Co-doped ZnO Nanowires for Low Temperature Methane Sensing Operational in Humid Environments

Sensitive and selective detection of methane is essential due to its role in the greenhouse effect, relevance to industrial safety and recently discovered importance as a biomarker for gastrointestinal health. However, obtaining a reliable response to low concentrations (<100 ppm) of methane at low temperatures, especially in presence of humidity still remains a great challenge. In this work, a metal-oxide based sensor capable of low methane concentration detection and humidity resistance is reported. Chemiresistive sensors based on ZnO nanowire films were grown by a hydrothermal process and doped with Co. In terms of methane detection, Co-doping of the ZnO nanowires enabled the sensor to operate optimally at the low operating temperature of 50oC and an improved sensitivity of response (lowest measured concentration: 1 ppm) was observed when compared to that of pure ZnO nanowire films. This increased sensitivity was attributed to an increase in donor-type vacancies and enhanced oxygen adsorption on the surface. A mesoporous silica molecular sieve was further integrated as a moisture filter layer to mitigate the effect of humidity. It is envisaged that based on the sensors’ performance characteristics reported here, that the sensor could be applicable for emerging diagnostic applications tracking methane emissions from the breath.