Interpenetrated Zirconium–Organic Frameworks: Small Cavities versus Functionalization for CO₂ Capture

Porous interpenetrated zirconium–organic frameworks (PIZOFs) with various functional groups are explored for CO₂ capture using molecular simulation and experiment. Functionalization enhances the CO₂ uptake and selectivity over other gases, but small cavities play an even more important role. Particularly at low pressures, small cavities enhance the CO₂ adsorption density nearly 5 times greater than the functionalization. PIZOF-2 outperforms the other PIZOF structures for CO₂ separation from methane and nitrogen (related to raw natural gas and postcombustion of coal mixtures) due to the combination of small cavities around 5 Å in diameter and functionalized linkers with methoxy groups attached to the central ligand. The small cavities within the interpenetrated structures are crucial for achieving high selectivities, especially for cavities surrounded by a combination of 6 benzene rings, 2 metal clusters, and 4 methoxy groups that offer a tight overlapping potential energy field, ideal for “catching” CO<sub>2