Metal-organic Framework Systems Research Articles

Leveraging Isothermal Titration Calorimetry to Obtain Thermodynamic Insights into the Binding Behavior and Formation of Metal-Organic Frameworks.

Isothermal titration calorimetry (ITC) is a technique which directly measures the thermodynamic parameters of binding events. Although historically it has been used to investigate interactions in biological macromolecules and the kinetics of enzyme-catalyzed reactions, ITC has also been demonstrated to provide relevant thermodynamic information about interactions in synthetic systems, such as those in metal-organic frameworks (MOFs). MOFs are a family of crystalline porous materials that have been widely studied as supports for molecules ranging from gases to biomolecules through physisorption and chemisorption. Herein, we offer a perspective on the current applications of ITC in MOFs, including the mechanism of small molecule adsorption and the formation of MOF-based composite materials through noncovalent interactions. Experimental considerations specific to running ITC experiments in MOF systems are reviewed on the basis of existing reports. We conclude by discussing underexplored, but promising, MOF-related research directions which could be elucidated by ITC.

Confinement Matters: Stabilization of CdS Nanoparticles inside a Postmodified MOF toward Photocatalytic Hydrogen Evolution.

Insights into developing innovative routes for the stabilization of photogenerated charge-separated states by suppressing charge recombination in photocatalysts is a topic of immense importance. Herein, we report the synthesis of a metal-organic framework (MOF)-based composite where CdS nanoparticles (NPs) are confined inside the nanosized pores of Zr4+-based MOF-808, namely, CdS@MOF-808. Anchoring l-cysteine into the nanospace of MOF-808 via postsynthetic ligand exchange allows the capture of Cd2+ ions from their aqueous solution, which are further utilized for in situ growth of CdS NPs inside the nanosized MOF pores. The formation of CdS@MOF-808 opens up a possibility for visible-light photocatalysis as CdS NPs (1-2 nm) are a well-studied semiconductor system with a band gap of ∼2.6 eV. The confinement of the CdS NPs inside the MOF pores, close to the Zr4+ cluster, opens up a shorter electron transfer route from CdS to the catalytic Zr4+ cluster and shows a high rate of H2 evolution (10.41 mmol g-1 h-1) from water with a loading of 3.56 wt % CdS. In contrast, a similar composite in which CdS NPs are stabilized on the external surface of MOF-808 reveals poor activity (0.15 mmol g-1 h-1). CdS NPs stabilized on the MOF-808 surface show slower and inefficient electron transfer kinetics compared to CdS stabilized inside the nanospace of the MOF, as realized by the transient absorption measurements. Therefore, this work unveils the critical role of stabilizing the photosensitizer NPs in close proximity of the catalytic sites in MOF systems towards developing highly efficient H2 evolution photocatalysts.

Efficient Xe/Kr Separation Based on a Lanthanide-Organic Framework with One-Dimensional Local Positively Charged Rhomboid Channels.

Efficient xenon/krypton (Xe/Kr) separation has played an important role in industry due to the wide application of high-purity Xe and with regard to the safe disposal of radioactive noble gases (85Kr and 133Xe). A less energy-demanding separation technology, adsorptive separation using porous solid materials, has been proposed to replace the traditional cryogenic distillation with intensive energy consumption. As a cutting-edge class of porous materials, metal-organic frameworks (MOFs) featuring permanent porosity, designable chemical functionalities, and tunable pore sizes hold great promise for Xe/Kr separation. Here, we report a two-dimensional (2D) lanthanide-organic framework (termed LPC-MOF, [Eu(Ccbp)(NO3)(HCOO)]·DMF0.3(H2O)2.5) with one-dimensional (1D) local positively charged rhomboid channels whose size matches well with the kinetic diameter of Xe, leading to its superior Xe/Kr separation performance. Column breakthrough experiments demonstrate that LPC-MOF exhibits a high Xe/Kr selectivity of 12.4 and an Xe adsorption amount of 3.39 mmol kg-1 under simulated conditions for real used nuclear fuel (UNF)-reprocessing plants. Furthermore, density functional theory (DFT) calculations elucidate not only the intrinsic mechanisms of Xe/Kr separation at the molecular level but also the detailed influence of the local positive charge (N+) on the performance of Xe/Kr separation in the MOF system.

