The impact of carrier gas on room-temperature trace nitrogen dioxide sensing of ZnO nanowire-integrated film under UV illumination

Abstract

Chemiresistive gas sensors have been extensively explored for hazardous gas detection. Currently, an overwheming majority of previous attention was focused on the parameter improvement of sensor performance while the impact of carrier gas species on the performance was severely ignored. Aiming to a deep insight into this issue, in this work we prepared zinc oxide (ZnO) nanowire-network sensor and explored its UV-activated sensing performance toward trace nitrogen dioxide gas (NO2) at room temperature (25 °C) under two carrier gases, i.e., dry nitrogen (N2) and air. Within N2, the sensor exhibited a reversible response of 157 toward 50 ppb NO2 and a sensitivity of 7.8/ppb, which was not only among the best showcases of the existing work, but much larger than those within air (11 and 0.091/ppb, respectively). Moreover, decent selectivity and long-term stability were demonstrated. Far more UV irradiation-induced electrons which reacted with adsorbed NO2 molecules on ZnO surface as well as smaller baseline resistance under N2 than those under air jointly led to the superior response and sensitivity. After long-time UV exposure prior to gas-sensing tests within both carrier gas cases, the remaining oxygen ions (O2−) were weakly bonded on ZnO surface, contributing to the reversible behaviors at room temperature. The interconversion between physisorbed O2 molecules and ionic O2− on ZnO surface was proposed to rationalize the sensing phenomena especially when no continuous oxygen was supplied under N2 atmosphere, which enriched the current transduction mechanisms.