Thermal stability evolution of carbon nanotubes caused by liquid oxidation

Abstract

Carbon nanotubes (CNTs) grown by chemical vapor decomposition of ethylene on alumina- and silica-supported Fe–Co bimetallic catalysts were examined before and after purification encompassing chemical oxidation treatment in 3 M NaOH and 3 M HNO3 solutions, sequentially. Thermal properties were investigated and correlated with structural changes followed by TEM, X-ray diffraction and Raman spectroscopy characterization. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were employed simultaneously in the regime of TPO and TPH, in diluted flow of either O2 or H2. TG revealed almost complete burning of both refined CNT samples in diluted O2, indicating the efficiency of the purification method used to remove the catalyst remains. However, different trends and significant magnitudes of changes in the heat of combustion demonstrate changes in CNTs stability after purification as a function of the catalyst support type. This is the consequence of changes in carbon type, CNTs order degree and morphology, as well as the degree of functionalization, which have their own effects on the CNTs thermal stability.