Fig. 1 Molecular structures of (a) graphite, (b) graphene, and (c) graphane

Hydrogenated Graphite / Graphane

Graphane’ typically refers to the fully hydrogenated single layer product. Multilayer partially hydrogenated materials are usually described as hydrogenated graphene or hydrogenated graphite. Hydrogenation changes the properties of graphite/graphene in a number of important ways. While graphene is a zero band gap semiconductor, hydrogenated graphene/graphite can have a band gap of up to 5 eV depending on the level of hydrogenation [5,6]. Electrical conductivity changes from highly conducting to insulating, and magnetic properties shift from diamagnetic to ferromagnetic [7-9].

Hydrogenation also weakens the van der Waals adhesive forces between a graphane sheet and its substrate. This allows for facile delamination of graphane from a substrate by dipping in water or other solvent [10], and exfoliation of graphane from hydrogenated graphite by ultrasonic disruption to produce a graphane dispersion.

Multi-layer graphane or hydrogenated graphite is generally reported to be stable at room temperature [11,12] while single layer graphane seems prone to slow loss of hydrogen in some cases [13,14]. Annealing at 200 to 500oC releases hydrogen, restoring graphane to its original graphene or graphitic form [15]. This in turn allows for the deposition of graphane coatings onto target substrates, with subsequent conversion into graphene by relatively mild thermal annealing. Graphane can also be dehydrogenated chemically, and this can allow for functionalization with other chemical groups [16].

Graphene Derivatives

Other graphene derivatives include graphene oxide and fluorinated graphene. These derivatives also provide for band gap modification, exfoliation, and use as substrates for devices and active molecules. Graphene oxide and oxidized graphite are widely used in research in applications including lithium intercalation battery materials, supercapacitor electrodes, solar cell coatings, biomaterials, biosensors, and chemical sensors [4,17,18]. Graphene oxide is a more heterogeneous material than graphane having a variety of epoxy, hydroxyl, carboxyl, and carbonyl groups attached to the graphitic backbone. Reduction of graphene oxide to graphene by chemical or thermal processes is possible but incomplete, leaving residual oxidation and damage to the graphite structure so that the original graphite structure is never fully recovered [18].

Fluorinated graphite/graphene is structurally similar to graphane, with one fluorine atom per carbon in the fully saturated state. It shares many of the same characteristics including increasing band gap, exfoliation, and reversion to graphene by thermal or chemical reduction [4,19]. Because of the higher binding energy of fluorine to carbon, fluorinated graphene is more stable than graphane which makes the reversion to graphene or further functionalization of the material more difficult.

Graphene derivatives such as fluorinated graphite/graphene, graphene oxide, and others are commercially available through chemical supply outlets. Graphane, however, is not currently available on the market because it is difficult to synthesize and has not yet gained market traction.


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