Tetrapod-like ZnO/ZnFe₂O₄ based heterostructure for enhanced ethanol detection

Tetrapod-like ZnO/ZnFe₂O₄ heterostructure composites were designed and fabricated for ethanol detection. Sensitivity and selectivity of ZnO were significantly enhanced after coating with ZnFe₂O₄, as it formed heterostructure and special morphology. The tetrapod-like structure formed numerous three-dimensional hollow holes as channels for the gas diffusion in the inner and outer surfaces of materials simultaneously, providing large specific areas as “reaction field” for gas adsorption. Additionally, the heterojunction increased oxygen adsorption, resulting in the formation of more chemisorbed oxygen species for reaction with the target gas. Further, in contrast to aggregated structures, the ZnO/ZnFe₂O₄ tetrapods were separated from each other, and the electrons conducting between the tetrapod-shape ZnO/ZnFe₂O₄ had to pass through the modified surface sensing layer at the boundary; thus, the response of the heterojunction to target gas significantly affected the overall resistance. Consequently, ZnO/ZnFe₂O₄ exhibited an excellent responses value of 28.11–500 ppm ethanol gas. The sensor exhibited good sensing repeatability and long-term stability, which maintained 93% of its original response after 30 days. The response time and selectivity to ethanol were also enhanced compared with the pristine T-ZnO. Therefore, the proposed strategy may facilitate the design and fabrication of binary transition metal oxide based heterostructure for ethanol vapor sensing.