Catalysis is a ubiquitous element of the modern economy, representing a cornerstone of many sectors including energy, materials, and pharmaceuticals. Within this realm, 80% of reactions are carried ...out by heterogeneous catalysts due to their advantageous physical and chemical characteristics. In some heterogeneous systems, the reaction rate can be optimized through rational catalyst design, in which support materials can be tailored structurally and stereoelectronically for targeted purposes to better facilitate the catalytic reaction. To this end, metal–organic frameworks (MOFs) have garnered recent attention due to their high porosity, crystallinity, and chemical tunability, which can be used to derive structure–activity relationships in the design of catalysts. In this Perspective, we survey examples of catalytically active guest metals on the inorganic nodes of MOFs. This is done with the intention of providing design guidelines for tailoring chemical reactivity and insights into the opportunities for future growth in this field. Strategies for rational design in MOF catalysis include electronic tuning of the metal node in the MOF support, installing promoter ions onto the node to effect the reactivity of grafted metals, modulation of the spatial environment around the transition metal using the metal node structure, and achieving site uniformity in supported catalysts. By highlighting these efforts, we seek to underscore the role of MOF nodes as nonspectator supports for catalytic metal complexes and provide future directions for rational catalyst design by tuning reactivity on these anchoring platforms.
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Enzymes are promising catalysts with high selectivity and activity under mild reaction conditions. However, their practical application has largely been hindered by their high cost and poor ...stability. Metal-organic frameworks (MOFs) as host materials show potential in protecting proteins against denaturing conditions, but a systematic study investigating the stabilizing mechanism is still lacking. In this study, we stabilized enzyme cytochrome c (cyt c) by encapsulating it in a hierarchical mesoporous zirconium-based MOF, NU-1000 against denaturing organic solvents. Cyt c@NU-1000 showed a significantly enhanced activity compared to the native enzyme, and the composite retained this enhanced activity after treatment with five denaturing organic solvents. Moreover, the composite was recyclable without activity loss for at least three cycles. Our cyt c@NU-1000 model system demonstrates that enzyme@MOF composites prepared via post-synthetic encapsulation offer a promising route to overcome the challenges of enzyme stability and recyclability that impede the widespread adoption of biocatalysis.
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•Catalytic activity of cytochrome c was protected against denaturing organic solvents•The mesoporous MOF stabilized cytochrome c by preventing enzyme aggregation•The enzyme@MOF composite was recyclable for at least three cycles•This enzyme@MOF system is promising for developing robust biocatalyst
Chemistry; Green chemistry; Engineering; Biocatalysis; Materials chemistry;
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Zirconium-based metal-organic frameworks (Zr-MOFs) have been explored for applications including but not limited to water adsorption, gas storage and separation, heterogeneous catalysis, and chemical ...sensing. Zr-MOFs serve as a major class of functional MOFs thanks to their high thermal, chemical and hydrolytic stability, large surface area, and tunable structures with the versatile connectivity. In this work, we highlight the design and synthesis of zirconium-based MOFs as well as their applications. Specifically, we demonstrate how reticular chemistry can direct the rational design and synthesis of functional Zr-MOFs and describe their structure–property relationship. In addition, we feature synthetic strategies, including isoreticular expansion, linker functionalization, node functionalization, and defect engineering, as toolkits to construct tailored material for specific applications.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Metal–organic frameworks (MOFs) have demonstrated their versatility in a wide range of applications, including chemical separation, gas capture, and storage. In industrial adsorption processes, MOFs ...are integral to the creation of selective gas adsorption fixed beds. In this context, the assessment of their separation performance under relevant conditions often relies on breakthrough experiments. One aspect frequently overlooked in these experiments is the shaping of MOF powders, which can significantly impact the accuracy of breakthrough results. In this study, we present an approach for immobilizing MOF particles on the surface of glass beads (GBs) utilizing trimethylolpropane triglycidyl ether (TMPTGE) as a binder, leading to the creation of MOF@GB materials. We successfully synthesized five targeted MOF composites, namely, SIFSIX-3-Ni@GB, CALF-20@GB, UiO-66@GB, HKUST-1@GB, and MOF-808@GB, each possessing distinct pore sizes and structural topologies. Characterization studies employing powder X-ray diffraction and adsorption isotherm analyses demonstrated that MOFs@GB retained their crystallinity and 73–90% of the Brunauer–Emmett–Teller area of their parent MOFs. Dynamic breakthrough experiments revealed that, in comparison to their parent MOFs, MOF@GB configurations enhanced the accuracy of breakthrough measurements by mitigating pressure buildup and minimizing reductions in the gas flow rate. This work underscores the significance of meticulous experimental design, specifically in shaping MOF powders, to optimize the efficacy of breakthrough experiments. Our proposed strategy aims to provide a versatile platform for MOF powder processing, thereby facilitating more reliable breakthrough experiments.
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Efficient separation of xenon (Xe) and krypton (Kr) mixtures through vacuum swing adsorption (VSA) is considered the most attractive route to reduce energy consumption, but discriminating between ...these two gases is difficult due to their similar properties. In this work, we report a cubic zirconium-based MOF (Zr-MOF) platform, denoted as NU-1107, capable of achieving selective separation of Xe/Kr by post-synthetically engineering framework polarizability in a programmable manner. Specifically, the tetratopic linkers in NU-1107 feature tetradentate cyclen cores that are capable of chelating a variety of transition-metal ions, affording a sequence of metal-docked cationic isostructural Zr-MOFs. NU-1107-Ag(I), which features the strongest framework polarizability among this series, achieves the best performance for a 20:80 v/v Xe/Kr mixture at 298 K and 1.0 bar with an ideal adsorbed solution theory (IAST) predicted selectivity of 13.4, placing it among the highest performing MOF materials reported to date. Notably, the Xe/Kr separation performance for NU-1107-Ag(I) is significantly better than that of the isoreticular, porphyrin-based MOF-525-Ag(II), highlighting how the cyclen core can generate relatively stronger framework polarizability through the formation of low-valent Ag(I) species and polarizable counteranions. Density functional theory (DFT) calculations corroborate these experimental results and suggest strong interactions between Xe and exposed Ag(I) sites in NU-1107-Ag(I). Finally, we validated this framework polarizability regulation approach by demonstrating the effectiveness of NU-1107-Ag(I) toward C3H6/C3H8 separation, indicating that this generalizable strategy can facilitate the bespoke synthesis of polarized porous materials for targeted separations.
