Metal Organic Framework Polymer Research Articles

Sustainable and Efficient Manufacturing of Metal-Organic Framework-Based Polymer Nanocomposites by Reactive Extrusion

Over the past decades, metal–organic frameworks (MOFs) have been considered to be a promising category of materials for gas storage, separation, and catalysis. However, industrial commercialization of MOFs is restricted by their intrinsic operating conditions due to poor processability in powder shape. An integration of MOFs with a polymer matrix has been considered as an efficient way to improve the practical utility of powder MOFs. In contrast to the conventionally discrete bottom-up principle in milligram scale, in this work, a continuously rapid and solvent-free approach is developed to directly manufacture MOF–polymer nanocomposites from solid reagents (polymer matrix, metal irons, and ligands) via reactive extrusion, which can reach a space time yield as high as ∼1.2 × 105 kg/m3/day. To investigate the feasibility of this one-step reactive extrusion method, two types of widely used polymer matrixes, polypropylene and polystyrene, are chosen to manufacture different MOF-based nanocomposites using a Process 11 parallel twin-screw extruder. Specific MOFs, zeolitic imidazolate frameworks (ZIFs), namely, ZIF-8 and ZIF-67, are used herein. The improvements of thermal stability, flammability, and mechanical properties of the polymer matrix are investigated in detail. The catalytic application for activating peroxymonosulfate by ZIF-67 for contaminant degradation is also explored. With a small amount of ZIF-67/polymer nanocomposite films, more than 90% of methylene blue can be catalytically degraded in 25 min. This newly developed manufacturing approach can be extended to other functional polymers in combination with different MOFs to resolve global challenges in carbon neutrality and clean water.

Polymer metal-organic clusters based on hyperbranched polyester polybenzoylthiocarbamate and Cu(II) and Co(II) ions

Polymer metal-organic framework (MOF) are a new class of hybrid porous materials that combine the advantages of both organic polymers and metal-organic frameworks. In this regard, a new ligand was synthesized - a hyperbranched polyester polybenzoylthiocarbamate, the structure of which was established by IR, 1H NMR, electron spectroscopy and elemental analysis. Complexing properties have been studied using the example of Cu(II) and Co(II) ions. The formation of metal-polymer clusters with metal ions with the participation of benzoylthiocarbamate groups of the polyester has been proved by IR, electron spectroscopy and electron microscopy. It was found that the structure of coordination sites is octahedral with tetragonal distortions. The compositions and conditional logarithms of the stability constants of the complexes were determined.

Mixed Matrix Membranes for Efficient CO2 Separation Using an Engineered UiO-66 MOF in a Pebax Polymer.

Mixed matrix membranes (MMMs) have attracted significant attention for overcoming the limitations of traditional polymeric membranes for gas separation through the improvement of both permeability and selectivity. However, the development of defect-free MMMs remains challenging due to the poor compatibility of the metal–organic framework (MOF) with the polymer matrix. Thus, we report a surface-modification strategy for a MOF through grafting of a polymer with intrinsic microporosity onto the surface of UiO-66-NH2. This method allows us to engineer the MOF–polymer interface in the MMMs using Pebax as a support. The insertion of a PIM structure onto the surface of UiO-66-NH2 provides additional molecular transport channels and enhances the CO2 transport by increasing the compatibility between the polymer and fillers for efficient gas separation. As a result, MMM with 1 wt% loading of PIM-grafted-MOF (PIM-g-MOF) exhibited very promising separation performance, with CO2 permeability of 247 Barrer and CO2/N2 selectivity of 56.1, which lies on the 2008 Robeson upper bound. Moreover, this MMM has excellent anti-aging properties for up to 240 days and improved mechanical properties (yield stress of 16.08 MPa, Young’s modulus of 1.61 GPa, and 596.5% elongation at break).

Oriented self-assembly of metal-organic frameworks driven by photoinitiated monomer polymerization.

