Metal-organic Frameworks Research Articles

Hydroxamate-Based Metal-Organic Frameworks.

This mini-review focuses on recent developments in hydroxamate-based metal-organic frameworks (MOFs), which exhibit unique structures and properties distinct from those of carboxylate-based MOFs. Hydroxamates (RCONHO-), which are bioisosteres of carboxylates (RCOO-), form MOFs with novel structural motifs and functionalities. In this review, synthetic strategies, structural characteristics, and functional applications of key examples of hydroxamate-based MOFs are described, providing insights into the influence of the hydroxamate ligand on the MOF properties compared to the carboxylate-based analogues.

Highly Porous Scandium(III) Tetrafluoroisophthalate Framework for Adsorptive Separation of Light Alkanes.

The separation of light alkanes is one of the most important tasks for modern industry due to the widespread use of ethane and propane as chemical feedstocks. Their extraction from natural gas is a challenging task and is now carried out by cryogenic distillation at a limited number of plants around the world. The development of new materials for adsorption separation is therefore important. Among the different types of adsorbents, metal-organic frameworks (MOFs) are one of the most interesting due to their infinite design possibilities. Here we present a highly porous perfluorinated MOF [Sc(OH)(1,3-tFbdc)] (1,1,3-tFbdc2-─1,3-C6F4(COO)22- tetrafluoroisophthalate linker) with a BET surface area greater than 1000 m·g-1 and its ability to separate light alkanes was investigated. The ability of 1 to separate light hydrocarbons at 0 and 25 °C is demonstrated by IAST calculation of selectivity factors as well as by dynamic breakthrough experiments. The role of fluorine substituents within the organic linker of MOF 1 in gas adsorption is revealed by quantum chemical calculations.

Increasing the dual-enzyme cascade biocatalysis efficiency and stability of metal-organic frameworks via one-step coimmobilization for visual detection of glucose.

In biosensing analysis, the activity of enzyme systems is limited by their fragility, and substrates catalyzed by monoenzymes tend to undergo spontaneous decomposition during ineffective mass transfer processes. In this study, we propose a novel strategy to encapsulate the glucose oxidase and horseradish peroxidase (GOx&HRP) cascade catalytic system within the hydrophilic zeolite imidazole framework ZIF-90. By leveraging the specific pore structure of ZIF-90, we effectively immobilized GOx and HRP molecules in their three-dimensional conformations, which improved the catalytic activity of the encapsulated enzymes compared with that of free GOx and HRP in various harsh environments. Additionally, our strategy reduced the occurrence of ineffective mass transfer and enhanced the sensitivity of the biosensor through an enzyme cascade system. When this biosensor was applied to serum samples containing complex biological matrices, the degradation of GOx&HRP by various proteases and the surface adsorption of diverse biomolecules were effectively prevented, thereby generating stable and reliable signals of glucose levels. The sensor shows remarkable sensitivity and selectivity for determining glucose concentrations ranging from 0 to 2.5 μg ml-1, with a detection limit as low as 0.034 μg ml-1. Furthermore, we developed a paper-based colorimetric sensor utilizing GOx&HRP@ZIF-90 integrated with a smartphone platform for the visual detection of blood glucose.

Polymer-MOF Network Enabling Ultrathin Coating for Post-Combustion Carbon Capture.

Permeance-selectivity trade-off and high temperature resilience are key challenges in development of membranes for post-combustion carbon capture. While mixed matrix membranes (MMMs) consisting of polymers and metal organic frameworks (MOFs) offer the potential to address the challenges, they are limited by the low loading of MOFs in the thin film layer. Herein, we propose an inverse synthesis strategy to form polymer-MOF networks by copolymerizing monomers with functionalized UiO-66 nanoparticles. This process yields a finely dispersed, easily processable solution, enabling defect-free, thin polymer-MOF coatings with up to 40 wt% MOF loading within the polyethylene oxide-based polymers on polyacrylonitrile supports. The membrane with 40 wt% MOF demonstrated a 212% increment in CO2 permeance at 25 °C and maintained a selectivity of 20 at 60 °C, which is attributed to the stable diffusivity selectivity of MOFs at high temperature. Furthermore, the membrane was evaluated with mixed gas and 83% relative humidity (RH) at 60°C, achieving a CO2 permeance up to 2793 GPU and a CO2/N2 selectivity of 21.6. This work offers insights into the design of practical mixed matrix membranes, which not only paves the way towards energy efficient carbon capture from flue gas, but also provides more possibilities for other applications.

