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 (Ovs) 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 Ni0.4Fe2.6O4 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 Ni0.4Fe2.6O4 NRs have higher Ovs 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-Ni0.4Fe2.6O4 NRs show a higher sensitivity to diethylamine (DEA) (Ra/Rg = 23 @ 5 ppm, 175 °C), low detection limit (Ra/Rg = 1.2 @ 200 ppb), wide dynamic response (Ra/Rg = 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 Ovs, 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 Ovs in metal oxides without the need for any additives.