Effects of Gas Adsorption Properties of an Au-Loaded Porous InO Sensor on NO-Sensing Properties.

Gas adsorption properties of semiconductor-type gas sensors using porous (pr-) InO powders loaded with and without 0.5 wt % Au (Au/pr-InO and pr-InO sensors, respectively) at 100 °C were examined by using diffuse reflectance infrared Fourier transform spectroscopy, and the effect of the Au loading onto pr-InO on the NO-sensing properties were discussed in this study. We found the following: the resistance of the Au/pr-InO sensor in dry air is lower than that of the pr-InO sensor; the DRIFT spectra of both the sensors show a broad positive band between 1600 and 1000 cm in dry air (reference: in dry N at 100 °C), which mainly originates from oxygen adsorbates and/or lattice oxygen, and that this band is much larger for the Au/pr-InO sensor than for the pr-InO sensor; the Au loading also increases the adsorption amount of HO and the reactivity of NO on the pr-InO surface; and the NO response of the Au/pr-InO sensor in dry air is marginally higher than that of the pr-InO sensor in the examined concentration range of NO (0.6-5 ppm) in dry air. The obtained results strongly support the enhancement of the NO adsorption onto the pr-InO surface by Au loading, which contributed to the improvement of the NO-sensing properties.