Simultaneous purification and spectrophotometric determination of nickel present in as-prepared single-walled carbon nanotubes (SWCNT)

The quality of single-walled nanotubes (SWCNT) is usually assessed by means of electron microscopic techniques or Raman spectroscopy. However, these sophisticated techniques are not widely available and do not reliably estimate the impurities in highly heterogeneous samples containing metal particles, fullerenes and other carbonaceous materials. We have developed a simple, inexpensive and convenient spectrophotometric method to assess the purity of arc-discharge grown as-prepared SWCNT. Purification process consists of initial gas phase oxidation and refluxing with nitric acid at the optimal conditions including short time period during acid refluxing. We have shown that this method could remove the metal particles effectively with a good yield of high quality SWCNTs, as shown by the spectrophotometric and scanning tunneling microscope studies described here. The extent of removal of the nickel present in as-prepared carbon nanotube sample is followed by spectrophotometeric analysis of the dissolved nickel analyte. The composition of nickel in the SWCNT sample is found to be 17.56%. The method is based on the chelating of Ni²⁺ with dimethylglyoxime in ammoniacal citrate medium to form nickel dimethylglyoxime complex. A second stage purification of SWCNT eliminates the residual metal particles. The purified SWCNT has been studied using scanning tunneling microscopy which shows clearly resolved individual carbon nanotubes.