Generation of Oxygen Vacancies in Metal–Organic Framework-Derived One-Dimensional Ni0.4Fe2.6O4 Nanorice Heterojunctions for ppb-Level Diethylamine Gas Sensing

Metal-organic frameworks (MOFs) are ideal sensing materials due to their distinctive morphologies, high surface area, and simple calcination to remove sacrificial MOF scaffolds. Oxygen vacancies (O_vs) can be efficiently generated by the thermal annealing of metal oxides in an inert atmosphere. Herein, MIL-53-based Fe and Fe/Ni-MOFs nanorices (NRs) were first prepared by using a solvothermal method, and then one-dimensional (1D) Fe₂O₃ and Ni_0.4Fe_2.6O₄ NRs were derived from the MOFs after calcination at 350 °C in an air and argon (Ar) atmosphere, respectively. It was found that Ar-annealed Ni_0.4Fe_2.6O₄ NRs have higher O_vs concentrations (82.11%) and smaller NRs (24.3 nm) than air-annealed NRs (65.68% & 31.5 nm). Beneficially, among the synthesized NRs, the Ar-Ni_0.4Fe_2.6O₄ NRs show a higher sensitivity to diethylamine (DEA) (R_a/R_g = 23 @ 5 ppm, 175 °C), low detection limit (R_a/R_g = 1.2 @ 200 ppb), wide dynamic response (R_a/R_g = 93.5@ 30 ppm), high stability (30 days), and faster response/recovery time (4 s/38 s). Moreover, the 1D nanostructure containing heterostructures offers excellent sensing selectivity and a wide detection range from 200 ppb to 30 ppm in the presence of DEA. The outstanding gas sensing behavior can be attributable to synergistic impact, structural advantages, high concentration of O_vs, and the heterojunction interface, which can have profound effects on gas sensor performance. This study provides a unique technique for constructing high-performance gas sensors for ppb-level DEA detection and the formation of O_vs in metal oxides without the need for any additives.