Bimetal Au-Pd decorated hierarchical WO3 nanowire bundles for gas sensing application

[Display omitted] •A facile hydrothermal method was used for the synthesis of self-assembled hierarchical WO3 nanowire bundles.•The oriented attachment, segregation based on rational concentrations of WO42−, Na+, SO42−, and citrate ions are studied.•Bimetal Au-Pd nanoparticles decorated on the hierarchical WO3 bundles by an in-situ redox reaction in aqueous medium.•The synergistic effect of Au-Pd nanoparticles improved WO3 sensing performance towards n-butanol at 200 ºC highly. This study has developed a simple but effective synthesis method to deposit bimetal Au-Pd nanoparticles onto WO3 hierarchical bundle nanowires through an in-situ redox reaction in a reducing aqueous medium. Hydrothermal method was used for the synthesis of WO3 hierarchical bundles ultrathin nanowire subunits, and the mechanisms controlling the segregation behavior and growth based on Na2SO4, citric acid, and ethylene glycol are discussed. It was found that the Pd-WO3 and/or Au-Pd-WO3 nanocomposites decorated with Au 2.4 wt% and Pd 0.48 wt% showed exemplary sensitivity (S) for 50 ppm n-butanol as S = 91 at 200 °C, approximately 14 and 1.4 times better than pristine WO3 (S = 5.7) and Pd-WO3 (S = 59), respectively. Moreover, the Pd-WO3 sensing results demonstrated that the Pd decoration could significantly reduce the operating temperature, similarly to the Au-Pd-WO3 sensor, which is particularly effective for n-butanol gas among common volatile organic compounds (VOCs). The analysis demonstrates that the bimetal Au-Pd decoration have resulted a synergistic effect in boosting the sensitivity of the WO3-based sensor toward n-butanol gas. The underlying sensing mechanism of such an Au-Pd-WO3 hybrid nanostructure is further discussed, based on chemical and electronic sensitizations in promoting the spillover of oxygen species and rectifying Schottky barriers at the interface of noble metal(s) and semiconductor oxide (e.g., WO3). This work may be beneficial for designing a unique Au-Pd-WO3 sensor with great potential to develop oxide-based sensors for detecting other hazardous gases at low temperature.