Aerosol-assisted chemical vapour deposition synthesis of multi-wall carbon nanotubes: II. An analytical study Seyyed Shayan Meysami, Antal A. Koo ´s, Frank Dillon, Nicole Grobert * Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom ARTICLE INFO Article history: Received 4 December 2012 Accepted 18 February 2013 Available online 27 February 2013 ABSTRACT We report the study of different aspects of the aerosol-assisted chemical vapour deposition (ACVD) method for the optimised synthesis of multi-wall carbon nanotubes (MWCNTs). Fif- teen hydrocarbons (alkanes, benzene derivatives, and cyclohexane derivatives) were used in conjunction with catalyst concentrations of 1–15 wt.% in order to investigate their effect on morphology, residual catalyst content, diameter distribution, defect density and oxida- tion resistance of MWCNTs. The conversion yield of the precursors was measured and their thermocatalytic cracking behaviour was studied in situ using an integrated mass spectrom- eter. We believe that each hydrocarbon interacts differently with the catalyst and follows a characteristic cracking route involving the creation of certain intermediate hydrocarbon fragments which are responsible for the formation of MWCNTs with different properties. We show that the properties of MWCNTs can be tuned by altering the composition of the precursor and that the synthesis rate and the precursor conversion yield can be improved by 60% and 80%, respectively, compared to the commonly used carbon sources such as toluene or xylene. Moreover, while maintaining MWCNT sample quality, i.e. MWCNTs have similar or fewer defects densities and higher oxidation resistance, the amount of residual catalyst particles in the MWCNT samples could also be reduced by ca. 50%. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Aerosol-assisted chemical vapour deposition (ACVD) tech- niques are amongst the most efficient methods for the syn- thesis of large quantities of vertically aligned multi-wall carbon nanotubes (MWCNTs) with low defect density [1–3]. Liquid hydrocarbons can efficiently dissolve organometallic compounds, such as metallocenes, which act as the source of catalyst particles. Hence, separate catalyst preparation is not necessary. Moreover, controlled doping of MWCNTs can be easily accomplished by using hydrocarbons containing the dopants of interest [4–9]. It is noteworthy that the majority of previous reports on ACVD focused on the precursors composed of benzene deriv- atives in conjunction with metallocene [1–19]. Non-aromatic hydrocarbons with linear structures [19], ring structures [18– 21] and metal complexes [22] were also reported to yield MWCNTs. It is widely accepted that in the presence of catalyst nano- particles at sufficiently high temperatures (700–1000 °C, Table SI1 in supplementary information), these hydrocarbons crack down and form carbon fragments which dissolve in the metal nanoparticles and eventually form CNTs [23,24]. Since the identification of ‘vapor-phase-grown carbon fibers’ (VGCFs) by Endo [25], much effort was put into understanding the mechanism of the catalytic formation of CNTs [26]. How- ever, to the best of our knowledge, there is no comparative study to reveal the thermocatalytic cracking route which 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.02.041 * Corresponding author. E-mail address: nicole.grobert@materials.ox.ac.uk (N. Grobert). CARBON 58 (2013) 159 – 169 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon