Nylon–MOF Composites through Postsynthetic Polymerization

Measuring Mass Transfer of n-Hexane and 2-Chloroethyl Ethyl Sulfide in Sorbent/Polymer Fiber Composites Using a Volumetric Adsorption Apparatus

The integration of metal-organic frameworks (MOFs) into composite systems serves as an effective strategy to increase the processability of these materials. Notably, MOF/fiber composites have shown much promise as protective equipment for the capture and remediation of chemical warfare agents. However, the practical application of these composites requires an understanding of their mass transport properties, as both mass transfer resistance at the surface and diffusion within the materials can impact the efficacy of these materials. In this work, we synthesized composite fibers of MOF-808 and amidoxime-functionalized polymers of intrinsic microporosity (PIM-1-AX) and measured the adsorption and mass transport behavior of n-hexane and 2-chloroethyl ethyl sulfide (CEES), a sulfur mustard simulant. We developed a new Fickian diffusion model for cylindrical shapes to fit the dynamic adsorption data obtained from a commercial volumetric adsorption apparatus and found that mass transport behavior in composite fibers closely resembled that in the pure PIM fibers, regardless of MOF loading. Moreover, we found that n-hexane adsorption mirrors that of CEES, indicating that it could be used as a structural mimic for future adsorption studies of the sulfur mustard simulant. These preliminary insights and the new model introduced in this work lay the groundwork for the design of next-generation composite materials for practical applications.

Eco-friendly zinc-metal-organic framework as a nucleating agent for poly (lactic acid)

Eco-friendly poly(L-lactic acid) (PLA) can be made more versatile, and its crystallization rate is accelerated by adding Zinc-based metal-organic framework (Zn-MOF) particles. Using differential scanning calorimetry (DSC), the non-isothermal melt crystallization behavior of biodegradable PLA nucleated by 0.3 to 3 wt% of Zn-MOF was examined. The non-isothermal melt crystallization kinetics parameters were determined using a modified Avrami model and Mo approach. Zn-MOF dramatically accelerated the crystallization process, as evidenced by several non-isothermal crystallization metrics, including the crystallization half-time and crystallization rate constant. The melt crystallization temperatures of the PLA-Zn-MOF composites, with contents of 0.7 and 1 wt%, were increased by 21 °C compared to the neat PLA. Using the Friedman isoconversional kinetic method, the neat PLA and PLA-Zn-MOF composites' effective activation energy values, ∆E, were determined. The ∆E values of PLA-Zn-MOF from 0.3 to 1 wt% Zn-MOF composites were lower than that of neat PLA. Moreover, polarized optical microscopy revealed the formation of numerous small-sized PLA spherulites upon Zn-MOF addition. The results indicate that the Zn-MOF (at concentrations of 0.7 to 1.0 wt%) can be used as an efficient nucleating agent for PLA, where it increases the melt crystallization temperature, nucleation density, and crystallinity without changing the crystalline structure, while also significantly reduces the effective activation energy and the size of spherulites. Additionally, scanning electron microscopy confirms good dispersion of Zn-MOF (0.3 to 1 wt%) within the PLA matrix.

Fibrous Zr-MOF Nanozyme Aerogels with Macro-Nanoporous Structure for Enhanced Catalytic Hydrolysis of Organophosphate Toxins

Metal-organic frameworks (MOFs) with Lewis acid catalytic sites, such as zirconium-based MOFs (Zr-MOFs), comprise a growing class of phosphatase-like nanozymes that can degrade toxic organophosphate pesticides and nerve agents. Rationally engineering and shaping MOFs from as-synthesized powders into hierarchically porous monoliths is essential for their use in emerging applications, such as filters for air and water purification and personal protection gear. However, several challenges still limit the production of practical MOF composites, including the need for sophisticated reaction conditions, low MOF catalyst loadings in the resulting composites, and poor accessibility to MOF-based active sites. To overcome these limitations, a rapid synthesis method is developed to introduce Zr-MOF nanozyme coating into cellulose nanofibers, resulting in the formation of processable monolithic aerogel composites with high MOF loadings. These composites contain Zr-MOF nanozymes embedded in the structure, and hierarchical macro-micro porosity enables excellent accessibility to catalytic active sites. This multifaceted rational design strategy, including the selection of a MOF with many catalytic sites, fine-tuning the coating morphology, and the fabrication of a hierarchically structured monolithic aerogel, renders synergistic effects toward the efficient continuous hydrolytic detoxification of organophosphorus-based nerve agent simulants and pesticides from contaminated water.

