Construction of Hierarchical SnO₂/SnS₂ Heterostructures for NO₂ Detection at Low Temperatures

NO2 detection is important for monitoring indoor and outdoor air pollution. However, the development of SnS2-based sensors is limited by their low response value and low selectivity. Therefore, adopting strategies to improve the sensing properties of SnS2, such as by constructing heterostructures, is necessary. In this study, hierarchical SnO2/SnS2 nanoflower heterostructures were synthesized using a solvothermal method followed by calcination. By regulating the calcination time and adjusting the SnO2 content of the SnO2/SnS2 composites, SnO2 nanoparticles were deposited on the SnS2 nanoflower surface. Among the as-synthesized sensors, the SnS2-30-based sensor (annealed for 30 min) yielded a response signal of 44.32 for 5-ppm NO2 at 120 degree celsius, which is 24.25 times higher than that achieved for the SnS2-based sensor (4.52). The SnS2-30-based sensor exhibited specific selectivity for NO2 (compared to methanol, ethanol, formaldehyde, acetone, and ammonia solution), reduced operating temperature (120 degree celsius versus 140 degree celsius), wide detection range (10 ppb-15 ppm), and excellent long-term stability (the response after 4 weeks is 42.41). The enhancement of NO2 gas sensing performance is mainly attributed to the synergistic effect between the hierarchical structure of SnS2 and the SnO2/SnS2 heterostructure. The sensor prepared in this study is a suitable candidate for monitoring environmental NO2 gas.