Synthesis of high purity narrow-width carbon nanotubes

We have succeeded in controlling the width of multi-walled carbon nanotubes (MWCNT) by physical manipulation and pretreatment of the catalyst prior to reaction in a CO/H2 reactant mixture. Since the size of the metal catalyst particle determines the width of the nanotube, we have investigated the notion of introducing a dispersing agent into the catalyst formulation that facilitates fragmentation and prevents sintering of the granules during the reduction step. Inclusion of 5 wt.% silica into a Fe–Ni (6:4) catalyst was found to reduce the average width of MWCNT from about 40 to 20 nm, when the bimetallic was reacted in CO/H2 (1:4) at 670 °C. On the other hand, when 5 wt.% NaCl was used as the dispersant the average width of the MWCNT was decreased to about 11 nm. The impact of both the catalyst pre-treatment and various post-treatment procedures on the width and purity of the final MWCNT product is discussed.