Omar Farha

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 …

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 …

Control of humidity within confined spaces is critical for maintaining air quality and human well-being, with implications for environments ranging from international space stations and pharmacies to granaries and cultural relic preservation sites. However, existing techniques rely on energy-intensive electrically driven equipment or complex temperature and humidity control (THC) systems, resulting in imprecision and inconvenience. The development of innovative techniques and materials capable of simultaneously meeting the stringent requirements of practical applications holds the key to creating intelligent and energy-efficient humidity control devices. In this study, we introduce chiral reticular chemistry as a tailored synthetic approach, targeting a highly porous hea topological framework characterized by intrinsic interpenetrating pore architecture. This groundbreaking design successfully circumvents the …

CALF-20, a Zn-triazolate-based metal–organic framework (MOF), is one of the most promising adsorbent materials for CO2 capture. However, competitive adsorption of water severely limits its performance when the relative humidity (RH) exceeds 40%, limiting the potential implementation of CALF-20 in practical settings where CO2 is saturated with moisture, such as postcombustion flue gas. In this work, three newly designed MOFs related to CALF-20, denoted as NU-220, CALF-20M-w, and CALF-20M-e that feature hydrophobic methyltriazolate linkers, are presented. Inclusion of methyl groups in the linker is proposed as a strategy to improve the uptake of CO2 in the presence of water. Notably, both CALF-20M-w and CALF-20M-e retain over 20% of their initial CO2 capture efficiency at 70% RH─a threshold at which CALF-20 shows negligible CO2 uptake. Grand canonical Monte Carlo simulations reveal that the …

Sulfur dioxide (SO2) is a harmful acidic gas generated from power plants and fossil fuel combustion and represents a significant health risk and threat to the environment. Benzimidazole-linked polymers (BILPs) have emerged as a promising class of porous solid adsorbents for toxic gases because of their chemical and thermal stability as well as the chemical nature of the imidazole moiety. The performance of BILPs in SO2 capture was examined by synergistic experimental and theoretical studies. BILPs exhibit a significantly high SO2 uptake of up to 8.5 mmol g–1 at 298 K and 1.0 bar. The density functional theory (DFT) calculations predict that this high SO2 uptake is due to the dipole–dipole interactions between SO2 and the functionalized polymer frames through O2S(δ+)···N(δ–)-imine and O═S═O(δ–)···H(δ+)-aryl and intermolecular attraction between SO2 molecules (O═S═O(δ–)···S(δ+)O2). Moderate …

Enzymes are natural catalysts for a wide range of metabolic chemical transformations, including selective hydrolysis, oxidation, and phosphorylation. Herein, we demonstrate a strategy for the encapsulation of enzymes within a highly stable zirconium-based metal-organic framework. UiO-66-F4 was synthesized under mild conditions using an enzyme-compatible amino acid modulator, serine, at a modest temperature in an aqueous solution. Enzyme@UiO-66-F4 biocomposites were then formed by an in situ encapsulation route in which UiO-66-F4 grows around the enzymes and, consequently, provides protection for the enzymes. A range of enzymes, namely, lysozyme, horseradish peroxidase, and amano lipase, were successfully encapsulated within UiO-66-F4. We further demonstrate that the resulting biocomposites are stable under conditions that could denature many enzymes. Horseradish peroxidase …

Metal-organic frameworks (MOF) are a subclass of porous framework materials that have been used for a wide variety of applications in sensing, catalysis, and remediation. Among these myriad applications is their remarkable ability to capture substances in a variety of environments ranging from benign to extreme. Among the most common and problematic substances found throughout the world’s oceans and water supplies is [UO2]2+, a common mobile ion of uranium, which is found both naturally and as a result of anthropogenic activities, leading to problematic environmental contamination. While some MOFs possess high capability for the uptake of [UO2]2+, many more of the thousands of MOFs and their modifications that have been produced over the years have yet to be studied for their ability to uptake [UO2]2+. However, studying the thousands of MOFs and their modifications presents an incredibly difficult …

The local environment of a metal active site plays an important role in affecting the catalytic activity and selectivity. In recent studies, tailoring the behavior of a molybdenum-based active site via modulation of the first coordination sphere has led to improved thioanisole oxidation performance, but disentangling electronic effects from steric influences that arise from these modifications is nontrivial, especially in heterogeneous systems. To this end, the tunability of metal–organic frameworks (MOFs) makes them promising scaffolds for controlling the coordination sphere of a heterogeneous, catalytically active metal site while offering additional attractive features such as crystallinity and high porosity. Herein, we report a variety of MOF-supported Mo species, which were investigated for catalytic thioanisole oxidation to methyl phenyl sulfoxide and/or methyl phenyl sulfone using tert-butyl hydroperoxide (tBHP) as the …

Hydrogen (H2) is a clean alternative to fossil fuels and can be produced by using renewable energy sources. However, due to its low volumetric energy density, H2 storage requires low temperatures and/or high pressures for practical applications. H2 storage using metal–organic frameworks (MOFs) has gained traction due to the large surface areas and highly tunable nature of MOFs, but suitable materials for room-temperature storage remain elusive. In this study, we performed ab initio calculations to study H2 storage at room temperature in two anionic MOFs (NOTT-200 and SU-102) and examined the effects of different exchanged metal cations (Li+, Na+, K+, Mg2+, and Ca2+) on hydrogen adsorption. Our results show that the H2 adsorption enthalpy on Mg2+ cations is the highest among the cations studied, with average adsorption enthalpies of −18.7 and −23.3 kJ/mol at three H2 molecules per Mg2+ in NOTT …

Despite global efforts to reduce carbon dioxide (CO2) emissions, continued industrialization threatens to exacerbate climate change. This work investigates methods to capture CO2, with a focus on the SIFSIX-3-Ni metal–organic framework (MOF) as a direct air capture (DAC) sorbent. SIFSIX-3-Ni exhibits promising CO2 adsorption properties but suffers from degradation processes under accelerated aging, which are akin to column regeneration conditions. Herein, we have grown the largest SIFSIX-3-Ni single crystals to date, facilitating single crystal X-ray diffraction analyses that enabled direct observation of the H2O and CO2 dynamics through adsorption and desorption. In addition, a novel space group (I4/mcm) for the SIFSIX-3-Ni is identified, which provided insights into structural transitions within the framework and elucidated water’s role in degrading CO2 uptake performance as the material ages. In situ X-ray …

Although metal–organic frameworks (MOFs) composed of Zr-based nodes and phosphonate-based linkers show promise in terms of their excellent stability, synthetic strategies to access them are underdeveloped due to the less reversible coordination between Zr-based nodes and phosphonate groups. In this work, we developed a generalizable strategy to access Zr–phosphonate MOFs in two steps via post-synthesis modification which allows for retaining the topology of parent Zr MOFs. Solvent-assisted ligand exchange (SALE) replaces carboxylate linkers with phosphinate linkers, and post-synthetic oxidation affords phosphonate-based linkers. We confirmed the structures through single-crystal X-ray diffraction (SCXRD) studies and fully characterized each MOF through a variety of other techniques. Water and ammonia sorption isotherms reveal that incorporation of phosphonate groups yields a more …

Organophosphorus chemicals, including chemical warfare agents (CWAs) and insecticides, are acutely toxic materials that warrant capture and degradation. Metal–organic frameworks (MOFs) have emerged as a class of tunable, porous, crystalline materials capable of hydrolytically cleaving, and thus detoxifying, several organophosphorus nerve agents and their simulants. One such MOF is M-MFU-4l (M = metal), a bioinspired azolate framework whose metal node is composed of a variety of divalent first-row transition metals. While Cu-MFU-4l and Zn-MFU-4l are shown to rapidly degrade CWA simulants, Ni-MFU-4l and Co-MFU-4l display drastically lower activities. The lack of reactivity was hypothesized to arise from the strong binding of the phosphate product to the node, which deactivates the catalyst by preventing turnover. No such study has provided detailed insight into this mechanism. Here, we leverage …

Defect engineering proves to be a highly effective approach for introducing additional open metal sites and porosity into metal–organic frameworks (MOFs), thereby enhancing their gas storage, separation, and chemical catalysis capabilities. However, characterizing defective MOFs, which often exhibit nonuniform pores, presents a significant challenge. While probe molecules have been widely utilized to explore the physical and chemical properties of MOF pores, their application has predominantly been limited to gas- or vapor-phase molecules. In this study, we present a novel approach by employing a size-selective fluorescent protein probe to characterize macroporous defects induced by tartaric acid in a zirconium-based MOF, NU-1000. The spatial visualization of defects using a hemoglobin-based fluorescent probe allows for the identification of distinct structural weak points and defect formation mechanisms …

