Density Functional Investigation on α-MoO₃ (100): Amines Adsorption and Surface Chemistry

The (100) surface of α-MoO₃ should possess overwhelmingly more exposed Mo atoms than the (010), and the exposed Mo has been extensively considered as an active site for amine adsorption. However, α-MoO₃ (100) has drawn little attention concerning the amine sensing mechanism. In this research, adsorption of ammonia (NH₃), monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) is systematically investigated by density functional theory (DFT). All four of these molecules have high affinity to α-MoO₃ (100) through interaction between the N and the exposed Mo, and the affinity is mainly influenced by both the characteristics of the molecules and the geometric environment of the surface active site. Adsorption and dissociation of water and oxygen molecule on stoichiometric and defective α-MoO₃ (100) surfaces are then simulated to fully understand the surface chemistry of α-MoO₃ (100) in practical conditions. At low temperature, α-MoO₃ (100) must be covered with a large number of water molecules; the water can desorb or dissociate into hydroxyl groups at high temperature. Oxygen vacancy (V_O) can be generated through the annealing process during sensor device fabrication; V_O must be filled with an O₂ molecule, which can further interact with adsorbed water nearby to form hydroxyl groups. According to this research, α-MoO₃ (100) must be the active surface for amine sensing and its surface chemistry is well understood. In the near future, further reaction and interaction will be simulated at α-MoO₃ (100), and much more attention should be paid to α-MoO₃ (100) not only theoretically but also experimentally.