Quartz Crystal Microbalance Sensor Based on ZnO Nanofilm for Methanol Detection

Quartz crystal microbalance (QCM) gas sensors modified by ZnO nanofilms were prepared using a layer-by-layer self-assembly (LBLSA) technique for methanol detection under parts-per-million (ppm) concentration at room temperature. The ZnO nanofilm characterization results revealed the impact of the uniformly distributed surface, porous nanostructure, and the presence of oxygen vacancies on sensing performance. Moreover, a comparison was made on the gas sensing performance of ZnO nanofilms with various layer numbers (four–ten layers), and the results demonstrated that the eight-layer QCM sensor exhibited the best sensing performance, including a sensitivity of 0.17 Hz/ppm, a response time/recovery time of (10/179 s), a low detection limit of 1 ppm. The sensor exhibited an outstanding selectivity (48.6 Hz at 280 ppm) to methanol. Furthermore, the adsorption mechanism was presented to verify the gas adsorption–desorption phenomenon at different concentrations and the selectivity to methanol with the aid of density functional theory (DFT) calculation.