Ultrathin Two-Dimensional Porous Fullerene Membranes for Ultimate Organic Solvent Separation.

Two-dimensional (2D) materials with high chemical stability have attracted intensive interest in membrane design for the separation of organic solvents. As a novel 2D material, polymeric fullerenes (C60)∞ with distinctive properties are very promising for the development of innovative membranes. In this work, we report the construction of a 2D (C60)∞ nanosheet membrane for organic solvent separation. The pathways of the (C60)∞ nanosheet membrane are constructed by sub-1-nm lateral channels and nanoscale in-plane pores created by the depolymerization of the (C60)∞ nanosheets. Attributing to ordered and shortened transport pathways, the ultrathin porous (C60)∞ membrane is superior in organic solvent separation. The hexane, acetone, and methanol fluxes are up to 1146.3±53, 900.4±41, and 879.5±42 kg ⋅ m-2 ⋅ h-1, respectively, which are up to 130 times higher than those of the state-of-the-art membranes with similar dye rejection. Our findings demonstrate the prospect of 2D (C60)∞ as a promising nanofiltration membrane in the separation of organic solvents from macromolecular compounds such as dyes, drugs, hormones, etc.

Layered Zeolite for Assembly of Two-Dimensional Separation Membranes for Hydrogen Purification.

Membrane separation is an energy-efficient and environmentally friendly process. Two-dimensional (2D) molecular sieving membranes featuring unique nanopores and low transport resistance have the potential to achieve highly permeable and selective mixture separation with low energy consumption. High-aspect-ratio zeolite nanosheets with intrinsic molecular-sieving pores perpendicular to the layers are desirable building blocks for fabricating high-performance 2D zeolite membrane. However, a wider application of 2D zeolitic membranes is restricted by the limited number of recognized zeolite nanosheets. Herein, we report a swollen layered zeolite, ECNU-28, with SZR topology and eight-member ring (8-MR, 3.0 Å×4.8 Å) pores normal to the nanosheets. It can be easily exfoliated to construct 2D membrane, which shows a high hydrogen selectivity up to 130 from natural gas and is promising for hydrogen purification and greenhouse gas capture.

Core-Shell Carbon-Based Bifunctional Electrocatalysts Derived from COF@MOF Hybrid for Advanced Rechargeable Zn-Air Batteries.

The development of highly active carbon-based bifunctional electrocatalysts for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired, but still full of challenges in rechargeable Zn-air batteries. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have gained great attention for various applications due to their attractive features of structural tunability, high surface area and high porosity. Herein, a core-shell structured carbon-based hybrid electrocatalyst (H-NSC@Co/NSC), which contains high density active sites of MOF-derived shell (Co/NSC) and COF-derived hollow core (H-NSC), is successfully fabricated by direct pyrolysis of covalently-connected COF@ZIF-67 hybrid. The core-shell H-NSC@Co/NSC hybrid manifests excellent catalytic properties toward both OER and ORR with a small potential gap (∆E = 0.75 V). The H-NSC@Co/NSC assembled Zn-air battery exhibits a high power-density of 204.3 mW cm-2 and stable rechargeability, outperforming that of Pt/C+RuO2 assembled Zn-air battery. Density functional theory calculations reveal that the electronic structure of the carbon frameworks on the Co/NSC shell can be effectively modulated by the embedded Co nanoparticles (NPs), facilitating the adsorption of oxygen intermediates and leading to enhanced catalytic activity. This work will provide a strategy to design highly-efficient electrocatalysts for application in energy conversion and storage.

Two-Dimensional Fluorinated Covalent Organic Frameworks with Tunable Hydrophobicity for Ultrafast Oil-Water Separation.

