Facile synthesis of few-layer graphene by mild solvent thermal exfoliation of highly oriented pyrolytic graphite

• Novel and green approach, omitting harsh chemicals in the synthesis of graphene.
• Comprehensive parametric study yielding optimised synthesis parameters.
• As produced graphene is few layered, pristine and unoxidized.
• Proposed approach omits the need for an additional reduction step.
• Parametric study includes various key characterisation methods for graphene.

Applications that harness the remarkable properties of graphene are unfortunately hampered by the lack of a scalable, reproducible and cost-effective synthesis method. In this study, a combination of thermal and facile exfoliation of graphite intercalated compounds (GICs) is thus, proposed. Graphite was intercalated in a mixture of sulphuric acid and hydrogen peroxide before being subjected to a rapid heat treatment at 900 °C. The thermally expanded graphite was then exfoliated in solvents to produce graphene sheets. An optimisation of the limiting parameters was also carried out to determine the best approach. Results showed that an increase in the amount of oxidiser, extension of the thermal expansion time as well as an increase in the starting graphite flake size resulted in larger, thinner flakes. Tapping mode AFM analysis showed that the as produced flakes had minimal thicknesses ranging between 2 and 2.5 nm with average lengths ranging from 0.5 μm to 10 μm. This study has improved upon existing syntheses methods resulting in the use of lower toxicity solvents, lowered costs and increase in dispersibility concentrations of up to a 100 times improvement from current syntheses.