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

Abstract

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.