Covalent organic frameworks (COFs) hold great potentials for addressing the challenge of highly efficient oil-water separation, but they are restricted by the poor wettability and processability as crystalline membranes. Here we report the design and synthesis of two-dimensional (2D) robust COFs with controllable hydrophobicity and processability, allowing the COF layers to be directly grown on the support surfaces. Three 2D COFs with AA or ABC stacking are prepared by condensation of triamines with fluorine and/or isopropyl groups and perfluorodialdehyde. They all show excellent tolerance to water, acid, and base, with water contact angles (CA) of 111.5-145.8°. The two COFs with isopropyl and fluorine mixtures can grow as a coating on a stainless-steel net (SSN) substrate, whereas the one with only fluorine substituents cannot. The superhydrophobic COF@SSN coating with water CA of up to 150.1° displays high water-resistance and self-cleaning properties, enabling high oil-water separation performances with an efficiency of over 99.5 % and a permeation flux of 2.84×105  L m-2 h-1 , which are among the highest values reported for state-of-the-art membranes.

Synthesis of Co3 O4 /Carbon Heteroaerogels with Ultrahigh Capacitance via Polyethyleneimine Intercalation of Co2 BIM4 Nanosheets.

The development of metal-organic frameworks (MOFs)-based supercapacitors have attracted intense concentration in recent years due to their regularly arranged porous and tunable pore sizes. However, the performance of the MOFs-derived supercapacitors is also low because of their poor electrical conductivity and rarely accessible active sites. In the present work, we developed a Co-MOF (namely Co2 BIM4 , BIM=benzimidazole) nanosheets derived Co3 O4 /nitrogen-doped carbon (Co2 BIM4 -Co3 O4 /NC) heteroaerogel as a novel supercapacitor electrode. The 3D Co2 BIM4 -Co3 O4 /NC heteroaerogels were obtained by directly intercalating polyethyleneimine (PEI) into the interlayers of Co2 BIM4 nanosheets and following by carbonizing the resulting Co2 BIM4 /PEI composite. The Co2 BIM4 -Co3 O4 /NC electrode possessed 3D conductive framework with an overlapped hetero-interface and expanded interlayers, leading to fast and stable charge transfer/diffusion and an enhanced pseudocapacitance performance. Therefore, the Co2 BIM4 -Co3 O4 /NC electrode showed ultrahigh capacitance of 2568 F g-1 at 1 A g-1 , 1747 F g-1 at 10 A g-1 , and excellent long cycling time with a capacitance preservation of 92.7 % following 10000 cycles at 10 A g-1 , which is very promising for applications in supercapacitors and other energy storage devices.

Highly Selective CO2 Conversion to Methanol in a Bifunctional Zeolite Catalytic Membrane Reactor.

The hydrogenation of sequestrated CO2 to methanol can reduce CO2 emission and establish a sustainable carbon circuit. However, the transformation of CO2 into methanol is challenging because of the thermodynamic equilibrium limitation and the deactivation of catalysts by water. In the present work, different reactor types have been evaluated for CO2 catalytic hydrogenation to methanol. Best results have been obtained in a bifunctional catalytic membrane reactor (CMR) based on a zeolite LTA membrane and a catalytic Cu-ZnO-Al2 O3 -ZrO2 layer on top. Due to the in situ and rapid removal of the produced water from the catalytic layer through the hydrophilic zeolite LTA membrane, it is effective to break the thermodynamic equilibrium limitation, thus significantly increasing the CO2 conversion (36.1 %) and methanol selectivity (100 %). Further, the catalyst deactivation by the produced water can be effectively inhibited, thus maintaining a high long-term activity of the CMR.

Elimination of Grain Boundary Defects in Zeolitic Imidazolate Framework ZIF-95 Membrane via Solvent-Free Secondary Growth.

