Oxidation of carbon nanotubes with ozone and hydroxyl radicals

Carbon Nanotubes (CNTs) have been oxidized with ozone in the gas phase and different Advanced Oxidation Processes (AOPs) in the aqueous phase such as H2O2/UV, Fenton reaction and ozonation, in order to functionalize them. A significant difference between the amounts and types of oxygen containing groups were generated using different oxidants. To investigate the efficiency of the oxidation methods, we monitored the depletion of the oxidants, using a titration of H2O2 with KMnO4 and an ozone analyzer for the ozonolysis experiments. Furthermore, we investigated the formation of hydroxyl radicals during the oxidation experiments by decolorization of methylene blue and depletion of salicylic acid. Boehm titration, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, temperature programmed desorption and thermogravimetric analysis have been utilized to characterize the CNTs. Our results demonstrate that direct ozonolysis with water vapor produces the highest amount of oxygen containing surface in comparison to the other oxidation methods, and this by using only a small amount of the available oxidant. With our results we confirm different previous assumptions about the oxidation mechanisms and theoretical calculations for oxidation processes practically.