Confinement of Ionic Liquids in Nanocages: Tailoring the Molecular Sieving Properties of ZIF‐8 for Membrane‐Based CO₂ Capture

Abstract

Fine-tuning of effective pore size of microporous materials is necessary to achieve precise molecular sieving properties. Herein, we demonstrate that room temperature ionic liquids can be used as cavity occupants for modification of the microenvironment of MOF nanocages. Targeting CO2 capture applications, we tailored the effective cage size of ZIF-8 to be between CO2 and N2 by confining an imidazolium-based ionic liquid [bmim][Tf2 N] into ZIF-8's SOD cages by in-situ ionothermal synthesis. Mixed matrix membranes derived from ionic liquid-modified ZIF-8 exhibited remarkable combinations of permeability and selectivity that transcend the upper bound of polymer membranes for CO2 /N2 and CO2 /CH4 separation. We observed an unusual response of the membranes to varying pressure, that is, an increase in the CO2 /CH4 separation factor with pressure, which is highly desirable for practical applications in natural gas upgrading.

Improving Gas Separation Performance of ZIF-8 by [BMIM][BF4] Incorporation: Interactions and Their Consequences on Performance

“…The latter one in high frequency region (3121 cm -1 ) assigned to ν(C2H) sym provide consistent data with the literature. 16 Parameters of these models are provided in Table S5. GCMC simulations were also performed for each gas in the same pressure range and at the same temperature to complement the experimental measurements.…”

“…[8][9] IL-MOF combinations have been considered recently in the gas separation field. [10][11][12][13][14][15][16] For instance, Chen et al 17 incorporated IRMOF-1 composite and reported a CO 2 /N 2 selectivity of 70 at ambient conditions. To understand the effect of different types of ILs on the separation performances of IL-MOF systems, ILs with the same cations but different anions were studied.…”

Ionic Liquid/Metal–Organic Framework Composites: From Synthesis to Applications

“…[84] Here, it is importantt on ote that in these studies ILs are not incorporated into MOFs but molecular simulations were used to predict the solubility and adsorption of gases (COa nd CO 2 )i nI Ls and MOFs,r espectively.E xperiments werec onducted to measuret he gas solubility in bulk ILs and IL-MOF mixtures,w hich were prepared by dispersing MOFs into the liquid phase and exploring the effect of MOF suspension on the gas captureo fI Ls. [45] The separation performances of IL/MOF composites are generally quantified by using selectivity,w hich is the ratio of the adsorbed amount of gas components. [84] The new approach to obtain better performing MOFs for gas storagea nd gas separation is to incorporate ILs as guest molecules into the MOFs' pores and hence to tune the gas affinity of the MOFs.…”

Boron Nitride Membranes with a Distinct Nanoconfinement Effect for Efficient Ethylene/Ethane Separation

“…TheC 2 H 4 /C 2 H 6 selectivity increases significantly with the increase of membrane thickness,the C 2 H 4 permeance and the C 2 H 4 /C 2 H 6 selectivity of the RIL-BN/Nylon membrane reach up to 138 GPU and 128 at the membrane thickness of 2 mm. [22] Compared with controlled membranes, as ignificant improvement in C 2 H 4 /C 2 H 6 selectivity (128) is achieved, far exceeding that of pure BN/Nylon (1.6) and supported RIL membrane (32). Controlled experiments are also conducted, including BN/Nylon membranes and supported RIL membranes, which verify the remarkable enhancement of gas separation performance by the confinement effect (Supporting Information, Figure S20).…”