Carbon nanotubes (CNTs) possess unique structural,
mechanical, thermal and electronic properties, and have been
proposed to be used for applications in many fields. However, to
reach the full potential of the CNTs, many problems still need to be
solved, including the development of an easy and effective
purification procedure, since synthesized CNTs contain impurities,
such as amorphous carbon, carbon nanoparticles and metal particles.
Different purification methods yield different CNT characteristics
and may be suitable for the production of different types of CNTs. In
this study, the effect of different purification chemicals on carbon
nanotube quality was investigated. CNTs were firstly synthesized by
chemical vapor deposition (CVD) of acetylene (C2H2) on a
magnesium oxide (MgO) powder impregnated with an iron nitrate
(Fe(NO3)3·9H2O) solution. The synthesis parameters were selected
as: the synthesis temperature of 800°C, the iron content in the
precursor of 5% and the synthesis time of 30 min. The liquid phase
oxidation method was applied for the purification of the synthesized
CNT materials. Three different acid chemicals (HNO3, H2SO4, and
HCl) were used in the removal of the metal catalysts from the
synthesized CNT material to investigate the possible effects of each
acid solution to the purification step. Purification experiments were
carried out at two different temperatures (75 and 120 °C), two
different acid concentrations (3 and 6 M) and for three different time
intervals (6, 8 and 15 h). A 30% H2O2 : 3M HCl (1:1 v%) solution
was also used in the purification step to remove both the metal
catalysts and the amorphous carbon. The purifications using this
solution were performed at the temperature of 75°C for 8 hours.
Purification efficiencies at different conditions were evaluated by
thermogravimetric analysis. Thermal and electrical properties of
CNTs were also determined. It was found that the obtained electrical
conductivity values for the carbon nanotubes were typical for organic
semiconductor materials and thermal stabilities were changed
depending on the purification chemicals.
 P.X. Hou, C. Liu, H.M. Cheng, "Purification of Carbon Nanotubes",
Carbon, 46 (2008) 2003.
 Z. Li, W. Lin, K. Moon, S. J. Wilkins, Y. Yao, K. Watkins, L.
Morato, C. Wong, "Metal catalyst residues in carbon nanotubes
decrease the thermal stability of carbon nanotube/silicone
composites", Carbon, S0008-6223(11)00405-2 (Accepted
 G. Sun, G. Chen, Z. Liu, M. Chen, "Preparation, crystallization,
electrical conductivity and thermal stability of syndiotactic
polystyrene/carbon nanotube composites", Carbon 48 (2010) 1434-
 B. Scheibe, E. Borowiak-Palen, R.J. Kalenczuk, "Enhancement of
thermal stability of multiwalled carbon nanotubes via different
silanization routes", Journal of Alloys and Compounds 500 (2010)
 Y. Yu, C. Ouyang, Y. Gao, Z. S─▒, W. Chen, Z. Wang, G. Xue,
"Synthesis and Characterization of Carbon Nanotube/Polypyrrole
Core-Shell Nanocomposites via In Situ Inverse Microemulsion",
Journal of Polymer Science Part A: Polymer Chemistry 43(2005) 23
 Q. Zhang, S.Rastogi, D. Chen, D. Lippits, P. J. Lemstra, "Low
percolation threshold in single-walled carbon nanotube/high density
polyethylene composites prepared by melt processing technique",
Carbon 44 (2006) 778-785
 S. Curran, D.L. Carroll, P.M. Ajayan, P. Redlich, S. Roth, M. R├╝hle,
W. Blau, "Picking needles from the nanotube-haystack", Advanced
 H. Athalin, S. Lefrant, "A correlated method for quantifying mixed
and dispersed carbon nanotubes: analysis of the Raman band
intensities and evidence of wavenumber shift". J. Raman Spectrosc.
 W.E. Alvarez, B. Kitiyana, , A. Borgn, , D.E. Resasc, "Synergism of
Co and Mo in the catalytic production of single-wall carbon
nanotubes by decomposition of CO", Carbon 2001;39: 547-58.
 E. Dujardin, T. Ebbesen, A. Krishnan, M. Treacy , "Purification of
single shell nanotubes". Adv Mater 1998;10:611-3.