Pristine, oxidized and defunctionalized carbon nanotubes (CNTs) were studied by Raman spectroscopy, X-ray diffraction, transmission electron microscopy and low temperature nitrogen adsorption. The Raman spectra of the studied samples in the range of 900-1800 cm were deconvoluted into five components to reveal the CNT oxidation mechanism. It was found that the oxidation resulted in the reduction of graphite components and ordering of both the structured and defect part of CNTs. Acid treatment also led to different types of disorders in the surface layers of CNTs. Polyene-type, polyphenylene-type and turbostratic fragments were detected as a result of partial exfoliation. Investigation of defunctionalized CNTs showed the ordering of edge carbon atoms as well as the invariability of the total amount of defects. The study of CNTs as supports for Co-based catalysts revealed a simultaneous decrease in the number of defect fragments and increase in the number of edge carbon atoms during catalyst preparation and reduction.

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The mechanism of thermal defunctionalization of multiwalled carbon nanotubes (CNTs) oxidized by nitric acid was studied. X-ray photoelectron spectroscopy and thermal analysis under different heating rates combined with mass spectrometry of evolved gases (TGA–MS) were used to reveal the transformations on the CNT surface. Hydrogen–deuterium exchange and mathematical handling of TGA–MS curves were carried out to evaluate the impact of a small amount of residual oxygen on CNT defunctionalization. Water, CO, CO2, and NO/CH2O mass curves recorded during TGA–MS study were curve fitted. The resultant peaks were attributed to the different stages of CNT defunctionalization. Deuterium exchanged CNTs allowed one to reveal the mechanism of water release during heating. Kissinger’s model was applied to estimate the activation energy of the decomposition of different functional groups on the surface of CNTs.

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