Water-stable metal-organic frameworks (MOFs): rational construction and carbon dioxide capture

Metal-organic frameworks (MOFs) are considered to be a promising porous material due to their excellent porosity and chemical tailorability. However, due to the relatively weak strength of coordination bonds, the stability (e.g., water stability) of MOFs is usually poor, which severely inhibits their practical applications. To prepare water-stable MOFs, several important strategies such as increasing the bonding strength of building units and introducing hydrophobic units have been proposed, and many MOFs with excellent water stability have been prepared. Carbon dioxide not only causes a range of climate and health problems but also is a by-product of some important chemicals (e.g., natural gas). Due to their excellent adsorption performances, MOFs are considered as a promising adsorbent that can capture carbon dioxide efficiently and energetically, and many water-stable MOFs have been used to capture carbon dioxide in various scenarios, including flue gas decarbonization, direct air capture, and purified crude natural gas. In this review, we first introduce the design and synthesis of water-stable MOFs and then describe their applications in carbon dioxide capture, and finally provide some personal comments on the challenges facing these areas.

Exceptionally Stable And Super-Efficient Electrocatalysts Derived From Semiconducting Metal Phosphonate Frameworks

Two new isostructural semiconducting metal-phosphonate frameworks are reported. Co2 [1,4-NDPA] and Zn2 [1,4-NDPA] (1,4-NDPA4- is 1,4-naphthalenediphosphonate) have optical bandgaps of 1.7 eV and 2.5 eV, respectively. The electrocatalyst derived from Co2 [1,4-NPDA] as a precatalyst generated a low overpotential of 374 mV in the oxygen evolution reaction (OER) with a Tafel slope of 43 mV dec-1 at a current density of 10 mA cm-2 in alkaline electrolyte (1 mol L-1 KOH), which is indicative of remarkably superior reaction kinetics. Benchmarking of the OER of Co2 [1,4-NPDA] material as a precatalyst coupled with nickel foam (NF) showed exceptional long-term stability at a current density of 50 mA cm-2 for water splitting compared to the state-of-the-art Pt/C/RuO2 @NF after 30 h in 1 mol L-1 KOH. In order to further understand the OER mechanism, the transformation of Co2 [1,4-NPDA] into its electrocatalytically active species was investigated.

High Capacity Adsorption and Degradation of a Nerve Agent Simulant and a Pesticide by a Nickel Pyrazolate Metal-Organic Framework

The development of materials that enable the efficient removal of toxic compounds is important for the improvement of current protective materials or decontamination technologies. Current materials rely either on agent removal by adsorption or by effecting (catalytic) degradation. Ideally, both of these mechanisms are combined in a single material in order to target a more broad spectrum of toxic agents and to improve the performance of the materials. Recent attempts to combine materials with either adsorptive or catalytic properties into a composite material are promising, although the overall performance often suffers from competition for the agent between the adsorptive and catalytic domains in the composites. In this work, we propose that metal-organic frameworks (MOFs) could feature both adsorptive properties as well as catalytic properties in a single structural domain, thereby avoiding a reduction in the overall performance originating from competitive agent interactions. We showcase this concept using the MOF Ni3(BTP)2, which exhibits strong affinity and high capacity for the storage of a nerve agent simulant and a pesticide. Moreover, it is demonstrated that the adsorbed agents are efficiently degraded and that the nontoxic degradation products are rapidly expelled from the MOF pores. Its ability to catalyze the hydrolytic degradation of both organophosphate and organophosphorothioate compounds highlights another unique feature of this material. The presented concept illustrates the feasibility for developing materials that target a broader spectrum of agents via adsorption, catalysis, or both and by their broader reactivity toward different types of agents.

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.

Facet-controlled assembly for organizing metal-organic framework particles into extended structures

Metal-organic frameworks (MOFs) are crystalline porous materials characterized by their high porosity and chemical tailorability. To realize the full potential of synthesized MOFs, it is important to transform them from crystalline solid powders into materials with integrated morphologies and properties. One promising approach is facet-controlled assembly, which involves arranging individual crystalline MOF particles into ordered macroscale structures by carefully controlling the interactions between particles. The resulting assembled MOF structures maintain the characteristics of individual particles while also exhibiting improved properties overall. In this article, we emphasize the essential concepts of MOF assembly, highlighting the impact of building blocks, surface interactions, and Gibbs free energy on the assembly process. We systematically examine three methods of guiding facet-controlled MOF assembly, including spontaneous assembly, assembly guided by external forces, and assembly through surface modifications. Lastly, we offer outlooks on future advancements in the fabrication of MOF-based material and potential application exploration.

In Situ Growth of Sub-50-nm Zirconium Aminobenzenedicarboxylate Metal-Organic Framework Nanocrystals for Carbon Dioxide Capture

Controlled synthesis of sub-50-nm metal-organic frameworks (MOFs), which are usually called porous coordination polymers, exhibits huge potential applications in gas storage and separation. Herein, surface-confined growth of zirconium aminobenzenedicarboxylate MOF (UIO-66-NH2) nanocrystals on polypyrrole hollow spheres (PPyHSs) is achieved through covalently grafted benzene dicarboxylic acid ligands using bridged molecules. PPyHSs modified with ligand molecules prohibit excessive growth of UIO-66-NH2 nanocrystals on their confined surface, resulting in smaller-sized nanocrystals (<50 nm) and a monolayer UIO-66-NH2 coating. Benefiting from the homogeneous dispersion of UIO-66-NH2 nanocrystals with a smaller size (40 ± 10 nm), the as-prepared PPyHSs@UIO-66-NH2 hybrids with high specific surface area and pore volume exhibit remarkable CO2 capture performance. Moreover, the time required to reach the maximum CO2 adsorption capacity shortens with decreasing UIO-66-NH2 crystals size. As a proof of concept, the proposed covalent grafting strategy can be used for synthesizing sub-50-nm UIO-66-NH2 nanocrystals for CO2 capture.

