Multiwalled carbon nanotubes embedded in sol–gel derived TiO2 matrices and their use as room temperature gas sensors

Sol–gel TiO2/Multiwall Carbon Nanotubes composites obtained by the Ti-isopropoxide route are reported as room temperature sensitive coatings. The effect of functionalizing the carbon nanotubes in strong oxidizing acids prior to the sol–gel synthesis is studied in the detection of acetone (CH3COCH3) and ammonia (NH3). Although, mixed oxide phases were found in the sol–gel oxide and composites, sensing was highly reproducible in the composites, with fast adsorption/desorption cycles at room temperature. Composites based on as-received multiwalled carbon nanotubes show an increase in films resistance during acetone and ammonia adsorption, while composites based on functionalized carbon nanotubes show longer acetone desorption times and a decrease in resistance during ammonia sensing. Acetone sensing in both composites contrast with the slight decrement in resistance observed in either pure titanium oxide or carbon nanotubes, in agreement with preliminary theoretical results. In contrast, the strong dependence of NH3 to the presence of oxygen and hydroxyl atoms on the carbon nanotube surface is not well understood.

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