Hydrogen is considered a crucial clean energy vector to mitigate climate change, but due to the low volumetric energy density of gaseous hydrogen, it is difficult to store hydrogen for many practical applications. Cryogenic sorption-based methods, particularly using metal–organic frameworks (MOFs), have been considered as viable solutions to enhance the deliverable capacity of stored hydrogen, and among the many available MOFs, those with rht topology have demonstrated exceptional capacity. MOFs with rht topology are formed by the assembly of supermolecular building blocks (SBBs), but the diversity of SBBs in the literature on rht-MOFs is limited, resulting in an underexplored structural design space. In this study, we designed 380 MOFs made of 20 novel SBBs to investigate the effect of cavity size on hydrogen storage capacity and the underlying structure–property relationships. We performed grand …

The development of reticular chemistry has enabled the construction of a large array of metal–organic frameworks (MOFs) with diverse net topologies and functions. However, dominating this class of materials are those built from discrete/finite secondary building units (SBUs), yet the designed synthesis of frameworks involving infinite rod‐shaped SBUs remain underdeveloped. Here, by virtue of a global linker desymmetrization approach, we successfully targeted a novel Cu‐MOF (Cu‐ASY) incorporating infinite Cu‐carboxylate rod SBUs with its structure determined by micro electron diffraction (MicroED) crystallography. Interestingly, the rod SBU can be simplified as a unique cylindric sphere packing qbe tubule made of [43.62] tiles, which further connect the tritopic linkers to give a newly discovered 3,5‐connected gfc net. Cu‐ASY is a permanent ultramicroporous material featuring 1D channels with highly inert …

Three copolymers with conjugated structures, PTB1–PTB3, were produced utilizing a palladium-catalyzed cyclopentannulation polymerization by reacting a specially designed diethynyl Tröger’s base surrogate with different dihalogenated polycondensed aromatic hydrocarbons. Brunauer, Emmet, and Teller nitrogen gas adsorption investigation revealed the surface areas of the copolymers, attaining ∼365 m2 g–1. Gas uptake studies demonstrated a considerable carbon dioxide uptake for PTB2 of 44.41 mg g–1 at 273 K and a promising H2 gas uptake of 3.18 mg g–1 at 77 K. PTB1–PTB3 displayed a sizable iodine adsorption capacity, achieving 4000 mg g–1, and mechanistic investigations demonstrated the prevalence of a pseudo-second-order kinetic model. Recyclability experiments proved the effective regeneration of the copolymers, even after performing several adsorption and desorption tests.

Metal–organic frameworks (MOFs) are some of the best materials for energy-efficient separations, like membranes and adsorption processes, due to their nanoporosity and tunability. To tune a MOF for optimum separation of molecules with sub-angstrom differences in size, which is a common challenge in industrial separations, precise control of the local pore environment is required. Here, we explore the concept of “3-dimensional” linkers, i.e., linkers that contain sterically bulky non-planar cores, as a means to attain sub-angstrom control over MOF pore size and to control structural flexibility. In particular, the introduction of 3-dimensional linkers (3DLs) is shown to hinder global breathing transitions in MOFs. Because these linkers occupy a consistent volume regardless of their orientation, they also allow for precise size-based separation of very similar molecules, such as hexane isomers. Furthermore, we discuss …

Metal–organic frameworks (MOFs) make up a class of crystalline, nanoporous materials that are recognized for their tunability. While some MOFs demonstrate flexibility, this characteristic can pose challenges in achieving precise pore control or establishing permanent porosity. Specifically, MIL-88B is notable for its high flexibility, as it is constructed from metal trimer clusters and two-dimensional linkers (2DLs) featuring planar, aromatic cores, allowing significant structural changes. In this study, we synthesized two new MOFs, NU-2010 and NU-2011, which are structurally analogous to MIL-88B but incorporate ditopic three-dimensional linkers (3DLs) with sterically bulky cores and higher symmetry. Our aim was to investigate whether the introduction of 3DLs could mitigate the flexibility observed in MIL-88B. We employed a combination of single-crystal and powder X-ray diffraction techniques to assess the flexibility …

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 …

The development of stable physisorbents for water adsorption-related applications has attracted considerable attention owing to the demands of efficient water vapor capture in industrial production and processes. Metal-organic frameworks (MOFs), which feature high porosity and tunable porous structures and topologies, show promise as efficient water adsorbents and may afford significant energy savings in applications such as atmospheric water harvesting, adsorptive heat transformation, autonomous indoor humidity control, and desiccation of natural gases. This review focuses on recent progress in the development of MOF materials for water adsorption-related applications, covering the rational design and synthesis of MOFs with improved water adsorption performance via reticular chemistry. In particular, we highlight some of the latest advances in MOFs used in water adsorption application devices. Finally …

Proteins play important roles in the therapeutic, medical diagnostic, and chemical catalysis industries. However, their potential is often limited by their fragile and dynamic nature outside cellular environments. The encapsulation of proteins in solid materials has been widely pursued as a route to enhance their stability and ease of handling. Nevertheless, the experimental investigation of protein interactions with rationally designed synthetic hosts still represents an area in need of improvement. In this work, we leveraged the tunability and crystallinity of metal–organic frameworks (MOFs) and developed a series of crystallographically defined protein hosts with varying chemical properties. Through systematic studies, we identified the dominating mechanisms for protein encapsulation and developed a host material with well-tailored properties to effectively encapsulate the protein ubiquitin. Specifically, in our …

As we continue to develop metal–organic frameworks (MOFs) for potential industrial applications, it becomes increasingly imperative to understand their mechanical stability. Notably, amongst flexible MOFs, structure-property relationships regarding their compressibility under pressure remain unclear. In this work, we conducted in situ variable pressure powder X-ray diffraction (PXRD) measurements up to moderate pressures (<1 GPa) using a synchrotron source on two families of flexible MOFs: (i) NU-1400 and NU-1401, and (ii) MIL-88B, MIL-88B-(CH3)2, and MIL-88B-(CH3)4. In this project scope, we found a positive correlation between bulk moduli and degree of flexibility, where increased rigidity (e.g., smaller swelling or breathing amplitude) arising from steric hindrance was deleterious, and observed reversibility in the unit cell compression of these MOFs. This study serves as a primer for the community to …

Developing innovative porous solid sorbents for the capture and storage of toxic SO2 is crucial for energy-efficient transportation and subsequent processing. Nonetheless, the quest for high-performance SO2 sorbents, characterized by exceptional uptake capacity, minimal regeneration energy requirements, and outstanding recyclability under ambient conditions, remains a significant challenge. In this study, we present the design of a unique tertiary amine-embedded, pyrene-based quadripod-shaped ligand. This ligand is then assembled into a highly porous Zr-metal–organic framework (MOF) denoted as Zr-TPA, which exhibits a newly discovered 3,4,8-c woy net structure. Remarkably, our Zr-TPA MOF achieved an unprecedented SO2 sorption capacity of 22.7 mmol g–1 at 298 K and 1 bar, surpassing those of all previously reported solid sorbents. We elucidated the distinct SO2 sorption behaviors observed in …

CALF-20 is a zinc-triazole-oxalate-based metal–organic framework (MOF) that exhibits selective CO2 physisorption, which makes it attractive for potential applications in CO2 capture. However, to implement such applications, the CALF-20 structure must endure extended exposure to environmental conditions that may lead to changes in structure, chemistry, and, hence, performance. Here we find that the originally reported CALF-20 phase (now denoted α-CALF-20) undergoes a structure transformation following exposure to humid environments to generate a new polymorph, β-CALF-20, identified here through combined synchrotron powder X-ray diffraction and pair distribution function (PDF) analysis. This α-to-β transformation is fully reversible with α-CALF-20 being regenerated by treating β-CALF-20 under dry air or vacuum. The rapid reversion of β- to α-CALF-20 under conditions relevant to measuring the gas …

The increase in the atmospheric carbon dioxide level is a significant threat to our planet, and therefore the selective removal of CO2 from the air is a global concern. Metal–organic frameworks (MOFs) are a class of porous materials that have shown exciting potential as adsorbents for CO2 capture due to their high surface area and tunable properties. Among several implemented technologies, direct air capture (DAC) using MOFs is a promising strategy for achieving climate targets as it has the potential to actively reduce the atmospheric CO2 concentration to a safer levels. In this study, we investigate the stability and regeneration conditions of N,N′-dimethylethylenediamine (mmen) appended Mg2(dobpdc), a MOF with exceptional CO2 adsorption capacity from atmospheric air. We employed a series of systematic experiments including thermogravimetric analysis (TGA) coupled with Fourier transformed infrared …

