Viktor G. Makotchenko

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.

Conductive composites based on chitosan and polyvinylpyrrolidone-stabilized graphene

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.

Functional Composites Based on Polylactide and Graphene

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.

Electrically conductive composites of collagen and graphene

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.

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.