Controlling the free volume of type Ⅲ porous liquids by tailoring solvent for enhanced CO2 capture

Abstract

Porous liquids (PLs) are an emerging class of liquid materials that combine the porosity of solids with the fluidity of liquids, showing great potential in carbon dioxide (CO2) capture. Meanwhile, understanding the factors that govern CO2 absorption is critical to development of high-capacity PLs. Based on this, we report two novel 1,8-diazabicyclo[7.7.2]dec-7-ene (DBU) based PLs by comprising ZIF-8 porous framework in two ionic liquids (ILs) – DBU-2-Methylimidazole ([DBUH][2-MeIm], IL1) and DBU-Acetic acid ([DBUH][AC], IL2). Their physicochemical properties and CO2 absorption mechanisms are studied by combining spectroscopic investigations, molecular dynamics simulations and quantitative calculations. The research objective is to create a fundamental understanding of how IL enables PL formation and shows the higher efficiency for CO2 capture. The results show that ZIF-8 can be uniformly dispersed in IL1 through non-covalent interaction. The formed PL1 has better fluidity, containing the greater free volumes of CO2 transmission and storage as well as more efficient absorption active sites, which endow PL1 with excellent CO2 absorption capacity. And the CO2 absorption of PL1 is a combination of physical adsorption through van der Waals interaction and reversible chemical absorption, so the cyclic absorption can be achieved by adjusting temperature and pressure. Moreover, the synergistic effect between the absorption active sites of PLs and the nano-confined spaces of the interface between ILs and ZIF-8 in PLs is identified as a powerful internal driving force for the improvement of CO2 absorption capacity. This work will pave the way for the rational design of novel PLs for industrial CO2 capture.