High-Performance H2S Sensor Based on a Cube-in-Cage ZnO/ZnFe2O4 Superstructure

The elaborate and controlled fabrication of complex inorganic nanomaterials is an attractive challenge. In this study, a structure-directed anisotropic chemical etching combined with anion-exchange strategy, followed by an annealing process, was developed for the controlled synthesis of a novel cube-in-cage ZnO/ZnFe2O4 superstructure rich in oxygen vacancies. The prepared ZnO/ZnFe2O4 nanostructures exhibited excellent sensing performance for hydrogen sulfide (H2S) gas, benefiting from the open 3-D structure, the small primary particle sizes, the high specific surface area, and abundant oxygen vacancies. At a relatively low operating temperature ( $120~^{\circ }$ C), the material showed a response of 23.75 for 10-ppm H2S and a response/recovery time of 8/179 s. Even for 20-ppb H2S, the material still exhibited a significant response ( ${S} =1.43$ ), good selectivity, reversibility, and long-term stability. In addition, the quasi-in situ X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FTIR) showed that during the sensitive response, H2S reacted with the material itself in addition to the adsorbed oxygen on the material surface, generating a small amount of ZnS intermediates. Density functional theory calculations suggested that the superb adsorption capacity of the ZnO/ZnFe2O4 superstructure for the H2S gas enhanced the gas-sensitive selectivity of the material. This article provides a new design for high-performance H2S gas sensors and a new opportunity for the controllable design of complex superstructures of metal oxides.