Comparison of single and binary oxide sol-gel gas sensors based on titania

A systematic comparison of single and binary metal oxides TiO₂, TiO₂-Ga₂O₃ and TiO₂-Er₂O₃ thin film gas sensors with nanocrystalline and mesoporous microstructure, prepared by a new particulate sol-gel route, was conducted. The gas sensitivity was increased by introduction of Ga₂O₃ and Er₂O₃ into TiO₂ film via two mechanisms, firstly through the inhibition of anatase-to-rutile transformation, since the anatase phase accommodates larger amounts of adsorbed oxygen, and secondly through the retardation of grain growth, since the higher surface area provides more active sites for gas molecule adsorption. The binary metal oxide gas sensors exhibited a remarkable response towards low concentrations of CO (25 ppm) and NO₂ (0.5 ppm) gases at a low operating temperature of 200 °C, resulting in increasing thermal stability of sensing films as well as decreasing their power consumption. TiO₂-Ga₂O₃ sensor with molar ratio of TiO₂:Ga₂O₃ = 50:50 (TG11) showed the highest response towards CO concentrations in the range 25-400 ppm operated at 200 °C, whereas TiO₂-Er₂O₃ sensor with molar ratio of TiO₂:Er₂O₃ = 75:25 (TE31) had the highest response towards NO₂ concentrations in the range 0.5-10 ppm at 200 °C. The response magnitude of 13.7 and 4.4 were achieved for TG11 and TE31 sensors towards 400 ppm CO and 10 ppm NO₂, respectively. Furthermore, calibration curves revealed that all sensors followed the power law, S = A [gas]^B (where S is sensor response, coefficients A and B are constants and [gas] is gas concentration), for the two kinds of gases.