Thermo-oxidative degradation of carbon nanotubes and related nanostructures: role of acidic environment and chloride ions

Abstract

It is shown that acid activation of ultralong carbon nanotubes synthesis products increases their reactivity during subsequent thermochemical treatment in air at 480 °C. Such an integrated approach of CNTs processing provides high purity and maximum yield of the target product. For example, the non-CNT fraction decreases by 3.2 times, while the residual iron content decreases by 17–24 times in comparison with thermochemical treatment without acid. Raman spectroscopy and low-temperature nitrogen adsorption showed that acid activation does not lead to extra surface defects, which could initiate further oxidation of carbon matrix in air. It is suggested that the increased reactivity of CNT synthesis products after acid activation during thermo-oxidative degradation may be due to the formation of an “adduct” of carboxyl groups on the surface of nanotube carbon matrix with hydrogen chloride. It was shown by thermogravimetric studies coupled with mass-spectra investigation of gas evolved, that under the constant heating, at the temperatures of the beginning of intensive oxidation (500–600 °C), the decomposition of the “adduct” occurs, bypassing the stage of formation of more temperature-resistant phenolic groups, which can inhibit further oxidation. Water released during the decomposition of the “adduct” can also accelerate the process of thermal oxidation.

Keywords:

• Carbon nanotube
• CVD
• degradation
• catalyst removal
• thermal analysis
• differential thermogravimetry
• Raman spectroscopy

Acknowledgments

The authors would like to acknowledge Nikita V. Kazennov for samples supplying, Sergey A. Urvanov for discussion, Taisia E. Drozdova for Raman measurements, Natalia I. Batova for SEM and EDX measurements The work was carried out using the equipment of FSBI TISNCM SUEC «Structural Measurements in the Laboratory of the Department of Structural Research.»

Author contributions

Conceptualization, Aida R. Karaeva and Maxim A. Khaskov; methodology, Aida R. Karaeva and Maxim A. Khaskov; validation, Vladimir Z. Mordkovich; investigation, Maxim A. Khaskov, Viktor V. De and Veronika A. Naumova; writing—original draft preparation, Maxim A. Khaskov; writing—review and editing, Veronika A. Naumova and Vladimir Z. Mordkovich; supervision, Vladimir Z. Mordkovich and Aida R. Karaeva; project administration, Vladimir Z. Mordkovich. All authors have read and agreed to the published version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported through State Assignment # FNRW-2022-0002. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.