Synthesis of Pd@ZnO Core-shell Nanoparticles with Different Size and Their Gas Sensing Properties

Two different sizes of Pd@ZnO core-shell nanoparticles (NPs) have been prepared by using two different sizes of Pd NPs (15 and 50 nm) as metal cores and applied for acetaldehyde gas sensing. Transmission electron microscopy images revealed that the overall size of two sensing materials such as Pd15@ZnO and Pd-50@ZnO core-shell NPs are 80-100 nm and 100-120 nm, respectively. Xray-diffraction pattern revealed that the oxidation of Pd metal core was started from 300 degrees C. The spherical shape and size are maintained after the Pd@ZnO core-shell NPs was calcined at 500 degrees C for 2 h. PdO15@ZnO core-shell NPs showed higher response to acetaldehyde. The maximum response of PdO15@ZnO core-shell NPs to 100 ppm of acetaldehyde at 350 degrees C was 75, whereas the maximum response of PdO50@ZnO core-shell NPs to 100 ppm of acetaldehyde was 28 as compared to the pure ZnO NPs (Rs=18). The high response of PdO15@ZnO core-shell NPs than PdO50@ZnO core-shell NPs is due to the smaller size of PdO core, which has more catalytic activity than 50 nm sized PdO core.