The self-assembly of metal–organic frameworks (MOFs) is crucial for the functional design of materials, including energy storage materials, catalysts, selective separation materials and optical crystals. However, oriented self-assembly of MOFs is still a challenge. Herein, we propose a novel strategy to drive oriented self-assembly of MOF polyhedral particles at the water–liquid interface by photoinitiated monomer polymerization. The MOF polyhedral particles self-assemble into ordered close-packed structures with obvious orientation in the polymer film, and the orientation is determined by the casting solvent on the water surface. The prepared large-area MOF polymer films show a Janus structure, containing a MOF monolayer and a polymer layer, and can be easily transferred to a variety of substrates. In addition, mixed MOF particles with different sizes and morphologies can also be assembled by this method. This novel method can be foreseen to provide a powerful driving force for the development of MOF self-assembly and to create more possibilities for utilizing the anisotropic properties of MOFs.

A low vanadium permeability sulfonated polybenzimidazole membrane with a metal-organic framework for vanadium redox flow batteries

A proton selective membrane based on a metal-organic framework (MOF) and polybenzimidazole (PBI) with a controllable sulfonation degree is designed for vanadium redox flow battery (VRFB) applications. The size of UiO-66 is between hydrated multivalent vanadium ions and stokes radius of protons, and its suitable pore size can obstruct the penetration of vanadium ions, resulting in a high vanadium resistance rate. Simultaneously, the imidazole groups and sulfonic acid groups in the sulfonated polybenzimidazole compose the acid-base pairs, which block the penetration of vanadium ions. Therefore, sulfonated PBI together with UiO-66 forms a denser network structure for as a vanadium ion barrier. Compare with the Nafion117 film, the vanadium transmittance of prepared composite film is lower (5.15 × 10−7 cm2 min−1 vs. 2.95 × 10−9 cm2 min−1). Compare with the Nafion117 membrane, VRFB with MOF polymer exhibits higher voltage efficiency (94.54%–74.93%) and energy efficiency (84.82%–73.98%) at 40-200 mA•cm−2.

A Water-Soluble Polyacid Polymer Based on Hydrophilic Metal-Organic Frameworks Using Amphoteric Carboxylic Acid Ligands as Linkers for Hydroxycamptothecin Loading and Release In Vitro.

The poor water solubility and severe side effects of hydroxycamptothecin (HCPT) limit its clinical application; therefore, it is necessary to synthesize applicable nanodrug carriers with good solubility to expand the applications of HCPT. In this study, a hydrophilic metal–organic framework (MOF) with amphoteric carboxylic acid ligands as linkers was first synthesized and characterized. Then, water-soluble acrylamide and methacrylic acid were applied as monomers to prepare a water-soluble polyacid polymer MOF@P, which had a solubility of 370 μg/mL. The effects of the MOF@P material on the HCPT loading and solubility were investigated. The results showed that the polymer material could improve the HCPT solubility in water. Moreover, the in vitro release study indicated that the MOF@P polymeric composite exhibited a sustained-release effect on HCPT, with a cumulative release rate of 30.18% in 72 h at pH 7.4. Furthermore, the cytotoxicity test demonstrated that the hydrophilic MOF and the MOF@P had low cell toxicities. The results indicate that the prepared MOF@P polymeric complex can be applied for the sustained release of HCPT in clinics.

Assembly of Colloidal Clusters Driven by the Polyhedral Shape of Metal-Organic Framework Particles.

Control of the assembly of colloidal particles into discrete or higher-dimensional architectures is important for the design of myriad materials, including plasmonic sensing systems and photonic crystals. Here, we report a new approach that uses the polyhedral shape of metal–organic-framework (MOF) particles to direct the assembly of colloidal clusters. This approach is based on controlling the attachment of a single spherical polystyrene particle on each face of a polyhedral particle via colloidal fusion synthesis, so that the polyhedral shape defines the final coordination number, which is equal to the number of faces, and geometry of the assembled colloidal cluster. As a proof of concept, we assembled six-coordinated (6-c) octahedral and 8-c cubic clusters using cubic ZIF-8 and octahedral UiO-66 core particles. Moreover, we extended this approach to synthesize a highly coordinated 12-c cuboctahedral cluster from a rhombic dodecahedral ZIF-8 particle. We anticipate that the synthesized colloidal clusters could be further evolved into spherical core–shell MOF@polystyrene particles under conditions that promote a higher fusion degree, thus expanding the methods available for the synthesis of MOF–polymer composites.

Understanding the Mechanical Reinforcement of Metal-Organic Framework-Polymer Composites: The Effect of Aspect Ratio.

