High ionic strength carbon nanotubes and graphene have numerous applications ranging from use in DNA diagnostics to prevent non-specific DNA interactions, to use in electrostatic assembly processes that can be used to coat surfaces. Highly charged carbon nanotube and graphene materials can also be used as structural reinforcing elements. They may also be of interest for optical applications, and may be capable of displaying photo-injected charges necessary for photovoltaic applications and display photo-currents with illumination.
Due to their high aspect-ratio geometries, carbon nanotubes and graphene are difficult materials to process and disperse in solvents. Various approaches to process these materials include covalent and zwitterionic functionalization, which can lead to high charge densities and a diversity of functionality in nanocarbon materials.
This present invention describes how to synthesize materials to introduce high degrees of charge to carbon-based material including carbon nanotubes and graphene. The inventors have discovered that attaching two charge groups to each cyclopentanone ring of the carbon nanotube generates ultra-high charge density materials. This effect is realized when observing carbon nanotubes with two terminal acetylene groups for every site of functionalization. In the presence copper base and an organic azide, these acetylene groups can be quantitatively reacted to create new triazole groups bearing other functionality, ideally that of an organic sulfate group.
This allows for carbon nanotubes and graphene to be highly charged and for multi-walled carbon nanotubes to form stable dispersions at concentrations of orders of magnitude higher than previously possible. Specifically, chemically functionalized ionic carbon nanotubes were typically soluble only to levels of about 1.5 mg/ml of solvent. With this present invention, 50 mg of sulfonated, functionalized, multi-walled carbon is soluble in 1 ml of water. These solutions are sufficiently stable such that they can evaporate without precipitation to give free-standing films of the carbon nanotubes.
Simple method to introduce high degrees of
charge to carbon materials
Highly charged carbon nanotubes and
graphene are easier to disperse and more stable