Permselective metal-organic framework gel membrane enables long-life cycling of rechargeable organic batteries

Rechargeable organic batteries show great potential as a low-cost, sustainable and mass-producible alternatives to current transition-metal-based cells; however, serious electrode dissolution issues and solubilization of organic redox intermediates (shuttle effect) have plagued the capacity retention and cyclability of these cells. Here we report on the use of a metal-organic framework (MOF) gel membrane as a separator for organic batteries. The homogeneous micropores, intrinsic of the MOF-gel separator, act as permselective channels for targeted organic intermediates, thereby mitigating the shuttling problem without sacrificing power. A battery using a MOF-gel separator and 5,5'-dimethyl-2,2'-bis-p-benzoquinone (Me₂BBQ) as the electrode displays high cycle stability with capacity retention of 82.9% after 2,000 cycles, corresponding to a capacity decay of ~0.008% per cycle, with a discharge capacity of ~171 mA h g^-1 at a current density of 300 mA g^-1. The molecular and ionic sieving capabilities of MOF-gel separators promise general applicability, as pore size can be tuned to specific organic electrode materials. The use of MOF-gel separators to prevent side reactions of soluble organic redox intermediates could lead to the development of rechargeable organic batteries with high energy density and long cycling life.

Hydrophobicity-Adjustable MOF Constructs Superhydrophobic MOF-rGO Aerogel for Efficient Oil-Water Separation

Accurate hydrophobicity adjustment of single-phase material is quite challenging and meaningful for water treatment. Here, a strategy combining crystal morphology regulation and post-synthetic modification is reported based on a novel metal-organic framework (MOF, Eu-bdo-COOH, H₄bdo = 2,5-bis(3,5-dicarboxylphenyl)-1,3,4-oxadiazole). The hydrophobicity is regulated by crystal size and morphology regulation, and a rough microspherical MOF is successfully synthesized. Meanwhile, the obtained MOF microspheres exhibit high water, chemical, and thermal stability. The post-synthetic modification of alkyl chains achieves fine-tuning of hydrophobicity of MOF microspheres. The static water contact angles can controllably range from 43 to 142°, and the amylamine-modified MOF (AM) obtains the strongest hydrophobicity. In addition, a superhydrophobic aerogel is constructed with AM microspheres and reduced graphene oxide (rGO) for efficient oil-water separation. The AM-rGO aerogel (AM-rGA) exhibits fast and efficient absorption of various oily substances from water, and the adsorption capacity of dibromoethane reaches up to 14,728 wt %. This outstanding oil adsorption capacity can maintain even beyond 50 cycles by the support of the stable aerogel. The strategy of morphology regulation and post-synthetic modification provides a broad approach for the hydrophobic adjustment of numerous MOF materials.

Preparation of MOF Film/Aerogel Composite Catalysts via Substrate-Seeding Secondary-Growth for the Oxygen Evolution Reaction and CO2 Cycloaddition

Substrate-supported metal-organic frameworks (MOFs) films are desired to realize their potential in practical applications. Herein, a novel substrate-seeding secondary-growth strategy is developed to prepare composites of uniform MOFs films on aerogel walls. Briefly, the organic ligand is "pre-seeded" onto the aerogel walls, and then a small amount of metal-ion solution is sprayed onto the prepared aerogel. The sprayed solution diffuses along the aerogel walls to form a continuous thin layer, which confines the nucleation reaction, promoting the formation of uniform MOFs films on the aerogel walls. The whole process is simple in operation, highly efficient, and eco-friendly. The resulting hierarchical MOFs/aerogel composites have abundant accessible active sites and enable excellent mass transfer, which endows the composite with outstanding catalytic activity and stability in both liquid-phase CO₂ cycloaddition and electrochemical oxygen evolution reaction (OER) process.

A Robust Mixed-Lanthanide PolyMOF Membrane for Ratiometric Temperature Sensing

Temperature sensors play a significant role in biology, chemistry, and engineering, especially those that can work accurately in a noninvasive manner. We adopted a photoinduced post-synthetic copolymerization strategy to realize a membranous ratiometric luminescent thermometer based on the emissions of two lanthanide ions. This novel mixed-lanthanide polyMOF membrane exhibits not only the integrity and temperature sensing behaviour of the Ln-MOF powder but also excellent mechanical properties, such as flexibility, elasticity, and processability. Moreover, the polyMOF membrane shows remarkable stability under harsh conditions, including high humidity, strong acid and alkali (pH 0-14), which allowed the mapping of temperature distributions in extreme circumstances. This work highlights a simple strategy for polyMOF membrane formation and pushes forward the further practical application of Ln-MOF-based luminescent thermometers in various fields and conditions.

