Engineering low-viscosity and low-cost porous liquids using deep eutectic solvents for CO₂ selective separation

AbstractPorous Liquids (PLs) integrate the permanent porosity of porous solids and the superior fluidity of liquids, offering substantial potential for CO₂ sorption. However, previous ionic liquids (ILs)/oligomers-based steric solvents exhibit limitations in terms of scalability due to the relative high cost and viscosity. Moreover, gas sorption-separation mechanisms require more rigorous analysis. Herein, we fabricated novel PLs with low-viscosity and low-cost by employing green deep eutectic solvents (DESs) and MIL-101(Cr)@ZIF-8, achieving excellent CO₂/N₂ and CO₂/CH₄ separation performances. Subsequently, four sorption isotherm models were fitted and the optimal SS-Langmuir-Freundlich reveals sorption process is not dominated by a single mechanism. Instead, it simultaneously exhibits the homogeneous and heterogeneous sorption characteristics. Meanwhile, four kinetic models were applied to evaluate the separation process, the best-fitting intraparticle diffusion (IPD) and Boyd models indicate a three-step mechanism in which both surface-layer and intraparticle diffusion are rate-limiting. This study not only demonstrates the superior separation potential of green DESs-based PLs but also elucidates the fundamental mass transfer mechanisms in PLs for optimizing gas separation.