Copper-Based Metal-Organic Framework with a Tetraphenylethylene-Tetrazole Linker for Visible-Light-Driven CO2 Photoconversion.

The design of efficient and inexpensive photocatalysts for CO2 photoreduction under visible light is of great significance for the sustainable development of the entire society. Herein, a copper-based metal-organic framework (MOF) (CUST-804) using a bulky tetraphenylethylene-tetrazole linker is synthesized and successfully used as a photocatalyst for CO2 reduction. The structural characterizations, as well as the photophysical properties, are investigated systematically. In the heterogeneous catalytic system, CUST-804 exhibits a robust CO production activity up to 2.71 mmol g-1 h-1 with excellent recyclability along with a selectivity of 82.8%, which is comparable with those of the reported copper-based MOF system. Theoretical calculations demonstrated that, among three kinds of coordinated model, only the 5-coordinated Cu site is active for CO2 reduction, in which the *COOH intermediate is stabilized and CO is readily desorbed. The results obtained herein can provide fresh insights into the realization of efficient copper-functionalized crystalline photocatalysts for CO2 reduction.

Metal-Organic Framework (MOFs) tethered to cotton fibers display antimicrobial activity against relevant nosocomial bacteria

Despite antibiotic treatments, bacteria remain outstanding etiological agents of hospital-acquired infections. This work assessed the antimicrobial activity of copper, zinc, and aluminum Metal-Organic framework (MOFs) immobilized onto cotton fibers against nosocomial bacteria. The MOF systems were synthesized over cotton carboxymethylated fibers (CMCs) through a friendly environmental insitu method. SEM and XRD analyses showed that MOFs uniformly anchored on cotton fibers were resistant to sterilization by autoclaving processes.On the other hand, using the ASTM E2149-13a method, it was observed that all the MOF systems exhibited antibacterial activity against Escherichia coli ATCC25922TM, Staphylococcus aureus ATCCR6538TM and Klebsiella pneumoniae ATCCR13882TM. In general, Gram-negative bacteria were the most susceptible to the cellulose-MOF systems; in fact, the cotton-Cu-MOF (MOF-199) displayed antimicrobial activity greater than 99% against Gram-negative bacteria in less than 5 min. On the other hand, the cotton-Zn-MOFs (MOF-74 and MOF-5) systems inhibited the growth of E. coli and K. pneumonia, displaying a bacterial growth inhibition range between 80% and 99.9%. In addition, the cotton-Al-MOF (MIL-53) exhibited a greater spectrum of antibacterial activity, indeed inhibited the growth of S. aureus (Gram-positive), K. pneumoniae, and E. coli (Gram-negative) at 50.2%, 53.6%, and 93.4%, respectively. Noteworthy, the antibacterial activity of Al+3 based MOFs has not been reported previously. All these results expand the potential of cellulose-MOF systems as attractive materials in the production of antibacterial fabrics, especially for hospital environments.

Direct Observation of Modulated Radical Spin States in Metal-Organic Frameworks by Controlled Flexibility.