Hierarchical Graphene/Metal-Organic Framework Composites with Tailored Wettability for Separation of Immiscible Liquids

Membrane filtration is a promising technology for the separation of organic immiscible liquids. Surface topography has a direct impact on the wettability of membranes, and it remains largely unexplored. Here, we introduce on-demand liquid separation by coating porous graphene/metal-organic framework (MOF) composites with tunable wettability on porous substrates. Our results have shown that polydopamine (PDA) coating mediates the controlled growth of MOF nanostructures and subsequent fluorination on the porous graphene framework. Surface topography of the graphene frameworks strongly depends on the loading content of MOF nanostructures. The concurrent control of surface coverage of MOF and surface chemistry allows tailoring of the trapped air fraction underneath the porous graphene frameworks in the range of 0.97 to 0.8. As a result, the surface energy of the graphene/MOF coatings can be programmed to afford the change in surface properties from superamphiphobicity to lyophobicity and the selective penetration of low-surface-energy (SE) liquids and the interception of high-SE liquids were achieved. The tailored wettability of graphene/MOF coatings allows for the separation of liquid mixtures of different ranges of SE, making it a general strategy for complex liquid treatment and chemical purification.

Metal-Organic Material Polymer Coatings for Enhanced Gas Sorption Performance and Hydrolytic Stability under Humid Conditions

Physisorbent metal-organic materials (MOMs) have shown benchmark performance for highly selective CO₂ capture from bulk and trace gas mixtures. However, gas stream moisture can be detrimental to both adsorbent performance and hydrolytic stability. One of the most effective methods to solve this issue is to transform the adsorbent surface from hydrophilic to hydrophobic. Herein, we present a facile approach for coating MOMs with organic polymers to afford improved hydrophobicity and hydrolytic stability under humid conditions. The impact of gas stream moisture on CO₂ capture for the composite materials was found to be negligible under both bulk and trace CO₂ capture conditions with significant improvements in regeneration times and energy requirements.

Surface-coordinated metal-organic framework thin films (SURMOFs) for electrocatalytic applications

The design and development of highly efficient electrocatalysts are very important in energy storage and conversion. As a kind of inorganic organic hybrid material, metal-organic frameworks (MOFs) have been used as electrocatalysts in electrocatalytic reactions due to their structural diversities and fascinating functionalities. Particularly, MOF thin films are coordinated on substrate surfaces by a liquid phase epitaxial (LPE) layer by layer (LBL) growth method (called surface-coordinated MOF thin films, SURMOFs), and recently have been studied in various applications due to their precisely controlled thickness, preferred growth orientation and homogeneous surface. In this review, we will summarize the preparation and electrocatalysis of SURMOFs and their derived thin films (SURMOF-D). The SURMOF based thin films possess diverse topological structures and flexible properties, providing abundant catalytically active sites and fast charge transfer for efficient electrocatalytic performance in the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CRR), supercapacitors, tandem electrocatalysis and so on. The research challenges and problems of SURMOFs for electrocatalytic applications are also discussed at the end of the review.

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

Metal-Organic Complexes@Melamine Foam Template Strategy to Prepare Three-Dimensional Porous Carbon with Hollow Spheres Structures for Efficient Organic Vapor and Small Molecule Gas Adsorption

Three-dimensional (3D) porous carbon materials have received substantial attention owing to their unique structural features. However, the synthesis of 3D porous carbon, especially 3D porous carbon with hollow spheres structures at the connection points, still pose challenges. Herein, we first develop a metal-organic complexes@melamine foam (MOC@MF) template strategy, by using hot-pressing and carbonization method to synthesize 3D porous carbon with hollow spheres structures (denoted as NOPCs). The formation mechanism of NOPCs can be attributed to the difference in Laplace pressure and surface energy gradient between the carbonized MOC and carbonized MF. These rare 3D porous carbons exhibit high BET surface area (2453.8 m² g^-1), N contents (10.5%), and O contents (16.3%). Moreover, NOPCs show significant amounts of toluene and methanol at room temperature, reaching as high as 1360 and 1140 mg g^-1. The adsorption amounts of SO₂ and CO₂ for NOPCs are up to 93.1 and 445 mg g^-1. Theoretical calculation indicates surfaces of porous carbon with N and O coexistence could strongly enhance adsorption with high adsorption energy of -65.83 kJ mol g^-1.

Vapor-phase linker exchange of metal-organic frameworks

Metal-organic frameworks (MOFs) have been attracting intensive attention because of their commendable potential in many applications. Postsynthetic modification for redesigning chemical characteristics and pore structures can greatly improve performance and expand functionality of MOF materials. Here, we develop a versatile vapor-phase linker exchange (VPLE) methodology for MOF modification. Through solvent-free and environment-friendly VPLE processing, various linker analogs with functional groups but not for straightforward MOF crystallization are inserted into frameworks as daughter building blocks. Besides single exchange for preparing MOFs with dual linkers, VPLE can further be performed by multistage operations to obtain MOF materials with multiple linkers and functional groups. The halogen-incorporated ZIFs exhibit good porosity, tunable molecular affinity, and impressive CO₂/N₂ and CH₄/N₂ adsorption selectivities up to 31.1 and 10.8, respectively, which are two to six times higher than those of conventional adsorbents. Moreover, VPLE can substantially enhance the compatibility of MOFs and polymers.

