Sensory Properties of Co2+- and Fe3+-Doped h-WO3 Towards Toxic Gases

The sensory properties of h-CoxWO3 (0 ≤ x ≤ 0.09) and h-W1 – xFexO3 (0 ≤ x ≤ 0.06) solid solutions, as well as m-WO3, have been studied in relation to various toxic gases at the maximum permissible concentrations in the air. Doping h-WO3 with Co2+ or Fe3+ ions does not affect the sensitivity of the sensory response to CH3COCH3 and NH3 but leads to a decrease in the sensory signal towards NO2. A comparative analysis of the sensory properties of hexagonal and monoclinic tungsten trioxide has been performed. When detecting CH3COCH3 and NH3, the sensitivity of h-WO3 is, respectively, ~1.5 and ~1.3 times higher than that of m-WO3. The oxygen vacancy concentration and pore volume are the key parameters responsible for the higher sensitivity of m-WO3 to NO2 compared to h-WO3.