Polymer‐MOF Network Enabling Ultrathin Coating for Post‐Combustion Carbon Capture

Permeance‐selectivity trade‐off and high temperature resilience are key challenges in development of membranes for post‐combustion carbon capture. While mixed matrix membranes (MMMs) consisting of polymers and metal organic frameworks (MOFs) offer the potential to address the challenges, they are limited by the low loading of MOFs in the thin film layer. Herein, we propose an inverse synthesis strategy to form polymer‐MOF networks by copolymerizing monomers with functionalized UiO‐66 nanoparticles. This process yields a finely dispersed, easily processable solution, enabling defect‐free, thin polymer‐MOF coatings with up to 40 wt% MOF loading within the polyethylene oxide‐based polymers on polyacrylonitrile supports. The membrane with 40 wt% MOF demonstrated a 212% increment in CO2 permeance at 25 °C and maintained a selectivity of 20 at 60 °C, which is attributed to the stable diffusivity selectivity of MOFs at high temperature. Furthermore, the membrane was evaluated with mixed gas and 83% relative humidity (RH) at 60°C, achieving a CO2 permeance up to 2793 GPU and a CO2/N2 selectivity of 21.6. This work offers insights into the design of practical mixed matrix membranes, which not only paves the way towards energy efficient carbon capture from flue gas, but also provides more possibilities for other applications.

Metal-organic frameworks as nanoplatforms for combination therapy in cancer treatment.

The integration of nanotechnology into cancer treatment has revolutionized chemotherapy, boosted its effectiveness while reduced side effects. Among the various nanotherapeutic approaches, metal-organic frameworks (MOFs) stand out as promising carriers for targeted chemotherapy, with the added benefit of enabling combination therapies. MOFs, composed of metal ions or clusters linked by coordination bonds, tackle critical issues in traditional cancer treatments, such as poor stability, limited efficacy, and severe side effects. Their key advantages include customizable size and shape, diverse compositions, controlled porosity, large surface areas, ease of modification, and biocompatibility. This review highlights recent advancements in the use of MOFs for cancer therapy, showcasing their role in both monotherapies and combination strategies. Additionally, it explores the future potential and challenges of MOF-based platforms in tumor treatment.

High‐Nuclearity Polyoxometalate‐Based Metal‐Organic Frameworks for Photocatalytic Oxidative Cleavage of C‐C Bond

High‐nuclearity polyoxometalate (POM) clusters are attractive building blocks (BBs) for the synthesis of metal‐organic frameworks (MOFs) due to their high connectivity and inherently multiple metal centers as functional sites. This work demonstrates a strategy of step‐wise growth on ring‐shaped [P8W48O184]40‐ precursor, which produced two new high‐nuclearity polyoxotungstates, a half‐closed [H16P8W58O218]32‐ {W58} and a fully‐closed [H16P8W64O236]32‐ {W64}. By in‐situ synthesis, unique MOFs of copper triazole‐benzoic acid (HL) complexes incorporating the negatively‐charged {W58} and {W64} as nodes, {Cu11(HL)8LW58} HNPOMOF‐1 and {Cu9(HL)9W64} HNPOMOF‐2, were constructed by delicately tuning the reaction conditions, mainly solution pH, which controls the formation of {W58} and {W64}, and at the same time the protonation of triazole‐benzoic acid ligand thus its coordination mode to copper ion that creates the highest nuclearity POM‐derived MOFs reported to date. HNPOMOF‐1 features 3D framework possessing cage‐like cavities filled with exposed carboxyl groups, while the inherent 2D layer‐like HNPOMOF‐2 allows for facile exfoliation into ultrathin nanosheets, and the resulted HNPOMOF‐2NS exhibits superior activity towards photocatalytic oxidative cleavage of C‐C bond for a series of lignin models. This work not only provides a strategy to build high‐nuclearity POM cluster‐based frameworks, but also demonstrates their great potential as functional materials for green catalysis.

