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.     

A Spiderweb‐Like Metal–Organic Framework Multifunctional Foam

Processing metal–organic frameworks (MOFs) into hierarchical macroscopic materials can greatly extend their practical applications. However, current strategies suffer from severe aggregation of MOFs and limited tuning of the hierarchical porous network. Now, a strategy is presented that can simultaneously tune the MOF loading, composition, spatial distribution, and confinement within various bio‐originated macroscopic supports, as well as control the accessibility, robustness, and formability of the support itself. This method enables the good dispersion of individual MOF nanoparticles on a spiderweb‐like network within each macrovoid even at high loadings (up to 86 wt %), ensuring the foam pores are highly accessible for excellent adsorption and catalytic capacity. Additionally, this approach allows the direct pre‐incorporation of other functional components into the framework. This strategy provides precise control over the properties of both the hierarchical support and MOF.     

Coordination Polymers: From Metal–Organic Frameworks to Spheres

Sphere of destiny : Metal–organic spheres with remarkable encapsulation properties are readily prepared and their ability to host a wide range of guest species, including nanoparticles, fluorescent dyes, and quantum dots, is demonstrated. Both the metal–organic spheres and the encapsulated species maintain their fluorescent or magnetic properties, highlighting the importance of these systems as new multifunctional materials.

     

Microporous La–Metal–Organic Framework (MOF) with Large Surface Area

A microporous La–metal‐organic framework (MOF) has been synthesized by the reaction of La(NO₃)₃ ? 6 H₂O with a ligand 4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐p‐aminobenzoate (TATAB) featuring three carboxylate groups. Crystal structure analysis confirms the formation of 3D MOF with hexagonal micropores, a Brunauer–Emmett—Teller (BET) surface area of 1074 m² g^?1 and high thermal and chemical stability. The CO₂ adsorption capacities are 76.8 cm³ g^?1 at 273 K and 34.6 cm³ g^?1 at 293 K, a highest measured CO₂ uptake for a Ln–MOFs.     

Interactive Thermal Effects on Metal–Organic Framework Polymer Composite Membranes

Polymeric membranes are important tools for intensifying separation processes in chemical industries, concerning strategic tasks such as CO₂ sequestration, H₂ production, and water supply and disposal. Mixed‐matrix and supported membranes have been widely developed; recently many of them have been based on metal–organic frameworks (MOFs). However, most of the impacts MOFs have within the polymer matrix have yet to be determined. The effects related to thermal behavior arising from the combination of MOF ZIF‐8 and polysulfone have now been quantified. The catalyzed oxidation of the polymer is strongly affected by the MOF crystal size and distribution inside the membrane. A 16 wt % 140 nm‐sized ZIF‐8 loading causes a 40 % decrease in the observed activation energy of the polysulfone oxidation that takes place at a temperature (545 °C) 80 °C lower than in the raw polymer (625 °C).     

Photoconductivity in Metal–Organic Framework (MOF) Thin Films

Photoconductivity is a characteristic property of semi‐conductors. Herein, we present a photo‐conducting crystalline metal–organic framework (MOF) thin film with an on–off photocurrent ratio of two orders of magnitude. These oriented, surface‐mounted MOF thin films (SURMOFs), contain porphyrin in the framework backbone and C₆₀ guests, loaded in the pores using a layer‐by‐layer process. By comparison with results obtained for reference MOF structures and based on DFT calculations, we conclude that donor–acceptor interactions between the porphyrin of the host MOF and the C₆₀ guests give rise to a rapid charge separation. Subsequently, holes and electrons are transported through separate channels formed by porphyrin and by C₆₀, respectively. The ability to tune the properties and energy levels of the porphyrin and fullerene, along with the controlled organization of donor–acceptor pairs in this regular framework offers potential to increase the photoconduction on–off ratio.     

