Development of Dual-Selective Chemiresistive Sensor for NH₃ and NO_x at Room Temperature Using MoS₂/MoO₂ Heterostructures

Molybdenum oxides and sulfides stand out as promising materials for chemiresistive gas sensors. In this study, we tailored MoS₂/MoO₂ heterostructures, adapting pyrolysis-assisted in situ sulfidation of hydrothermally grown MoO₃ by tuning the concentration of the sulfur source. The MoS₂ flakes adorning a MoO₂ cuboid rod heterostructure represent the n-type semiconducting property, confirmed by Hall measurement. Notably, the sensor demonstrated dual selectivity toward NH₃ and NO_x at room temperature. To our knowledge, the dual selectivity of the MoS₂/MoO₂ heterostructure has not been reported previously. The heterostructure, characterized by a higher carrier concentration, displayed enhanced sensitivity, yielding responses of 10.3 and 8.4% to 10 ppm of NH₃ and NO_x, respectively. The lowest detection limits were 0.32 ppm for NH₃ and 0.29 ppm for NO_x. Furthermore, the heterostructure sensor exhibited commendable cyclic stability and device reproducibility. A long-term stability assessment over 50 days revealed that the response of the sensor remained at 98.6 and 98.4% toward NH₃ and NO_x, respectively. Our results show that the optimized n–n heterojunction between MoO₂ and MoS₂ offers superior sensitivity to NH₃ and NO_x at room temperature. The results could have potential for the development of dual gas sensors suitable for real-time applications.