Graphane is a two-dimensional polymer of carbon and hydrogen with the formula unit (CH)n where n is large.[1] Partial hydrogenation is then hydrogenated graphene.[2]
Synthesis
Its preparation was reported in 2009. Graphane can be formed by electrolytic hydrogenation of graphene, few-layer graphene or high-oriented pyrolytic graphite. In the last case mechanical exfoliation of hydrogenated top layers can be used.[3]
Structure
The first theoretical description of graphane was reported in 2003.[4] The structure was found, using a cluster expansion method, as the most stable of all the possible hydrogenation ratios of graphene in 2003.[5] In 2007, researchers found that the compound is more stable than other compounds containing carbon and hydrogen, such as benzene, cyclohexane and polyethylene.[6] This group named the predicted compound graphane, because it is the fully saturated version of graphene. The compound is an insulator. Chemical functionalization of graphene with hydrogen may be a suitable method to open a band gap in graphene.[6]
P-doped graphane is proposed to be a high-temperature BCS theory superconductor with a Tc above 90 K.[7]
Any disorder in hydrogenation conformation tends to contract the lattice constant by about 2.0%.[8]
Variants
Partial hydrogenation leads to hydrogenated graphene rather than (fully hydrogenated) graphane.[2] Such compounds are usually named as "graphane-like" structures. Graphane and graphane-like structures can be formed by electrolytic hydrogenation of graphene or few-layer graphene or high-oriented pyrolytic graphite. In the last case mechanical exfoliation of hydrogenated top layers can be used.[9]
Hydrogenation of graphene on substrate affects only one side, preserving hexagonal symmetry. One-sided hydrogenation of graphene is possible due to the existence of ripplings. Because the latter are distributed randomly, the obtained material is disordered in contrast to two-sided graphane.[2] Annealing allows the hydrogen to disperse, reverting to graphene.[10] Simulations revealed the underlying kinetic mechanism.[11]
Density functional theory calculations suggested that hydrogenated and fluorinated forms of other group IV (Si, Ge and Sn) nanosheets present properties similar to graphane.[12]
Potential applications
p-Doped graphane is postulated to be a high-temperature BCS theory superconductor with a Tc above 90 K.[13]
Graphane has been proposed for hydrogen storage.[6] Hydrogenation decreases the dependence of the lattice constant on temperature, which indicates a possible application in precision instruments.[8]