Functionalization and defunctionalization of single walled carbon nanotubes: Electrochemical and morphologic consequences

Abstract

Electrochemical oxidation and subsequent electrochemical reduction of single walled carbon nanotubes was carried out by cyclic voltammetry. Using methods of Raman and absorption spectra it was revealed that oxidation of SWCNT electrodes leads to significant disruption of electronic structure of nanotubes; the structure can be substantially restored in the course of subsequent cathodic polarization. The quantitative relationship between the concentration of various oxygen-containing functional groups present on the pristine surface, electrochemically oxidized and subsequently reduced single walled carbon nanotubes was demonstrated with the use of XPS. It was shown that upon application of anodic potentials, functionalization of metallic SWCNTs proceeds deeper than in the case of semiconductor ones. The correlation between the degree of functionalization of SWCNT electrodes and kinetic parameters of electron transfer were studied using redox couples: [Ru(NH3)6]2+/3+, [Fe(CN)6]4−/3−, and Fe2+/3+. The essential growth of the electron transfer rate constant observed for couple Fe+2/+3 was suggested to results from the coordination of iron ion to oxygen from functional groups, formed at water electrolysis. It was demonstrated that the maximum rate constant for the system is reached at the medium functionalization degree.