Deoxygenation of Exfoliated Graphite Oxide under Alkaline Conditions: A Green Route to Graphene Preparation

Graphene – a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice – is the basal building block in all graphitic materials. Since it was first reported in 2004, graphene has attracted great interest because of the unique electronic, thermal, and mechanical properties arising from its strictly 2D structure, and to its potential technical applications. However, producing graphene on a large scale using existing mechanical methods is still unfeasible. Searching for alternative chemical approaches is an urgent matter. However, the hydrophobic nature of graphene and its strong tendency to agglomerate in solvents present a great challenge to the development of fabrication methods, and severely restrict its promising applications. Although the mechanism involved remains unproven, the chemical reduction of readily available exfoliated graphite oxide (GO) with reducing agents such as hydrazine and dimethylhydrazine is a promising strategy in the large-scale production of graphene. Unfortunately, the reducing agents involved are very hazardous, and the graphene obtained presents irreversibly agglomerated features in solvents that do not contain polymer surfactants. Here, we report a new green route for the synthesis of processable graphene on a large scale. We observed that a stable graphene suspension could be quickly prepared by simply heating an exfoliated-GO suspension under strongly alkaline conditions at moderate temperatures (50–90 8C) (Figure 1a). Our initial purpose was to introduce functional groups to exfoliated GO by free-radical addition. Surprisingly, the addition of NaOH to the GO suspension – to improve the solubility of the alkyl free-radical initiator, which is carboxyl-terminated – was accompanied by a fast, unexpected color change (from yellow-brown to homogeneous black). Careful experiments revealed that exfoliated GO can undergo fast deoxygenation in strongly alkaline solutions, resulting in stable aqueous graphene suspensions