Covalent modification of single wall carbon nanotubes upon gamma irradiation in aqueous media

Abstract

Single wall carbon nanotubes (SWCNTs) were exposed to gamma radiation, absorbing the doses of 25, 50 and 100 kGy in aqueous environment. After the irradiation treatment, the changes in the structure were studied using Fourier transform Infrared and Raman spectroscopy, thermogravimetric analysis and atomic force microscopy. Fourier Transform Infrared Spectroscopy has shown that the irradiation of SWCNTs in aqueous environment leads to covalent functionalization of SWCNTs. The irradiation of water leads to its radiolysis and the formation of free radical species of different types. These species react with nanotube sidewalls and in such way carboxylic and hydroxylic groups are covalently bonded to the sidewalls of SWCNTs. Thermogravimetric analysis was used to estimate the total amount of covalently bonded groups. The highest ratio of covalently bonded groups appears in nanotubes irradiated with the 100 kGy dose. Raman spectroscopy proved that the increase in irradiation doses leads to an increase of structural disorder of SWCNTs, presumably in the form of defects in carbon nanotube walls. Examination of ID to IG ratio shows a three times larger degree of structural disorder after the irradiation treatment with 100 kGy. The analysis of carbon nanotube Raman spectra RBM bands determined the presence of both semiconducting and metallic carbon nanotubes after gamma irradiation treatment. These measurements prove that gamma irradiation treatments have a nonselective effect regarding different chirality and therefore conductance of nanotubes. Atomic force microscopy shows a significant carbon nanotube shortening as the effect of gamma radiation treatment. Nanotubes with length between 500 nm and 1 μm are predominant.