MoS 2 /WO 3 Nanosheets for Detection of Ammonia

This article demonstrates the use of a p-MoS 2 /n-WO 3 heterojunctions based ultra sensitive and selective chemiresistive ammonia sensor that operates at 200 ◦ C. Surprisingly, the composite based sensor exhibited significant enhancement in ammonia sensing as compared to MoS 2 (p-type) and WO 3 (n-type) counterparts. The device also displayed excellent response-recovery features over a wider range of ammonia concentration together with superior selective nature toward ammonia as compared acetone, ethanol, methanol, isopropanol, formaldehyde, benzene, and hydrogen sulfide. Empowered by better signal-to-noise ratio, ammonia detection down to 1 ppm has become possible and can be further improved with the use of serpentine type electrodes. The device has shown a relative response of 207% for 200 ppm of ammonia with response and recovery times of 80 and 70 s, respectively. Moreover, these experimental results were further supplemented by density functional theory (DFT) simulation that were used to understand the adsorption kinetics and the sensing mechanism. A significant amount of charge transfer (0.082 e) between the adsorbed ammonia molecule and the MoS 2 /WO 3 surface has been predicted by Bader analysis. Analysis also revealed a large negative adsorption energy ≈3.86 eV (373 kJ/mol) per ammonia molecule, implying the adsorption process to be chemisorption in nature. The band structure analysis further confirmed that ammonia adsorption on MoS 2 /WO 3 is accompanied by an increase in band gap (by ≈ 96 meV). The present work illustrates the potential use of composite based heterostructures for monitoring ammonia gas in real fields.