Carbon Nanotube aggregation

Murr, L.E., Garza, K.M., Soto, K.F., Carrasco, A., Powell, T.G., Ramirez, D.A., Guerrero, P.A., Lopez, D.A., and Venzorlll, J. (2005) Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment. International Journal of Environmental Research and Public Health, 2 (1), 31-42. 

Barone PW, Strano MS. Reversible control of carbon nanotube aggregation for a glucose affinity sensor. Angewandte Chemie, International Edition 2006, 45, 8138-8141. 

Yang CM, Kaneko K, Yudasaka M, lijima S (2002) Effect of purification on pore structure of HiPco single-walled carbon nanotube aggregates. Nano Lett 2(4) 385-388... 

Carbon nanotubes are also of considerable interest with regard to both reinforcement and possible increases in electrical conductivity [237-239]. There is considerable interest in characterizing the flexibility of these nanotube structures, in minimizing their tendencies to aggregate, and in maximizing their miscibilities with organic and inorganic polymers. 

Unlike the smaller, spheroidal fullerenes discussed previously, carbon nanotubes are not easily solubilized, even in organic solution. The reality is that all SWNTs and MWNTs are insoluble in all solvent systems. They also have a strong tendency to bind together and aggregate due to van der Waals attractive forces along the length of the nanotube. Since the length-to-diameter... 

An important route to solubilization of carbon nanotubes is to functionalize their surface to form groups that are more soluble in the desired solvent environment. It has been shown that acid treatment of nanotube bundles, particularly with HC1 or HNO3 at elevated temperatures, opens up the aggregate structure, reduces nanotube length, and facilitates dispersion (An et al., 2004 Kordas et al., 2006). Nitric acid treatment oxidizes the nanotubes at the defect sites of the outer graphene sheet, especially at the open ends (Hirsch, 2002 Alvaro et al., 2004), and creates carbonyl, carboxyl, and hydroxyl groups, which aid in their solubility in polar solvents. 

Murr LE, Bang JJ, Esquivel EV, Guerrero PA, Lopez A (2004) Carbon nanotubes, nanocrystal forms, and complex nanoparticle aggregates in common fuel-gas combustion sources and the ambient air. J Nanopart Res 6 241-251. 

Raja PMV, Connolley J, Ganesan GP, Ci LJ, Ajayan PM, Nalamasu O, Thompson DM (2007) Impact of carbon nanotube exposure, dosage and aggregation on smooth muscle cells. Toxicol Lett 169 51-63. 

R. H. Schmidt, I. A. Kinloch, A. N. Burgess, A. H. Windle, The effect of aggregation on the electrical conductivity of spin-coated polymer/carbon nanotube composite films, Langmuir, vol. 23, pp. 5707-5712, 2007. 

Eerguson, P. E. DeMarco, A. Aggregation and Sorptive Properties of Single-Walled Carbon Nanotubes in the Estuarine Environment. Proceedings of the 233rd American Chemical Society National Meeting, Chicago, IE, March 25-29, 2007. 

Self-assembled objects of various nature bear the name nanotubes. Some of them are covalently bound structures while other are self-assembled aggregates.The best known among them are probably elongated fullerenoid structures called carbon nanotubes obtained, in addition to spheroidal fullerenes,... 

In many cases the potential application of single-walled carbon nanotubes is associated with solubility of this nanomaterial in different solvents. Unfortunately, nanotubes are poorly soluble in the most of organic solvents and are insoluble in water, and this fact especially hinders biological using SWNT. Weak solubility of SWNT is a result of substantial van der Waals attractions between nanotubes aggregated in bundles. To solve nanotubes in water without any covalent functionalization, a surfactant would be added into aqueous solution, and then this mixture is suspended by sonication. It is supposed that the sound wave splits bundles in aqueous solution. A surfactant in suspension adsorbed onto the nanotube surfaces precludes aggregation of nanotubes in bundles. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

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