Two-step hydrothermal synthesis of α-MoO3@ZIF-8 nanoswords: An effective strategy to improve the selectivity and response value of ammonia detection

The α-MoO₃ nanoswords were successfully synthesized on Al₂O₃ ceramic tubes via a hydrothermal method. Subsequently, α-MoO₃@ZIF-8 composites were fabricated in a second hydrothermal synthesis step, utilizing the α-MoO₃ nanoswords as the core. The ZIF-8 material's multistage microporous structure enables selective gas screening, effectively blocking the contact between sensitive materials and interfering gases. Gas-sensing experimental results indicated that the α-MoO₃@ZIF-8 composite exhibited a significantly enhanced selectivity towards the target gas (NH₃) compared to pure α-MoO₃. Specifically, the response value to TEA decreased from 116.0 to 7.4, while the response value to NH₃ increased from 20.3 to 36.5. To elucidate the gas-sensing mechanism of the α-MoO₃@ZIF-8 composite, molecular dynamics (MD) simulations and grand canonical Monte Carlo (GCMC) method were conducted to investigate the gas adsorption properties of ZIF-8. Additionally, the adsorption of NH₃ by both α-MoO₃ and α-MoO₃@ZIF-8 was studied using density functional theory (DFT) simulations. These simulations revealed that the adsorption of NH₃ on both materials is a chemisorption process. Furthermore, the interaction of NH₃ with the material surfaces was characterized using partial density of states (PDOS), charge density difference, and Hirshfeld charge analysis.