The adsorption mechanism of formaldehyde molecules on ZnO-SAW sensor at a different relative humidity

Abstract

In this paper, the ZnO-SAW sensor is exposed to different concentrations of HCHO/H2O mixed gas, and the sensing performance of formaldehyde moisture is evaluated by testing the resonance frequency shift. The experimental results show that the sensitivity of the ZnO-SAW sensor to detect formaldehyde increases with the increase of relative humidity (RH). Moreover, the formaldehyde moisture adsorbed on the surface of ZnO cannot be completely desorbed, and the unrecovered value of the resonance frequency of the ZnO-SAW sensor increases with the increase of humidity and formaldehyde concentration. Density functional theory (DFT) calculations indicate that due to the strong hydrogen bond between formaldehyde and water molecules, the adsorption of formaldehyde molecules shortens the bonding distance between water molecules and ZnO, thereby increasing the average binding energy of the entire system.