Porous, Tremella-like NiFe₂O₄ with Ultrathin Nanosheets for ppb-Level Toluene Detection

As a typical spinel ferrite, NiFe₂O₄ is suitable for use in gas sensors. Herein, we report the fabrication of porous, tremella-like NiFe₂O₄ assembled using porous, ultrathin nanosheets via the coordination of Ni²⁺ and Fe²⁺ with 1,4-phenylenediboronic acid. The optical band gap of the NiFe₂O₄ is estimated to be about 1.7 eV. Furthermore, the NiFe₂O₄ sensor annealed at 400 °C exhibits a low detection limit of 50 ppb, a fast response/recovery time (11.6 s/41.9 s to 10 ppm toluene), good reproducibility, and long-term stability at 220 °C. The suitable sensing performances can be attributed to the good catalytic activity of NiFe₂O₄ to toluene oxidation. Moreover, the ultrathin nanosheets with porous structures provide a large number of active sites to significantly favor the diffusion and adsorption/desorption of toluene molecules. This current work provides an insight into fabricating NiFe₂O₄ using 1,4-phenylenediboronic acid, which is promising for ppb-level toluene detection.