Flexible and Hierarchical Metal–Organic Framework Composites for High‐Performance Catalysis

The development of porous composite materials is of great significance for their potentially improved performance over those of individual components and extensive applications in separation, energy storage, and heterogeneous catalysis. Now mesoporous metal–organic frameworks (MOFs) with macroporous melamine foam (MF) have been integrated using a one‐pot process, generating a series of MOF/MF composite materials with preserved crystallinity, hierarchical porosity, and increased stability over that of melamine foam. The MOF nanocrystals were threaded by the melamine foam networks, resembling a ball‐and‐stick model overall. The resulting MOF/MF composite materials were employed as an effective heterogeneous catalyst for the epoxidation of cholesteryl esters. Combining the advantages of interpenetrative mesoporous and macroporous structures, the MOF/melamine foam composite has higher dispersibility and more accessibility of catalytic sites, exhibiting excellent catalytic performance.     

N‐Doped Carbon Aerogel Derived from a Metal–Organic Framework Foam as an Efficient Electrocatalyst for Oxygen Reduction

Metal–organic frameworks (MOFs) are promising alternative precursors for the fabrication of heteroatom‐doped carbon materials for energy storage and conversion. However, the direct pyrolysis of bulk MOFs usually gives microporous carbonaceous materials, which significantly hinder the mass transportation and the accessibility of active sites. Herein, N‐doped carbon aerogels with hierarchical micro‐, meso‐, and macropores were fabricated through one‐step pyrolysis of zeolitic imidazolate framework‐8/carboxymethylcellulose composite gel. Owing to the hierarchical porosity, high specific surface area, favorable conductivity, excellent thermal and chemical stability, the as‐prepared N‐doped carbon aerogel exhibits excellent oxygen reduction reaction (ORR) activity, long‐term durability, and good methanol tolerance in alkaline medium. This work thus provides a new way to fabricate new types of MOF‐derived carbon aerogels for various applications.     

Metal–Organic Framework (MOF)‐Derived Nanoporous Carbon Materials

Metal–organic framework (MOF)‐derived nanoporous carbon materials have attracted significant interest due to their advantages of controllable porosity, good thermal/chemical stability, high electrical conductivity, catalytic activity, easy modification with other elements and materials, etc. Thus, MOF‐derived carbons have been used in numerous applications, such as environmental remediations, energy storage systems (i.e. batteries, supercapacitors), and catalysts. To date, many strategies have been developed to enhance the properties and performance of MOF‐derived carbons. Herein, we introduce and summarize recent important approaches for advanced MOF‐derived carbon structures with a focus on precursor control, heteroatom doping, shape/orientation control, and hybridization with other functional materials.     

Synthesis of MOF‐525 Derived Nanoporous Carbons with Different Particle Sizes for Supercapacitor Application

Nanoporous carbon (NC) materials have attracted great research interest for supercapacitor applications, because of their excellent electrochemical and mechanical stability, good electrical conductivity, and high surface area. Although there are many reports on metal–organic framework (MOF)‐derived carbon materials, previous synthetic studies have been hindered by imperfect control of particle sizes and shapes. Here, we show precise control of the particle sizes of MOF‐525 from 100 nm to 750 nm. After conversion of MOF‐525 to NC, the effects of variation of the particle size on the electrochemical performance have been carefully investigated. The results demonstrate that our NC is a potential candidate for practical supercapacitor applications.     

Highly Selective Water Adsorption in a Lanthanum Metal–Organic Framework

We present a new metal–organic framework (MOF) built from lanthanum and pyrazine‐2,5‐dicarboxylate (pyzdc) ions. This MOF, [La(pyzdc)_1.5(H₂O)₂] ? 2 H₂O, is microporous, with 1D channels that easily accommodate water molecules. Its framework is highly robust to dehydration/hydration cycles. Unusually for a MOF, it also features a high hydrothermal stability. This makes it an ideal candidate for air drying as well as for separating water/alcohol mixtures. The ability of the activated MOF to adsorb water selectively was evaluated by means of thermogravimetric analysis, powder and single‐crystal X‐ray diffraction and adsorption studies, indicating a maximum uptake of 1.2 mmol g^?1 MOF. These results are in agreement with the microporous structure, which permits only water molecules to enter the channels (alcohols, including methanol, are simply too large). Transient breakthrough simulations using water/methanol mixtures confirm that such mixtures can be separated cleanly using this new MOF.     

