Olympic Five-Ring-Fenced MOF with Anion-Hybrid Cluster Nodes for Highly Efficient CO 2 Capture from Flue Gas and Natural Gas

Abstract

The simultaneous achievement of high CO2 uptake, exceptional selectivity, and moderate regeneration energy remains a critical challenge for MOF-based CO2 capture from flue gas and natural gas. Herein, we report ZNU-28, a new microporous MOF that uniquely combines Olympic five-ring-fenced pore channels with anion-hybrid cobalt-cluster nodes (Co3SiF6O3(TPA)3, TPA = 1,3,5-tris(4-pyridyl)amine). This topology─never observed in anion-pillared or anion-hybrid MOFs─creates a confined yet accessible pore environment (pore size ∼ 5.2 Å) decorated with strong hydrogen-bonding sites. As a result, ZNU-28 delivers a high CO2 adsorption capacity of 86.8 cm3 g–1 at 298 K and 1 bar, which is 4.7 times that of CH4 and 11.6 times that of N2, respectively. The IAST selectivities of ZNU-28 at 298 K and 100 kPa for CO2/N2 and CO2/CH4 are 87.5 and 37.2, respectively, surpassing those of most reported materials. Moderate isosteric heats of adsorption (CO2: 33.1 kJ/mol at zero coverage) indicate facile regeneration. Dynamic breakthrough experiments confirm efficient CO2 separation from both CO2/N2 and CO2/CH4 mixtures under various conditions. In situ single-crystal X-ray diffraction reveals that CO2 molecules form an extended hydrogen-bonding network within the five-ring-fenced channels, accounting for the preferential capture. This work demonstrates that integrating Olympic five-ring fence motifs with anion-hybrid cluster nodes offers a new and powerful strategy for designing high-performance MOF adsorbents.