Evaluating the characteristics of multiwall carbon nanotubes

During the past 20 years, multiwall carbon nanotubes (MWCNTs) have become an important industrial material. Hundreds of tons are produced each year. This review is a survey of the scientific literature, motivated by industrial requirements and guidelines for environment, health and safety compliance. Sampling, size, area, density, color, crystallinity, as well as purity compared to properties of non-MWCNT carbon and catalyst metals, are presented. No single measurement tool provides a complete characterization; therefore, we summarize methods that include scanning electron microscopy, transmission electron microscopy (TEM), fast Fourier transform of high-resolution TEM, Raman spectroscopy, reflectance and thermogravimetric analysis. Fourier transform infrared spectroscopy reveals information with regard to functional groups interacting the tube surface. Brunauer-Emmett-Teller (BET) analysis is reviewed as the basis for evaluating specific surface area. We extend the review by presenting taxonomy of defects present in MWCNTs. Finally, we provide an appendix from documentary standards that are pertinent and reasonable for bulk measurements.