MoS₂/WO₃ Nanosheets for Detection\nof Ammonia

Abstract

This article demonstrates the use\nof a p-MoS₂/n-WO₃ heterojunctions based ultra\nsensitive and selective chemiresistive\nammonia sensor that operates at 200^◦ C. Surprisingly,\nthe composite based sensor exhibited significant enhancement in ammonia\nsensing as compared to MoS₂ (p-type) and WO₃ (n-type) counterparts. The device also displayed excellent response-recovery\nfeatures over a wider range of ammonia concentration together with\nsuperior selective nature toward ammonia as compared acetone, ethanol,\nmethanol, isopropanol, formaldehyde, benzene, and hydrogen sulfide.\nEmpowered by better signal-to-noise ratio, ammonia detection down\nto 1 ppm has become possible and can be further improved with the\nuse of serpentine type electrodes. The device has shown a relative\nresponse of 207% for 200 ppm of ammonia with response and recovery\ntimes of 80 and 70 s, respectively. Moreover, these experimental results\nwere further supplemented by density functional theory (DFT) simulation\nthat were used to understand the adsorption kinetics and the sensing\nmechanism. A significant amount of charge transfer (0.082 e) between\nthe adsorbed ammonia molecule and the MoS₂/WO₃ surface has been predicted by Bader analysis. Analysis also revealed\na large negative adsorption energy ≈3.86 eV (373 kJ/mol) per\nammonia molecule, implying the adsorption process to be chemisorption\nin nature. The band structure analysis further confirmed that ammonia\nadsorption on MoS₂/WO₃ is accompanied by an\nincrease in band gap (by ≈ 96 meV). The present work illustrates\nthe potential use of composite based heterostructures for monitoring\nammonia gas in real fields.