Effects of noble-metal loading and ultraviolet-light irradiation on gas-sensing properties of porous indium oxide films at room temperature

Fundamental gas-sensing properties of porous (pr-)In2O3 powders loaded with and without 0.5 mass % noble metal (pr-0.5N/In2O3 and pr-In2O3, respectively, N: noble metal (Au or Pd)) to NO2, H2, and ethanol balanced with dry air were investigated at 30 °C under UV-light irradiation (main wavelength: 365 nm). The spherical pr-0.5N/In2O3 and pr-In2O3 powders were prepared by ultrasonic-spray pyrolysis employing polymethylmethacrylate microspheres with a diameter of ca. 70 nm, which were synthesized by ultrasonic-assisted emulsion polymerization. The Au loading largely improved the NO2 response of the pr-In2O3 sensor, a ratio of the resistance in NO2 to that in air, especially under weak UV-light irradiation, because of the relatively large resistance in air. On the other hand, the Pd loading efficiently increased the difference in the conductance of the pr-In2O3 sensor between in NO2 and in air under the whole UV-light irradiation range. The UV-light irradiation is effective in improving the NO2-sensing properties of these sensors at room temperature, but the sensing performance was a little inferior to that operated at elevated temperatures under no UV-light irradiation. These sensors also responded to reducing gases, H2 and ethanol, under UV-light irradiation, and the responses to ethanol were much larger than those to H2. However, the responses to both the gases were much smaller than that to NO2