UV–VIS–NIR spectroscopy study of sensitivity of single-wall carbon nanotubes to chemical processing and Van-der-Waals SWNT/SWNT interaction. Verification of the SWNT content measurements by absorption spectroscopy

Abstract

Spectrophotometric measurements of a large number of suspensions of SWNTs-containing soots in aqueous solutions of a surfactant with known weight/volume ratio have been carried out. SWNTs were purified by two methods, by gas-phase oxidation and by centrifugation of suspension. In contrast with gas-phase oxidation, centrifugation does not lead to chemical modification of SWNTs and to irreversible waste of substance. It was shown that gas-phase oxidation, as compared with centrifugation, weakly (by 5%) enriches samples (in which more than 60% of SWNTs were burned) by SWNTs with large diameters. Gas-phase oxidation of nanotubes produces no shift of the van Hove singularity peak positions of solitary nanotubes. It increases relative height of the van Hove bands of solitary nanotubes due to predominant combustion of defective nanotubes. The red shift of the van Hove singularity peaks can be used as a qualitative measure of agglomeration. Comparison of suspension spectra after powerful centrifugation at 160 000g (spectra of solitary nanotubes) shows that different catalysts of the arc discharge synthesis (Ni/Co, Ni/Y, Ni/La, Ni/Ce, Ni/Gd, Ni/Pr) produce almost the same diameter set of SWNTs, but with different distribution. A careful examination of the spectrophotometric method of determination of the abundance of SWNTs in aqueous surfactant suspensions with known weight/volume ratio was carried out.