Owing to their switchable spin states and dynamic electronic character, organic-based radical species have been invoked in phenomena unique to a variety of fields. When incorporated in solid state materials, generation of organic radicals proves challenging due to aggregation. Metal-organic frameworks (MOFs) are promising candidates for immobilization and stabilization of organic radicals because of the tunable spatial arrangement of organic linkers and metal nodes, which sequesters the reactive species. Herein, a flexible, redox-active tetracarboxylic acid linker bearing two imidazole units was chosen to construct a new Zr6-MOF, NU-910, with scu topology. By exploiting the structural flexibility of NU-910, we successfully modulate the dynamics between an isolated organic radical species and an organic radical π-dimer species in the MOF system. Single-crystal X-ray diffraction analysis reveals that through solvent exchange from N,N-diethylformamide to acetone, NU-910 undergoes a structural contraction with interlinker distances decreasing from 8.32 Å to 3.20 Å at 100 K. Organic radical species on the bridging linkers are generated via UV light irradiation. Direct observation of temperature-induced spin switches from an isolated radical species to a magnetically silent radical π-dimer in NU-910 after irradiation in the solid state was achieved via variable-temperature single-crystal X-ray diffraction and variable-temperature electron paramagnetic resonance spectroscopy. Ultraviolet-visible-near infrared spectroscopy and density functional theory calculations further substantiated the formation of a radical cation π-dimer upon irradiation. This work demonstrates the potential of using flexible MOFs as a platform to modulate radical spin states in the solid phase.

Metal-organic frameworks as O2-selective adsorbents for air separations.

Oxygen is a critical gas in numerous industries and is produced globally on a gigatonne scale, primarily through energy-intensive cryogenic distillation of air. The realization of large-scale adsorption-based air separations could enable a significant reduction in associated worldwide energy consumption and would constitute an important component of broader efforts to combat climate change. Certain small-scale air separations are carried out using N2-selective adsorbents, although the low capacities, poor selectivities, and high regeneration energies associated with these materials limit the extent of their usage. In contrast, the realization of O2-selective adsorbents may facilitate more widespread adoption of adsorptive air separations, which could enable the decentralization of O2 production and utilization and advance new uses for O2. Here, we present a detailed evaluation of the potential of metal–organic frameworks (MOFs) to serve as O2-selective adsorbents for air separations. Drawing insights from biological and molecular systems that selectively bind O2, we survey the field of O2-selective MOFs, highlighting progress and identifying promising areas for future exploration. As a guide for further research, the importance of moving beyond the traditional evaluation of O2 adsorption enthalpy, ΔH, is emphasized, and the free energy of O2 adsorption, ΔG, is discussed as the key metric for understanding and predicting MOF performance under practical conditions. Based on a proof-of-concept assessment of O2 binding carried out for eight different MOFs using experimentally derived capacities and thermodynamic parameters, we identify two existing materials and one proposed framework with nearly optimal ΔG values for operation under user-defined conditions. While enhancements are still needed in other material properties, the insights from the assessments herein serve as a guide for future materials design and evaluation. Computational approaches based on density functional theory with periodic boundary conditions are also discussed as complementary to experimental efforts, and new predictions enable identification of additional promising MOF systems for investigation.

Biotemplating of Metal–Organic Framework Nanocrystals for Applications in Small‐Scale Robotics

AbstractBiotemplating is a powerful approach for manufacturing small‐scale devices. Here, the assembly of metal–organic framework (MOF) nanocrystals onto biotemplated magnetic helical structures on the cyanobacterium Spirulina platensis is reported. It is demonstrated that the authors’ approach is universal and can be used to equip biotemplated structures with different functional MOF systems. The successful assembly of MOF nanocrystals on magnetically coated helical biotemplates is achieved by decorating the magnetic surface with gelatin, a naturally occurring macromolecule with synthon moieties that allows anchoring of the MOF nanocrystals via electrostatic interactions. Furthermore, as gelatin is a thermally responsive material, it can serve to free the magnetic biotemplates from the MOF nanocrystal cargoes. As such, the systems can be used as highly integrated magnetically driven microrobots with multiple functionalities. To this end, the potential of these composite helical architectures is demonstrated as MOF‐based small‐scale robots with applications in biomedicine and environmental remediation.

