Acids nanotube purification

Many chromatographic methods such as permeation chromatography, column chromatography, and size exclusion chromatography have been used to purify CNTs. The size exclusion chromatography (SEC) is the only carbon nanotube purification method in the literature that is not subjected to the acid treatments which tend to create the carboxylic functionality on CNTs. 

The hydrothermal process, that is, the treatment of the sample with water at high pressure and temperature (often in the supercritical range), proved a suitable method for nanotube purification. Water evolves surprising reactivity in redox processes at these conditions. It is then capable of dissolving from the samples both amorphous carbon and metallic impurities (especially in the presence of acids during reaction). Choosing the conditions too harsh, however, will do severe... 

Stobinski L, Lesiak B, Kover L, Toth J, Biniak S, Trykowski G, Judek J (2010) Multiwall carbon nanotubes purification and oxidation by nitric acid studied by the FTIR and electron spectroscopy methods. J Alloy Compd 501 77-84 Sudesh K, Abe H, Doi Y (2000) Synthesis, structure and properties of polyhydroxyalkanoates biological polyesters. Prog Polym Sci 25 1503-1555 Tang W, Santare MH, Advani SG (2003) Melt processing and mechanical property characterization of multi-walled carbon nanotube/high density polyethylene (MWNT/HDPE) composite films. Carbon 41 2779-2785... 

Various oxidative processes used for the purification of carbon nanotubes such as refluxing in acid, sonication in sulfuric and nitric acid (3 1) solution, and treatment with... 

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. 

Another strategy is pursued in the direct functionalization of nanotubes. The solubihty of the carbon material in different solvents can be controlled by the attachment of various functional groups. In Section 3.5, numerous examples for a solubility enhancement of single- and multiwalled carbon nanotubes are described. A rather simple functionalization usually occurs already in the first steps of purification. The reaction with concentrated mineral acids does not... 

If a catalytic process has been appUed, residual catalyst must be removed from the crude nanotubes obtained. Further impurities include amorphous carbon and, in parts, fuUerenes. A customary purification comprises an acid treatment which, at the same time, removes the end caps of the formerly closed tubes. 

CN s of exceptionally high purity are required for optimum performance in applications but the synthetic products usually contain impurities such as amorphous carbon, carbon nanoparticles, and some metal catalyst. Different methods have been described for the purification of nanotubes [77] most involve oxidation by use of mineral acids and/or gas phase oxidation to remove catalytic metal particles... 

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