Practical MOF Nanoarchitectonics: New Strategies for Enhancing the Processability of MOFs for Practical Applications

Over the past decades, the development of porous materials has directly or indirectly affected industrial production methods. Metal-organic frameworks (MOFs) as an emerging class of porous materials exhibit some unique advantages, including controllable composition, a large surface area, high porosity, and so on. These attractive characteristics of MOFs have led to their potential applications in energy storage and conversion devices, drug delivery, adsorption and storage, sensors, and other areas. However, powdered MOFs have limited practical applications owing to poor processability, safety hazards from dust formation, and poor recyclability. In addition, the inherent micro/mesoporosities of MOFs also reduce the accessibility and diffusion kinetics for large molecules. To improve their processability for practical applications, MOFs are often deposited as MOF layers or films (i.e., MOF-coated composites) on supporting materials or are formed into 3D structured composites, such as aerogels and hydrogels. In this article, we review recent researches on these MOF composites, including their synthetic methods and potential applications in energy storage devices, heavy metal ion adsorption, and water purification. Finally, the future outlook and challenges associated with the large-scale fabrication of MOF-based composites for practical applications are discussed.

Regulating Hydrogenation Chemoselectivity of α,β-Unsaturated Aldehydes by Combination of Transfer and Catalytic Hydrogenation

Two hydrogenation mechanisms, transfer and catalytic hydrogenation, were combined to achieve higher regulation of hydrogenation chemoselectivity of cinnamyl aldehydes. Transfer hydrogenation with ammonia borane exclusively reduced C=O bonds to get cinnamyl alcohol, and Pt-loaded metal-organic layers efficiently hydrogenated C=C bonds to synthesize phenyl propanol with almost 100 % conversion rate. The hydrogenation could be performed under mild conditions without external high-pressure hydrogen and was applicable to various α,β-unsaturated aldehydes.

Metal–Organic Framework Thin Films: Fabrication, Modification, and Patterning

Metal–organic frameworks (MOFs) have been of great interest for their outstanding properties, such as large surface area, low density, tunable pore size and functionality, excellent structural flexibility, and good chemical stability. A significant advancement in the preparation of MOF thin films according to the needs of a variety of applications has been achieved in the past decades. Yet there is still high demand in advancing the understanding of the processes to realize more scalable, controllable, and greener synthesis. This review provides a summary of the current progress on the manufacturing of MOF thin films, including the various thin-film deposition processes, the approaches to modify the MOF structure and pore functionality, and the means to prepare patterned MOF thin films. The suitability of different synthesis techniques under various processing environments is analyzed. Finally, we discuss opportunities for future development in the manufacturing of MOF thin films.

Highly Stable Zinc-Based Metal-Organic Frameworks and Corresponding Flexible Composites for Removal and Detection of Antibiotics in Water

Antibiotic contamination of water bodies is a major environmental concern. Exposure to superfluous antibiotics is an ecological stressor correlated to the development of antibiotic resistance. Thus, it is imperative that effective methods are developed to simultaneously detect and remove such antibiotics so as to avoid inadvertent release. Herein, two flexible three-dimensional (3D) zinc-based metal-organic frameworks (MOFs) {[Zn₂(bcob)(OH)(H₂O)]·DMA}_n (ROD-Zn1) and {[Zn(Hbcob)]·(solvent)}_n (ROD-Zn2) (H₃bcob = 1,3-bis((4'-carboxylbenzyl)oxy)benzoic acid) with rod second building units (SBUs) are successfully prepared. Their exceptional water and chemical stabilities (toward both acid and base), fast sorption kinetics, and unique framework endow the MOFs with excellent uptake capacity toward various antibiotics in the aqueous environment. The adsorption performance was further optimized by one-pot preparation of MOF-melamine foam (MF) hybrid composites, resulting in a hierarchical microporous-macroporous MOF@MF system (ROD-Zn1@MF and ROD-Zn2@MF), which are readily recyclable after adsorptive capture. The mechanisms of adsorption have been deeply investigated by static and competitive adsorption experiments. In addition, the MOFs exhibit excellent fluorescent properties and quenched by trace amounts of antibiotics in water solution. Therefore, ROD-Zn1 and ROD-Zn2 present a dual-functional performance, being promising candidates for detection and removal of antibiotics.

Zeolitic Imidazolate Framework-8/Polypropylene-Polycarbonate Barklike Meltblown Fibrous Membranes by a Facile in Situ Growth Method for Efficient PM2.5 Capture

Environmental pollution, especially air pollution, seriously endangers public health globally. Due to severe air pollution, air filters still face many challenges, especially in terms of filtration performance and filtration stability. Herein, a zeolitic imidazolate framework-8/polypropylene-polycarbonate barklike meltblown fibrous membrane (PPC/ZIF-8) was designed through meltblown and an in situ growth method, achieving efficient PM_2.5 capture and high filtration stability under a harsh environment. After in situ growth, the PPC/ZIF-8 membrane could dramatically enhance the PM_2.5 filtration efficiency without increasing the pressure drop; the PM_2.5 filtration efficiency and quality factor were up to 32.83 and 116.86% higher than those of the pure PPC membrane, respectively. Moreover, through five filtration-wash-dry cycles, the PM_2.5 filtration performance is still at a high level. This PPC/ZIF-8 membrane provides a new strategy for the preparation of an air filter with excellent comprehensive filtration performance.