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.

Synthesis and photochemical modification of monolayer thin MOF flakes for incorporation in defect free polymer composites

Metal-organic frameworks (MOFs) with benzophenone linker molecules are characterized by their ability to undergo photochemical postsynthetic modification. While this approach opens up almost unlimited possibilities for tailoring materials to specific applications, the processability of the large particles is still lacking. In this work, we present a new approach to fabricate micro flakes of the stable Zr-bzpdc-MOF (bzpdc = benzophenone-4-4'-dicarboxylate) with a thickness of only a few monolayers. The crystalline and nanoporous flakes form dispersions in acetone that are stable for months. Embedding the flakes in polymer composites was investigated as one of many possible applications. Zr-bzpdc-MOF micro flakes were decorated with poly(dimethylsiloxane) (PDMS) via a photochemical postsynthetic modification and incorporated into silicon elastomers. The PDMS functionalization allows covalent cross-linking between the MOF and the polymer while maintaining the porosity of the MOF. The resulting hybrid materials provide defect-free interfaces and show preferential adsorption of CO2 over CH4, making them attractive for gas separation or sensing applications. The work should serve as a basis for bringing bzpdc-MOFs into real-world applications - in polymeric membranes, but also beyond.

Post-Synthetic Surface Modification of Metal-Organic Frameworks and Their Potential Applications

Metal-organic frameworks (MOFs) are porous hybrid materials with countless potential applications. Most of these rely on their porous structure, tunable composition, and the possibility of incorporating and expanding their functions. Although functionalization of the inner surface of MOF crystals has received considerable attention in recent years, methods to functionalize selectively the outer crystal surface of MOFs are developed to a lesser extent, despite their importance. This article summarizes different types of post-synthetic modifications and possible applications of modified materials such as: catalysis, adsorption, drug delivery, mixed matrix membranes, and stabilization of porous liquids.

Tuning Magnetic and Photophysical Properties of Luminomagnetic Metal-Organic Framework Composites in an Inverse Core-Satellite Structure

Luminomagnetic composites have been synthesized that allow for an individual tuning of luminescence intensity, chromaticity and magnetization by combination of superparamagnetic, citrate-stabilized iron oxide nanoparticles with the luminescent MOFs ³ _∞ [Ln₂ (BDC)₃ (H₂ O)₄ ] (Ln=Eu, Tb; BDC^2- =terephthalate). The components are arranged to a concept of inverse structuring compared to previous luminomagnetic composites with MOF@magnetic particle (shell@core) composition so that the luminescent MOF now acts as core and is covered by magnetic nanoparticles forming the satellite shell. Thereby, the magnetic and photophysical properties are individually tuneable between high emission intensity (1.2 ⋅ 10⁶  cps mg^-1 ) plus low saturation magnetization (6 emu g^-1 ) and the direct opposite (0.09 ⋅ 10⁶  cps mg^-1 ; 42 emu g^-1 ) by adjusting the particle coverage of the MOF. This is not achievable with a core-shell structure having a magnetic core and a dense MOF shell. The composition of the composites and the influence of different synthesis conditions on their properties were investigated by SEM/EDX, PXRD, magnetization measurements and photoluminescence spectroscopy.

MOF-Polymer Mixed Matrix Membranes as Chemical Protective Layers for Solid-Phase Detoxification of Toxic Organophosphates

Zirconium-based metal-organic frameworks (Zr-MOFs) have been demonstrated as potent catalysts for the hydrolytic detoxification of organophosphorus nerve agents and their simulants. However, the practical implementation of these Zr-MOFs is limited by the poor processability of their powdered form and the necessity of water media buffered by a volatile liquid base in the catalytic reaction. Herein, we demonstrate the efficient solid-state hydrolysis of a nerve agent simulant (dimethyl-4-nitrophenyl phosphate, DMNP) catalyzed by Zr-MOF-based mixed matrix membranes. The mixed matrix membranes were fabricated by incorporating MOF-808 into the blending matrix of poly(vinylidene fluoride) (PVDF), poly(vinylpyrrolidone) (PVP), and imidazole (Im), in which MOF-808 provides highly active catalytic sites, the hydrophilic PVP helps to retain water for promoting the hydrolytic reaction, and Im serves as a base for catalytic site regeneration. Impressively, the mixed matrix membranes displayed excellent catalytic performance for the solid-state hydrolysis of DMNP under high humidity, representing a significant step toward the practical application of Zr-MOFs in chemical protective layers against nerve agents.

