Revealing the adsorption mechanisms of nitroxides on ultra-pure, metallicity-sorted carbon nanotubes

ACS Nano 8, 1375 - 1383 (2014)

Revealing the adsorption mechanisms of nitroxides on ultra-pure, metallicity-sorted carbon nanotubes

Georgina Ruiz-Soria, Alejandro Pérez Paz, Markus Sauer, Duncan J. Mowbray, Paolo Lacovig, Matteo Dalmiglio, Silvano Lizzit, Kazuhiro Yanagi, Angel Rubio, Andrea Goldoni, Paola Ayala, Thomas Pichler

Carbon nanotubes are a natural choice as gas sensor components given their high surface to volume ratio, electronic properties and capability to mediate chemical reactions. However, a realistic assessment of the interaction of the tube wall and the adsorption processes during gas phase reactions has always been elusive. Making use of ultra-clean single-walled carbon nanotubes, we have followed the adsorption kinetics of NO2 and found a physisorption mechanism. Additionally, the adsorption reaction directly depends on the metallic character of the samples. Franck-Condon satellites, hitherto undetected in nanotube-NOx systems, were resolved in the N 1s X-ray absorption signal, revealing a weak chemisorption, which is intrinsically related to NO dimer molecules. This has allowed us to identify that an additional signal observed in the higher binding energy region of the core level C 1s photoemission signal is due to the C=O species of ketene groups formed as reaction by-products. This has been supported by density functional theory calculations. These results pave the way toward the optimization of nanotube-based sensors with tailored sensitivity and selectivity to different species at room temperature.

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This work was supported by the Austrian Science Fund through Project FWF P21333-N20 and by the EU Proposal No. 20105285 for ELETTRA. P.A. was supported by a Marie Curie Intra European Fellowship within the Seventh European Community Framework Programme. D.J.M. acknowledges funding through the Spanish “Juan de la Cierva” program (JCI-2010-08156). We acknowledge funding by the European Research Council Advanced Grant DYNamo (ERC-2010-AdG - Proposal No. 267374), Spanish Grants (FIS2010-21282-C02-01 and PIB2010US-00652), “Grupos Consolidados UPV/EHU del Gobierno Vasco” (IT-319-07 and IT-578-13), and the European Commission project CRONOS (280879-2 CRONOS CP-FP7) and POCAONTAS (FP7-PEOPLE-2012-ITN). A.G. thanks the COST ACTION EuNetAir (No. TD1105).

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