Room-Temperature NO₂ Sensor Based on Oxygen Vacancy-Rich SnO Nanosheets

Nitrogen dioxide (NO2) is a hazardous air pollutant that poses significant threats to both human health and the environment. The development of NO2 sensors with high sensitivity, exceptional selectivity, and ultralow detection limits is of critical scientific and practical importance. However, conventional metal oxide-based NO2 sensors often suffer from inherent limitations, including high operating temperatures and relatively low sensitivity. Given that oxygen vacancies in metal oxides serve as active sites for NO2 adsorption and facilitate charge transfer at the gas–solid interface, this study demonstrates the room-temperature sensing capabilities of two-dimensional (2D) SnO nanosheets with a high concentration of oxygen vacancies, achieved without external excitation (e.g., light). Notably, the sensor exhibits n-type behavior, attributed to free electrons originating from oxygen vacancies. More importantly, the proposed sensor outperforms pure SnO and other metal oxide-based sensors, achieving a remarkably low detection limit of 10 ppb and a record-high response value of 136.43 toward 800 ppb of NO2. Furthermore, it demonstrates outstanding repeatability, exceptional selectivity, and long-term stability over two months. These findings highlight the feasibility of achieving ppb-level NO2 detection at room temperature through morphological control and defect engineering, paving the way for the development of ultrasensitive and high-performance NO2 sensors.