Surfactant-induced hierarchically porous MOF-based catalysts prepared under sustainable conditions and their ability to remove bisphenol A from aqueous solutions

Metal-Organic Frameworks (MOFs) are extensively used in different applications, including heterogeneous catalysis given the fact that practically any center can be designed on demand and is accessible for reactants. Just like any other microporous catalysts, the limited diffusion of reactants and products is an endemic drawback also in MOFs. To face it, the use of nanocrystalline MOFs is a proven alternative, which in addition is often accompanied by improvements in sustainability of synthesis procedure (room temperature, water as solvent, etc.). This work goes further adding surfactant-induced mesoporosity to the nanocrystallinity of these materials. As a proof of concept, the nanocrystalline NH2-MIL-53(Al) and CTA+ (cetyltrimethylammonium) were selected as the sustainably-prepared nanocrystalline MOF and a cationic surfactant, respectively. The MOF system is formed by massive and practically instantaneous precipitation entrapping the surfactant, which generates mesopores in the aggregates. The simple washing with ethanol at room temperature leads to a nanocrystalline NH2-MIL-53(Al) material containing outstanding intercrystalline mesoporosity. The so-obtaining hierarchically-porous NH2-MIL-53(Al) is able to effectively remove bisphenol A (BPA) from aqueous solution (more than 90% of a 25 ppm BPA aqueous solution in just 10 min at room temperature), duplicating the performance given by its counterpart nanocrystalline NH2-MIL-53(Al) prepared in the absence of surfactant.

Host-Guest Interactions Between Metal–Organic Frameworks and Air-Sensitive Complexes at High Temperature

The host-guest chemistry of metal–organic frameworks (MOFs) has been attracting increasing attention owing to the outstanding properties derived from MOFs-guests combinations. However, there are large difficulties involved in the syntheses of the host-guest MOF systems with air-sensitive metal complexes. In addition, the behaviors on host-guest interactions in the above systems at high temperature are not clear. This study reported the synthetic methods for host-guest systems of metal–organic framework and air-sensitive metal complexes via a developed chemical vapor infiltration process. With the synchrotron X-ray powder diffraction (XRPD) measurements and Fourier Transform infrared spectroscopy (FTIR), the successful loadings of Fe(CO)5 in HKUST-1 and NH2-MIL-101(Al) have been confirmed. At high temperatures, the structural and chemical componential changes were investigated in detail by XRPD and FTIR measurements. HKUST-1 was proven to have strong interaction with Fe(CO)5 and resulted in a heavy loading amount of 63.1 wt%, but too strong an interaction led to deformation of HKUST-1 sub-unit under heating conditions. NH2-MIL-101(Al), meanwhile, has a weaker interaction and is chemically inert to Fe(CO)5 at high temperatures.

Synthesis of a 2D copper(II)-carboxylate framework having ultrafast adsorption of organic dyes

Two-dimensional (2D) coordination polymers are very interesting materials for their attractive applications. A novel 2D metal-organic framework (MOF) was derived from copper(II) and amino benzoic acid under both room temperature and solvothermal reaction conditions using different solvents. From both of the synthesis methods, an identical MOF was crystalized with monoclinic crystal system having P21/c space group. Hirshfeld surface analysis is carried out to explore the non-covalent interactions obtained from single crystal XRD investigation in terms of percentage contribution of each interatomic contact involved in packing of molecules into MOF structure. The microstructure analysis and surface morphology studies revealed the 2D layered regular pattern of rhombus disks of ~5 μm thickness throng together via clustering of these rhombic shaped flakes as flowers (ranging 50–100 μm in size) having uniform elemental composition. This 2D MOF efficiently adsorbed organic dyes (methylene blue, methyl orange, and methyl red) from their aqueous solutions. The 2D copper-carboxylate framework (1.2 g/L) exhibited high adsorption rates for organic dyes (0.15–0.19 mM), and >90% of these dyes could be captured as soon as they are exposed to MOF suspension (1 min) in each case. The dye removal efficiency is credited to synergy among structure, ionic strength, shapes and dimensions of dyes with respect to MOF structure. The microstructure of MOF along with electronic interactions like electrostatic, hydrogen bonding, π-π interactions and coordination to open metal sites, might contribute to the ultrafast dye adsorption process by MOF. The adsorption phenomenon is spontaneous and followed the pseudo-second order kinetic mechanism. DFT calculations revealed important electronic parameters of the dyes and model MOF systems, and novel insights with respect to possible dye-MOF interactions. The MOF remained quite stable during the dye adsorption and was regenerated easily for the successful subsequent use.

