Structural improvement of CVD multi-walled carbon nanotubes by a rapid annealing process

Generally, due to structural disorders in multi-walled carbon nanotubes (MWCNTs) synthesized by chemical vapor deposition (CVD), most of their properties are much below the expected values. A novel technique has been developed in this investigation for structural improvement of CVD MWCNTs using a rapid annealing process. Direct observation by transmission electron microscope (TEM) indicates obvious structural changes in the nanotubes after a rapid annealing process between 2000 °C and 2800 °C, while nanotubes with twisty shells and kinked walls have been observed as the annealing temperature approaches 3000 °C. Decrease of ID/IG ratio in Raman spectra, increase of the starting oxidation temperature observed in Thermogravimetric analysis (TGA), as well as increase in electrical conductivity of nanotube powders suggests the reconstruction toward more ordered nanotube structure after a rapid high temperature annealing process.

Graphical abstractSchematic illustration of MWCNT rapid annealing process in a graphite tube system.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A rapid annealing process was be used for structural improvement of CVD MWCNTs. ► Electric current directly went through MWCNTs for fast heating to high temperature. ► Advantages of the process were rapid heating, low energy consumption and convenient. ► The CNT structure became more ordered and stable annealed from 2000 °C to 2800 °C. ► The CNT structure was disturbed as the annealing temperature reaches 3000 °C.