Au/SnO2 core-shell structure nanoparticles (NPs) with different shell thicknesses as a CO gas sensing material were synthesized by microwave-assistant hydrothermal method. The thickness of SnO2 shell was controlled from 7 nm to 22 nm. The concentrated Au/SiO2 NPs colloid was loaded on alumina circuit board with interdigitated Pt electrodes for gas sensing test, and then heat-treated 500°C in electric furnace for 24 h. The sensor device showed the highest response for CO gas when the thickness of SnO2 shell was 18 nm and the test temperature was 200°C. This sensor device showed high response even at 100°C of test temperature.
In the present work, ZnO nanostructures were synthesized by monoethanolamine (MEA)-assisted ultrasonic method at low temperature. Structural analysis was carried out by X-ray diffraction (XRD) confirmed the formation of hexagonal wurtzite structure of ZnO. The effect of ammonia water on the molecular structure of MEA, and its effect on the morphology of ZnO nanostructures were monitored by electron microscopy. Scanning electron microscopy (SEM) results suggest that ZnO nanoparticles with 100 nm in diameter were produced in case of MEA-assisted ultrasonic method. However, as ammonia water was added into the reaction system the morphology of ZnO nanoparticles changed into nanorods, flower-like nanostructures and finally microrods. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies showed that as prepared ZnO nanostructures were single crystalline in nature and grew in different directions resulted in the formation of various structures. The growth mechanism of as prepared ZnO nanostructures was discussed in detail. It was proposed that the addition of ammonia water into the reaction system resulted into the formation of ethylene diamine (EDA) which directed the growth of ZnO. The optical property was studied by photoluminescence (PL) spectroscopy showed only UV emission and no defects mediated visible emission.
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