Metal-organic Framework Framework Research Articles

In Situ Mapping and Local Negative Uptake Behavior of Adsorbates in Individual Pores of Metal-Organic Frameworks.

Herein, we report the adsorbate behavior in individual local pores of MIL-101, which is a metal-organic framework (MOF) with two heterogeneous mesopores and different metal sites, by combining adsorbate isotherms and in situ crystallography profiles. The in situ mapping shows that the substrate-adsorbate interaction affects the initial adsorption and pore condensation steps. The monolayer adsorption gradient changes greatly depending on the framework metal-adsorbate attraction force. Also, broad inflection points are found in adsorption isotherms, and the initial shape depends on the different metals. Besides, the capillary condensation at a pore draws adsorbates from other local pores. This leads to the local negative uptake behavior in individual pore isotherms. At higher pressure, they move to a larger space, whereas in a relatively low-pressure range the attraction force between the MOF framework and guest molecule influences the amount of rearranged guest molecules. Furthermore, the origin of the characteristic adsorption behavior based on the metals constituting the MOFs and the relative strength of substrate-adsorbate and adsorbate-adsorbate interactions are elucidated through the combined study of electron densities in pores, electron paramagnetic resonance spectroscopy spectra, and density functional theory and Monte Carlo simulations to uncover the previously veiled information on adsorption behavior.

MOFs in the time domain.

Many of the proposed applications of metal-organic framework (MOF) materials may fail to materialize if the community does not fully address the difficult fundamental work needed to map out the 'time gap' in the literature - that is, the lack of investigation into the time-dependent behaviours of MOFs as opposed to equilibrium or steady-state properties. Although there are a range of excellent investigations into MOF dynamics and time-dependent phenomena, these works represent only a tiny fraction of the vast number of MOF studies. This Review provides an overview of current research into the temporal evolution of MOF structures and properties by analysing the time-resolved experimental techniques that can be used to monitor such behaviours. We focus on innovative techniques, while also discussing older methods often used in other chemical systems. Four areas are examined: MOF formation, guest motion, electron motion and framework motion. In each area, we highlight the disparity between the relatively small amount of (published) research on key time-dependent phenomena and the enormous scope for acquiring the wider and deeper understanding that is essential for the future of the field.

Metal-Organic Frameworks (MOFs) for Cancer Therapy.

MOFs exhibit inherent extraordinary features for diverse applications ranging from catalysis, storage, and optics to chemosensory and biomedical science and technology. Several procedures including solvothermal, hydrothermal, mechanochemical, electrochemical, and ultrasound techniques have been used to synthesize MOFs with tailored features. A continued attempt has also been directed towards functionalizing MOFs via “post-synthetic modification” mainly by changing linkers (by altering the type, length, functionality, and charge of the linkers) or node components within the MOF framework. Additionally, efforts are aimed towards manipulating the size and morphology of crystallite domains in the MOFs, which are aimed at enlarging their applications window. Today’s knowledge of artificial intelligence and machine learning has opened new pathways to elaborate multiple nanoporous complex MOFs and nano-MOFs (NMOFs) for advanced theranostic, clinical, imaging, and diagnostic purposes. Successful accumulation of a photosensitizer in cancerous cells was a significant step in cancer therapy. The application of MOFs as advanced materials and systems for cancer therapy is the main scope beyond this perspective. Some challenging aspects and promising features in MOF-based cancer diagnosis and cancer therapy have also been discussed.

Tetrathiafulvalene-Cobalt Metal-Organic Frameworks for Lithium-Ion Batteries with Superb Rate Capability.

Although pristine metal-organic framework (MOF) anodes for lithium-ion batteries (LIBs) show moderate activities and relatively stable cycling, the poor rate capability of the MOF anodes limited their applications in the development of a new generation of energy storage. Herein, the electric active CoII ion is selected to coordinate with redox-active S-rich tetrathiafulvalene (TTF) derivatives to create two TTF-Co-MOFs, formulated as [Co2(py-TTF-py)2(BDC)2]·2DMF·H2O (TTF-Co-MOF 1) and [Co2(py-TTF-py)2(BPDC)2]·3DMF·3H2O (TTF-Co-MOF 2), where py-TTF-py = 2,6-bis(4'-pyridyl)tetrathiafulvalene, H2BDC = terephthalic acid, H2BPDC = biphenyl-4,4'-dicarboxylic acid, and DMF = N,N-dimethylformamide. Crystallographic characterization indicated that the two MOFs possess similar 2-fold-interpenetrating 3D frameworks but with two different pore sizes. The pore-size-dependent performances of the TTF-Co-MOFs were explored to optimize the MOFs as the anode materials for LIBs. TTF-Co-MOF 1 presents a high reversible specific capacity of 1186.6 mAh g-1 at 200 mA g-1 after 287 cycles. The rate capability is greatly enhanced by the introduction of CoII into TTF-based MOFs with specific capacities of 1028.6 mAh g-1 at 5 A g-1 and 966.5 mAh g-1 at 10 A g-1. On the basis of the series analysis of theoretical calculations, electrochemical impedance spectroscopy, and crystal structures, it is found that the CoII metal centers play a bridging role in charge transport within the MOF framework, which is beneficial for the transportation of Li ions. The competitive performances of TTF-Co-MOF 1 are attributed to the synergistic effect of the CoII metal centers and S-rich TTF ligand as well as suitable porosity. The study shed some light for the fabrication of advanced energy storage devices through the rational design of MOF-based anode materials.

