Tungsten oxysulfide nanosheets for highly sensitive and selective NH3 sensing

The detection of ammonia is in high demand on account of its deleteriousness and inflammability, affecting human health and the environment. However, there still remain challenges in the sensing of ammonia with simultaneous high response, fast kinetics, selectivity and low operation temperature. Herein, ultrathin tungsten oxysulfide (WS2|O) nanosheets are fabricated through a one-step hydrothermal process and employed for NH3 sensing. The incorporation of oxygen is found to retain the nanosheet morphology and WS2 phase, offering interesting possibilities for tuning electronic states and the redox reaction with target molecules. With exposure to different gases, the WS2|O nanosheets exhibit superior sensing responses (resistance ratio 450.23%, 100 ppm NH3) at 125 °C in comparison to their counterparts, including WS2/WO3 composites and WS2 nanosheets. In the meantime, such a WS2|O sensor also achieves high selectivity to NH3 gas as well as excellent sensing repeatability. The enhanced sensing behaviors could be readily understood from the strong electron-accepting characteristics and efficient ammonia adsorption arising from the incorporated oxygen with high electronegativity. Furthermore, density functional theory (DFT) calculations were performed to elucidate the enhanced ammonia sensing mechanism, evidencing the greater charge transfer and higher NH3 absorption energy (−0.258 eV) of WS2|O compared to those of WS2 (−0.172 eV) and WO3 (−0.170 eV). The strategy of incorporating nonmetallic elements developed here may have great potential for tuning the electronic states of materials towards advanced gas sensors.