Switchable p-n gas response for 3D-hierarchical NiFe₂O₄ porous microspheres for highly selective and sensitive toluene gas sensors

Rationally designed gas sensing materials have become essential for modern efficient gas sensor with enhanced performance. This study designed and prepared ordered porous, three-dimensional hierarchical NiFe₂O₄ (NFO) nanoarchitectures for highly selective and sensitive toluene sensors. Two hierarchical NFO nanostructures including nanospheres and microsphere were fabricated by facile hydrothermal (NFO-Hy) and temperature-programmed calcination (NFO-550), respectively. Physicochemical characterization confirmed structure, composition, and morphology for the as-prepared materials. Nitrogen adsorption-desorption revealed improved surface area and porous properties for NFO-550 compared with NFO-Hy sensing materials, and the NFO-550 sensor achieved the maximum response 5.65 higher than NFO-Hy at optimal operating temperature. Primary analyses for carcinogenic analyte detection suggest NFO as a gas-sensitive material to be potential applicants for real-world toluene gas sensing applications.