Oxidation and Reduction of Single-Wall Carbon Nanotube Materials

Temperature programmed desorption (TPD) and in situ deffuse reflectance Fourier transform infrared (DRFTIR) spectroscopy have been employed to compare the oxidation of arc- and laser-generated carbon single-wall nanotube (SWNT) materials. We have found the oxidation behavior of these two materials to be surprisingly different. Both arc- and laser-generated SWNT materials undergo 'self-oxidation'while annealing in vacuum. Surface hydroxyl and carbonyl species are decomposed during heating with a corresponding desorption of H2O and CO2. These oxidizers can then react with the surfaces to remove carbon in the form of CO. The arc-generated SWNTs are selectively opened by oxidation in 1 torr H2O but consumed by oxidation in 1 torr O2 between 600 - 975 K. In contrast, temperatures of approx.1050 K are required for significant oxidation of the laser-generated soots in approx. 1 torr O2. Here O2 oxidation results in the purification of the laser-generated SWNTs rather than complete consumption. DRFTIR studies and TPD experiments following oxidation in D2O indicate that the more selective removal of the nanotube caps resulting from oxidation in water is due to hydrogen (deuterium)termination of surface carbon dangling bonds. Finally, the reduction of laser-generated soots has also been studied. Hydrogenation of the carbon material occurs at 775 K in 650 psi H2. However, the reaction is undetected at a lower H2 pressure of 2 torr.