Direct growth of ZnO@ZIF-71 nanosheets on Al2O3 ceramic tubes for fabricating a highly selective and humidity-resistant NH3 sensor

Abstract

Ammonia detection is crucial for ensuring production safety, ecosystem protection, and human health. In this study, ZnO@ZIF-71 gas sensing elements were fabricated through a two-step hydrothermal method, demonstrating significantly enhanced NH₃ selectivity compared to pristine ZnO. Stability evaluations demonstrated that the developed sensor exhibited excellent long-term stability and humidity resistance, ensuring reliable operation. A comprehensive characterization of the composites, including surface morphology, specific surface area, and surface chemical state, was systematically performed. The evaluation of the NH₃ sensing performance showed that the incorporation of ZIF-71 significantly improved the NH₃ sensing capability of the material. The ZIF-71 coating significantly increased the specific surface area and adsorbed oxygen species content of ZnO, thereby increasing the number of active sites on the material surface. These enhancements enabled the ZnO@ZIF-71 sensor to exhibit a high response (22.6 to 50 ppm) to NH₃, excellent selectivity and a rapid response (34 s to 50 ppm). Density functional theory was used to analyze the characteristics of small molecule gases such as NH₃, simulate the adsorption sites of NH₃, and rationally explain the variation in sensitivity of the ZnO@ZIF-71 core-shell gas sensing material.