The Aqueous Dispersion of Carbon Nanotubes

Abstract

This work has focused on the use of biological molecules such as amino acids, glycolic acids, ribonucleosides and simple sugars to improve MWCNT aqueous dispersibility through both covalent and non-covalent functionalisation.

Oxidative treatment of MWCNTs with 6 M nitric acid has been shown to be a mild,
yet effective method for introducing carboxylic acid groups, which are known to improve their dispersion, to the surface. The subsequent ionic interactions of these carboxylic acid groups with selected acidic, basic and neutral amino acids was investigated with a view to this further increasing the aqueous dispersibility of the MWCNTs. Of the amino acids considered basic arginine was found to provide the greatest improvement with the MWCNT concentration increasing from 0.35 to 6.79 mg/mL.

The carboxylic acid groups of the oxidised MWCNTs were also used to covalently
attach the amino acids through formation of an amide bond. In this instance taurine was found to be the most effective amino acid with dispersibility more than doubling. Non-covalent functionalisation of the MWCNTs was also achieved with taurine functionalised poly(acrylic acid), which resulted in a vefold increase in the concentration of MWCNTs dispersed when compared with poly(acrylic acid).

Diazonium chemistry is widely used for the functionalisation of CNTs with aryl
groups and in this work a diazonium reaction was used to covalently functionalise
MWCNTs with pyridine. These pyridine groups were then used as the basis for the
covalent attachment of the sugars ribose, fructose and sucrose. Functionalisation with pyridine alone did not improve the aqueous dispersion of the MWCNTs, however the subsequent attachment of the sugars led to enhanced MWCNT dispersibility with sucrose the most effective at 20 ug/mL.

The effect of functionalisation on MWCNT dispersibility was probed using UV-vis-
NIR spectroscopy. The modied MWCNTs were further characterised using TGA,
TEM, Raman and FTIR spectroscopy.