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

Abstract

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 Ti₃C₂T_X MXene@TiO₂/MoS₂ nanocomposite gas sensor for ammonia detection at room temperature. MoS₂ nanosheets are grown on an etched Ti₃C₂T_X MXene surface by a hydrothermal method, and rectangular TiO₂ particles are derived from Ti₃C₂T_X MXene in the hydrothermal process. Meanwhile, nanocomposites with different Ti₃C₂T_X 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 Ti₃C₂T_X MXene and MoS₂ gas sensors, respectively. And its detection limit for ammonia is 500 ppb. The sensing mechanisms of the Ti₃C₂T_X MXene@TiO₂/MoS₂ nanocomposites toward ammonia are attributed to the layered nanostructure, p–n heterojunction created at the interface of p-type Ti₃C₂T_X 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 Ti₃C₂T_X MXene@TiO₂/MoS₂ nanocomposite can be regarded as a promising candidate for high-performance ammonia detection at room temperature.