Polymer Infiltration into Metal–Organic Frameworks in Mixed-Matrix Membranes Detected in Situ by NMR

Solid-State Electrolytes: Probing Interface Regulation from Multiple Perspectives

Solid-state electrolytes (SSEs), as the heart of all-solid-state batteries (ASSBs), are recognized as the next-generation energy storage solution, offering high safety, extended cycle life, and superior energy density. SSEs play a pivotal role in ion transport and electron separation. Nonetheless, interface compatibility and stability issues pose significant obstacles to further enhancing ASSB performance. Extensive research has demonstrated that interface control methods can effectively elevate ASSB performance. This review delves into the advancements and recent progress of SSEs in interfacial engineering over the past years. We discuss the detailed effects of various regulation strategies and directions on performance, encompassing enhancing Li+ mobility, reducing energy barriers, immobilizing anions, introducing interlayers, and constructing unique structures. This review offers fresh perspectives on the development of high-performance lithium-metal ASSBs.

Efficient Nickel and Cobalt Recovery by Metal-Organic Framework-Based Mixed Matrix Membranes (MMM-MOFs)

Green energy transition has supposed to give a huge boost to the electric vehicle rechargeable battery market. This has generated a compelling demand for raw materials, such as cobalt and nickel, which are key common constituents in lithium-ion batteries (LIBs). However, their existing mining protocols and the concentrated localization of such ores have made cobalt and nickel mineral conundrums, and their supplies experience shortages, which threaten to slow the progress of the renewable energy transition. Aiming to contribute to the sustainable recycling of these valuable metals from LIBs and wastewater, in this work, we explore the use of four mixed matrix membranes (MMMs) embedding different metal-organic frameworks (MOFs), i.e., MIL-53(Al), MIL-53(Fe), MIL-101(Fe), and {SrIICuII 6[(S,S)-serimox]3(OH)2(H2O)}·39H2O (SrCu 6 Ser) in polyether sulfone (PES), for the recovery of cobalt(II) and nickel(II) metal cations from mixed cobalt-nickel aqueous solutions containing common interfering ions. Whereas the neat PES membrane slightly contributes to the adsorption of metal ions, showing reduced removal efficiency values of 10.2 and 9.5% for Ni(II) and Co(II), respectively, the inclusion of MOFs in the polymeric matrix substantially improves the adsorption performances. The four MOF@PES MMMs efficiently remove these metals from water, with MIL-53(Al)@PES being the one that presents better performance, with a removal efficiency up to 95% of Ni(II) and Co(II). Remarkably, SrCu 6 Ser@PES exhibits outstanding selectivity toward cobalt(II) cations compared to of nickel(II) ones, with removal efficiencies of 63.7 and 15.1% for Co(II) and Ni(II), respectively. Overall, the remarkable efficiencies, versatility, high environmental robustness, and cost-effective synthesis shown by this family of MOF@PES MMMs situate them among the best adsorbents for the extraction of this kind of contaminants.

Selective Removal of Denatured Proteins Using MOF Nanopores

Here we present, for the first time, the selective adsorption of denatured proteins using a metal-organic framework (MOF), demonstrating promising potential for protein purification. Typical proteins, such as lysozyme and carbonic anhydrase B, enter the pores of MIL-101 through their narrow apertures when they are denatured to an unfolded state. Selective adsorption is achieved by finely tuning two key features: the sizes of the aperture and cage of the MOF nanopores, which are responsible for sorting unfolded polypeptide chains and inhibiting the translocation of the native form into the pores, respectively. By leveraging this selective adsorption, we successfully purified a mixture of native and denatured proteins by adding MOF to the mixture, achieving a native purity of over 99%.

Understanding Electrolyte Ion Size Effects on the Performance of Conducting Metal-Organic Framework Supercapacitors

Layered metal-organic frameworks (MOFs) have emerged as promising materials for next-generation supercapacitors. Understanding how and why electrolyte ion size impacts electrochemical performance is crucial for developing improved MOF-based devices. To address this, we investigate the energy storage performance of Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with a series of 1 M tetraalkylammonium tetrafluoroborate (TAABF4) electrolytes with different cation sizes. Three-electrode experiments show that Cu3(HHTP)2 exhibits an asymmetric charging response with all ion sizes, with higher energy storage upon positive charging and a greater charging asymmetry with larger TAA+ cations. The results further show that smaller TAA+ cations demonstrate superior capacitive performances upon both positive and negative charging compared to larger TAA+ cations. To gain further insights, electrochemical quartz crystal microbalance measurements were performed to probe ion electrosorption during charging and discharging. These reveal that Cu3(HHTP)2 has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging process with larger cations. Overall, the results of this study suggest that larger TAA+ cations saturate the pores of the Cu3(HHTP)2-based electrodes. This leads to more asymmetric charging behavior and forces solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and they will guide the design of improved MOF-based supercapacitors.

Opportunities and challenges for plastic depolymerization by biomimetic catalysis

Plastic waste has imposed significant burdens on the environment. Chemical recycling allows for repeated regeneration of plastics without deterioration in quality, but often requires harsh reaction conditions, thus being environmentally unfriendly. Enzymatic catalysis offers a promising solution for recycling under mild conditions, but it faces inherent limitations such as poor stability, high cost, and narrow substrate applicability. Biomimetic catalysis may provide a new avenue by combining high enzyme-like activity with the stability of inorganic materials. Biomimetic catalysis has demonstrated great potential in biomass conversion and has recently shown promising progress in plastic degradation. This perspective discusses biomimetic catalysis for plastic degradation from two perspectives: the imitation of the active centers and the imitation of the substrate-binding clefts. Given the chemical similarity between biomass and plastics, relevant work is also included in the discussion to draw inspiration. We conclude this perspective by highlighting the challenges and opportunities in achieving sustainable plastic recycling via a biomimetic approach.

