Cage-Interconnected Metal–Organic Framework with Tailored Apertures for Efficient C₂H₆/C₂H₄ Separation under Humid Conditions

Abstract

Metal−organic frameworks (MOFs) with open metal sites (OMSs) have been shown to preferentially adsorb unsaturated hydrocarbons such as C 2 H 4 due to the formation of π-complexation. However, the adsorption capacity and selectivity might well be dampened under humid conditions because OMSs could be easily poisoned in the presence of water vapor. C 2 H 6selective adsorbents with less hydrophilic environments, on the other hand, not only could effectively minimize the impact of humidity on separation capacity but also could directly produce high-purity C 2 H 4 from C 2 H 6 /C 2 H 4 mixtures. Here, we report a C 2 H 6 -selective MOF (JNU-2) underlying a rare xae topology. Its cage-like cavities are interconnected through apertures with a limiting diameter of ca. 3.7 Å, which is in the domain of kinetic diameters of C 2 H 4 and C 2 H 6 molecules. Molecular modeling studies suggest the four oxygen atoms on aperture are poised to preferentially interact with C 2 H 6 through multiple C−H•••O hydrogen bonding, rendering JNU-2 an enhanced C 2 H 6 selectivity. Indeed, experimental results reveal that JNU-2 not only takes up a great amount of C 2 H 6 comparable to other top-performing C 2 H 6 -selective MOFs but also displays excellent separation capacity even under humid conditions; moreover, it can be easily regenerated at room temperature owing to its moderate adsorption enthalpy. This work successfully demonstrated a strategy of balancing adsorption capacity and selectivity for C 2 H 6 by designing MOF materials with cavities interconnected through tailored apertures. The apertures function as screening sites for C 2 H 6 selectivity, while the internal cavities provide space for large adsorption.

A Series of Mesoporous Metal‐Organic Frameworks with Tunable Windows Sizes and Exceptionally High Ethane over Ethylene Adsorption Selectivity

“…As it was already pointed out, the inversed C 2 H 6 /C 2 H 4 adsorption selectivity is a rather unusual phenomenon. The corresponding selectivity factors for MOFs reported up to now at ambient conditions are typically quite low ( S <3) with MAF‐49 being the only exception with appreciable selectivity S =9.0 [22, 28–34, 42–55] . The best C 2 H 6 /C 2 H 4 absorption selectivity obtained for NIIC‐20‐Bu at similar conditions ( S =15.4) is 1.7 times higher than that for MAF‐49 and greatly surpasses the majority of other literature results reported so far (Table S9).…”

“…The corresponding selectivity factors for MOFs reported up to now at ambient conditions are typically quite low (S < 3) with MAF-49 being the only exception with appreciable selectivity S = 9.0. [22,[28][29][30][31][32][33][34][42][43][44][45][46][47][48][49][50][51][52][53][54][55] Theb est C 2 H 6 /C 2 H 4 absorption selectivity obtained for NIIC-20-Bu at similar conditions (S = 15.4) is 1.7 times higher than that for MAF-49 and greatly surpasses the majority of other literature results reported so far (Table S9). Other than the adsorption selectivity,the adsorption uptake is an equally important parameter for an adsorbent for gas separation applications.I nt his regard, am ore accurate evaluation of porous materials should be revealed from the selectivity vs.uptake plot.…”

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments

“…During our development of this work, one of these MOFs was reported by Li and coworkers, who studied its application in ethane/ethylene separations. 40 Here, we examine their structures and demonstrate, both computationally and experimentally, how their unusual pore space confers a benet in terms of H 2 /CO 2 separations compared to various canonical twocomponent MOF materials. Signicantly, we fabricate membranes using these MOFs, we perform membrane permeation studies, and we show that a slight structural difference between the two isoreticular analogues leads to a signicant improvement in the H 2 /CO 2 separation factor.…”

Enhanced Desalination Performance of Capacitive Deionization Using Nanoporous Carbon Derived from ZIF-67 Metal Organic Frameworks and CNTs

“…Metal-organic frameworks (MOFs) have been widely investigated porous materials with periodic three-dimensional structures consisting of metal center and organic ligands. MOFs have attracted substantial attention due to their high surface area, adjustable pore size, periodical unsaturated pores of metal center, and high thermal and chemical stabilities [17][18][19][20][21][22][23]. Therefore, MOFs have been regarded as ideal materials for various applications including gas separation, catalysis, drug delivery systems, and so on [24].…”