Authors: Sanjit Manohar Majhi and Yeon-Tae Yu
Over the past few years, metal oxide semiconductors (MOS) have been widely researched as promising gas sensing materials, mainly due to their advantages such as low cost, simple sensing mechanism, facile fabrication and high sensitivity. However, a number of problems such as high operating temperature, lower sensitivity, poor selectivity associated with such type of sensors is needed to be solved in order to further expand in the area of sensor nanotechnology. Recently, core-shell nanostructures with metal nanoparticles (NPs) as inner core and oxide semiconductor as outer shell has been the subject of intense research in gas sensing.These core-shell structures show multifunctional properties, which are different from those of single components. More importanatly, in this core–shell structure the core is isolated from the shell and prevents it from aggregation and sintering at high temperature operations while retaining its individual physico-chemical properties. Among various semiconductors, Zinc oxide (ZnO) is a well known n-type semiconductor with a band-gap of 3.37eV, large exciton binding energy (60 meV) and high electron mobility, has been extensively investigated for gas sensing applications In this work, we present a facile strategy to synthesize Pd@ZnO core-shell nanoparticles (NPs) based gas sensor for the detection of acetaldehyde. Transmission electron microscopy (TEM) study showed that such Pd@ZnO core-shell NPs were formed having 10-15 nm Au NPs at the centre of the ZnO shell (40-45 nm). The as prepared Pd@ZnO core-shell NPs sensor was tested at different temperatures from 150-400C to various gases such as H2, ethanol, acetaldehyde, CO and their sensing performances were compared with that of pure ZnO NPs. Among all gases, Pd@ZnO core-shell NPs sensor showed the maximum response of 128.6 to acetaldehyde for 100 ppm at 350 oC operating temperature. Whereas, the maximum response of pure ZnO NPs was found to be 18.6 at 350 oC. The high response of Pd@ZnO NPs as compared to bare ZnO NPs is due to the formation more depletion layer resulted from the electronic and chemical sensitization (number of oxygen absorption) of Pd NPs. The high selectivity of Pd@ZnO NPs to acetaldehyde gas as compared to other gases is due to the more number of electrons was released during the reaction of Pd@ZnO and acetaldehyde as well as catalytically activated Pd NPs accelerates the absorption of acetaldehyde gases on the surface of ZnO to faster the reaction .
Keywords: sensors,sensitivity, core-shell