A Room Temperature High-Performance Visible-Light-Assisted NO2 Gas Sensor Based on Ultrathin Zinc Oxysulfide

Metal oxysulfides are an emerging group of sensitive materials for high-performance NO2 sensing owing to their room-temperature operation capacity, excellent selectivity of NO2, the part-per-billion-leveled limit of detection, as well as high stability against the ambient environment. Here, the room-temperature NO2 sensing performances of zinc oxysulfide 3D micro-self-assembly composed of ultrathin nanoflakes are investigated. The combined hydrothermal-annealing approach is applied to first synthesize zinc sulfide micro-self-assembly and then transform it into zinc oxysulfide in a controlled environment. As a result, the majority of S atoms in zinc sulfide are replaced with O atoms, leading to the crystal structure variation from cubic/hexagonal to an orthorhombic configuration. Simultaneously, the corresponding optical bandgap is reduced from approximate to 3.6 - 3.8 eV to approximate to 1.92 eV, enabling the visible light harvesting capability. The sensor demonstrates a fully reversible and repeatable sensing response toward 1.26 ppm NO2 gas at room temperature with a response magnitude of approximate to 2.27 under the 460 nm excitation, a limit of detection (LOD) of 294.8 part-per-trillion (ppt), and almost an order of magnitude larger compared to other commonly used gas species. This work demonstrates the great potential of the metal oxysulfide framework for developing next-generation room-temperature NO2 gas sensors.