| Abstract
| - Room-temperature detection of acetone by TiO2/multiwall carbon nanotube (MWCNT) sol−gel compositesis reported. We found a sizable increase in the resistance during acetone adsorption, the best performancebeing obtained on sol−gel composites synthesized by the Ti-isopropoxide route and containing functionalizedMWCNTs. Sensors based on these composites were highly reproducible, with fast adsorption/desorption cyclesat room temperature, and showing a linear response to acetone concentration up to 4000 ppm. In order tobetter understand our experimental results, some relevant surface reactions have been analyzed in detail byperforming both ab initio Hartree−Fock and density functional theory calculations of acetone adsorption onmodel bare and chemically functionalized (by attaching O, Ti, and OH groups as well as small TixOy clusters)single-wall carbon nanotubes. Interestingly, acetone adsorption on the surface of TiO2/carbon nanotubecompounds seems to be mainly dependent on the precise details of the coordination environment around thesurface Ti sites, explaining the fast desorption of composites based on functionalized MWCNTs. Our theoreticalresults are consistent with our measured nanotube resistance variations upon acetone exposure and confirmsthus the hole as the primary carrier in our TiO2/carbon nanotube hybrid materials
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