Gas sensing characteristics and porosity control of nanostructured films composed of TiO₂ nanotubes

Preparation and morphology control of TiO₂ nanostructured films for gas sensor applications were investigated. To examine the effect of the morphology of sensing films on the sensing characteristics, TiO₂ with different morphologies, nanoparticles and nanotubes, were used for the film preparation. TiO₂ nanotubes were prepared by a hydrothermal treatment of TiO₂ nanoparticles in a NaOH solution at 160, 200, and 230 °C for 24 h and subsequent washing with an HCl solution. Uniform sized TiO₂ nanotubes of 1 μm in length and 50 nm in diameter were formed at 230 °C. The sensing films composed of nanotubes prepared at 230 °C showed a high sensor response to toluene at 500 °C as compared with those composed of TiO₂ nanoparticles. Scanning electron microscope (SEM) analysis and pore size distribution measurements indicated that the sensing films composed of the TiO₂ nanotubes had a high porous morphology with a peak pore size of around 200 nm, which can promote the diffusion of toluene deep inside the films and improve the sensor response. The obtained results demonstrated the importance of microstructure control of sensing layers for improving the sensitivity to large size molecules like volatile organic compounds (VOCs).