Catalytic growth of carbon nanotubes

Published: 2 May 2013

We strive for a better understanding of the catalytic growth mechanism of carbon nanotubes (CNTs) by first-principles calculation of the binding energies and thus contribute to the development of the growth mechanism of CNT with special properties. This activity was started in collaboration with Dr. Feng Ding, Professor Kim Bolton and Professor Arne Rosén, at Chalmers. The important function of the catalytic nanoparticles had previously been considered to be both the breakdown of the raw material gas, for supply of carbon, and the seeding of the CNT, which requires the formation of graphitic domes on the particles. We were the first to show that an additional function is also important - to stabilize the growing end of the CNT, which is fulfilled for magnetic metals (Fe, Co, Ni) commonly used to produce CNTs. With our work, the phenomenological knowledge of CNTs growth mechanism extended with caclulated bond strengths, opening up an avenue for investigation of factors such as single-walled vs. multi-walled CNT growth, defective induction energy, alloy catalysts and the effect of pollution. Our theoretical prediction of the importance of the carbon-metal bond strength, one of several criteria for CNT growth, has been demonstrated experimentally in collaboration with Dr. Justin Holmes (University College Cork) by combining two catalytically inactive non-magnetic metals, one that has been too weak metal- carbon bonds (Cu, Pd), and one that has too strong metal-carbon bonds (Mo, W), to active catalyst particle alloys (Mo/Cu, Mo/Pd, and W/Cu). The collaboration with Prof. Justin Holmes has also resulted in a study of the growth of N-doped CNTs. Our study of CNT growth contributes to an increased specific product control, which has not been possible, and thus delayed the use of CNTs in engineering contexts.