Surface Chemistry and Thermal Stability in Air of Carbon Nanotubes Functionalised via a Novel Eco-Friendly Approach to HNO3 Vapor Oxidation

Some crucial aspects of the functionalisation of carbon nanotubes by nitric acid vapors are investigated, namely selectivity of the process and thermal stability in air of the functionalised materials. Results obtained by varying duration (0.5–5.0 h) of the conventional treatment with vapors at azeotropic HNO3 concentration are compared with those obtained, for fixed duration (2.0 h), by using sub-azeotropic HNO3+H2O+Mg(NO3)2 solution to generate acid vapors with acid concentration in the range 25–93 wt%, as recently proposed by us. A thorough picture is drawn based on evidences of high-resolution transmission electron microscopy, micro Raman spectroscopy, thermo-gravimetry, derivative thermo-gravimetry, and temperature-programmed desorption systematic analyses.