Reticular chemistry allows for the rational assembly of metal–organic frameworks (MOFs) with designed structures and desirable functionalities for advanced applications. However, it remains challenging to construct multi-component MOFs with unprecedented complexity and control through insertion of secondary or ternary linkers. Herein, we demonstrate that a Zr-based MOF, NU-600 with a (4,6)-connected she topology, has been judiciously selected to employ a linker installation strategy to precisely insert two linear linkers with different lengths into two crystallographically distinct pockets in a one-pot, de novo reaction. We reveal that the hydrolytic stability of these linker-inserted MOFs can be remarkably reinforced by increasing the Zr6 node connectivity, while maintaining comparable water uptake capacity and pore-filling pressure as the pristine NU-600. Furthermore, introducing hydrophilic −OH groups into the …

Mesoporous zirconium metal-organic frameworks (MOFs) having insulin immobilized therein and methods of using the MOFs in insulin delivery are provided. The insulin-loaded metal-organic framework molecules include a porous zirconium metal-organic framework molecule and insulin molecules within pores of the porous zirconium metal-organic framework.

Metal–organic frameworks (MOFs) have been proposed as a promising material for non‐thermal chemical separations owing to their high structural diversity and tunability. Here, we report the synthesis of a zinc‐based MOF containing a three‐dimensional (3D) linker, bicyclo[2.2.2]octane‐1,4‐dicarboxylic acid, with high thermal stability towards the separation of hexane isomers. The incorporation of the 3D linker enhances the structural stability and provides well‐defined pore apertures/channels with sub‐Ångstrom precision. This precision allowed for the separation of similarly sized hexane isomers based on subtle differences in their kinetic diameters. Multi‐component liquid phase batch experiments confirmed the separation of hexanes mixture into linear, monobranched, and dibranched isomers. This work represents a significant milestone in the construction of stable Zn‐based MOFs and the incorporation of 3D …

Metal–organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo[1.1.1]pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different …

The interactions between uranium and non‐innocent organic species are an essential component of fundamental uranium redox chemistry. However, they have seldom been explored in the context of multidimensional, porous materials. Uranium‐based metal–organic frameworks (MOFs) offer a new angle to study these interactions, as these self‐assembled species stabilize uranium species through immobilization by organic linkers within a crystalline framework, while potentially providing a method for adjusting metal oxidation state through coordination of non‐innocent linkers. We report the synthesis of the MOF NU‐1700, assembled from U4+‐paddlewheel nodes and catecholate‐based linkers. We propose this highly unusual structure, which contains two U4+ ions in a paddlewheel built from four linkers—a first among uranium materials—as a result of extensive characterization via powder X‐ray diffraction …

Synthetic organic polymers are typically insoluble polycrystalline or amorphous products rather than single crystals. Here we demonstrate that covalent polymer chains can achieve single-crystal form through the rational design of their hierarchical structure. Single-crystal X-ray diffraction analysis reveals that the polycondensation of 1,4-phenylenebisboronic acid yields a B4O52− cluster-based tetramer, which further extends into one-dimensional covalent chains that are physically crosslinked by hydrogen bonds and electrostatic interactions. These interactions ultimately afford a single crystal porous framework denoted as PHOF-1. Cryogenic electron microscopy and gel permeation chromatography studies indicate that the dissolved PHOF-1 maintains the consecutive one-dimensional chain structure with a very narrow molecular weight distribution. This solution processibility enables the continuous coating PHOF …

Developing materials that can more efficiently and cheaply capture carbon dioxide from ambient atmospheric conditions is essential for improving negative emission technologies. This study builds on the promising moisture-swing modality for direct air capture of carbon dioxide by investigating the use of several new anions─orthosilicate, borate, pyrophosphate, tripolyphosphate, and dibasic phosphate─that when introduced into ion-exchange resins allow for the cyclable capture of CO2 under dry conditions and its release under wet conditions. These ions, as well as many others that failed to show moisture-swing performance, are tested and directly compared thermodynamically and kinetically to understand their differences. This includes the use of analytical approaches new to the carbon capture field, such as the correlation of adsorption isotherms to moisture-swing performance, the use of phase lag kinetics …

In acute skin injury, healing is impaired by the excessive release of reactive oxygen species (ROS). Melanin, an efficient scavenger of radical species in the skin, performs a key role in ROS scavenging in response to UV radiation and is upregulated in response to toxic insult. In a chemical injury model in mice, we demonstrate that the topical application of synthetic melanin particles (SMPs) significantly decreases edema, reduces eschar detachment time, and increases the rate of wound area reduction compared to vehicle controls. Furthermore, these results were replicated in a UV-injury model. Immune array analysis shows downregulated gene expression in apoptotic and inflammatory signaling pathways consistent with histological reduction in apoptosis. Mechanistically, synthetic melanin intervention increases superoxide dismutase (SOD) activity, decreases Mmp9 expression, and suppresses ERK1/2 …

Functional porous metal–organic frameworks (MOFs) have been explored for a number of potential applications in catalysis, chemical sensing, water capture, gas storage, and separation. MOFs are among the most promising candidates to address challenges facing our society related to energy and environment, but the successful implementation of functional porous MOF materials are contingent on their stability; therefore, the rational design of stable MOFs plays an important role towards the development of functional porous MOFs. In this Focus article, we summarize progress in the rational design and synthesis of stable MOFs with controllable pores and functionalities. The implementation of reticular chemistry allows for the rational top-down design of stable porous MOFs with targeted topological networks and pore structures from the pre-selected building blocks. We highlight the reticular synthesis and …

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 …

Carbon capture, storage, and utilization (CCSU) represents an opportunity to mitigate carbon emissions that drive global anthropogenic climate change. Promising materials for CCSU through gas adsorption have been developed by leveraging the porosity, stability, and tunability of extended crystalline coordination polymers called metal–organic frameworks (MOFs). While the development of these frameworks has yielded highly effective CO2 sorbents, an in-depth understanding of the properties of MOF pores that lead to the most efficient uptake during sorption would benefit the rational design of more efficient CCSU materials. Though previous investigations of gas–pore interactions often assumed that the internal pore environment was static, discovery of more dynamic behavior represents an opportunity for precise sorbent engineering. Herein, we report a multifaceted in situ analysis following the adsorption of …

Countries around the world have sought efficient protective coverings, including masks, gowns, and fabrics, for air purification to protect people against infectious diseases. However, the demand for significant quantities of disposable protective textiles poses a global challenge, especially when the production of protective gear is suspended due to COVID-19 outbreaks in factories and along supply lines. Therefore, the development of reusable, self-decontaminating protective masks and coverings loaded with disinfectants, such as antibacterial peroxide species, presents an attractive strategy to fight against bacteria risks. In this work, we incorporated persulfate ions, which serve as stable active peroxide precursors, into two porous zirconium-based metal–organic frameworks (Zr-MOFs), enabling these materials to act as regenerable reservoirs for the slow release of biocidal hydrogen peroxide upon hydrolysis by …

Metal‐organic frameworks (MOFs) are a class of porous materials with high surface areas, which are acquiring rapid attention on an exponential basis. A significant characteristic of MOFs is their ability to act as adsorbents to selectively separate component mixtures of similar size, thereby addressing the technological need for an alternative approach to conventional distillation methods. Recently, MOFs comprising a 3‐Dimensional (3D) linker have shown outstanding capabilities for difficult separations compared to the parent 2‐Dimensional (2D) analogue. 3D‐linkers with a polycyclic core are underrepresented in the MOF database due to the widespread preferred use of 2D‐linkers and the misconceived high‐cost of 3D linkers. We summarize the recent research of 3D‐linker MOFs and highlight their beneficial employment for selective gas and hydrocarbon adsorption and separation. Furthermore, we outline …

The fine-tuning of metal–organic framework (MOF) pore structures is of critical importance in developing energy-efficient xenon/krypton (Xe/Kr) separation techniques. Capitalizing on reticular chemistry, we constructed a robust Y-based MOF (NU-1801) that is isoreticular to NPF-500 with a shortened organic ligand and a larger metal radius while maintaining the 4,8-connected flu topology, giving rise to a narrowed pore structure for the efficient separation of a Xe/Kr mixture. At 298 K and 1 bar, NU-1801 possessed a moderate Xe uptake of 2.79 mmol/g but exhibited a high Xe/Kr selectivity of 8.2 and an exceptional Xe/Kr uptake ratio of about 400%. NU-1801 could efficiently separate a Xe/Kr mixture (20:80, v/v), as validated by breakthrough experiments, due to the outstanding discrimination in van der Waals interactions of Xe and Kr toward the framework confirmed by grand canonical Monte Carlo simulations. This …

