Metal-organic Framework Membranes Research Articles

Continuous photo-oxidation of methane to methanol at an atomically tailored reticular gas-solid interface

Photo-oxidation of methane (CH4) using hydrogen peroxide (H2O2) synthesized in situ from air and water under sunlight offers an attractive route for producing green methanol while storing intermittent solar energy. However, in commonly used aqueous-phase systems, photocatalysis efficiency is severely limited due to the ultralow availability of CH4 gas and H2O2 intermediate at the flooded interface. Here, we report an atomically modified metal-organic framework (MOF) membrane nanoreactor that promotes direct CH4 photo-oxidation to methanol at the gas-solid interface in a reticular open framework. We show that the domino synergy between colocalized single-atom palladium and iron on MOF nodes enables efficient generation and in situ utilization of H2O2 in the absence of liquid water, thus circumventing H2O2 dilution. Meanwhile, the “breathable” MOF membrane, optimized by solar-driven interfacial water management, provides high-flux channels to facilitate efficient gas diffusion and rapid methanol desorption and transfer. As a result, we demonstrate over 210 hours of continuous photosynthesis of 0.25 M methanol with unity selectivity, achieving an exceptional methanol productivity of 14.4 millimoles per gram of catalyst per hour.

Tunning the Wettability of the PVDF Membrane using the PVA-Stabilized TA-UiO-66-NH2 MOF Membranes to Separate Layered Oil-Water Mixture and Surfactant-Stabilized Emulsion.

This study introduces a UiO-66-NH2/Tannic acid/Polyvinylidene fluoride (UTP) composite membrane for efficient oil-water separation. Pristine polyvinylidene fluoride (PVDF) membranes, due to their hydrophobic nature, tend to foul during oil-in-water emulsion separation. By incorporating the metal-organic framework (MOF) UiO-66-NH2 and stabilizing it with tannic acid (TA) and polyvinyl alcohol (PVA), the membrane's hydrophilicity and antifouling properties were significantly enhanced. The water contact angle of the UTP membrane decreased from 121° to 3°, indicating a dramatic increase in hydrophilicity, while the underwater oil contact angle (UWOCA) of 119° demonstrated excellent oleophobicity. The modified membrane achieved over 99 % separation efficiency and improved flux by 15 times compared to the pristine PVDF. TA acted as a binder, ensuring uniform MOF dispersion and improving the composite's stability. The PVA further reinforced the structure, enhancing durability under operational conditions. Durability tests showed no significant MOF detachment after repeated use, confirming the stability of the UTP composite. The results highlight the potential of the UTP membrane for oil-water separation with superior permeability and fouling resistance.

Metal-organic framework membranes and their advanced oxidation processes in water treatment: From material regulation to stability evaluation

Metal-organic framework membranes and their advanced oxidation processes in water treatment: From material regulation to stability evaluation

Angstrom‐Scale Defect‐Free Crystalline Membrane for Sieving Small Organic Molecules

AbstractCrystalline membranes, represented by the metal‐organic framework (MOF) with well‐defined angstrom‐sized apertures, have shown great potential for molecular separation. Nevertheless, it remains a challenge to separate small molecules with very similar molecular size differences due to angstrom‐scale defects during membrane formation. Herein, a stepwise assembling strategy is reported for constructing MOF membranes with intrinsic angstrom‐sized lattice aperture lattice to separate organic azeotropic mixtures separation. The membrane is synthesized by redesigning the metal source, which reduces the coordination reaction rate to avoid cluster‐missing defects. Then, extra ligands are introduced to overcome the coordination steric hindrance to heal the linker‐missing defects. Ultralow‐dose transmission electron microscopy is used to realize a direct observation of the angstrom‐scale defects. For separating the challenging methanol‐containing ester or ether azeotropic mixtures with molecular size difference as small as <1 Å, the angstrom‐scale defect‐free MOF membrane exhibits an outstanding flux of ≈3700 g·m−2 h−1 and separation factor of ≈247–524, far beyond the upper‐bound of state‐of‐the‐arts membranes. This study offers a feasible strategy for precisely constructing angstrom‐confined spaces for diverse applications (e.g., separation, catalysis, and storage).

Directly Gel-Thermal Processing of Linker-Mixed Crystal-Glass Composite Membranes for Sorption-Preferential Gas Separation.

