CO2 capture requires materials with high adsorption
selectivity and an industrial ease of implementation. To address these
needs, a new class of porous materials was recently developed that
combines the fluidity of solvents with the porosity of solids. Type
3 porous liquids (PLs) composed of solvents and metal–organic
frameworks (MOFs) offer a promising alternative to current liquid
carbon capture methods due to the inherent tunability of the nanoporous
MOFs. However, the effects of MOF structural features and solvent
properties on CO2–MOF interactions within PLs are
not well understood. Herein experimental and computational data of
CO2 gas adsorption isotherms were used to elucidate both
solvent and pore structure influences on ZIF-based PLs. The roles
of the pore structure including solvent size exclusion, structural
environment, and MOF porosity on PL CO2 uptake were examined.
A comparison of the pore structure and pore aperture was performed
using ZIF-8, ZIF-L, and amorphous-ZIF-8. Adsorption experiments here
have verified our previously proposed solvent size design principle
for ZIF-based PLs (1.8× ZIF pore aperture). Furthermore, the
CO2 adsorption isotherms of the ZIF-based PLs indicated
that judicious selection of the pore environment allows for an increase
in CO2 selectivity greater than expected from the individual
PL components or their combination. This nonlinear increase in the
CO2 selectivity is an emergent behavior resulting from
the complex mixture of components specific to the ZIF-L + 2′-hydroxyacetophenone-based
PL.