Two methods have been developed for functionalizing carbon nanotubes in solvent-free conditions. In one method, purified single-walled carbon nanotubes (SWNTs) and a diazonium salt are added to a metal vial, which is loaded with a stainless steel ball bearing. The metal vial is clamped into a mill mixer, and is mixed for one hour. The unreacted diazonium salt is then dissolved in a volume of acetonitrile that efficiently solubilizes the salt to remove the unreacted functionalization reagent. The functionalized nanotubes are then collected by filtration.
Any conventional or non-conventional dry mixing (mill mixing) or analogous technique that drives these reagents together could effect such a reaction. The tubes seem to be far more amenable to exfoliating and reaction with the reagents under these solventfree reactions.
In a second method, purified SWNTs and 4-chloroaniline are added to a flask and purged with nitrogen. The flask is then heated to 60 °C and is agitated with magnetic stirring. After one hour, isoamyl nitrite is slowly added via syringe to the reaction flask, after which there is an additional hour of stirring. Once the addition is complete, the reaction mixture is heated and stirred for an additional hour. The reaction mixture is then cooled and diluted with a volume of acetonitrile, which serves to solubilize any unreacted diazonium salt. Finally, the functionalized nanotubes are collected by filtration. This should also work with many other reaction types.
Functionalizing SWNTs can enhance solubility and improve compatibility in composite materials. The use of mill mixing, or any other type of dry mixing with high pounding, grinding, or sheer, allows for the functionalization of single and multi-walled carbon nanotubes. Different diazonium salts can be used with mill mixing technique in order to covalently modify nanotubes with varying functional groups.
This work was done by James M. Tour of Rice University for Johnson Space Center. MSC-24061-1/275-1