A Universal Synthesis Strategy for Ferrite Nanocage Superstructures and Their Enhanced Gas Sensing Properties

Ferrites with superstructures exhibit great potential for gas sensing applications, benefiting from their open structure, high specific surface area, and fully exposed active sites. However, the preparation of these superstructures is often cumbersome and requires some surfactants. In this study, Zn–Fe Prussian blue analogue (PBA) nanocages were synthesized through Ostwald ripening using a simple liquid-phase coprecipitation method without any other etchants or surfactants. A series of MFe₂O₄ (M = Fe, Co, Ni, Cu) nanocages, including n-type and p-type semiconductors, were obtained using the Zn–Fe PBA nanocages as templates via a metal ion exchange strategy and annealing process. Gas sensing investigations revealed that Zn–CuFe₂O₄, Zn–Fe₃O₄, and Zn–CoFe₂O₄ materials exhibited high sensitivity and selectivity for H₂S, ZnFe₂O₄ for H₂, and Zn–NiFe₂O₄ for NO₂ at relatively low operating temperatures (50–150 °C). Quasi-in situ X-ray photoelectron spectroscopy and in situ infrared spectroscopy analyses indicated that during the H₂S sensing response process, H₂S reacted with the adsorbed oxygen on the surface of Zn-doped Fe₃O₄ and CuFe₂O₄ materials, as well as with the materials themselves, resulting in the formation of metal sulfide intermediates in small quantities. This work advances the controllable preparation of nanosuperstructures and lays a sound foundation for their widespread applications.