Hydrocarbon detection with metal oxide semiconducting gas sensors modified by overlayer or admixture of zeolites Na-A, H-Y and H-ZSM-5

A control thick-film SnO2 gas sensor was modified with zeolites holding LTA, FAU and MFI frameworks using two different approaches to integrate them into the gas-sensing interface. The objective was to prompt selectivity and sensitivity enhancements that were otherwise unattained with the unmodified material when detecting a range of hydrocarbon vapours with similar molecular structures and kinetic diameters. Molecules with different functional groups were also explored. Overlayers were designed by screen-printing 1 or 3 zeolite depositions on top of the control sensor. Admixtures were prepared by screen-printing composites of the control material with 10% (w/w) and 30% (w/w) of zeolite. Tests were performed against ethane, propane, butane, ethanol, isopropanol, acetone, toluene and carbon monoxide at concentrations in the 2.5–125 ppm range and sensors were heated to temperatures in the 250–500 °C range. Sensors were also exposed to humid air and to a mixture of ethane and humid air to assess the selective capabilities of the sensing materials in mixed-gas environments. Both fabrication methods provided sensor responses that, combined, favoured vapour discrimination in a way unachievable with the control sensor and the presence of zeolite was seen to assist in sensitivity and selectivity enhancements towards vapours, whilst providing stable and repeatable responses over time.