High-Nuclearity Polyoxometalate-Based Metal-Organic Frameworks for Photocatalytic Oxidative Cleavage of C-C Bond.

High-nuclearity polyoxometalate (POM) clusters are attractive building blocks (BBs) for the synthesis of metal-organic frameworks (MOFs) due to their high connectivity and inherently multiple metal centers as functional sites. This work demonstrates a strategy of step-wise growth on ring-shaped [P8W48O184]40- precursor, which produced two new high-nuclearity polyoxotungstates, a half-closed [H16P8W58O218]32- {W58} and a fully-closed [H16P8W64O236]32- {W64}. By in-situ synthesis, unique MOFs of copper triazole-benzoic acid (HL) complexes incorporating the negatively-charged {W58} and {W64} as nodes, {Cu11(HL)8LW58} HNPOMOF-1 and {Cu9(HL)9W64} HNPOMOF-2, were constructed by delicately tuning the reaction conditions, mainly solution pH, which controls the formation of {W58} and {W64}, and at the same time the protonation of triazole-benzoic acid ligand thus its coordination mode to copper ion that creates the highest nuclearity POM-derived MOFs reported to date. HNPOMOF-1 features 3D framework possessing cage-like cavities filled with exposed carboxyl groups, while the inherent 2D layer-like HNPOMOF-2 allows for facile exfoliation into ultrathin nanosheets, and the resulted HNPOMOF-2NS exhibits superior activity towards photocatalytic oxidative cleavage of C-C bond for a series of lignin models. This work not only provides a strategy to build high-nuclearity POM cluster-based frameworks, but also demonstrates their great potential as functional materials for green catalysis.

Controlling the Mechanism of Nucleation and Growth Enables Synthesis of UiO‐66 Metal–Organic Framework with Desired Macroscopic Properties

AbstractBy combining in situ X‐ray diffraction, Zr K‐edge X‐ray absorption spectroscopy and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, we show that the properties of the final MOF are influenced by H2O and HCl via affecting the nucleation and crystal growth at the molecular level. The nucleation implies hydrolysis of monomeric zirconium chloride complexes into zirconium‐oxo species, and this process is promoted by H2O and inhibited by HCl, allowing to control crystal size by adjusting H2O/Zr and HCl/Zr ratios. The rate‐determining step of crystal growth is represented by the condensation of monomeric and oligomeric zirconium‐oxo species into clusters, or nodes, with the structure identical to that in secondary building units (SBU) of UiO‐66 framework. The rapid crystallization in the absence of HCl leads to formation of defective secondary building units with missing zirconium atoms, providing a pathway to control the number of defects in UiO‐66 crystals. Remarkably, we have shown that assembling of the metal nodes and linkers into the UiO‐66 structure is not the rate‐limiting step, and the degree of deprotonation of the linker has no direct effect on the crystallization kinetics or crystal size of product.

Hybrid materials based on covalent organic frameworks for photocatalysis

AbstractCovalent organic frameworks (COFs) feature π‐conjugated structure, high porosity, structural regularity, large specific surface area, and good stability, being considered as ideal platform for photocatalytic application. Although single COFs have achieved significant progress in photocatalysis benefiting from their distinctive properties, the COFs‐based hybrids provide an extraordinary opportunity to achieve superior photocatalytic performance. From the perspective of carrier transfer mechanism, a systematic summary of hybrids based on COFs and other functional materials (metal single atoms, metal clusters/nanoparticles, inorganic semiconductors, metal–organic frameworks, and other polymers) can offer valuable guidance for the design of COFs‐based hybrids. In this review, the photocatalytic mechanism for hybrid materials (such as Schottky junction, type II heterojunction, Z‐scheme heterojunction, and S‐scheme heterojunction) is briefly introduced. Subsequently, the performance of COFs‐based hybrids in photocatalytic water splitting, CO2 reduction, and pollutant degradation are comprehensively reviewed. Specifically, the carrier separation and transfer in different types of hybrids are highlighted. Finally, the challenges and prospects of COFs‐based hybrids for photocatalysis are envisaged. The insights presented in this review are expected to be helpful in the rational design of COFs‐based hybrids to obtain outstanding photocatalytic activity.image