Crystalline materials undergo valuable phase transformations, and the energetic processes that underlie these transformations can be fully characterized through a combination of thermodynamic and kinetic studies. Here, we report the first complete reaction energy landscape of metal–organic framework (MOF) interpenetration, specifically in the phase transformation of NU-1200 to its doubly interpenetrated counterpart, STA-26. We characterized the thermodynamics of this phase transformation by pairing experiments with density functional theory (DFT) calculations. This analysis revealed that factors such as the increase in crystal density likely drive Zr- and Hf-NU-1200 to STA-26 interpenetration, while other chemical interactions such as steric repulsions prevent Th-NU-1200 from interpenetrating. Using time-resolved in situ X-ray diffraction, we monitored phase transformation reaction profiles and extracted …

Hydrogen is an essential gas to multiple industrial processes, and due to its high gravimetric density, it promises a large potential as a clean energy source. The risks of hydrogen at low pressures, however, have deterred substantial progress in improving hydrogen storage technology. Metal-organic frameworks (MOFs) are crystalline porous materials that have emerged as excellent gas adsorbents, and their gas storage properties can be tuned using a variety of synthetic methods. Herein, we leveraged the tunability and porosity of MOFs to introduce defect engineering as a method to improve hydrogen storage technology at low pressure regimes in two zirconium-based MOFs (Zr-MOFs), UiO-66 and NU-403, which feature ideal pore apertures (7 Å) for studying the confinement effect and ease of defect engineering. By reducing the number of defects in these Zr-MOFs, and thereby decreasing the quantity of larger …

Hexane isomers play a vital role as feedstocks and fuel additives in the petrochemical industry. However, their similar physical and chemical properties lead to significant challenges in the separation process. Traditional thermal separation techniques are energy-intensive and lead to significant carbon footprint penalties. As such, there is a growing demand for the development of less energy-intensive nonthermal separation methods. Adsorption-based separation methods, such as using solid sorbents or membranes, have emerged as promising alternatives to distillation. Here, we report the successful synthesis of two novel metal–organic frameworks (MOFs), NU-2004 and NU-2005, by incorporating a carborane-based three-dimensional (3D) linker and using aluminum and vanadium nodes, respectively. These MOFs exhibit exceptional thermal stability and structural rigidity compared to other MIL-53 analogues …

Located at the foot of the periodic table, uranium is a relatively underexplored element possessing rich chemistry. In addition to its high relevance to nuclear power, uranium shows promise for small molecule activation and photocatalysis, among many other powerful functions. Researchers have used metal–organic frameworks (MOFs) to harness uranium's properties, and in their quest to do so, have discovered remarkable structures and unique properties unobserved in traditional transition metal MOFs. More recently, (e.g. the last 8–10 years), theoretical calculations of framework energetics have supplemented structure–property studies in uranium MOFs (U-MOFs). In this Perspective, we summarize how these budding energy–structure–property relationships in U-MOFs enable a deeper understanding of chemical phenomena, enlarge chemical space, and elevate the field to targeted, rather than exploratory …

The SARS-CoV-2 pandemic outbreak and the unfortunate misuse of toxic chemical warfare agents (CWAs) highlight the importance of developing functional materials to protect against these chemical and pathogen threats. Metal–organic frameworks (MOFs), which comprise a tunable class of crystalline porous materials built from inorganic nodes and organic linkers, have emerged as a class of heterogeneous catalysts capable of rapid detoxification of multiple classes of these harmful chemical or biological hazards. In particular, zirconium-based MOFs (Zr-MOFs) feature Lewis acidic nodes that serve as active sites for a wide range of catalytic reactions, including the hydrolysis of organophosphorus nerve agents within seconds in basic aqueous solutions. In addition, postsynthetic modification of Zr-MOFs enables the release of active species capable of reacting with and deactivating harmful pathogens. Despite this …

Recent research on metal–organic frameworks (MOFs) has shown a shift from considering only the crystalline high-porosity phases to exploring their amorphous counterparts. Applying pressure to a crystalline MOF is a common method of amorphization, as MOFs contain large void spaces that can collapse, reducing the accessible surface area. This can be either a desired change or indeed an unwanted side effect of the application of pressure. In either case, understanding the MOF’s pressure response is extremely important. Three such MOFs with varying pore sizes (UiO-66, MOF-808, and NU-1000) were investigated using in situ high-pressure X-ray diffraction and Raman spectroscopy. Partial crystallinity was observed in all three MOFs above 10 GPa, along with some recovery of crystallinity on return to ambient conditions if the frameworks were not compressed above thresholds of 13.3, 14.2, and 12.3 GPa for …

The mechanism of photochemical CO2 reduction to formate by PCN-136, a Zr-based metal–organic framework (MOF) that incorporates light-harvesting nanographene ligands, has been investigated using steady-state and time-resolved spectroscopy and density functional theory (DFT) calculations. The catalysis was found to proceed via a “photoreactive capture” mechanism, where Zr-based nodes serve to capture CO2 in the form of Zr–bicarbonates, while the nanographene ligands have a dual role of absorbing light and storing one-electron equivalents for catalysis. We also find that the process occurs via a “two-for-one” route, where a single photon initiates a cascade of electron/hydrogen atom transfers from the sacrificial donor to the CO2-bound MOF. The mechanistic findings obtained here illustrate several advantages of MOF-based architectures in molecular photocatalyst engineering and provide insights on …

Textile fibers at least partially coated with a coating that includes particles of metal-organic frameworks dispersed in a polymeric base are provided. Also provided are fabrics formed from the textile fibers, protective gear and articles of clothing made from the fabrics, and methods of using the fibers and fabrics to catalyze the hydrolysis of organic molecules, such as organophosphate-based nerve agents, having hydrolysable bonds.

Starting with ferrocyanide ions in acidic aqueous solution, cyano-ferrate(II) species are post-synthetically grafted to the nodes of a mesoporous zirconium-based MOF, NU-1000. As indicated by single-crystal X-ray crystallography, grafting occurs by substitution of cyanide ligands by node-based hydroxo and oxo ligands rather than by substitution of node aqua ligands by cyanide ligands as bridges between Fe(II) and Zr(IV). The installed moieties yield a broad absorption band that is tentatively ascribed to iron-to-zirconium charge transfer. Consistent with Fe(III/II) redox activity, a modest fraction of the installed iron complexes are directly electrochemically addressable.

As carbon dioxide (CO2) levels rise to record levels an inexpensive low energy solution for sequestration of CO2 from the air is becoming more urgent. Many current carbon capture technologies focus on scrubbing CO2 from large scale industrial processes. This work by contrast aims to selectively remove CO2 from atmospheric conditions. Metal–organic frameworks (MOFs) are comprised of inorganic nodes joined by organic linkers which self-assemble to form crystalline ultra-microporous materials. By altering either the node or the linker the structure can be fine-tuned to a wide array of applications such as: gas capture, storage, and separation applications as well as biomedicine and catalysis [1]. The SIF-SIX-nM MOF family is comprised of SiF6 linkers which connect via pyrazine and metal M2+ nodes (M: Fe, Co, Ni, Cu, Zn) to form 3D microporous networks (Fig. 1a). This family of MOFs have a strong affinity to …

While uranyl-based metal–organic frameworks (MOFs) boast impressive photocatalytic abilities, significant questions remain regarding their excitation pathways and methods to fine-tune their performance due to the lack of information regarding heterogeneous uranyl catalysis. Herein, we investigated how linker identity and photoexcitation impact uranyl photocatalysis when the uranyl coordination environment remains constant. Toward this end, we prepared three uranyl-based MOFs (NU-1301, NU-1307, and ZnTCPP-U2) and then examined the structural and photochemical properties of each through X-ray diffraction, X-ray absorption, and photoluminescence. We then correlated our observations to the photocatalytic performance for fluorination of cyclooctane. The excitation profile from NU-1301 and NU-1307 exhibited spin-forbidden linker transitions and uranyl vibronic progressions, with uranyl excitation and …