Membrane processes are promising for energy-saving industrial applications. However, efficient separation for some valuable gas mixtures with similar characteristics, such as CH4/N2 and O2/N2, remains extremely challenging. Metal-organic framework (MOF) membranes have been attracting intensive attention for gas sieving, but it is difficult to manufacture MOF membranes in scalability and precisely tune their transport property. In this study, Gel-thermal processing of linker-mixed MOF crystal-glass composite membranes is reported directly, with the mechanism of adjusting metal-linker bond strengths and angles to disrupt long-range periodicity of MOFs and promote glass phase formation, for sharply sorption-preferential gas separation. This strategy can be realized by using a simple, solvent/precursor-less, and cost-effective gel-thermal approach with two steps of gel coating and thermal conversion, thereby constructing crystal-glass composite membranes in a controllable, processable, versatile, and environmentally friendly route. Moreover, the mixed linkers enable preferential gas affinities and the ultramicroporous glasses can eliminate any membrane defects. The membranes exhibit outstanding gas separation performance for the challenging systems of CH4/N2 and O2/N2, with mixture selectivities up to 9.3 and 9.6, respectively, far exceeding those of polymer, MOF, and mixed-matrix membranes. The study provides an available route for architecting high-performance membranes for gas separations.

Optically Modulated Nanofluidic Ionic Transistor for Neuromorphic Functions

AbstractNeuromorphic systems that can emulate the behavior of neurons have garnered increasing interest across interdisciplinary fields due to their potential applications in neuromorphic computing, artificial intelligence and brain‐machine interfaces. However, the optical modulation of nanofluidic ion transport for neuromorphic functions has been scarcely reported. Herein, inspired by biological systems that rely on ions as signal carriers for information perception and processing, we present a nanofluidic transistor based on a metal–organic framework membrane (MOFM) with optically modulated ion transport properties, which can mimic the functions of biological synapses. Through the dynamic modulation of synaptic weight, we successfully replicate intricate learning‐experience behaviors and Pavlovian associate learning processes by employing sequential optical stimuli. Additionally, we demonstrate the application of the International Morse Code with the nanofluidic device using patterned optical pulse signals, showing its encoding and decoding capabilities in information processing process. This study would largely advance the development of nanofluidic neuromorphic devices for biomimetic iontronics integrated with sensing, memory and computing functions.

Metal-organic framework membranes with scale-like structure for efficient propylene/propane separation

The fabrication of metal-organic framework (MOF) membranes with high propylene/propane selectivity, high mechanical endurance and ease of scaling up always remains a challenge. Inspired by the ubiquitous biological wear-resistant structure, here we show ZIF-67 membranes with a tangential-normal interlaced structure (TN-ZIF-67) for one-step acquisition of polymer-grade propylene, which is endowed with the merits of intergranular defect elimination, partial ZIF-67 lattice flexibility restriction and anti-wear of the membrane surface. The TN-ZIF-67 membrane exhibits an optimal propylene/propane mixture separation factor of 221, and the separation performance remained unchanged after 1.5 years of storage or abrasion by repeated sanding. The distinctive membrane structure can be further scaled up on 4 mm-diameter tubular substrates. This work demonstrates a strategy to extend the rational design of defect-free, anti-wear MOF membranes with superior separation performance and stability that could fulfill future industrial applications.

Biomineralized metal-organic framework membrane with high-crystallinity for ultrafast molecular separation

Metal-organic frameworks (MOFs) possess uniform and controllable pore structure, holding significant promise for the creation of efficient molecular separation membranes. Nevertheless, the challenge lies in constructing MOF membranes with high crystallinity and effectively utilizing their ordered crystal channels for molecular separation. Drawing inspiration from natural biomineralization processes, an in-situ trace graphene oxide (GO)-mediated crystallization strategy was adopted here to manipulate the crystallization of Zr-MOF (MIP-202(Zr)) membranes. GO nanosheets with abundant oxygen-containing groups could interact with the MOF precursor, furnishing numerous growth sites for the subsequent MOF growth, thereby facilitating the crystallization process during membrane formation within only 60 min. The resultant GO/MIP-202(Zr) composite membrane, composed of highly crystalline MIP-202(Zr) and trace amount of GO nanosheets, overcame the trade-off between MOF crystallinity and membrane formation. Benefiting from the interconnected pore structure, the resulting GO/MIP-202(Zr) membrane presented ultrahigh water permeability (1698.9 L m−2 h−1 bar−1), surpassing that of the pure GO membrane (258.9 L m−2 h−1 bar−1) by 6.5 times, while maintaining a comparable rejection for common dye molecules. Furthermore, the membrane displayed satisfied recyclability and structural stability. This study provides important perspectives for the fabrication of advanced membranes derived from MOFs aimed at enhancing molecular separation processes.

