Purification of multi-walled carbon nanotubes by microwave digestion method

Here developed is an efficient method for purification of multi-walled carbon nanotubes synthesized by electron cyclotron resonance chemical vapor deposition (ECRCVD). Carbon nanotubes may find their limited use for some applications as they contain a small fraction of metal catalysts in the tubes and tend to have defects along the graphene tube wall. Defects within the multi-walled carbon nanotubes would reduce electrical and structure properties. A two-step acidic treatment in microwave digestion system is used to dissolve metal catalysts. HNO₃ or HCl can rapidly absorb microwave heat and energy and completely dissolve metal, which reside in carbon nanotubes without damage. The processing time of the two-step microwave-assisted and acid-treated time to dissolve metal in the MWCNTs is below 1 h. After purification, the amount of residual catalyst metals in samples is estimated by using the thermogravimetric analysis (TGA). The results show that a high-yield of multi-walled carbon nanotubes with approximately 5% of metal is obtained.