Functionalized reactive polymers for the removal of chemical warfare agents: A review

Protection from and removal of chemical warfare agents (CWAs) from the environment remains a global goal. Activated charcoal, metal oxides, metal organic frameworks (MOFs), polyoxometalates (POMs) and reactive polymers have all been investigated for CWA removal. Composite polymeric materials are rapidly gaining traction as versatile building blocks for personal protective equipment (PPE) and catalytic devices. Polymers are inexpensive to produce and easily engineered into a wide range of materials including films, electro-spun fibers, mixed-matrix membranes/reactors, and other forms. When containing reactive side-chains, hydrolysis catalysts, and/or oxidative catalysts polymeric devices are primed for CWA decontamination. In this review, recent advances in reactive polymeric materials for CWA removal are summarized. To aid in comparing the effectiveness of the different solid catalysts, particular attention is paid to the stoichiometric ratio of reactive species to toxic substrate (CWA or CWA simulant).

Recent advances in determination applications of emerging films based on nanomaterials

Sensitive and facile detection of analytes is crucial in various fields such as agriculture production, food safety, clinical diagnosis and therapy, and environmental monitoring. However, the synergy of complicated sample pretreatment and detection is an urgent challenge. By integrating the inherent porosity, processability and flexibility of films and the diversified merits of nanomaterials, nanomaterial-based films have evolved as preferred candidates to meet the above challenge. Recent years have witnessed the flourishment of films-based detection technologies due to their unique porous structures and integrated physical/chemical merits, which favors the separation/collection and detection of analytes in a rapid, efficient and facile way. In particular, films based on nanomaterials consisting of 0D metal-organic framework particles, 1D nanofibers and carbon nanotubes, and 2D graphene and analogs have drawn increasing attention due to incorporating new properties from nanomaterials. This paper summarizes the progress of the fabrication of emerging films based on nanomaterials and their detection applications in recent five years, focusing on typical electrochemical and optical methods. Some new interesting applications, such as point-of-care testing, wearable devices and detection chips, are proposed and emphasized. This review will provide insights into the integration and processability of films based on nanomaterials, thus stimulate further contributions towards films based on nanomaterials for high-performance analytical-chemistry-related applications.

In-situ compatibilized starch/polyacylonitrile composite fiber fabricated via dry-wet spinning technique

An in-situ compatibilized starch (St) and polyacrylonitrile (PAN) composite spinning solution was designed by preparing starch-graft-polyacrylonitrile (St-g-PAN) through graft copolymerizing acrylonitrile from soluble starch and using ammonium cerium nitrate (CAN) as initiator. As dimethyl sulfoxide (DMSO) was used as the solvent, St/St-g-PAN/PAN/DMSO spinning solution was prepared and St/St-g-PAN/PAN composite fibers were obtained by dry-wet spinning technique. The effects of air gap, coagulation bath, hot drawing and stretching, and thermal-setting process were studied in detail. Fourier transform infrared spectroscopy (FT-IR), solid state nuclear magnetic resonance (¹³C NMR), thermogravimetric analysis (TGA), X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM) were used to characterize the structure and morphology of the copolymer and the fibers. Single fiber strength tester and sonic orientation instrument were performed to measure the fiber mechanical properties and orientation degrees. The results showed that as the grafting ratio ~150.0% and the reacting mixture containing St ~9.8%, St-g-PAN ~81.6%, and homo-PAN ~8.6% in DMSO solution with 6.0 wt% in concentration were used, the spinning parameters such as air gap ~35 mm, coagulation bath concentration ~70%, temperature ~25 °C, and positive stretching ~48%, hot drawing and stretching 6 times at 80 °C, thermal-setting at 90 °C for 3 h under constant length mode were met, composite fibers with breaking strength 3.41 cN·dtex^-1, breaking elongation 14.41%, sonic orientation factor 0.625, moisture recovery ratio 10.53% under standard condition (1 atm, 22 °C, and relative humidity 65%), and boiling water shrinkage ratio 9.60% were obtained. The as prepared composite fiber was better than common viscose fiber 2.11 cN·dtex^-1 and cotton fiber ~3.24 cN·dtex^-1 and expected to be used in the fields of medical gauze, bandage, protective clothing, et al. besides of common textiles. The in-situ compatibilization method can be applied in preparation of other composite polymer materials.

Aqueous-Phase Destruction of Nerve-Agent Simulants at Copper Single Atoms in UiO-66

Metal-organic frameworks (MOFs) have shown great success in aqueous-phase hydrolysis of nerve agents, with some even showing promise in the gas phase. However, both aqueous-phase reactivity and gas-phase reactivity are hindered because of the binding of the hydrolyzed products to the MOF nodes in a stable, bridging configuration, which limits turnover. Single transition-metal atoms in MOFs have been a growing field of interest for catalytic applications, and single atoms have been proposed to prevent the unwanted bridged conformation and increase catalytic turnover. To date, there has been little experimental evidence to support the hypothesis. Herein, we report two copper single atom-modified UiO-66 MOFs for nerve-agent simulant degradation. Despite the capping of highly active Zr⁴⁺ nodes with fewer Lewis acidic Cuⁿ⁺ atoms, the reactivity of both CuMOFs approaches that of native UiO-66 under aqueous conditions. Computational studies reveal that the Cu coordination environment impairs product inhibition with respect to the native MOF.

