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

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

Wrinkled metal-organic framework thin films with tunable Turing patterns for pliable integration

Flexible integration spurs diverse applications in metal-organic frameworks (MOFs). However, current configurations suffer from the trade-off between MOF loadings and mechanical compliance. We report a wrinkled configuration of MOF thin films. We established an interfacial synthesis confined and controlled by a polymer topcoat and achieved multiple Turing motifs in the wrinkled thin films. These films have complete MOF surface coverage and exhibit strain tolerance up to 53.2%. The enhanced mechanical properties allow film transfer onto various substrates. We obtained membranes with large H2/CO2 selectivity (41.2) and high H2 permeance (8.46 × 103 gas permeation units), showcasing negligible defects after transfer. We also achieved soft humidity sensors on delicate electrodes by avoiding exposure to harsh MOF synthesis conditions. These results highlight the potential of wrinkled MOF thin films for plug-and-play integration.

Hierarchically Structured Metal-Organic Framework Polymer Composites for Chemical Warfare Agent Degradation

Metal-organic frameworks (MOFs) have captured the imagination of researchers for their highly tunable properties and many potential applications, including as catalysts for a variety of transformations. Even though MOFs possess significant potential, the challenges associated with processing of these crystalline powders into usable form factors while retaining their functional properties limit their end use applications. Herein, we introduce a new approach to construct MOF-polymer composites via 3D photoprinting to overcome these limitations. We designed photoresin composite formulations that use polymerization-induced phase separation to cause the MOF catalysts to migrate to the surface of the printed material, where they are accessible to substrates such as chemical warfare agents. Using our approach, MOF-polymer composites can be fabricated into nearly any shape or architecture while retaining both the excellent catalytic activity at 10 wt % loading of the MOF components and the flexible, elastomeric mechanical properties of a polymer.

Metal Organic Frameworks: Current State and Analysis of Their Use as Modifiers of the Vulcanization Process and Properties of Rubber

The interest in and application of metal organic frameworks (MOF) is increasing every year. These substances are widely used in many places, including the separation and storage of gases and energy, catalysis, electrochemistry, optoelectronics, and medicine. Their use in polymer technology is also increasing, focusing mainly on the synthesis of MOF-polymer hybrid compounds. Due to the presence of metal ions in their structure, they can also serve as a component of the crosslinking system used for curing elastomers. This article presents the possibility of using zeolitic imidazolate framework ZIF-8 or MOF-5 as activators for sulfur vulcanization of styrene-butadiene rubber (SBR), replacing zinc oxide in conventional (CV) or effective (EF) curing systems to different extents. Their participation in the curing process and influence on the crosslinking density and structure, as well as the mechanical and thermal properties of the rubber vulcanizates, were examined.

Insight into the Structure of MOF-Containing Hybrid Polymeric Microspheres

Polymer science exploited metal organic frameworks (MOFs) for various purposes, which is due to the fact that these materials are ideal platforms for identifying design features for advanced functional materials. The mechanism of polymerization using MOFs, is still largely unexplored and the detailed characterization of both materials in essential to understand the important interactions between the components. In this work modern advanced research methods were used to investigate the properties of MOF-containing hybrid polymeric microspheres. Hydrothermal conversion of CFA-derived iron particles was used to obtain MOF nanostructures, which were then introduced to the structure of hybrid polymer microspheres based on ethylene glycol dimethylacrylate (EGDMA) and triethoxyvinylsilane (TEVS). Chemical structures were confirmed by ATR-FTIR method. To provide information about the elemental composition of the tested materials and for the determination of chemical bonds present in the tested samples XPS method was applied. Morphology was studied using SEM microscopy, whereas porosity was investigated using ASAP technique. Swellability coefficients were determined using typical organic solvents and distilled water. Moreover, the ecological aspect concerning the use of fly ashes deserves to be emphasized.

