First-principles investigations on the mechanism of highly sensitive and selective trimethylamine sensing in MoO₃

Molybdenum trioxide (MoO₃) is an important oxide semiconductor with a broad range of potential applications in electronics, catalysts and gas sensors. Experimentally, it has been demonstrated that MoO₃ exhibits ultrahigh sensitivity and selectivity towards trimethylamine (TMA) detection, but the physical mechanism remains elusive. In this work, by using density functional theory based first-principles calculations, we systematically investigated the geometric, energetic and electronic properties of TMA adsorption on the most stable (0 1 0) surface of α-MoO₃, in comparison with the adsorption of other biological molecules, including dimethylamine, ammonia, benzene, toluene, acetone, acetaldehyde, formaldehyde and ethanol, on the surface without and with defect. Analyses on the interaction between molecular orbitals and surface electronic states reveal that the simplest single oxygen vacancy generally enhances the molecular adsorption. Remarkably, on both pristine surface and surface with defect, TMA exhibits the strongest adsorption among all the considered molecules, suggesting excellent selectivity, and a clear relationship between the adsorption strength and charge transfer was identified. These results not only provide fundamental insight into the experimental observations, but also shed light on future design and fabrication of solid-state gas sensors for environmental and biomedical applications.