Regulating Metal Centers of MOF-74 Promotes PEO-Based Electrolytes for All-Solid-State Lithium-Metal Batteries

Poly(ethylene oxide) (PEO)-based electrolytes have been extensively studied for all-solid-state lithium-metal batteries due to their excellent film-forming capabilities and low cost. However, the limited ionic conductivity and poor mechanical strength of the PEO-based electrolytes cannot prevent the growth of undesirable lithium dendrites, leading to the failure of batteries. Metal-organic frameworks (MOFs) are functional materials with a periodic porous structure that can improve the electrochemical performance of PEO-based electrolytes. However, the enhancement effect of MOFs with different metal centers and the interaction mechanism with PEO remain unclear. Herein, MOF-74s with Cu or Ni centers are prepared and used as fillers of PEO-based electrolytes. Adding 15 wt % of Cu-MOF-74 to the PEO-based electrolyte (15%Cu-MOF/P-Li) effectively improves the ionic conductivity, lithium transference number, and mechanical strength of the PEO-based electrolyte simultaneously. Furthermore, the ordered pore channels of Cu-MOF-74 provide uniform Li-ion transport pathways, facilitating homogeneous Li+ deposition. As a result, the lithium symmetric cell with 15%Cu-MOF/P-Li shows stable cycles for 1080 h at 0.1 mA cm-2 and 0.1 mAh cm-2, and the Li | 15% Cu-MOF/P-Li | LFP full cell exhibits a long cycle life up to 200 cycles at 60 °C and 0.5 C, with a capacity retention rate of 89.7%.

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

The propensity for covalent organic frameworks to template polymer entanglement

The introduction of molecularly woven three-dimensional (3D) covalent organic framework (COF) crystals into polymers of varying types invokes different forms of contact between filler and polymer. Whereas the combination of woven COFs with amorphous and brittle polymethyl methacrylate results in surface interactions, the use of the liquid-crystalline polymer polyimide induces the formation of polymer-COF junctions. These junctions are generated by the threading of polymer chains through the pores of the nanocrystals, thus allowing for spatial arrangement of polymer strands. This offers a programmable pathway for unthreading polymer strands under stress and leads to the in situ formation of high-aspect-ratio nanofibrils, which dissipate energy during the fracture. Polymer-COF junctions also strengthen the filler-matrix interfaces and lower the percolation thresholds of the composites, enhancing strength, ductility, and toughness of the composites by adding small amounts (~1 weight %) of woven COF nanocrystals. The ability of the polymer strands to closely interact with the woven framework is highlighted as the main parameter to forming these junctions, thus affecting polymer chain penetration and conformation.

Interfacing metal organic frameworks with polymers or carbon-based materials: from simple to hierarchical porous and nanostructured composites

In the past few years, metal organic frameworks (MOFs) have been assembled with (bio)polymers and a series of carbon-based materials (graphene, graphene oxide, carbon nanotubes, carbon quantum dots, etc.) leading to a wide range of composites differing in their chemical composition, pore structure and functionality. The objective was mainly to overcome the limitations of MOFs in terms of mechanical properties, chemical stability and processability while imparting novel functionality (electron conductivity, (photo)catalytic activity, etc.) and hierarchical porosity. These composites were considered for numerous applications including gas/liquid adsorption and separation, (photo)catalysis, biomedicine, energy storage, conversion and so on. The performance of such composites depends strongly on their microstructural and physico-chemical properties which are mainly driven by the chemical strategies used to design and process such composites. In this perspective article, we propose to cover this topic and provide a useful survey of recent progress in the synthesis and design of MOFs-carbon material composites. This article will describe the development of composites with increasing complexity in terms of porous architecture, spatial structuration and organisation, and functionality.

Developing Mixed Matrix Membranes with Good CO2 Separation Performance Based on PEG-Modified UiO-66 MOF and 6FDA-Durene Polyimide

The use of mixed matrix membranes (MMMs) comprising metal-organic frameworks (MOFs) for the separation of CO2 from flue gas has gained recognition as an effective strategy for enhancing gas separation efficiency. When incorporating porous materials like MOFs into a polymeric matrix to create MMMs, the combined characteristics of each constituent typically manifest. Nevertheless, the inadequate dispersion of an inorganic MOF filler within an organic polymer matrix can compromise the compatibility between the filler and matrix. In this context, the aspiration is to develop an MMM that not only exhibits optimal interfacial compatibility between the polymer and filler but also delivers superior gas separation performance, specifically in the efficient extraction of CO2 from flue gas. In this study, we introduce a modification technique involving the grafting of poly(ethylene glycol) diglycidyl ether (PEGDE) onto a UiO-66-NH2 MOF filler (referred to as PEG-MOF), aimed at enhancing its compatibility with the 6FDA-durene matrix. Moreover, the inherent CO2-philic nature of PEGDE is anticipated to enhance the selectivity of CO2 over N2 and CH4. The resultant MMM, incorporating 10 wt% of PEG-MOF loading, exhibits a CO2 permeability of 1671.00 Barrer and a CO2/CH4 selectivity of 22.40. Notably, these values surpass the upper bound reported by Robeson in 2008.

Mixed Metal-Organic Framework Mixed-Matrix Membranes: Insights into Simultaneous Moisture-Triggered and Catalytic Delivery of Nitric Oxide using Cryo-scanning Electron Microscopy

The fundamental chemical and structural diversity of metal-organic frameworks (MOFs) is vast, but there is a lack of industrial adoption of these extremely versatile compounds. To bridge the gap between basic research and industry, MOF powders must be formulated into more application-relevant shapes and/or composites. Successful incorporation of varying ratios of two different MOFs, CPO-27-Ni and CuBTTri, in a thin polymer film represents an important step toward the development of mixed MOF mixed-matrix membranes. To gain insight into the distribution of the two different MOFs in the polymer, we report their investigation by Cryo-scanning electron microscopy (Cryo-SEM) tomography, which minimizes surface charging and electron beam-induced damage. Because the MOFs are based on two different metal ions, Ni and Cu, the elemental maps of the MOF composite cross sections clearly identify the size and location of each MOF in the reconstructed 3D model. The tomography run was about six times faster than conventional focused ion beam (FIB)-SEM and the first insights to image segmentation combined with machine learning could be achieved. To verify that the MOF composites combined the benefits of rapid moisture-triggered release of nitric oxide (NO) from CPO-27-Ni with the continuous catalytic generation of NO from CuBTTri, we characterized their ability to deliver NO individually and simultaneously. These MOF composites show great promise to achieve optimal dual NO delivery in real-world medical applications.

