Investigation of Homologous Series as Precursory Hydrocarbons for Aligned Carbon Nanotube Formation by the Spray Pyrolysis Method

The precursory carbon source is one of the key parameters which govern the formation of carbon nanotubes (CNTs). In this work, by selecting four homologous series, namely n-pentane, n-hexane, n-heptane and n-octane, as investigated targets, we comparatively study the relationship between thermodynamic properties of the precursory carbon source and formation of aligned CNTs. We find that all of these alkanes are favored for the growth of aligned CNTs in a suitable growth environment. But only n-heptane can yield the aligned CNTs with relatively high quality, high yield and narrow diameter distribution. Furthermore, after considering the link between thermodynamic properties of the precursory carbon source and the morphology characteristic of the nanotube samples, we find that the Gibbs free energy and formation enthalpy of precursory carbon sources play critical roles in the nanotube formation. In additions some possible explanations are proposed to better understand these phenomena. These rules will be very helpful in making clearer the formation mechanism from the precursory carbon sources to the CNTs, and preparing large-scale aligned CNTs with diameter control at low cost.