High-strength carbon nanotube fibers with near 100% purity acquired via isothermal vacuum annealing

The Fe and carbonaceous particles are the main impurities in a carbon nanotube fiber (CNTF) fabricated by the floating catalyst chemical vapor deposition (FCCVD) method, which have an adverse effect on various applications, leading to strong demand for purification process to obtain high-purity CNTFs. However, the commonly used purification methods combining oxidation and acid refluxing cannot remove the impurities thoroughly, and will introduce undesired damage onto CNT wall at the same time. Herein, we propose an efficient purification strategy involving an isothermal annealing process under high vacuum to achieve mass preparation of CNTFs with high purity and mechanical/electrical properties. The Fe and carbonaceous impurities can be almost completely removed after vacuum annealing at 1800 degrees C. The purified CNTFs exhibit enhanced oxidation resistance due to the removal of Fe catalyst particles. The diffusion and evaporation of Fe atoms are most likely responsible for the removal of Fe particles enclosed with graphitic shells. The purified CNTF shows a high specific tensile strength of 1.82 +/- 0.04 N/tex due to the high alignment of the CNT bundles within fibers, which can retain 80% of the value for pristine CNTF. The purified CNTF exhibits similar trends of electrical conductivity as the specific tensile strength and has a high conductivity of 3.65 +/- 0.11 x 105 S/m. The large-scale preparation of high-purity CNTFs with high-performance will promote the real application of CNTFs.