Hierarchical Core-shell metal hydroxide-derived NiO/NiFe₂O₄ microflowers with interior heterojunction for wheat...

1-octen-3-ol is reported as a representative biomarker among volatile organic compounds (VOCs) associated with wheat mildew, and the corresponding chemiresistive sensors reported to date are still under development due to their limited sensitivity. To achieve excellent 1-octen-3-ol sensing performance, a two-/three-dimension (2D/3D) hierarchical core-shell structure NiO/NiFe₂O₄ with abundant interior heterojunction interfaces was synthesized. This simple strategy achieves a triple effect: (i) the pre-concentration effect arising from the core-shell structure, (ii) charge transfer and interfacial modulation between the core and shell, and (iii) the interfacial interaction of the NiO/NiFe₂O₄ heterojunction formed within the 2D nanosheets of the shell. The optimal NiO/NiFe₂O₄ sensor demonstrated superior overall performance at 275 °C, whose response value to 100 ppm 1-octen-3-ol reached 1109 ± 79, with excellent selectivity (S_1-octen-3-ol/the max of S_{other VOCs} = 4.0), significantly outperforming previously reported sensors. A significant enhancement in response to complex VOCs generated during wheat storage was achieved, demonstrating the practical feasibility of NiO/NiFe₂O₄. This work may serve as a guideline for developing high-performance hierarchical core-shell gas sensing materials.