Conspectus Current global crises related to clean energy and the environment entail the development of materials that are capable of addressing these challenges. Metal–organic frameworks (MOFs), a ...class of functional materials assembled from metal-containing nodes and organic ligands via coordination bonds, have been successfully developed for various applications, including catalysis, toxic chemical removal, and gas storage and separation, as a result of their highly tailorable nature and precisely engineered pore structures. In particular, the exceptionally high surface areas and porosities of MOFs are two of their most attractive characteristics and place them among the best porous materials for the storage of clean energy gases, such as hydrogen and methane. Reticular chemistry stands out as a prominent approach to the design of MOFs as this strategy allows for the rational top-down design of frameworks guided by topological nets to afford extended framework structures with precise architectural arrangements at the molecular level. Bridging the gap between reticular chemistry design strategies and highly porous MOFs can facilitate the development of next-generation high-performance materials through state-of-the-art chemical design. In this Account, we summarize our group’s efforts over the past few years toward the synthesis and applications of highly porous MOFs inspired by reticular chemistry. First, we describe how we leveraged reticular chemistry to synthesize NU-1500, which is based on the 6-connected edge-transitive acs net, from the assembly of triptycene-based ligands and high-valent metal trimers. This delicate design is amenable to isoreticular expansion, and including an additional phenyl group in the rigid triptycene-based ligand of NU-1500 yields NU-1501. Importantly, NU-1501-Al exhibits both a high gravimetric Brunauer–Emmett–Teller (BET) area of 7310 m2 g–1, which is the current record after satisfying the four BET consistency criteria, and a volumetric BET area of 2060 m2 cm–3. The high porosity and surface area place NU-1501 among the most promising adsorbents for the storage of methane and hydrogen. Second, we illustrate the rational synthesis of highly porous and stable Zr-MOFs based on edge-transitive nets: (1) the successful isoreticular expansions of NU-1000 (a 4,8-connected csq net) form hierarchical mesoporous MOFs with pore sizes of up to 6.7 nm; (2) the assembly of Zr6 clusters and tetracarboxylates yields the NU-1100 series (4,12-connected ftw net) with BET areas of 4300–6500 m2 g–1; and (3) the use of hexacarboxylates in combination with Zr6 clusters results in the formation of the NU-1600 series (a 6,12-connected alb net) with BET areas of 2000–4500 m2 g–1. Third, we leveraged a reticular exploration strategy to access mesoporous uranium-based MOFs, NU-1300 (a 3,4-connected tbo net, 2100 m2 g–1) and NU-1301 (a 3-connected nun net, 4750 m2 g–1). In particular, we investigated the structurally complex NU-1301, which formed serendipitously from the combination of uranyl clusters and triangular carboxylates to afford a structure with the largest unit cell among all reported MOFs. Finally, we provide an overview of potential applications of these highly porous MOFs, including water capture, catalysis, methane storage, hydrogen storage, and the separation of organic dyes and biological macromolecules. We hope that this Account may serve as a blueprint and stimulate researchers to develop the next generation of highly porous materials for energy- and environment-related applications and beyond.
Polyoxometalates (POMs) can benefit from immobilization on solid supports to overcome their difficulty in processability and stability. Among the reported solid supports, metal–organic frameworks ...(MOFs) offer a crystalline, versatile platform for depositing highly active POMs. The combination of these structures can at times benefit from the combined reactivity of both the POM and MOF, sometimes synergistically, to improve catalysis while balancing desirable properties like porosity, substrate diffusion, or stability. In this Review, we survey the strategies for immobilizing POMs within MOF structures, with an emphasis on how physical and catalytic properties of the parent materials are affected in the composite when employed in organic transformations.
