Structural design of nanoporous materials allows for the development and commercialization of new materials with targeted environmental and energy applications. A critical area of interest is the development of new materials for the capture of CO2 directly from the atmosphere. Current nanoporous materials used in these technologies lack selectivity for CO2 in the presence of humidity and require energy intensive regeneration procedures. Porous liquids (PLs) are an emerging material that have shown promise as CO2 capture materials. PLs are a liquid phase system with stable intrinsic porosity available for gas capture originating from the incorporation of a nanoporous host. Several PL systems are based on the suspension of metal–organic frameworks (MOFs) in solvent mixtures. However, there is limited understanding on the influence of the MOF structure on the CO2 adsorption and system stabilities. This work develops a fundamental understanding of the structure-property relationships of selective CO2 adsorption in PLs to design targeted carbon capture technologies. Multiple PLs were synthesized based on the zeolitic imidazole framework (ZIF) MOF family. The PLs comprised of ZIF-8, ZIF-67, or ZIF-69 suspended in a water-ethylene glycol-imidazole ligand mixture. These three ZIFs were utilized for comparison of morphological effects on the stability and CO2 adsorption properties of the PLs. Long term stabilities of the ZIFs and the PL were monitored using X-ray diffraction. Synthesized PLs were exposed to CO2 at varying concentrations through simple bubbling of the gas into the liquid. Nuclear magnetic resonance spectroscopy was used to determine the CO2 speciation within the PLs. Neutron scattering data was used to determine the CO2 binding sites with these complex and dynamic systems.

Structure-property relationships of ZIF-based porous liquids for CO2 adsorption

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