Construction of MOF/COF Hybrids for Boosting Sunlight-Induced Fenton-like Photocatalytic Removal of Organic Pollutants.

In this work, a metal-organic framework (MOF) material of NH2-MIL88B was hybridized with TpPa-1-COF through covalent bonding, and the hybrid was subsequently employed for the degradation of Rhodamine B (RhB) and tetracycline (TC) by simulated sunlight-induced Fenton-like exciting H2O2. The obtained results show that its photocatalytic activity is much better than those of its parent MOF and covalent organic framework (COF). Moreover, it is much higher than that of bare photocatalysis without Fenton-like excitation of H2O2. The high degradation efficiency is ascribed to two factors. One is the formation of hybrid, which promotes charge separation and light absorbance. Another is the Fenton-like excitation of H2O2, which produces more hydroxyl radicals (•OH). This report presents a facile approach to greatly improve the photocatalytic property of MOF materials by the formation of hybrid with COFs and Fenton-like excitation of H2O2.

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Quantifying diffusion of organic liquids in a MOF component of MOF/Polymer mixed-matrix membranes by high field NMR

Confinement of crystals of metal–organic frameworks (MOFs) in polymers to form MOF/polymer mixed-matrix membranes (MMMs) can lead to changes in intra-MOF diffusion. Such changes in intra-MOF diffusion were previously demonstrated for light gases, and attributed to a reduction in MOF framework flexibility. However, to our knowledge, no direct measurements of intra-MOF diffusion in MMMs and of the related MOF confinement effect on diffusion have been reported for organic liquids. In this work, 13C pulsed field gradient (PFG) NMR was used to quantify self-diffusion of methanol, ethanol, p-xylene, and o-xylene inside MOF crystals of the type ZIF-71, which were dispersed in a Torlon polymer to form MMMs. The intra-ZIF self-diffusivities in the MMMs were compared with the corresponding self-diffusivities measured in beds of ZIF-71 crystals. The observed self-diffusivity dependencies on diffusion time were explained by crystal boundary effects. The corresponding values of intra-ZIF self-diffusivities not perturbed by such effects were found to be the same, within uncertainty, in the MMMs and ZIF-71 beds. The observed lack of an influence of the ZIF-71 confinement in Torlon on diffusion is explained, and an option to increase diffusion selectivity is discussed.

Highly sensitive fluorescent quantification of acid phosphatase activity and its inhibitor pesticide Dufulin by a functional metal–organic framework nanosensor for environment assessment and food safety

Developing a rapid and accurate strategy of sensing Dufulin is a vital challenge for risk assessment and food crops along with its spreading usage. Herein a dye-encapsulated azoterephthalate metal–organic framework (MOF)-based fluorescent sensing system was designed for Dufulin analysis by acid phosphatase (ACP) enzyme-controlled collapse of MOF framework and subsequent release of the encapsulated dye. The fluorescence intensity of the DMOF/AAP/ACP system was negatively related to the dosage of Dufulin (0–5 μg mL−1) with detection limit of 2.96 ng mL−1. The sensing system able to rapidly and sensitively sense the activity of ACP and Dufulin, and was also applicable for assessment of the real samples including paddy water and soil, polished rice and cucumber. Accordingly, this study illustrated the feasibility and the potential of MOF-derived nanosensors for improving pesticide analysis and opening up the design of the enzyme-based probes for pesticide sensing in environmental assessment and food safety.

Versatility vs stability. Are the assets of metal–organic frameworks deployable in aqueous acidic and basic media?