Nature-inspired chemistry toward hierarchical superhydrophobic, antibacterial and biocompatible nanofibrous membranes for effective UV-shielding, self-cleaning and oil-water separation

Fabrication of environmental-friendly, low-cost, and free-standing superhydrophobic nanofibrous membranes with additional functionalities such as self-cleaning and UV-shielding properties is highly demanded for oil-water separation. Herein, we describe the preparation of multifunctional superhydrophobic nanofibrous membrane by using a facile and novel nature-inspired method, i.e., plant polyphenol (tannic acid) metal complex is introduced to generate rough hierarchical structures on the surface of an electrospun polyimide (PI) nanofibrous membrane, followed by modification of poly (dimethylsiloxane) (PDMS). Taking an as-prepared tannic acid - Al³⁺-based superhydrophobic membrane as an example, it not only exhibits anti-impact, low-adhesive and self-cleaning functions, but also presents excellent performance in the separation of various oil-water mixtures. A high flux up to 6935 l m^-2 h^-1 with a separation efficiency of over 99% and the oil contents in water below 5 ppm is obtained even after repeating use for twenty separation cycles. Additionally, the membrane exhibits excellent UV-shielding property, attributing to the inherent UV-absorbing ability of tannic acid. Furthermore, the membrane also possesses additional properties including antibacterial activity, good biocompatibility, robust mechanical strength, and excellent resistance to various harsh conditions. These attractive properties of the as-prepared membrane make it a promising candidate for potential applications in industrial oil-contaminated water treatments and oil-water separation.

Localized Electrical Induction Heating for Highly Efficient Synthesis and Regeneration of Metal-Organic Frameworks

Based on carbon fibers (CFs) delivered localized electrical induction heat, a novel electrical induction framework synthesis (EIFS) strategy has been developed to in-situ grow versatile metal-organic frameworks (MOFs) on CFs, resulting in the production of a set of MOF-coated CF (MOF@CF) fibers. Detailed studies on the production of UiO-66-NH₂@CFs indicate that the use of EIFS leads to dramatically accelerated MOF growth at dozen times higher reaction rate than that of the conventional solvothermal reaction. By periodically switching anodes during EIFS reactions, uniform MOF@CF fibers with well-controlled MOF loadings have been achieved depending on the reaction conditions. Mediated by the embedded CFs in the resulting MOF@CFs, MOF@CFs exhibit well-regulated electrical induction heating capacities depending on MOF loadings and the applied voltages. Driven by such localized heat, up to 100% of the adsorbed CO₂ in UiO-66-NH₂@CF can be rapidly released, demonstrating an electrical induction framework regeneration (EIFR) process for highly efficient regeneration of MOFs. As CFs enable to rapidly deliver localized electrical induction with over 90% of electrothermal conversion efficiency and at rather low operation voltage, currently developed EIFS and EIFR process provide a highly efficient, low-energy, low operation cost, and safe way to highly efficient synthesis and regeneration of MOF materials.

Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

We give a comprehensive overview of how the morphology control is an effective and versatile way to control the physicochemical properties of metal oxides that can be transferred to metal–organic frameworks and porous carbon materials.

3D Printing of Mixed Matrix Films Based on Metal-Organic Frameworks and Thermoplastic Polyamide 12 by Selective Laser Sintering for Water Applications

The fabrication of metal-organic framework (MOF)-based macro-materials is considered as a promising strategy toward the practical applications of powdered MOF crystals. In this study, selective laser sintering (SLS), an advanced three-dimensional (3D) powder printing technique, has been employed to fabricate MOF-polymer mixed matrix films (MMFs) by using thermoplastic polyamide 12 (PA12) powder as the matrix material and five types of MOFs including ZIF-67, NH₂-MIL-101(Al), MOF-801, HKUST-1, and ZIF-8 crystals as the fillers. A three-layer HKUST-1-PA12 complex with a grid pattern is fabricated to demonstrate the printability of 3D MOF-polymer structure. Single-layer MMFs with grid patterns are printed by using the five types of MOF fillers with different mass loadings to study their free-standing characteristic, thickness, specific surface area, hydrophilia, water permeate flux, and mechanical stability. The methylene blue (MB) adsorption tests are conducted using the NH₂-MIL-101(Al)-PA12 MMFs with different grid patterns to exemplify the applications of the MMFs for water purification. It is confirmed that the MOF components retain their high maximum adsorption capacity, and the printed MMFs can be conveniently regenerated for cyclic utilization. This work provides an insight into the utilization of advanced 3D printing technology to manufacture macro-MOF-polymer materials for practical applications.

Facile and Scalable Coating of Metal-Organic Frameworks on Fibrous Substrates by a Coordination Replication Method at Room Temperature

Coating of metal-organic frameworks (MOFs) on flexible substrates is a crucial technology for applications such as purification/separation, sensing, and catalysis. In this work, a facile coordination replication strategy was developed to coat various MOFs onto flexible fibrous materials where a dense layer of an insoluble precursor template, such as a layered hydroxide salt, was first deposited onto a fiber substrate via a mild interfacial reaction and then rapidly transformed into a MOF coating in a ligand solution at room temperature. Spatiotemporal harmonization of solid precursor dissolution and MOF crystallization enabled precise replication of the precursor layer morphology to form a continuous MOF coating composed of intergrown crystals. The resulting flexible, highly robust, and processable fibrous MOF/textile composites demonstrated tremendous potential for industrially relevant applications such as continuous removal of the organosulfur compound dibenzothiophene from simulated gasoline and ammonia capture. This rapid, versatile, eco-friendly, and scalable MOF coating process at room temperature gives rise to new possibilities for preparing MOF-coated functional materials.

