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

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 degrees 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 degrees 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 (H-2, 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.