Metal–organic frameworks with multicomponents in order

Facile Layer Diffusion Technique for Synthesis of Terbium-Based Metal Organic Framework for Fluorometric Sensing of Hydroquinone

A photoluminescent terbium (III)-based Metal Organic Framework (MOF) was synthesized at room temperature by layer diffusion method utilizing mixed carboxylate linkers (4,4'-oxybis(benzoic acid) and benzene-1,3,5 tricarboxylic acid). Synthesized MOF has crystalline nature and rod-shaped morphology and is thermally stable up to 455 °C. The fluorescence emission spectra and theoretical results revealed that carboxylate linkers functioned as sensitizers for Tb(III) photoluminescence which resulted in four distinct emission peaks at 495, 547, 584, and 621 nm corresponding to the transitions 5D4 → 7F6, 5D4 → 7F5, 5D4 → 7F4, and 5D4 → 7F3. Using synthesized MOF as fluorescent probe, hydroquinone was detected in aqueous medium with a detection limit of 0.048 μM, remarkable recovery (95.6-101.1%), and relative standard deviation less than 2.25%. The quenching phenomenon may be ascribed to electron transfer from synthesized probe to oxidized hydroquinone via carboxylic groups on the surface of MOF, which is further supported by photo-induced electron transfer mechanism. This study introduces a cheaper, faster, and more accurate method for hydroquinone detection.

MOF-Based Photocatalytic Membrane for Water Purification: A Review

Photocatalytic membranes can effectively integrate membrane separation and photocatalytic degradation processes to provide an eco-friendly solution for efficient water purification. It is of great significance to develop highly efficient photocatalytic membranes driven by visible light to ensure the long-term stability of membrane separation systems and the maximum utilization of solar energy. Metal-organic framework (MOF) is an emerging photocatalyst with a well-defined structure and tunable chemical properties, showing a broad application prospect in the construction of high-performance photocatalytic membranes. Herein, this work provides a comprehensive review of recent advancements in MOF-based photocatalytic membranes. Initially, this work outlines the main tailoring strategies that facilitate the enhancement of the photocatalytic activity of MOF-based photocatalysts. Next, this work introduces commonly used methods for fabricating MOF-based photocatalytic membranes. Subsequently, this work discusses the application and mechanisms of MOF-based photocatalytic membranes toward organic pollutant degradation, metal ion removal, and membrane fouling mitigation. Finally, challenges in developing MOF-based photocatalytic membranes and their practical applications are presented, while also pointing out future research directions toward overcoming these existing limitations.

One-Pot Synthesis of MOF@MOF: Structural Incompatibility Leads to Core-Shell Structure and Adaptability Control Makes the Sequence

Core-shell metal-organic frameworks (MOF@MOF) are promising materials with sophisticated structures that cannot only enhance the properties of MOFs but also endow them with new functions. The growth of isotopic lcore-shell MOFs is mostly limited to inconvenient stepwise seeding strategies with strict requirements, and by far one-pot synthesis is still of great challenge due to the interference of different components. Through two pairs of isoreticular MOFs, it reveals that the structural incompatibility is a prerequisite for the formation of MOFs@MOFs by one-pot synthesis, as illustrated by PMOF-3@HHU-9. It further unveils that the adaptability of the shell-MOF is a more key factor for nucleation kinetic control. MOFs with flexible linkers has comparably slower nucleation than MOFs with rigid linkers (forming PMOF-3@NJU-Bai21), and structural-flexible MOFs built by flexible linkers show the lowest nucleation and the most adaptability (affording NJU-Bai21@HHU-9). This degree of adaptability variation controls the sequence and further facilitates the synthesis of a first triple-layered core-shell MOF (PMOF-3@NJU-Bai21@HHU-9) by one-pot synthesis. The insight gained from this study will aid in the rational design and synthesis of other multi-shelled structures by one-pot synthesis and the further expansion of their applications.