Exploring the deployment of metal–organic frameworks (MOFs) in a plethora of applications is a growing research area. More importantly, this evolving class of solid materials has attracted recent interest in relevant applications that involve aqueous acids or bases. This mounting interest, mainly at a low readiness level, is driven by the high degree of structural tunability of MOFs vs other families of solid-state materials. However, the advantage of organic–inorganic hybridization in MOFs, for fine-tuning the structural properties-performances, is very often limited by their degree of chemical and hydrolytic stability. Herein, we offer an overview of the progress made in the design and assembly of MOFs with potential robustness in harsh aqueous acidic and basic media. In this review, we analyze critically the different works carried out on the use of MOFs as separation and catalytic agents in neutral and acidic-basic conditions. Prominently, this work finely evaluates the impact of different chemical, functional and topological parameters on the robustness of the resultant MOF frameworks. Future directions that guide material chemists towards designing frameworks with long-term stability in harsh liquid phases will also be debated.

A metal-organic framework for C2H2/CO2 separation under highly humid conditions: Balanced hydrophilicity/hydrophobicity

Metal-organic frameworks (MOFs) intended for C2H2/CO2 separation should possess high C2H2/CO2 adsorption selectivity and large C2H2 adsorption capacity. Here we report the scalable synthesis of a cage-interconnected microporous MOF (JNU-2). Dynamic column breakthrough experiments on JNU-2 manifest a C2H2-capture capacity of 3.08 mmol g−1 for an equimolar C2H2/CO2 mixture at 298 K and 1 bar, exceeding the benchmark materials such as UTSA-74a and FeNi-M’MOF. Meanwhile, the selectivity factor was estimated to be ca. 1.5 for JNU-2 and consistent with the increasing flow rate. Theoretical calculations confirm that the surface of the JNU-2 framework enables preferential binding of C2H2 over CO2via multiple C–H···O, C–H···N, and π-complexation interactions. More importantly, JNU-2 retains its C2H2/CO2 separation capacity under highly humid conditions. Although the equilibrium adsorption of H2O is much higher than those of C2H2 and CO2, kinetic studies reveal that the diffusion of C2H2 and CO2 in JNU-2 is more than two orders of magnitude faster than that of H2O. A balanced hydrophobicity/hydrophilicity of the MOF framework surface might be the key to achieving large adsorption capacity for nonpolar gas molecule while minimizing the competition of water vapor adsorption.

Orthogonal-array dynamic molecular sieving of propylene/propane mixtures.

Rigid molecular sieving materials work well for small molecules with the complete exclusion of large ones1-3, and molecules with matching physiochemical properties may be separated using dynamic molecular sieving materials4-6. Metal-organic frameworks (MOFs)7-9 are known for their precise control of structures and functions on a molecular level10-15. However, the rational design of local flexibility in the MOF framework for dynamic molecular sieving remains difficult and challenging. Here we report a MOF material (JNU-3a) featuring one-dimension channels with embedded molecular pockets opening to propylene (C3H6) and propane (C3H8) at substantially different pressures. The dynamic nature of the pockets is revealed by single-crystal-to-single-crystal transformation upon exposure of JNU-3a to an atmosphere of C3H6 or C3H8. Breakthrough experiments demonstrate that JNU-3a can realize high-purity C3H6 (≥99.5%) in a single adsorption-desorption cycle from an equimolar C3H6/C3H8 mixture over a broad range of flow rates, with a maximum C3H6 productivity of 53.5litresper kilogram. The underlying separation mechanism-orthogonal-array dynamic molecular sieving-enables both large separation capacity and fast adsorption-desorption kinetics. This work presents a next-generation sieving material design that has potential for applications in adsorptive separation.

Strategic Defect Engineering of Metal–Organic Frameworks for Optimizing the Fabrication of Single‐Atom Catalysts

AbstractSingle‐atom catalysts (SACs) have garnered enormous interest due to their remarkable catalysis activity. However, the exploitation of universal synthesis strategy and regulation of coordination environment of SACs remain a great challenge. Herein, a versatile synthetic strategy is demonstrated to generate a series of transition metal SACs (M SAs/NC, M = Co, Cu, Mn; NC represents the nitrogen‐doped carbon) through defect engineering of metal‐organic frameworks (MOFs). The interatomic distance between metal sites can be increased by deliberately introducing structural defects within the MOF framework, which inhibits metal aggregation and consequently results in an approximately 70% increase in single metal atom yield. Additionally, the coordination structures of metal sites can also be facilely tuned. The optimized Co SAs/NC‐800 exhibits superior activity and excellent reusability for the selective hydrogenation of nitroarenes, surpassing several state‐of‐art non‐noble‐metal catalysts. This study provides a new avenue for the universal fabrication of transition metal SACs.

Confined Magnetic-Dielectric Balance Boosted Electromagnetic Wave Absorption.

