Amino-Functionalized Microporous MOFs for Capturing Greenhouse Gases CF₄ and NF₃ with Record Selectivity

The capture and separation of fluorinated gases (F-gases) from N₂ has the potential to not only reduce greenhouse gas emissions but also provide economic benefits for the semiconductor industry. In this work, two Ni-based metal-organic frameworks (MOFs), Ni-MOF (Ni(ina)₂, ina = isonicotinic acid) and amine-functionalized NH-Ni-MOF (Ni(3-ain)₂, 3-ain = 3-aminoisonicotinic acid), were constructed for capturing F-gases (CF₄ and NF₃). At ambient conditions, both materials exhibit very high CF₄ sorption capacities (2.92 mmol g^-1 for Ni-MOF and 2.69 mmol g^-1 for NH-Ni-MOF). In addition, NH-Ni-MOF exhibited a record selectivity of 46.3 for the CF₄/N₂ mixture at 298 K and 100 kPa, surpassing all benchmark adsorbents, including Ni-MOF (34.7). The kinetic adsorption tests demonstrated that Ni-MOF and NH-Ni-MOF performed well for CF₄/N₂ and NF₃/N₂ mixtures. According to grand canonical Monte Carlo (GCMC) simulations, CF₄ or NF₃ interacts with NH-Ni-MOF by multiple van der Waals interactions, resulting in stronger interaction than N₂. More importantly, dynamic breakthrough experiments verified the practical separation potential of the two materials for CF₄/N₂ and NF₃/N₂ mixtures.