We compare popular analytical techniques, including scanning and transmission electron microscopy (SEM and TEM), thermogravimetric analysis (TGA), and Raman and near-infrared (NIR) spectroscopy, for the evaluation of the purity of bulk quantities of single-walled carbon nanotubes (SWNTs). Despite their importance as imaging techniques, SEM and TEM are not capable of quantitatively evaluating the purity of typical inhomogeneous bulk SWNT samples because the image frame visualizes less than 1 pg of SWNT material; furthermore, there is no published algorithm to convert such images into numerical data. The TGA technique is capable of measuring the amount of metal catalyst in an SWNT sample, but does not provide an unambiguous separation between the content of SWNTs and carbonaceous impurities. We discuss the utilization of solution-phase near-infrared spectroscopy and solution-phase Raman spectroscopy to quantitatively compare arbitrary samples of bulk SWNT materials of different purities. The primary goal of this paper is to provide the chemical community with a realistic evaluation of current analytical tools for the purity evaluation of a bulk sample of SWNTs. The secondary goal is to draw attention to the growing crisis in the SWNT industry as a result of the lack of quality control and the misleading advertising by suppliers of this material.
The influence of Ni−Y catalyst composition on the bulk scale synthesis of single-walled carbon nanotubes
(SWNTs) is studied using solution phase near-infrared spectroscopy. We found that a wide range of catalyst
concentrations (3−6 atom % Ni and 1−2 atom % Y), allow efficient production of high-purity as-prepared
(AP-) SWNT soot. The broad window of acceptable synthetic parameters found in this study suggests that
there is an opportunity to scale-up the electric arc (EA) discharge synthesis of SWNTs to the industrial level.
Significant deviations of the concentrations of either Ni or Y outside the optimum parameters result in a
degradation in the quality and yield of the AP-SWNT soot.
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