Metal-organic framework membranes are usually prepared by in situ or secondary growth in a solution/hydrogel. The use of organic solvents may cause safety and environmental problems and produce solvent-induced defects. Here, highly oriented and permselective ZIF-95 membranes are prepared for the first time via a solvent-free secondary growth method. The solvent-free growth is not only helpful to control the membrane microstructure and thickness, but also to reduce the intercrystalline defects. In case of solvent-free growth, a perfectly oriented structure leads to an outstanding reduction of intercrystalline defects and transport resistances. For the separation of equimolar binary gas mixtures by using the highly oriented ZIF-95 membrane at 25 °C and 1 bar, the mixture separation factors of H2 /CO2 and H2 /CH4 are 184 and 140, respectively, with H2 permeance of over 1.9×10-7  mol m-2 s-1 Pa-1 which are much higher than those of the randomly oriented ZIF-95 membrane.

Anisotropic Gas Separation in Oriented ZIF-95 Membranes Prepared by Vapor-Assisted In-Plane Epitaxial Growth.

Control of the microstructure grain orientation, grain boundaries and thickness are crucial for MOF membranes. We report a novel synthesis strategy to prepare highly c-oriented ZIF-95 membranes through vapor-assisted in-plane epitaxial growth. In a mixed DMF/water vapor atmosphere, in-plane epitaxial growth of a ZIF-95 seeds layer was achieved to obtain an oriented and well-intergrown ZIF-95 membrane with a thickness of only 600 nm. Demonstrated by both experimental and simulation studies, the c-oriented ZIF-95 membrane displayed superior separation performance because a perfectly oriented structure resulted in a notable reduction of intercrystalline defects and transport pathways. For the separation of equimolar binary mixtures at 100 °C and 1 bar, the mixture separation factors of H2 /CO2 and H2 /CH4 were 32.2 and 53.7, respectively, with an H2 permeance of over 7.9×10-7  mol m-2 s-1 Pa-1 , which was 4.6 times higher than that of a randomly oriented ZIF-95 membrane.

Polymer Composite Membrane with Penetrating ZIF-7 Sheets Displays High Hydrogen Permselectivity.

Oriented and penetrating molecular sieving membranes display enhanced separation performance. A polyimide (PI) solution containing highly dispersed ZIF-7(III) sheets in CHCl3 was deposited on a glass side and subjected to flat-scraping with a membrane fabricator. In this way we developed a novel oriented and penetrating ZIF-7@PI mixed matrix membrane (MMM) with 50 wt. % ZIF-7 loading. Because the height of the ZIF-7 sheets (5 µm) is higher than the film thickness, every ZIF-7 sheet penetrates both surfaces of the polyimide film. Since the ZIF-7 channels are the dominant pathway for gas permeation, the ZIF-7@PI MMM displays a high molecular sieve performance for the separation of H2 (0.29 nm) from larger gas molecules. At 100 °C and 2 bar, the mixture separation factors of H2 /CO2 and H2 /CH4 are 91.5 and 128.4, with a high H2 permeance of about 3.0×10-7  mol m-2 s-1 Pa-1 , which is promising for hydrogen separation by molecular sieving.

High-Flux High-Selectivity Metal-Organic Framework MIL-160 Membrane for Xylene Isomer Separation by Pervaporation.

Separation of p-xylene (kinetic diameter ca. 0.58 nm) from its bulkier isomers (o-xylene and m-xylene, ca. 0.68 nm) is challenging, but important in the petrochemical industry. Herein, we developed a highly selective and stable metal-organic framework (MOF) MIL-160 membrane for selective separation of p-xylene from its isomers by pervaporation. The suitable pore size (0.5∼0.6 nm) of the MIL-160 membrane selectively allows p-xylene to pass through, while excluding the bulkier o-xylene and m-xylene. For the separation of equimolar binary p-/o-xylene mixtures at 75 °C, high p-xylene flux of 467 g m-2 h-1 and p-/o-xylene selectivity of 38.5 could be achieved. The stability of MIL-160, ensured the separation performance of the MIL-160 membrane was unchanged over a 24 h measurement. The high separation performance combined with its high thermal and chemical stability makes the MIL-160 membrane a promising candidate for the separation of xylene isomers.

Efficient Synthesis of Dimethyl Ether from Methanol in a Bifunctional Zeolite Membrane Reactor.

