Recent advances in 2D/nanostructured metal sulfides-based gas sensors: mechanisms, applications, and perspectives

2D- and nanostructured metal sulfide materials promise to advance several gas sensing applications due to the abundant choice of materials with easily tunable electronic, optical, physical, and chemical properties. Of these applications, they are particularly attractive for gas sensing in environmental monitoring and breath analysis. This review gives a systematic description of various gas sensors based on 2D- and nanostructured metal sulfide materials. Firstly, the crystal structures of metal sulfides are introduced. Secondly, the gas sensing mechanism of different metal sulfides based on density-functional theory analysis is summarised. Various gas-sensing concepts of metal sulfide-based devices, including chemiresistor, functionalized-metal sulfides, Schottky junction, heterojunction, field-effect transistor, optical, and surface acoustic wave sensor, are comparatively presented. It then discusses the extensive applications of metal sulfide-based sensors to different gas molecules, including volatile organic compounds (i.e., acetone, benzene, methane, formaldehyde, ethanol, and liquefied petroleum gas) and inorganic gas (i.e., CO2, O2, NH3, H2S, SO2, NOx, CH4, H2, and humidity). Finally, a strengths-weaknesses-opportunities-threats (SWOT) analysis is proposed for future development and commercialization in this field.