Chemistry of single-wall Carbon Nanotubes: Studies in purification, non-covalent modifîcation by tertiary phosphines and covalent functionalisation via Nucleophilic reduction

Abstract

Carbon nanotubes (CNTs) have attracted considerable research interest owing to their exciting properties and potential for a wide range of applications. However, major challenges must be overcome before these applications can be realised. As-prepared CNT material contains a significant proportion of impurities, such as amorphous carbon, fullerenes and metal catalyst particles. The raw CNT material must be purified before the CNTs can be studied and utilised. Also, CNTs tend to aggregate into bundles or "ropes”, and have poor solubility in common solvents, making their handling and processing extremely difficult. Also, many applications require individually separated CNTs. To improve the solubility of CNTs, and amenability to processing on a large scale, chemical modification of CNT surfaces is necessary. To this end, non-covalent as well as covalent strategies have been developed. However, chemical modification may perturb the electronic structure of CNTs, thereby compromising their interesting properties. The challenge, therefore, is to develop chemical modification routes that improve CNT solubility while not seriously affecting their properties. In this work, we firstly study the problem of purification of as-produced CNT material. We have resolved a major controversy concerning the use of oxidising acids for purifying CNTs, which has profound implications for the spectroscopy and subsequent chemical modification of the CNTs. Secondly, we have developed a route for the non- covalent modification of CNTs by tertiary phosphines. This method has the advantages of significantly improving the solubility of CNTs in organic solvents while being extremely simple, not seriously perturbing the CNT electronic structure, as well as not rendering large areas of the CNT inaccessible^ Thirdly, we describe a method for the covalent derivatisation of CNTs based on reduction, followed by electrophilic substitution. This route is considerably more facile and versatile than other covalent functionalisation methods reported to date, and does not cause significant disruption of the CNT electronic structure. Finally, we demonstrate the covalent attachment of formyl (-CHO) groups to CNT walls, which could potentially open the gateway for a plethora of of coupling and modification reactions.