Pt-Decorated ZnO Nanorods for Light-Assisted Ethanol Sensing and In Situ Analysis of the Sensing Mechanism under Light Irradiation

ZnO nanorods have attracted much attention owing to their outstanding properties for chemical gas sensors. Although they show greater sensing properties than conventional nanoparticulate ZnO, high operation temperature (>250–350 °C) is required for them to work even if precious metals are deposited on them to sensitize their sensing properties. Light irradiation is one solution for overcoming the high operation temperature and the gas selectivity because it assists the oxidation activity on the surface that affects the sensor response. In this work, the sensing properties of Pt/ZnO nanorods and ZnO nanorods are examined under light irradiation, and the relationship between their sensing properties and surface reaction (ethanol oxidation) is elucidated. Pt/ZnO nanorods show selective sensor responses to ethanol (conditions: 150 °C, 50 ppm ethanol; sensor response, 843; response time, 4.0 min; recovery time, 22 min). In situ spectroscopic observations reveal that the largest amount of oxidation intermediates (acetate species) and oxidation products (CO2 and acetaldehyde) is confirmed during light irradiation. The oxidation reaction of ethanol is facilitated by the deposition of Pt and light irradiation. Thus, the operation temperature of ZnO nanorods decreases, and the selectivity to ethanol is enhanced.