Gas sensing with Carbon Nanotubes

Carbon nanotubes (CNTs) are attractive materials both as benchmarks of fundamental physical properties in a one-dimensional nanosystem and for a wide variety of nanotechnology applications. Due to their high surface to volume ratio and being characterized by a conductance that can be easily perturbed by interaction with gas molecules, CNTs are promising candidates as active elements for extremely sensitive gas-sensing devices. However, the response of pristine CNTs to gases is weak and scarcely selective since the ideal carbon hexagonal network is held together by strong sp2 bonds characterized by a low chemical reactivity with the molecular environment. Consequently, the functionalization of the CNT sidewalls is mandatory to improve both the sensitivity and the selectivity of CNT-based gas sensors.

In collaboration with Prof. J.-C. Charlier we have used combined DFT/NEGF approach to have show that carbon nanotubes with oxygenated-vacancy defects [Phys. Rev. B 80, 155447 (2009)] or  – better – decorated with Au nanoparticles [Nanotechnology 20, 375501 (2009); ACS Nano 5 (6), 4592–4599 (2011); Procedia Chemistry 1, 1, 931-934 (2009)] can lead to highly sensitive and selective gas sensors thanks to the extraordinary catalytic properties of metal nanoparticles.

ToC_metals_web

Electronic device for gas sensing (left) whose active element is a mat of carbon nanotubes functionalized with Au nanoparticles (middle). The ball-and-stick model of a CNT decorated with a Au13 nanocluster with adsorbed a NO2 molecule is shown to the right
[ACS Nano 5(6), 4592–4599 (2011)]

This work has been performed with the “Nano2Hybrids” EU STREP project, including Université catholique de Louvain, Université de Namur, Université Libre de Bruxelles, University of Tarragona and the Gabriel Lippmann CRP in Luxembourg. Gas sensors based on this concept have been produced and are commercialized by the SENSOTRAN company based in Barcelona. Our work led to three patents of a micro sensor that can selectively detect trace amounts of benzene (Spanish patent P200930969, year: 2009, Patent Cooperation Treaty Application WO2011055298, year 2011, EU patent EP2499482 year:2012).

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