Carbon Isotopic Measurements of Nanotubes to Differentiate Carbon Sources

Stable carbon isotope (δ(¹³C)) analysis can provide information concerning the starting materials and the production process of a material. Carbon nanotubes (CNTs) are produced using a variety of starting materials, catalysts, and production methods. The use of δ(¹³C) as a tool to infer the nature of starting materials to gain insight into the mechanics of CNT growth was evaluated. The production process of NRC's SWCNT-1 was traced via the δ(¹³C) measurement of the available starting materials, intermediate products, and the final product. As isotopic fractionation is likely negligible at high temperatures, the δ(¹³C) value of the starting materials was reflected in the δ(¹³C) value of the final CNT product. For commercially available CNTs, the estimated δ(¹³C) values of identified starting materials were related to the δ(¹³C) signatures of CNTs. Using this information and the δ(¹³C) values of CNTs, the nature of unknown carbon sources was inferred for some samples. The use of δ(¹³C) analysis may be used as a tracer to differentiate between those processes that use relatively ¹³C-depleted carbon source(s) such as carbon monoxide, methane, or natural gas, and those that do not.