A sandwich FAU-LTA zeolite dual-layer membrane has been developed and used as a catalytic membrane reactor for the synthesis of dimethyl ether (DME). In the top H-FAU layer with mild acidity, methanol is dehydrated to DME. The other reaction product, water, is removed in situ through a hydrophilic Na-LTA layer, which is located between the porous alumina support and the H-FAU top layer. The combination of mild acidity with the continuous removal of water results in high methanol conversion (90.9 % at 310 °C) and essentially 100 % DME selectivity. Furthermore, owing to the selective and continuous removal of water through the Na-LTA membrane, catalyst deactivation can be effectively suppressed.

Bicontinuous zeolitic imidazolate framework ZIF-8@GO membrane with enhanced hydrogen selectivity.

Through layer-by-layer (LBL) deposition of a graphene oxide (GO) suspension on a semicontinuous ZIF-8 layer, we have developed a novel bicontinuous ZIF-8@GO membrane. Since only the gaps between the ZIF-8 crystals are sealed by the GO layer due to capillary forces and covalent bonds, the gas molecules can only permeate through the ZIF-8 micropore system (0.34 nm). Therefore, the ZIF-8@GO membranes show high hydrogen selectivity. At 250 °C and 1 bar, the mixture separation factors of H2/CO2, H2/N2, H2/CH4, and H2/C3H8 are 14.9, 90.5, 139.1, and 3816.6, with H2 permeances of about 1.3 × 10(-7) mol·m(-2)·s(-1)·Pa(-1), which is promising for hydrogen separation and purification by molecular sieving.

Accurate prediction of solvent flux in sub-1-nm slit-pore nanosheet membranes.

Nanosheet-based membranes have shown enormous potential for energy-efficient molecular transport and separation applications, but designing these membranes for specific separations remains a great challenge due to the lack of good understanding of fluid transport mechanisms in complex nanochannels. We synthesized reduced MXene/graphene hetero-channel membranes with sub-1-nm pores for experimental measurements and theoretical modeling of their structures and fluid transport rates. Our experiments showed that upon complete rejection of salt and organic dyes, these membranes with subnanometer channels exhibit remarkably high solvent fluxes, and their solvent transport behavior is very different from their homo-structured counterparts. We proposed a subcontinuum flow model that enables accurate prediction of solvent flux in sub-1-nm slit-pore membranes by building a direct relationship between the solvent molecule-channel wall interaction and flux from the confined physical properties of a liquid and the structural parameters of the membranes. This work provides a basis for the rational design of nanosheet-based membranes for advanced separation and emerging nanofluidics.

Bio-inspired polydopamine: a versatile and powerful platform for covalent synthesis of molecular sieve membranes.

Inspired by the bioadhesive ability of the marine mussel, a simple, versatile, and powerful synthesis strategy was developed to prepare highly reproducible and permselective molecular sieve membranes by using polydopamine as a novel covalent linker. Attributing to the formation of strong covalent and noncovalent bonds, ZIF-8 nutrients are attracted and bound to the support surface, thus promoting the ZIF-8 nucleation and the growth of uniform, well intergrown, and phase-pure ZIF-8 molecular sieve membranes. The developed ZIF-8 membranes show high hydrogen selectivity and thermal stability. At 150 °C and 1 bar, the mixture separation factors of H2/CO2, H2/N2, H2/CH4, and H2/C3H8 are 8.9, 16.2, 31.5 and 712.6, with H2 permeances higher than 1.8 × 10(-7) mol·m(-2)·s(-1)·Pa(-1), which is promising for hydrogen separation and purification.

Covalent organic framework-derived fluorine, nitrogen dual-doped carbon as metal-free bifunctional oxygen electrocatalysts.