Metal–organic frameworks (MOFs) have been reported to effectively detoxify chemical warfare agents (CWAs) and their simulants. Early studies of Zr-MOF-catalyzed hydrolytic degradation of an organophosphoester type CWA, Sarin, and its simulant, dimethyl-4-nitrophenylphosphate (DMNP), suggested that the activity originates from ZrIV–OH–ZrIV moieties that resemble the structure of the active-site phosphotriesterase enzyme. Measurements of pKa values for hexa-zirconium-node-sited bridging hydroxo, terminal hydroxo, and aqua ligands reveal essentially complete conversion of mu-hydroxo ligands to substitution-inert mu-oxo ligands at alkaline pHs, ruling out a primary role for ZrIV–OH–ZrIV moieties, despite the resemblance to the phosphotriesterase enzyme active-site. The measurements also rule out a secondary role as a hydrogen bond donor/stabilizer of bound DMNP. Additionally, the measurements …

Integrating metal-organic frameworks (MOFs) onto textile fibers enables the preparation of MOF-based solid catalysts for practical protective applications such as the degradation of chemical warfare agents (CWAs). While MOF-coated fiber composites show promise for nerve agent hydrolysis under relevant conditions, it is critical to optimize the preparation of these composites to maximize their catalytic activity, permeability, and capture capabilities. Here, we systematically study multiple variables that can affect the catalytic activity and permeability of an MOF-polymer fiber composite based on a zirconium MOF and a non-volatile amine-based crosslinked polyethyleneimine: activation method, MOF mass loading, MOF particle size, and crosslinker amount. We determine that activation methods, MOF mass loadings, and MOF particle size are the most crucial parameters that affect the resulting composite. Ultimately …

Zirconium-based metal organic frameworks (MOFs) are of great significance in supramolecular coordination chemistry, mainly as catalysts, due to their chemical stability and structural diversity. We report the synthesis of zirconium-clathrochelate based crystalline MOFs (Zr-GU-1to -4) made from hexanuclear zirconium inorganic nodes and iron(II) clathrochelate-based ditopic carboxylic acid ligands bearing various lateral moieties, namely, butyl, cyclohexyl, phenyl and methyl groups. Among the various iron(II) clathrochelate linkers, the one with butyl side chains, i.e., Zr-GU-1, forms stable crystalline MOFs as confirmed by single-crystal X-ray crystallography and exhibits a promising porosity with a BET surface area of ∼650 m2 g−1 after its activation with supercritical CO2 (ScCO2) from acetonitrile.

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 …

The interplay of primary organic ligands and inorganic secondary building units (SBUs) has led to a continual boom of reticular chemistry, particularly metal–organic frameworks (MOFs). Subtle variations of organic ligands can have a significant impact on the ultimate structural topology and consequently, the material’s function. However, the role of ligand chirality in reticular chemistry has rarely been explored. In this work, we report the organic ligand chirality-controlled synthesis of two zirconium-based MOFs (Spiro-1 and Spiro-3) with distinct topological structures as well as a temperature-controlled formation of a kinetically stable phase (Spiro-4) based on the carboxylate-functionalized inherently axially chiral 1,1′-spirobiindane-7,7′-phosphoric acid ligand. Specifically, Spiro-1 is a homochiral framework comprising only enantiopure S-spiro ligands and has a unique 4,8-connected sjt topology with large 3D …

Metal–organic framework (MOF)-derived nanocarbons have emerged as promising materials for energy and environmental applications owing to their high surface area, structural and chemical tunability, and hierarchical porosity. Although various carbon-based materials such as graphene and carbon nanotubes have been extensively used as secondary sintering additives to develop advanced ceramics with improved mechanical, thermal, and electrical properties, the potential of MOF-derived nanocarbon-based materials has not been explored. Here, we report the first use of MOF-derived nanocarbons as a reinforcement phase in ceramic composites. To this end, Al2O3 and zeolitic imidazolate framework (ZIF-8) are used as the ceramic matrix and nanocarbon source, respectively. The ceramic composites are produced by densifying Al2O3 and ZIF-8 powder mixtures using spark plasma sintering (SPS) at 1550 …

A two-component undergraduate laboratory experience has been developed by students in a senior level capstone course. The first component is a 3 h laboratory experience dedicated to the rapid synthesis of a metal–organic framework (MOF-808) in aqueous solution using readily available reagents and equipment. During the second component, MOF-808 was characterized via a suite of instruments: powder X-ray diffraction (PXRD), thermal gravimetric analysis (TGA), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In addition, quantitative 19F{1H} NMR spectroscopy was utilized to quantify the amount of perfluorobutanesulfonate (PFBS), one example of a poly- or perfluoroalkyl substance (aka PFAS), adsorbed from solution. The two 3 h laboratory experiences were subsequently deployed in a foundation level inorganic chemistry course. This two-component, multi-instrument lab …

Acid modulator has been the most widely employed ingredient for highly crystalline metal–organic framework (MOF) synthesis. However, the mechanistic understanding of thorium (Th)-based MOF crystallization remains a great challenge due to the intrinsic properties of fast olation and oxolation reactions of Th species in solution. Here, we constructed a series of Th-based MOFs by adding different modulators (formic acid, acetic acid, trifluoroacetic acid, and benzoic acid) to a synthetic solution along with tetratopic 1,3,5,7-adamantane tetracarboxylic acid (H4ATC), a three-dimensional (3D) ligand with a rigid aliphatic backbone. This work presents an in-depth study of the structure–modulator relationship between the H4ATC ligand and coordinating modulators in the Th-based MOF crystallization process. Crystal structures of these Th-based MOFs reveal that formic acid and acetic acid modulators can compete with …

Benefiting from inherent lightweight, flexibility, and good adaptability to human body, functional textiles are attracting tremendous attention to cope with wearable issues in sustainable applications around human beings. In this feature article, a comprehensive and thoughtful review is proposed regarding research activities of functional textiles with smart properties. Specifically, a brief exposition of highlighting the significance and rising demands of novel textiles throughout the human society is begun. Next, a systematic review is provided about the fabrication of functional textiles from 1D spinning, 2D modification, and 3D construction, their diverse functionality as well as sustainable applications, showing a clear picture of evolved textiles to the readers. How to engineer the compositions, structures, and properties of functional textiles is elaborated to achieve different smart properties. All these tunable, upgraded, and …

Metal–organic frameworks (MOFs) that contain open metal sites have the potential for storing hydrogen (H2) at ambient temperatures. In particular, Cu(I)-based MOFs demonstrate very high isosteric heats of adsorption for hydrogen relative to other reported MOFs with open metal sites. However, most of these Cu(I)-based MOFs are not stable in ambient conditions since the Cu(I) species display sensitivity toward moisture and can rapidly oxidize in air. As a result, researchers have focused on the synthesis of new air-stable Cu(I)-based materials for H2 storage. Here, we have developed a de novo synthetic strategy to generate a robust Cu(I)-based MOF, denoted as NU-2100, using a mixture of Cu/Zn precursors in which zinc acts as a catalyst to transform an intermediate MOF into NU-2100 without getting incorporated into the final MOF structure. NU-2100 is air-stable and displays one of the initial highest isosteric …

Boron trifluoride (BF3) is a highly corrosive gas widely used in industry. Confining BF3 in porous materials ensures safe and convenient handling and prevents its degradation. Hence, it is highly desired to develop porous materials with high adsorption capacity, high stability, and resistance to BF3 corrosion. Herein, we designed and synthesized a Lewis basic single‐crystalline hydrogen‐bond crosslinked organic framework (HCOF‐50) for BF3 storage and its application in catalysis. Specifically, we introduced self‐complementary ortho‐alkoxy‐benzamide hydrogen‐bonding moieties to direct the formation of highly organized hydrogen‐bonded networks, which were subsequently photo‐crosslinked to generate HCOFs. The HCOF‐50 features Lewis basic thioether linkages and electron‐rich pore surfaces for BF3 uptake. As a result, HCOF‐50 shows a record‐high 14.2 mmol/g BF3 uptake capacity. The BF3 uptake …

Global reliance on fossil fuel combustion for energy production has contributed to the rising concentration of atmospheric CO2, creating significant global climate challenges. In this regard, direct air capture (DAC) of CO2 from the atmosphere has emerged as one of the most promising strategies to counteract the harmful effects on the environment, and the further development and commercialization of this technology will play a pivotal role in achieving the goal of net‐zero emissions by 2050. Among various DAC adsorbents, metal–organic frameworks (MOFs) show great potential due to their high porosity and ability to reversibly adsorb CO2 at low concentrations. However, the adsorption efficiency and cost‐effectiveness of these materials must be improved to be widely deployed as DAC sorbents. To that end, this perspective provides a critical discussion on several types of benchmark MOFs that have …