Covalent connections between metal-organic frameworks and polymers including covalent organic frameworks

Hybrid composite materials combining metal-organic frameworks (MOFs) and polymers have emerged as a versatile platform for a broad range of applications. The crystalline, porous nature of MOFs and the flexibility and processability of polymers are synergistically integrated in MOF-polymer composite materials. Covalent bonds, which form between two distinct materials, have been extensively studied as a means of creating strong molecular connections to facilitate the dispersion of "hard" MOF particles in "soft" polymers. Numerous organic transformations have been applied to post-synthetically connect MOFs with polymeric species, resulting in a variety of covalently connected MOF-polymer systems with unique properties that are dependent on the characteristics of the MOFs, polymers, and connection modes. In this review, we provide a comprehensive overview of the development and strategies involved in preparing covalently connected MOFs and polymers, including recently developed MOF-covalent organic framework composites. The covalent bonds, grafting strategies, types of MOFs, and polymer backbones are summarized and categorized, along with their respective applications. We highlight how this knowledge can serve as a basis for preparing macromolecular composites with advanced functionality.

Design Principles for Using Amphiphilic Polymers To Create Microporous Water

Aqueous dispersions of microporous nanocrystals with dry, gas-accessible pores─referred to as "microporous water"─enable high densities of gas molecules to be transported through water. For many applications of microporous water, generalizable strategies are required to functionalize the external surface of microporous particles to control their dispersibility, stability, and interactions with other solution-phase components─including catalysts, proteins, and cells─while retaining as much of their internal pore volume as possible. Here, we establish design principles for the noncovalent surface functionalization of hydrophobic metal-organic frameworks with amphiphilic polymers that render the particles dispersible in water and enhance their hydrolytic stability. Specifically, we show that block co-polymers with persistence lengths that exceed the micropore aperture size of zeolitic imidazolate frameworks (ZIFs) can dramatically enhance ZIF particle dispersibility and stability while preserving porosity and >80% of the theoretical O2 carrying capacity. Moreover, enhancements in hydrolytic stability are greatest when the polymer can form strong bonds to exposed metal sites on the external particle surface. More broadly, our insights provide guidelines for controlling the interface between polymers and metal-organic framework particles in aqueous environments to augment the properties of microporous water.

Magnetic porous carbon materials derived from metal-organic framework in-situ growth on natural cellulose of wood for sulfadiazine degradation: Role of delignification and mechanisms

Magnetic porous carbon materials as peroxymonosulfate (PMS) activators for sulfadiazine degradation were derived from metal-organic frameworks (MOFs) grown in-situ on the cellulose of wood through the one-step pyrolysis method. The cellulose was obtained by treating wood powder with sodium chlorite to remove lignin, and Fe-MOFs (MIL-101(Fe)) nanoparticles were in-situ grown on the cellulose through hydrothermal reaction. The delignification of wood effectively enhanced the in-situ growth of MIL-101(Fe) on the wood tracheid skeleton, increased the specific surface area of magnetic porous carbon material (Fe@PC-50) after pyrolysis, and improved the performance of Fe@PC-50 as a PMS activator for the degradation of sulfadiazine. With the presence of 0.04 g L-1 Fe@PC-50 and 0.12 g L-1 PMS, the degradation percentage of sulfadiazine (20 mg L-1) could reach 100 % within 15 min, indicating excellent catalytic activity. Quenching tests and electron paramagnetic resonance (EPR) indicated that both free and non-free radicals played important roles in PMS activation. X-ray photoelectron spectroscopy (XPS) suggested that Fe0 and Fe3C were the possible important active sites for sulfadiazine degradation. This work offered an effective method to synthesize PMS activators from biomass/MOF materials for water treatment.

The Difference in Performance and Compatibility between Crystalline and Amorphous Fillers in Mixed Matrix Membranes for Gas Separation (MMMs)

An increasing number of high-performing gas separation membranes is reported almost on a daily basis, yet only a few of them have reached commercialisation while the rest are still considered pure research outcomes. This is often attributable to a rapid change in the performance of these separation systems over a relatively short time. A common approach to address this issue is the development of mixed matrix membranes (MMMs). These hybrid systems typically utilise either crystalline or amorphous additives, so-called fillers, which are incorporated into polymeric membranes at different loadings, with the aim to improve and stabilise the final gas separation performance. After a general introduction to the most relevant models to describe the transport properties in MMMs, this review intends to investigate and discuss the main advantages and disadvantages derived from the inclusion of fillers of different morphologies. Particular emphasis will be given to the study of the compatibility at the interface between the filler and the matrix created by the two different classes of additives, the inorganic and crystalline fillers vs. their organic and amorphous counterparts. It will conclude with a brief summary of the main findings.

An approach to MOFaxanes by threading ultralong polymers through metal-organic framework microcrystals

Mechanically interlocked architecture has inspired the fabrication of numerous molecular systems, such as rotaxanes, catenanes, molecular knots, and their polymeric analogues. However, to date, the studies in this field have only focused on the molecular-scale integrity and topology of its unique penetrating structure. Thus, the topological material design of such architectures has not been fully explored from the nano- to the macroscopic scale. Here, we propose a supramolecular interlocked system, MOFaxane, comprised of long chain molecules penetrating a microcrystal of metal-organic framework (MOF). In this study, we describe the synthesis of polypseudoMOFaxane that is one of the MOFaxane family. This has a polythreaded structure in which multiple polymer chains thread a single MOF microcrystal, forming a topological network in the bulk state. The topological crosslinking architecture is obtained by simply mixing polymers and MOFs, and displays characteristics distinct from those of conventional polyrotaxane materials, including suppression of unthreading reactions.

