Functionalization Of Carbon Nanotubes And Their Properties

Water-soluble carbon nanotubes (CNTs) have great potential in the applications of biology, medicine, electronics, energy, and national defense etc.. The functionalization of CNTs, especially the water solubilization of CNTs is the key to the real applications. Thus, functionalization of CNTs becomes as important as their preparation and purification. This dissertation reviews the development and the current status of water solubilization of CNTs, explores the applications of water soluble CNTs in biosensors, and presents the main research contents and results which are listed as follows:1. Multi-walled carbon nanotubes (MWNTs) were treated with K₂S₂O₈ under a mild acidic condition to remove the amorphous carbon impurities. Polymer dispersant hydrolyzed poly(styrene-co-maleic anhydride) (HSMA) was synthesized and used to prepare water soluble MWNTs by an assisted exfoliation and centrifugation. Characterizations of transmission electron microscopy (TEM), UV-vis, fluorescence spectroscopy, and thermal gravimetric analysis (TGA) showed that the as-prepared HSMA-coated MWNTs showed good dissolvability and stability in water with a high solubility of 29.2 mg/mL. The net MWNT solubility reached 8.7 mg/mL.2. In order to further improve the solubility of CNTs, HSMA were derivatized with pyrene to prepare a polymer of HSMA carrying pyrene (HPSMAP), and used to solublize CNTs in water based upon the above-developed dispersant assisted exfoliation and centrifugation, resulting in a highly water-soluble multi-walled carbon nanotubes by irreversible noncovalent functionalization of HPSMAP. Characterizations of TEM, UV-vis, fluorescence spectroscopy, and TGA were conducted. The results showed that HPSMAP wrapped on MWNTs tightly with strong interaction. The composite of HPSMAP-MWNTs showed a high solubility of 46.2 mg/mL. The net MWNT solubility reached 7.4 mg/mL.3. Hydroxyl groups were induced by a mild oxidization of CNTs, and utilized to graft citric acid. The grafted citric were utilized to connect the polymer of citric acid and D-sorbitol by condensation through heating initiation of an anhydride intermediate without any catalysts, solvents, or harsh acid. Thus, multihydroxyl and multicarboxyl groups were introduced onto the surface of MWNTs, making MWNTs soluble in water. Ag nanoparticles were in situ loaded onto the water soluble MWNTs through the mild reduction of Ag⁺ by hydroxyl groups in aqueous solution. The as-described method has the following advantages: (a) It is a green functionalization of CNTs without using any solvents. (b) The solubility of the modified CNTs can be controlled by adjusting the mole ratio of the reactants. (c) Utilizing the hydroxyl and carboxyl groups, further functionalization of CNTs can be conducted targeting CNT-based materials for applications such as biosensors and nanocatalysis.4. Water soluble CNTs prepared by the above described condensation of citric acid and D-sorbitol were used for biosensors application. The immobilization of enzyme and the electrochemical catalysis of the immobilized enzyme on the CNT-modified electrodes were investigated. The results showed that CNTs modified by citric acid and D-sorbitol were able to immobilize enzyme firmly in the absence of any other cross-linking agent. The modified CNTs enhanced the current greatly and maintained the biocatalytic activity of enzyme well toward the reactants.