Chemical functionalisation is critical to a wide range of nanocarbon technologies, 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) and graphenes 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 followed by reaction with functional organic monomers. This approach allows the introduction of a wide variety of functional groups 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. 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, including with lung epithelial cells and macrophages, as well as microglial cells.
A different approach to nanotube processing, relies on reductive charging. Pure nanotubides (nanotube anions) and graphenides can be redissolved, purified, or optionally functionalised, whist avoiding the damage typically associated with sonication and oxidation based processing. 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 nanotubides/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. In all these charged systems, the optimal absolute charge concentration has been found to correlate consistently and systematically with the efficiency of individualisation, subsequent functionalization, and the properties of constructs. Dispersed nanocarbon related materials can be assembled, by electrophoresis, cryogel formation, or direct cross-linking to form reinforced fibres, Joule heatable networks, protein nucleants, supercapacitor electrodes, and catalyst supports, particularly suited to combination with other 2d materials, such as layered double hydroxides. Comparative studies allow the response of nanocarbons with different dimensionalities to be assessed to identify fundamental trends and the most appropriate form for specific situations.