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 NH₃ 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/SnS₂ heterojunction-based chemiresistive-type sensor presents superior gas-sensing performance toward sub-ppm ammonia at room temperature. The sensor can detect NH₃ 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 NH₃ relative to some potential interferents, such as HCHO, C₂H₅OH, CH₃OH, C₃H₆O, benzene, and NO₂. 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/SnS₂. Density functional theory (DFT) based on the first principles was implemented to compute the adsorption ability of NH₃ at the surface of the MXene/SnS₂ heterostructure. This indicates that the enhancement in the sensing properties of the MXene/SnS₂ heterostructure-based chemosensor could be ascribed to the stronger NH₃ 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.