Multi-walled carbon nanotubes for volatile organic compound detection

Oxygen plasma functionalized multiwall carbon nanotubes (MWCNTs) were used for detecting volatile organic compounds at room temperature. Alumina substrates with interdigitated gold electrodes were employed as transducers and the air-brushing method was used to coat them with carbon nanotube mats. The electrical properties of the carbon nanotubes mats in the presence of benzene, toluene, methanol, ethanol and acetone vapors are studied by impedance spectroscopy. The resistance variation of the prepared MWCNTs films increases with the concentration of the different vapors tested. For benzene and toluene, the sensors are highly responsive and fully recover their baseline resistance when operated at room temperature. On the other hand, in the presence of methanol, ethanol and acetone some baseline drift is present. Additionally, the response time of the sensors to the aromatic vapors is compared against those obtained for alcohols and acetone vapors. The fast response kinetics for alcohols and acetone together with the baseline drift present for these vapors suggest that these species are chemisorbed at the carbon nanotube surface. The slower response kinetics and absence of baseline drift suggest that the aromatic volatile organic compounds tested physisorb at the carbon nanotube surface. Within aromatic volatiles, discrimination seems to be possible based on the presence/absence of methyl groups.