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About Graphene

Fig. 1. Graphite (2D material), carbon sp2

Graphene is a monolayer platelet (flake) of graphite available through either a mechanical cleaving of HOPG (highly oriented pyrolytic graphite) sample using, for example, a Scotch tape or deposition of hexagonal carbon layer from the vapor involving, for instance, the CVD (chemical vapor deposition) method. Such layer can take from few nanometers to several centimeters and more (for instance for the CVD epitaxial growth).

Fig. 2

Graphene platelets (flakes) (Fig. 2) usually exist as a powder or slurry, have a form of stacks of below 10 graphene monolayers. Their size may range from a few nanometers to a dozen micrometers and interlayer distance takes usually from 0.35 to 0.40 nm. Such graphene platelets are usually manufactured from powdered graphite.

Fig. 3 (H. He et. al, Chem. Phys. Lett., 1998, 287, 53–56).

GO (Fig. 3), few layer graphene oxide platelets (flakes) showing stack structure with height below 10 monolayers of oxidized graphene. In contrast to graphene or graphite, carbon atoms therein are bound solely by single chemical σ-bonds and the aromatic system of π-electrons is almost absent. There are numerous oxygen atoms containing moieties such as OH, COOH, C-O-C, C=O and others. Distance between particular layers of graphite oxide of “diameter” from a few nanometers to a dozen micrometers varies usually from 0.6 to 0.9 nm and is always above 0.4 nm. Light to dark yellow-brown GO is highly hydrophilic and forms stable aqueous suspension. It is an organic semiconductor which depending on its degree of oxidation disposes with band gap of 2–3 eV.

Fig. 4. π bonds (delocalized π electrons) and sp2 hybridized orbitals in benzene C6H6

rGO (Fig. 2) few layer reduced graphene oxide platelets (flakes) showing stack structure with height below 10 monolayers of reduced graphene oxide. It is almost free of the oxygen containing groups. Its “diameter” is between a few nm to a dozen μm and the interlayer distance reaches 0.36–0.40 nm. This highly hydrophobic, black material has a low resistivity with the band gap of the order of meV. It does not form stable aqueous suspensions.

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