Promotional effects of ZnO-branching and Au-functionalization on the surface of SnO2 nanowires for NO2 sensing

Branched nanowires (b-NWs) have been used for advanced applications because of their nanoscale dimensions, high surface area, and scalable synthetic methods. Herein, for the first time, we report the fabrication of Au-functionalized ZnO-branched SnO2 NWs for enhanced gas sensing application. As-fabricated NWs were structurally and morphologically investigated by X-ray diffraction, scanning electron microscopy as well as transmission electron microscopy to reveals the crystallinity and morphology of NWs. By comparing the gas sensing properties of Au-functionalized b-NWs, b-NWs, and pristine SnO2 NWs gas sensors, in terms of their sensitivity and cross-sensitivity towards NO2, we demonstrate the superior sensing properties of Au-functionalized b-NWs sensors. In particular the Au-functionalized b-NWs sensor showed a response (Rg/Ra) of 13.07 to 10 ppm NO2 gas which was higher than those of b-NWs, and pristine SnO2 NWs gas sensors. In addition to the special architecture of sensors (i.e. ZnO b-NWs on SnO2 NWs), which produces a large number of hetero- and homojunctions (a branching effect), Au acts as a catalyst to further improve the sensing characteristics of this particular sensor (a functionalization effect). According to the obtained results, we believe that metal oxide gas sensors based on noble metal-functionalized b-NWs, which use a facile synthesis procedure and produce enhanced sensing performance, will play a vital role in the future of the sensor industry.