Highly selective NH₃ gas sensor based on Au loaded ZnO nanostructures prepared using microwave-assisted method

ZnO nanorods synthesized using microwave-assisted approach were functionalized with gold (Au) nanoparticles. The Au coverage on the surface of the functionalized ZnO was controlled by adjusting the concentration of the Au precursor. According to X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results, it was confirmed that Au form nanoparticles loaded on the surface of ZnO. The small Au loading level of 0.5 wt% showed the highest response of 1600–100 ppm of NH₃ gas at room temperature (RT) whereas further increase of Au loading level resulted in poor detection of NH₃. All Au loaded ZnO (Au/ZnO) based sensors exhibited very short recovery and response times compared to unloaded ZnO sensing materials. The responses of ZnO and Au/ZnO based sensors (0.5–2.5 wt%) to other flammable gases, including H₂, CO and CH₄, were considerably less, demonstrating that Au/ZnO based sensors were highly selective to NH₃ gas at room temperature. Spill over mechanism which is the main reason for the observed enhanced NH₃ response with 0.5 Au loading level is explained in detail.