Direct In Situ Fabrication of Strong Bonding ZIF-8 Film on Zinc Substrate and Its Formation Mechanism

There is much promise for creating metal organic framework (MOF) films on metal substrates in fields including sensing and electrical conduction. For these applications, direct production of MOF films with strong bonding on metal substrates is extremely desirable. In this study, a simple one-step method without the need for additives or pre-modification is used to directly create zeolitic imidazolate framework-8 (ZIF-8) films with strong bonding on zinc substrate. The formation mechanisms of ZIF-8 film are analyzed. The strong bonding ZIF-8 film can be attributed to an in-situ grown ZnO interlayer between the ZIF-8 and substrate. The growth process shows the formation time of zinc oxide on the substrate, which is subsequently covered by ZIF-8 crystals. The ZnO interlayer results from a combination of decomposition products of the solvent and the zinc ions. Furthermore, the ZnO interlayer serves as a sacrificial precursor for the in-situ nucleation and continuous growth of ZIF-8 film. It serves as an anchoring site between ZIF-8 film and substrate, resulting in strong adhesion. This paper describes a simple and straightforward production process that is expected to provide a theoretical basis for the laboratory preparation of ZIF films.

Post-Synthetically Modified Metal Organic Framework Functionalized with a 1,2-Dihydroxybenzene Chelating Unit for Efficient Removal of Thorium and Uranyl Ions from Radioactive Waste

Post-Synthetically Modified Metal Organic Framework Functionalized with a 1,2-Dihydroxybenzene Chelating Unit for Efficient Removal of Thorium and Uranyl Ions from Radioactive Waste

Tumor-Targeted Metal-Organic Framework for Improved Photodynamic Therapy and Inhibited Tumor Metastasis in Melanoma.

Tumor hypoxia and elevated intracellular glutathione (GSH) levels significantly compromise the effectiveness of photodynamic therapy (PDT) in treating melanoma. In this study, we synthesized positively charged nanoparticles through a self-assembly method, incorporating photosensitizer verteporfin (VER), mitochondrial respiratory inhibitor atovaquone (ATO), and Fe3+. Subsequently, the nanoparticles were modified with sodium hyaluronate (HA) to obtain HA-ATO-Fe3+-VER nanoparticles (HAFV NPs). The fabricated HAFV NPs demonstrated excellent stability and in vitro Fenton reaction activity. HA facilitated the cellular internalization of HAFV NPs by targeting CD44 receptors, hence relieving tumor hypoxia through the disruption of the mitochondrial respiratory chain and involvement in the Fenton reaction. Simultaneously, ATO directly impeded the biosynthesis of GSH by diminishing ATP levels, while Fe3+ was supposed to oxidate GSH to GSSG, thereby doubly depleting GSH. The integration of these multiple mechanisms markedly enhanced the PDT efficacy of VER. Following intravenous administration, HAFV NPs preferentially accumulated in tumor tissues with minimal accumulation in the skin, demonstrating favorable biocompatibility in vivo. Furthermore, HAFV NPs effectively inhibited tumor growth and lung metastasis, which presents a promising strategy for melanoma treatment.

Polystyrene-MOF-Derived 3D Hierarchical Porous Carbon for High-Performance Supercapacitors.

