DFT studies of COOH tip-functionalized zigzag and armchair single wall carbon nanotubes

Structure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory. From 1 to 9 COOH groups were added at the end of the nanotube. The differences in structure and energetics of partially and fully functionalized SWCNTs at one end of the nanotube are observed. Up to nine COOH groups could be added at one end of (9,0) zigzag SWCNT in case of full functionalization. However, for (5,5) armchair SWCNT, the full functionalization was impossible due to steric crowding and rim deformation. The dependence of substituent attachment energy on the number of substituents at the carbon nanotube rim was observed

OH-functionalized open-ended armchair single-wall carbon nanotubes (SWCNT) studied by density functional theory

The structures of ideal armchair (5,5) single-wall carbon nanotubes (SWCNTs) of different lengths (3.7, 8.8, and 16.0 Å for C40H20, C80H20, and C140H20) and with 1–10 hydroxyl groups at the end of the nanotube were fully optimized at the B3LYP/3-21G level, and in some cases at the B3LYP/6-31G* level, and the energy associated with the attachment of the OH substituent was determined. The OH-group attachment energy was compared with the OH functionalization of phenanthrene and picene models and with previous results for zigzag (9.0) SWCNT systems. In comparison to zigzag SWCNTs, the armchair form is more (by about 5 to 10 kcal mol−1) reactive toward hydroxylation

Preliminary Investigations into the Purification and Functionalization of Multiwall Carbon Nanotubes

The purification and functionalization of commercial multiwall carbon nanotubes was investigated. Carbon nanotubes (CNT CO., Ltd, Korea) were treated with boiling concentrated HNO_3 under a reflux condenser for about 50 h at 120°C in order to purify and oxidize the raw material. The oxidized multiwall carbon nanotubes were rinsed with deionized water until stabilization of the filtrate pH. Measurement techniques included elemental analysis (CHN), scanning electron microscopy with energy dispersive X-ray spectrometer, inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy and thermal analysis. With the measurement techniques used the following information was obtained: CHN analysis provided information about the quantitative composition of the following elements carbon, hydrogen, nitrogen, scanning electron microscopy imaging provided information on shape, thickness and length of the nanotubes, energy dispersive X-ray spectrometry analysis of information about surface atomic composition of the quantitative analysis, inductively coupled plasma mass spectrometry quantitative analysis of the atomic composition (metals, especially Fe, Al), the Fourier transform infrared studies provided information about qualitative analysis of surface functional groups $C_{x}O_{y}H_{z}$ (COOH, OH, COO) and thermal gravimetric-differential thermal analysis - quantitative analysis of thermal decomposition products. It was found that oxidation leads to the removal of amorphous carbon and forms mainly carboxylic functional groups linked to the nanotubes. The Fourier transform infrared spectra indicate the presence of some other structures, like ketone (quinone), acid anhydride, ether and epoxy groups. Nitric acid treatment also effectively removes aluminum oxide catalyst and iron catalyst from commercial multiwall carbon nanotubes