Thermal Stability of Plasma Generated Oxygenated Functionalities on Carbon Nanotubes

Colloidal suspensions of functionalized carbon nanotubes (CNT nanofluids) have the potential to be used in a variety of applications, many of which require operation at elevated temperatures. In this study, we examine what effect exposure to an argon/oxygen/ethane RF glow discharge plasma has on the surface chemistry and structure of CNTs and what happens to the plasma-generated functionalities at high temperatures. An analysis performed using X-ray photoelectron spectroscopy and Raman spectroscopy indicates that longer and higher power plasma treatments decrease the sp2 graphitic nature of the CNTs without increasing the degree of oxygen functional groups. Heating of the functionalized-CNTs up to 350 °C in air and 600 °C in argon, both lead to a substantial decrease in the surface oxygen concentration, which can be attributed to the decomposition of carboxylic functionalities at low temperatures (< 350 °C).