Construction of pine-branch-like α-Fe₂O₃/TiO₂ hierarchical heterostructure for gas sensing

For real-time environmental monitoring and gas detection under harsh conditions, gas sensors with high reliability, sensitivity, and selectivity are in increasing demand. Therefore, pine-branch-like α-Fe₂O₃/TiO₂ with a core–shell hierarchical heterojunction structure was designed and fabricated for ethanol sensing. The heterojunction increased the O adsorption, resulting in the formation of more chemisorbed O species for reaction with the target gas. Moreover, the pine-branch-like morphology formed three-dimensional hollow holes as channels for molecule diffusion and adsorption. Compared with gas-proof structures, the hollow regions can realize gas diffusion in the inner and outer surfaces of materials simultaneously. Further, in contrast to aggregated structures, the fibers were separated from each other, and charge conduction between the fibers needed to pass through the surface sensing layer at the fiber boundary; thus, the overall resistance change of the sensors was significantly affected by the response of the heterojunction to the target gas. Consequently, the α-Fe₂O₃/TiO₂ sensor exhibited a high response value of 40.4 toward 500 ppm ethanol gas and had excellent selectivity to ethanol. The proposed strategy may facilitate the design and construction of effective heterojunctions and nanostructures for gas sensing.