Solvent‐Mediated Transformation from Achiral to Chiral Nickel(II) Metal–Organic Frameworks and Reassembly in Solution

Reactions of 5‐nitroisophthalic acid (NO₂‐H₂ip), 1,4‐bis(imidazol‐1′‐yl)butane (bimb), and Ni(NO₃)₂ ? 6 H₂O gave rise to four metal–organic frameworks (MOFs), [Ni₂(NO₂‐ip)₂(bimb)_1.5]_n ( 1 ), [Ni₄(NO₂‐ip)₃(bimb)₂(OH)₂(H₂O)]_n ? (CH₃CH₂OH)_{0.5 n} ( 2 ), [Ni(NO₂‐ip)(bimb)_1.5(H₂O)]_n ? (H₂O)_n ? (CH₃CH₂OH)_{0.5 n} ( 3 ), and [Ni(NO₂‐ip) (bimb)(μ‐H₂O)]_n ? (H₂O)_n ( 4 ). The metal/ligand ratio, pH value, and solvent exerted a subtle but crucial influence on the formation of complexes 1 – 4 , which possess different visual color and crystal structures. Complex 1 exhibits a twofold interpenetrating 3D pillared bilayer framework composed of binuclear and mononuclear Ni^II units, whereas complex 2 is a 3D chiral network that consists of asymmetric tetranuclear Ni^II units. Complexes 3 and 4 are 3D layer‐pillared frameworks that consist of mononuclear Ni^II ions and a 3D six‐connected network of μ‐water‐bridged dinuclear Ni^II units, respectively. Interestingly, achiral 4 can be transformed into chiral 2 by using a solvent‐mediated single‐crystal‐to‐single‐crystal process without any chiral auxiliary. Magnetic analyses of 2 and 4 show the occurrence of antiferromagnetic interactions. Complex 3 is difficult to obtain directly as a single solid phase, but it can be homogeneously formed by solvent‐mediated transformations from 1 , 2 , and 4 .     

Influence of Solvent‐Like Sidechains on the Adsorption of Light Hydrocarbons in Metal–Organic Frameworks

A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal–organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low‐density solvent with restricted degrees of freedom, offer tunable control of dispersive host–guest interactions. The performance of a series of frameworks of the type Zn₂(fu‐bdc)₂(dabco) (fu‐bdc^2?=functionalized 1,4‐benzenedicarboxylate; dabco=1,4‐diazabicyclo[2.2.2]octane), which feature a pillared layer structure, were investigated for the adsorption and separation of methane, ethane, ethylene, and acetylene. The four frameworks exhibit low methane uptake, whereas C2 hydrocarbon uptake is substantially higher as a result of the enhanced interaction of these molecules with the ligand sidechains. Most significantly, the adsorption quantities and selectivity were found to depend strongly upon the type of sidechains attached to the framework scaffold.     

Metal–Organic Framework (MOF) Nanorods,Nanotubes, and Nanowires

New mechanisms for the controlled growth of one‐dimensional (1D) metal–organic framework (MOF) nano‐ and superstructures under size‐confinement and surface‐directing effects have been discovered. Through applying interfacial synthesis templated by track‐etched polycarbonate (PCTE) membranes, congruent polycrystalline zeolitic imidazolate framework‐8 (ZIF‐8) solid nanorods and hollow nanotubes were found to form within 100 nm membrane pores, while single crystalline ZIF‐8 nanowires grew inside 30 nm pores, all of which possess large aspect ratios up to 60 and show preferential crystal orientation with the {100} planes aligned parallel to the long axis of the pore. Our findings provide a generalizable method for controlling size, morphology, and lattice orientation of MOF nanomaterials.     

Reversible Breaking and Forming of Metal–Ligand Coordination Bonds: Temperature‐Triggered Single‐Crystal to Single‐Crystal Transformation in a Metal–Organic Framework

The novel Yb succinate metal–organic framework exhibits a reversible single‐crystal to single‐crystal polymorphic transformation (see figure) when it is heated above 130 °C, returning to its initial form when back at room temperature. This transformation produces a change in the coordination sphere of the Yb atoms, which influences the catalytic activity of the material.

     

Electrochemical Synthesis of a Microporous Conductive Polymer Based on a Metal–Organic Framework Thin Film

A new approach to preparing 3D microporous conductive polymer has been demonstrated in the electrochemical synthesis of a porous polyaniline network with the utilization of a MOF thin film supported on a conducting substrate. The prepared porous polyaniline with well‐defined uniform micropores of 0.84 nm exhibits a high BET surface area of 986 m² g^?1 and a high electric conductivity of 0.125 S cm^?1 when doped with I₂, which is superior to existing porous conducting materials of porous MOFs, CMPs, and COFs.     

