(264e) Non-Additive CO2 Uptake of Type II Porous Liquids Based on Imine Cages

Type II porous liquids are rigid, discrete, porous host molecules dissolved in solvents that are too bulky to enter the pores. Porosity can be maintained in the liquid state, and the gas solubility in these porous liquids can be drastically increased over that of pure solvents. While Type II porous liquids (PL) are an intriguing class of materials, there is little research on the thermodynamic properties of the porous liquid + gas solutions. Here, we utilized solution phase and adsorption thermodynamics to understand the role of host molecules in Type II porous liquids, as well as analysis using molecular dynamics simulations. We developed low-viscosity Type II PLs with enhanced gas solubility by dissolving porous organic cages (CC13 and CC19) in bulky solvents (2’-HAP, 2-IPP, and 2-CP). CO₂ isotherms for these PLs, measured at concentrations of 1–10 wt.% and pressures up to 8 bar, demonstrated significant increases in gas uptake compared to neat solvents. The non-additive behavior of the porous liquid, where the total CO₂ loading surpassed the sum of individual components, was observed in porous liquids made from both cages and three solvents. For example, 10 wt.% 2’-HAP-CC13 porous liquid showed 0.51 mmol CO₂/g PL non-additive absorption than the ideal weight average at 5.3 bar. This non-additivity does not seem to be related to the chemistry of the cage, as two different cages exhibited this effect, while a chemically similar control molecule did not. We discovered from simulations that incorporation of cages may introduce additional sorption sites on the cages’ surface, as a result amplifying CO₂ uptake in the liquid phase, which may be the reason for non-additive behavior. The results of this study provide valuable insights into the potential gas separation applications of Type II porous liquids.