Hierarchically ordered porous materials with tailored and inter‐connected macro‐, meso‐, and micro‐pores would facilitate the heterogeneous adsorption and catalysis processes for a wide range of applications but remain a challenge for synthetic chemists. Here, a general and efficient strategy for the synthesis of inverse opal metal–organic frameworks (IO MOFs) with a tunable size of macro‐, meso‐, and micro‐pores is reported. The strategy is based on the step‐wise template formation, precursor infiltration, solvo‐thermal reaction, and chemical etching. As a proof of the general applicability of this strategy, a series of inverse opal zirconium‐based MOFs with intrinsic micro‐ and/or meso‐pores, including UiO‐66, MOF‐808, NU‐1200, NU‐1000 and PCN‐777, and tunable macropores (1 µm, 2 µm, 3 µm, 5 µm, and 10 µm), have been prepared with outstanding yields. These IO MOFs demonstrate significantly …

Ladder polymers are synthetically challenging targets that comprise a sequence of rings in which each repeat unit shares at least two atoms with the adjacent one. Ladder polymers with sp3-hybridized backbones feature kinked structures with restricted bond rotation. Such ladder polymers are typically synthesized through a mechanism that allows simultaneous formation of both bonds during polymerization, such as the Diels–Alder cycloaddition. Prior Diels–Alder polymerizations required elevated temperature and/or pressure to achieve the desired reactivity, and the resulting products include aromatic linkages within the backbone. Here, we show that photoredox catalysis provides access to unique ladder polymers with sp3 backbones under mild reaction conditions. We design 2-arylbutadiene monomers that enable propagation of the cyclohexene formed by each successive cycloaddition by stabilizing the …

Polymer/metal–organic framework (MOF) composites have been widely studied for their favorable combination of polymer flexibility and MOF crystallinity. While traditional polymer-coated MOFs maximize the polymer properties at the surface, the dramatic loss of MOF porosity due to blockage by the nonporous polymeric coating remains a problem. Herein, we introduce intrinsically microporous synthetic allomelanin (AM) as a porous coating on the zirconium-based MOF (Zr-MOF) UiO-66 via an in situ surface-constrained oxidative polymerization of the AM precursor, 1,8-dihydroxynaphthalene (1,8-DHN). Transmission electron microscopy images verify the formation of well-defined nanoparticles with a core–shell morphology (AM@UiO-66), and nitrogen sorption isotherms indicate the porosity of the UiO-66 core remains constant and is not disturbed by the AM coating. Notably, such a strategy could be adapted to …

We have screened an array of 23 metals deposited onto the metal–organic framework (MOF) NU-1000 for propyne dimerization to hexadienes. By a first-of-its-kind study utilizing data-driven algorithms and high-throughput experimentation (HTE) in MOF catalysis, yields on Cu-deposited NU-1000 were improved from 0.4 to 24.4%. Characterization of the best-performing catalysts reveal conversion to hexadiene to be due to the formation of large Cu nanoparticles, which is further supported by reaction mechanisms calculated with density functional theory (DFT). Our results demonstrate both the strengths and weaknesses of the HTE approach. As a strength, HTE excels at being able to find interesting and novel catalytic activity; any a priori theoretical approach would be hard-pressed to find success, as high-performing catalysts required highly specific operating conditions difficult to model theoretically, and initial …

Metal-organic frameworks (MOFs) are a class of materials with diverse chemical and structural properties, and have been shown to effectively adsorb various types of guest molecules. The mechanism of water adsorption in NU-1500-Cr, a high-performance atmospheric water harvesting MOF, is investigated using a combination of molecular dynamics simulations and infrared spectroscopy. Calculations of thermodynamic and dynamical properties of water as a function of relative humidity allow for following the adsorption process from the initial hydration stage to complete filling of the MOF pores. Initial hydration begins at the water molecules that saturate the open Cr3+ sites of the framework, which is then followed by the formation of water chains that extend along the channels connecting the hexagonal pores of the framework. Water present in these channels gradually coalesces and fills the hexagonal pores …

Organophosphorus nerve agents are among the most toxic chemicals known and remain threats to humans due to their continued use despite international bans. Metal–organic frameworks (MOFs) have emerged as a class of heterogeneous catalysts with tunable structures that are capable of rapidly detoxifying these chemicals via hydrolysis at Lewis acidic active sites on the metal nodes. To date, the majority of studies in this field have focused on zirconium-based MOFs (Zr-MOFs) that contain hexanuclear Zr(IV) clusters, despite the large toolbox of Lewis acidic transition metal ions that are available to construct MOFs with similar catalytic properties. In particular, very few reports have disclosed the use of a Ti-based MOF (Ti-MOF) as a catalyst for this transformation even though Ti(IV) is a stronger Lewis acid than Zr(IV). In this work, we explored five Ti-MOFs (Ti-MFU-4l, NU-1012-NDC, MIL-125, Ti-MIL-101, MIL-177 …

Hydrocarbon separations using porous materials such as metal–organic frameworks (MOFs) have been proposed to reduce the energy demands associated with current distillation-based methods. Despite the potential of these materials to distinguish hydrocarbons through thermodynamic or kinetic mechanisms, experimental data quantifying hydrocarbon transport in MOFs is lacking. Such mass transfer measurements are vital to elucidate structure–property relationships and design future high-performing separation materials. In this work, we aim to isolate the influence of pore size on hydrocarbon diffusion by studying a pair of isoreticular MOFs, Co2Cl2BBTA and Co2Cl2BTDD. We use a volumetric method to extract mass transport coefficients for six hydrocarbon probe molecules of varying size and chemical functionality. From these nonequilibrium mass transport measurements, we determine the rate-limiting …

The structural elucidation of catalyst active sites in heterogeneous catalysts when supported by traditional metal oxides remains a challenge despite the advanced characterization techniques that have been developed. The catalyst-deposition-site nonuniformity in metal oxides inhibits clear structural characterization through bulk spectroscopic methods and rules out the use of single-crystal X-ray diffraction. However, for metal–organic framework (MOF)-supported catalysts, the crystallinity and uniform structures of the underlying support enhance our ability to identify the precatalyst and catalytically active sites and open the door to using single-crystal X-ray diffraction coupled with spectroscopy under reaction conditions. The use of in situ X-ray absorption spectroscopy identifies the catalytically active site in diethylaluminum chloride (DEAC)-pretreated Cr-SIM-NU-1000 to be a Cr-ethyl when used for ethylene …

Polyethylene terephthalate (PET) is utilized as one of the most popular consumer plastics worldwide, but difficulties associated with recycling PET have generated a severe environmental crisis with most PET ending its lifecycle in landfills. We report that zirconium‐based metal–organic framework (Zr‐MOF) UiO‐66 deconstructs waste PET into the building blocks terephthalic acid (TA) and mono‐methyl terephthalate (MMT) within 24 hours at 260 °C (total yield of 98 % under 1 atm H2 and 81 % under 1 atm Ar). Extensive structural characterization studies reveal that during the degradation process, UiO‐66 undergoes an intriguing transformation into MIL‐140A, which is another Zr‐MOF that shows good catalytic activity toward PET degradation under similar reaction conditions. These results illustrate the diversity of applications for Zr‐MOFs and establish MOFs as a new class of polymer degradation catalysts …

The mechanism of photochemical CO2 reduction to formate by PCN-136, a Zr-based metal-organic framework (MOF) that incorporates light-harvesting nanographene ligands, has been investigated using steady-state and time-resolved spectroscopy and density functional theory (DFT) calculations. The catalysis was found to proceed via a “photoreactive capture” mecha-nism, where Zr-based nodes serve to capture CO2 in the form of Zr-bicarbonates, while the nanographene ligands have a dual role to absorb light and to store one-electron equivalents needed for catalysis. We also find that the process occurs via a “two-for-one” route, where a single photon initiates a cascade of electron/hydrogen atom transfers from the sacrificial donor to the CO2-bound MOF. The mechanistic findings obtained here illustrate several advantages of MOF-based architectures in the molecular photocatalyst engineering and provide insights on ways to achieve high formate selectivity.

