Understanding Reduced CO₂ Uptake of Ionic Liquid/Metal–Organic Framework (IL/MOF) Composites

Reduced CO2 uptake of ionic liquid/metal–organic framework (IL/MOF) composites has been observed in many experiments. However, simulation study gives rise to the opposite tendency. To understand such a phenomenon, both experiment and simulation were performed in this work. Two amino acid ionic liquids (AAILs) (i.e., [Emim][Gly] and [Emim][Phe]) and two Zr-based MOFs (i.e., UiO-66 and NU-1000) were used to prepare a variety of IL/MOF composites. The reduced CO2 uptake observed in all IL/MOF composites upon ILs loading regardless of the amount of ILs is consistent with previous experimental reports. According to pore size distribution, similar pore sizes of the composites to those of pristine MOFs revealed that the blocking of channels by loaded AAILs into MOFs occurred, leading to decreased uptakes. Moreover, molecular simulation demonstrated that the blockage in channels significantly decreased CO2 uptake compared with the model consisting of randomly distributed ILs, which approximates experimental observations. This study provides experimental and theoretical evidence for the existing blockage in MOF channels upon ILs introduction, which contributed to the reduced CO2 uptakes of IL/MOF composites.