Embedding Functional Biomacromolecules within Peptide‐Directed Metal–Organic Framework (MOF) Nanoarchitectures Enables Activity Enhancement

Rationally tailoring a robust artificial coating can enhance the life‐time of fragile biomacromolecules. However, the coating also can restrain the activity of the guest because of the decreased substrate accessibility. Herein, we report a peptide‐directed strategy that enables in situ tailoring of the MOF‐shrouded biohybrids into controllable nanoarchitectures. The MOF biohybrid can be shaped from different 3D microporous architectures into a 2D mesoporous layer by a peptide modulator. Using this mild strategy, we show that the nanoarchitectures of the MOF coatings significantly affect the biological functions of the contained biomacromolecules. The biomacromolecules entrapped within the novel 2D mesoporous spindle‐shaped MOFs (2D MSMOFs) have significantly increased bioactivity compared to when encased within the hitherto explored 3D microporous MOFs. The improvement results from the shortened diffusion path and enlarged pore channel in 2D MSMOFs. Meanwhile, the thin 2D MSMOF layer also can provide excellent protection of the hosted biomacromolecules or protein‐scaffolded biominerals through structural confinement.     

Real‐Time Detection of Traces of Benzaldehyde in Benzyl Alcohol as a Solvent by a Flexible Lanthanide Microporous Metal–Organic Framework

Luminescent 3D lanthanide metal–organic framework (Ln‐MOF) {[Tb₂(TATAB)₂] ? 4 H₂O ? 6 DMF}_n ( 1 ) was synthesized under solvothermal conditions by using flexible ligand 4,4′,4′′‐s‐triazine‐1,3,5‐triyltri‐p‐aminobenzoate (TATAB). A phase transition was observed between low temperature and room temperature. The luminescence of 1 could be enhanced by formaldehyde and quenched efficiently by trace amounts of benzaldehyde in solvents such as benzyl alcohol (0.01–2.0 vol %) and ethanol (0.01–2.5 vol %). This is the first use of a Ln‐MOF as chemical sensor for both formaldehyde and benzaldehyde. The high sensitivity and selectivity of the luminescence response of 1 to benzaldehyde allows it to be used as an excellent sensor for identifying benzaldehyde and provides a simple and convenient method for detecting traces of benzaldehyde in benzyl alcohol based injections. This work establishes a new strategy for detection of benzaldehyde in benzyl alcohol by luminescent MOFs.     

An Interwoven Metal‐Organic Framework Combining Mechanically Interlocked Linkers and Interpenetrated Networks

New dibenzo[24]crown‐8 ether derivatives were prepared that contain appendages with thioether donors that can coordinate to a metal ion. These macrocycles were then combined with 1,2‐bis(pyridinium) ethane axles to create two types of [2]rotaxane ligands; those with the four thioether donors on the crown ether and those with six donor groups, four from the crown ether and two more attached to the stoppering groups of the dumbbell. The crown ethers and both types of [2]rotaxane ligands were allowed to react with Ag^I ions to form metal‐organic rotaxane framework (MORF) style coordination polymers. The interlocked hexadentate ligand forms the first example of a new type of lattice containing interwoven frameworks resulting from both interpenetration of frameworks due to the presence of an interlocked ligand and more classical interpenetration of independent frameworks.     

Catalytically Active Hollow Fiber Membranes with Enzyme‐Embedded Metal–Organic Framework Coating

Metal–organic frameworks (MOFs) are suitable enzyme immobilization matrices. Reported here is the in situ biomineralization of glucose oxidase (GOD) into MOF crystals (ZIF‐8) by interfacial crystallization. This method is effective for the selective coating of porous polyethersulfone microfiltration hollow fibers on the shell side in a straightforward one‐step process. MOF layers with a thickness of 8 μm were synthesized, and fluorescence microscopy and a colorimetric protein assay revealed the successful inclusion of GOD into the ZIF‐8 layer with an enzyme concentration of 29±3 μg cm^?2. Enzymatic activity tests revealed that 50 % of the enzyme activity is preserved. Continuous enzymatic reactions, by the permeation of β‐d ‐glucose through the GOD@ZIF‐8 membranes, showed a 50 % increased activity compared to batch experiments, emphasizing the importance of the convective transport of educts and products to and from the enzymatic active centers.     