The world is currently suffering socially, economically, and politically from the recent pandemic outbreak due to the coronavirus disease 2019 (COVID-19), and those in hospitals, schools, and elderly nursing homes face enhanced threats. Healthcare textiles, such as masks and medical staff gowns, are susceptible to contamination of various pathogenic microorganisms, including bacteria and viruses. Metal–organic frameworks (MOFs) can potentially address these challenges due to their tunable reactivity and ability to be incorporated as porous coatings on textile materials. Here, we report how incorporating titanium into the zirconium–pyrene-based MOF NU-1000, denoted as NU-1012, generates a highly reactive biocidal photocatalyst. This MOF features a rare ligand migration phenomenon, and both the Ti/Zr center and the pyrene linker act synergistically as dual active centers and widen the absorption band for …

Despite the importance of noncovalent interactions in the utilization of metal–organic frameworks (MOFs), using these interactions to functionalize MOFs has rarely been explored. The ease of functionalization and potential for surface-selective functionalization makes modification via noncovalent interactions promising for the creation of porous photocatalytic assemblies. Using isothermal titration calorimetry, photoluminescence measurements, and desorption experiments, we have explored the nature and magnitude of the interactions of [Ru(bpy)2(bpy-R)]2+-functionalized dyes with the surface of MIL-96, where R = C3, C8, C12, and C18 alkyl chains of either straight-chain or cyclic conformations. The orientation of the dyes appears to be flat against the surface with respect to the long alkyl chains, and the surface concentration approaches a monolayer at high initial concentrations of dye. Strangely, the dodecyl …

A series of isoreticular metal-organic frameworks composed of metal nodes connected by rigid trigonal prismatic organic linkers and having a 6, 12-coordinatled alb network topology are provided. Also provided are methods of synthesizing the metal-organic frameworks and methods of using the metal-organic frameworks to catalyze the hydrolysis of organic molecules, such as nerve agents, having hydrolysable bonds.

To increase catalytic efficiency, mesoporous supports have been widely applied to immobilize well-defined metal oxide clusters due to their ability to stabilize highly dispersed clusters. Herein, a redox-active heterometallic Ce12V6-oxo cluster (CeV) was first presynthesized and then incorporated into mesoporous silica, SBA-15, via a straightforward impregnation method. Scanning transmission electron microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR), in concert with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), verified the successful introduction of the CeV cluster inside the pore of SBA-15. The 51V magic angle spinning solid-state nuclear magnetic resonance (51V MAS NMR) spectroscopy and differential pair distribution function (dPDF) analysis confirmed the structural integrity of the CeV cluster inside the SBA-15. The composite was then …

Hydrogen-bonded organic frameworks (HOFs), self-assembled from strategically pre-designed molecular tectons with complementary hydrogen-bonding patterns, are rapidly evolving into a novel and important class of porous materials. In addition to their common features shared with other functionalized porous materials constructed from modular building blocks, the intrinsically flexible and reversible H-bonding connections endow HOFs with straightforward purification procedures, high crystallinity, solution processability, and recyclability. These unique advantages of HOFs have attracted considerable attention across a broad range of fields, including gas adsorption and separation, catalysis, chemical sensing, and electrical and optical materials. However, the relatively weak H-bonding interactions within HOFs can potentially limit their stability and potential use in further applications. To that end, this Perspective …

Over the past 25 years, metal–organic frameworks (MOFs) have developed into an increasingly intricate class of crystalline porous materials in which the choice of building blocks offers significant control over the physical properties of the resulting material. Despite this complexity, fundamental coordination chemistry design principles provided a strategic basis to design highly stable MOF structures. In this Perspective, we provide an overview of these design strategies and discuss how researchers leverage fundamental chemistry concepts to tune reaction parameters and synthesize highly crystalline MOFs. We then discuss these design principles in the context of several literature examples, highlighting both relevant fundamental chemistry principles and additional design principles required to access stable MOF structures. Finally, we envision how these fundamental concepts may offer access to even more …

Industrial-scale thermal separation processes have contributed greatly to the rise in carbon dioxide emissions. Porous materials, such as metal–organic frameworks (MOFs), can potentially reduce these emissions by achieving nonthermal chemical separations through the physical adsorption of targeted species with high selectivity. Here, we report the synthesis of the channel-based MOFs NU-2000 and NU-2001, which are constructed from three-dimensional (3D) linkers, to separate the industrially relevant xylene isomers under ambient conditions by leveraging sub-Ångstrom differences in the sizes of each isomer. While the rotation of two-dimensional (2D) linkers in MOFs often affords changes in pore apertures and pore sizes that are substantial enough to hinder separation efficiency, increasing the linker dimensionality from 2D to three-dimensional (3D) enables precise control of the MOF pore size and aperture …

The rapid, discriminative, and portable detection of highly toxic chemical warfare agents is extremely important for response to public security emergencies but remains a challenge. One plausible solution involves the integration of porous molecular traps onto a photoelectrochemical (PEC) sensor. Here, a fast and facile protocol is developed to fabricate sub‐1 nm AgNPs encapsulated hydrogen‐bonded organic framework (HOF) nanocomposite materials through an in situ photoreduction and subsequent encapsulation process. Compared to traditional semiconductors and selected metal–organic frameworks (MOF) materials, these AgNPs@HOFs show significantly enhanced photocurrent. Most importantly, the portable PEC device based on AgNPs@HOF‐101 can selectively recognize 13 different mustard gas simulants, including 2‐chloroethyl ethyl sulfide (CEES), based on synergistic size‐exclusion and specific …

Metal–organic frameworks (MOFs) are receiving increased attention due to their well-defined structures that allow the determination of structure–property relationships. MOFs have been used as heterogeneous catalyst supports in a variety of fashions including for confinement of metal nanoparticles, which have demonstrated enhanced resistance to aggregation, a common issue in amorphous metal oxide supports. Cu and In catalysts were installed in the Zr-based MOF NU-907, being confined within the nanoporous structure. The Cu catalyst is known to, under various conditions, either selectively hydrogenate acetylene to ethylene or generate C4 products such as butenes and 1,3-butadiene, an important feedstock for rubber and adhesives. The addition of indium to the Cu catalyst is intended to serve as a promoter to produce C4 products by decreasing the surface coverage of copper while still allowing for C–C …

Allomelanin is a class of nitrogen-free melanin mostly found in fungi and, like all naturally occurring melanins, is hydrophilic. Herein, we develop a facile method to modify synthetic hydrophilic allomelanin to yield hydrophobic derivatives through post-synthetic modifications. Amine-functionalized molecules of various kinds can be conjugated to allomelanin nanoparticles under mild conditions with high loading efficiencies. Hydrophobicity is conferred by introducing amine-terminated alkyl groups with different chain lengths. We demonstrate that the resulting hydrophobic allomelanin nanoparticles undergo air/water interfacial self-assembly in a controlled fashion, which enables the generation of large-scale and uniform structural colors. This work provides an efficient and tunable surface chemistry modification strategy to broaden the scope of synthetic melanin structure and function beyond the known diversity found …

Enzyme-immobilizing MOFs and methods for their use in enzymatically catalyzed reactions are provided. The MOFs are channel-type MOFs that present a hierarchical pore structure comprising a first set of large channels sized for enzyme immobilization and a second set of smaller channels running alongside of the large channels that remain enzyme free and allow for reactant delivery to the enzymes and product expulsion from the larger channels. a

Ceria-based materials have been highly desired in photocatalytic reactions due to their redox properties and strong oxygen storage and transfer ability. Herein, we report the structures of one CeCe70 oxysulfate cluster and four MCe70 clusters (M = Cu, Ni, Co, and Fe) with the same Ce70 core. As noted, single-crystal X-ray diffraction confirmed the structures of CeCe70 and the MCe70 series, while Raman spectroscopy indicated an increase in oxygen defects upon the introduction of Cu and Fe ions. The clusters catalyzed the oxidation of 4-methoxybenzyl alcohol under ultraviolet light. CuCe70 and FeCe70 exhibited enhanced reactivity compared to CeCe70 and improved aldehyde selectivity compared to control experiments. In comparison with their homogeneous congeners, the CeCe70/MCe70 clusters altered the location of radical generation from the bulk solution to the clusters’ surfaces. Mechanistic studies …

Chemical nerve agents employed in warfare can induce paralysis and death within minutes of exposure. Zirconium-based metal–organic frameworks (MOFs), such as UiO-66-NH2, show promise for the fast and efficient decontamination of nerve agents, which motivates their incorporation into textiles as protective layers. Few scalable methods to produce MOF/textile composites for personal protective applications have been developed; however, they mainly require the use of toxic and flammable solvents. Here, we describe a scalable, single-step method to synthesize UiO-66-NH2 on cotton fabrics by hot pressing the monomers onto the fabric samples. The use of a preformed hexanuclear zirconium benzoate cluster with 1,8-bis(dimethylamine)naphthalene as a non-nucleophilic base improved the quality of MOFs synthesized from the hot press method, as determined by an increase in their surface area and …

