Effect of Zn Concentration in Zinc-Doped 2D Layered Indium Oxides for Room-Temperature Optoelectronic Sensing of NO2

The growing imperative for real-time monitoring of nitrogen dioxide (NO₂)─a criterion air pollutant with chronic health impacts─necessitates the development of room-temperature, high-performance gas sensors. Two-dimensional (2D) metal oxides have emerged as a promising material group for high-performance and energy-efficient gas sensing. The transition metal doping strategy is deemed an effective method to enhance their gas interaction properties, especially at room temperature. 2D indium oxide nanostructures (In₂O₃) have garnered significant research interest due to their remarkable gas-sensing properties. Building on this interest, we present the gas sensing properties of zinc (Zn)-doped ultrathin 2D In₂O₃ nanocrystals. To this end, a range of mass concentrations of Zn-doped 2D In₂O₃, with a uniform thickness of approximately 4.0 ± 0.2 nm, was achieved by transferring the surface oxide layer from liquid In–Zn alloys under controlled conditions. The room-temperature optoelectronic NO₂ sensing behavior and underlying mechanisms of Zn-doped 2D In₂O₃ were systematically investigated through combined experimental and theoretical approaches. The 2% Zn doping concentration sample demonstrated optimal NO₂ sensing performance, with a response value of 6.16 and response/recovery times of 46.17 min/36.52 min, exhibiting good moisture resistance and selectivity. This work provides a viable approach for the preparation of 2D metal-doped oxides and demonstrates the effect of doping on gas sensitivity.