As the field of metal-organic frameworks (MOFs) continues to grow, the physical stability and mechanical properties of these porous materials has become a topic of great interest. While strategies ...for synthesizing MOFs with desirable chemical functionalities or pore sizes have been established over the past twenty years, design principles to modulate the response of MOFs to mechanical stress are still underdeveloped. The inherent porosity of these frameworks results in many interesting and sometimes unexpected phenomena upon exposure to elevated pressures and other physical stimuli. Beyond its fundamental importance, an understanding of mechanical properties (
e.g.
bulk modulus, shear modulus, Young's modulus, linear compressibility, and Poisson's ratio) plays an essential role in the post-synthetic processing of MOFs, which has implications in the successful transition of these materials from academic interest to industrial relevance. This perspective provides a concise overview of the efforts to understand the mechanical properties of MOFs through experimental and computational methods. Additionally, current limitations and possible future directions for the field are also discussed briefly.
As the field of metal-organic frameworks (MOFs) continues to grow, the physical stability and mechanical properties of these porous materials has become a topic of great interest.
The emergence of metal−organic frameworks (MOFs) as functional ultrahigh surface area materials is one of the most exciting recent developments in solid-state chemistry. Now constituting thousands of ...distinct examples, MOFs are an intriguing class of hybrid materials that exist as infinite crystalline lattices with inorganic vertices and molecular-scale organic connectors. Useful properties such as large internal surface areas, ultralow densities, and the availability of uniformly structured cavities and portals of molecular dimensions characterize functional MOFs. Researchers have effectively exploited these unusual properties in applications such as hydrogen and methane storage, chemical separations, and selective chemical catalysis. In principle, one of the most attractive features of MOFs is the simplicity of their synthesis. Typically they are obtained via one-pot solvothermal preparations. However, with the simplicity come challenges. In particular, MOF materials, especially more complex ones, can be difficult to obtain in pure form and with the optimal degree of catenation, the interpenetration or interweaving of identical independent networks. Once these two issues are satisfied, the removal of the guest molecules (solvent from synthesis) without damaging the structural integrity of the material is often an additional challenge. In this Account, we review recent advances in the synthetic design, purification, and activation of metal−organic framework materials. We describe the rational design of a series of organic struts to limit framework catenation and thereby produce large pores. In addition, we demonstrate the rapid separation of desired MOFs from crystalline and amorphous contaminants cogenerated during synthesis based on their different densities. Finally, we discuss the mild and efficient activation of initially solvent-filled pores with supercritical carbon dioxide, yielding usable channels and high internal surface areas. We expect that the advances in the synthesis, separation, and activation of metal−organic frameworks could lead to MOFs with new structures and functions, better and faster separation and purification of these materials, and processing methods that avoid pore blockage and pore collapse.
Metal–organic frameworks (MOFs) are periodic, hybrid, atomically well-defined porous materials that typically form by self-assembly and consist of inorganic nodes (metal ions or clusters) and ...multitopic organic linkers. MOFs as a whole offer many intriguing properties, including ultrahigh porosity, tunable chemical functionality, and low density. These properties point to numerous potential applications, including gas storage, chemical separations, catalysis, light harvesting, and chemical sensing, to name a few. Reticular chemistry, or the linking of molecular building blocks into predetermined network structures, has been employed to synthesize thousands of MOFs. Given the vast library of candidate nodes and linkers, the number of potentially synthetically accessible MOFs is enormous. Nevertheless, a powerful complementary approach to obtain specific structures with desired chemical functionality is to modify known MOFs after synthesis. This approach is particularly useful when incorporation of particular chemical functionalities via direct synthesis is challenging or impossible. The challenges may stem from limited stability or solubility of precursors, unwanted secondary reactivity of precursors, or incompatibility of functional groups with the conditions needed for direct synthesis. MOFs can be postsynthetically modified by replacing the metal nodes and/or organic linkers or via functionalization of the metal nodes and/or organic linkers. Here we describe some of our efforts toward the development and application of postsynthetic strategies for imparting desired chemical functionalities in MOFs of known topology. The techniques include methods for functionalizing MOF nodes, i.e., solvent-assisted ligand incorporation (SALI) and atomic layer deposition in MOFs (AIM) as well as a method to replace structural linkers, termed solvent-assisted linker exchange (SALE), also known as postsynthethic exchange (PSE). For each functionalization strategy, we first describe its chemical basis along with the requirements for its successful implementation. We then present a small number of examples, with an emphasis on those that (a) convey the underlying concepts and/or (b) lead to functional structures (e.g., catalysts) that would be difficult or impossible to access via direct routes. The examples, however, are only illustrative, and a significant body of work exists from both our lab and others, especially for the SALE/PSE strategy. We refer readers to the papers cited and to the references therein. More exciting, in our view, will be new examples and new applications of the functionalization strategiesespecially applications made possible by creatively combining the strategies. Underexplored (again, in our view) are implementations that impart electrical conductivity, enable increasingly selective chemical sensing, or facilitate cascade catalysis. It will be interesting to see where these strategies and others take this compelling field over the next few years.
