Chemical and structural characterization of carbon nanotube surfaces.

To utilize carbon nanotubes (CNTs) in various commercial and scientific applications, the graphene sheets that comprise CNT surfaces are often modified to tailor properties, such as dispersion. In this article, we provide a critical review of the techniques used to explore the chemical and structural characteristics of CNTs modified by covalent surface modification strategies that involve the direct incorporation of specific elements and inorganic or organic functional groups into the graphene sidewalls. Using examples from the literature, we discuss not only the popular techniques such as TEM, XPS, IR, and Raman spectroscopy but also more specialized techniques such as chemical derivatization, Boehm titrations, EELS, NEXAFS, TPD, and TGA. The chemical or structural information provided by each technique discussed, as well as their strengths and limitations. Particular emphasis is placed on XPS and the application of chemical derivatization in conjunction with XPS to quantify functional groups on CNT surfaces in situations where spectral deconvolution of XPS lineshapes is ambiguous.