Nitrogen Dioxide Gas Sensor Based on Liquid-Phase-Exfoliated Black Phosphorus Nanosheets

Black phosphorus (BP) nanosheets represent a promising class of two-dimensional (2D) materials for nitrogen dioxide (NO₂) sensing, but its practical application is limited by complex preparation processes. In this paper, we present an ultrasensitive and selective chemiresistive NO₂ sensor based on liquid-phase-exfoliated BP nanosheets. The unique combination of probe sonication and ice-water bath sonication is capable of producing BP nanosheets of various controllable sizes. Sensing characterization shows that the BP nanosheet-based sensor exhibits a large sensing response of 88%, a high selectivity, and a full recovery toward 100 ppb NO₂ gas at room temperature, which represents a substantial improvement over recently reported designs. The proposed preparation method for nanosheets with tunable gas-sensing properties is instrumental to the practical applications of BP toward high-performance, portable, and ubiquitous NO₂-sensing applications.