Metal–organic frameworks (MOFs) are a class of porous materials with immense chemical tunability derived from their organic and inorganic building blocks. Presynthetic approaches have been used to ...construct tailor-made MOFs, but with a rather restricted functional group scope limited by the typical MOF solvothermal synthesis conditions. Postsynthetic modification (PSM) of MOFs has matured into an alternative strategy to broaden the functional group scope of MOFs. PSM has many incarnations, but two main avenues include (1) covalent PSM, in which the organic linkers of the MOF are modified with a reagent resulting in new functional groups, and (2) coordinative PSM, where organic molecules containing metal ligating groups are introduced onto the inorganic secondary building units (SBUs) of the MOF. These methods have evolved from simple efforts to modifying MOFs to demonstrate proof-of-concept, to becoming key synthetic tools for advancing MOFs for a range of emerging applications, including selective gas sorption, catalysis, and drug delivery. Moreover, both covalent and coordinative PSM have been used to create hierarchal MOFs, MOF-based porous liquids, and other unusual MOF materials. This Outlook highlights recent reports that have extended the scope of PSM in MOFs, some seminal reports that have contributed to the advancement of PSM in MOFs, and our view on future directions of the field.
A UiO‐66‐NCS MOF was formed by postsynthetic modification of UiO‐66‐NH2. The UiO‐66‐NCS MOFs displays a circa 20‐fold increase in activity against the chemical warfare agent simulant ...dimethyl‐4‐nitrophenyl phosphate (DMNP) compared to UiO‐66‐NH2, making it the most active MOF materials using a validated high‐throughput screening. The −NCS functional groups provide reactive handles for postsynthetic polymerization of the MOFs into functional materials. These MOFs can be tethered to amine‐terminated polypropylene polymers (Jeffamines) through a facile room‐temperature synthesis with no byproducts. The MOFs are then crosslinked into a MOF–polythiourea (MOF–PTU) composite material, maintaining the catalytic properties of the MOF and the flexibility of the polymer. This MOF–PTU hybrid material was spray‐coated onto Nyco textile fibers, displaying excellent adhesion to the fiber surface. The spray‐coated fibers were screened for the degradation of DMNP and showed durable catalytic reactivity.
MOF–polythiourea hybrid materials were synthesized by postsynthetic polymerization of a UiO‐66 derivative bearing isothiocyanate groups (UiO‐66‐NCS). These were screened for the degradation of a chemical warfare agent simulant. The MOF–polythiourea materials spray‐coated onto textile fibers displayed activity against a chemical warfare agent simulant, maintaining activity after physical agitation.
We report the first self-assembled porous monolayer and free-standing multilayer films composed of metal–organic framework (MOF) nanoparticles. Self-assembled MOF monolayers (SAMMs) were assembled at ...a liquid–air interface to produce films that are 87 wt % (89 vol %) MOF. Monolayer self-assembly was aided by growing a layer of poly(methyl methacrylate) (PMMA) on the particle surface using a histamine anchor. SAMMs could be stacked to obtain MOF multilayers, including alternating MOF/polymer heterostructures. SAMMs were coated on silicon microparticles, and a MOF film constructed of only five stacked layers could be manipulated as a free-standing, opalescent film. These monolayers are a significant advancement for obtaining highly functional porous membranes and coatings.
Hybridization of metal–organic frameworks (MOFs) and polymers into composites yields materials that display the exceptional properties of MOFs with the robustness of polymers. However, the ...realization of MOF–polymer composites requires efficient dispersion and interactions of MOF particles with polymer matrices, which remains a significant challenge. Herein, we report a simple, scalable, bench‐top approach to covalently tethered nylon–MOF polymer composite materials through an interfacial polymerization technique. The copolymerization of a modified UiO‐66‐NH2 MOF with a growing polyamide fiber (PA‐66) during an interfacial polymerization gave hybrid materials with up to around 29 weight percent MOF. The covalent hybrid material demonstrated nearly an order of magnitude higher catalytic activity for the breakdown of a chemical warfare simulant (dimethyl‐4‐nitrophenyl phosphate, DMNP) compared to MOFs that are non‐covalently, physically entrapped in nylon, thus highlighting the importance of MOF–polymer hybridization.
