Palladium embedded in SnO2 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. SnO2). Possible Pd incorporation or embedding into the support rarely has been considered. Here, SnO2 particles (15 - 21 nm in diameter measured by N2 adsorption) with different Pd contents (0 - 3 mol%) were prepared by flame spray pyrolysis (FSP). Leaching these particles with HNO3 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 SnO2 surface). The rest was embedded within the SnO2 particles. Annealing prior to leaching decreased by ~30% that Pd surface content. Most interestingly, such SnO2 particles (with only embedded Pd) show higher sensor response to acetone, ethanol and CO at 350 °C compared to SnO2 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 SnO2 nanoparticles with embedded and surface Pd (triangles) exhibit lower sensor response to acetone, ethanol and CO than SnO2 from which the surface Pd had been removed by leaching (circles).