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Purification and Processing of Graphitic Carbons


Carbon materials exist in several forms and have a wide range of applications that are commonly encountered in everyday life. The more familiar applications range from car tires to cosmetics. The breadth of applications is solely due to the various graphitic and amorphous structures of carbon, which gives rise to a wide range of properties that can be engineered to obtain the desired feature or function. Allotropes of carbon include diamond, fullerenes, graphite (graphene) and carbon nanotubes. The latter two are the focus of this dissertation and their characterization, purification, and functionalization will be described in detail.

High solubility of purified single-walled carbon nanotubes (SWNTs) and graphene is desired for their utilization in various applications. In the case of SWNTs, concentrated nitric acid treatment is the most common form of purification currently used. It is highly effective in the removal of residual metal catalysts, but generates unwanted carbonaceous byproducts known as carboxylated carbons (CCs). Little is known about the nature of these species (CCs), and it is has been suggested that because of their high carboxylic acid functionality and their adhesion to the SWNT side wall, that upon functionalization of an oxidized nanotube sample, the majority of the functionalization is occurring on the CCs and not the SWNTs, and that upon their removal, the SWNTs are rendered insoluble. Similar to SWNTs, soluble graphene is desirable to achieve facile manipulation of the material for device applications although the exfoliation of graphite to form a single layer has proven to be challenging.

In this dissertation, the characterization of the CCs will be discussed and upon their removal, it is demonstrated that solubility of the purified SWNTs is retained upon covalent functionalization with octadecylamine (ODA). Soluble graphene layers were formed by reacting graphite fluoride with alkyl lithium reagents. Functionalized graphene can be readily prepared by this technique and dispersed in organic solvent and upon annealing, the intrinsic properties can be partially restored. This dissertation serves to extend the achievements previously developed by the Haddon research group and adds to the continued progress in the advancement of carbon materials chemistry.

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