Purification and structural evolution of carbon nanoscrolls by heat treatment

We performed high temperature heat-treatment to remove metallic impurities from carbon nanoscrolls and evaluated their structures. It was found from elemental analysis that samples heat-treated above 1500 °C had been effectively purified, and became free of metallic species. In addition, the amount of oxygen was reduced to about 2 at.%. Further analysis revealed that interlayer distance became 0.336 nm which is comparable to that of ideal graphite (0.335 nm), at a relatively low temperature such as 1200 °C. It was experimentally and theoretically shown that open-edges started to bond with each other above 2000 °C and mainly transformed into a larger diameter cylindrical structure. Moreover, it was found that the Raman D’ band associated with open-edges disappeared above 2000 °C. On the other hand, the D’ band was still apparent in samples heat-treated below 1800 °C. The study suggests that metal-free carbon nanoscrolls with active edges can be effectively obtained by heat-treating the pristine sample at 1500–1800 °C.