Ultra-high sensitive and selective NO2 gas sensing performance of Au/Pd co-functionalized ZnO nanowires by a one-pot hydrothermal method

Abstract

The gas sensing properties of semiconducting metal oxides will be further improved by the co-functionalization of bimetallic noble elements. However, most methods for the preparation of co-functionalized metal oxides of two noble metals are complex and costly. In this study, the Au/Pd co-functionalized ZnO nanowires were prepared by a facile one-pot hydrothermal method. The crystal structure, nano-size, chemical composition and morphology of the samples were tested by XRD, TEM, XPS and SEM, respectively. The Au and Pd elements were distributed on the ZnO nanowire surface in the form of Au, Pd and PdO nanoparticles, and some of them were doped into the lattice of ZnO. The gas sensing results showed that the response of 1 mol% Au/Pd–ZnO was 732.4 to 5 ppm NO2 gas at optimal operating temperature of 100 °C, which was 32 times higher than that of pristine ZnO, and the response/recovery times were significantly reduced to only 36/6 s. This sample also exhibits a good reproducibility. Moreover, the Au/Pd co-functionalization can significantly enhance the selectivity of the ZnO nanowires to NO2 gas. Our work showed that the activation energy can be further reduced to 0.172 eV by Au/Pd co-functionalization.