ZnO–SnO2 nano-heterostructures with high-energy facets for high selective and sensitive chlorine gas sensor

The n-ZnO/n-SnO2 nano-heterostructures surrounded by high-energy facets have been designed and synthesized via a simple two-stage route and used as functional materials of chlorine gas sensor. The composition, morphology and structure of ZnO–SnO2 nano-heterostructures are characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). It is found that both the SnO2 octahedra nanoparticles and the ZnO–SnO2 nano-heterostructures are surrounded by high-energy (221) facets. The sensor with the ZnO–SnO2 nano-heterostructure nanoparticles presents a much higher response (230.52) to Cl2 (upgrade to 50 times) than that of the sensor with the pure SnO2 nanoparticles. Moreover, a new and reasonable method is used to calculate the detection limit of two sensors. The sensor with 10% ZnO–SnO2 sample (ZnO: SnO2 = 10%, mol%) reveals lower detection limit (0.06 ppm) than that of pure SnO2 sample (1.10 ppm). The superior Cl2 sensing performance is closely related to the effects of the high-energy facets and the formation of energy barrier between ZnO and SnO2.