Tracing of Ammonia Gas by Solution-Combustion-Derived Pristine and Nb-Doped TiO2 Films: Beneficial Impact of Crystallinity and Adsorbed Oxygen on the Gas Response

Abstract

The current work delivers room-temperature ammonia (NH<inf>3</inf>) gas-detectable pristine, Nb-doped TiO<inf>2</inf> air- and vacuum-annealed films obtained through the solution-combustion process. Polycrystalline anatase crystal structured films without any dopant oxide phases were processed at 400°C on glass substrates. The crystallinity was higher in pristine films than in doped films; the morphological features were similar in all the films. The films were > 50% transparent, and the estimated optical energy band gap was greater in doped films than in pristine films. All the films detected NH<inf>3</inf> gas (25 ppm to 100 ppm) at room temperature, and the gas response was highly dependent on the crystallinity and relative area fraction of adsorbed oxygen (% of O<inf>A</inf>). The vacuum-annealed pristine film exhibited a better gas response than the other films at all NH<inf>3</inf> gas concentrations due to high crystallinity and % of O<inf>A</inf> (10.15%). The film demonstrated maximum gas response of ~16 towards 100 ppm of NH<inf>3</inf> gas and displayed good selectivity. Even though the doping reduced the crystallite size from ~17 nm to ~9 nm, it also diminished the crystallinity of the films, which significantly impacted the deterioration of their gas response. © 2023, The Minerals, Metals & Materials Society.