In this paper, a room-temperature NO₂ sensor based on a polyaniline (PANI)/black phosphorus (BP) composite material was proposed to solve the power consumption problem of traditional metal-oxide sensors operating at high temperatures. PANI was synthesized by chemical oxidative polymerization, whereas BP was synthesized by low-pressure mineralization. The PANI/BP composite materials were prepared via ultrasonic exfoliation and mixing. Various characterization techniques, including scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), confirmed the successful preparation of the PANI/BP composites and their excellent structural properties. The sensor demonstrated outstanding gas sensitivity in the NO₂ concentration range of 2–60 ppm. In particular, the sensor showed a response exceeding 2200% at 60 ppm NO₂ concentration when using a 1:1 mass ratio of PANI to BP in the composite material.

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.

This paper presents a ZnO-Pt/Ru sensor prepared by a two-step hydrothermal method with in situ-grown ZnO nanorods and doped with Pt and Ru elements by immersion sintering. Characterization results showed that Pt and Ru were successfully modified on the surface of ZnO nanorods. ZnO-Pt/Ru achieved a response of 25–50 ppm H₂S at the optimum operating temperature of 198 °C. In addition, the lower limit of H₂S detection of ZnO-Pt/Ru reached 50 ppb with a response of about 10%, indicating a wide concentration detection range. Due to the good catalytic properties of Pt, the recovery characteristics of ZnO at high concentrations of H₂S were significantly improved. The response time of ZnO-Pt/Ru (30 s) was also significantly shorter than pristine ZnO (56 s), with excellent selectivity. As far as the gas-sensitive enhancement mechanism is concerned, at the macroscopic level, the ZnO surface was modified by Pt and Ru, and this special structure of ZnO-Pt/Ru significantly increased the specific surface area. At the microscopic level, the PN junction formed between Pt/Ru and ZnO provided abundant holes for electron migration.