2D Semiconducting Metal–Organic Framework Thin Films for Organic Spin Valves

2D conductive metal–organic frameworks (2D c‐MOFs) feature promising applications as chemiresistive sensors, electrode materials, electrocatalysts, and electronic devices. However, exploration of the spin‐polarized transport in this emerging materials and development of the relevant spintronics have not yet been implemented. In this work, layer‐by‐layer assembly was applied to fabricate highly crystalline and oriented thin films of a 2D c‐MOF, Cu₃(HHTP)₂, (HHTP: 2,3,6,7,10,11‐hexahydroxytriphenylene), with tunable thicknesses on the La_0.67Sr_0.33MnO₃ (LSMO) ferromagnetic electrode. The magnetoresistance (MR) of the LSMO/Cu₃(HHTP)₂/Co organic spin valves (OSVs) reaches up to 25 % at 10 K. The MR can be retained with good film thickness adaptability varied from 30 to 100 nm and also at high temperatures (up to 200 K). This work demonstrates the first potential applications of 2D c‐MOFs in spintronics.     

Selective and Sensitive Aqueous‐Phase Detection of 2,4,6‐Trinitrophenol (TNP) by an Amine‐Functionalized Metal–Organic Framework

Highly selective and sensitive aqueous‐phase detection of nitro explosive 2,4,6‐trinitrophenol (TNP) by a hydrolytically stable 3D luminescent metal–organic framework is reported. The compound senses TNP exclusively even in the presence of other nitro‐compounds, with an unprecedented sensitivity in the MOF regime by means of strategic deployment of its free amine groups. Such an accurate sensing of TNP, widely recognized as a harmful environmental contaminant in water media, establishes this new strategic approach as one of the frontiers to tackle present‐day security and health concerns in a real‐time scenario.     

A New Dimension for Coordination Polymers and Metal–Organic Frameworks: Towards Functional Glasses and Liquids

There are two categories of coordination polymers (CPs): inorganic CPs (i‐CPs) and organic ligand bridged CPs (o‐CPs). Based on the successful crystal engineering of CPs, we here propose noncrystalline states and functionalities as a new research direction for CPs. Control over the liquid or glassy states in materials is essential to obtain specific properties and functions. Several studies suggest the feasibility of obtaining liquid/glassy states in o‐CPs by design principles. The combination of metal ions and organic bridging ligands, together with the liquid/glass phase transformation, offer the possibility to transform o‐CPs into ionic liquids and other ionic soft materials. Synchrotron measurements and computational approaches contribute to elucidating the structures and dynamics of the liquid/glassy states of o‐CPs. This offers the opportunity to tune the porosity, conductivity, transparency, and other material properties. The unique energy landscape of liquid/glass o‐CPs offers opportunities for properties and functions that are complementary to those of the crystalline state.     

Solvent‐Vapor‐Induced Reversible Single‐Crystal‐to‐Single‐Crystal Transformation of a Triphosphaazatriangulene‐Based Metal–Organic Framework

A triphosphaazatriangulene (H₃L) was synthesized through an intramolecular triple phospha‐Friedel–Crafts reaction. The H₃L triangulene contains three phosphinate groups and an extended π‐conjugated framework, which enables the stimuli‐responsive reversible transformation of [Cu(HL)(DMSO)?(MeOH)]_n, a 3D‐MOF that exhibits reversible sorption characteristics, into (H₃L?0.5 [Cu₂(OH)₄?6 H₂O] ?4 H₂O), a 1D‐columnar assembled proton‐conducting material. The hydrophilic nature of the latter resulted in a proton conductivity of 5.5×10^?3 S cm^?1 at 95 % relative humidity and 60 °C.