Diabetes affects millions of people worldwide and the number of diagnoses continues to climb annually. Though several effective medications and therapeutic methods have been developed to treat type 1 ...(T1DM) and type 2 (T2DM) diabetes mellitus, direct insulin injection remains the only effective treatment for insulin resistant (IR) diabetes patients. Here, we immobilize insulin in a crystalline mesoporous metal–organic framework (MOF), NU-1000, and obtain a high loading of ∼40 wt % in only 30 min. The acid-stable MOF capsules are found to effectively prevent insulin from degrading in the presence of stomach acid and the digestive enzyme, pepsin. Furthermore, the encapsulated insulin can be released from NU-1000 under simulated physiological conditions.
•Metal–organic frameworks have been explored as supports for enzyme immobilization.•MOF immobilization enhances enzyme chemical and thermal stability and reusability.•Hierarchically porous MOFs allow ...both enzyme encapsulation and substrate diffusion.•Mutlienzyme-MOF composites catalyze cascade reactions.
The global catalyst industry is valued at nearly 20 billion USD and demand continues to rise. Enzymes, biological macromolecules, are highly selective and efficient catalysts; however, their commercial implementation has been hindered due to their poor chemical and thermal stability and low reusability. Numerous strategies have been investigated to stabilize enzymes and improve their processability. Recently, metal–organic frameworks (MOFs) have been investigated as enzyme immobilization supports. Herein, we highlight the immobilization of enzymes in MOF cages and pores for catalysis applications and discuss the future of this enzyme encapsulation strategy.
Materials capable of the safe and efficient capture or degradation of toxic chemicals, including chemical warfare agents (CWAs) and toxic industrial chemicals (TICs), are critically important in the ...modern age due to continuous threats of these chemicals to human life, both directly and indirectly. Metal–organic frameworks (MOFs), atomically precise hybrid materials that are synthesized via the self-assembly of metal cations or clusters and organic linkers, offer a unique solid adsorbent design platform due to their great synthetic versatility. This review will focus on recent advancements in MOF-based adsorbent design for protection against chemical warfare agents (organophosphorus nerve agents, blistering agents, and their simulants) and toxic industrial chemicals such as H2S, NH3, SO2, CO, NO2, and NO.
Due to their large size, charged surfaces, and environmental sensitivity, proteins do not naturally cross cell-membranes in intact form and, therefore, are difficult to deliver for both diagnostic ...and therapeutic purposes. Based upon the observation that clustered oligonucleotides can naturally engage scavenger receptors that facilitate cellular transfection, nucleic acid–metal organic framework nanoparticle (MOF NP) conjugates have been designed and synthesized from NU-1000 and PCN-222/MOF-545, respectively, and phosphate-terminated oligonucleotides. They have been characterized structurally and with respect to their ability to enter mammalian cells. The MOFs act as protein hosts, and their densely functionalized, oligonucleotide-rich surfaces make them colloidally stable and ensure facile cellular entry. With insulin as a model protein, high loading and a 10-fold enhancement of cellular uptake (as compared to that of the native protein) were achieved. Importantly, this approach can be generalized to facilitate the delivery of a variety of proteins as biological probes or potential therapeutics.
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