Effect of multiwalled carbon nanotube functionalization on the gas sensing properties of carbon nanotube–titanium dioxide hybrid materials

The effect of multiwalled carbon nanotube functionalization on the sensing properties of carbon nanotube–titanium dioxide hybrid materials during ammonia exposure was investigated. Strongly adherent films were evaluated by impedance spectroscopy, finding highly sensitive and completely reversible capacitance values when the materials were exposed to ammonia vapors at room temperature. The abundance of oxygenated functional groups caused by functionalization of carbon nanotubes in strong acid solutions correlates with the formation of carbon nanotube–titania hybrids with synergistic sensing properties, such as faster adsorption/desorption cycles, lower impedance values, and high sensitivity for ammonia. X-ray diffraction and atomic force microscopy studies showed that oxygenated functional groups on the carbon surface act as nucleation points for titania growth, resulting in thinner films with smaller crystallite size for the titania phase than those obtained with untreated carbon nanotubes. The better integration between both components produced films with unique sensing properties.

► Trilayer films of hybrid materials based on titanium dioxide and carbon nanotubes were prepared by dip-coating and spray. ► Chemical and microstructural characterization was done by X-ray diffraction and atomic force microscopy. ► Films were characterized in capacitor platform by impedance spectroscopy as ammonia sensors at room temperature. ► The electrical behavior was studied as a function of chemical functionalization of carbon nanotubes. ► Chemical oxidation is a key step to obtain reversible sensors with high sensitivity.