Chemical functionalisation is critical to a wide range of nanotube applications, but needs to be versatile and applicable at scale. Existing approaches tend to rely on liquid phase reactions, often requiring damaging sonication or lengthy work up through filtration or centrifugation. The formation of individualized functionalised single wall nanotubes (SWNTs) is a particular challenge.
One approach is to shift the modification reaction into the gas phase. We have developed a generic, scalable furnace treatment, based on the thermochemical activation of the CNTs, followed by reaction with functional organic monomers. This approach allows the introduction of a wide variety of functional groups onto the CNT surface whilst maintaining the excellent properties of the untreated materials. The reaction is extremely versatile and can be carried out with a variety of monomers and carbon-based materials. The surface properties of these products have been studied by direct wetting experiments on the nanoscale, dispersion studies, and inverse gas chromatography (IGC). Water dispersible materials with cationic, anionic, and non-ionic surface functionalities provide simple processing routes to a range of applications, and are particularly well suited to studying biological interactions. The interaction with the lung epithelial and macrophages is particularly interesting.
A different approach to nanotube processing, relies on reductive charging. Using a liquid ammonia process, pure nanotubides can be redissolved, purified, or optionally functionalised without sonication. The G/D ratios observed during the dissolution sequence, as a function of metal:carbon ratio, demonstrate a new purification method for removing carbonaceous impurities from pristine SWNTs. The production of individualised SWNT solutions has been confirmed by neutron scattering. A similar approach can be applied to graphene nanoplatelets. The resulting nanocarbon ions can be readily chemically grafted for a variety of applications, depending on the reagent, charge density, and ionic concentration in the reaction medium. The nature of the reactivity of charged graphenides is unusual, due to the continuum density of states of these otherwise molecularly discrete species. Interestingly, the chemical charging agent can be avoided by a pure electrochemical process that yields both nanotube anions and cations, suitable for purification, functionalization, or electrodeposition, as desired. Dispersed nanocarbon related materials can be assembled, by electrophoresis, cryogel formation, or direct cross-linking to form Joule heatable networks and catalyst supports, particularly suited to combination with other 2d materials, such as layered double hydroxides.