Quality Control
Carbon Solutions, Inc (CSI) was the first company to introduce quality control into the carbon nanotube industry and remains the only company that offers single-walled carbon nanotubes of certified purity for commercial sale.
Carbon nanotubes are macromolecules that should be ideal constituents of specialty polymers, copolymers, polymer composites, electronic materials and biological structures where their outstanding physical properties, such as high strength, exceptional thermal conductivity, and singular electronic properties distinguish them from all other nanomaterials.
The issues that face the nascent carbon nanotube industry are frequently underestimated in the scientific literature and the press releases. Quality control is virtually nonexistent. Carbon nanotubes still cost more than gold, most preparations are highly impure and many of the purifications reported in the literature do not work as stated for bulk materials. CSI was established to aid in the transition of carbon nanotubes from a research curiosity to a specialty chemical and finally into a commodity that is found in a wide range of useful products that require the performance of the ultimate carbon nanofiber.
The first step that must be taken in meeting the requirements for a specialty chemical (and certainly a commodity chemical), is an agreed upon definition of chemical purity. This is complicated in a nanomaterial by the dual requirements that are imposed by the desire for a molecularly perfect material that is also homogeneous and of high bulk purity. For example, the presence of one or two perfect single-walled carbon nanotubes (SWNTs), may be all that is required in a sample for nanoscopic studies, whereas this quantity of SWNTs in a sample that is primarily composed of amorphous carbon and which is intended for bulk applications is of limited usefulness. For the first application, a microscopic analysis involving such techniques as SEM, TEM, AFM, or STM may be appropriate, but bulk applications require an analysis that is representative of the whole sample. It is this latter measure of purity that is usually of interest in the chemical industry. The study of bulk materials is usually carried out with spectroscopic techniques that sample a macroscopic quantity of material and thereby provide a measure of bulk purity.
The electronic transitions that arise from the band structure of SWNTs give rise to characteristic spectra that may be observed in suitably dispersed samples in the near-IR (NIR) region of the electromagnetic spectrum. This technique can be used to provide quantitative information on the carbonaceous purity of electric arc (EA) produced SWNTs. (Itkis, M. E.; Perea, D.; Niyogi, S.; Rickard, S.; Hamon, M.; Hu, H.; Zhao, B.; Haddon, R. C., Purity Evaluation of As-Prepared Single-Walled Carbon Nanotube Soot by Use of Solution Phase Near-IR Spectroscopy. Nano Lett. 2003, 3, 309-314). This technique is particularly advantageous because it provides a measure of the bulk purity of a sample by using a technique that is dependent on the band electronic structure of the SWNTs – thus it fulfils both of the purity requirements mentioned above for nanomaterials, as it is sensitive to the detailed electronic structure and to the composition of a sample. The metal catalyst content of SWNT samples is available from TGA measurements, and thus these two techniques together can provide the purity of arbitrary samples.
CSI will now provide purity evaluations of all materials that it offers for commercial sale. In addition, CSI will undertake purity evaluations of other SWNT samples on a contract basis.