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Isothermal titration calorimetry (ITC) is a technique which directly measures the thermodynamic parameters of binding events. Although historically it has been used to investigate interactions in ...biological macromolecules and the kinetics of enzyme-catalyzed reactions, ITC has also been demonstrated to provide relevant thermodynamic information about interactions in synthetic systems, such as those in metal–organic frameworks (MOFs). MOFs are a family of crystalline porous materials that have been widely studied as supports for molecules ranging from gases to biomolecules through physisorption and chemisorption. Herein, we offer a perspective on the current applications of ITC in MOFs, including the mechanism of small molecule adsorption and the formation of MOF-based composite materials through noncovalent interactions. Experimental considerations specific to running ITC experiments in MOF systems are reviewed on the basis of existing reports. We conclude by discussing underexplored, but promising, MOF-related research directions which could be elucidated by ITC.
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The encapsulation of enzymes within porous materials has shown great promise, not only in protecting the enzymes from denaturation under nonbiological environments, but also, in some cases, in ...facilitating their enzymatic reaction rates at favorable reaction conditions. While a number of hypotheses have been developed to explain this phenomenon, the detailed structural changes of the enzymes upon encapsulation within the porous material, which are closely related to their activity, remain largely elusive. Herein, the structural change of cytochrome c (Cyt c) upon encapsulation within a hierarchical metal–organic framework, NU-1000, is investigated through a combination of experimental and computational methods, such as electron paramagnetic resonance, solid-state ultraviolet–visible spectroscopy, and all-atom explicit solvent molecular dynamics simulations. The enhanced catalytic performance of Cyt c after being encapsulated within NU-1000 is supported by the physical and in silico observations of a change around the heme ferric active center.
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Hydrolytically stable materials exhibiting a wide range of programmable water sorption behaviors are crucial for on-demand water sorption systems. While notable advancements in employing ...metal–organic frameworks (MOFs) as promising water adsorbents have been made, developing a robust yet easily tailorable MOF scaffold for specific operational conditions remains a challenge. To address this demand, we employed a topology-guided linker installation strategy using NU-600, which is a zirconium-based MOF (Zr-MOF) that contains three vacant crystallographically defined coordination sites. Through a judicious selection of three N-heterocyclic auxiliary linkers of specific lengths, we installed them into designated sites, giving rise to six new MOFs bearing different combinations of linkers in predetermined positions. The resulting MOFs, denoted as NU-606 to NU-611, demonstrate enhanced structural stability against capillary force-driven channel collapse during water desorption due to the increased connectivity of the Zr6 clusters in the resulting MOFs. Furthermore, incorporating these auxiliary linkers with various hydrophilic N sites enables the systematic modulation of the pore-filling pressure from about 55% relative humidity (RH) for the parent NU-600 down to below 40% RH. This topology-driven linker installation strategy offers precise control of water sorption properties for MOFs, highlighting a facile route to design MOF adsorbents for use in water sorption applications.
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The removal of hexavalent chromium, Cr(VI), from wastewater remains a significant environmental challenge. In this study, we explored the effectiveness of a novel cationic metal–organic framework ...(MOF), designated as NU-56, for Cr(VI) removal from wastewater. NU-56, composed of a Zr6O8 cluster, monomeric Ni2+, and 3-aminoisonicotinic acid, exhibits a remarkable Cr(VI) removal capacity. Several factors contribute to its efficacy, including the presence of free exchangeable Cl– ions within the network, protonated amino groups on the ligand, and μ3-O/OH on the Zr6O8 cluster, all of which synergistically enhance NU-56’s ability to capture Cr(VI) efficiently under acidic aqueous conditions ranging from pH 4 to 6. In comparison to its isostructural counterpart lacking amino-functionalized isonicotinic acid, amino-functionalized NU-56 demonstrates superior structural integrity during the Cr(VI) elimination process. Additionally, we conducted comprehensive studies on the adsorption kinetics, isotherms, and selectivity of NU-56 for Cr(VI) removal, revealing its potential as a promising candidate with a maximum adsorption capacity of 68 mg/g. This research underscores the significance of developing functionalized MOFs as a viable approach for the removal of oxy-anions from wastewater, offering a straightforward and effective solution to address this pressing environmental concern.
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Polyoxometalates (POMs) are discrete anionic clusters whose rich redox properties, strong Bro̷nsted acidity, and high availability of active sites make them potent catalysts for oxidation reactions. ...Metal–organic frameworks (MOFs) have emerged as tunable, porous platforms to immobilize POMs, thus increasing their solution stability and catalytic activity. While POM@MOF composite materials have been widely used for a variety of applications, little is known about the thermodynamics of the encapsulation process. Here, we utilize an up-and-coming technique in the field of heterogeneous materials, isothermal titration calorimetry (ITC), to obtain full thermodynamic profiles (ΔH, ΔS, ΔG, and K a) of POM binding. Six different 8-connected hexanuclear Zr-MOFs were investigated to determine the impact of MOF topology (csq, scu, and the) on POM encapsulation thermodynamics.
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