Search

The work reports a study of the processes of multilayer graphene (MLG) preparation using the action of microwave (MW) radiation on polyfluoridedicarbon intercalation compounds with general composition C2F·xR (R is chlorine trifluoride, acetone, acetonitrile, carbon tetrachloride, and benzene). Under the action of MW heating, these intercalation compounds undergo exfoliation (splitting) at temperature values that are 40–55% lower than in the case of traditional convective heating. It is shown that microwave heating increases the exfoliation degree and specific surface area of fluorinated graphite and decreases residual content of fluorine and chlorine in MLG. A key role in the process of MW exfoliation is due to the absorption of MW radiation by the polar dielectric intercalated into the interlayer space of fluorinated graphite.

In this paper we present an experimental study of the electron transport in composite samples based on an insulating matrix of polybenzimidazole with graphite nanoparticles as conducting filler. Based on a qualitative analysis of the temperature dependences of electrical resistance obtained for the samples with different filler concentrations, it was established that the electron transport occurred mostly by tunneling between conducting filler particles, with variable-range hopping conduction taking place at low temperatures.

The interlayer space of 2D materials can be a slit reactor where transformations not typical for the gas phase occur. We report redox reactions involving acetonitrile and nitrogen oxide guests in galleries of fluorinated graphite. Fluorinated graphite intercalation compounds with acetonitrile are treated with dinitrogen tetraoxide and the synthesis products are studied by a set of experimental methods. Data analysis reveals that N2O4 dissociates in fluorinated graphite matrices to form nitrogen-containing species NO3, NO2, NO, and N2. The interaction of NO3 with acetonitrile yields HNO3, which predominates as a guest in the synthesis products independently of the fluorination degree of the matrix. This reaction is accompanied by the removal of fluorine atoms weakly bonded to the graphite layers, leading to partial defluorination of the matrices. Our work demonstrates the possibility of using fluorinated graphite as a test nanoreactor whose dimension can be controlled by fluorination of the layers.

Microwave (MW) irradiation is often used in preparation of nanomaterials. Here, we investigate MW exfoliation patterns of intercalated fluorinated graphite (C2F) depending on the nature of the "guest". The resulting highly exfoliated graphites (multi-layer graphenes) show advantageous characteristics, as compared to the products of convective heating.

Highly concentrated dispersions of few-layer graphene stabilized by amphiphilic block copolymer Pluronic F-108 are obtained. According to transmission electron and atomic force microscopy, the thickness of the graphene particles is on average from one to ten layers and their lateral sizes vary from 150 nm to 1 μm. Using these dispersions, new chitosan-based film composites with the filler content up to 5 wt % are obtained; the electrical conductivity of these composites reaches 4.3 × 10–1 S/cm.

New composite materials based on polylactide and graphene, suitable for creating three-dimensional objects using the 3D printing technology, were prepared. Introduction of the nanoadditive into the matrix of the biodegradable polymer enhances the tensile strength of the materials by more than 57%. In addition, the composites exhibit high electrical conductivity, reaching 0.9 S cm–1 for the composite with 3 wt % filler, which determines the possibility of using them for the development of various electrotechnical devices and tissue engineering structures.

We studied the usefulness of dispersions of gold nanoparticles (Au-NPs) stabilized by abietic acid for manufacturing films on glass and silicon substrates and composites with nanosized and powder materials exemplified by SiO2 and TiO2 NPs, expanded graphite (EG), carbon nanotubes (CNTs), a porous carbon material (PCM), PCM containing 6% nitrogen, and CeO2 powder.

Highly concentrated dispersions of polyvinylpyrrolidone-stabilized graphene were prepared. Using transmission electron microscopy, it was found that the graphene particles consisted, on average, of one to four layers, with the lateral size of 50–400 nm. From these dispersions, new film composites of chitosan with the filler content up to 4 wt % characteristic of electrical conductivity as high as 1.9 × 10–2 S/cm were formed.

It presented a comparative consideration of General Motors long-term activities on the current subject of fuel-cell-powered electric vehicles vs Toyota Mirai recent results, relevant to prospects on more efficient and safe technologies of the hydrogen on-board storage. It also presented a call on the project International cooperation. The main aim of this paper is to attract attention of General Motors, Toyota and/or other large car companies to a real possibility of developing and using, in the nearest future, of the break-through hydrogen on-board storage technology based on the solid H2 intercalation into graphite nanostructures.

New composite materials of collagen with electrical conductivity up to 6.1•10–4 S cm–1 were obtained using colloidal dispersions of polyvinylpyrrolidone-stabilized graphene.

New three-dimensional grids based on graphene oxide and 3,3’,4,4’-tetraaminodiphenyl oxide were obtained using a one-step hydrothermal synthesis. The formation of benzimidazole rings was confirmed by IR spectroscopy and elemental analysis, and the nitrogen content was 13.8 wt%. Because of the redox activity of benzimidazole rings, the specific capacitance was 330 F g–1 at a scan rate of 2 mV s–1.

N-doped graphene based on graphene oxide and 3,3′,4,4′-tetraaminodiphenyl oxide (TADPO) was obtained using a one-step hydrothermal process. The resulting materials were fully characterized using elemental analysis, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron micrographs, and transmission electron microscopy. The findings reveal that benzimidazole rings were formed during the reaction, and the mass content of nitrogen in the obtained material varied from 12.3% to 14.7%, depending on the initial concentration of TADPO. Owing to the redox activity of benzimidazole rings, the new N-doped graphene materials demonstrated a high specific capacitance, reaching 340 F g−1 at 0.1 A g−1, which was significantly higher than that of the sample of reduced graphene oxide obtained under similar conditions without the use of TADPO (169 F g−1 at 0.1 A g−1). The resulting material also exhibited good cyclic stability after 5000 cycles.

Results are given of measurements of X-ray and neutron diffraction, small-angle neutron scattering, and field dependences of the magnetization for nanocomposites formed by multilayer graphene and iron particles. Four samples have been investigated that differed in the content of Fe as follows: 0.75, 30, 45, and 70 wt %. The calculations of the X-ray diffraction and neutron diffraction patterns show that the size of graphene particles is about 4 nm, and the size of the iron domains of coherent scattering is no less than 50 nm. The content of the Fe particles in the composites has been estimated based on the data of the measurements of neutron diffraction, small-angle neutron scattering, and magnetization. The values of the iron concentration obtained by different methods differ quite significantly. The difference is caused by the specific character of the methods of measurements.

The paper reports experimental study of piezoresistive effect in composite films based on polybenzimidazole with few-layered graphene nanoparticles filler. Colloidal dispersions of few-layered graphene (FLG) were obtained by ultrasonic treatment of synthesized FLG in the solution of poly[2,2′-(p-oxydiphenylen)-5,52′-bisbenzimidazole] (OPBI) in N-methyl-2-pyrrolidone (NMP). Electroconductive films were formed from the dispersions by flow coating. To investigate dependence of electrical resistance on mechanical strain strips of the films were bonded onto beams of uniform strength (in bending) with cyanoacrylate adhesive, the beams being insulated with polymer glue. The strain gauge factors were measured for two films with filler content being 0.75 and 2.00 mass per cent. Electrical resistances were measured by two- and four-point methods, the factors being independent on the method used. The factors are the same within the error for both filler contents and equal to 21 on average.

Highly exfoliated graphite (HEG) containing multi-, bi- and monolayer graphenes has been prepared from an alternative class of precursors – fluorinated graphite intercalation compounds, namely, poly(dicarbon fluoride) intercalation compounds C2F·xR. Treatment of HEG by mixture of concentrated nitric and sulfuric acids results in chemically modified graphenes (CMG) dispersible in water or alcohol medium without any surfactants or stabilizers. The samples were examined by elemental analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), IR, Raman and UV-vis spectroscopies. Elemental analysis and IR data indicate that covalent functionalization with oxygen-containing groups, such as carboxyl group, occurs upon acid treatment. AFM images show thin sheets of about 1 nm, confirming the well-dispersed state of the material. Dispersions of CMG sheets from highly exfoliated graphite are very stable colloids (over a year) and can serve for further functionalization.

In chemical analysis and XRPA studies, it has been found that the products of fluorination of graphite, graphite bifluoride, and tetracarbon polyfluoride with gaseous and liquid fluorooxidants (ClF3, ClF5, XeF2, and FNO3) and their solutions in anhydrous hydrogen fluoride and freon-113 at 20–100°C, having a limiting composition, are second stage intercalated compounds based on dicarbon polyfluoride with the corresponding fluorooxidant, or the reduced form of fluorooxidant, or a fluorooxidant and a solvent. The degree of C-F bond ionicity in C2F was higher than in CF, but lower than in C4F. However, the bond is closer in character to the covalent C-F bond in monocarbon polyfluoride.

The effect of the modification of curvilinear carbon nanostructures (nanotubes) on their electrical properties has been studied. The samples were prepared using a special method of synthesis, which excluded the formation of amorphous carbon particles in multiwalled carbon nanotubes and in expanded graphite. Such materials exhibit a quadratic growth in the positive magnetoconductivity in the fields of up to B ∼ 1 T, which is not observed in the samples synthesized by usual methods.

The surface properties of graphite, carbon fiber, and their fluorination products were studied using gas chromatography. The retention volumes and Kovatz indices for saturated and aromatic hydrocarbons and oxygenated and nitrogenated compounds were determined. Regardless of the properties of the matrix, fluorination produces materials with chemically homogeneous and apolar surfaces. For fluorinated graphite, the decrease in the retention of branched alcohols compared to that of linear alcohols is more significant than for fluorinated carbon fiber.

The structural state of nanocrystalline samples of expanded graphite is investigated using X-ray diffraction and neutron diffraction analyses. The expanded graphite samples are prepared by a rapid thermal decomposition of intercalation compounds of oxidized graphite based on fluorinated graphite, graphite oxide, and graphite aminofluoride. It is established that the main phase of expanded graphite belongs to the hexagonal crystal system (space group P63/mmc) and that carbon atoms in the structure occupy the 2b and 2c positions. The unit cell parameters and the unit cell volume in the structure of expanded graphite samples are larger than those in the structure of massive graphite.

The subatomic structure of expanded graphite has been investigated by small-angle neutron scattering. Samples were synthesized during quick thermal decomposition of intercalated compounds based on oxidized graphite. They had a low bulk density (up to 0.1 g/cm3) and were characterized by considerable small-angle scattering. It has been established that majority of the volume of expanded graphite samples is occupied by participles with characteristic sizes in two ranges: from 6 to 8 nm and from 20 to 30 nm. Small particles have properties of a surface fractal with the dimension Ds = 2.4–2.6, whereas the larger particles are mainly smooth and have the dimension Ds = 2.0–2.1. The specific surface of the samples studied was determined from the small-angle scattering data.

The decomposition of C x FCl y · zR (R = N2O4, N2O, SO2) fluorinated graphite intercalation compounds at 370–420 K leads to the formation of C x FCl y graphite fluorides with x close to 2 and y close to 0.1. The C x FCl y fluorides are first-stage compounds with an interlayer spacing of 0.60–0.61 nm. According to the synthesis conditions and their structure, these compounds can be classed with low-temperature C2F graphite fluorides. They are stable in air and inert atmospheres up to 720–750 and 750–780 K, respectively, which is comparable to the thermal stability of high-temperature CF and C2F graphite fluorides.

Graphite fluoride with a C : F atomic ratio close to 2 was prepared by reacting graphite with liquid ClF3 (20°C), solutions of ClF3 in anhydrous hydrogen fluoride and Freon-113 (20°C), ClF3 gas (50–100°C), and ClF3 + HF gas mixtures (20–100°C). The results on the thermal stability of C2F intercalated with various organic compounds, in conjunction with earlier reported data, demonstrate that, below the exothermic decomposition temperatures of the intercalates, C2F is a suitable host material for the containment of volatile compounds, which is superior to the other known inclusion compounds in thermal stability and versatility.

For intercalation compounds of fluorinated graphite at 77–300 K, the parameters of the spin Hamiltonian are determined from the angular dependence of the ESR spectra, the NO2 and ClO2 radicals are located, and their mobility at low temperatures is studied. At 77–200 K, vibrational and rotational motions around the oxygen-oxygen axis are defreezed. This is attributed to donor-acceptor interactions between the negatively charged oxygen atoms of NO2 and ClO2 radicals and the positively charged carbon atoms of fluorinated graphite. The calculated activation energies (0.35 kcal/mole for ClO2 and 0.6 kcal/mole for NO2) for defreezing the rotational-vibrational motions of these two radicals are close. Using NO2 radicals as spin probes allowed us to find two types of regions in ICFG, which differ in the rate of NO2 diffusion. These regions are supposed to be the filled and unfilled parts of graphite fluoride layers. It is attempted to explain the low pressure of the saturated vapor of the intercalate over ICFG by the presence of unfilled layers near the boundaries of ICFG flakes.

We have fluorinated few-layer graphene (FLG) by using a low-temperature fluorination route with gaseous ClF3. The treatment process resulted in a new graphene derivative with a finite approximate composition of C2F. TEM studies showed that the product consisted of thin transparent sheets with no more than 10 fluorographene layers stacked together. Spectroscopic methods revealed a predominantly covalent nature of the C-F bonds in the as-synthesized product and we found no evidence for the existence of so-called "semi-ionic" C-F bonds, as observed in bulk C(x)F. In contrast to the case of graphite and typical (thick) expanded graphites, fluorination of FLG did not lead to the intercalation of ClF3 molecules, owing to the lack of a 3D layered structure. The approximate "critical" number of graphene layers that were necessary to form a phase of intercalated compound was estimated to be more than 12, thus providing a "chemical proof" of the difference between the properties of few-layered graphenes and bulk graphites. Fluorographene C2F was successfully delaminated into thinner layers in organic solvents, which is an important property for its integration into electronic devices, nanohybrids, etc.

Highly exfoliated graphite have been prepared from fluorinated graphite intercalation compounds of various flake sizes and stably dispersed in dimethylformamide. Further, we have processed the colloid into thin films or paper-like materials. The dispersion and films have been characterized by a set of physico-chemical methods including UV/vis, Raman and IR spectroscopies, X-ray diffraction (XRD), scanning electron microcopy (SEM) and dynamic and electrophoretic light scattering (DLS/ELS) techniques. The studies have shown that the use of the special type of expanded graphite allowed to reach higher concentrations than with natural graphite or conventional expanded graphites. Graphene plates in colloid have larger lateral sizes reaching several micrometers that is superior comparing to other methods like graphite oxide reduction.

In this paper an alternative precursor for exfoliated graphite-C2F*R used to produce a highly exfoliated graphitic material which is a multilayered graphene containing on average 10-15 layers is studied. This material is further exfoliated and functionalized with oxygen groups by acid treatment to yield very stable surfactant-free colloidal dispersions of chemically modified graphene nanosheets in water or alcohol medium.

Since the carbon nanotubes (CNTs) have received a considerable attention because of their interesting properties such as high aspect ratio, electrical and thermal conductivity, and chemical and mechanical stability1. Various low-dimensional carbon materials have been extensively studied to explore their applications as the electron source2,3. Recently, graphene have attracted enormous scientific attention on account of its extraordinary electronic and mechanical properties resulting from one-atom-thick layers and hexagonally arrayed sp2-hybridized carbon atom structure. Field emission studies on graphitic sheets have become important issue from the point of view of technological applications as well as fundamental sciences4. So far, a few papers has been paid to field emission studies of graphene sheet (thickness 1-2 nm)5, synthesized via composite approach which is scalable for vacuum microelectronics and other applications, because the difficulty of graphene dispersion in solvent as well as matrix.