Au and Pt Nanoparticles Effects on the Optical and Electrical Gas Sensing Properties of Sol–Gel-Based ZnO Thin-Film Sensors

The optical and conductometric responses of sol-gel-based ZnO thin films with embedded 5% mol. Au or Pt nanoparticles (NPs) have been compared at different operating temperatures, to assess the effect of noble metal additions on to H2, CO and NO2gases sensors response. The scanning electron microscopy and X-ray diffraction techniques have been utilized for morphological characterization of the crystal structures of the films after annealing at 400°C for 30 min and the effect of Au and Pt NPs additions on crystallite growth is discussed. Au NPs additions is effective to enhance the optical response to H2and CO at 390 nm and in the 500-700-nm wavelength range at 300- °C temperature. No optical response to NO2gas, even at low concentrations has been measured in the optical mode. The catalytic action of Pt NPs additions powerfully improves both the optical to H2and CO at 390 nm, and the conductometric gas responses. Detection limits as low as 20-ppb NO2and 50-ppm H2, in line with the best performances reported to the best of our knowledge in literature for ZnO-based sensors, have been measured in the conduction mode. Response times have been also compared, highlighting the positive effects played by Pt additions.