Production and Purification of Carbon Nanotubes

Most methods of nanotube production aim to vaporize a carbon source to allow for the growth of nanotubes from out of the gas phase. Only approaches of rational synthesis that intend a step-by-step construction of the lattice can do without this detour via the gas phase. 

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Figure 23-10 Purification of carbon nanotubes by molecular exclusion chromatography. An electric arc struck between graphite rods creates nanometer-size carbon products, including tubes with extraordinary strength and possible use in electronic devices. Molecular exclusion chromatography separates nanotubes (fraction i) from other forms of carbon in fractions 2 and 3. The stationary phase is PLgel MIXED-A, a polystyrene-divinylbenzene resin with pore sizes corresponding to a molecular mass range of 2 000 to 40 000 000 Da. Images of carbon in each fraction were made by atomic force microscopy. [B. Zao, H. Hu, S. Niyogi, M. E. Itkis. M. A. Hamon, P. Bhowmik, M. S. Meier, and R. C. Haddon, . Am. Chem. Soc. 2001, i23,11673.]...

In conclusion, we have successfully demonstrated that, by using a fluorous label and a fluorous solvent, we can affect the phase transfer of gold and CdSe nanoparticles from an aqueous or hydrocarbon medium to the fluorous phase. Single-walled carbon nanotubes and ZnO nanorods can be solubilized in a fluorous solvent after interaction with a fluorous amine. Phase transfer of the nanostructures to a fluorous solvent represents solubilization in a highly nonpolar solvent, accompanied by purification. The high nonpolarity of the fluorocarbon makes it possible to study the optical and other properties of nanostructures in a medium of very low refractive index. Since the fluorocarbon extracts only the species attached to the fluorous label, the process enables one to obtain solely one product in the pure state. We believe that fluorous chemistry may have practical utility in carrying out studies of nanostructures. 

For an industrial-scale production of carbon nanomaterials, it is important to use a simple and environmentally friendly purification method to selectively remove sp -bonded carbon from nanodiamond and amorphous carbon from nanotubes with minimal or no loss of diamond or nanotubes. In contrast to current purification techniques, which usually use mixtures of oxidizing acids, controlled air oxidation does not require the use of toxic or aggressive chemicals, catalysts, or inhibitors, thus opening avenues for numerous new applications of carbon nanomaterials. 

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