Template‐based Synthesis of a Formate Metal–Organic Framework/Activated Carbon Fiber Composite for High‐performance Methane Adsorptive Separation

Simultaneous improvement in adsorption selectivity and capacity for single adsorbents is challenging but counting for much in adsorptive separations. To this end, a formate metal–organic framework and activated carbon fiber composite was synthesized in our work by a simple two‐step process, involving homogeneous precipitation of a MOF precursor on an activated carbon fiber and subsequent template replication. The resultant core–shell composite, ACF@[Ni₃(HCOO)₆], exhibited optimized adsorption performance both in selectivity and capacity for the separation of CH₄/N₂ to most of state‐of‐the‐art adsorbents.     

Template‐Directed Synthesis of Porous and Protective Core–Shell Bionanoparticles

Metal–organic frameworks (MOFs) are promising high surface area coordination polymers with tunable pore structures and functionality; however, a lack of good size and morphological control over the as‐prepared MOFs has persisted as an issue in their application. Herein, we show how a robust protein template, tobacco mosaic virus (TMV), can be used to regulate the size and shape of as‐fabricated MOF materials. We were able to obtain discrete rod‐shaped TMV@MOF core–shell hybrids with good uniformity, and their diameters could be tuned by adjusting the synthetic conditions, which can also significantly impact the stability of the core–shell composite. More interestingly, the virus particle underneath the MOF shell can be chemically modified using a standard bioconjugation reaction, showing mass transportation within the MOF shell.     

Design and Synthesis of a Water‐Stable Anionic Uranium‐Based Metal–Organic Framework (MOF) with Ultra Large Pores

Ionic metal–organic frameworks (MOFs) are a subclass of porous materials that have the ability to incorporate different charged species in confined nanospace by ion‐exchange. To date, however, very few examples combining mesoporosity and water stability have been realized in ionic MOF chemistry. Herein, we report the rational design and synthesis of a water‐stable anionic mesoporous MOF based on uranium and featuring tbo‐type topology. The resulting tbo MOF exhibits exceptionally large open cavities (3.9 nm) exceeding those of all known anionic MOFs. By supercritical CO₂ activation, a record‐high Brunauer‐Emmett‐Teller (BET) surface area (2100 m² g^?1) for actinide‐based MOFs has been obtained. Most importantly, however, this new uranium‐based MOF is water‐stable and able to absorb positively charged ions selectively over negatively charged ones, enabling the efficient separation of organic dyes and biomolecules.     

Robust Superhydrophobic/Superoleophilic Wrinkled Microspherical MOF@rGO Composites for Efficient Oil–Water Separation

Graphene/MOF‐based composite materials in three‐dimensional (3D) architectures are promising for the treatment of oil‐containing wastewater by absorption owing to their intrinsic properties of graphene and metal‐organic frameworks (MOFs), such as high porosity, ultralow density, and facilely tailored superwettability. In this study, novel wrinkled 3D microspherical MOF@rGO composites with both superhydrophobic and superoleophilic properties were developed by embedding MOF nanoparticles between graphene oxide (GO) nanosheets, followed by high‐temperature reduction self‐assembly. The microspherical composites feature a unique micro/nano hierarchy consisting of crumpled reduced GO (rGO) nanosheets intercalated with well‐dispersed MOF nanoparticles. Combined with the superwettability and abundant meso/microporosity, the peculiar architectures of wrinkled ZIF‐8@rGO microspheres show very fast absorption rates and high sorption selectivity for organic solvents and oils from water.     

