Detection of Redox Properties of (6,5)-Enriched Single-Walled Carbon Nanotubes Using Potassium Permanganate (KMnO4)

Abstract

It has been reported that even if single-walled carbon nanotubes (SWNTs) are coated with the same polymer, the redox characteristics change of each chirality may differ. Particularly, the addition of hydrogen peroxide (H2O2) minimally affects the near-infrared (NIR) absorption spectra of the dsDNA-(6,5)-enriched SWNT complex (DNA-SWNT complex). Detecting the redox properties of (6,5) chirality using NIR absorption spectra has been one of the issues to be solved. We hypothesized that an oxidizing agent with high oxidizing power is required to detect the absorption spectra of (6,5) chirality. In this study, we used KMnO4, which contains atoms with a high oxidation number. A dispersion was prepared by mixing 0.5 mg of (6,5)-enriched SWNT powder with 1 mg/mL of DNA solution. After adding H2O2 or KMnO4 to this dispersion and oxidizing it, catechin solutions were added to reduce the dispersion. The absorption peak of the DNA-SWNT complex decreased by 23.9% following the addition of KMnO4 (final concentration: 0.5 µM) and recovered 30.7% following the addition of the catechin solution. We revealed that the changes in the absorption spectra change of (6,5) chirality, which could not be detected by H2O2, can be detected by using KMnO4. We also varied the concentration of KMnO4 and verified whether the adsorption of KMnO4 can be modeled as a Langmuir adsorption isotherm.