Mixed hierarchical local structure in a disordered metal\u2013organic framework

Amorphous metal–organic frameworks (MOFs) are an emerging class of materials. However, their structural characterisation represents a significant challenge. Fe-BTC, and the commercial equivalent Basolite® F300, are MOFs with incredibly diverse catalytic ability, yet their disordered structures remain poorly understood. Here, we use advanced electron microscopy to identify a nanocomposite structure of Fe-BTC where nanocrystalline domains are embedded within an amorphous matrix, whilst synchrotron total scattering measurements reveal the extent of local atomic order within Fe-BTC. We use a polymerisation-based algorithm to generate an atomistic structure for Fe-BTC, the first example of this methodology applied to the amorphous MOF field outside the well-studied zeolitic imidazolate framework family. This demonstrates the applicability of this computational approach towards the modelling of other amorphous MOF systems with potential generality towards all MOF chemistries and connectivities. We find that the structures of Fe-BTC and Basolite® F300 can be represented by models containing a mixture of short- and medium-range order with a greater proportion of medium-range order in Basolite® F300 than in Fe-BTC. We conclude by discussing how our approach may allow for high-throughput computational discovery of functional, amorphous MOFs.

Defective Hierarchical Pore Engineering of a Zn-Ni MOF by Labile Coordination Bonding Modulation.

The construction and modulation of hierarchical pore structure in metal-organic frameworks (MOFs) has become a hot topic owing to the advantages of hierarchical pore MOFs (HP-MOFs) in matter storage and mass transfer related applications. Herein, we report the engineering of crystalline defect in a bimetallic MOF for the construction and tuning of HP-MOF. A microporous MOF system showing metal-center-dependent water stability, namely, {[M3F(bdc)3 tpt] (solvents)}n (M = Zn2+ and Ni2+, H2bdc = 1,4-benzenedicarboxylic acid, tpt = 2,4,6-tris(4-pyridyl)triazine), was utilized as a platform for the construction of HP-MOF. By tuning the Zn2+/Ni2+ ratio in the reactant, a bimetallic MOF with a highly tunable Zn2+/Ni2+ ratio could be obtained. The relatively labile Zn2+-based coordination bonding in the bimetallic MOF could be readily and targeted broken through water treatment for the engineering of crystalline defects-based hierarchical pore structure. The resultant HP-MOF reveals a dramatically increased pore volume with the presence of mesopore and macropore. In addition, the anionic framework of HP-MOF could be utilized for the selective adsorption of a cationic dye methylene blue, and a relatively high capacity (250 mg·g-1, five times compared with the pristine microporous MOF) could be achieved.

Integration of High‐Performance Cost‐Effective Copper‐Metal‐Organic‐Nanocluster‐based Gate Dielectric for Next‐Generation CMOS Applications

AbstractThe suitability of metal‐organic frameworks (MOFs) as functional materials for future electronic logic devices with desirable dielectric constant, bandgap, high‐quality interface, low leakage current, and better compatibility is still an open challenge. Owing to the synergistic complementary properties of MOFs systems, a low‐cost copper‐metal‐organic nanoclusters (Cu‐MOCs) has been synthesized comprising inorganic copper metal unit allied organic m‐toluic acid ligand by facile sol–gel strategy. It offers large‐area thin‐films uniformity, high dielectric constant (κ ≈ 5.49), improved interfacial properties, dynamic switching behavior with the stimuli field, and extends the realization of metal‐organic‐framework dielectric for scalable complementary‐metal‐oxide‐semiconductor (CMOS) logic applications over customary hybrid counterparts. Various techniques such as single crystal X‐ray diffraction, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and energy dispersive X‐ray spectroscopy have been used to validate the Cu‐MOCs formulation. In particular, the fabricated Cu‐MOCs, metal–insulator–semiconductor structures exhibit promising dynamic switching behavior responsive to the applied field, hysteresis‐free capacitance–voltage characteristics, low interfacial trap density (≈1.4 × 1011 eV−1 cm−2), low effective oxide charges (≈1.1 × 1011 cm−2), and noteworthy small leakage current density (≈1.29 nA cm−2 @ 1 V) ever since in electrical analysis. Cost‐effective novel Cu‐MOCs successfully demonstrate high‐performance, reliable gate dielectrics for next‐generation CMOS logic devices.

