Ammonia Detection Based on Core–Shell Nanoparticle ZnS/Co₉S₈ Composites

In this paper, the Co/Zn-based zeolite imidazole framework (Co/Zn-ZIF) was synthesized by an etching method. Then, a certain amount of sulfur powder was doped into it and annealed to synthesize ZnS/Co9S8 composites with a core–shell structure mechanism (CS-ZnS/Co9S8). Compared with the single-metal ZIF, which is more studied at present, the application of a bimetallic ZIF shows remarkable excellent performance in gas sensing. The test results show that the sensor with a CS-ZnS/Co9S8 film has ultrahigh sensitivity to ammonia. At its optimal operating temperature of 240 °C, the detection limit of ammonia concentration can be detected to be 0.2 ppm. At the same time, the response of the CS-ZnS/Co9S8 thin-film sensor to 5 ppm concentration of ammonia is 4.56, which is 2.85 times and 3.26 times that of the single ZnS and Co9S8 thin-film sensors. In addition, the CS-ZnS/Co9S8 thin-film sensor has a response/recovery time of 7 s/9 s and has excellent repeatability, long-term stability, selectivity, and antihumidity interference. In addition to the polyhedral core–shell mechanism formed by ZnS/Co9S8, the p–n heterojunction directly formed by ZnS and Co9S8 is also a very important factor for the substantial improvement of its sensing performance.