The aspect ratio (AR) of filler particles is one of the most critical determinants for the mechanical properties of particle-reinforced polymer composites. However, it has been challenging to solely study the effect of particle AR due to the difficulties of controlling AR without altering the physical and chemical properties of the particle. Herein, we synthesized PCN-222, a zirconium-based porphyrinic metal-organic framework (MOF) with preferential longitudinal growth as a series of particles with ARs increasing from 3.4 to 54. The synthetic MOF conditions allowed for the chemical properties of the particles to remain constant over the series. The particles were employed as reinforcers for poly(methyl methacrylate) (PMMA). MOF-polymer composite films were fabricated using doctor-blading techniques, which facilitated particle dispersion and alignment in the PMMA matrix, as revealed by optical microscopy and wide-angle X-ray diffraction. Mechanical measurements showed that both elastic and dynamic moduli increased with particle AR and particle concentrations but started to decrease as particle loading increased beyond 0.5 wt % (1.12 vol %). The data obtained at low particle loadings were fitted well with the Halpin-Tsai model. In contrast, the percolation model and the Cox model were unable to adequately fit the data, indicating the mechanical reinforcement in our system mainly originated from efficient load transfer between particles and the matrix in the particle orienting direction. Finally, we showed that the thermal stability of composite films increased with the addition of MOF particles because of the high thermal degradation temperature and restricted polymer chain mobility.

Shaping of a Metal-Organic Framework-Polymer Composite and Its CO2 Adsorption Performances from Humid Indoor Air.

Diamine-functionalized metal-organic frameworks (MOFs) are known as desirable adsorbents that can capture CO2 even at low pressures, but the humidity instability of bare MOF powders as well as their shaping have not yet adequately addressed for practical applications. Herein, we report an effective synthetic strategy for fabricating millimeter-sized MOF/poly(vinylidene fluoride) (PVDF) composite beads with different amounts of PVDF binders (30, 40, and 50 wt %) via a phase inversion method, followed by the postfunctionalization of 1-ethylpropane-1,3-diamine (epn). Compared with the pristine MOF powder, the diamine-grafted bead, epn-MOF/PVDF40, upon mixing with 40% binder polymers, exhibited a superior long-term performance without structural collapse for up to 1 month. The existence of the hydrophobic PVDF polymer in the composite material is responsible for such durability. This work provides a promising preparative route toward developing stable and shaped MOFs for the removal of indoor CO2.

Fibre-based composites from the integration of metal–organic frameworks and polymers

The integration of metal–organic frameworks (MOFs) with polymer fibres enables the formation of fibrous composite materials with advantages over traditional single-component polymer films and mixed-matrix membranes. In comparison with mixed-matrix membranes, MOF–polymer fibrous composites offer improved molecular transport through the material and easier access to the active sites of MOFs. These attributes make fibrous composites appealing for clothing, personal protective equipment, air purification and filtration, biomedical equipment and delivery of therapeutics, along with detection and sensing applications. In this Review, we outline approaches for the incorporation of MOFs into, or onto, polymer fibres and present some applications for MOF–polymer fabrics. The integration of MOFs and polymers can either occur prior to fibre formation (namely, MOF-first), via particle deposition (resulting in either covalent or non-covalent attachment) of MOFs to the fibre or by in situ MOF growth after fibre formation (namely, fibre-first). We focus on the structure–processing–activity relationships — for example, MOF loading, MOF crystal size, polymer concentration and processing parameters — that impact the behaviour of fibrous composites. We conclude with a discussion of research avenues that can advance this burgeoning field. Composites made from metal–organic frameworks and polymer fibres are gaining popularity in many applications because of their tailorable morphologies and properties. This Review summarizes various methods for fabricating these composites, explores structure–processing–activity relationships and discusses future research opportunities.

Design and evaluation of novel MOF-polymer core-shell composite as mixed-mode stationary phase for high performance liquid chromatography.

