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

Nitrogen dioxide (NO 2 ) is a hazardous air pollutant that poses significant threats to both human health and the environment. The development of NO 2 sensors with high sensitivity, exceptional selectivity, and ultralow detection limits is of critical scientific and practical importance. However, conventional metal oxide-based NO 2 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 NO 2 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 NO 2 . Furthermore, it demonstrates outstanding repeatability, exceptional selectivity, and long-term stability over two months. These findings highlight the feasibility of achieving ppb-level NO 2 detection at room temperature through morphological control and defect engineering, paving the way for the development of ultrasensitive and high-performance NO 2 sensors.