Self-healing mixed matrix membranes containing metal-organic frameworks

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

A membrane solid-phase extraction method based on MIL-53-mixed-matrix membrane for the determination of estrogens and parabens: polyvinylidene difluoride membrane vs. polystyrene-block-polybutadiene membrane

In this work, MIL-53(Al), as an inorganic 'filler' component, was embedded in polyvinylidene difluoride (PVDF) and polystyrene-block-polybutadiene (SBS) matrices to prepare two mixed-matrix membranes (MMMs), using a simpler method than that previously reported. The PVDF and SBS membranes retained much of the properties of PVDF, SBS, and native MIL-53(Al). The prepared MMMs were then placed in a vortex-stirred sample solution to develop a membrane solid-phase extraction method to extract estrogens and parabens which were determined by high-performance liquid chromatography with fluorescence detection. The extraction efficiencies of the two membranes were compared, with the PVDF membrane exhibiting superior performance. In addition, the PVDF membrane was more free-standing and flexible, and its preparation method was also more facile and simple. The extraction conditions were optimized, and the analytical method showed low limits of detection (0.005-0.18 ng/mL), good linearity, and high accuracy, with recoveries ranging from 90.7 to 102.5%. As a result, this membrane solid-phase extraction method indicated its potential for application in aqueous sample pretreatment. For metal-organic framework based MMM used in this method, in addition to being durable, free-standing, mechanically stable, and possessing a large area, it should also exhibit high MOF incorporation, good flexibility, and appropriate thickness and weight.

Facile and Fast Transformation of Nonluminescent to Highly Luminescent Metal-Organic Frameworks: Acetone Sensing for Diabetes Diagnosis and Lead Capture from Polluted Water

Metal-organic frameworks (MOFs) stand as one of the most promising materials for the development of advanced technologies owing to their unique combination of properties. The conventional synthesis of MOFs involves a direct reaction of the organic linkers and metal salts; however, their postsynthetic modification is a sophisticated route to produce new materials or to confer novel properties that cannot be attained through the traditional methods. This work describes the postsynthetic MOF-to-MOF transformation of a nonluminescent MOF (Zn-based Oxford University-1 material [Zn-BDC, where BDC = 1,4-benzene dicarboxylate] (OX-1)) into a highly luminescent framework (Ag-based Oxford University-2 material [Ag-BDC] (OX-2)) by a simple immersion of the former in a silver salt solution. The conversion mechanism exploits the uncoordinated oxygen atoms of terephthalate linkers found in OX-1, instead of the unsaturated metal sites commonly employed, making the reaction much faster. The materials derived from the OX-1 to OX-2 transformation are highly luminescent and exhibit a selective response to acetone, turning them into a promising candidate for manufacturing fluorometric sensors for the diagnosis and monitoring of diabetes mellitus. Our methodology can be extended to other metals such as lead (Pb). The fabrication of a polymer mixed-matrix membrane containing OX-1 is used as a proof-of-concept for capturing Pb ions (as pollutants) from water. This research instigates the exploration of alternative methodologies to confer MOFs with special aptitudes for photochemical sensing or for environmental applications such as water purification.

In situ reconstruction of ZIF-8 loaded on fibrous supports

The fibre-supported ZIF-8 can undergo a full degradation–recrystallization cycle in a vapor phase with partial recovery of its porosity.

Understanding the opportunities of metal–organic frameworks (MOFs) for CO2 capture and gas-phase CO2 conversion processes: a comprehensive overview

The rapid increase in the concentration of atmospheric carbon dioxide is one of the most pressing problems facing our planet.

