On the Formation of SWCNTs and MWCNTs by Arc-Discharge in Aqueous Solutions: The Role of Iron Charge and Counter Ions

Abstract

Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized in aqueous solutions containing FeCl2, FeCl3, FeSO4 and Fe2(SO4)3. The effects of iron charge and the counter ions on the formation of carbon nanotubes (CNTs) were investigated. Thermogravimetric (TG) analysis indicated that carbon multilayer structures including CNTs and multishell graphite particles were formed in deionized (DI) water without the iron precursor. SWCNTs were also synthesized in the presence of the iron ions. It was also found that the mole ratio of [Fe2+]/[Fe3+] in the solution has a significant influence on the purity of CNTs and the process yield. The highest yield was obtained at [Fe2+]/[Fe3+] = 1. The results revealed that the two-stage nucleation and growth mechanisms of CNTs formation were affected by ferric and ferrous ions, respectively. The chloride anions exhibited more pronounced effect on the CNTs formation compared with that of sulfate ions; that is, CNTs with smaller diameter and thinner wall were synthesized.