A general method was developed for preparing ametal-organic framework-polymer composite coated silica core-shell stationary phase. Silica microspheres were comodified with metal-organic framework and polyvinylpyrrolidone rather than the in situ method of silica modification by original metal-organic framework particles. Metal-organic framework particles and polyvinylpyrrolidone on silica surface were beneficial to suppress silanol activity and enhance composite material tolerance, as well as increasing the water compatibility of the original metal-organic framework-based stationary phases. The stationary phase exhibited superior hydrophilic and hydrophobic performance in terms of separation for various analytes including seven alkaloids, six sulfonamides, five antibiotics, and five polycyclic aromatic hydrocarbons. Moreover, the composite material also showed excellent stability with the relative standard deviation of the retention time of 0.4 to 0.7%. The separation performance with real samplesproved that the column has good practical application potential. In summary, the poposed method provides a general way for preparing metal-organic framework-polymer composite material and changed the current status of original metal-organic framework particles modified silica as a single mode chromatographic stationary phase.

Constructing Mesoporous Adsorption Channels and MOF-Polymer Interfaces in Electrospun Composite Fibers for Effective Removal of Emerging Organic Contaminants.

Recently, metal-organic framework (MOF)-based electrospun fibers have attracted considerable attention as adsorbents for organic contaminant removal from water. To prepare these fibers, two common strategies including blending electrospinning and surface coating are employed. However, fibers obtained from the two strategies still have some disadvantages, such as adsorption site blockage and unstable loading. Here, we constructed interconnected mesopores in the electrospun zeolitic imidazolate framework-8 (ZIF-8)/polyacrylonitrile (PAN) fibers with the assistance of poly(vinylpyrrolidone) to expose more adsorption sites of ZIF-8 and make ZIF-8 more stable. Moreover, the mesopores could also enhance the diffusion of contaminant molecules and create MOF-polymer interfaces in the fiber, which improve the adsorption rate and adsorption capacity, respectively. The obtained fibers were used to adsorb antibiotic tetracycline from water. Benefiting from the mesoporous adsorption channels and the MOF-polymer interface, porous ZIF-8/PAN fibers showed faster adsorption kinetics than ZIF-8/PAN blending fibers and larger adsorption capacity than ZIF-8-coated PAN fibers and ZIF-8/PAN blending fibers. The maximum adsorption capacity of porous ZIF-8/PAN fibers was 885.24 mg/g, which is close to that of pure ZIF-8. After 10 adsorption-desorption cycles, the removal efficiency was still above 97%. In addition, porous ZIF-8/PAN fibers could act as the membrane adsorbents to dynamically separate tetracycline with a treated capacity of 9.93 × 103 bed volumes. These results demonstrate that our prepared porous ZIF-8/PAN fibers have great potential in antibiotic drug removal.

STRUCTURE AND LUMINESCENT PROPERTIES OF COORDINATION POLYMERS CONTAINING LEAD(II) AND THIOPHENE LIGANDS

Three new metal-organic framework polymers [Pb2(btdc)2] (1), [Pb3(ttdc)3(dma)2] (2), and [Pb(ttdc)(dma)] (3) (H2btdc = 2,2′-bithiophene-5,5′-dicarboxylic acid, H2ttdc = thieno[3,2-b]thiophene-2,5-dicarboxylic acid, dma = N,N-dimethylacetamide) are synthesized under solvatothermal conditions. The compounds are characterized by single crystal and powder X-ray diffraction, elemental, thermogravimetric, and IR spectroscopic analyses. All three compounds are three-dimensional coordination polymers with layered (1) or chain (2, 3) motifs. The study of luminescent properties reveals the intraligand nature of radiative transitions. For 1 luminescence quenching is observed because of the strengthening of vibrational states and long-range interactions between π-systems of thiophene groups. The luminescence spectrum of 2 contains two bands corresponding to two types of ttdc2– ligands with principally different structural environments. For the ligands isolated from each other the position of the luminescence maximum corresponds to that of the free ttdc2– ion. For the ligands associated in closely packed chains by continuous π-stacking the appearance of a new maximum in the red range is observed, which is due to the delocalization of electron orbitals.

