Interaction of Acetone Molecules with Carbon-Nanotube-Supported TiO₂ Nanoparticles:  Possible Applications as Room Temperature Molecular Sensitive Coatings

Abstract

Room-temperature detection of acetone by TiO2/multiwall carbon nanotube (MWCNT) sol−gel composites is reported. We found a sizable increase in the resistance during acetone adsorption, the best performance being obtained on sol−gel composites synthesized by the Ti-isopropoxide route and containing functionalized MWCNTs. Sensors based on these composites were highly reproducible, with fast adsorption/desorption cycles at room temperature, and showing a linear response to acetone concentration up to 4000 ppm. In order to better understand our experimental results, some relevant surface reactions have been analyzed in detail by performing both ab initio Hartree−Fock and density functional theory calculations of acetone adsorption on model 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 nanotube compounds seems to be mainly dependent on the precise details of the coordination environment around the surface Ti sites, explaining the fast desorption of composites based on functionalized MWCNTs. Our theoretical results are consistent with our measured nanotube resistance variations upon acetone exposure and confirms thus the hole as the primary carrier in our TiO2/carbon nanotube hybrid materials