Carbon nanotubes functionalizing oxidation

I. Gerber, M. Oubenali, R. Bacsa, J. Durand, A. Gonsalves, M. F. R. Pereira, F. Jolibois, L. Perrin, R. Poteau, P. Serp, Theoretical and experimental studies on the carbon-nanotube surface oxidation by nitric acid Interplay between functionalization and vacancy enlargement, Chem. Eur. J., vol. 17, pp. 11467-11477, 2011. 

Arabale G, Wagh D, Kulkami M, Mulla IS, Vemekar SP, Vijayamohanan K, Rao AM (2003) Enhanced supercapacitance of multiwalled carbon nanotubes functionalized with ruthenium oxide. Chem Phys Lett 376 207-213... 

Khene S, Nyokong T (2012) Single walled carbon nanotubes functionalized with nickel phthalocyanines effects of point of substitution and nature of functionalization on the electro-oxidation of 4-chlorophenol. J Porphyrins Phthalocyanines 16(1) 130-139... 

Carbon nanotubes mixed with ruthenium oxide powder, and immersed in a liquid electrolyte, have been shown by a Chinese research group to function as supercapacilors with much larger capacitance per unit volume than is normally accessible (Ma et al. 2000). 

New applications of nitrile oxide 1,3-DC have been reported. Soluble, single-wall carbon nanotubes (SWNT) 32 functionalized with pentyl esters at the tips and pyridyl isoxazoline rings along the walls were prepared using pentyl ester-SWNT as dipolarophile. The complex... 

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. 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

As with fullerenes, carbon nanotubes are also hydrophobic and must be made soluble for suspension in aqueous media. Nanotubes are commonly functionalized to make them water soluble although they can also be non-covalently wrapped with polymers, polysaccharides, surfactants, and DNA to aid in solubilization (Casey et al., 2005 Kam et al., 2005 Sinani et al., 2005 Torti et al., 2007). Functionalization usually begins by formation of carboxylic acid groups on the exterior of the nanotubes by oxidative treatments such as sonication in acids, followed by secondary chemical reactions to attach functional molecules to the carboxyl groups. For example, polyethylene glycol has been attached to SWNT to aid in solubility (Zhao et al., 2005). DNA has also been added onto SWNT for efficient delivery into cells (Kam et al., 2005). 

Wu, B., et al., Functionalization of carbon nanotubes by an ionic-liquid polymer Dispersion ofPt and PtRu nanoparticles on carbon nanotubes and their electrocatalytic oxidation of methanol. Angewandte Chemie International Edition, 2009. 48(26) p. 4751-4754. 

Velickovic, Z., et ah, Adsorption of arsenate on iron(lll) oxide coated ethylenediamine functionalized multiwall carbon nanotubes. Chemical Engineering Journal, 2012.181-182(0) p. 174-181. 

Carbon nanotubes inevitably contain defects, whose extent depends on the fabrication method but also on the CNT post-treatments. As already seen, oxidizing treatments, such as acid, plasma or electrochemical, can introduce defects that play an important role in the electrochemical performance of CNT electrodes. For instance, Collins and coworkers have published an interesting way to introduce very controlled functionalization points or defects on individual SWNTs by electrochemical means [96]. Other methodologies to introduce artificial defects comprise argon, hydrogen and electron irradiation. Under this context, a number of recent works have appeared with the goal of tailoring the electrochemical behavior of CNT surfaces by the controlled introduction of defects [97, 98]. 

In general, on chemical modification carbon nanotubes exhibit much less toxicity or nontoxicity to living cell lines that have been investigated so far.117,118 For instance, Dumortier et al. conducted an in vitro cell uptake study of the functionalized SWNTs with B and T lymphocytes and macrophages.117 Two types of functionalized SWNTs were used, one prepared via 1,3-dipolar cycloaddition reaction and the other obtained through oxidation/amidation treatment. Both types of the functionalized nanotubes were rapidly taken up by lymphocytes and macrophages without affecting the overall... 

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