Rapid Fabrication of High-Permeability Mixed Matrix Membranes at Mild Condition for CO2 Capture

Mixed matrix membranes (MMMs), conjugating the advantages of flexible processing-ability of polymers and high-speed mass transfer of porous fillers, are recognized as the next-generation high-performance CO₂ capture membranes for solving the current global climate challenge. However, controlling the crystallization of porous metal-organic frameworks (MOFs) and thus the close stacking of MOF nanocrystals in the confined polymer matrix is still undoable, which thus cannot fully utilize the superior transport attribute of MOF channels. In this study, the "confined swelling coupled solvent-controlled crystallization" strategy is employed for well-tailoring the in-situ crystallization of MOF nanocrystals, realizing rapid (<5 min) construction of defect-free freeway channels for CO₂ transportation in MMMs due to the close stacking of MOF nanocrystals. Consequently, the fabricated MMMs exhibit approximately fourfold enhancement in CO₂ permeability, i.e., 2490 Barrer with a CO₂ /N₂ selectivity of 37, distinctive antiplasticization merit, as well as long-term running stability, which is at top-tier level, enabling the large-scale manufacture of high-performance MMMs for gas separation.

Polymer-Infiltrated Metal-Organic Frameworks for Thin-Film Composite Mixed-Matrix Membranes with High Gas Separation Properties

Thin-film composite mixed-matrix membranes (TFC-MMMs) have potential applications in practical gas separation processes because of their high permeance (gas flux) and gas selectivity. In this study, we fabricated a high-performance TFC-MMM based on a rubbery comb copolymer, i.e., poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl] ethyl methacrylate)-co-poly(oxyethylene methacrylate) (PBE), and metal-organic framework MOF-808 nanoparticles. The rubbery copolymer penetrates through the pores of MOF-808, thereby tuning the pore size. In addition, the rubbery copolymer forms a defect-free interfacial morphology with polymer-infiltrated MOF-808 nanoparticles. Consequently, TFC-MMMs (thickness = 350 nm) can be successfully prepared even with a high loading of MOF-808. As polymer-infiltrated MOF is incorporated into the polymer matrix, the PBE/MOF-808 membrane exhibits a significantly higher CO₂ permeance (1069 GPU) and CO₂/N₂ selectivity (52.7) than that of the pristine PBE membrane (CO₂ permeance = 431 GPU and CO₂/N₂ selectivity = 36.2). Therefore, the approach considered in this study is suitable for fabricating high-performance thin-film composite membranes via polymer infiltration into MOF pores.

Topological entrapment of macromolecules during the formation of metal-organic framework

Here we present our preliminary results on a novel approach to encapsulate large guest molecules in nanoporous materials, metal-organic frameworks (MOFs), via a newly discovered in situ crystal formation. This method has exciting prospects not only in the design of new organic/inorganic hybrids but also in capturing and separating molecules that are significantly larger than the actual pore size of the host MOF.

Experimental observation of metal-organic framework-polymer interaction forces and intercalation

We attach a MOF crystallite to an atomic force microscope cantilever to realize a system for rapidly and quantitatively studying the interaction between single-crystal MOFs and polymer films. Using this method, we find evidence of polymer intercalation into MOF pores. This approach can accelerate composite design.

Self-healing mixed matrix membranes containing metal-organic frameworks

Mixed-matrix membranes (MMMs) provide a means to formulate metal-organic frameworks (MOFs) into processable films that can help to advance their use in various applications. Conventional MMMs are inherently susceptible to craze or tear upon exposure to impact, cutting, bending, or stretching, which can limit their intended service life and usage. Herein, a simple, efficient, and scalable in situ fabrication approach was used to prepare self-healing MMMs containing Zr(iv)-based MOFs. The ability of these MMMs to self-heal at room temperature is based on the reversible hydrolysis of boronic-ester conjugates. Thiol-ene 'photo-click' polymerization yielded robust MMMs with ∼30 wt% MOF loading and mechanical strength that varied based on the size of MOF particles. The MMMs could undergo repeated self-healing with good retention of mechanical strength. In addition, the MMMs were catalytically active toward the degradation of the chemical warfare agent (CWA) simulant dimethyl-4-nitrophenyl phosphate (DMNP) with no change in activity after two damage-healing cycles.

Dialytic Synthesis of Two-Dimensional Cu-Based Metal-Organic Frameworks for Gas Separation: Designable MOF-Polymer Interface

We demonstrate a dialytic strategy for the synthesis of congeneric two-dimensional metal-organic framework (2D MOF) nanosheets with a dialysis membrane using 1,4-benzenedicarboxylic acid (BDC), 1,4-naphthalenedicarboxylic acid (NDC), and 9,10-anthracenedicarboxylic acid (ADC) as organic linkers and copper(II) as a metal precursor, respectively. Polyimide (PI) membranes containing these empty 2D MOF nanosheets exhibit distinct molecular sieve effects. Molecular dynamic simulation results reveal that the structures of MOF-polymer interfaces are designable by modifying the MOF interlayer distance and aperture size, which has significant influences on gas permeability and selectivity. As a result, Cu-NDC/PI with the moderate composite interface structure shows superior performance toward H₂/CH₄ and CO₂/CH₄ separations with a selectivity of 199 and 63 over Cu-BDC (121 and 53) and Cu-ADC (135 and 54), respectively.

