Chemistry of carbon nanomaterials: Uses of lithium nanotube salts in organic syntheses and functionalization of graphite
Doctor of Philosophy
The effective utilization of carbon nanomaterials, such as single-walled carbon nanotubes (SWNTs) and graphite, has been hindered due to difficulties (poor solubility, poly-dispersity) in processing. Therefore, a high degree of sidewall functionalization, either covalent or non-covalent, is often required to overcome these difficulties as the functionalized nanomaterials exhibit better solubility (either in organic solvents or in water), dispersity, manipulation, and processibility. This thesis presents a series of convenient and efficient organic synthetic routes to functionalize carbon nanomaterials. Carbon nanotube salts, prepared by treating SWNTs with lithium in liquid ammonia, react readily with aryl halides to yield aryl-functionalized SWNTs. These arylated SWNTs are soluble in methanol and water upon treatment with oleum. Similarly, SWNTs can be covalently functionalized by different heteroatoms (nitrogen, oxygen, and sulfur). Using the reductive alkylation approach, a synthetic scheme is designed to prepare long chain carboxylic acid functionalized SWNTs [SWNTs-(RCOOH)] that can react with (1) amine-terminated polyethylene glycol (PEG) chains to yield water-soluble biocompatible PEGylated SWNTs that are likely to be useful in a variety of biomedical applications; (2) polyethyleneimine (PEI) to prepare a SWNTs-PEI based adsorbent material that shows a four-fold improvement in the adsorption capacity of carbon dioxide over commonly used materials, making it useful for regenerable carbon dioxide removal in spaceflight; (3) chemically modified SWNTs-(RCOOH) to permit covalent bonding to the nylon matrix, thus allowing the formation of nylon 6,10 and nylon 6,10/SWNTs-(RCOOH) nanocomposites. Furthermore, we find that the lithium salts of carbon nanotubes serve as a source of electrons to induce polymerization of simple alkenes and alkynes onto the surface of carbon nanotubes. In the presence of sulfide/disulfide bonds, SWNT salts can initiate the single electron transfer (SET) mechanism to functionalize carbon nanotubes with different alkyl/aryl groups. Using the reductive alkylation approach, we can also functionalize graphites by alkyl/carboxylic acid groups, making graphite soluble in organic solvents and water. Tailoring of graphite layers is also accomplished by using different metals in liquid ammonia. Finally, SWNT-epoxides/graphite epoxides are synthesized using m-CPBA. Quantification of the epoxide substituents on the nanotube/graphite surface is evaluated through the catalytic de-epoxidation reaction using MeReO 3/PPh3 as heterogeneous catalyst. In summary, the proposed covalent functionalization methods yield derivatized nanomaterials that can provide a solid platform for a number of exciting applications, ranging from material science to biomedical devices. Furthermore, the results presented in this thesis provide insight into the molecular chemistry at nano-resolution.
Organic chemistry; Engineering; Materials science