Encapsulation of Ultrafine Metal–Organic Framework Nanoparticles within Multichamber Carbon Spheres by a Two-Step Double-Solvent Strategy for High-Performance Catalysts

Carbon-encapsulated metal-organic framework (MOF) composite is one kind of emerging new catalyst with high efficiency and has gained much attention. However, for this kind of composite catalyst, the key to improving its catalytic activity and durability is to realize the effective dispersion of MOF nanoparticles (NPs) and enhance the interaction between MOF NPs and the carbon matrix, which remain a significant challenge. Herein, ultrafine MOF NPs within multichamber carbon spheres (MOF@MCCS), for the first time, have been rationally synthesized by a two-step double-solvent strategy for high-performance catalysts. The precise loading of guest MOFs can be achieved by adjusting the multichamber structure and calcination extent of the multichamber polymer (MCP), and the particle size of MOFs can be as low as 13.2 nm. Due to the formation of abundant carbon defects in the pyrolysis process of MCPs, the special structure and synergistic effect make the material exhibit higher catalytic activity and durability. More importantly, this method is universal and can be extended to different MOF systems. The two-step double-solvent strategy not only prepares a unique structure of MOF@MCCS-type host-guest-encapsulated catalysts but also provides a new idea for the design of high-efficiency catalysts with better performance and higher durability.

Coordination Geometry Changes in Amorphous Cyanide-Bridged Metal-Organic Frameworks upon Water Adsorption.

Amorphous coordination polymers and metal-organic frameworks (MOFs) have attracted much attention owing to their various functionalities. Here, we demonstrate the tunable water adsorption behavior of a series of amorphous cyanide-bridged MOFs with different metals (M[Ni(CN)4]: MNi; M = Mn, Fe, and Co). All three compounds adsorb up to six water molecules at a certain vapor pressure (Pads) and undergo conversion to crystalline Hofmann-type MOFs, M(H2O)2[Ni(CN)4]·4H2O (MNi-H2O; M = Mn, Fe, and Co). The Pads of MnNi, FeNi, and CoNi for water adsorption is P/P0 = 0.4, 0.6, and 0.9, respectively. Although the amorphous nature of these materials prevented structural elucidation using X-ray crystallography techniques, the local-scale structure around the N-coordinated M2+ centers was analyzed using L2,3-, K-edge X-ray absorption fine structure, and magnetic measurements. Upon hydration, the coordination geometry of these metal centers changed from tetrahedral to octahedral, resulting in significant reorganization of the MOF local structure. On the other hand, Ni[Ni(CN)4] (NiNi) containing square-planar Ni2+ centers did not undergo significant structural transformation and therefore abruptly adsorbed H2O in the low-pressure region. We could thus define how changes in the bond lengths and coordination geometry are related to the adsorption properties of amorphous MOF systems.

Two new uncommon 3D cobalt-based metal organic frameworks: Temperature induced syntheses and enhanced photocatalytic properties against aromatic dyes

