Novel SnO2(ZnO:Sn)m superlattice nanoparticles for ultra-low ppb-level H2S detection

Abstract

Novel zero-dimensional SnO₂(ZnO:Sn)_m superlattice nanoparticles were synthesized by a simple method of annealing ZnO nanoparticles precoated with a sol–gel Sn–Zn–O precursor. The annealing temperature and duration were systematically evaluated, and the optimum condition was confirmed as 900 °C for 45 min to obtain ideally fully developed layered structures. Cs-corrected scanning transmission electron microscopy (STEM) revealed that the SnO₂(ZnO:Sn)_m was composed of alternate stacking of a Sn–O octahedral layer and Sn-doped ZnO slab, which resulted from the anisotropic diffusion of Sn atoms in the ZnO basal plane. A gas sensor based on the SnO₂(ZnO:Sn)_m superlattice nanoparticles exhibited a superior selectivity towards the poisonous gas of hydrogen sulphide (H₂S) among six different types of gases (ethanol, H₂, CO, NO₂, NH₃ and H₂S), and an extreme low H₂S detection limit of 5 ppb at the working temperature of 400 °C, which was about 3–5 orders lower than that of most ZnO-based H₂S gas sensors in the literature. The drastic enhancement of the sensing properties of the SnO₂(ZnO:Sn)_m superlattice nanoparticles was believed to originate from its unique layered structure, which forms a microcirculation of electrons between the Sn–O atomic layers and Sn-doped ZnO slabs with different work functions, thus greatly accelerating the adsorption and desorption rate of gas molecules and increasing the sensor sensitivity. These new SnO₂(ZnO:Sn)_m superlattice nanoparticles were demonstrated to be a competitive H₂S sensing material candidate for practical application. In addition, the facile superlattice nanoparticles fabrication method presented here could be extended to synthesize other ZnO-based superlattice material systems.