Tungsten oxysulfide nanosheets for highly sensitive and selective NH3 sensing

Abstract

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.