Palladium embedded in SnO enhances the sensitivity of flame-made chemoresistive gas sensors.

Palladium is used commonly to enhance the performance of chemoresistive metal-oxide gas sensors. Typically, this enhancement is attributed to the presence of Pd clusters on the surface of their metal-oxide support (i.e. SnO). Possible Pd incorporation or embedding into the support rarely has been considered. Here, SnO particles (15 - 21 nm in diameter measured by N adsorption) with different Pd contents (0 - 3 mol%) were prepared by flame spray pyrolysis (FSP). Leaching these particles with HNO and characterization by inductively coupled plasma - optical emission spectrometry (ICP-OES) indicated that only 36 - 60% of Pd have been removed (e.g., from the SnO surface). The rest was embedded within the SnO particles. Annealing prior to leaching decreased by ~30% that Pd surface content. Most interestingly, such SnO particles (with only embedded Pd) show higher sensor response to acetone, ethanol and CO at 350 °C compared to SnO particles containing both surface and embedded Pd (i.e. before leaching). As a result, such sensors can detect acetone with high (> 25) signal-to-noise ratio at levels down to 5 ppb at 50% relative humidity. Graphical abstractFlame-made SnO nanoparticles with embedded and surface Pd (triangles) exhibit lower sensor response to acetone, ethanol and CO than SnO from which the surface Pd had been removed by leaching (circles).