Synergistic NaCl-modulated refinement and in-situ SnO₂ embedding for ultrasensitive isobutanol sensing in SnO₂-Fe₂O₃ heterojunctions

The development of gas sensors for trace isobutanol detection remains challenging due to the trade-offs among sensitivity, selectivity, and stability. Herein, we propose a synergistic multi-scale engineering strategy, integrating NaCl-assisted structural refinement with in-situ SnO₂ embedding, to construct hierarchical SnO₂-Fe₂O₃ heterojunctions. The NaCl modulator not only confines particle growth and creates interconnected mesopores, but also promotes the formation of oxygen defects during calcination. Concurrently, the in-situ generated SnO₂ nanocrystals establish intimate electronic coupling with the Fe₂O₃ matrix, inducing interfacial band bending and a built-in electric field. The resulting heterostructure possesses a high specific surface area (55.04 ± 7.78 m²g⁻¹), abundant oxygen defects, and well-defined heterointerfaces. When deployed for isobutanol sensing, the optimized sensor exhibits exceptional performance: a high response of 113 (20 ppm, 200 °C), an ultralow detection limit of 0.05 ppm, rapid response/recovery kinetics (4 s/5 s), excellent selectivity over common interferences, and remarkable long-term stability. Mechanism studies reveal that the hierarchical porosity facilitates efficient gas diffusion, the heterojunction amplifies resistance modulation through enhanced charge separation, and the oxygen defects lower the activation barrier for surface oxidation reactions. This work demonstrates a rational material design paradigm that synergistically coordinates structural, interfacial, and defect engineering, offering a generalizable route to advanced metal-oxide sensors for practical volatile organic compound monitoring.