Dual-Channel, Molecular-Sieving Core/Shell ZIF@MOF Architectures as Engineered Fillers in Hybrid Membranes for Highly Selective CO₂ Separation

Abstract

A novel core/shell porous crystalline structure was prepared using a large pore metal organic framework (MOF, UiO-66-NH, pore size, ∼ 0.6 nm) as core surrounded by a small pore zeolitic imidazolate framework (ZIF, ZIF-8, pore size, ∼ 0.4 nm) through a layer-by-layer deposition method and subsequently used as an engineered filler to construct hybrid polysulfone (PSF) membranes for CO capture. Compared to traditional fillers utilizing only one type of porous material with rigid channels (either large or small), our custom designed core/shell fillers possess clear advantages via pore engineering: the large internal channels of the UiO-66-NH MOFs create molecular highways to accelerate molecular transport through the membrane, while the thin shells with small pores (ZIF-8) or even smaller pores generated at the interface by the imperfect registry between the overlapping pores of ZIF and MOF enhance molecular sieving thus serving to distinguish slightly larger N molecules (kinetic diameter, 0.364 nm) from smaller CO molecules (kinetic diameter, 0.33 nm). The resultant core/shell ZIF@MOF and as-prepared hybrid PSF membranes were characterized by transmission electron microscopy, X-ray diffraction, wide-angle X-ray scattering, scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, and contact angle tests. The dependence of the separation performance of the membranes on the MOF/ZIF ratio was also studied by varying the number of layers of ZIF coatings. The integrated PSF-ZIF@MOF hybrid membrane (40 wt % loading) with optimized ZIF coating cycles showed improved hydrophobicity and excellent CO separation performance by simultaneously increasing CO permeability (CO permeability of 45.2 barrer, 710% higher than PSF membrane) and CO/N selectivity (CO/N selectivity of 39, 50% higher than PSF membrane), which is superior to most reported hybrid PSF membranes. The strategy of using dual-channel molecular sieving core/shell porous crystals in hybrid membranes thus provides a promising means for CO capture from flue gas.

A nature-inspired hydrogen-bonded supramolecular complex for selective copper ion removal from water

“…ZIF-8 crystals were prepared following the procedure reported by Song and coworkers 61 . Briefly, Zn(NO 3 ) 2 ‧6H 2 O (0.438 g, 1.47 mmol) and 2-methylimidazole (0.972 g, 11.8 mmol) were separately dissolved in methanol (20 mL) and then mixed together under ambient conditions with vigorous stirring for 4 h. Solid ZIF-8 was then separated from the suspension by centrifuging for 5 min at 8000 rpm and removal of the reaction solvent.…”

Selective Dye Adsorption by Zeolitic Imidazolate Framework-8 Loaded UiO-66-NH2

“…ZIF-8-loaded UiO-66-NH 2 was prepared via the layer-by-layer solution deposition method according to the procedure reported in the previous literature [21]. The amino groups of UiO-66-NH 2 can act as a covalent linker between seed layers and supports in this reaction [22,23].…”

Super‐Stable, Highly Efficient, and Recyclable Fibrous Metal–Organic Framework Membranes for Precious Metal Recovery from Strong Acidic Solutions

“…Thus far, the UiO‐66 series has been incorporated into various matrixes bearing versatile characteristics for different purposes, and their incorporated mixed matrix membranes (MMM) and thin‐film nanocomposite (TFN) are famous functional materials that are applied in separation, adsorption, or dehydration in either gas or fluid phase, as well as in desalination, catalysis, sensing, and proton or ion transport in aqueous or other liquid phases. However, these types of composite membranes or films still encounter a set of problems and challenges to some extent, including uniform dispersion of MOFs, the compatibility and stability of matrix‐MOFs in the operating environment, the permeability or diffusivity of the flowing phase, the output efficacy compared to pristine MOFs, and so on.…”