Microwave-Assisted Synthesis of Porous Composites MOF-Textile for the Protection against Chemical and Nuclear Hazards

Since the emergence of chemical, biological, radiological, and nuclear risks, significant efforts have been made to create efficient personal protection equipment. Recently, metal-organic framework (MOF) materials have emerged as new promising candidates for the capture and degradation of various threats, like chemical warfare agents (CWAs) or radioactive species. Herein, we report a new synthesis method of MOF-textile composites by microwave irradiation, with direct anchoring of MOFs on textiles. The resistance of the composite has been tested using normed abrasion measurements, and non-stable samples were optimized. The protection capacity of the MOF-textile composite has been tested against dimethyl 4-nitrophenyl phosphate, a common CWA simulant, showing short degradation half-life (30 min). Radiological/nuclear protection has also been tested through uranium uptake (up to 15 mg g^-1 adsorbent) and the capture of Kr or Xe gas at 0.9 and 2.9 cm³/g, respectively.

Environmentally Benign Biosynthesis of Hierarchical MOF/Bacterial Cellulose Composite Sponge for Nerve Agent Protection

The fabrication of MOF polymer composite materials enables the practical applications of MOF-based technology, in particular for protective suits and masks. However, traditional production methods typically require organic solvent for processing which leads to environmental pollution, low-loading efficiency, poor accessibility, and loss of functionality due to poor solvent resistance properties. For the first time, we have developed a microbial synthesis strategy to prepare a MOF/bacterial cellulose nanofiber composite sponge. The prepared sponge exhibited a hierarchically porous structure, high MOF loading (up to ≈90 %), good solvent resistance, and high catalytic activity for the liquid- and solid-state hydrolysis of nerve agent simulants. Moreover, the MOF/ bacterial cellulose composite sponge reported here showed a nearly 8-fold enhancement in the protection against an ultra-toxic nerve agent (GD) in permeability studies as compared to a commercialized adsorptive carbon cloth. The results shown here present an essential step toward the practical application of MOF-based protective gear against nerve agents.

Hybridization of Synthetic Humins with a Metal-Organic Framework for Precious Metal Recovery and Reuse

The number of synthetic strategies used to functionalize MOFs with polymers is rapidly growing; this stems from the knowledge that non-native polymeric guests can significantly boost MOF performance in a number of desirable applications. The current work presents a scalable and solid-state method for MOF/polymer composite production. This simple method constitutes mixing a MOF powder, namely, Fe-BTC (BTC = 1,3,5-benzenetricarboxylate), with a biomass-derived solid monomer, 5-hydroxymethylfurfural (HMF), and subsequently heating the solids; the latter promotes both solid-state diffusion of HMF into the MOF and the formation of polymeric humin species with a high density of accessible hydroxyl functionality within the MOF pore. The resulting composite, Fe-BTC/humin, was found to selectively extract Ag⁺ ions from laundry wastewater. Subsequent reduction of the Ag⁺ species yields a novel catalyst, Fe-BTC/humin/Ag, that is able to drive the organic transformation of cinnamaldehyde in a highly selective manner. Moreover, the catalyst exhibited recyclability up to five cycles, which is in contrast to the Fe-BTC/Ag catalyst without the humin-based polymer. It is envisioned that MOF/polymer composites that are able to selectively extract precious metals from liquid waste streams can be used for the future production of sustainable catalysts; this work was aimed at demonstrating a proof of concept in this regard. Moreover, this study brings more understanding of the impact that MOFs can have on polymer functionalities. Understanding the polymer structure and how it can be manipulated will help us realize the high degree of future potential of this distinct class of composite materials.

Synchronous Construction of the Hierarchical Pores and High Hydrophobicity of Stable Metal-Organic Frameworks through a Dual Coordination-Competitive Strategy

Hierarchical-pore construction and functionalities are critical to further extend the applications of some stable MOFs, such as water remediation, fuel purification, oil/water separation, and self-cleaning, which are rarely achieved simultaneously. Herein, we demonstrate a method of synchronously constructing high-hydrophobicity Zr-based metal-organic frameworks with hierarchical pores (HP-UiO-66) through a dual coordination-competitive strategy. The addition of alkanoic acids and Zn²⁺ ions as coordination-competitors could reduce the coordinative degree between the ligand and Zr⁴⁺ ions to effectively induce defect formation. The resulting unsaturated Zr⁴⁺ ions could fully combine with the existing alkanoic acid with a long chain to afford HP-UiO-66 with high-hydrophobicity characteristics. In addition, the particle size of pristine UiO-66 could be adjusted effectively from around 280 to 120 nm using different alkanoic acids when Zn²⁺ ions are not added. This study provided a simple way for effectively controlling the morphology and structure of UiO-66 at the same time. Moreover, this kind of high-hydrophobicity HP-UiO-66 showed potential applications in oil/water separation and selective adsorption of organic mixtures.

