Effect of Ag on the ZnO nanoparticles properties as an ethanol vapor sensor

Pristine and Ag-added (1.5, 3.5 and 5.5 wt%) ZnO nanoparticles (NPs) were synthesized by a Pechini sol-gel route for evaluation of their gas sensing properties. The samples were fully characterized by different characterization techniques. Based on the sensing results obtained in this study, the promising effects of Ag on the ethanol vapor response of ZnO were demonstrated. In particular, the optimized sensor, namely 3.5 wt % Ag-ZnO gas sensor exhibited a response (Ra/Rg) of 32.5 to 50 ppm ethanol vapor at 325°C. A second notable finding revealed that this optimized sensor had a better selectivity to the ethanol vapor relative to the pristine ZnO gas sensor. The sensing mechanism was associated with the catalytic effect of Ag, the formation of Ag-ZnO heterojunctions and the basic characteristics of ZnO. This work highlights the importance of a systematic study for adding noble metals in gas sensing researches.