Monolithic Column Prepared with UiO-66-2COOH MOF as Monomer for Enrichment and Purification of Ursolic Acid in Plants by Online Solid-Phase Extraction

A method for preparing a metal–organic framework (MOF)–polymeric monolith was established by in situ radical polymerization with derivatized UiO-66-2COOH and N-isopropylacrylamide (NIPAAm) as co-monomers. It was worth noting that the obtained monolith possessed characteristics of relatively uniform porous structure and a high surface area (84.16 m2 g−1). The adsorption capacity of the monolith increased from 22.87 to 44.92 mg−1 due to the addition of MOF. The monolith was used as adsorbent and coupled with HPLC for the online purification and extraction of ursolic acid (UA) in medicinal plant. The limit of detection (LOD, S/N = 3) and the limit of quantification (LOQ, S/N = 10) were 0.17 μg mL−1 and 0.57 μg mL−1, respectively; the relative standard deviation (RSD) of intra-day and inter-day assays for five plant samples were 1.00–3.67% and 2.43–5.76%, respectively; a good accuracy was demonstrated by the recovery of 92.2–103.28%. The results indicated that the MOF–polymer monolith was feasible for the online enrichment and purification of UA in plant.

Polymer Matrix Incorporated with ZIF-8 for Application in Nonlinear Optics.

Polymers with embedded metal–organic frameworks (MOFs) have been of interest in research for advanced applications in gas separation, catalysis and sensing due to their high porosity and chemical selectivity. In this study, we utilize specific MOFs with high thermal stability and non-centrosymmetric crystal structures (zeolitic imidazolate framework, ZIF-8) in order to give an example of MOF–polymer composite applications in nonlinear optics. The synthesized MOF-based polymethyl methacrylate (PMMA) composite (ZIF-8–PMMA) demonstrates the possibility of the visualization of near-infrared laser beams in the research lab. The resulting ZIF-8–PMMA composite is exposed to a laser under extreme conditions and exhibits enhanced operating limits, much higher than that of the widely used inorganic materials in optics. Overall, our findings support the utilization of MOFs for synthesis of functional composites for optical application.

Lead Sequestration from Perovskite Solar Cells Using a Metal–Organic Framework Polymer Composite

Perovskite solar cells (PSCs) have increased in power conversion efficiency in the last 10 years, from ≈3% to now over 25%. While the best perovskite photovoltaics have remarkable efficiencies, the Pb‐based absorber is likely problematic for commercialization due to environmental concerns. To address this inevitable issue, a porous metal–organic framework (MOF) polymer composite is applied, known as FeBTC/PDA that is used in “safe‐by‐design” perovskite solar panels. The material is based on a porous MOF scaffold containing a polymeric metal binding agent. Herein, the activity of this material to sequester lead from several solutions is demonstrated, including simulated perovskite solutions, solutions containing decomposed perovskite thin films, and real‐world solutions obtained from damaged solar cell devices in a range of temperatures and conditions, and contaminated water derived from damaged PSCs is brought below the drinkable standards set by the Environmental Protection Agency (EPA).

Microstructure of polymer-imprinted metal–organic frameworks determined by absorption edge tomography

Abstract Mechanochemically synthesized metal–organic framework material HKUST-1 in combination with acrylonitrile butadiene styrene polymer was used to form a polymer metal–organic framework composite material by a simple extruder. This composite filament was used for 3D printing. X-ray diffraction measurements were used to prove the homogeneous distribution of the metal–organic framework in the polymer on a centimeter scale, whereas X-ray Absorption Edge Tomography using a synchrotron radiation source was able to evaluate the 3D distribution of the metal–organic framework material both in the filament and the resultant printed sample with a resolution of a few μm. Our very first data indicate that, apart from a few clusters having significantly higher Cu concentration, HKUST-1 is distributed homogeneously down to the 100 μm length scale in both polymer bulk materials in the form of clusters with a size of a few μm. Absorption Edge Tomography in combination with data fusion also allows for the calculation of the metal–organic framework amount located on the external polymer surface.

Novel Nanostructured Metal–Organic Framework-Bonded Silica Amine and Polymer: Facile Synthesis, Kinetics, Isotherms, and Thermodynamics Evaluation for Adsorption of Yttrium(III) Ions