The ability to tailor surface area, porosity, and morphologies has driven extensive research into the synthesis of metal-organic frameworks derived carbons and their applications in energy storage. This study presents the development of three-dimensional hierarchically porous carbon derived from polystyrene and small-sized zeolitic imidazolate framework-8 (ZIF-8) particles. Incorporating nanometer-sized ZIF-8 particles forms a core-shell structure in the pre-carbonization stage, transforming into a porous carbon material with a range of pores from micro to macropores after carbonization. The carbonized material's electrode demonstrates a high capacitance of 428.8 F g-1 at 1 mV s-1 in the three-electrode setup and a very high specific energy of 48.75 Wh kg-1 at 50 mA g-1 in the packed flat cell configuration. This exceptional electrochemical performance is attributed to the composite carbon material's high surface area, well-developed pore structure, and self-doped nitrogen content.

3,6-Dipyridyl-1,2,4,5-tetrazine in the Synthesis of Zinc and Cadmium Metal-Organic Frameworks with Anilate-Type Ligands

New heteroleptic metal-organic frameworks (MOF) of zinc (3D MOF) and cadmium (2D MOF) are prepared by the two-stage synthesis: [Zn(pQ)(DPT)]·2DMF (I) and Cd2(NO3)2-(pQ)(DPT)3]·2DMF·2MeOH (II), where pQ is the 2,5-dihydroxy-3,6-di-tert-butyl-para-benzoquinone dianion, DPT is 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine, and DMF is N,N-dimethylformamide (DMF). The structures of the compounds are studied by XRD (CIF files CCDC nos. 2332754 (I) and 2332755 (II)). The thermal stability of the MOF is studied by thermogravimetry.

Non-Aqueous Electrochemical CO2 Reduction to Multivariate C2-Products Over Single Atom Catalyst at Current Density up to 100mAcm-2.

Electrochemical CO2 reduction reaction (CO2-RR) in non-aqueous electrolytes offers significant advantages over aqueous systems, as it boosts CO2 solubility and limits the formation of HCO3 - and CO3 2- anions. Metal-organic frameworks (MOFs) in non-aqueous CO2-RR makes an attractive system for CO2 capture and conversion. However, the predominantly organic composition of MOFs limits their electrical conductivity and stability in electrocatalysis, where they suffer from electrolytic decomposition. In this work, electrically conductive and stable Zirconium (Zr)-based porphyrin MOF, specifically PCN-222, metalated with a single-atom Cu has been explored, which serves as an efficient single-atom catalyst (SAC) for CO2-RR. PCN- 222(Cu) demonstrates a substantial enhancement in redox activity due to the synergistic effect of the Zr matrix and the single-atom Cu site, facilitating complete reduction of C2 species under non-aqueous electrolytic conditions. The current densities achieved (≈100mAcm- 2) are 4-5 times higher than previously reported values for MOFs, with a faradaic efficiency of up to 40% for acetate production, along with other multivariate C2 products, which have never been achieved previously in non-aqueous systems. Characterization using X-ray and various spectroscopic techniques, reveals critical insights into the role of the Zr matrix and Cu sites in CO2 reduction, benchmarking PCN-222(Cu) for MOF-based SAC electrocatalysis.

Ba/Ti MOF: A Versatile Heterogeneous Photoredox Catalyst for Visible-Light Metallaphotocatalysis.

The field of sustainable heterogeneous catalysis is evolving rapidly, with a strong emphasis on developing catalysts that enhance efficiency. Among various heterogeneous photocatalysts, metal-organic frameworks (MOFs) have gained significant attention for their exceptional performance in photocatalytic reactions. In this context, contrary to the conventional homogeneous iridium or ruthenium-based photocatalysts, which face significant challenges in terms of availability, cost, scalability, and recyclability, a new Ba/Ti MOF (ACM-4) is developed as a heterogeneous catalyst that can mimic/outperform the conventional photocatalysts, offering a more sustainable solution for efficient chemical processes. Its redox potential and triplet energy are comparable to or higher than the conventional catalysts, organic dyes, and metal semiconductors, enabling its use in both electron transfer and energy transfer applications. It facilitates a broad range of coupling reactions involving pharmaceuticals, agrochemicals, and natural products, and is compatible with various transition metals such as nickel, copper, cobalt, and palladium as co-catalysts. The effectiveness of the ACM-4 as a photocatalyst is supported by comprehensive material studies, photophysical, and recycling experiments. These significant findings underscore the potential of ACM-4 as a highly versatile and cost-effective photoredox catalyst, providing a sustainable, one-material solution for efficient chemical processes.

