Low operating temperature and highly selective NH₃ chemiresistive gas sensors based on a novel 2D Ti₃C₂T_x/ZnO composite with p–n heterojunction

Ammonia monitoring in our daily life is significant. In this work, Ti₃C₂T_x/ZnO materials were prepared by hydrothermal method. The results of XRD, SEM, TEM, and XPS analyses demonstrated the successful preparation of the Ti₃C₂T_x/ZnO composite. Ti₃C₂T_x/ZnO (3:1) material exhibited the best morphology as ZnO grows evenly on it as ultrathin nanosheets. The gas sensing performance of Ti₃C₂T_x, ZnO, and Ti₃C₂T_x/ZnO (1:1, 2:1, 3:1, and 5:1) materials were studied. The Ti₃C₂T_x/ZnO (3:1) sensor has an excellent response to 50 ppm ammonia at a low operating temperature (∼28 °C), and the value of response is 196%, which is the highest response in this work. Furthermore, it was found that Ti₃C₂T_x/ZnO (3:1) detects ammonia selectively against other volatile organic compounds at a low operating temperature (∼28 °C). The actual lowest detection ability was measured at 1 ppm, and the corresponding response is 14%. The ultra-thin ZnO nanosheets on the Ti₃C₂T_x MXene and the p–n heterojunctions in Ti₃C₂T_x/ZnO (3:1) are designed to achieve better ammonia sensing performance. This paper provided a route to enhance the p-type characteristic of Ti₃C₂T_x MXene, which is meaningful to Ti₃C₂T_x MXene application at a low operating temperature in the future.