Visible-Light-Driven Two-Dimensional Indium Oxysulfide for Sensitive NO2 Detection

Room-temperature optoelectronic gas sensing presents a viable solution for efficient and low-cost NO2 gas monitoring. Two-dimensional (2D) metal oxychalcogenides, induced by the partial sulfur replacement with oxygen in metal chalcogenide, have been considered to be suitable sensitive materials owing to their excellent long-term stability and complete reversibility. However, the correlation of oxygen-to-sulfur content with gas sensing performances has yet to be known, hindering the optimization process of such an emerging NO2 gas sensing approach. In this work, we realize 2D ultrathin indium oxysulfide by combining the annealing of bulk In2S3 crystals and subsequently liquid phase exfoliation, while the degree of sulfur replacement with oxygen is controlled by the initial annealing temperature. At an optimum annealing temperature of 800 degrees C, the sample exhibits an optical bandgap of 2.19 eV and a photoexcited carrier lifetime of 272.82 ns. As a result, it demonstrates a response factor of 7.26 for 126 ppb of NO2 under blue light illumination at room temperature, while complete reversibility, high selectivity, and excellent long-term stability are also achieved. An extremely low limit-of-detection of 0.0342 ppb is shown, far beyond that of reported room-temperature optoelectronic NO2 sensors. This work presents the optimization of the implementation of 2D metal oxychalcogenides in NO2 gas sensing, paving the way to develop next-generation NO2 monitoring systems.