Spray‐Coating of Catalytically Active MOF–Polythiourea through Postsynthetic Polymerization

A UiO‐66‐NCS MOF was formed by postsynthetic modification of UiO‐66‐NH₂. The UiO‐66‐NCS MOFs displays a circa 20‐fold increase in activity against the chemical warfare agent simulant dimethyl‐4‐nitrophenyl phosphate (DMNP) compared to UiO‐66‐NH₂, making it the most active MOF materials using a validated high‐throughput screening. The ?NCS functional groups provide reactive handles for postsynthetic polymerization of the MOFs into functional materials. These MOFs can be tethered to amine‐terminated polypropylene polymers (Jeffamines) through a facile room‐temperature synthesis with no byproducts. The MOFs are then crosslinked into a MOF–polythiourea (MOF–PTU) composite material, maintaining the catalytic properties of the MOF and the flexibility of the polymer. This MOF–PTU hybrid material was spray‐coated onto Nyco textile fibers, displaying excellent adhesion to the fiber surface. The spray‐coated fibers were screened for the degradation of DMNP and showed durable catalytic reactivity.     

Nylon–MOF Composites through Postsynthetic Polymerization

Hybridization of metal–organic frameworks (MOFs) and polymers into composites yields materials that display the exceptional properties of MOFs with the robustness of polymers. However, the realization of MOF–polymer composites requires efficient dispersion and interactions of MOF particles with polymer matrices, which remains a significant challenge. Herein, we report a simple, scalable, bench‐top approach to covalently tethered nylon–MOF polymer composite materials through an interfacial polymerization technique. The copolymerization of a modified UiO‐66‐NH₂ MOF with a growing polyamide fiber (PA‐66) during an interfacial polymerization gave hybrid materials with up to around 29 weight percent MOF. The covalent hybrid material demonstrated nearly an order of magnitude higher catalytic activity for the breakdown of a chemical warfare simulant (dimethyl‐4‐nitrophenyl phosphate, DMNP) compared to MOFs that are non‐covalently, physically entrapped in nylon, thus highlighting the importance of MOF–polymer hybridization.     

Toward 3D printed hydrogen storage materials made with ABS‐MOF composites

The push to advance efficient, renewable, and clean energy sources has brought with it an effort to generate materials that are capable of storing hydrogen. Metal–organic framework materials (MOFs) have been the focus of many such studies as they are categorized for their large internal surface areas. We have addressed one of the major shortcomings of MOFs (their processibility) by creating and 3D printing a composite of acrylonitrile butadiene styrene (ABS) and MOF‐5, a prototypical MOF, which is often used to benchmark H₂ uptake capacity of other MOFs. The ABS‐MOF‐5 composites can be printed at MOF‐5 compositions of 10% and below. Other physical and mechanical properties of the polymer (glass transition temperature, stress and strain at the breaking point, and Young's modulus) either remain unchanged or show some degree of hardening due to the interaction between the polymer and the MOF. We do observe some MOF‐5 degradation through the blending process, likely due to the ambient humidity through the purification and solvent casting steps. Even with this degradation, the MOF still retains some of its ability to uptake H₂, seen in the ability of the composite to uptake more H₂ than the pure polymer. The experiments and results described here represent a significant first step toward 3D printing MOF‐5‐based materials for H₂ storage.     

Flower‐like Ni(II)‐based Metal‐organic Framework‐decorated Ag Nanoparticles: Fabrication,Characterization and Electrochemical Detection of Glucose

Glucose concentration monitoring is important for the prevention, diagnosis and treatment of diabetes. In this work, a composite material of AgNPs/MOF‐74(Ni) was prepared for electrochemical determination of glucose. AgNPs/MOF‐74(Ni) was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy (XPS). The electrochemical properties of the glassy carbon electrodes modified with the AgNPs/MOF‐74(Ni) composites were characterized by cyclic voltammetry (CV) and current‐time curve (I‐t curve) with three electrode system. The determination of glucose with the electrode modified by AgNPs/MOF‐74(Ni) has a linear range of 0.01～4 mM with the correlation coefficient (R²) of 0.994. The detection limit is 4.7 μM (S/N=3) and the sensitivity is 1.29 mA ? mM^?1 ? cm^?2. In addition, this sensing system possesses reasonable reproducibility and stability. The good performance of electrochemical determination for glucose is attributed to the concerted effect of silver nanoparticles and MOF‐74(Ni) on the promotion of glucose oxidation     