Magnetic-dielectric property plays a critical significance for the functional expression toward advanced materials. Within nanoscale, the simultaneous regulation of the electrical and magnetic properties of electromagnetic (EM) wave absorption materials faces huge challenges. Herein, using the metal-organic frameworks (MOF) as templates, highly-dispersed ZnO and Co nanoparticles are uniformly confined inside graphited N-doped carbon skeleton, constructing the balanced EM property in the Co@NC-ZnO absorbers. Meanwhile, a dynamics and symmetrical morphology optimization of MOF-derived Co@NC-ZnO are dependent on the Co/Zn mass ratio and adjusting MOF frameworks, which evolves from the cube, truncated cube, dodecahedron, and to the final microsphere. Simultaneously, both the electronic conduction network and magnetic coupling network are compatible together in the in situ transformed Co@NC-ZnO system. Boosted magnetic responding ability and unique magnetic coupling are verified by the off-axis electronic holography. Plentiful heterojunction interfaces and special electronic conduction paths can be built in this Co-Zn-MOF derivatives, facilitating the dielectric loss behaviors. As expected, MOF-derived Co@NC-ZnO absorber displays outstanding EM wave absorption ability with strongest reflection loss value of -69.6 dB at only 1.9 mm thickness and wideband absorption covering 6.8 GHz at 2.4 mm. Confined EM balance provides new design strategy toward MOF-derived excellent MA materials and functional devices.

Controlled Thermal Conversion Strategy to Provide Metal-Organic Framework-Supported Composite Catalysts.

Metal-organic framework (MOF)-supported metal/metal compound nanoparticles (NPs) have emerged as a new class of composite catalysts. However, huge challenges prevail in placing such NPs in the MOF pores because of the poor solubility of metal/metal oxides, limited availability of suitable precursors, metastable attribute of given metal ions, and lower thermal stability of MOFs compared to conventional porous materials. Based on the difference between the thermal stability of the precursor and MOFs, we successfully developed a controlled thermal conversion (CTC) method to load cobalt(II) oxide (CoO) NPs into the framework of MOF (MIL-101) to conveniently obtain a composite catalyst, CoO@MIL-101, which is a very rare example of pure CoO NP-loaded composite catalyst that shows excellent catalytic activity in the selective oxidation of benzyl alcohol. This CTC strategy opens up a pathway for impregnating MOF supports with specific NPs, which is further confirmed by preparing the first CuBr@MOF-type composite catalyst.

Multiple functional groups in metal–organic frameworks and their positional regioisomerism

Abstract Metal-organic frameworks (MOFs) have been considered an emerging material for various applications. The fine tunability of both their inorganic nodes and organic ligands make MOFs a good platform for target-specific utilization. Generally, two coordinating groups (e.g., carboxylate) are necessary for MOF formations in case of representative, benzene-dicarboxylic acid type MOFs, and the additional functional groups could be installed in the remaining sites of organic ligands. Various functional groups could be introduced on the ligands such as amino-, halo-, hydroxy-, ether, thiol, and etc. In addition, multiple functional groups could be installed at specific position on the ligand by implementing positional regioisomerism, which helps elucidate the individual effects that each substituent imposes on the organic linkers. Therefore, deliberate structural and functional features can be introduced into a pristine framework. Indeed, this relatively ease functionalizations and positional isomerism of functional groups are the unique features of MOFs compare to other porous materials. In this review, we systematically categorized and described positional regioisomerism with multiple functional groups in MOF organic linkers. Specifically, regioisomeric MOFs bearing two identical groups, two different groups, more than three dissimilar groups, or miscellaneous moieties were discussed in terms of their structures and functions. A comprehensive overview of studies investigating the structures and properties triggered by the different positioning of functional groups in MOF frameworks could provide a base for the molecular design of desirable materials with advanced functionality.

Chemical conversion of CO2 into cyclic carbonates using a versatile and efficient all-in-one catalyst integrated with DABCO ionic liquid and MIL-101(Cr)

