A. S. Nazarov

One-Step Exfoliation Synthesis of Easily Soluble Graphite and Transparent Conducting Graphene Sheets

Easily soluble expanded graphite is synthesized in a one-step exfoliation process that can be used for the lowcost mass production of graphene for various applications because of the simplicity and speed of the process. The graphene obtained is sufficiently expanded to be dispersed in aqueous solutions with an ordinary surfactant and in organic solvents.

The superior dispersion of easily soluble graphite

Graphene is a 2D one-atom-thick layer that has attracted enormous scientific attention on account of its extraordinary electronic and mechanical properties resulting from the hexagonally arrayed sp-hybridized carbon atom structure. Several efforts have been made to use graphene in devices and composites. The strong covalent bonds of carbon atoms provide high mechanical and thermal properties and chemical stability. The theoretical Young’s modulus of graphene is approximately 1060GPa. In addition, the high electrical conductivity (mobility: 20 000 cmV 1 s , velocity: c/300) through the p-electron cloud makes graphene a promising material in conducting composites and quantum electronics. As in other new materials (such as carbon nanotubes, various quantum dots, etc.), the development of mass productionmethods that can support the demand for graphene in a variety of large-scale applications is of high priority. Thus far, several methods for graphene production have been developed and can be summarized into three areas:mechanical exfoliation, graphene in solution, and epitaxial growth. Mechanical exfoliation produces the highest quality graphene, which is suitable for fundamental studies. Epitaxial growth provides the shortest path to graphene-based electronic circuits. Graphene in solution can offer lower costs and higher throughputs and may be used in a wide range of applications because of the significant practical utility of this material. However, the method is quite complicated and

Chemically modified graphene sheets by functionalization of highly exfoliated graphite

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.

Preparation of low-temperature graphite fluorides through decomposition of fluorinated-graphite intercalation compounds

The decomposition of CxFCly · zR (R = N2O4, N2O, SO2) fluorinated graphite intercalation compounds at 370–420 K leads to the formation of CxFCly graphite fluorides with x close to 2 and y close to 0.1. The CxFCly 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 intercalation compounds for manufacturing composites with metal nanoparticles

The feasibility of using graphite fluoride intercalation compounds (GFICs) containing metal compounds for manufacturing metal nanoparticles in a graphite or graphite fluoride matrix is shown using the hydrogen reduction of a dicarbon fluoride matrix intercalated with a chloroform solution of palladium acetylacetonate Pd(AA)2. The composite manufactured with a GFIC containing about 10.5 wt % Pd(AA)2 at 80°C is Pd-fluorographite; at 450°C, Pd-graphite is manufactured. The palladium particle size in the composites is about 20–30 nm; the palladium concentration is about 5 and 9 wt %, respectively.

Graphene dispersion and graphene paper from highly exfoliated graphite

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.

Highly exfoliated graphite as a precursor for graphene materials

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.

Graphene composite using easy soluble expanded graphite: Synthesis and emission parameters

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.