Nitroxides adsorption on carbon nanotubes

XPS and XAS experiments, combined with DFT calculations, revealed that the reactivity of single-walled CNTs towards NOx depends on their metallicity. Ultrapure metallic CNTs are twice more prone to NO2 physisorption than their semiconducting counterparts, while the latter induce more dissociation on the adsorbed NO2.

G. Ruiz-Soria et al., ACS Nano 8, 1375 (2014).

CNTs are one of the most attractive alternatives for detection of environmentally harmful gaseous species. The assessment of the interaction betweenthe nanotubes' external walls and the molecules, however, remains a challenging issue. As pilot experiment, we investigated the physicochemical effects in the interaction of NOx and the outer wall of SWCNTs sorted according to their metallic character.
Observations on the lineshape and shifts in the C 1s and N 1s core levels and the Franck Condon satellites resolved in the XAS spectra (related to NO dimers) strongly suggest that the reaction pathways of the NOx molecules are very different to what had been reported so far. The adsorption reaction is charge transfer mediated physisorption, and is more effective for metallic CNTs. Moreover adsorbed NO2 transforms into NO dimers following the endothermic chemical reaction of 2NO2 → 2NO+ 2O. The oxygen from the chemical reaction with the SWCNTs may be physisorbed as O2 or

chemisorbed on pristine SWCNTs forming epoxide groups or at defects as carbonyl or ketene groups. The amount of reaction products, however, is smaller than observed for mixed CNTs, the semiconducting structures being the more active ultrapure material.
Complementary experiments on the desorption of the system show a very fast recovery and hence provide evidence of the reversibility of the process.

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Revealing the Adsorption Mechanisms of Nitroxides on Ultrapure, Metallicity-Sorted Carbon Nanotubes;
Georgina Ruiz-Soria, Alejandro Pérez Paz, Markus Sauer, Duncan John Mowbray, Paolo Lacovig, Matteo Dalmiglio, Silvano Lizzit, Kazuhiro Yanagi, Angel Rubio, Andrea Goldoni, Paola Ayala, and Thomas Pichler;
ACS Nano 8, 1375-1383 (2014).
Last Updated on Monday, 07 May 2018 16:26