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/ZnFe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> superstructure rich in oxygen vacancies. The prepared ZnO/ZnFe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanostructures exhibited excellent sensing performance for H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>S gas, benefiting from the open 3D structure, the small primary particle sizes, the high specific surface area, and abundant oxygen vacancies. At a relatively low operating temperature (120 °C), the material showed a response of 23.75 for 10 ppm H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>S and a response/recovery time of 8 s/179 s. Even for 20 ppb H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>S, the material still exhibited a significant response (S = 1.43), good selectivity, reversibility, and long-term stability. In addition, quasi-in situ X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that during the sensitive response, H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>S 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/ZnFe<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> superstructure for the H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>S gas enhanced the gas-sensitive selectivity of the material. This paper provides a new design for high-performance H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>S gas sensors and a new opportunity for the controllable design of complex superstructures of metal oxides.