Nano Paper

Functionalization of Carbon Nanotubes by Chemical Vapor Deposition method with Nitrogen: Chemical vapor deposition is a method used to produce materials of high performance and purity. It is a common bottom up approach for the production of carbon nanotubes and is also a means of depositing atoms on them for their functionalization. The type of chemical vapor deposition used in this case is the catalytic type, which involves the use of one or more catalysts, and the growth of the nanotubes is initiated and carried on by process gas like ammonia, nitrogen or hydrogen and a carbon containing gas (Wikipedia). As mentioned above, CVD can be used as method of carbon nanotube functionalization with atoms like nitrogen. There is available evidence of studies performed to produce and characterize carbon nanotubes functionalized with nitrogen using CVD. The chemical deposition of nitrogen on carbon nanotubes involved n-doping of nitrogen atoms on the CNTs. Ayala et al describe the process of chemical deposition of nitrogen on CNTs energetically unfavorable, explaining the reason of limited literature available for the process. They used the hot-wall CVD method maintaining a low pressure of about 10-8 mbar, using benzylamine and acetonitrile as carbon and nitrogen feedstocks while iron coating compounds were used as catalysts.

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Figure 1-SEM and TEM characterization of acetonitrile and benyzlamine nanotubes. The resultant CNTs had nitrogen content of 0.2% and 6% respectively from benzylamine and acetonitrile feedstocks. Figure 1 shows, the overall morphology of the products from benzylamine and acetonitrile in images a and d respectively, while b and e show the same in lower resolution from SEM. Images c and f are the TEM images of nanotubes obtained from benzylamine and acetonitrile feedstocks respectively (Ayala et al). The following figure shows the XPS comparative analysis of the C1s line in the two types of CNTs formed with the formulas C7H9N and C2H3N and nitrogen content analysis in the two typed of CNTs obtained (Ayala et al).

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Figure 2- (a) XPS comparative analysis of C1s line, (b) N-content analysis of C7H9N CNT, and (c) N-content of C2H3N CNT In a similar study performed by Abou-Rachid et al, floating catalyst method CVD was used for the synthesis of CNTs encapsulated cubane N8 and N4 doped on to them. They were then studied using molecular simulations to determine their electronic structure, thermodynamic and chemical properties. The study revealed that while the nitrogen atoms bearing a positive charge maintain the aromatic nature of the CNTs, the one with a negative charge give rise o defects in the structure. The authors mention that the synthesis confirmed the doping of nitrogen onto the doping sites, however, the resulting structures are yet not clear (Abou-Rachid et al). As mentioned before, not much has been done in this direction of CNT functionlaization with nitrogen and the research is still active to find the most efficient method. References: Abou-Rachid, Hakima, Anguang Hu, David Arato, Xueliang Sun, and Sylvain Desilets. "Novel Nanoscale High Energetic Materials: Nanostructred Polymeric Nitrogen and polynitrogen." Ayala, Paola, Fernando Friere, Mark Rummeli, Alexander Gruneis, and Thomas Pichler. "Chemical vapor deposition of functionalized singlewalled carbon nanotubes with defined nitrogen doping." phys. stat. sol. (b) 244, No. 11, 4051–4055 (2007) "Carbon Nanotube." Wikipedia. Web. 24 Nov. 2009. http://en.wikipedia.org/wiki/Carbon_nanotube#Chemical_vapor_deposit ion_.28CVD.29