Microporous water with high gas solubilities

Liquids with permanent microporosity can absorb larger quantities of gas molecules than conventional solvents¹, providing new opportunities for liquid-phase gas storage, transport and reactivity. Current approaches to designing porous liquids rely on sterically bulky solvent molecules or surface ligands and, thus, are not amenable to many important solvents, including water^2-4. Here we report a generalizable thermodynamic strategy to preserve permanent microporosity and impart high gas solubilities to liquid water. Specifically, we show how the external and internal surface chemistry of microporous zeolite and metal-organic framework (MOF) nanocrystals can be tailored to promote the formation of stable dispersions in water while maintaining dry networks of micropores that are accessible to gas molecules. As a result of their permanent microporosity, these aqueous fluids can concentrate gases, including oxygen (O₂) and carbon dioxide (CO₂), to much higher densities than are found in typical aqueous environments. When these fluids are oxygenated, record-high capacities of O₂ can be delivered to hypoxic red blood cells, highlighting one potential application of this new class of microporous liquids for physiological gas transport.

Metal-Organic Frameworks in Mixed-Matrix Membranes for High-Speed Visible-Light Communication

Mixed-matrix membranes (MMMs) based on luminescent metal-organic frameworks (MOFs) and emissive polymers with the combination of their unique advantages have great potential in separation science, sensing, and light-harvesting applications. Here, we demonstrate MMMs for the field of high-speed visible-light communication (VLC) using a very efficient energy transfer strategy at the interface between a MOF and an emissive polymer. Our steady-state and ultrafast time-resolved experiments, supported by high-level density functional theory calculations, revealed that efficient and ultrafast energy transfer from the luminescent MOF to the luminescent polymer can be achieved. The resultant MMMs exhibited an excellent modulation bandwidth of around 80 MHz, which is higher than those of most well-established color-converting phosphors commonly used for optical wireless communication. Interestingly, we found that the efficient energy transfer further improved the light communication data rate from 132 Mb/s of the pure polymer to 215 Mb/s of MMMs. This finding not only showcases the promise of the MMMs for high-speed VLC but also highlights the importance of an efficient and ultrafast energy transfer strategy for the advancement of data rates of optical wireless communication.

Energy Transfer in Metal-Organic Frameworks for Fluorescence Sensing

The development of materials with outstanding performance for sensitive and selective detection of multiple analytes is essential for the development of human health and society. Luminescent metal-organic frameworks (LMOFs) have controllable surface and pore sizes and excellent optical properties. Therefore, a variety of LMOF-based sensors with diverse detection functions can be easily designed and applied. Furthermore, the introduction of energy transfer (ET) into LMOFs (ET-LMOFs) could provide a richer design concept and a much more sensitive and accurate sensing performance. In this review, we focus on the recent five years of advances in ET-LMOF-based sensing materials, with an emphasis on photochemical and photophysical mechanisms. We discuss in detail possible energy transfer processes within a MOF structure or between MOFs and guest materials. Finally, the possible sensing applications of the ET-LMOF-based sensors are highlighted.

Superselective Hg(II) Removal from Water Using a Thiol-Laced MOF-Based Sponge Monolith: Performance and Mechanism

Point-of-use (POU) devices with satisfying mercury (Hg) removal performance are urgently needed for public health and yet are scarcely reported. In this study, a thiol-laced metal-organic framework (MOF)-based sponge monolith (TLMSM) has been investigated for Hg(II) removal as the POU device for its benchmark application. The resulting TLMSM was characterized by remarkable chemical resistance, mechanical stability, and hydroscopicity (>2100 wt %). Importantly, the TLMSM has exhibited high adsorption capacity (∼954.7 mg g^-1), fast kinetics (k_f ∼ 1.76 × 10^-5 ms^-1), broad working pH range (1-10), high selectivity (K_d > 5.0 × 10⁷ mL g^-1), and excellent regeneration capability (removal efficiency >90% after 25 cycles). The high applicability of TLMSM in real-world scenarios was verified by its excellent Hg(II) removal performance in various real water matrices (e.g., surface waters and industrial effluents). Moreover, a fixed-bed column test demonstrated that ∼1485 bed volumes of the feeding streams (∼500 μg L^-1) can be effectively treated with an enrichment factor of 12.6, suggesting the great potential of TLMSM as POU devices. Furthermore, the principal adsorption complexes (e.g., single-layer -S-Hg-Cl and double-layer -S-Hg-O-Hg-Cl and -S-Hg-O-Hg-OH) formed during the adsorption process under a wide range of pH were synergistically and systematically unveiled using advanced tools. Overall, this work presents an applicable approach by tailoring MOF into a sponge substrate to achieve its real application in heavy metal removal from water, especially for Hg(II).

Taguchi-Assisted Optimization Technique and Density Functional Theory for Green Synthesis of a Novel Cu-MOF Derived From Caffeic Acid and Its Anticancerious Activities

In this paper, we have reported an innovative greener method for developing copper-metal organic frameworks (Cu-MOFs) using caffeic acid (CA) as a linker extracted from Satureja hortensis using ultrasonic bath. The density functional theory is used to discuss the Cu-MOF-binding reaction mechanism. In order to achieve a discrepancy between the energy levels of the interactive precursor orbitals, the molecules have been optimized using the B3LYP/6-31G method. The Taguchi method was used to optimize the key parameters for the synthesis of Cu-MOF. FT-IR, XRD, nitrogen adsorption, and SEM analyses are used to characterize it. The adsorption/desorption and SEM analyses suggested that Cu-MOF has a larger surface area of 284.94 m2/g with high porosity. Cu-MOF has shown anticancer activities against the human breast cancer (MDA-MB-468) cell lines, and it could be a potent candidate for clinical applications.