The construction of heteroatom-doped metal-free carbon catalysts with bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired for Zn-air batteries, but remains a great challenge owing to the sluggish kinetics of OER and ORR. Herein, a self-sacrificing template engineering strategy was employed to fabricate fluorine (F), nitrogen (N) co-doped porous carbon (F-NPC) catalyst by direct pyrolysis of F, N containing covalent organic framework (F-COF). The predesigned F and N elements were integrated into the skeletons of COF precursor, thus achieving uniformly distributed heteroatom active sites. The introduction of F is beneficial for the formation of edge-defects, contributing to the enhancement of the electrocatalytic activity. Attributing to the porous feature, abundant defect sites induced by F doping, as well as the strong synergistic effect between N and F atoms to afford a high intrinsic catalytic activity, the resulting F-NPC catalyst exhibits excellent bifunctional catalytic activities for both ORR and OER in alkaline mediums. Furthermore, the assembled Zn-air battery with F-NPC catalyst shows a high peak power density of 206.3 mW cm-2 and great stability, surpassing the commercial Pt/C + RuO2 catalysts.

Monitoring molecular mass transfer in cation-free nanoporous host crystals of type AlPO-LTA.

Micro-imaging is employed to monitor the evolution of intra-crystalline guest profiles during molecular adsorption and desorption in cation-free zeolites AlPO-LTA. The measurements are shown to provide direct evidence on the rate of intra-crystalline diffusion and surface permeation and their inter-relation. Complemented by PFG NMR and integral IR measurements, a comprehensive overview of the diffusivities of light hydrocarbons in this important type of host materials is provided.

Organosilica-functionalized zeolitic imidazolate framework ZIF-90 membrane with high gas-separation performance.

A clear separation: A post-synthetic functionalization method is reported to obtain a highly permselective zeolitic imidazolate framework (ZIF-90) membrane. The intercrystalline defects of the ZIF-90 membrane are minimized to enhance the separation selectivity while a high permeance is maintained.

Detection of sialic acid using boronic-acid-functionalized metal organic framework UiO-66-NH2@B(OH)2.

Sialic acid (SA) is a crucial component of glycoproteins and glycolipids on the cellular membrane, which is essential for maintaining the function of cell membranes, such as cell recognition and communication. Simultaneously, sialic acid plays a significant role in many physiological and pathological processes. Hence, it is urgent to develop a simple and sensitive strategy for determining sialic acid. In this work, a new metal-organic framework called UiO-66-NH2@B(OH)2 has been designed and synthesized for the recognition and detection of sialic acid. The boronic acid functional group in UiO-66-NH2@B(OH)2 can bind to a diol moiety of the glycerol side chain of sialic acid, which will attenuate or even quench the fluorescence of UiO-66-NH2@B(OH)2, thus opening a new road to detect sialic acid. Based on the measurement results, sialic acid can be quantitatively measured in a linear range of 0.05-2.5 mmoL/L with the UiO-66-NH2@B(OH)2 probe. The detection limit of sialic acid is as low as 0.025 mmol/L. Furthermore, the boronic-acid functionalized probe UiO-66-NH2@B(OH)2 displays high sensitivity and high selectivity to recognize the sialic acid in mouse serum samples. Therefore, the developed UiO-66-NH2@B(OH)2 can be used as a promising probe to identify and detect sialic acid in the practical application.

Steam-stable zeolitic imidazolate framework ZIF-90 membrane with hydrogen selectivity through covalent functionalization.

A novel covalent functionalization strategy was developed to prepare reproducible ZIF-90 molecular sieve membranes by using 3-aminopropyltriethoxysilane as a covalent linker between the ZIF-90 layer and Al(2)O(3) support via imines condensation. The ZIF-90 membranes show high thermal and hydrothermal stabilities, and they allow the separation of hydrogen from larger gases by molecular sieving.

Neutral and cation-free LTA-type aluminophosphate (AlPO(4)) molecular sieve membrane with high hydrogen permselectivity.

A novel neutral and cation-free LTA-type AlPO(4) membrane has been prepared on porous asymmetric ceramic supports. Hydrogen can be effectively separated from other gases by molecular sieving.