Oxide Films through Electroreduction

Graphene materials are generally prepared from the exfoliation of graphite oxide (GO) to graphene oxide, followed by subsequent chemical or thermal reduction. These methods, although efficient in removing most of the oxygen functionalities from the GO material, lack control over the extent of the reduction process. We demonstrate here an electrochemical reduction procedure that not only allows for precise control of the reduction process to obtain a graphene material with a well-defined C/O ratio in the range of 3 to 10, but also one that is able to tune the electrocatalytic properties of the reduced material. A method that is able to precisely control the amount and density of the oxygen functionalities on the graphene material as well as its electrochemical behaviour is very important for several applications such as electronics, bio-composites and electrochemical devices.

Thermal Stability of Polymers Confined in Graphite Oxide

In this study, polymer–graphite oxide (GO) interactions are demonstrated to induce thermal instability in both the polymer and GO phase in conditions of maximum polymer uptake, in which the polymer chains are either intercalated into the GO interlayer or adsorbed on the GO sheets. We investigate the thermal stability of poly(ethylene oxide) (PEO) intercalated in GO (PEO/GO) in detail, using a combination of techniques including X-ray diffraction (XRD), thermogravimetry (TGA) and TGA–mass spectroscopy (TGA–MS) in dynamic (nonisothermal) and static (isothermal) modes. Our results show that intercalated PEO decomposes at 160 °C lower than neat PEO, and that GO decomposes at 50 °C lower than pristine GO, due to a synergistic instability between GO and intercalated PEO upon heating. Other hydrophilic polymers—such as poly(vinyl methyl ether) (PVME), poly(vinyl alcohol) (PAA), poly(vinylpyrrolidone) (PVP) and poly(acrylic acid) (PAA)—forming polymer-adsorbed GO structures are also observed to decompose at noticeably lower temperatures than either pristine GO or their own corresponding neat polymers. Unlike PEO/GO intercalation compounds, the excess of PEO phase in PEO–GO composites decomposes at temperatures close to that of neat PEO, which demonstrates that those polymer chains far from the adsorbing GO surface are not significantly affected by the presence of GO sheets. Furthermore, isothermal TGA data for PEO/GO intercalation compounds with PEO chains from 5 to 2135 monomeric units are well described by an autocatalytic model similar to that we found for pristine GO in a previous study, which suggests that the overall decomposition of PEO/GO is dominated by the reduction and exfoliation of GO. However, when PEO is adsorbed on graphene substrate, which is thermally stable at the studied temperatures, the kinetic mechanisms follow a first-order reaction similar to neat PEO, but the decomposition occurs with a considerably lower activation energy.

Preparation and Characterization of Reduced Graphene Oxide Sheets via Water-Based Exfoliation and Reduction Methods

This research studied the synthesis of graphene oxide and graphene via a low-cost manufacturing method. The process started with the chemical oxidation of commercial graphite powder into graphite oxide by modified Hummer’s method, followed by the exfoliation of graphite oxide in distilled water using the ultrasound frequency from a laboratory ultrasonic bath. Finally, the oxygen functional groups on exfoliated graphite oxide or graphene oxide were eliminated by stirring in hot distilled water at 95°C, as a replacement for highly toxic and dangerously unstable hydrazine. The results assured that stirring in hot distilled water could give the product of graphene or reduced graphene oxide. The samples were characterized by FTIR, XRD, TGA, Raman spectroscopy, SEM, and TEM methods.

Boron and nitrogen doping of graphene via thermal exfoliation of graphite oxide in a BF3 or NH3 atmosphere: contrasting properties

The fabrication of graphenes doped with electron withdrawing/donating elements can be realized through the synthesis procedures reported in this paper. Doping of the graphenes occurs during the thermal exfoliation step of graphite oxide in the presence of the dopant containing gas (BF3 or NH3). The materials are extensively characterized by high-resolution X-ray photoelectron spectroscopy, prompt gamma-ray activation analysis and Raman spectroscopy. Their electrical and electrochemical properties related to heterogeneous electron transfer rates and oxygen reductions are investigated. The doped materials display significant differences in their electronic properties where graphenes doped by electron donating dopants exhibit the largest conductivity as compared to those doped by electron accepting dopants. The scalable method reported here is able to successfully implant B and N into the graphene lattice and hence presented important future implications for the production of these materials on an industrial scale.

Thermally reduced graphene: synthesis, characterization and dye removal applications

Since its recent discovery, graphene has emerged as a promising material for a variety of applications. In this article, thermally reduced graphene (TRG) was produced by thermal exfoliation of graphite oxide; characterized using XRD, SEM, TEM, FTIR, XPS, BET, and elemental analysis; and used as an adsorbent to remove methyl orange (MO) dye from aqueous solution. Langmuir and Freundlich isotherm models are used to examine the nature of the adsorption process and the results indicate that MO adsorption on TRG can be described as monolayer type (Langmuir) adsorption. Moreover, the adsorption process is physical, spontaneous, and follows a second order kinetics as revealed by the analysis of the thermodynamic and kinetic data. Furthermore, the sorption capacity and the removal percentage strongly depend on the adsorbent-to-dye ratio, the solution pH and temperature. The current study indicates that graphene could be a very efficient adsorbent for removal of MO dye from colored-waters with a maximum sorption capacity of 100 mg of dye per g of TRG and a removal percentage of 98%. In addition, more than 80% of the adsorbed dye can be recovered and TRG can be regenerated and reused with no significant change in its sorption capacity.

Potassium assisted reduction and doping of graphene oxides: towards faster electron transfer kinetics

The current scientific interest and fervour in graphene research is fuelled by their potential uses in a variety of fields such as energy storage, electrochemical and biomolecule sensing applications. In particular, many of these require the bulk production of graphene materials, using approaches such as the oxidation of graphite to graphite oxide with chlorate or manganate oxidants in the presence of strong acids. This is followed by its reduction via thermal exfoliation, or through chemical and electrochemical reduction methods. Elemental potassium is a very strong reducing agent with a chemical potential of ca. E = −2.93 V versus the standard hydrogen electrode. Therefore, in this paper we evaluate the effects of the presence of elemental potassium as a strong reductant during the thermal exfoliation of graphite oxides. We employ both the Hofmann (concentrated sulfuric and nitric acids with KClO4) and Hummers (concentrated sulfuric acid with NaNO3 and KMnO4) methods of graphite oxidation, followed by their thermal reduction at 500 °C both in the absence and presence of elemental potassium. Collectively, these treatments invariably result in differences in morphologies, defect densities and the quantities of oxygen-containing groups within these materials, thus affecting their heterogeneous electron transfer rates and electrochemistry. Extensive analyses with scanning electron microscopy (SEM), Raman spectroscopy, high resolution X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), BET surface area analysis, combustible elemental analysis and cyclic voltammetry (CV) are performed to elucidate the different properties and characteristics of our materials. We observed that the elemental potassium-assisted thermal reduction of graphene oxide led to a product with increased heterogeneous electron transfer rates towards the Fe(CN)64−/3− redox probe, despite having more oxygen-containing groups. This is in contrast to prior reports where larger amounts of oxygen groups corresponded to poorer electrochemistry. There were also no significant differences in the density of sp3 defects between the graphene materials. Hence, this improved electrochemistry may be attributed to the formation of stable complexes between potassium and oxygen groups on the graphene surface in a manner we propose to be similar to carboxylic acid salts. These results would therefore have important implications in our understanding of oxygen-containing groups in graphene materials and their influence on their inherent electrochemistry.