Preparation and mechanism study of ZnO ammonia gas sensor based on precious metal nanoparticles (AuNPs, AgNPs) modification

A high-sensitivity NH3 sensor based on gold nanoparticles or silver nanoparticles (AuNPs or AgNPs) modified ZnO (Au/ZnO or Ag/ZnO) was synthesized using hydrothermal method and the sensing mechanism was explained by density functional theory (DFT). Experimental results indicate that AuNPs or AgNPs modification can effectively improve the sensing characteristics of the ZnO-based NH3 sensor, which is due to more hydroxyl groups, oxygen vacancies and oxygen free radicals on the surface of Au/ZnO or Ag/ZnO. The responses of AuZn2 and AgZn2 sensors to 1000 ppm NH3 at room temperature are 7321.07 and 9329.79, which are 22.48 and 28.65 times higher than that of the ZnO sensor respectively. The low detection limits of the AuZn2 and AgZn2 sensors is 0.495 ppm and 0.405 ppm. The fast response/recovery times to 15 ppm NH3 is 0.9 s / 0.9 s or 1.5 s / 0.9 s. DFT calculation results show that AuNPs or AgNPs on the ZnO surface make D-band center of ZnO moves to a higher energy level, which increases the chemical activity of AuZn2 or AgZn2, thereby improving the adsorption energy to NH3 molecule. This work provides a new idea for high-performance NH3 sensors fabrication and broadens the application field of ZnO materials.