Li+ Dynamics of Liquid Electrolytes Nanoconfined in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are excellent platforms to design hybrid electrolytes for Li batteries with liquid-like transport and stability against lithium dendrites. We report on Li⁺ dynamics in quasi-solid electrolytes consisting in Mg-MOF-74 soaked with LiClO₄-propylene carbonate (PC) and LiClO₄-ethylene carbonate (EC)/dimethyl carbonate (DMC) solutions by combining studies of ion conductivity, nuclear magnetic resonance (NMR) characterization, and spin relaxometry. We investigate nanoconfinement of liquid inside MOFs to characterize the adsorption/solvation mechanism at the basis of Li⁺ migration in these materials. NMR supports that the liquid is nanoconfined in framework micropores, strongly interacting with their walls and that the nature of the solvent affects Li⁺ migration in MOFs. Contrary to the "free'' liquid electrolytes, faster ion dynamics and higher Li⁺ mobility take place in LiClO₄-PC electrolytes when nanoconfined in MOFs demonstrating superionic conductor behavior (conductivity σ_rt > 0.1 mS cm^-1, transport number t_Li⁺ > 0.7). Such properties, including a more stable Li electrodeposition, make MOF-hybrid electrolytes promising for high-power and safer lithium-ion batteries.

Effects of mesoporous silica particle size and pore structure on the performance of polymer-mesoporous silica mixed matrix membranes

The fabrication of mixed matrix membranes (MMMs) has been regarded as an effective and economic approach to enhance the gas permeability and selectivity properties of conventional polymeric membranes for gas separation applications. However, the poor compatibility between polymeric matrix and inorganic filler in MMMs could lead to the generation of interfacial defects resulting in reduced gas selectivity. In this work, with the aim of studying the effect of particle size and pore structure of the filler on the performance of the resultant MMMs, nano/micro sized spherical mesoporous silicas with 2D/3D pore structure (MCM-41 and MCM-48) were synthesized and selected as fillers for the preparation of polydimethylsiloxane (PDMS)-based MMMs. The separation properties of the membranes prepared were characterized by permeability measurements for nitrogen and organic vapors (C₃H₆ and n-C₄H₁₀). Compared with microsized particles, nanosized fillers have better dispersion in the polymer matrix which could minimize the formation of non-selective microvoids around the particles, leading to higher vapor/N₂ ideal selectivities of the MMMs, even at the high loading (15 wt%). Moreover, due to the conventional random packing orientation of the particles in the polymer, vapor permeation was severely hindered in the MMMs fabricated from mesoporous silica with 2D pore channels. The interface morphologies and gas diffusion paths in the MMMs have also been proposed. With an optimum loading of nanosized MCM-48 (3D pore structure), the vapor permeabilities and vapor/N₂ ideal selectivities of the MMMs were shown to increase simultaneously, compared with the neat polymer membrane.

The effects of filler particle size and pore structure on the gas separation performance of mixed matrix membranes were comprehensively investigated via elaborate synthesis of mesoporous silicas.

Revisiting molecular adsorption: unconventional uptake of polymer chains from solution into sub-nanoporous media

Adsorption of polymers from the solution phase has been extensively studied to cope with many demands not only for separation technologies, but also for the development of coatings, adhesives, and biocompatible materials. Most studies hitherto focus on adsorption on flat surfaces and mesoporous adsorbents with open frameworks, plausibly because of the preconceived notion that it is unlikely for polymers to enter a pore with a diameter that is smaller than the gyration diameter of the polymer in solution; therefore, sub-nanoporous materials are rarely considered as a polymer adsorption medium. Here we report that polyethylene glycols (PEGs) are adsorbed into sub-nanometer one-dimensional (1D) pores of metal-organic frameworks (MOFs) from various solvents. Isothermal adsorption experiments reveal a unique solvent dependence, which is explained by the balance between polymer solvation propensity for each solvent and enthalpic contributions that compensate for potential entropic losses from uncoiling upon pore admission. In addition, adsorption kinetics identify a peculiar molecular weight (MW) dependence. While short PEGs are adsorbed faster than long ones in single-component adsorption experiments, the opposite trend was observed in double-component competitive experiments. A two-step insertion process consisting of (1) an enthalpy-driven recognition step followed by (2) diffusion regulated infiltration in the restricted 1D channels explains the intriguing selectivity of polymer uptake. Furthermore, liquid chromatography using the MOFs as the stationary phase resulted in significant PEG retention that depends on the MW and temperature. This study provides further insights into the mechanism and thermodynamics behind the present polymer adsorption system, rendering it as a promising method for polymer analysis and separation.

Metal-Organic Frameworks as Versatile Media for Polymer Adsorption and Separation

Molecular recognition is of paramount importance for modern chemical processes and has now been achieved for small molecules using well-established host-guest chemistry and adsorption-science principles. In contrast, technologies for recognizing polymer structure are relatively undeveloped. Conventional polymer separation methods, which are mostly limited in practice to size-exclusion chromatography and reprecipitation, find it difficult to recognize minute structural differences in polymer structures as such small structural alterations barely influence the polymer characteristics, including molecular size, polarity, and solubility. Therefore, most of the polymeric products being used today contain mixtures of polymers with different structures as it is challenging to completely control polymer structures during synthesis even with state-of-the-art substitution and polymerization techniques. In this context, development of novel techniques that can resolve the challenges of polymer recognition and separation is in great demand, as these techniques hold the promise of a new paradigm in polymer synthesis, impacting not only materials chemistry but also analytical and biological chemistry.In biological systems, precise recognition and translation of base monomer sequences of mRNA are achieved by threading them through small ribosome tunnels. This principle of introducing polymers into nanosized channels can possibly help us design powerful polymer recognition and separation technologies using metal-organic frameworks (MOFs) as ideal and highly designable recognition media. MOFs are porous materials comprising organic ligands and metal ions and have been extensively studied as porous beds for gas separation and storage. Recently, we found that MOFs can accommodate large polymeric chains in their nanopores. Polymer chains can spontaneously infiltrate MOFs from neat molten and solution phases by threading their terminals into MOF nanochannels. Polymer structures can be recognized and differentiated due to such insertion processes, resulting in the selective adsorption of polymers on MOFs. This enables the precise recognition of the polymer terminus structure, resulting in the perfect separation of a variety of terminal-functionalized polymers that are otherwise difficult to separate by conventional polymer separation methods. Furthermore, the MOFs can recognize polymer shapes, thus enabling the large-scale separation of high purity cyclic polymers from the complex crude mixtures of linear polymers, which are used as precursor materials in common cyclization reactions. In solution-phase adsorption, many factors, including molecular weight, terminal groups, polymer shape, polymer-MOF interaction, and coexisting solvent molecules, influence the selective adsorption behavior; this yields a new liquid chromatography-based polymer separation technology using an MOF as the stationary phase. MOF-packed columns, in which a novel separation mode based on polymer insertion into the MOF operates under a dynamic insertion/rejection equilibrium at the liquid/solid interface, exhibited excellent polymer separation capability. The polymer recognition principle described in this study thus has a high probability for realizing previously unfeasible polymer separations based on monomer composition and sequences, stereoregularity, regioregularity, helicity, and block sequences in synthetic polymers and biomacromolecules.

