A two-dimensional Ti3C2TX MXene@TiO2/MoS2 heterostructure with excellent selectivity for the room temperature detection of ammonia

Two-dimensional nanomaterials have exhibited considerable potential for gas sensing applications in recent years owing to their unique physical and chemical properties such as a large surface-to-volume ratio, abundant edge sites, versatile surface chemistry, etc. Herein, we demonstrate a two-dimensional Ti3C2TX MXene@TiO2/MoS2 nanocomposite gas sensor for ammonia detection at room temperature. MoS2 nanosheets are grown on an etched Ti3C2TX MXene surface by a hydrothermal method, and rectangular TiO2 particles are derived from Ti3C2TX MXene in the hydrothermal process. Meanwhile, nanocomposites with different Ti3C2TX MXene additions are also designed for gas sensing performance comparison. Such a novel hierarchical structure based gas sensor (MTM-0.2 sensor) exhibits fast response/recovery time and excellent long-term stability to ammonia. Meanwhile, outstanding selectivity to ammonia against triethylamine, trimethylamine, n-butanol, acetone, formaldehyde, and nitrogen dioxide at room temperature is also shown. The sensor shows 1.79-fold and 2.75-fold enhancement in the gas sensing response toward 100 ppm ammonia compared with the pristine Ti3C2TX MXene and MoS2 gas sensors, respectively. And its detection limit for ammonia is 500 ppb. The sensing mechanisms of the Ti3C2TX MXene@TiO2/MoS2 nanocomposites toward ammonia are attributed to the layered nanostructure, p-n heterojunction created at the interface of p-type Ti3C2TX MXene and n-type MoS2. Finally, density-functional theory (DFT) is performed to investigate the adsorption behavior and charge transfer of ammonia molecules on the surface of the nanocomposite. The synthesized Ti3C2TX MXene@TiO2/MoS2 nanocomposite can be regarded as a promising candidate for high-performance ammonia detection at room temperature.