A Fine-Tuned Fluorinated MOF Addresses the Needs for Trace CO₂ Removal and Air Capture Using Physisorption

The development of functional solid-state materials for carbon capture at low carbon dioxide (CO₂) concentrations, namely, from confined spaces (<0.5%) and in particular from air (400 ppm), is of prime importance with respect to energy and environment sustainability. Herein, we report the deliberate construction of a hydrolytically stable fluorinated metal–organic framework (MOF), NbOFFIVE-1-Ni, with the appropriate pore system (size, shape, and functionality), ideal for the effective and energy-efficient removal of trace carbon dioxide. Markedly, the CO₂-selective NbOFFIVE-1-Ni exhibits the highest CO₂ gravimetric and volumetric uptake (ca. 1.3 mmol/g and 51.4 cm³ (STP) cm^–3) for a physical adsorbent at 400 ppm of CO₂ and 298 K. Practically, NbOFFIVE-1-Ni offers the complete CO₂ desorption at 328 K under vacuum with an associated moderate energy input of 54 kJ/mol, typical for the full CO₂ desorption in conventional physical adsorbents but considerably lower than chemical sorbents. Noticeably, the contracted square-like channels, affording the close proximity of the fluorine centers, permitted the enhancement of the CO₂–framework interactions and subsequently the attainment of an unprecedented CO₂ selectivity at very low CO₂ concentrations. The precise localization of the adsorbed CO₂ at the vicinity of the periodically aligned fluorine centers, promoting the selective adsorption of CO₂, is evidenced by the single-crystal X-ray diffraction study on NbOFFIVE-1-Ni hosting CO₂ molecules. Cyclic CO₂/N₂ mixed-gas column breakthrough experiments under dry and humid conditions corroborate the excellent CO₂ selectivity under practical carbon capture conditions. Pertinently, the notable hydrolytic stability positions NbOFFIVE-1-Ni as the new benchmark adsorbent for direct air capture and CO₂ removal from confined spaces.