Double-shell enhanced CO₂ capture in metal-organic cage-based porous Liquids

This work introduces a double-shell CO₂ adsorption pattern in metal-organic cage (MOC)-based porous liquids (PLs). Through high-throughput in-silico screening of MOCs featuring open Cu(II) sites, MOC-755921 was identified as an effective porous host for CO₂. When dissolved in the ionic liquid IL-NTf₂, it forms a Type II porous liquid that exhibits remarkable CO₂ selectivity and capacity, achieving a benchmark CO₂ uptake of 0.195 mmol g⁻¹ at 298 K and 1 bar, which is 2.41 times that of the neat ionic liquid. Grand canonical Monte Carlo (GCMC) simulations uncover a distinctive double-layer adsorption structure surrounding MOC-755921 in the solvent: an inner layer of CO₂ molecules coordinated directly to the open Cu sites within the intrinsic cavity, and an outer layer stabilized at the cage–solvent interface through CO₂–IL interactions. Complementary molecular dynamics (MD) simulations reveal that this enhanced capture arises from a synergistic interplay between pore confinement and the formation of an interfacial cavity (IfC). Together, these findings elucidate the molecular origin of CO₂ capture in MOC-PLs and establish a rational framework for designing next-generation porous liquids with optimized host–solvent–guest cooperativity.