New research has shown1 that heating multiwalled carbon nanotubes (MWNTs) in inert atmosphere yields ordered graphene layers devoid of metal impurities. This technique is an effective and simple way of making graphene layers, which are promising for use in nanoelectronics and the production of clean energy.
Since their discovery, carbon nanotubes have demonstrated their outstanding benefits over conventional materials. However, carbon nanotubes require high consolidation temperatures when blended with other materials such as ceramic nanocomposites.
To study the stability and structural changes of carbon nanotubes at high temperatures, the researchers took MWNTs measuring 60–100 nm in diameter and 5–15 μm in length that contained trapped metal impurities such as nickel nanoparticles. They then exposed the MWNTs to high temperatures of 1,200 °C and 1,800 °C in argon in a graphite resistance heating furnace. Analysis revealed that the high-temperature treatment of nanotubes in an inert atmosphere is an effective way of forming ordered graphene layers containing no impurities.
Heat treatment led to the formation of a few nanoscale corrugations and to the splitting of some highly strained external graphene layers in the MWNTs. Compared with untreated nanotubes, the heat-treated nanotubes showed a significantly improved resistance towards high temperatures, owing to the successful removal of impurities and ordering of defect-free graphene layers, the researchers conclude.