Metal-Organic Frameworks of Cobalt(II) with 4,7-Di(1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole and Aromatic Dicarboxylic Acids: Synthesis, Crystal Structures, and Magnetic Properties

The reactions of cobalt(II) nitrate with 4,7-di(1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole (Tr2btd) and aromatic dicarboxylic acids (terephthalic (H2bdc), 2,6-naphthalenedicarboxylic (2,6-H2Ndc), and 2,5-furandicarboxylic (2,5-H2Fdc) acids) afford metal-organic frameworks [Co(Tr2btd)(bdc)]n (I) and {[Co2(Tr2btd)(Dmf)(2,6-Ndc)2]·Dmf}n (II) with the layered structures and chain metal-organic framework [Co(Tr2btd)2(H2O)(2,5-Fdc)]n (III). Compounds I and III are paramagnetic in a temperature range of 1.77–300 K without exchange interactions between the Co2+ cations, and compound II exhibits the antiferromagnetic interaction between the Co2+ cations in the binuclear building blocks with the exchange interaction constant J ≈ −100 K. Single crystals of the phase of compound IIIa with the identical composition but different structure are found when taking samples for X-ray diffraction (XRD) analysis. The molecular structures of metal-organic frameworks I, II, III, and IIIa are determined by XRD (CIF files CCDC nos. 2343141 (I), 2343297 (II), 2343296 (III), and 2343140 (IIIa)).

Scalable Approach for Grafting Qubit Candidates onto The Surface of MOF-808 Framework

The development of quantum bits (qubits) is crucial for the progress of quantum technologies. Among various approaches, the qubits based on paramagnetic centers have decent advantages, including their diversity and possibilities of regular ordering, for example, within the structure of metal-organic frameworks (MOFs). In the present work a simple and scalable approach to obtain qubit candidates based on stable organic radical 3-carboxy-proxyl and MOF-808 framework has been demonstrated. Investigation of the obtained compounds with different radical amounts using electron paramagnetic resonance (EPR) demonstrates the presence of two fractions of radicals, which is supported by simulations. Sufficiently long phase memory time at room temperature for the radicals adsorbed into MOF (0.39 μs), as well as the observed Rabi nutations, allow considering this material as a platform for qubits design. The developed approach is capable of incorporating various amounts of paramagnetic centers into the MOF structure and can be employed to obtain other spin qubit candidates.

Ligand Circuit Concept for Developing Gas Separation Materials from Pore-Space-Partitioned Metal-Organic Frameworks.

Isoreticular chemistry is among the most powerful strategies for designing novel materials with optimizable pore geometry and properties. Of great significance to the further advance of isoreticular chemistry is the development of broadly applicable new concepts capable of guiding and systematizing the ligand-family expansion as well as establishing correlations between dissimilar and seemingly uncorrelated ligands for better predictive synthetic design and more insightful structure and property analysis. Here ligand circuit concept is proposed and its use has been demonstrated for the synthesis of a family of highly stable, high-performance pore-space-partitioned materials based on an acyclic ligand, trans, trans-muconic acid. This work represents a key step toward developing highly porous and highly stable pore-space-partitioned materials from acyclic ligands. The new materials exhibit excellent sorption properties such as high uptake capacity for CO2 (81.3cm3g-1) and C2H2 (165.4cm3g-1) by CPM-7.3a-NiV. CPM-7.3a-CoV shows C2H6-selective C2H6/C2H4 separation properties and its high uptakes for C2H4 (134.0cm3g-1) and C2H6 (148.0cm3g-1) at 1bar and 298K contribute to the separation potential of 1.35mmolg-1. The multi-cycle breakthrough experiment confirms the promising separation performance for C2H2/CO2.