Reproducible high-yield purification process of multiwalled carbon nanotubes (CNTs) was developed by thermal annealing in ultrapure oxygen. The optimized condition involves thermal annealing via a PID controlled heater in high purity oxygen at temperature of 450°C for 180s, which burns out amorphous carbon and reactivate nickel catalyst. Controlling of the purification temperature is important for high yield CNTs, as excessive high annealing temperature results in deformation of the CNTs. Unlike hazardous wet purification treatments, purified CNTs remained vertically aligned and offer the possibility of tailored CNTs length through layer-by-layer process. The purification process is glass compatible and can be adapted to industrial synthesis of CNTs.
Diamond and Related Materials, 2011, Vol 20, Issue 5-6, p. 746-751