Rising Up: Hierarchical Metal-Organic Frameworks in Experiments and Simulations

Controlled synthesis across several length scales, ranging from discrete molecular building blocks to size- and morphology-controlled nanoparticles to 2D sheets and thin films and finally to 3D architectures, is an advanced and highly active research field within both the metal-organic framework (MOF) domain and the overall material science community. Along with synthetic progress, theoretical simulations of MOF structures and properties have shown tremendous progress in both accuracy and system size. Further advancements in the field of hierarchically structured MOF materials will allow the optimization of their performance; however, this optimization requires a deep understanding of the different synthesis and processing techniques and an enhanced implementation of material modeling. Such modeling approaches will allow us to select and synthesize the highest-performing structures in a targeted rational manner. Here, recent progress in the synthesis of hierarchically structured MOFs and multiscale modeling and associated simulation techniques is presented, along with a brief overview of the challenges and future perspectives associated with a simulation-based approach toward the development of advanced hierarchically structured MOF materials.

Metal-Organic Framework Films and Their Potential Applications in Environmental Pollution Control

Metal-organic frameworks (MOFs), an emerging class of porous hybrid inorganic-organic crystals, exhibit very important application prospects in gas storage and separation, heterogeneous catalysis, sensing, drug release, environmental decontamination, etc., due to their competitive advantages over other traditional porous materials (e.g., activated carbon and zeolite), including high surface areas, adjustable pore size, uniformly distributed metal centers, and tunable functionalities. However, MOF particles are usually difficult to be processed into application-specific devices because of their brittleness, insolubility, difficulty in molding, and low compatibility with other materials. It is an urgent need to shape MOF nanocrystals into various useful configurations by developing effective fabrication methods. Specifically, versatile functional MOF films with robustness and operation flexibility are highly desired. Although an increasing number of MOF films and their diverse applications have been demonstrated, this field is still at an emerging stage with challenging issues. In this Account, we describe our recent research progress on controllable synthesis of MOF films, highlighting postsynthetic polymerization, in situ interweaving, and solvent-free hot-pressing methods. Basically, two main synthesis concepts are involved, including incorporation of the performed MOF particles into polymer matrix and in situ growth of MOF coatings on surface. In MOF/polymer hybrid films, MOF nanocrystals were covalently linked by flexible polymer chains via graft copolymerization, interconnected by functional polymer chains via in situ polymerization, or adhered to polymer matrix via specific interactions at interface, consequently leading to a molecular-level homogeneous membrane or functional coating layer or foam. In these examples, the existence of polymer endows MOF films with favorable features of processability and flexibility, along with new functions. Moreover, we developed an in situ solvent-free hot-pressing method as a general approach for efficient fabrication of MOF coatings on various commercial substrates (e.g., cloth and metal foils), where metal ions or ligands were chemically bonded to the surface functional groups or metal sites at the early stage of nucleation and subsequently assembled into continuous, uniform, and stable MOF layers under confined conditions. We further extended it to a scalable manufacturing method, roll-to-roll production. MOF films severing as filters (MOFilters) have significant applications in air and water purification. They show high and stable performance in PM capture along with a low pressure drop, holding promise of application in both industrial and residential environments. Moreover, MOFilters can remove SO₂ and O₃ from air by adsorption and catalytic decomposition, respectively. Given the functional diversity of MOFs, mixed pollutants in solution could also be efficiently trapped by multifunctional MOF hollow tubes. We believe this Account will offer new insights for design and preparation of functional MOF films and coatings and accelerate the practical applications of MOFs.

Metal-organic frameworks with photocatalytic bactericidal activity for integrated air cleaning

Air filtration has become an essential need for passive pollution control. However, most of the commercial air purifiers rely on dense fibrous filters, which have good particulate matter (PM) removal capability but poor biocidal effect. Here we present the photocatalytic bactericidal properties of a series of metal-organic frameworks (MOFs) and their potentials in air pollution control and personal protection. Specifically, a zinc-imidazolate MOF (ZIF-8) exhibits almost complete inactivation of Escherichia coli (E. coli) (>99.9999% inactivation efficiency) in saline within 2 h of simulated solar irradiation. Mechanistic studies indicate that photoelectrons trapped at Zn⁺ centers within ZIF-8 via ligand to metal charge transfer (LMCT) are responsible for oxygen-reduction related reactive oxygen species (ROS) production, which is the dominant disinfection mechanism. Air filters fabricated from ZIF-8 show remarkable performance for integrated pollution control, with >99.99% photocatalytic killing efficiency against airborne bacteria in 30 min and 97% PM removal. This work may shed light on designing new porous solids with photocatalytic antibiotic capability for public health protection.

Personal protective air filtration masks are becoming increasingly desirable, but most commercial air purifiers have poor biocidal capabilities. Here the authors fabricate metal–organic framework-based air filters with both high particulate matter removal efficiencies and photocatalytic bactericidal properties.