Biological Chitin–MOF Composites with Hierarchical Pore Systems for Air‐Filtration Applications

Metal–organic frameworks (MOFs) are promising materials for gas‐separation and air‐filtration applications. However, for these applications, MOF crystallites need to be incorporated in robust and manageable support materials. We used chitin‐based networks from a marine sponge as a non‐toxic, biodegradable, and low‐weight support material for MOF deposition. The structural properties of the material favor predominant nucleation of the MOF crystallites at the inside of the hollow fibers. This composite has a hierarchical pore system with surface areas up to 800 m² g⁻¹ and pore volumes of 3.6 cm³ g⁻¹, allowing good transport kinetics and a very high loading of the active material. Ammonia break‐through experiments highlight the accessibility of the MOF crystallites and the adsorption potential of the composite indicating their high potential for filtration applications for toxic industrial gases.     

Encapsulating Perovskite Quantum Dots in Iron‐Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

Improving the stability of lead halide perovskite quantum dots (QDs) in a system containing water is the key for their practical application in artificial photosynthesis. Herein, we encapsulate low‐cost CH₃NH₃PbI₃ (MAPbI₃) perovskite QDs in the pores of earth‐abundant Fe‐porphyrin based metal organic framework (MOF) PCN‐221(Fe_x) by a sequential deposition route, to construct a series of composite photocatalysts of MAPbI₃@PCN‐221(Fe_x) (x=0–1). Protected by the MOF the composite photocatalysts exhibit much improved stability in reaction systems containing water. The close contact of QDs to the Fe catalytic site in the MOF, allows the photogenerated electrons in the QDs to transfer rapidly the Fe catalytic sites to enhance the photocatalytic activity for CO₂ reduction. Using water as an electron source, MAPbI₃@PCN‐221(Fe_0.2) exhibits a record‐high total yield of 1559 μmol g^?1 for photocatalytic CO₂ reduction to CO (34 %) and CH₄ (66 %), 38 times higher than that of PCN‐221(Fe_0.2) in the absence of perovskite QDs.     

Hydrangea‐like NiCo‐based Bimetal‐organic Frameworks,and their Pros and Cons as Supercapacitor Electrode Materials in Aqueous Electrolytes

Hydrangea‐like NiCo‐based bimetal‐organic frameworks (NiCo‐MOF) are synthesized in DMF‐EtOH solution via a solvothermal method, using 4,4′‐biphenyldicarboxylic acid as a ligand. NiCo‐MOF having a highest capacity of 1056.6 F · g^–1 at 0.5 A · g^–1 and 457.7 F · g^–1 even at 10 A · g^–1 is achieved at a Ni/Co/BPDC molar ratio of 1:1:1, a temperature of 170 °C and a reaction time of 12 hours. It exhibits secondary 3D microsphere structures assembled by primary 2D nanosheet structures, good crystalline structure and good thermal stability below 350 °C in air. All the electrochemical data show that NiCo‐MOF has the pros and cons as supercapacitor electrode materials in aqueous electrolytes. On the one hand, NiCo‐MOF has a high capacity even at a high current density, low internal resistance, charge‐transfer resistance and ion diffusion impendence, owing to the ordered coordination structure, 2D nanosheet structure and 3D assembled microsphere structure of NiCo‐MOF. On the other hand, the cycling stability and rate capability are not ideal enough due to the hydrolysis of coordination bonds in aqueous electrolytes, especially, in alkaline solution. The good dispersion and high electrochemical activity of metal ions bring a high capacity for NiCo‐MOF, but they result in the poor stability of NiCo‐MOF. In the future work, finding a suitable organic electrolyte is an effective way to enhance the cycling stability of NiCo‐MOF as well as deriving more stable skeleton materials from NiCo‐MOF.     

