MXene/SnS₂ Heterojunction for Detecting Sub-ppm NH₃ at Room Temperature

Detection of ultralow concentrations of ammonia is very important in many applications such as fishing, poultry, agriculture, industry, biomedicine, and clinical diagnosis. However, detecting sub-ppm NH 3 remains a challenge for chemiresistive-type gas sensors. Two-dimensional (2D) materials display tremendous potential for effective gas detectors that can be used in these applications. The as-developed MXene/SnS 2 heterojunction-based chemiresistive-type sensor presents superior gas-sensing performance toward sub-ppm ammonia at room temperature. The sensor can detect NH 3 concentrations down to 10 ppb at room temperature. It also displays excellent long-term stability, with a decline in the response at ∼3.4% for 20 days. The developed sensor also displays good selectivity toward NH 3 relative to some potential interferents, such as HCHO, C 2 H 5 OH, CH 3 OH, C 3 H 6 O, benzene, and NO 2 . The measured in situ diffuse-reflectance infrared Fourier transform (DRIFT) spectra confirm that the products of nitric oxides during the chemical reactions occurred at the surface of MXene/SnS 2 . Density functional theory (DFT) based on the first principles was implemented to compute the adsorption ability of NH 3 at the surface of the MXene/SnS 2 heterostructure. This indicates that the enhancement in the sensing properties of the MXene/SnS 2 heterostructure-based chemosensor could be ascribed to the stronger NH 3 adsorption, better catalytical activity, and more effective charge transfer bestowed by the formed heterostructure and the electron-redistribution-assisted stronger extraction of electrons from the sensing material.