Immobilized Regenerable Active Chlorine within a Zirconium-Based MOF Textile Composite to Eliminate Biological and Chemical Threats

The most recent global health crisis caused by the SARS-CoV-2 outbreak and the alarming use of chemical warfare agents highlight the necessity to produce efficient protective clothing and masks against biohazard and chemical threats. However, the development of a multifunctional protective textile is still behind to supply adequate protection for the public. To tackle this challenge, we designed multifunctional and regenerable N-chlorine based biocidal and detoxifying textiles using a robust zirconium metal-organic framework (MOF), UiO-66-NH₂, as a chlorine carrier which can be easily coated on textile fibers. A chlorine bleaching converted the amine groups located on the MOF linker to active N-chlorine structures. The fibrous composite exhibited rapid biocidal activity against both Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus) with up to a 7 log reduction within 5 min for each strain as well as a 5 log reduction of SARS-CoV-2 within 15 min. Moreover, the active chlorine loaded MOF/fiber composite selectively and rapidly degraded sulfur mustard and its chemical simulant 2-chloroethyl ethyl sulfide (CEES) with half-lives less than 3 minutes. The versatile MOF-based fibrous composite designed here has the potential to serve as protective cloth against both biological and chemical threats.

Rational Design and Growth of MOF-on-MOF Heterostructures

Multiporous metal-organic frameworks (MOFs) have emerged as a subclass of highly crystalline inorganic-organic materials, which are endowed with high surface areas, tunable pores, and fascinating nanostructures. Heterostructured MOF-on-MOF composites are recently becoming a research hotspot in the field of chemistry and materials science, which focus on the assembly of two or more different homogeneous or heterogeneous MOFs with various structures and morphologies. Compared with one single MOF, the dual MOF-on-MOF composites exhibit unprecedented tunability, hierarchical nanostructure, synergistic effect, and enhanced performance. Due to the difference of inorganic metals and organic ligands, the lattice parameters in a, b, and c directions in the single crystal cells could bring about subtle or large structural difference. It will result in the composite material with distinct growth methods to obtain secondary MOF grown from the initial MOF. In this review, the authors wish to mainly outline the latest synthetic strategies of heterostructured MOF-on-MOFs and their derivatives, including ordered epitaxial growth, random epitaxial growth, etc., which show the tutorial guidelines for the further development of various MOF-on-MOFs.

Ultrathin Zirconium Hydroxide Nanosheet-Assembled Nanofibrous Membranes for Rapid Degradation of Chemical Warfare Agents

Organophosphorus-based chemical warfare agents (CWAs) are highly poisonous, and recent attacks using nerve agents have stimulated researchers to develop breakthrough materials for their fast degradation. Zr-based materials have been identified as the most effective catalysts for breaking down CWAs, but in their powdered form, their practical application in personal protective equipment is limited. Herein, a surface-confined strategy for the direct growth of vertically aligned zirconium hydroxide (Zr(OH)₄ ) nanosheets with ultrathin and tortuous structures on nanofibers is reported. The freestanding Zr(OH)₄ nanosheet-assembled nanofibrous membranes (NANMs) show superior catalytic performance to degrade dimethyl methylphosphonate, a nerve agent simulant, with a half-life of 4 min. In addition, intriguing membrane-type NANMs feature integrated properties of exceptional breathability, prominent flexibility, and robust fatigue resistance over one million buckling loads. This facile strategy provides a novel route to manufacture new classes of nanosheet-supported membranes for chemical-protective materials, in particular for gas filters, protective suits, and clothing.

Preparation of Superhydrophobic Metal-Organic Framework/Polymer Composites as Stable and Efficient Catalysts

Metal-organic frameworks (MOFs), as a chemical platform, combined with multifunctional polymers are of interest in catalytic applications, which can not only inherit the outstanding properties of the two components but also lead to unique synergistic effects. Nonetheless, most MOFs possess varying degrees of water instability, which limits their real application. Herein, we fabricated highly hydrophobic MOF/polymer composites via a universal post-synthetic polymerization strategy as efficient catalysts. Polyaniline (PANI) was first hybridized with MOFs by vapor deposition polymerization, and then, hydrophobic molecules were grafted to the PANI by a covalent linking process, thereby forming a superhydrophobic MOF/PANI hybrid material (MOF/PANI-shp). The resultant MOF/PANI-shp not only obtains superior moisture/water resistance without significantly disturbing the original features but also exhibits a novel catalytic selectivity in styrene oxidation because of the accessible sites and synergistic effects. Such a synthetic strategy for the MOF/polymer catalyst opens a new avenue for the design of a unique catalyst with outstanding catalytic efficiency, selectivity, and stability.