Two become one: The hybridization of metal‐organic frameworks (MOFs) and nylon polymers into composites through postsynthetic polymerization is reported. This simple, scalable, bench‐top approach provides a new method to design hybrid materials containing MOFs and polymers while maintaining the desired properties of both materials.
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.
Bending the linear uranyl (UO2 2+) cation represents both a significant challenge and opportunity within the field of actinide hybrid materials. As part of related efforts to engage the nominally ...terminal oxo atoms of uranyl cation in noncovalent interactions, we synthesized a new uranyl complex, UO2(C12H8N2)2(C7H2Cl3O2)2·2H2O (complex 2), that featured both deviations from equatorial planarity and uranyl linearity from simple hydrothermal conditions. Based on this complex, we developed an approach to probe the nature and origin of uranyl bending within a family of hybrid materials, which was done via the synthesis of complexes 1–3 that display significant deviations from equatorial planarity and uranyl linearity (O–U–O bond angles between 162° and 164°) featuring 2,4,6-trihalobenzoic acid ligands (where Hal = F, Cl, and Br) and 1,10-phenanthroline, along with nine additional “nonbent” hybrid materials that either coformed with the “bent” complexes (4–6) or were prepared as part of complementary efforts to understand the mechanism(s) of uranyl bending (7–12). Complexes were characterized via single crystal X-ray diffraction and Raman, infrared (IR), and luminescence spectroscopy, as well as via quantum chemical calculations and density-based quantum theory of atoms in molecules (QTAIM) analysis. Looking comprehensively, these results are compared with the small library of bent uranyl complexes in the literature, and herein we computationally demonstrate the origin of uranyl bending and delineate the energetics behind this process.
A new uranyl containing metal–organic framework, RPL‐1: (UO2)2(C28H18O8) . H2O (RPL for Radiochemical Processing Laboratory), was prepared, structurally characterized, and the solid‐state ...photoluminescence properties explored. Single crystal X‐ray diffraction data reveals the structure of RPL‐1 consists of two crystallographically unique three dimensional, interpenetrating nets with a 4,3‐connected tbo topology. Each net contains large pores with an average width of 22.8 Å and is formed from monomeric, hexagonal bipyramidal uranyl nodes that are linked via 1,2,4,5‐tetrakis(4‐carboxyphenyl)benzene (TCPB) ligands. The thermal and photophysical properties of RPL‐1 were investigated using thermogravimetric analysis and absorbance, fluorescence, and lifetime spectroscopies. The material displays excellent thermal stability and temperature dependent uranyl and TCPB luminescence. The framework is stable in aqueous media and due to the large void space (constituting 76 % of the unit cell by volume) can sequester organic dyes, the uptake of which induces a visible change to the color of the material.
A new luminescent uranyl containing metal–organic framework, RPL‐1: (UO2)2(C28H18O8) . H2O (RPL for Radiochemical Processing Laboratory), was prepared and structurally characterized. The structure consists of interpenetrating nets with large pores (Avg. 22.8 Å) and a 4,3‐connected tbo topology. The material exhibits high thermal and aqueous stability and due to the large void space (constituting 76 % of the unit cell by volume) can sequester organic dyes of various size and charge.
Hybrid materials bearing elements from the 5f block display a rich diversity of coordination geometries, connectivities, and assembly motifs. Exemplary in this regard have been uranyl coordination ...polymers, which feature a wide range of secondary building units resulting from hydrolysis and oligomerization of the UO22+ cation. An alternative approach to novel materials, however, suppresses hydrolysis and relies on non‐covalent interactions (e.g. hydrogen or halogen bonding) to direct assembly of a more limited suite of species or building units. This may be achieved through the use of high‐anion media to promote singular actinyl anions that are assembled with organic cations, or by way of functionalized chelating ligands that produce complexes suited for assembly through peripheral donor/acceptor sites. Presented in this Concept article is therefore an overview of our efforts in this arena. We highlight examples of each approach, share our thoughts regarding delineation of assembly criteria, and discuss the opportunities for exploring structure–property relationships in these systems.
The concept of restricting aqueous actinyl speciation as a route to generating families of solid‐state hybrid materials is delineated using examples from both high anion media and coordination chemistry. Design principles relying on non‐covalent interactions for assembly are highlighted, as are structural trends across families of related complexes. Structure–property relationships as well as paths forward for continued work in this arena are described.
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.
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