The reaction of 5-fluorine-3-(3,5-dicarboxylphenxoy)benzoic acid (H3L) with cobalt(II) salt in presence of 1,1'-(1,4-butanediyl)bis (imidazole) (bib) linker yielded two new metal–organic frameworks (MOFs) with compositions [Co4(μ3-OH)2(H2O)2(L)2 (bib)1.5(CH3CN)·3H2O·CH3CN] (1) and [Co8(μ3-OH)4(L)4 (bib)4·8CH3CN] (2). The single crystal X-ray diffraction revealed that 1 exhibited an unusual 3D 3,8-connected framework with 3,8T25 topology based on [Co4(μ3-OH)2] tetranuclear cobalt clusters as secondary building units (SBU) with a (43) (412·54·64·88) Schläfli symbol. In 2, by substituting the CH3CN with neutral N-ligand, a 3D 3,8-connected MOF with 3,10T9 topology and a point symbol of {418.624.83}.{43}2 has been obtained. This represents a highly connected uninodal network topology presently known for flexible carboxylate-based MOF systems. Both the MOFs have been used as photocatalysts for photodegradation of a model organic dye methyl violet (MV). The photocatalytic experiments demonstrated that both 1 and 2 displayed efficient photocatalytic performances to degrade MV under UV irradiation. The plausible mechanism through which both the MOFs displayed photocatalytic properties have been proposed by using band gap calculations.

Encapsulation of Cobalt Oxide into Metal-Organic Frameworks for an Improved Photocatalytic CO2 Reduction.

The increased emission of CO2 has negative impacts on the environment. Among the strategies, photocatalytic reduction is promising to convert the CO2 into chemicals. In this report, CoOx nanoparticles were loaded in the channels of MIL-101(Cr), a kind of metal-organic frameworks (MOF), to construct a novel CoOx /MIL-101(Cr) system to facilitate CO2 photoreduction. Under the optimal conditions, the CoOx /MIL-101(Cr) showed a significantly enhanced performance for photocatalytic CO2 reduction compared with bare CoOx and MIL-101(Cr). Our findings provide a pathway for a rational design of efficient MOF systems for the photocatalytic reduction of CO2 .

Coordination‐Driven Assembly of Metal–Organic Framework Coating for Catalytically Active Superhydrophobic Surface

AbstractHere, a superhydrophobic and catalytically active metal–organic framework (MOF) coating is reported by coordination‐driven assembly of MOF nanoparticles and a catechol‐functionalized polysiloxane polymer. This MOF coating can be fabricated by casting MOF‐polymer precursor onto diverse substrates with varied coating techniques, for example, spray coating, bar coating, and dip coating. The catechol‐functionalized polymer can not only coordinate to the open metal sites on MOF surface which enables the surface functionalization and assembly of MOF nanoparticles, but also allow non‐covalent interactions with casting substrates—thus improving the substrate adhesion of the MOF coating. With the well‐preserved porosity and surface hydrophobicity, the MOF coating demonstrates superhydrophobicity as well as improved catalytic activity toward the Knoevenagel condensation at room temperature. Such coordination‐driven assembly approach can be extended to a range of MOF systems for preparing highly functional composite materials toward various applications.

Graphene-Metal-Organic Framework Composite Sulfur Electrodes for Li-S Batteries with High Volumetric Capacity.

In an age of rapid acceleration toward next-generation energy storage technologies, lithium-sulfur (Li-S) batteries offer the desirable combination of low weight and high specific energy. Metal-organic frameworks (MOFs) have been recently studied as functionalizable platforms to improve Li-S battery performance. However, many MOF-enabled Li-S technologies are hindered by low capacity retention and poor long-term performance due to low electronic conductivity. In this work, we combine the advantages of a Zr-based MOF-808 loaded with sulfur as the active material with a graphene/ethyl cellulose additive, leading to a high-density nanocomposite electrode requiring minimal carbon. Our electrochemical results indicate that the nanocomposites deliver enhanced specific capacity over conventionally used carbon/binder mixtures, and postsynthetic modification of the MOF with lithium thiophosphate results in further improvement. Furthermore, the dense form factor of the sulfur-loaded MOF-graphene nanocomposite electrodes provides high volumetric capacity compared to other works with significantly more carbon additives. Overall, we have demonstrated a proof-of-concept paradigm where graphene nanosheets facilitate improved charge transport because of enhanced interfacial contact with the active material. This materials engineering approach can likely be extended to other MOF systems, contributing to an emerging class of two-dimensional nanomaterial-enabled Li-S batteries.