Water-stable zirconium-based metal-organic frameworks armed polyvinyl alcohol nanofibrous membrane with enhanced antibacterial therapy for wound healing

Inadequate water-stability and antibacterial activity limit the biomedical application of polyvinyl alcohol (PVA)-based membranes in moist environments. In this work, we propose a strategy to improve the water-stability of PVA membranes via metal complexation and heat treatment. We report a simple routine where the zirconium-based UiO-66-NH₂ metal-organic frameworks (MOFs) are nucleated as a layer on the surface of PVA nanofibrous membranes (UiO-66-NH₂@PVA NFMs). We find that the chemical modification of membranes increases their hydrophilicity and adds on mechanical support for the brittle UiO-66-NH₂ MOFs. Additionally, we demonstrate the application of UiO-66-NH₂ MOFs as drug carriers for antibacterial drug, levofloxacin (LV). The active drug component is preloaded during the one-step nucleation process. The obtained LV loaded UiO-66-NH₂@PVA NFMs (LV@UiO-66-NH₂@PVA) are shown to be bactericidal with the efficiency > 99.9% at 100 μg/mL against two bacterial species, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Compared with the commercially available gauzes, the UiO-66-NH₂@PVA and LV@UiO-66-NH₂@PVA treatments will significantly improve the wound healing process. Animal studies show that the LV@UiO-66-NH₂@PVA will effectively offer a safe alternative solution for the patients to protect against bacterial infections, demonstrating the potential application of MOF-based NFMs as wound dressing agents.

A Novel Design of Water-Activated Variable Stiffness Endoscopic Manipulator with Safe Thermal Insulation

In natural orifice transluminal endoscopic surgery (NOTES), an ideal endoscope platform should be flexible and dexterous enough to go through the natural orifices to access the lesion site inside the human body, and meanwhile provide sufficient rigidity to serve as a base for the end-effectors to operate during the surgical tasks. However, the conventional endoscope has limited ability for maintaining high rigidity over the length of the body. This paper presents a novel design of a variable stiffness endoscopic manipulator. By using a new bioplastic named FORMcard, whose stiffness can be thermally adjusted, water at different temperatures is employed to switch the manipulator between rigid mode and flexible mode. A biocompatible microencapsulated phase change material (MEPCM) with latent heat storage properties is adopted as the thermal insulation for better safety. Experiments are conducted to test the concept design, and the validated advantages of our proposed variable stiffness endoscopic manipulator include: shorter mode activation time (25 s), significantly improved stiffness in rigid mode (547.9–926.3 N·cm2) and larger stiffness-adjusting ratio (23.9–25.1 times).

Chemical targets to deactivate biological and chemical toxins using surfaces and fabrics

The most recent global health and economic crisis caused by the SARS-CoV-2 outbreak has shown us that it is vital to be prepared for the next global threat, be it caused by pollutants, chemical toxins or biohazards. Therefore, we need to develop environments in which infectious diseases and dangerous chemicals cannot be spread or misused so easily. Especially, those who put themselves in situations of most exposure - doctors, nurses and those protecting and caring for the safety of others - should be adequately protected. In this Review, we explore how the development of coatings for surfaces and functionalized fabrics can help to accelerate the inactivation of biological and chemical toxins. We start by looking at recent advancements in the use of metal and metal-oxide-based catalysts for the inactivation of pathogenic threats, with a focus on identifying specific chemical bonds that can be targeted. We then discuss the use of metal-organic frameworks on textiles for the capture and degradation of various chemical warfare agents and their simulants, their long-term efficacy and the challenges they face.

Encapsulation of Ultrafine Metal-Organic Framework Nanoparticles within Multichamber Carbon Spheres by a Two-Step Double-Solvent Strategy for High-Performance Catalysts

Carbon-encapsulated metal-organic framework (MOF) composite is one kind of emerging new catalyst with high efficiency and has gained much attention. However, for this kind of composite catalyst, the key to improving its catalytic activity and durability is to realize the effective dispersion of MOF nanoparticles (NPs) and enhance the interaction between MOF NPs and the carbon matrix, which remain a significant challenge. Herein, ultrafine MOF NPs within multichamber carbon spheres (MOF@MCCS), for the first time, have been rationally synthesized by a two-step double-solvent strategy for high-performance catalysts. The precise loading of guest MOFs can be achieved by adjusting the multichamber structure and calcination extent of the multichamber polymer (MCP), and the particle size of MOFs can be as low as 13.2 nm. Due to the formation of abundant carbon defects in the pyrolysis process of MCPs, the special structure and synergistic effect make the material exhibit higher catalytic activity and durability. More importantly, this method is universal and can be extended to different MOF systems. The two-step double-solvent strategy not only prepares a unique structure of MOF@MCCS-type host-guest-encapsulated catalysts but also provides a new idea for the design of high-efficiency catalysts with better performance and higher durability.