Facile orientation control of MOF-303 hollow fiber membranes by a dual-source seeding method

Metal‒organic frameworks (MOFs) are nanoporous crystalline materials with enormous potential for further development into a new class of high-performance membranes. However, the preparation of defect-free and water-stable MOF membranes with high permselectivity and good structural integrity remains a challenge. Herein, we demonstrate a dual-source seeding (DS) approach to produce high-performance, water-stable MOF-303 membranes with hollow fiber (HF) geometry and preferentially tailored crystallographic orientation. By controlling the nucleation site density during secondary growth, MOF-303 membranes with a preferred crystallographic orientation (CPO) on the (011) plane were fabricated. The MOF-303 membrane with CPO on (011) provides straight one-dimensional permeation channels with a superior water flux of 18 kg m−2 h−1 in pervaporative water/ethanol separation, which is higher than that of most of the reported zeolite membranes and 1–2 orders of magnitude greater than that of previously reported MOF membranes. The straight water permeation channels also offer a promising water permeance of 15 L m−2 h−1 bar−1 and a molecular weight cut-off (MWCO ≈ 269) for dye nanofiltration. These results provide a concept for developing ultrapermeable MOF membranes with good selectivity and structural integrity for pervaporation and nanofiltration.

Non‐selective Defect Minimization towards Highly Efficient Metal‐Organic Framework Membranes for Gas Separation

AbstractThe persistence of defects in polycrystalline membranes poses a substantial obstacle to reaching the theoretical molecular sieving separation and scaling up production. The low membrane selectivity in most reported literature is largely due to the unavoidable non‐selective defects during synthesis, leading to a mismatch between the well‐defined pore structure of polycrystalline molecular sieve materials. This paper presents a novel approach for minimizing non‐selective defects in metal–organic framework (MOF) membranes by a constricted crystal growth strategy in a confined environment. The in situ ZIF formation using the densely packed seeding array between the substrate and the pre‐grown top ZIF layer yields a confined membrane interlayer, which is highly uniform with a tightly packed crystalline structure. Unlike uncontrolled crystal growth, we purposely regulate the interlayer membrane growth in the direction parallel to the substrate. A notable 99 % decrease in defects in the confined interlayer was achieved compared to the random‐grown top layer, leading to a ~353 % increment in H2/N2 selectivity over the non‐confined reference MOF membrane. The performance of this new membrane sits in the optimal range above the Robeson upper bound. The membrane boasts a balanced high H2 permeability (>5000 Barrer) and selectivity (>50), significantly surpassing peer ZIF membranes.

Non-selective Defect Minimization towards Highly Efficient Metal-Organic Framework Membranes for Gas Separation.

The persistence of defects in polycrystalline membranes poses a substantial obstacle to reaching the theoretical molecular sieving separation and scaling up production. The low membrane selectivity in most reported literature is largely due to the unavoidable non-selective defects during synthesis, leading to a mismatch between the well-defined pore structure of polycrystalline molecular sieve materials. This paper presents a novel approach for minimizing non-selective defects in metal-organic framework (MOF) membranes by a constricted crystal growth strategy in a confined environment. The in situ ZIF formation using the densely packed seeding array between the substrate and the pre-grown top ZIF layer yields a confined membrane interlayer, which is highly uniform with a tightly packed crystalline structure. Unlike uncontrolled crystal growth, we purposely regulate the interlayer membrane growth in the direction parallel to the substrate. A notable 99 % decrease in defects in the confined interlayer was achieved compared to the random-grown top layer, leading to a ~353 % increment in H2/N2 selectivity over the non-confined reference MOF membrane. The performance of this new membrane sits in the optimal range above the Robeson upper bound. The membrane boasts a balanced high H2 permeability (>5000 Barrer) and selectivity (>50), significantly surpassing peer ZIF membranes.

Lattice-defective metal-organic framework membranes from filling mesoporous colloidal networks for monovalent ion separation

Ionic separations are critical to various chemical, environmental, and energy-related industries, but precise discrimination of monovalent ions with similar properties is extremely difficult. Nanoporous metal-organic framework (MOF) membranes attract intensive attention for ionic separations. However, precise adjusting transport nanochannels of frameworks and simplifying formation mechanisms of membranes remain extremely challenging. In this study, we report controllable construction of lattice-defective MOF membranes for sharp ion sieving, through filling mesoporous MOF colloidal layers by confined interior growth. By utilizing highly processable mesoporous colloidal networks to provide abundant nucleation sites, decelerate precursor diffusions, and serve as membrane-forming hosts, interior MOF growth can be confined in the mesopores of hosts, thereby eliminating any avoid spaces and constructing pinhole-free membranes in a scalable route. Moreover, through creating linker-missing lattice defects in frameworks, the microporous pathways can be accurately expanded at angstrom level, consequently, selectively improving the accessibilities for specific monovalent cations but maintaining the large resistances for others. Importantly, the prepared 150-nm MOF membranes exhibit good long-term stability and superb ion-sieving performance, especially for monovalent cations, with mixture selectivities as high as 7.5 for K+/Li+ and 51 for K+/Mg2+ during concentration-driven separations, which outperform most membranes. This study provides an alternative methodology to construct high-performance ion-sieving polycrystalline membranes.

