Construction of novel hybrid PdO-ZnO p-n heterojunction nanostructures as a high-response sensor for acetaldehyde gas

P-n heterojunction nanostructures (NSs) are emerging as a promising class of hybrid materials for gas-sensing applications. In this work, we report a facile, cost-effective synthesis technique to fabricate unique, hybrid PdO@ZnO p-n heterojunction NSs as high response and selective acetaldehyde gas sensors. Initially, Pd@ZnO core-shell NSs (CSNSs) were synthesized, and subsequently transformed into hybrid PdO@ZnO p-n heterojunction NSs by a simple high-temperature calcination method. The morphological study of the prepared hybrid NSs was carried out by transmission electron microscopy (TEM), which revealed that 10 ± 5 nm sized Pd nanoparticles (Pd NPs) were encapsulated in the center of the ZnO shell of 40-50 nm to form approximately 75-135 nm sized Pd@ZnO CSNSs. The more crystalline, flower-shaped PdO@ZnO p-n heterojunction NSs were formed after the Pd@ZnO CSNSs were calcined at 500 °C for 2 h. When employed as a gas sensor, the hybrid PdO@ZnO p-n heterojunction NSs demonstrated high sensitivity and selectivity to acetaldehyde gas amongst other gases (ethanol, CO, H₂, and CH₄). The PdO@ZnO p-n heterojunction NSs-based sensor delivered the highest response (R_a/R_g = 76) to 100 ppm acetaldehyde at 350 °C, as compared to the pristine ZnO NSs sensor (R_a/R_g = 18). The improved sensing performance of the hybrid PdO@ZnO p-n heterojunction NSs-based sensor over the pristine ZnO NSs-based sensor was attributed to the combination of the resulting synergistic effect due to the formation of the p-n heterojunction between PdO and ZnO NPs, the catalytic dissociation effect of PdO, and the high surface area of the PdO@ZnO p-n heterojunction NSs.