Textiles/Metal-Organic Frameworks Composites as Flexible Air Filters for Efficient Particulate Matter Removal

The health-threatening air pollution, especially from particulate matter (PM), has triggered increasing demands for developing low-cost and long-service-life air-cleaning technologies. In the present contribution, a range of high-efficiency textiles/metal-organic framework (MOF) composites (MOFs@textiles) air filters with excellent washable reusability is presented. By processing MOFs onto textile substrates via an eco-friendly solvent-free method to enable the microporous feature and also strong PM adhesion, we develop flexible, highly effective air filters with >95.00% PM removal efficiency (e.g., MiL-53(Al)@Aramid, PM_2.5: 95.30%, PM₁₀: 96.11%) under harmful air quality conditions (average PM_2.5 mass concentration > 280 μg m^-3 and PM₁₀ > 360 μg m^-3). Therefore, these MOFs@textiles are promising composites for producing efficient and recyclable out-/indoor air purifiers.

A new post-synthetic polymerization strategy makes metal-organic frameworks more stable

Metal-organic frameworks are of interest in a number of host-guest applications. However, their weak coordination bonding often leads to instability in aqueous environments, particularly at extreme pH, and hence, is a challenging topic in the field. In this work, a two-step, post-synthetic polymerization method is used to create a series of highly hydrophobic, stable MOF composites. The MOFs are first coated with thin layers of polydopamine from free-base dopamine under a mild oxygen atmosphere, which then undergoes a Michael addition to covalently graft hydrophobic molecules to the external MOF surface. This easy, mild post-synthetic modification is shown to significantly improve the stability of a number of structurally diverse MOFs including HKUST-1 (Cu), ZIF-67 (Co), ZIF-8 (Zn), UiO-66 (Zr), Cu-TDPAT (Cu), Mg-MOF-74 (Mg) and MIL-100 (Fe) in wet, caustic (acidic and basic) environments as determined by powder X-ray diffraction and surface area measurements.

Free-standing graphene oxide membrane with tunable channels for efficient water pollution control

In this study, a graphene oxide (GO) membrane with tunable interlayer spacing was fabricated by a facile method combining the inter-layer modification with external treatment. Congo red (CR), a negatively charged dye with π-orbital-rich groups, was adsorbed on nonoxide regions (G regions) of GO nano-sheets; thus, the interlayers were cross-linked by Ca²⁺ ions through chelating reaction. GO@CR nano-sheets π-π stacking interactions were changed by thermal reduction of the GO/Ca/CR membrane using a hot-pressing method. A broader effective inter-layer spacing control of the GO membrane in wet condition was achieved (from 7.7 ± 0.2 Å to 11.7 ± 0.25 Å). With the decrease of effective inter-layer spacing, the rejection of dyes and heavy metal ions gradually increased (i.e., methylene blue (99.5%), Cu²⁺ (98.6%), Ni²⁺ (97.2%), Pb²⁺ (97.2%) and Cd²⁺ (99.1%) at 7.7 Å) and a sufficient permeation flux was also achieved (17.1 L/m²·h·bar). Meanwhile, the diffusion mechanism of water molecules inside the interlayer gallery of GO laminates was explored by climbing image nudged elastic band (cNEB) method. The hydrogen bonding between water molecules and hydroxyl groups constrained the diffusion of water molecules; consequently, partially reduced hybrid GO membrane can show a better permeability for water and superior rejection for heavy metal ions.

Superhydrophobic/Superoleophilic MOF Composites for Oil-Water Separation

A universal strategy is developed to construct metal-organic framework (MOF)-based superhydrophobic/superoleophilic materials by the reaction of activated MOFs and octadecylamine. In particular, S-MIL-101(Cr) composite can efficiently separate chloroform, toluene, petroleum ether, and n-hexane from water with excellent oil-water separation performance, with potential application in the environmental field.

Preparation of a ZIF-67 Derived Thin Film Electrode via Electrophoretic Deposition for Efficient Electrocatalytic Oxidation of Vanillin

The electrophoretic deposition method is employed to deposit uniform metal organic framework thin films. ZIF-67 particles dispersed in isopropanol move to a cathode as an electric field is applied on two conducting glass electrodes, the uniform ZIF-67 thin film can be formed on the conducting glass substrate. As the deposition time is fixed at 1 min, the prepared film thickness can be adjusted from 1.0 to 7.0 μm by applying different electric fields from 20 to 60 V·cm^-1. The deposited ZIF-67 thin film is further converted into porous Co₉S₈ thin films by the vulcanization with S powder. The porous thin films vulcanized at different temperatures are characterized by the measurements of scanning electron microscope, X-ray photoelectron spectroscopy, X-ray powder diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectra. The prepared porous Co₉S₈ thin films are used as the thin film electrode to catalyze the degradation of vanillin. The Co₉S₈ thin film vulcanized at 500 °C shows better catalytic performance than the bare glassy carbon electrode and the electrodes vulcanized at other temperatures. The electrocatalytic degradation enhancement mechanism is analyzed by the measurements of Tafel curves and electrochemical impedance spectroscopies. It can be developed as a feasible method for the electrocatalytic detection of vanillin.

