Potentiometric titration as a straightforward method to assess the number of functional groups on shortened carbon nanotubes

The conditions for oxidizing multi-walled carbon nanotubes to shorten them to a narrow length distribution have been optimized. One of the most difficult achievements is to fully characterize this material from a chemical point of view, and to find a good quantitative correlation among different techniques. Herein, we report on the combination of different methods to determine the number of functional groups generated during strong acid treatment and a further amidation reaction. A good correlation was found using the colorimetric Kaiser test, thermogravimetric analysis and potentiometric argentometric titration. The final technique, used for the first time in this field, is highly versatile and, being non-destructive, allows a complete recovery of the starting material. Short carbon nanotubes are particularly useful for applications in biomedicine, and the control and precise assessment of their functionalization is critical when used as carriers for therapeutic molecules. (C) 2010 Elsevier Ltd. All rights reserved.