MOF-Polymer Hybrid Materials: From Simple Composites to Tailored Architectures

Metal-organic frameworks (MOFs) are inherently crystalline, brittle porous solids. Conversely, polymers are flexible, malleable, and processable solids that are used for a broad range of commonly used technologies. The stark differences between the nature of MOFs and polymers has motivated efforts to hybridize crystalline MOFs and flexible polymers to produce composites that retain the desired properties of these disparate materials. Importantly, studies have shown that MOFs can be used to influence polymer structure, and polymers can be used to modulate MOF growth and characteristics. In this Review, we highlight the development and recent advances in the synthesis of MOF-polymer mixed-matrix membranes (MMMs) and applications of these MMMs in gas and liquid separations and purifications, including aqueous applications such as dye removal, toxic heavy metal sequestration, and desalination. Other elegant ways of synthesizing MOF-polymer hybrid materials, such as grafting polymers to and from MOFs, polymerization of polymers within MOFs, using polymers to template MOFs, and the bottom-up synthesis of polyMOFs and polyMOPs are also discussed. This review highlights recent papers in the advancement of MOF-polymer hybrid materials, as well as seminal reports that significantly advanced the field.

Metal-organic framework UiO-66 membranes

Metal-organic frameworks (MOFs) have emerged as a class of promising membrane materials. UiO-66 is a prototypical and stable MOF material with a number of analogues. In this article, we review five approaches for fabricating UiO-66 polycrystalline membranes including in situ synthesis, secondary synthesis, biphase synthesis, gas-phase deposition and electrochemical deposition, as well as their applications in gas separation, pervaporation, nanofiltration and ion separation. On this basis, we propose possible methods for scalable synthesis of UiO-66 membranes and their potential separation applications in the future.

Enhanced Hydrophilicity and Water Flux of Poly(ether sulfone) Membranes in the Presence of Aluminum Fumarate Metal-Organic Framework Nanoparticles: Preparation and Characterization

The aim of this study is to examine the effect of the addition of aluminum fumarate (AlFu) nanoparticles on the properties of poly(ether sulfone) (PES) membranes, where the AlFu nanoparticles were synthesized as the nanofillers with the metal-organic framework and their structure was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FESEM) analyses. Subsequently, PES/AlFu mixed-matrix membranes (MMMs) were fabricated in different weight percentages of nanofiller through the phase inversion method and the membrane characterization was accomplished by FTIR, XRD, FESEM, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, and elemental mapping analyses. The effect of the addition of nanoparticles on the membrane properties was investigated by measuring the membrane hydrophilicity, pure water flux, solute rejection, and fouling resistance using a dead-end cell under constant pressure and bovine serum albumin as a foulant. The molecular weight cutoff (MWCO) of MMMs was measured by the rejection of poly(ethylene glycol) in various molecular weights, and the membrane surface roughness, porosity, and mean pore radius were calculated. The results showed that AlFu nanoparticles increased the hydrophilicity and porosity of the neat PES membranes and consequently increased the water permeability such that MMM including 0.75 wt % of AlFu possessed the maximum porosity (62.2%), mean pore radius (10.2 nm), and MWCO (154 kDa). Furthermore, this membrane exhibits a superlative flux recovery and minimal total resistance in the antifouling properties examinations.

Diagnosis of penicillin allergy: a MOFs-based composite hydrogel for detecting β-lactamase in serum

A MOFs-based composite hydrogel 1@SA is presented for the diagnosis of penicillin anaphylaxis. This composite hydrogel reflects the enzymatic hydrolysis profiles of penicillin via β-lactamase. The determination of β-lactamase by this hydrogel was achieved through an “ON–OFF–OFF–ON” fluorescence trigger pattern. The potency of 1@SA was further demonstrated for its selectivity, sensitivity and convenient visual detection.