Epoxy Functional Composites Based on Lanthanide Metal-Organic Frameworks for Luminescent Polymer Materials

The integration of metal-organic frameworks (MOF) into organic polymers represents a direct and effective strategy for developing innovative composite materials that combine the exceptional properties of MOFs with the robustness of organic polymers. However, the preparation of MOF@polymer hybrid composites requires an efficient dispersion and interaction of MOF particles with polymer matrices, which remains a significant challenge. In this work, a new simple and direct approach was applied for the development of Ln-MOF@polymer materials. A series of Ln-MOF@TGIC composites {Ln-MOF = [Ln(μ₃-BTC)(H₂O)₆]_n (Ln-BTC), where Ln = Eu, Tb, Eu_0.05Tb_0.95; H₃BTC = 1,3,5-benzenetricarboxylic acid; TGIC = triglycidyl isocyanurate} were successfully obtained by applying a grinding method via the chemical bonding between uncoordinated carboxylate groups in Ln-BTC and epoxy groups in TGIC. The Ln-BTC@TGIC materials possess significant fluorescence characteristics with superior emission lifetimes and quantum yields if compared to parent Ln-MOFs. Interestingly, under the UV irradiation, a considerable color change from yellow in Eu_0.05Tb_0.95-BTC to red in Eu_0.05Tb_0.95-BTC@TGIC was observed. The energy-transfer mechanism was also rationalized by the density functional theory (DFT) calculations. The developed Ln-BTC@TGIC composites were further applied as functional fluorescent coatings for the fabrication, via a simple spraying method, of the flexible polyimide (PI) films, Ln-BTC@TGIC@PI. Thus, the present work unveils a new methodology and expands its applicability for the design and assembly of stable, multicomponent, and soft polymer materials with remarkable fluorescence properties.

Fabrication of a robust MOF/aerogel composite via a covalent post-assembly method

A covalent post-assembly strategy is developed to prepare a composite of dispersive MOF particles in an aerogel matrix. Briefly, the anhydride group-decorated MOF (UiO-66-NH2) particles covalently coupled with polyimide (PI) monomers through a one-pot amidation polymerization reaction, succeeding a process of gel-sol, freeze-drying and thermal-imidization to obtain the UiO-66-PI aerogel. The designed composite shows outstanding catalytic activity in CO2 cycloaddition and excellent adsorption capacity for dyes.

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.

Testing Metal–Organic Framework Catalysts in a Microreactor for Ethyl Paraoxon Hydrolysis

We explored the practical advantages and limitations of applying a UiO-66-based metal–organic framework (MOF) catalyst in a flow microreactor demonstrated by the catalytic hydrolysis of ethyl paraoxon, an organophosphorus chemical agent. The influences of the following factors on the reaction yield were investigated: a) catalyst properties such as crystal size (14, 200, and 540 nm), functionality (NH2 group), and particle size, and b) process conditions: temperature (20, 40, and 60 °C), space times, and concentration of the substrate. In addition, long-term catalyst stability was tested with an 18 h continuous run. We found that tableting and sieving is a viable method to obtain MOF particles of a suitable size to be successfully screened under flow conditions in a microreactor. This method was used successfully to study the effects of crystal size, functionality, temperature, reagent concentration, and residence time. Catalyst particles with a sieved fraction between 125 and 250 µm were found to be optimal. A smaller sieved fraction size showed a major limitation due to the very high pressure drop. The low apparent activation energy indicated that internal mass transfer may exist. A dedicated separate study is required to assess the impact of pore diffusion and site accessibility.

Inside polyMOFs: layered structures in polymer-based metal-organic frameworks

In this report, we explore the internal structural features of polyMOFs consisting of equal mass ratios of metal-coordinating poly(benzenedicarboxylic acid) blocks and non-coordinating poly(ethylene glycol) (PEG) blocks. The studies reveal alternating lamellae of metal-rich, crystalline regions and metal-deficient non-crystalline polymer, which span the length of hundreds of nanometers. Polymers consisting of random PEG blocks, PEG end-blocks, or non-coordinating poly(cyclooctadiene) (COD) show similar alternation of metal-rich and metal-deficient regions, indicating a universal self-assembly mechanism. A variety of techniques were employed to interrogate the internal structure of the polyMOFs, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and small-angle synchrotron X-ray scattering (SAXS). Independent of the copolymer architecture or composition, the internal structure of the polyMOF crystals showed similar lamellar self-assembly at single-nanometer length scales.

In this report, we explore the internal structural features of polyMOFs consisting of equal mass ratios of metal-coordinating poly(benzenedicarboxylic acid) blocks and non-coordinating poly(ethylene glycol) (PEG) blocks.

Free-standing metal-organic framework (MOF) monolayers by self-assembly of polymer-grafted nanoparticles

We report a general method for the synthesis of free-standing, self-assembled MOF monolayers (SAMMs) at an air-water interface using polymer-brush coated MOF nanoparticles. UiO-66, UiO-66-NH2, and MIL-88B-NH2 were functionalized with a catechol-bound chain-transfer agent (CTA) to graft poly(methyl methacrylate) (PMMA) from the surface of the MOF using reversible addition-fragmentation chain transfer polymerization (RAFT). The polymer-coated MOFs were self-assembled at the air-water interface into monolayer films ∼250 nm thick and capable of self-supporting at a total area of 40 mm2. Mixed-particle films were prepared through the assembly of MOF mixtures, while multilayer films were achieved through sequential transfer of the monolayers to a glass slide substrate. This method offers a modular and generalizable route to fabricate thin-films with inherent porosity and sub-micron thickness composed of a variety of MOF particles and functionalities.