Preprocessed Monomer Interfacial Polymerization for Scalable Fabrication of High-Valent Cluster-Based Metal-Organic Framework Membranes.

Current research on emergent membrane materials with ordered and stable nanoporous structures often overlooks the vital facet of manufacturing scalability. We propose the preprocessed monomer interfacial polymerization (PMIP) strategy for the scalable fabrication of high-valent cluster-based metal-organic framework (MOF) membranes with robust structures. Using a roll-to-roll device on commercial polymer supports, Zr-fum-MOF membranes are continuously processed at room temperature through the PMIP approach. These large-area membranes demonstrate the preeminent hydrogen separation capabilities, boasting an order of magnitude of permeance and a thrice-enhanced selectivity when juxtaposed with conventional polymeric membranes. The obtained PMIP-Zr-fum-MOF membranes possess superior stability in water compared with interfacial polymerization (IP)-processed low-valent metal-ion-based ZIF-8 membranes. Moreover, we have implemented the PMIP strategy's universality to process the other four diverse MOF membranes. The proposal of PMIP significantly advances the scalable fabrication of water-stable high-valent cluster MOF membranes.

Anisotropic Porosity and Interface Synergy Enhanced Gas Permselectivity in Heterolayer Metal-Organic Framework Membrane.

The pursuit of sustainable, carbon-free separation technology hinges on the efficient separation of gas mixtures with high separation factors and flow rates, i. e. high permselectivity. However, achieving this objective is arduous due to the meticulous engineering at the angstrom scale and intricate chemical manipulation required to design the pores within membranes. To address this challenge, a proof-of-concept for an anisotropic porous membrane has been devised. Employing a meticulous step-by-step methodology, two distinct porous metal-organic frameworks (MOFs) are integrated to form a monolithic anisotropic membrane. By harnessing pore anisotropy (3.4 to 6 Å) aligned with the gas permeation direction and a unique interface characterized by cross-linked pores derived from the two distinct MOFs, this membrane transcends the performance limitations inherent in the individual MOF membranes (~45 % enhanced selectivity). This approach not only sheds light on the heterolayer membrane design strategy but also elucidates the intricate CO2/N2 permselectivity relationship inherent in the interface structure.

Direct Epitaxial Growth of Polycrystalline MOF Membranes on Cu Foils for Uniform Li Deposition in Long-life Anode-free Li Metal Batteries.

Anode-free Li-metal battery (AFLMB) is being developed as the next generation of advanced energy storage devices. However, the low plating and stripping reversibility of Li on Cu foil prevents its widespread application. A promising avenue for further improvement is to enhance the lithophilicity of Cu foils and optimise their surfaces through a metal-organic framework (MOF) functional layer. However, excessive binder usage in the current approaches obscures the active plane of the MOF, severely limiting its performance. In response to this challenge, MOF polycrystalline membrane technology has been integrated into the field of AFLMB in this work. The dense and seamless HKUST-1 polycrystalline membrane was deposited on Cu foil (HKUST-1 M@Cu) via an epitaxial growth strategy. In contrast to traditional MOF functional layers, this binder-free polycrystalline membrane fully exposes lithophilic sites, effectively reducing the nucleation overpotential and optimising the deposition quality of Li. Consequently, the Li plating layer becomes denser, eliminating the effects of dendrites. When coupled with LiFePO4 cathodes, the battery based on the HKUST-1 membrane exhibits excellent rate performance and cycling stability, achieving a high reversible capacity of approximately 160 mAh g-1 and maintaining a capacity retention of 80.9 % after 1100 cycles.

The Key to MOF Membrane Fabrication and Application: the Trade-off between Crystallization and Film Formation.

Metal-organic frameworks (MOFs), owing the merits of ordered and tailored channel structures in the burgeoning crystalline porous materials, have demonstrated significant promise in construction of high-performance separation membranes. However, precisely because this crystal structure with strong molecular interaction in their lattice provides robust structural integrity and resistance to chemical and thermal degradation, crystalline MOFs typically exhibit insolubility, infusibility, stiffness and brittleness, and therefore their membrane-processing properties are far inferior to the flexible amorphous polymers and hinder their subsequent storage, transportation, and utilization. Hence, focusing on film-formation and crystallization is the foundation for exploring the fabrication and application of MOF membranes. In this review, the film-forming properties of crystalline MOFs are fundamentally analyzed from their inherent characteristics and compared with those of amorphous polymers, influencing factors of polycrystalline MOF membrane formation are summarized, the trade-off relationship between crystallization and membrane formation is discussed, and the strategy solving the film formation of crystalline MOFs in recent years are systematically reviewed, in anticipation of realizing the goal of preparing crystalline membranes with optimized processability and excellent performance.

Rational MOF Membrane Design for Gas Detection in Complex Environments.

Metal-organic frameworks (MOFs) hold significant promise in the realm of gas sensing. However, current understanding of their sensing mechanisms remains limited. Furthermore, the large-scale fabrication of MOFs is hampered by their inadequate mechanical properties. These two challenges contribute to the sluggish development of MOF-based gas-sensing materials. In this review, the selection of metal ions and organic ligands for designing MOFs is first presented, deepening the understanding of the interactions between different metal ions/organic ligands and target gases. Subsequently, the typical interfacial synthesis strategies (gas-solid, gas-liquid, solid-liquid interfaces) are provided, highlighting the potential for constructing MOF membranes on superhydrophobic and/or superhydrophilic substrates. Then, a multi-scale structure design strategies is proposed, including multi-dimensional membrane design and heterogeneous membrane design, to improve sensing performance through enhanced interfacial mass transfer and specific gas sieving. This strategy is anticipated to augment the task-specific capabilities of MOF-based materials in complex environments. Finally, several key future research directions are outlined with the aim not only to further investigate the underlying sensing principles of MOF membranes but also to achieve efficient detection of target gases amidst interfering gases and elevated moisture levels.

Channel construction and application of high-connectivity metal-organic framework membranes

Channel construction and application of high-connectivity metal-organic framework membranes

Investigation into the Simulation and Mechanisms of Metal-Organic Framework Membrane for Natural Gas Dehydration.

Natural gas dehydration is a critical process in natural gas extraction and transportation, and the membrane separation method is the most suitable technology for gas dehydration. In this paper, based on molecular dynamics theory, we investigate the performance of a metal-organic composite membrane (ZIF-90 membrane) in natural gas dehydration. The paper elucidates the adsorption, diffusion, permeation, and separation mechanisms of water and methane with the ZIF-90 membrane, and clarifies the influence of temperature on gas separation. The results show that (1) the diffusion energy barrier and pore size are the primary factors in achieving the separation of water and methane. The diffusion energy barriers for the two molecules (CH4 and H2O) are ΔE(CH4) = 155.5 meV and ΔE(H2O) = 50.1 meV, respectively. (2) The ZIF-90 is more selective of H2O, which is mainly due to the strong interaction between the H2O molecule and the polar functional groups (such as aldehyde groups) within the ZIF-90. (3) A higher temperature accelerates the gas separation process. The higher the temperature is, the faster the separation process is. (4) The pore radius is identified as the intrinsic mechanism enabling the separation of water and methane in ZIF-90 membranes.

Enhanced absorption capacity and fundamental mechanism of electrospun MIL-101(Cr)-NH2/PAN nanofibrous membranes for Mo(VI) removal

Amidst the escalating global concern over heavy metal discharge from industrial effluents, Mo(VI), as a potentially toxic trace element, poses significant risks to human and environmental health. Traditional treatment methods such as biodegradation and ion exchange have low removal efficiency, hence, the efficient removal of Mo (VI) ions from industrial wastewater assumes paramount importance. Emerging materials, Metal-Organic Frameworks (MOFs), have garnered extensive attention in water treatment due to their strong adsorption properties, and MOFs membrane materials are hailed as the most promising adsorbents. Therefore, this study aims to prepare a novel membrane material with high efficiency for the removal of Mo (VI) by loading MOFs into nanofibers. Given the water stability of MIL-101, MIL-101-R(-H, -NH2, -NO2) with different functional groups were prepared and subsequently loaded into PAN nanofibrous for the adsorption of Mo(VI). Adsorption kinetics and isotherm studies revealed PAN/MIL-101(Cr)-NH2 to exhibit superior adsorption performance, achieving a maximum adsorption capacity of 171.81 mg g-1. Density functional theory (DFT) calculations and molecular dynamics simulations elucidated the adsorption mechanism, highlighting the role of amino modification in facilitating Mo(VI) adsorption through electrostatic attraction and high reactivity. This work not only offers novel materials and approaches for Mo(VI) wastewater treatment but also advances the industrial application of MOF materials in the domain of heavy metal wastewater treatment.