Novel metal–organic framework materials: blends, liquids, glasses and crystal–glass composites

This Feature Article reviews a range of amorphisation mechanisms of Metal–Organic Frameworks (MOFs) and presents recent advances to produce novel MOF materials including porous MOF glasses, MOF crystal–glass composites, flux melted MOF glasses and blended zeolitic imidazolate framework glasses.

Mechanochemically synthesized MgAl layered double hydroxide nanosheets for efficient catalytic removal of carbonyl sulfide and H2S

Mechanochemically prepared MgAl-LDH nanosheets with high crystallinity and large surface areas show excellent activities in COS hydrolysis and H₂S oxidation.

Chemical Protective Textiles of UiO-66-Integrated PVDF Composite Fibers with Rapid Heterogeneous Decontamination of Toxic Organophosphates

Metal-organic frameworks (MOFs) are a new and growing area of materials with high porosity and customizability. UiO-66, a zirconium-based MOF, has shown much interest to the military because of the ability of the MOF to catalytically decontaminate chemical warfare agents (CWAs). Unfortunately, the applications for MOFs are limited because of their powder form, which is difficult to incorporate into protective clothing. As a result, a new area of research has developed to functionalize fabrics with MOFs to make a wearable multifunctional fabric that retains the desired properties of the MOF. In this work, UiO-66 was incorporated into poly(vinylidene) fluoride/Ti(OH)₄ composite fabric using electrospinning and evaluated for its use in chemical protective clothing. The base triethanolamine (TEA) was added to the composite fabric to create a self-buffering system that would allow for catalytic decontamination of CWAs without the need for a buffer solution. The fabrics were tested against the simulants methyl-paraoxon (dimethyl (4-nitrophenyl) phosphate, DMNP), diisopropyl fluorophosphate (DFP), and the nerve agent soman (GD). The results show that all of the samples have high moisture vapor transport and filtration efficiency, which are desirable for protective clothing. The incorporation of TEA decreased air permeation of the fabric, but increased the catalytic activity of the composite fabric against DMNP and DFP. Samples with and without TEA have rapid half-lives ( t_1/2) as short as 35 min against GD agent. These new catalytically active self-buffering multifunctional fabrics have great potential for application in chemical protective clothings.

Electrosynthesis of Well-Defined Metal-Organic Framework Films and the Carbon Nanotube Network Derived from Them toward Electrocatalytic Applications

An efficient and controllable method to synthesize continuous metal-organic framework (MOF) films is highly desired. Herein, we demonstrate a facile and universal electrochemical method to synthesize homogeneous and uniform zeolitic imidazolate framework (ZIF, a typical class of MOF family) films on various macroconductive substrates (e.g., conductive glass, Ni foam and carbon cloth) as well as nanostructured substrates (one-dimensional nanorod array, two-dimensional nanowall array, and three-dimensional nanoframework). Particularly, the MOF film can be easily transformed into hierarchical ordered carbon nanotube networks, which display multifunctional electrocatalytic performances, such as excellent activity and good long-term stability in overall water splitting and oxygen reduction. It is worth mentioning that this is the first reported work for electrosynthesis of ZIF films on various conductive substrates, illustrating the great potential of the fast and economical method for constructing functional and integrated films or electrodes toward energy-related applications.

Multicomponent metal-organic framework membranes for advanced functional composites

Several strategies are presented for combining different metal–organic frameworks (MOFs) into composite mixed-matrix membranes. Some membranes are shown to be component for multistep organic catalytic transformations.

The diverse chemical and structural properties of metal–organic frameworks (MOFs) make them attractive for myriad applications, but their native powder form is limiting for industrial implementation. Composite materials of MOFs hold promise as a means of exploiting MOF properties in engineered forms for real-world applications. While interest in MOF composites is growing, research to date has largely focused on utilization of single MOF systems. The vast number of different MOF structures provides ample opportunity to mix and match distinct MOF species in a single composite to prepare multifunctional systems. In this work, we describe the preparation of three types of multi-MOF composites with poly(vinylidene fluoride) (PVDF): (1) co-cast MOF MMMs, (2) mixed MOF MMMs, and (3) multilayer MOF MMMs. Finally, MOF MMMs are explored as catalytic membrane reactors for chemical transformations.

Flexible Metal-Organic Framework-Based Mixed-Matrix Membranes: A New Platform for H2 S Sensors

Metal-organic framework (MOF)-polymer mixed-matrix membranes (MMMs) have shown great potential and superior performance in gas separations. However, their sensing application has not been fully established yet. Herein, a rare example of using flexible MOF-based MMMs as a fluorescent turn-on sensor for the detection of hydrogen sulfide (H₂ S) is reported. These MOF-based MMMs are readily prepared by mixing a highly stable aluminum-based nano-MOF (Al-MIL-53-NO₂ ) into poly(vinylidene fluoride) with high loadings up to 70%. Unlike the intrinsic fragility and poor processability of pure-MOF membranes, these MMMs exhibit desirable flexibility and processability that are more suitable for practical sensing applications. The uniform distribution of Al-MIL-53-NO₂ particles combined with the permanent pores of MOFs enable these MMMs to show good water permeation flux and consequently have a full contact between the analyte and MOFs. The developed MMM sensor (70% MOF loading) thus shows a highly remarkable detection selectivity and sensitivity for H₂ S with an exceptionally low detection limit around 92.31 × 10^-9 m, three orders of magnitude lower than the reported powder-form MOFs. This work demonstrates that it is feasible to develop flexible luminescent MOF-based MMMs as a novel platform for chemical sensing applications.

