Adsorption/combustion-type gas sensors employing mesoporous γ-alumina loaded with core(Au)/shell(Pd) nanoparticles synthesized by sonochemical reduction

Adsorption/combustion-type gas sensors employing mesoporous γ-alumina (mp-Al2O3) powders loaded with core(Au)/shell(Pd) nanoparticles, which were synthesized by sonochemical reduction, (n(Au/Pd)/mp-Al2O3, n: the amount of Au/Pd nanoparticles loaded, (0.1–1.0 wt%), Au:Pd = 1:4 in weight) have been fabricated and their sensing properties to ethanol, toluene and n-hexane have been investigated in air. The n(Au/Pd)/mp-Al2O3 sensors showed larger responses to these target gases at lower temperatures than those of sensors fabricated with mp-Al2O3 powders loaded with Au and Pd by general impregnation technique (n(Au-Pd)/mp-Al2O3 sensors, Au:Pd = 1:4 in weight), especially when the amount of Au and Pd loaded onto the mp-Al2O3 powders was reduced (≤0.5 wt%). These sensing properties seem to be largely dependent on the morphological and compositional characteristics of Au and Pd loaded on the γ-alumina surface. In addition, the n(Au/Pd)/mp-Al2O3 sensors showed much larger response to ethanol than those to toluene and n-hexane, probably because of the difference in the magnitude of polarity (dipole moment and dielectric constant) of their molecules. However, the sensors obviously detected even 10 ppm n-hexane with the extremely low dipole moment and dielectric constant. These results promise that the n(Au/Pd)/mp-Al2O3 sensors can detect the lower concentration of these gases as well as other VOCs.