MoS2/MoO3 Nanocomposite for Selective NH3 Detection in a Humid Environment

Designing a material with novel sensing properties under extreme working conditions has remained a challenging task. Here, we report a facile two-step approach to develop a MoS2/MoO3 composite with enhanced surface properties. When used as a gas sensor at 25 °C, it displayed superior sensing properties, selectivity, and a stable response toward ammonia against various reducing and oxidizing gases under highly humid conditions (relative humidity ≈ 95%). The composite exhibited a relative response of ≈55% (15% for 1 ppm) toward 50 ppm of NH3 with smaller response τres. and recovery τrev. times of 45 and 53 s, respectively. It also displayed complete recovery without any external optical or thermal stimulus. The enhanced sensing properties of the composite are attributed to the synergistic effect arising from heterostructure formation between two base materials. The sensor displayed a decrease in resistance when exposed to NH3, a reducing gas, thus indicating its n-type character, which was further confirmed by performing Mott–Schottky (MS) measurements on MoS2 and the MoS2/MoO3 composite, both displaying n-type behavior with increased electron densities of the composite. Further, to understand the adsorption process and the resulting sensing properties, density functional theory simulations were performed using a pristine and a defect-enriched MoS2/MoO3 surface. Large negative adsorption energies (for NH3) of −344 and −519 meV, respectively, reflect that the adsorption process is feasible, and mechanism change from physisorption to chemisorption is predicted. Bader scheme was employed to evaluate the charge transfer between the NH3 molecule and the pristine (defect-enriched) MoS2/MoO3 surface and gave an amount of 0.073e (0.010e). Therefore, these results collectively justify the use of the MoS2/MoO3 composite as a selective NH3 sensor that can operate in humid air and environmental monitoring applications where such conditions exist.