A versatile, solvent-free methodology for the functionalisation of carbon nanotubes

Abstract

High temperature activation of carbon nanotubes (CNTs) provides a new and highly versatile functionalisation strategy. The reaction allows the attachment of a wide variety of functio nal species onto the nanotube surface at grafting ratios between 1 -8 wt%, whilst maintaining the 10 intrinsic properties of the untreated materials. The underlying reaction mechanism has been established by quenching experiments and EPR studies. The distrib ution of the functionalised sites has been investigated at the microscopic scale using tagging reactions. The grafted products have been characterized by electron microscopy, thermal analysis (TGA), Raman spectroscopy, and inverse gas chromatography (IGC). The change in the CNT surface properties after grafting has 15 been quantified in terms of dispersive and specific surface energies, and altered dispersibilities in a broad range of solvents. It is possible to carry out the reaction using gas phase reagents, providing a clean, efficient, and scalable methodology, relevant to a diverse range of applications.

Aqueous cationic, anionic and non-ionic multi-walled carbon nanotubes, functionalised with minimal framework damage, for biomedical application

“…The functionalisation of MWNTs was carried out using an adaptation of the solvent-free thermochemical ‘grafting from’ protocols reported previously [35], taking advantage of preexisting surface oxides on as-received MWNTs rather than an explicit oxidation step. The concentration of oxygen on the surface of typical ~10 nm (diameter) CVD MWNTs, as synthesised, is approximately one oxygen per 100–250 surface carbons [36]; some fraction of these groups will be suitable for generating radicals upon activation.…”

“…Other chemical methods have also been explored [33, 34], but a versatile, scalable method for varying surface character independently of other characteristics is still needed. The recent development of a solvent-free thermochemical grafting approach offers advantages in the preparation of large quantities of clean, functionalised MWNTs with minimal framework damage [35]. The approach takes advantage of existing defective groups on the MWNT surface, remaining from the synthesis process, which decompose at high temperatures and generate free radicals, allowing covalent grafting of a range of monomers [35].…”

“…The recent development of a solvent-free thermochemical grafting approach offers advantages in the preparation of large quantities of clean, functionalised MWNTs with minimal framework damage [35]. The approach takes advantage of existing defective groups on the MWNT surface, remaining from the synthesis process, which decompose at high temperatures and generate free radicals, allowing covalent grafting of a range of monomers [35]. The intrinsic framework of the MWNTs is preserved and there is no production of debris or use of corrosive solutions.…”

Charged Carbon Nanomaterials: Redox Chemistries of Fullerenes, Carbon Nanotubes, and Graphenes

“…However, the nature/reactivity of nanotube-bound radicals remains unclear. 364 For example, no nanotube radical cross-linking termination is reported, despite such reactions being reported through other SWCNTs radical routes. 365 The delocalized conduction band in CCNs may limit conventional localized radical propagation steps, representing an alternative termination.…”

Aqueous dispersions of oligomer-grafted carbon nanomaterials with controlled surface charge and minimal framework damage

“…25 In contrast to traditional acid oxidation protocols, the thermochemical method has significant advantages of minimising the damage to the nanotube framework, whilst avoiding production of debris or the use of corrosive solutions. 24 Here, the thermochemical functionalisation method is extended by using a broader range of monomers with intrinsic cationic or anionic functional groups to modify the surface characters of MWCNTs. The goal was to increase the surface charge on the MWCNTs, using the same set of pre-existing reactive sites, and to simplify the reaction scheme.…”