Fabrication of MOF Thin Films at Miscible Liquid-Liquid Interface by Spray Method

Metal-organic frameworks (MOFs) are an intriguing class of porous crystalline inorganic-organic hybrid materials. The fabrication of oriented, crystalline thin film of MOFs is expected to open novel avenues to traditional applications and to serve myriad advanced technologies. Here, a facile spray-assisted miscible liquid-liquid interface (MLLI) synthetic strategy is carried out and reported under mild condition that utilizes miscible interface for the rapid and controllable fabrication of large-area free-standing MOF thin films. The methodology can employ various metal nodes and organic ligands to yield various high quality lamellar/granulous MOF thin films at MLLI, which indicates the universality of the MLLI strategy.

Toxic Organophosphate Hydrolysis Using Nanofiber-Templated UiO-66-NH2 Metal-Organic Framework Polycrystalline Cylinders

Metal organic frameworks (MOFs), the UiO series in particular, have attracted much attention because of the high surface area and ability to capture and decontaminate chemical warfare agents. Much work has been done on incorporating these MOFs into or onto textile materials while retaining the desirable properties of the MOF. Many different techniques have been explored to achieve this. Atomic layer deposition (ALD) of TiO₂ followed by solvothermal synthesis of MOF has become one of the most adaptable techniques for growing MOFs on the surface of many different polymer fabric materials. However, little work has been done with using this technique on polymer composite materials. In this work, UiO-66-NH₂ was grown onto the surface of poly(methyl methacrylate) (PMMA)/Ti(OH)₄ and poly(vinylidene fluoride) (PVDF)/Ti(OH)₄ composite fibers by first modifying the surface with ALD of TiO₂ (@TiO₂) followed by solvothermal synthesis of MOF (@MOF). The catalytic activity of these materials was then evaluated using the simulant paraoxon-methyl (DMNP). These new MOF-functionalized composite fabrics were compared to polyamide-6 (PA-6)@TiO₂@MOF- and polypropylene (PP)@TiO₂@MOF-functionalized fabrics. PMMA/Ti(OH)₄@TiO₂@MOF fibers resulted in unique hollowed fibers with high surface area of 264 m²/g and fast catalytic activity. The catalytic activity of these samples was found to be related to the active MOF mass fraction on the MOF-functionalized composite fabric, with the hollowed PMMA/Ti(OH)₄@TiO₂@MOF having the highest weight percent of active MOF and a DMNP t_1/2 of 26 min followed by PA-6@TiO₂@MOF with 45 min, PVDF/Ti(OH)₄@TiO₂@MOF with 61 min, and PP@TiO₂@MOF with 83 min.

Hot-Pressing Method To Prepare Imidazole-Based Zn(II) Metal-Organic Complexes Coatings for Highly Efficient Air Filtration

Particulate matters (PMs) air pollution has become a serious environmental issue due to its great threat to human health. Herein, metal-organic complexes PBM-Zn1 and PBM-Zn2 coatings (noted as PBM-Zn-Filter) have been produced by the hot-pressing method on various substrates for the first time. Layer-by-layer PBM-Zn-Filters were also obtained through varying hot-pressing cycles. The obtained PBM-Zn-Filters with high robustness show excellent performance in PMs removal. In particular, benefiting from thelarger conjugation system, micropore structure, lower pressure drop, higher electrostatic potential ζ, and electron cloud exposed metal center of PBM-Zn2 (DFT calculations), PBM-Zn2@melamine foam-4 gives the highest removal rates, PM2.5:99.5% ± 1.2% and PM10:99.3% ± 1.1%, and the removal efficiency for capture PM2.5 and PM10 particles in cigarette smoke were both retained at high levels (>95.5%) after 24 h tests. More importantly, a homemade mask is made up by imbedding the PBM-Zn2@melamine foam-4 into a commercial breathing mask, which shows higher removal efficiency, lower pressure drop, smaller thickness, and higher quality factor than two commercial breathing masks, the PMs removal efficiencies for both PM2.5 and PM10 are 99.6% ± 0.5% and 99.4% ± 0.8%, and acceptable air resistance are demonstrated.

Hybridization of MOFs and polymers

Metal-organic frameworks (MOFs) have received much attention because of their attractive properties. They show great potential applications in many fields. An emerging trend in MOF research is hybridization with flexible materials, which is the subject of this review. Polymers possess a variety of unique attributes, such as softness, thermal and chemical stability, and optoelectrical properties that can be integrated with MOFs to make hybrids with sophisticated architectures. Hybridization of MOFs and polymers is producing new and versatile materials that exhibit peculiar properties hard to realize with the individual components. This review article focuses on the methodology for hybridization of MOFs and polymers, as well as the intriguing functions of hybrid materials.