Understanding defects in graphene

13-May-2013 - Singapore

The products of making graphene by thermally exfoliating Graphite oxide are much more complex than previously thought, new research shows.

The most common way to prepare graphene is by thermally reducing – or ‘exfoliating’ - graphite oxide. But the graphene produced in the process often contains defects and lacks the perfect ‘honeycomb’ structure. One explanation is that these defects may be the result of organic by-products forming and escaping as gases during the reaction.

Scientists in Singapore and the Czech Republic allowed exfoliation to take place in an autoclave at 500 degrees for two hours then analysed the gases produced using gas chromatography–mass spectrometry (GC-MS). They detected many other volatiles in addition to H₂O, CO and CO₂, including polycyclic aromatic molecules, and those containing sulphur and nitrogen heteroatoms that are present as contaminants in the graphite oxide.

Moreover, the nature of the volatiles released varies hugely depending on pressure (2 bar versus 100 bar) and the gaseous atmosphere in which the exfoliation was carried out (hydrogen versus inert argon). The method by which the graphite oxide itself was prepared also had an effect – the Hummers method yielded the highest number of volatiles.

Understanding these by-products is crucial as they can affect the structure of the resultant graphene which influences its future use. The team suggest that measuring the volatiles produced during exfoliation could help determine the nature of defects.