Tuning the Phase Composition of Metal–Organic Framework Membranes for Helium Separation through Incorporation of Fullerenes

Abstract

Metal–organic framework (MOF) membranes have attracted significant research interest in gas separation, but efficient helium (He) separation remains a challenge due to the weak polarizability of He and the intrinsic pore size flexibility of MOFs. Herein, incorporated fullerenes (C60 and C70) were used to tune the crystallographic phase composition of ZIF-8 membranes, thus creating small and fixed apertures for selective He permeation. The fullerene-modified ZIF-8 (C60@ZIF-8 and C70@ZIF-8) membranes contain about 20% of the rigid-lattice ZIF-8_I-43m phase and have been prepared as 200–350 nm thick supported layers through electrochemical synthesis. They show a significantly enhanced molecular sieving for He/N2,CH4 together with a satisfactory He permeance of >200 GPU. Specifically, the He/N2 selectivity of the C70@ZIF-8 membrane is up to 30.4, which is much higher than that of the fullerene-free ZIF-8 membrane (5.1) and nearly an order of magnitude higher than those of other reported He-selective MOF membranes. A continuous long-term gas permeation test over 780 h under dry and humid conditions proved the excellent stability of the fullerene-modified ZIF-8 membranes. The general validity and versatility of the proposed strategy for MOF membrane preparation are also demonstrated by the enhancement of the separation performance of a fullerene-modified ZIF-76 membrane.

Recent advances in supramolecular fullerene chemistry

“…483 Because most MOFs or COFs have relatively large pores, the encapsulation of guests has been widely explored and fullerenes are an evident choice due to their relatively large size and optoelectronic properties. 484–494 Berna and coworkers employed a flexible benzylic amide macrocycle attached with two carboxylic acid groups as the ligand to prepare copper( ii )- and zinc( ii )-based MOFs, which could selectively encapsulate C 60 from a mixture of C 60 and C 70 . 484 The encapsulation of fullerenes was used to modulate the optoelectronic properties of MOFs due to the electronic interaction with hosts, leading to the unique properties and applications.…”

Electro-driven multi-functional catalysis separation membrane reactor with switchable wettability for efficient water purification

“…The flow-through CSMRs were established by electrochemical synthesis because of the short synthesis time of only dozens of minutes and the mild conditions. 33,34 As the mother solutions, zinc acetate and dimethylimidazole solutions were first prepared and mixed thoroughly. The ZIF-8 shell layer was grown in situ on the carbon cloth using an electro-driven method; then, Pd nanoparticles (Pd NPs) were loaded by an impregnation-reduction technique to serve as catalytic active sites.…”

Vertical Graphene-Supported High-Hydrogen Permeance ZIF-8 Membranes

“…Fullerenes engage in van der Waals and π−π interactions with ZIF-8, thus creating small and fixed apertures for selective He permeation. 17 Although graphene-based materials exhibit excellent binding properties to MOF crystals, the uniform deposition of graphene-based materials is crucial for synthesizing continuous and dense MOF membranes. Most researchers use top-down methods, where preprepared graphene-based materials are dissolved in a solvent and then deposited onto a porous support through spin coating or vacuum filtration.…”

“…Recently, Wang and colleagues employed fullerenes (C60 and C70) to adjust the crystallographic phase composition of the ZIF-8 membrane. Fullerenes engage in van der Waals and π–π interactions with ZIF-8, thus creating small and fixed apertures for selective He permeation . Although graphene-based materials exhibit excellent binding properties to MOF crystals, the uniform deposition of graphene-based materials is crucial for synthesizing continuous and dense MOF membranes.…”