Abstract
NO2-sensing properties of semiconductor gas sensors using porous In2O3 powders loaded with and without 0.5 wt% Au (Au/In2O3 and In2O3 sensors, respectively) were examined in wet air (70% relative humidity at 25 °C). In addition, the effects of Au loading on the increased NO2 response were discussed on the basis of NO2 adsorption/desorption properties on the oxide surface. The NO2 response of the Au/In2O3 sensor monotonically increased with a decrease in the operating temperature, and the Au/In2O3 sensor showed higher NO2 responses than those of the In2O3 sensor at a temperature of 100 °C or lower. In addition, the response time of the Au/In2O3 sensor was much shorter than that of the In2O3 sensor at 30 °C. The analysis based on the Freundlich adsorption mechanism suggested that the Au loading increased the adsorption strength of NO2 on the In2O3 surface. Moreover, the Au loading was also quite effective in decreasing the baseline resistance of the In2O3 sensor in wet air (i.e., increasing the number of free electrons in the In2O3), which resulted in an increase in the number of negatively charged NO2 species on the In2O3 surface. The Au/In2O3 sensor showed high response to the low concentration of NO2 (ratio of resistance in target gas to that in air: ca. 133 to 0.1 ppm) and excellent NO2 selectivity against CO and ethanol, especially at 100 °C.
Highlights
Semiconductor gas sensors were firstly commercialized as gas leak detectors in the 1960s [1], and additional studies have been carried out in order to detect various gases such as alcohol and volatile organic compounds (VOCs) [2,3,4]
We reported that the Au loading on the porous In2 O3 fabricated by ultrasonic spray pyrolysis using a precursor solution containing In(NO3 )3 and PMMA microspheres was quite effective in increasing the
Conclusions and the effects of the Au loading on the enhancement of NO2 response were discussed
Summary
Semiconductor gas sensors were firstly commercialized as gas leak detectors in the 1960s [1], and additional studies have been carried out in order to detect various gases such as alcohol and volatile organic compounds (VOCs) [2,3,4]. Among the various semiconducting metal oxides, SnO2 [11,12,13], WO3 [5,14,15], In2 O3 [16,17,18,19,20,21,22,23,24,25,26], and ZnO [27,28,29] are well known as semiconducting NO2 -sensing materials. Kim et al fabricated nanowired SnO2 on an alumina substrate by a chemical vapor deposition
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