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

Abstract

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, 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.

Adsorption/combustion-type VOC sensors employing mesoporous γ-alumina co-loaded with noble-metal and oxide

“…The core/shell structure was completely destroyed after the heat treatment at 700 • C for 2 h in air and most of Au agglomerated as a large particle with a diameter of 20-25 nm, but the size of Pd (actually, PdO in air) nanoparticles remained almost unchanged and Pd nanoparticles were highly dispersed on the oxide surface with a small amount of Au. Therefore, we discussed that the highly-dispersed Pd-based nanoparticles and the relatively-large Au-based particles on the mp-Al 2 O 3 powder improved the catalytic combustion properties of the VOCs adsorbed on the oxide surface and the thermal conductivity, respectively, in the previous study [33].…”

“…The addition of thermally conductive ␣-Al 2 O 3 powders to the sensor materials was also effective in improving the ethanolsensing properties [32]. In addition, the high-dispersed loading with core(Au)/shell(Pd) nanoparticles on the mp-Al 2 O 3 powder by utilizing sonochemical reduction of Au and Pd chlorides with polyethylene glycol monostearate drastically enhanced the sensing properties to ethanol, toluene and n-hexane of the adsorption/combustion-type gas sensors [33]. The core/shell structure was completely destroyed after the heat treatment at 700 • C for 2 h in air and most of Au agglomerated as a large particle with a diameter of 20-25 nm, but the size of Pd (actually, PdO in air) nanoparticles remained almost unchanged and Pd nanoparticles were highly dispersed on the oxide surface with a small amount of Au.…”

“…We also have reported VOC-sensing properties of adsorption/combustion-type gas sensors developed by utilizing the MEMS technology and an oxide-film fabrication technique by drop coating employing an air-pulse fluid dispenser [27][28][29][30][31][32][33]. The sensor structure is similar to that of catalytic combustion-type gas sensors [34][35][36], but the sensor-operating conditions are quite different from that of the catalytic combustion-type gas sensors.…”

“…In this study, therefore, mp-Al 2 O 3 powders have been firstly loaded with other noble metal nanoparticles (pure Pt, Au/Pt, or Pt/Pd) by sonochemical reduction technique, to improve the catalytic combustion properties of the VOCs and/or the thermal conductivity of the sensing materials, and the ethanol-sensing properties of the adsorption/combustion-type gas sensors fabricated by employing the mp-Al 2 O 3 powders loaded with the noble metal nanoparticles have been investigated and compared with those of the sensor using the Au/Pd-loaded mp-Al 2 O 3 powder, which showed the largest ethanol response in the previous study [33]. Platinum is well-known as an excellent catalyst for VOC combustion from a few decades ago [37,38], and the coexistence and/or alloying of Pt with Pd largely improved the catalytic combustion behavior of some hydrocarbons [39][40][41].…”

Acetone-Sensing Properties of WO3-Based Gas Sensors Operated in Dynamic Temperature Modulation Mode —Effects of Loading of Noble Metal and/or NiO onto WO3—

“…Our group has actually demonstrated that catalytic combustion-type gas sensors that were operated in a mode of pulsed temperature heating (typical pulsed-heating period: 400 ms for 10 s), so-called adsorption/combustion-type gas sensors, showed large dynamic responses to various types of VOCs. (35)(36)(37)(38)(39)(40) In this work, we have attempted to improve the acetonesensing properties of WO 3 -based sensors, particularly in wet air, by the loading of noble metal and/ or NiO onto the surface of WO 3 , as well as by operation in dynamic temperature modulation mode. 3 powders loaded with and without noble metal and/or NiO HNO 3 aq.…”