Exploiting Water-Mediated Ethanol Sensing by Polycrystalline ZnO at Room Temperature

Abstract

Ambient moisture can dramatically promote the response of ZnO to ethanol vapor, a hydrophilic gas. By comparing sensor responses in a broad range of humidities, we show that there is a consistent enhancement in ethanol adsorption on ZnO when physisorbed water, detected by capacitance measurements, is present. The time constants related to the capacitive signal recovery during desorption are consistent with the formation of C2H5OH-(H2O)n clusters that have a different desorption rate than water alone. These room temperature results indicate that surface water mediates the dynamic adsorption/re-evaporation equilibrium of solvated ethanol molecules. Thus, attention to interactions between the target gas molecules and their environment is important for understanding the mechanisms behind selective gas sensing.