Incorporation of N‐Methyl‐d‐glucamine Functionalized Oligomer into MIL‐101(Cr) for Highly Efficient Removal of Boric Acid from Water

Polymeric resins are practically important adsorbents in a wide variety of applications, but they generally suffer from low surface areas and limited functionalized adsorption sites owing to their closely compacted and tangled polymeric chains. A metal–organic framework (MOF)–polymer composite with enhanced adsorption capacity against the compacted polymeric resins was reported. The strategy to incorporate functionalized oligomer within the cavities of the MOF was demonstrated by the preparation of MIL‐101(Cr) incorporated with N‐methyl‐d ‐glucamine‐based organosiloxane polymer. The resulting MOF composite shows high efficiency for the removal of boric acid from water because of exceptionally high loading of functional groups responsible for the boron adsorption. This material offers promising perspectives for boron removal applications in seawater desalination.     

Highly Dispersed Polyoxometalate‐Doped Porous Co3O4 Water Oxidation Photocatalysts Derived from POM@MOF Crystalline Materials

Rational design of earth‐abundant photocatalysts is an important issue for solar energy conversion and storage. Polyoxometalate (POM)@Co₃O₄ composites doped with highly dispersive molecular metal–oxo clusters, synthesized by loading a single Keggin‐type POM cluster into each confined space of a metal–organic framework (MOF), exhibit significantly improved photocatalytic activity in water oxidation compared to the pure MOF‐derived nanostructure. The systematic synthesis of these composite nanocrystals allows the conditions to be tuned, and their respective water oxidation catalytic performance can be efficiently adjusted by varying the thermal treatment temperature and the feeding amount of the POM. This work not only provides a modular and tunable synthetic strategy for preparing molecular cluster@TM oxide (TM=transition metal) nanostructures, but also showcases a universal strategy that is applicable to design and construct multifunctional nanoporous metal oxide composite materials.     

Metal–Organic Frameworks for Oxygen Storage

We present a systematic study of metal–organic frameworks (MOFs) for the storage of oxygen. The study starts with grand canonical Monte Carlo simulations on a suite of 10 000 MOFs for the adsorption of oxygen. From these data, the MOFs were down selected to the prime candidates of HKUST‐1 (Cu‐BTC) and NU‐125, both with coordinatively unsaturated Cu sites. Oxygen isotherms up to 30 bar were measured at multiple temperatures to determine the isosteric heat of adsorption for oxygen on each MOF by fitting to a Toth isotherm model. High pressure (up to 140 bar) oxygen isotherms were measured for HKUST‐1 and NU‐125 to determine the working capacity of each MOF. Compared to the zeolite NaX and Norit activated carbon, NU‐125 has an increased excess capacity for oxygen of 237 % and 98 %, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.     

Effect of Central Metal Ions of Analogous Metal–Organic Frameworks on Adsorption of Organoarsenic Compounds from Water: Plausible Mechanism of Adsorption and Water Purification

The adsorptive removal of organoarsenic compounds such as p‐arsanilic acid (ASA) and roxarsone (ROX) from water using metal–organic frameworks (MOFs) has been investigated for the first time. A MOF, iron benzenetricarboxylate (also called MIL‐100‐Fe) exhibits a much higher adsorption capacity for ASA and ROX than activated carbon, zeolite (HY), goethite, and other MOFs. The adsorption of ASA and ROX over MIL‐100‐Fe is also much more rapid than that over activated carbon. Moreover, the used MIL‐100‐Fe can be recycled by simply washing with acidic ethanol. Therefore, it is determined that a MOF such as MIL‐100‐Fe can be used to remove organoarsenic compounds from contaminated water because of its high adsorption capacity, rapid adsorption, and ready regeneration. Moreover, only one of three analogous MIL‐100 species (MIL‐100‐Fe, rather than MIL‐100‐Al or MIL‐100‐Cr) can effectively remove the organoarsenic compounds. This selective and high adsorption over MIL‐100‐Fe, different from other analogous MIL‐100 species, can be explained (through calculations) by the facile desorption of water from MIL‐100‐Fe as well as the large (absolute value) replacement energy (difference between the adsorption energies of the organoarsenic compounds and water) exhibited by MIL‐100‐Fe. A plausible adsorption/desorption mechanism is proposed based on the surface charge of the MOFs, FTIR results, calculations, and the reactivation results with respect to the solvents used in the experiments.