Alumina decorated TiO2nanotubes with ordered mesoporous walls as high sensitivity NOx gas sensors at room temperature

Abstract

Alumina (Al₂O₃) decorated anatase TiO₂ nanotubes with ordered mesoporous pore walls (Al₂O₃/meso-TiO₂ nanotubes) are successfully synthesized through vacuum pressure induction technology, and then combined with the thermal decomposition of a mesoporous TiO₂ sol precursor, inside the cylindrical nanochannels of an anodic aluminium oxide (AAO) template. The decorated Al₂O₃ was formed by in situ deposition via direct reaction of the strong acid sol precursor and the nanochannel wall of the AAO template. The resultant Al₂O₃/meso-TiO₂ nanotubes are characterized in detail by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and N₂ adsorption–desorption. The experimental results reveal that the Al₂O₃/meso-TiO₂ nanotubes have a tubular structure with an average diameter of ∼200 nm and highly ordered mesopores in the tubular walls. The Al₂O₃ is distributed evenly on the anatase TiO₂ nanotubes. Moreover, the Al₂O₃/meso-TiO₂ nanotubes possess a large specific surface area (136 m² g⁻¹) and narrow mesopore size distribution (∼10 nm). By using NO_x as a probe molecule, the Al₂O₃/meso-TiO₂ nanotube films exhibit better sensing performance than that of mesoporous TiO₂ nanotubes, in terms of their high sensitivity, fast response–recovery time, and good stability in air at room temperature. The outstanding performance in the gas sensing ability of Al₂O₃/meso-TiO₂ nanotubes is a result of their one-dimensional tubular and mesoporous nanostructures, advantageous for the adsorption and diffusion of NO_x gas. In addition, the sensing response is greatly improved by virtue of the decorated Al₂O₃ on the surfaces of the TiO₂ nanotubes, which acts as an energy barrier to suppress charge recombination. The structural properties of the Al₂O₃/meso-TiO₂ nanotubes makes them a viable novel gas sensor material at room temperature.