Crystalline Quality Evaluation of Carbon Nanotubes by Kinetic Analysis in Quasi‐Isothermal Conditions

Abstract

We demonstrate that the crystalline quality of multi‐walled carbon nanotubes (MWCNTs) is better estimated by the apparent activation energy of the oxidation reaction, obtained by kinetic analysis in quasi‐isothermal conditions, than by the peak‐temperature position in the derivative mass loss curves. This is proven by the existence of a good correlation, reported for the first time herein, between apparent activation energy and G′‐band to D‐band intensity ratio derived from micro‐Raman spectroscopy, which is largely accepted as an indicator of the overall MWCNT crystalline quality. In contrast, no clear reliance is found between G′/D intensity ratio and the peak‐temperature position in the derivative mass loss curves. These conclusions were drawn after investigation of a large number of commercially available and laboratory prepared MWCNTs.

Evaluation of the Overall Crystalline Quality of Amorphous Carbon Containing Multiwalled Nanotubes

“…The kinetic oxidation profiles of MWCNTs of set 1 are displayed in Figure . Two distinct regions can be identified in all profiles: the lower temperature region (200–400 °C), where, as mentioned above, the combustion of amorphous/disordered carbonaceous species takes place, and the higher temperature region (400–600 °C), where ordered phases burn following the Arrhenius law . In the former a broad contribution of very weak intensity (amplified by a factor of 100 in Figure a–c) is detected.…”

“…13,15,16,18 Instead, graphitization indexes are derived from the spectra recorded on the whole sample (namely, AC + CNTs), and hence, they include also the contribution arising from the disordered phases. Since the oxidation of the latter does not follow the Arrhenius law, 18 no attempt can be made to infer a value of activation energy that be representative of the reactivity of the whole sample. Although x AC never exceeds 5.1 wt %, this might represent the reason for the failure of Raman indexes in reliably depicting the graphitization degree of present samples.…”

“…Indeed, it has to be reminded that E A CNT is inferred from the region ( T > 400 °C) of the kinetic oxidation profiles where the ordered phases burn. ,,, Instead, graphitization indexes are derived from the spectra recorded on the whole sample (namely, AC + CNTs), and hence, they include also the contribution arising from the disordered phases. Since the oxidation of the latter does not follow the Arrhenius law, no attempt can be made to infer a value of activation energy that be representative of the reactivity of the whole sample. Although x AC never exceeds 5.1 wt %, this might represent the reason for the failure of Raman indexes in reliably depicting the graphitization degree of present samples.…”

“…The temperature ( T HOR ), at which the oxidation occurs at the highest rate, gives a measure of the oxidative resistance of the sample, while the apparent activation energy ( E A CNT ) for oxidation monitors its reactivity. E A CNT is calculated from the slope of the Arrhenius plot of the kinetic oxidation profile in the interval comprised between ignition temperature and T HOR . , …”

Study on the interfacial structures of Tin oxide/multiwalled carbon nanotube heterojunctions

“…In addition, the low G/D values, resulting from the strong interactions, also imply that the apparent activation energy for the oxidation of MWCNTs was decreased. 34 As a result, the strong interactions will favor the oxidation of the MWCNTs by SnO 2 particles in a similar manner to the Mars-van Krevelen mechanism. 35 In Fig.…”