Enhanced ethanol sensing response from nanostructured MoO3:ZnO thin films and their mechanism of sensing

Abstract

A novel ZnO incorporated MoO₃ nanostructured thin film system exhibiting high sensitivity and selectivity to ethanol has been developed. The MoO₃:ZnO nanostructures exhibit enhanced ethanol sensing performance in non-humid and humid (75% r.H. at 21 °C) atmospheres compared to the pure MoO₃ layer; with increase in ZnO concentrations, the sensitivity and stability increased, and the response/recovery time decreased. The response (G_ethanol/G_air) of the 25% MoO₃:ZnO sensor at an operating temperature of 300 °C against 500 ppm ethanol is up to 171 under non-humid and 117 under humid (75% r.H.) conditions. By comparing the response of the 25% ZnO added MoO₃ sensor toward various gases (H₂, CO, C₃H₆, CH₄ and C₂H₅OH), distinctive selectivity to ethanol is observed. The ethanol sensitivity action over MoO₃ nanostructures can be ascribed to the catalytic oxidation of ethanol to acetaldehyde, and the enhancement of gas sensing response of the MoO₃:ZnO system can be attributed to more active centers that are obtained from the enhanced oxygen vacancy defects induced by ZnO. The presence of a humid atmosphere has a dramatic influence on the sensor performance towards ethanol; the sensitivity diminishes drastically due to the partial site precluding nature of the adsorbed hydroxyl groups to the analyte. The ZnO incorporated MoO₃ nanostructure based sensing layers in the present work show significantly superior ethanol sensing performance to the works previously reported for various metal oxide systems.