Morphology and growth of carbon nanotubes catalytically synthesised by premixed hydrocarbon-rich flames

Synthesis of carbon nanotubes (CNTs) was performed by using a laminar premixed flame burner at open atmospheric condition. The growth of CNTs on the substrate was supported catalytically by a transition metal under high temperature, hydrocarbon-rich environment. Analysis of the CNTs using high resolution electron microscope reveals the structure of synthesised nano-materials in disarray, clustered and tubular form. The graphitic structure of the CNTs are rather similar for all fuel-rich equivalence ratios tested, with an average diameter of ∼11-13 nm. Removal of the amorphous carbon and catalyst in the CNTs was performed via purification treatment using H2O2 and HCl solutions. Detail characterisation indicates the oxidation temperature of purified CNTs ranges between 497 and 529 °C. Deconvolution of the Raman spectra in the range of 900-1800 cm−1 shows the distinct characteristic bands of CNTs with IG/ID ratio of 0.66-0.72 for all the samples tested. In addition, the high level carbon concentration and sp2 CC bond in the CNTs is shown by X-ray photoelectron spectroscopy analysis. The present study demonstrates that CNTs can be effectively synthesised from fuel-rich hydrocarbon flames at ϕ = 1.8-2.0 supported by nickel-based substrate.