Understanding heterogeneous catalysts is a challenging pursuit due to surface site nonuniformity and aperiodicity in traditionally used materials. One example is sulfated metal oxides, which function as highly active catalysts and as supports for organometallic complexes. These applications are due to traits such as acidity, ability to act as a weakly coordinating ligand, and aptitude for promoting transformations via radical cation intermediates. Research is ongoing about the structural features of sulfated metal oxides that imbue the aforementioned properties, such as sulfate geometry and coordination. To better understand these materials, metal–organic frameworks (MOFs) have been targeted as structurally defined analogues. Composed of inorganic nodes and organic linkers, MOFs possess features such as high porosity and crystallinity, which make them attractive for mechanistic studies of heterogeneous …

Photoactive metal–organic framework (MOF) thin films offer an opportunity for translating the advantages of periodic, crystalline, and tailorable light-harvesting materials directly into devices such as those for photoelectrochemical solar energy conversion. In this study, we report the fabrication of light-absorbing perylene-diimide-containing pillared-paddlewheel MOF thin films using an automated layer-by-layer (LbL) deposition technique. Our focus here is on optimizing the growth of representative chromophoric MOFs as oriented films of uniform and predefined thickness. Growth was examined as a function of metal identity, pillaring ligand composition, and supporting-surface chemical functionality. Application of atomic force microscopy (AFM) and complementary techniques revealed that the surface-supported MOFs initially display island-type film growth (Volmer–Weber growth), resulting in comparatively rough …

Tröger’s base (TB) and its derivatives have been studied extensively due to their unique concave shape stemming from the endomethylene strap. However, the strap-clipped TB chemistry has been largely overlooked in metal–organic framework (MOF) solids, leading to a gap in our knowledge within this field. In this work, we report the in situ strap elimination of a carboxylate-carrying TB in the presence of formic acid, both in solution and in Zr(IV)-based MOFs. In the solution system, the methanodiazocine nucleus can be exclusively transformed into an N,N′-diformyl-decorated phenhomazine derivative, regardless of the solvent used (DMF, DMA, or DEF), as unambiguously uncovered by single crystal X-ray crystallography. In contrast, while in the MOF synthetic system, the degree of derivatization reaction can be effectively controlled to give either the secondary diamine or formyl-decorated diamine, depending …

In article number 2201502, David Fairen-Jimenez and co-workers conduct a round-robin exercise by providing 18 already-measured adsorption isotherms to sixty-one labs and show that the reproducibility of the Brunauer–Emmett–Teller (BET) area determination in micro-and mesoporous materials remains a largely ignored issue. To solve this, a new computational approach—called BETSI—that expands on the Rouquerol criteria and makes an unambiguous BET area assignment possible is developed.

Atomically precise cerium oxo clusters offer a platform to investigate structure–property relationships that are much more complex in the ill-defined bulk material cerium dioxide. We investigated the activity of the MCe70 torus family (M = Cd, Ce, Co, Cu, Fe, Ni, and Zn), a family of discrete oxysulfate-based Ce70 rings linked by monomeric cation units, for CO oxidation. CuCe70 emerged as the best performing MCe70 catalyst among those tested, prompting our exploration of the role of the interfacial unit on catalytic activity. Temperature-programmed reduction (TPR) studies of the catalysts indicated a lower temperature reduction in CuCe70 as compared to CeCe70. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that CuCe70 exhibited a faster formation of Ce3+ and contained CO bridging sites absent in CeCe70. Isothermal CO adsorption measurements demonstrated a greater …

Proteins immobilized in metal–organic frameworks (MOFs) often show extraordinary stability. However, most efforts to immobilize proteins in MOFs have only been exploratory. Herein, we present the first systematic study on the thermodynamics of protein immobilization in MOFs. Using insulin as a probe, we leveraged isothermal titration calorimetry (ITC) to investigate how topology, pore size, and hydrophobicity of MOFs influence immobilization. ITC data obtained from the encapsulation of insulin in a series of Zr‐MOFs reveals that MOFs provide proteins with a hydrophobic stabilizing microenvironment, making the encapsulation entropically driven. In particular, the pyrene‐based NU‐1000 tightly encapsulates insulin in its ideally sized mesopores and stabilizes insulin through π‐π stacking interactions, resulting in the most enthalpically favored encapsulation process among this series. This study reveals critical …

Zirconium metal–organic frameworks (Zr-MOFs) are a structurally diverse and well-defined class of materials studied in heterogeneous catalysis. Previously, we showed that partial dehydration of the Zr6O8 node in NU-1000 results in heterolytic H2 cleavage over adjacent Lewis acid and base sites, leading to catalytic conversion of 1-butene. In this work, given the ubiquity of the Zr6O8 node as a secondary building unit (SBU) in Zr-MOFs, with many different potential MOF topologies and capping ligands surrounding the cluster, we study the influence of thermal pretreatments and MOF topology (MOF-808, NU-1000, UiO-66, and NU-1000-NDC) on the activity of the Zr6O8 cluster for H2 activation and 1-butene hydrogenation and isomerization. Diffuse reflectance IR in the presence of H2 and pyridine shows that both thermal pretreatment and MOF topology affect the Brønsted acidity of protons generated from H2 …

Dopant gases used in ion implantation are poisonous and flammable (hydrides), or toxic and corrosive (fluorides). Almost thirty years ago, adsorbent-based dopant gas delivery systems were developed to reduce the risks associated with handling and using dopant sources in ion implanters. Adsorbent-based gas sources are gas cylinders filled with high surface area porous materials that reversibly adsorb dopant gases inside their pores. These cylinders are considered intrinsically safe as the dopant gases are stored at sub-atmospheric pressures. Today, commercially available adsorbent-based dopant gas delivery systems use either activated carbon in the form of beads or monoliths, or metal organic frameworks (MOFs) sold under the brand ION-X® by NuMat Technologies, Inc. Metal–Organic Frameworks (MOFs) are a new class of nano-porous materials comprised of organic ligands and metal nodes creating …

We report the synthesis, characterization, and iodine capture application of a novel thorium–organic nanotube, TSN-626, [Th6O4(OH)4(C6H4NO2)7(CHO2)5(H2O)3]·3H2O. The classification as a metal–organic nanotube (MONT) distinguishes it as a rare and reduced dimensionality subset of metal–organic frameworks (MOFs); the structure is additionally hallmarked by low node connectivity. TSN-626 is composed of hexameric thorium secondary building units and mixed O/N-donor isonicotinate ligands that demonstrate selective ditopicity, yielding both terminating and bridging moieties. Because hard Lewis acid tetravalent metals have a propensity to bind with electron donors of rival hardness (e.g., carboxylate groups), such Th–N coordination in a MOF is uncommon. However, the formation of key structural Th–N bonds in TSN-626 cap some of the square antiprismatic metal centers, a position usually occupied by …

Ammonia (NH3), often stored in large quantities before being used in the production of fertilizer, and sulfur dioxide (SO2), a byproduct of fossil fuel consumption, particularly the burning of coal, are highly toxic and corrosive gases that pose a significant danger to humans if accidentally released. Therefore, developing advanced materials to enable their effective capture and safe storage is highly desired. Herein, advanced benzimidazole-derived carbons (BIDCs) with an exceptional capacity for NH3 and SO2 have been designed and tested. These heteroatom-doped porous carbon adsorbents were synthesized by thermolysis of imidazolate-potassium salts affording high surface area and controlled heteroatom content to optimize for rapid NH3 and SO2 gas uptake and release under practical conditions. According to gas uptake measurements, these nitrogen-doped carbons exhibit exceptional gas adsorption …

Robust and versatile metal–organic frameworks (MOFs) have emerged as sophisticated scaffolds to meet the critical needs of the nuclear community, but their performance depends on their underexplored structural integrities in high- radiation fields. The contributions of selected metal nodes in the radiation stability of MOFs within the isostructural M-UiO-66 series (where M = Zr, Ce, Hf, Th, and Pu; Zr-UiO-66 experiments were executed in a previous work) have been determined. Ce-, Hf-, and Th-UiO-66 MOF samples were irradiated via gamma and He-ion methodologies to obtain doses up to 3 MGy and 85 MGy, respectively, the latter strikingly higher than that obtained in most other studies. Appreciable self-irradiation constituted the total absorbed doses, up to 31 MGy of the gamma-irradiated Pu-UiO-66 samples. Structural degradation was ascertained by powder X-ray diffraction, X-ray total scattering, vibrational …