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

摘要

A systematic comparison of single and binary metal oxides TiO_2, TiO_2-Ga_2O_3 and TiO_2-Er_2O_3 thin firm gas sensors with nanocrystalline and mesoporous microstructure, prepared by a new paniculate sol-gel route, was conducted. The gas sensitivity was increased by introduction of Ga_2O_3 and Er_2O_3 into TiO_2 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 NO_2 (0.5 ppm) gases at a low operating temperature of 200 deg C, resulting in increasing thermal stability of sensing films as well as decreasing their power consumption. TiO_2-Ga_2O_3 sensor with molar ratio of TiO_2:Ga_2O_3 = 50:50 (TG11) showed the highest response towards CO concentrations in the range 25-400 ppm operated at 200 deg C, whereas TiO_2-Er_2O_3 sensor with molar ratio of TiO_2:Er_2O_3 = 75:25 (TE31) had the highest response towards NO_2 concentrations in the range 0.5-10 ppm at 200 deg C. The response magnitude of 13.7 and 4.4 were achieved for TG11 and TE31 sensors towards 400 ppm CO and 10 ppm NO_2, 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.