The effect of concentration of the catalyst precursor on the longitudinal profile of multiwalled carbon nanotube (MWCNT) arrays, synthesized by using xylene and ferrocene in a floating catalyst reactor, is reported. Optical microscopy, Raman spectroscopy, high resolution transmission electron microscopy and field emission scanning electron microscopy were employed for point-to-point analyses of the grown MWCNTs in the so-called “growth window” (GW). It was found that at lower catalyst concentrations longer MWCNT arrays are obtained. Furthermore, higher catalyst concentrations resulted in MWCNTs with lower diameter at the beginning and the end of the GW, the reverse order was seen in the middle. These trends are attributed to the relative saturation of catalyst nanoparticles, increased diameter of the catalyst nanoparticles, and competition between catalytic and pyrolytic reactions. It was also found that, the diameter of MWCNTs is influenced by both catalyst concentration as well as longitudinal position inside the GW. Therefore, for better understanding of these simultaneous effects, more careful comparison is suggested in study of MWCNT synthesis by floating catalyst reactors.

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