Coordination Polymer Glasses with Lava and Healing Ability for High-Performance Gas Sieving

Coordination polymer (CP) glasses offer a way to tackle the fabrication challenges encountered by inorganic porous membranes and show great potentials for size-exclusive gas separation. However, their processability and performance still cannot simultaneously meet the requirements for high-performance membrane separation. Herein, we have developed a series of CP glasses (M-P-dmbIm, M=Zn, Cd, Cu, and Mn), which possess low vitrification temperature as well as low viscosity (η) and lave capability above the transition temperatures. The derived glass (a_g M-P-dmbIm) membranes show outstanding performances for H₂ /CO₂ , H₂ /N₂ , and H₂ /CH₄ separation, which all far surpass the Robeson upper bound and even rival against the best of the state-of-the-art gas separation membranes. The low viscosities not only allow us to hot-cast or hot-press the CP glasses into thin membranes within 5 min without sacrificing their selectivity and permeability, but also endow the resulted glass membranes with healing ability.

Application of Metal-Organic Framework-Based Composites for Gas Sensing and Effects of Synthesis Strategies on Gas-Sensitive Performance

Gas sensing materials, such as semiconducting metal oxides (SMOx), carbon-based materials, and polymers have been studied in recent years. Among of them, SMOx-based gas sensors have higher operating temperatures; sensors crafted from carbon-based materials have poor selectivity for gases and longer response times; and polymer gas sensors have poor stability and selectivity, so it is necessary to develop high-performance gas sensors. As a porous material constructed from inorganic nodes and multidentate organic bridging linkers, the metal-organic framework (MOF) shows viable applications in gas sensors due to its inherent large specific surface area and high porosity. Thus, compounding sensor materials with MOFs can create a synergistic effect. Many studies have been conducted on composite MOFs with three materials to control the synergistic effects to improve gas sensing performance. Therefore, this review summarizes the application of MOFs in sensor materials and emphasizes the synthesis progress of MOF composites. The challenges and development prospects of MOF-based composites are also discussed.

PEG-stabilized coaxial stacking of two-dimensional covalent organic frameworks for enhanced photocatalytic hydrogen evolution

Two-dimensional covalent organic frameworks (2D COFs) featuring periodic frameworks, extended π-conjugation and layered stacking structures, have emerged as a promising class of materials for photocatalytic hydrogen evolution. Nevertheless, the layer-by-layer assembly in 2D COFs is not stable during the photocatalytic cycling in water, causing disordered stacking and declined activity. Here, we report an innovative strategy to stabilize the ordered arrangement of layered structures in 2D COFs for hydrogen evolution. Polyethylene glycol is filled up in the mesopore channels of a β-ketoenamine-linked COF containing benzothiadiazole moiety. This unique feature suppresses the dislocation of neighbouring layers and retains the columnar π-orbital arrays to facilitate free charge transport. The hydrogen evolution rate is therefore remarkably promoted under visible irradiation compared with that of the pristine COF. This study provides a general post-functionalization strategy for 2D COFs to enhance photocatalytic performances.

Insights into the Enhancement of MOF/Polymer Adhesion in Mixed-Matrix Membranes via Polymer Functionalization

MOF-based mixed-matrix membranes (MMMs) prepared using standard routes often exhibit poor adhesion between polymers and MOFs. Herein, we report an unprecedented systematic exploration on polymer functionalization as the key to achieving defect-free MMMs. As a case study, we explored computationally MMMs based on the combination of the prototypical UiO-66(Zr) MOF with polymer of intrinsic porosity-1 (PIM-1) functionalized with various groups including amidoxime, tetrazole, and N-((2-ethanolamino)ethyl)carboxamide. Distinctly, the amidoxime-derivative PIM-1/UiO-66(Zr) MMM was predicted to express the desired enhanced MOF/polymer interfacial interactions and thus subsequently prepared and evaluated experimentally. Prominently, high-resolution transmission electron microscopy confirmed optimal adhesion between the two components in contrast to the nanometer-sized voids/defects shown by the pristine PIM-1/UiO-66(Zr) MMM. Notably, single-gas permeation measurements further corroborated the need of optimal MOF/polymer adhesion in order to effectively enable the MOF to play a role in the gas transport of the resulting MMM.

Synthesis of Ionic Vinylene-Linked Covalent Organic Frameworks through Quaternization-Activated Knoevenagel Condensation

We developed a simple approach to synthesizing ionic vinylene-linked two-dimensional covalent organic frameworks (COFs) through a quaternization-promoted Knoevenagel condensation at three aromatic methyl carbon atoms of N-ethyl-2,4,6-trimethylpyridinium halide with multitopic aromatic aldehyde derivatives. The resultant COFs exhibited a honeycomb-like structure with high crystallinity and surface areas as large as 1343 m²  g^-1 . The regular shape-persistent nanochannels and the positively charged polymeric frameworks allowed the COFs to be uniformly composited with linear polyethylene oxide and lithium salt, displaying ionic conductivity as high as 2.72×10^-3  S cm^-1 .

