Repeatability and Stability of Room-Temperature Acetone Sensor Based on Nanotubes: Influence of Stoichiometry Variation

The oxygen vacancy (OV) variation of the electrochemically grown TiO₂ nanotube (NT) was achieved through stoichiometry variation by varying the volume of water in the electrolyte (NH₄F with ethylene glycol) during anodization. By varying the water content (0%, 2%, and 10% by volume) in the mixed electrolyte, the morphology and stoichiometry of NTs were found to be varied dramatically. After detailed structural and morphological characterization by X-ray diffraction and field-emission scanning electron microscope and photoluminescence spectroscopy, the room-temperature acetone sensing was investigated by employing three distinct nanoforms derived through anodization. The reliability (i.e., repeatability and stability) of the sensors, as well as their response magnitude, was found to be greatly influenced by the variation in stoichiometry. The NTs derived with 2 volume percent H₂O was found to offer the most promising response magnitude with excellent repeatability, whereas the best stability was ensured in the case of the NTs derived with 10 volume percent H₂O. It was observed that an optimization of stoichiometry (OVs) and the surface-to-volume ratio is important in determining the response magnitude and repeatability. On the contrary, the stability is mainly governed by the stoichiometry only.