Effect of purification treatment on adsorption characteristics of carbon nanotubes

Carbon nanotubes are novel materials with porous-rich structures and superior adsorption characteristics. In this report, multi-walled carbon nanotubes with different diameter were synthesized by thermal chemical vapor deposition. Amorphous carbon particles were highly removed by thermal oxidation process. Microwave digestion acidic procedure was used to dissolve metal catalysts and open tip of carbon nanotubes. The opened-end multi-walled carbon nanotubes are expected to be much more porous with more gas adsorption sites. The results indicated that the BET surface area decreases with their increasing of diameter of MWCNTs. The effective surface area of carbon nanotubes processed by thermal annealing treatment can increase with the increasing temperatures of 300 °C, 400 °C and 450 °C. Similarly, effective surface area of carbon nanotubes processed by microwave digestion acidic treatment can also increase with increasing processing time. Nitric acid can effectively absorb microwave energy and rapidly dissolve impurities in the carbon nanotubes during digestion process. The surface area increased about 30% with 20 min microwave digestion treatment time. However, microwave digestion acidic and thermal annealing treatments not only remove metallic catalysts and amorphous carbon particles and also increase effective surface area and the extent of purification of carbon nanotubes.