Metal-Organic Frameworks for Practical Separation of Cyclic and Linear Polymers

The purification step in the manufacturing of cyclic polymers is difficult as complete fractionation to eliminate linear impurities requires considerable effort. Here, we report a new polymer separation methodology that uses metal-organic frameworks (MOFs) to discriminate between linear and cyclic polyethylene glycols (PEGs) via selective polymer insertion into the MOF nanopores. Preparation of a MOF-packed column allowed analytical and preparative chromatographic separation of these topologically distinct pairs. In addition, gram-scale PEGs with only cyclic structures were successfully obtained from a crude reaction mixture by using MOF as an adsorbent.

Autonomous Self-Healing Strategy for Stable Sodium-Ion Battery: A Case Study of Black Phosphorus Anodes

Autonomic self-healing (SH), namely, the ability to repair damages from mechanical stress spontaneously, is polarizing attention in the field of new-generation electrochemical devices. This property is highly attractive to enhance the durability of rechargeable Li-ion batteries (LIBs) or Na-ion batteries (SIBs), where high-performing anode active materials (silicon, phosphorus, etc.) are strongly affected by volume expansion and phase changes upon ion insertion. Here, we applied a SH strategy, based on the dynamic quadruple hydrogen bonding, to nanosized black phosphorus (BP) anodes for Na-ion cells. The goal is to overcome drastic capacity decay and short lifetime, resulting from mechanical damages induced by the volumetric expansion/contraction upon sodiation/desodiation. Specifically, we developed novel ureidopyrimidinone (UPy)-telechelic systems and related blends with poly(ethylene oxide) as novel and green binders alternative to the more conventional ones, such as polyacrylic acid and carboxymethylcellulose, which are typically used in SIBs. BP anodes show impressively improved (more than 6 times) capacity retention when employing the new SH polymeric blend. In particular, the SH electrode still works at a current density higher than 3.5 A g^-1, whereas the standard BP electrode exhibits very poor performances already at current densities lower than 0.5 A g^-1. This is the result of better adhesion, buffering properties, and spontaneous damage reparation.

Potential utility of HKUST-1-graphite nanocomposite to endow alkane with high thermal properties and low electrical resistivity

It is desirable to develop novel multipurpose phase change materials (PCMs) with improved energy storage and release characteristics. In this study, the utility of a nanocomposite composed of a metal-organic framework (MOF) and graphite was explored for shape-stable PCMs. The prepared MOF-integrated graphite featured favorable structural characteristics (such as large specific surface area (550.6 m²/g), increased total pore volume, and dominant mesopore structure). The obtained composite with a high energy storage capacity (111.4 J/g) exhibited an electrical resistivity that was at least 7 orders of magnitude lower than that of the pristine PCM. In addition, the alkane possessed enhanced chemical compatibility with the supporting scaffolds, outstanding shape, and thermal stabilities. The strong structural connectivity, high specific surface area, and pore size distributions (micro/mesopores) of the scaffolds play a remarkable role in large PCM infiltration ratio, high electrical conductivity, and improved thermal properties of as-prepared composites. It was also suggested that the cavities of the MOF, filled with graphite and the π-π interactions between strand ligands, generate favorable pathways in the nanocomposites. Subsequently creates a supramolecular "wire-like" paths and reduce the resistivity of the parent materials. Therefore, this multifunctional material shows the potential for applications in electro/thermal energy management systems.

Scalable crystalline porous membranes: current state and perspectives

Crystalline porous materials (CPMs) with uniform and regular pore systems show great potential for separation applications using membrane technology. Along with the research on the synthesis of precisely engineered porous structures, significant attention has been paid to the practical application of these materials for preparation of crystalline porous membranes (CPMBs). In this review, the progress made in the preparation of thin, large area and defect-free CPMBs using classical and novel porous materials and processing is presented. The current state-of-the-art of scalable CPMBs with different nodes (inorganic, organic and hybrid) and various linking bonds (covalent, coordination, and hydrogen bonds) is revealed. The advances made in the scalable production of high-performance crystalline porous membranes are categorized according to the strategies adapted from polymer membranes (interfacial assembly, solution-casting, melt extrusion and polymerization of CPMs) and tailored based on CPM properties (seeding-secondary growth, conversion of precursors, electrodeposition and chemical vapor deposition). The strategies are compared and ranked based on their scalability and cost. The potential applications of CPMBs have been concisely summarized. Finally, the performance and challenges in the preparation of scalable CPMBs with emphasis on their sustainability are presented.

Tuning the Ion-Selectivity of Thin-Film Composite Nanofiltration Membranes by Molecular Layer Deposition of Alucone

This work addresses a key challenge of tailoring the ion selectivity of a thin-film composite nanofiltration membrane to a specific application, such as water softening, without altering the water permeability. We modified the active surface of a commercial NF270 membrane by molecular layer deposition (MLD) of ethylene glycol-Al (EG-alucone). With increasing deposition cycles, we found that the MLD precursors first infiltrated and deposited in the active layer of NF270, then inflated the active layer, and finally deposited on the surface as a distinct EG-alucone layer. The deposition process changed the morphology of the membrane active layer and decreased the overall density of its fixed negative charge by embedding the positively charged EG-alucone. Filtration experiments revealed that these modifications affected the ion separation properties of the membrane without significantly hindering the water permeability. Specifically, the permeation of Na⁺ increased relative to that of Mg²⁺, as indicated by the permselectivity of Na⁺ salts over Mg²⁺ salts. The changes in permselectivities with an increasing number of MLD cycles were rationalized using the dielectric, steric, and electrostatic ion exclusion mechanisms, which are related to the membrane material, pore size, and fixed charge, respectively. These relations open a path for the rational design of nanofiltration membranes with tailored selectivity by tuning the properties of the MLD layer. Filtration results of natural brackish groundwater using the MLD modified membranes agreed with the single salt experiments. As a result, water hardness was 26% lower for the permeate obtained using the MLD-modified membranes, which were found stable even during a 24 h filtration run. These results highlight the practical potential of this approach in enhancing water softening efficiency.