Heterojunction and exposed facet engineering of ZnO/ WO3 flower structure for fast and sensitive low-concentration NO2 sensing

A novel silybum flower-like ZnO/ hexagonal WO3 heterostructure is synthesized via hydrothermal method and applied in gas sensors for NO2 detection. The morphology, composition, and possible growth mechanism are systematically investigated by a series of characterizations. In comparison with the pure WO3 and other ZnO/WO3 samples, the silybum flower-like ZnO/ hexagonal WO3 sensor presents superior NO2 sensing performance at 190 °C, particularly at low concentrations, consisting of high response (5.9), quick response (7–12 s)/recovery time (9–13 s), strong selectivity and stability toward 100 ppb NO2. The excellent sensing characteristics are attributed to the synergy of heterojunction and exposed (001) facet with more oxygen vacancies. Furthermore, the well-defined open flower structure provides unique opportunities to form n-n heterostructures, inducing the adequate sensing reactions and ultrafast the response/recovery kinetics. The findings in this study open a new route for WO3-based hierarchical materials to detect NO2 efficiently and accurately.