Flexible SIS/HKUST-1 Mixed Matrix Composites as Protective Barriers against Chemical Warfare Agent Simulants

We fabricated and demonstrated, for the first time, metal-organic framework (MOF), polymer mixed-matrix composites (MMCs) as effective, low burden barriers against chemical warfare agent (CWA) simulants. We incorporated the MOF HKUST-1 into elastomeric triblock copolymers of polystyrene- block-polyisoprene- block-polystyrene (SIS) for use as semipermeable barrier against the CWA simulant 2-chloroethyl ethyl sulfide (CEES). MMCs containing up to 50 wt % HKUST-1 were cast and evaluated for CEES permeation, moisture vapor transport rate (MVTR), and mechanical properties, such as elastic modulus and percent elongation. Increasing the MOF content resulted in longer protection against CEES with breakthrough times ranging from immediate breakthrough for the baseline SIS to over 4000 min for the best-performing MMC. MVTRs of high-MOF-content MMCs were approximately 5-10 times higher than either SIS or typical laboratory gloves made from nitrile and latex. The elastic moduli increased with increased MOF content corresponding to a reduction in percent elongation. The triblock copolymer also was found to protect the MOF crystal structure after exposure to CEES and liquid water, which may lead to longer usage time and shelf life. The ability to resist degradation due to moisture shows the potential utility of these composites when exposed to rain, sweat, or other moisture-rich environments. Finally, the MOF-containing composites functioned as robust colorimetric indicators of CEES exposure. Thus, these MMC materials present a potential route toward next-generation personal protective equipment with a combination of detoxification, sensing, environmental stability, and thermal/user-comfort properties not present in current materials solutions.

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.

Chemically Active, Porous 3D-Printed Thermoplastic Composites

Metal-organic frameworks (MOFs) exhibit exceptional properties and are widely investigated because of their structural and functional versatility relevant to catalysis, separations, and sensing applications. However, their commercial or large-scale application is often limited by their powder forms which make integration into devices challenging. Here, we report the production of MOF-thermoplastic polymer composites in well-defined and customizable forms and with complex internal structural features accessed via a standard three-dimensional (3D) printer. MOFs (zeolitic imidazolate framework; ZIF-8) were incorporated homogeneously into both poly(lactic acid) (PLA) and thermoplastic polyurethane (TPU) matrices at high loadings (up to 50% by mass), extruded into filaments, and utilized for on-demand access to 3D structures by fused deposition modeling. Printed, rigid PLA/MOF composites display a large surface area (SA_avg = 531 m² g^-1) and hierarchical pore features, whereas flexible TPU/MOF composites achieve a high surface area (SA_avg = 706 m² g^-1) by employing a simple method developed to expose obstructed micropores postprinting. Critically, embedded particles in the plastic matrices retain their ability to participate in chemical interactions characteristic of the parent framework. The fabrication strategies were extended to other MOFs and illustrate the potential of 3D printing to create unique porous and high surface area chemically active structures.

Isoreticular expansion of polyMOFs achieves high surface area materials

The concept of isoreticular chemistry has become a core principle in metal-organic framework (MOF) materials. Isoreticular chemistry has shown that organic ligands of different sizes, but with a common geometry/symmetry can be used to generate MOFs of related topologies, but with expanded pore sizes and volumes. In this report, polymer-MOF hybrid materials (polyMOFs) with a UiO (UiO = University of Oslo) architecture are shown to adhere to the principle of isoreticular expansion, generating polyMOFs with large surface areas and enhanced stability.

MOFwich: Sandwiched Metal-Organic Framework-Containing Mixed Matrix Composites for Chemical Warfare Agent Removal

This work describes a new strategy for fabricating mixed matrix composites containing layered metal-organic framework (MOF)/polymer films as functional barriers for chemical warfare agent protection. Through the use of mechanically robust polymers as the top and bottom encasing layers, a high-MOF-loading, high-performance-core layer can be sandwiched within. We term this multifunctional composite "MOFwich". We found that the use of elastomeric encasing layers enabled core layer reformation after breakage, an important feature for composites and membranes alike. The incorporation of MOFs into the core layer led to enhanced removal of chemical warfare agents while simultaneously promoting moisture vapor transport through the composite, showcasing the promise of these composites for protection applications.

Understanding the origins of metal-organic framework/polymer compatibility

The microscopic interfacial structures for a series of metal-organic framework/polymer composites consisting of the Zr-based UiO-66 coupled with different polymers are systematically explored by applying a computational methodology that integrates density functional theory calculations and force field-based molecular dynamics simulations. These predictions are correlated with experimental findings to unravel the structure-compatibility relationship of the MOF/polymer pairs. The relative contributions of the intermolecular MOF/polymer interactions and the flexibility/rigidity of the polymer with respect to the microscopic structure of the interface are rationalized, and their impact on the compatibility of the two components in the resulting composite is discussed. The most compatible pairs among those investigated involve more flexible polymers, i.e. polyvinylidene fluoride (PVDF) and polyethylene glycol (PEG). These polymers exhibit an enhanced contact surface, due to a better adaptation of their configuration to the MOF surface. In these cases, the irregularities at the MOF surface are filled by the polymer, and even some penetration of the terminal groups of the polymer into the pores of the MOF can be observed. As a result, the affinity between the MOF and the polymer is very high; however, the pores of the MOF may be sterically blocked due to the strong MOF/polymer interactions, as evidenced by UiO-66/PEG composites. In contrast, composites involving polymers that exhibit higher rigidity, such as the polymer of intrinsic microporosity-1 (PIM-1) or polystyrene (PS), present interfacial microvoids that contribute to a decrease in the contact surface between the two components, thus reducing the MOF/polymer affinity.

Metal coordination and metal activation abilities of commonly unreactive chloromethanes toward metal–organic frameworks

The commonly inert chloromethanes, dichloromethane and trichloromethane, can exchange other solvents bonded at open coordination sites in metal–organic frameworks, providing a new route to activate the open coordination sites for subsequent use in applications.

Zirconium-Based Nanoscale Metal-Organic Framework/Poly(ε-caprolactone) Mixed-Matrix Membranes as Effective Antimicrobials

Metal-organic framework (MOF)-polymer mixed-matrix membranes (MMMs) have shown their superior performance in gas separation. However, their biological application has not been well-explored yet. Herein, a series of zirconium-based MOF MMMs with high MOF loading and homogeneous composition have been prepared through a facile drawdown coating process. Poly(ε-caprolactone) (PCL) has been selected as a binder for its good biocompatibility and biodegradability. Zr-MOF nanoparticles, UiO-66, and MOF-525, have been utilized as "filler" because of their superior chemical stability, good biological safety, and versatile functions. Both UiO-66/PCL MMMs and MOF-525/PCL MMMs have a uniform appearance even at the highest loading of 50 wt % for UiO-66 and 30 wt % for MOF-525, respectively. The integrity of pore structures of UiO-66 within MMMs maintains well, which is evidenced by dye separation. All obtained MMMs possess good biocompatibility and mechanical property. Upon irradiation, MOF-525/PCL MMMs generate reactive oxygen species and serve as effective antibacterial photodynamic agents against Escherichia coli. This study offers an alternative system for forming homogeneous MOF/polymer MMMs and represents the first example of exploiting hybrid MMMs for biological applications.

Mixed-Matrix Membranes

Research into extended porous materials such as metal-organic frameworks (MOFs) and porous organic frameworks (POFs), as well as the analogous metal-organic polyhedra (MOPs) and porous organic cages (POCs), has blossomed over the last decade. Given their chemical and structural variability and notable porosity, MOFs have been proposed as adsorbents for industrial gas separations and also as promising filler components for high-performance mixed-matrix membranes (MMMs). Research in this area has focused on enhancing the chemical compatibility of the MOF and polymer phases by judiciously functionalizing the organic linkers of the MOF, modifying the MOF surface chemistry, and, more recently, exploring how particle size, morphology, and distribution enhance separation performance. Other filler materials, including POFs, MOPs, and POCs, are also being explored as additives for MMMs and have shown remarkable anti-aging performance and excellent chemical compatibility with commercially available polymers. This Review briefly outlines the state-of-the-art in MOF-MMM fabrication, and the more recent use of POFs and molecular additives.