Synthesis of hierarchical ZnO/ZnFe2O4 nanoforests with enhanced gas-sensing performance toward ethanol

Abstract

Hierarchical ZnO/ZnFe₂O₄ nanoforests with ZnO backbones and ZnFe₂O₄ nanosheets were successfully prepared by a facile two-step process. The products were fabricated by immersion of the as-synthesized ZnO nanorod arrays in a 0.2 M aqueous solution of ferrous sulfate and subsequent calcination at 500 °C. Various techniques were employed for the characterization of the structure and morphology of the hybrid nanostructures. The results showed that a high density of ZnFe₂O₄ nanosheets was planted on the surface of the ZnO nanorods. Interestingly, the morphologies of the ZnO/ZnFe₂O₄ hierarchical nanostructures can be tailored by changing the concentration of the FeSO₄ solution and the immersion time. A possible formation process and growth mechanism was proposed as the ZnO nanorods were partly dissolved during the immersion period. In order to demonstrate the potential application of the nanorods, two sensors based on bare ZnO and ZnO/ZnFe₂O₄ composites were fabricated and their gas-sensing properties were investigated. The results indicated that the obtained advanced ZnO/ZnFe₂O₄ nanostructures exhibited enhanced sensing properties to ethanol compared to the primary ZnO nanorods. For example, upon exposure to 100 ppm ethanol, the response of the hierarchical ZnO/ZnFe₂O₄ composites was about 4 times higher than that of the primary ZnO nanorods at the operating temperature of 275 °C.