A novel heterogeneous catalyst, MIL-101(Cr)-DABCO IL, with DABCO serving as bridge agent to merge the advantages of ionic liquids (IL) and metal-organic framework (MOF) was prepared and evaluated as catalyst for the synthesis of cyclic carbonates from CO 2 and epoxides. The coordinatively unsaturated Cr(III) nodes in MOF framework function as specific centers to chelate tertiary N atom in DABCO, which offers a bridge that has strong affinity to ensure the active moieties facilely anchored on MOF. Notably, the MIL-101(Cr)-DABCO as an effective catalyst displays exceptional catalytic performance with 88.6% of yield and 99.2% of selectivity at 1.5 MPa and 100 °C for only 40 min, which is urgently required and of positive significance for the environment protection. When the DABCO moiety was further transformed to hydroxyl-functionalized IL, pivotal factors required to activate CO 2 and epoxide, including Lewis acid-basic sites and nucleophile, are combined together in MIL-101(Cr)-DABCO IL. The resultant all-in-one MIL-101(Cr)-DABCO IL catalyst doubles the activity in driving the cycloaddition reaction by comparing with MIL-101(Cr)-DABCO. The highest productivity of cyclic carbonate up to 97.0%, and 99.8% of selectivity are given by MIL-101(Cr)-DABCO IL. Moreover, benefited from the superb coordinative bonding interaction of the well built Cr(III)–N bonds, the MIL-101(Cr)-DABCO IL have excellent recyclability and chemical stability. • DABCO IL was facilely anchored into MIL-101(Cr) through the formation of coordination bonding between DABCO and Cr. • MIL-101(Cr)-DABCO displays exceptional catalytic performance with 88.6% of yield in 40 min. • The MIL-101(Cr)-DABCO IL doubles the activity by comparing with MIL-101(Cr)-DABCO due to its multiple active sites.

Hierarchical trimetallic Co-Ni-Fe oxides derived from core-shell structured metal-organic frameworks for highly efficient oxygen evolution reaction

Metal-organic frameworks (MOFs) have recently emerged as promising precursors to construct efficient non-noble metal electrocatalyst for oxygen evolution reaction (OER). Herein, a Co-Ni-Fe spinel oxide-carbonitrides hybrids (CoNiFeOx-NC) electrocatalyst with hierarchical structure was synthesized from Fe-MIL-101-NH2 through a unique ion-exchange based strategy. The ion exchange of Fe-MIL-101-NH2 with both Ni and Co ions induced a hierarchically structured 2-D ternary metal MOF shell layer encapsulated 3-D octahedral MOF crystals as a core. This prevents the collapse of MOF frameworks during the air calcination process and affords highly porous structure and large surface area. Additionally, the unique combination of Co-Ni-Fe in spinel oxides derived from calcination of the hierarchically structured core-shell MOF provides a favorable electronic environment for the adsorption of OER intermediates, which was further verified by the XPS characterizations and DFT calculations. DFT study revealed the Ni-Co coordinated Oh sites in the MFe2O4 reverse spinel structures as the main active sites, which tuned the binding strength of oxygen species with a catalyst through electron transfer of Fe→Co→Ni, thereby lowered the energy barriers for OER. As a result, the rationally designed CoNiFeOx-NC catalyst manifests superior OER performance with a low overpotential of 265 mV at 50 mA cm−2 and a decent Tafel slope of 64.1 mV dec-1. The ion-exchange based strategy may serve as a versatile platform for rational design and synthesis of multi-metallic MOF derived electrocatalysts.

Atomic resolution tracking of nerve-agent simulant decomposition and host metal\u2013organic framework response in real space

Gas capture and sequestration are valuable properties of metal–organic frameworks (MOFs) driving tremendous interest in their use as filtration materials for chemical warfare agents. Recently, the Zr-based MOF UiO-67 was shown to effectively adsorb and decompose the nerve-agent simulant, dimethyl methylphosphonate (DMMP). Understanding mechanisms of MOF-agent interaction is challenging due to the need to distinguish between the roles of the MOF framework and its particular sites for the activation and sequestration process. Here, we demonstrate the quantitative tracking of both framework and binding component structures using in situ X-ray total scattering measurements of UiO-67 under DMMP exposure, pair distribution function analysis, and theoretical calculations. The sorption and desorption of DMMP within the pores, association with linker-deficient Zr6 cores, and decomposition to irreversibly bound methyl methylphosphonate were directly observed and analyzed with atomic resolution.

Ultrathin Metal–Organic Framework Nanosheets-Derived Yolk–Shell Ni 0.85 Se@NC with Rich Se-Vacancies for Enhanced Water Electrolysis

We present a controlled fabrication of selective ultrathin metal–organic framework (MOF) nanosheets as preassembling platforms, yolk–shell structured with a few-layered N-doped carbon (NC) shell-en...

Mixed‐Metal MOF‐74 Templated Catalysts for Efficient Carbon Dioxide Capture and Methanation

AbstractThe vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. However, a lack of straightforward methods for producing nanoparticle‐encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed‐metal MOF, NiMg‐MOF‐74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in NiO and MgO coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X‐ray absorption fine structure and X‐ray photoelectron spectroscopy. By preserving a segment of the Mg2+‐containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization.