Hetero-metallic metal-organic frameworks for room-temperature NO₂ sensing

Metal-organic frameworks (MOFs) with exceptional features such as high structural diversity and surface area as well as controlled pore size has been considered a promising candidate for developing room temperature highly-sensitive gas sensors. In comparison, the hetero-metallic MOFs with redox-active open-metal sites and mixed metal nodes may create peculiar surface properties and synergetic effects for enhanced gas sensing performances. In this work, the Fe atoms in the Fe₃ (Porous coordination network) PCN-250 MOFs are partially replaced by transition metal Co, Mn, and Zn through a facile hydrothermal approach, leading to the formation of hetero-metallic MOFs (Fe₂^IIIM^II, M = Co, Mn, and Zn). While the PCN-250 framework is maintained, the morphological and electronic band structural properties are manipulated upon the partial metal replacement of Fe. More importantly, the room temperature NO₂ sensing performances are significantly varied, in which Fe₂Mn PCN-250 demonstrates the largest response magnitude for ppb-level NO₂ gas compared to those of pure Fe₃ PCN-250 and other hetero-metallic MOF structures mainly attributed to the highest binding energy of NO₂ gas. This work demonstrates the strong potential of hetero-metallic MOFs with carefully engineered substituted metal clusters for power-saving and high-performance gas sensing applications.