Black Phosphorus-Tungsten Oxide Sandwich-like Nanostructures for Highly Selective NO₂ Detection

Modern chemical production processes often emit complex mixtures of gases, including hazardous pollutants such as NO₂. Although widely used, gas sensors based on metal oxide semiconductors such as WO₃ respond to a wide range of interfering gases other than NO₂. Consequently, developing WO₃ gas sensors with high NO₂ selectivity is challenging. In this study, a simple one-step hydrothermal method was used to prepare WO₃ nanorods modified with black phosphorus (BP) flakes as sensitive materials for NO₂ sensing, and BP-WO₃-based micro-electromechanical system gas sensors were fabricated. The characterization of the as-prepared BP-WO₃ composite through X-ray diffraction scanning electron microscopy and X-ray photoelectron spectroscopy confirmed the successful formation of the sandwich-like nanostructures. The result of gas-sensing tests with 2-14 ppm NO₂ indicated that the sensor response was 1.25-2.21 with response-recovery times of 36 and 36 s, respectively, at 190 °C. In contrast to pure WO₃, which exhibited a response of 1.07-2.2 to 0.3-5 ppm H₂S at 160 °C, BP-WO₃ showed almost no response to H₂S. Thus, compared with pure WO₃, BP-WO₃ exhibited significantly improved NO₂ selectivity. Overall, the BP-WO₃ composite with sandwich-like nanostructures is a promising material for developing highly selective NO₂ sensors for practical applications.