Synthesis and gas sensor application of ZnFe2O4–ZnO composite hollow microspheres

In this contribution, ZnFe2O4–ZnO composite hollow microspheres were successfully synthesized by a glucose-assisted hydrothermal method only using Fe(NO3)3·9H2O, Zn(NO3)2·6H2O and glucose as starting materials, followed by a calcination treatment. The characterization results from scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the as-synthesized ZnFe2O4–ZnO composite hollow microspheres, with a diameter range of 1 to 2.5 μm and a shell thickness of about 60 nm, consist of numerous small cubic spinel ZnFe2O4 nanoparticles and hexagonal wurtzite ZnO nanoparticles. In order to investigate the potential applications, the resulting ZnFe2O4–ZnO composite hollow microspheres were employed to fabricate a gas sensor using four common volatile organic pollutants (VOPs) namely n-butanol, acetone, ethanol and methanol as probe gases. The gas sensing measurement results demonstrated that the sensor based on the as-obtained ZnFe2O4–ZnO composite hollow microspheres exhibited a high response, good reversibility and reproducibility, and quick response and recovery characteristics. The composite sensor also showed enhanced responses compared with the pure ZnO sensor, which could be contributed to the unique rough, porous and hollow structure of the ZnFe2O4–ZnO composite hollow microspheres, and the heterojunction action at the interfaces of ZnFe2O4–ZnO. It is expected that the current ZnFe2O4–ZnO composite hollow microspheres have promising applications in gas sensors and can be further applied in other fields such as photocatalysis and magnetic resonance imaging.