Experimental and density functional theory computational studies on highly sensitive ethanol gas sensor based on Au-decorated ZnO nanoparticles

Abstract

In this paper, a highly sensitive gas sensor based on zinc oxide nanoparticles decorated by gold nanoparticles is introduced. To achieve this purpose, the hydrothermal method was utilized to synthesize ZnO, which led to a highly porous surface with nanoparticles size less than 100 nm. Various effective parameters on the performance of a gas sensor, including the optimum annealing temperature from 500 °C to 800 °C and decorating different quantities of Au nanoparticle (0.5, 2, 4, and 7 wt%) on the ZnO surface were investigated. Results demonstrated that in the optimum annealing temperature (500 °C), 4 wt% Au-decorated ZnO sensor shows about five times better response than that of a ZnO sensor and improved response time from 36 seconds down to 3 seconds. Besides, repeatability, selectivity, and linearity of the responses were examined for increasing the reliability of the sensor. Also, experimental findings are supported by the theoretical calculations, using Density Functional Theory method. Results revealed that Au atoms on the surface lead to dehydrogenation of ethanol molecules, while this is not the case for the pure ZnO surface. Also, ethanol molecules adsorption on the Au decorated ZnO surface have optimum Au concentration, which is confirmed by theoretical and experimental results. Mulliken population and projected density of state analyses indicate that after adsorption of ethanol molecules on the surface, electrons migrate from ethanol toward the surface. As a consequence, the resistance of the slab decreases.