Synthesis and subsequent purification of carbon nanotubes by arc discharge in NaCl solution

Carbon nanotubes (CNTs) are fascinating structures with a wide range of applications and several methods have been developed for their fabrication. The arc-discharge in liquid method is a new technique for synthesis of nanocarbon structures and is recognized as a low-cost method. In this work, this method was used for fabrication of carbon nanotubes, and subsequently a modified acid treatment method was applied as a purification stage. In order to optimize the process, a statistical design of experimental (Taguchi method with L9 orthogonal array robust design) was implemented in this study. As the result of Taguchi analysis in this study, voltage, ratio of catalyst and solution were the most influencing parameters on the yield product of carbon nanotubes (7.9 mg/min purified CNTs). The maximum product yield of CNTs was obtained at a voltage of 25 V, NaCl 0.2N as a salt in solution, Ni/Fe as a catalyst and a 1 : 1 catalyst ratio. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as well as Raman spectra were utilized to study the morphology and purity of these carbon nanotubes.