Yttrium is a remarkable rare-earth element with multidiscipline applications, and it can be released into an aquatic system for its widespread industrial applications. The present work is devoted to evaluate the kinetics and isotherm models for adsorption of Y(III) ions by the action of a novel metal–organic framework (MOF) chemically bonded polymer with incorporated ion exchange and chelating characters. To assemble these MOFs, a number of synthetic procedures were designed and performed using microwave irradiation heating in only 12 min. (i) The selected MOFs were synthesized by the reaction of zinc acetate and glutaric to produce (ZnGA) in 3 min. (ii) Covalent bonding and coating of (ZnGA) with 3-aminopropyltrimethoxysilane were carried out to produce (ZnGA–Si–NH2) in 3 min. (iii) The polymeric compound was synthesized by coupling of p-chlorocresol with piperazine via formaldehyde to yield PC in 4 min. (iv) The final MOFs–polymer nanocomposite was synthesized by the functionalization of ZnGA–Si–NH2 with PC to assemble ZnGA–Si–NH–PC in 2 min. The impact of the polymer on stability of ZnGA–Si–NH–PC in aqueous solutions (pH 1–7) was confirmed and compared to the MOFs separately. Additionally, thermal stability and surface morphology of ZnGA–Si–NH–PC were also studied and evaluated. The metal sorption capacity values of Y(III) ions onto ZnGA–Si–NH–PC were optimized at pH 7 and established as 1175, 1925, and 4800 μmol g–1 using 0.025, 0.05, and 0.1 mol L–1 of Y(III), respectively. The interaction mechanisms for binding of Y(III) ions with ZnGA–Si–NH–PC were studied and evaluated by seven kinetics models and seven adsorption isotherm models, and the collected results confirmed that the adsorption process is well fitted with the pseudo-second-order and pore diffusion models. The collected data assured that the adsorption of Y(III) ions onto the ZnGA–Si–NH–PC nanocomposite is chemisorption (ΔH° = 42.44 kJ/mol) with the direct ion exchange mechanism of Y(III) ions with the surface hydrogen ions and coordinate bond formation mechanism with the nitrogen functional groups into the available pores of the ZnGA–Si–NH–PC nanocomposite.

Homochiral MOF–Polymer Mixed Matrix Membranes for Efficient Separation of Chiral Molecules

AbstractHomochiral metal–organic framework (MOF) membranes have been recently reported for chiral separations. However, only a few high‐quality homochiral polycrystalline MOF membranes have been fabricated due to the difficulty in crystallization of a chiral MOF layer without defects on porous substrates. Alternatively, mixed matrix membranes (MMMs), which combine potential advantages of MOFs and polymers, have been widely demonstrated for gas separation and water purification. Here we report novel homochiral MOF–polymer MMMs for efficient chiral separation. Homochirality was successfully incorporated into achiral MIL‐53‐NH2 nanocrystals by post‐synthetic modification with amino acids, such as l‐histidine (l‐His) and l‐glutamic acid (l‐Glu). The MIL‐53‐NH‐l‐His and MIL‐53‐NH‐l‐Glu nanocrystals were then embedded into polyethersulfone (PES) matrix to form homochiral MMMs, which exhibited excellent enantioselectivity for racemic 1‐phenylethanol with the highest enantiomeric excess value up to 100 %. This work, as an example, demonstrates the feasibility of fabricating diverse large‐scale homochiral MOF‐based MMMs for chiral separation.

A metal organic framework polymer monolithic column as a novel adsorbent for on-line solid phase extraction and determination of ursolic acid in Chinese herbal medicine

A metal organic framework (MOF)-polymer monolithic column was prepared by redox initiation using modified MOF and N-methylolacrylamide (NMA) as co-monomers. The obtained monolithic column was characterized by scanning electron microscopy (SEM) and nitrogen adsorption-desorption isotherm measurement. It was used as a solid phase extraction (SPE) absorbent for the online enrichment of ursolic acid (UA) by high performance liquid chromatography. The adsorption amount of UA on the monolith was compared with that of silica gel-C18 adsorbent and the monolith without MOF material. The MOF-polymer monolithic column showed high selectivity and good permeability. Under the optimum conditions for extraction and determination, the calibration equation was y = 79.854× + 0.1939; the linear range was 0.001–0.9 mg/mL; the linear regression coefficient was 0.9993; the limit of detection (LOD) and the limit of quantification (LOQ) were 0.17 μg/mL and 0.57 μg/mL, respectively; the inter-day and intra-day accuracies were <6.44%; the recovery was in the range of 86.52–105.26%. The MOF-polymer monolithic column was successfully used as SPE column for enrichment and determination of UA in Chinese herbal medicine.