Double-Shell Architectures of ZnFe2O4 Nanosheets on ZnO Hollow Spheres for High-Performance Gas Sensors.

In this study, double-shell composites consisting of inner ZnO hollow microspheres (ZHS) surrounded by outer ZnFe2O4 nanosheets were successfully synthesized. The growth of the ultrathin ZnFe2O4 nanosheets (∼10 nm) on the ZHS outer surface was carried out at room temperature via solution reactions in order to generate a double-shell configuration that could provide a large surface area. As a proof-of-concept demonstration of the design, a comparative sensing investigation between the sensors based on the as-obtained ZnO/ZnFe2O4 composites and its two individual components (ZnO hollow spheres and ZnFe2O4 nanosheets) was performed. As expected, the response of the ZnFe2O4-decorated ZnO composites to 100 ppm acetone was about 3 times higher than that of initial ZnO microspheres. Moreover, a dramatic reduction of response/recover time has been achieved at different operating temperature. Such favorable sensing performances endow these ZnO/ZnFe2O4 heterostructures with a potential application in gas sensing.