Target Design of Multinary Metal-Organic Frameworks for Near-Infrared Imaging and Chemodynamic Therapy

Imaging-guided chemodynamic therapy is widely considered a promising modality for personalized and precision cancer treatment. Combining both imaging and chemodynamic functions in one system conventionally relies on the hybrid materials approach. However, the heterogeneous, ill-defined, and dissociative/disintegrative nature of the composites tends to complicate their action proceedings in biological environments and thus makes the treatment imprecise and ineffective. Herein, a strategy to employ two kinds of inorganic units with different functions─reactive oxygen species generation and characteristic emission─has achieved two single-crystalline metal-organic frameworks (MOFs), demonstrating the competency of reticular chemistry in creating multifunctional materials with atomic precision. The multinary MOFs could not only catalyze the transformation from H2O2 to hydroxyl radicals by utilizing the redox-active Cu-based units but also emit characteristic tissue-penetrating near-infrared luminescence brought by the Yb4 clusters in the scaffolds. Dual functions of MOF nanoparticles are further evidenced by pronounced cell imaging signals, elevated intracellular reactive oxygen species levels, significant cell apoptosis, and reduced cell viabilities when they are taken up by the HeLa cells. In vivo NIR imaging is demonstrated after the MOF nanoparticles are further functionalized. The independent yet interconnected modules in the intact MOFs could operate concurrently at the same cellular site, achieving a high spatiotemporal consistency. Overall, our work suggests a new method to effectively accommodate both imaging and therapy functions in one well-defined material for precise treatment.

Stepwise construction of multi-component metal-organic frameworks

Multi-component metal-organic frameworks (MC-MOFs) are crystalline porous materials containing multiple organic ligands or mixed metals, which manifest new properties beyond the linear combination of the single component. However, the traditional one-pot synthesis method for MOFs is not always applicable for synthesizing MC-MOFs due to the competitive coordination of multiple ligands and metals. Therefore, the stepwise construction of MC-MOFs has been explored, which enables more precise control of the heterogeneity within the ordered MC-MOFs. This review provides a summary of the synthesis strategies, namely, ligand exchange, coordinative modification, covalent modification, ligand metalation, cluster metalation, and use of mixed-metal precursors, for the stepwise construction of MC-MOFs. Furthermore, we discuss the applications of MC-MOFs with ordered arrangements of multiple functionalities, focusing on gas adsorption and separation, water remediation, heterogeneous catalysis, luminescence, and chemical sensing.

Multicomponent Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are constructed from metal ions or clusters and organic linkers. Typical MOFs are rather simple, comprising just one type of joint and linker. An additional degree of structural complexity can be introduced by using multiple different components that are assembled into the same framework In the early days of MOF chemistry, conventional wisdom held that attempting to prepare frameworks starting from such a broad set of components would lead to multiple different phases. However, this review highlights how this view was mistaken and frameworks comprising multiple different components can be deliberately designed and synthesized. When coupled to structural order and periodicity, the presence of multiple components leads to exceptional functional properties that can be understood at the atomic level.

Hetero-interpenetrated metal-organic frameworks

Interpenetrated metal-organic frameworks (MOFs) comprise two or more lattices that are mutually entangled. Interpenetration can be used to tune the structures and pore architectures of MOFs to influence, for example, their stability or interactions with guest molecules. The interpenetrating sublattices are typically identical, but hetero-interpenetrated MOFs, which consist of sublattices that are different from one another, have also been serendipitously produced. Here we describe a strategy for the deliberate synthesis of hetero-interpenetrated MOFs. We use the cubic α-MUF-9 framework as a host sublattice to template the growth of a second sublattice within its pores. Three different secondary sublattices are grown-two of which are not known as standalone MOFs-leading to three different hetero-interpenetrated MOFs. This strategy may serve to combine different properties into one material. We produce an asymmetric catalysis by allocating separate roles to the interpenetrating sublattices in a hetero-interpenetrated MOF: an achiral secondary amine on one sublattice provides the catalytic activity, while the chiral α-MUF-10 host imparts asymmetry to aldol and Henry reactions.

Application of a novel hybrid MIL-53(Al)@rice husk for the adsorption of glyphosate in water: Characteristics and mechanism of the process

The development of new materials that have a high capacity to remove pollutants in water-based media is becoming increasingly important because of the serious contamination of water and the negative impact on biodiversity and public health. The presence of glyphosate in water, the most widely used herbicide worldwide, has triggered alerts owing to the collateral effects it may cause on human health. The main objective of the present study was to investigate the potential of the hybrid material MIL-53(Al)@RH for the adsorption of glyphosate in aqueous solution. The material was obtained following the methodology of MIL-53(Al) synthesis in the presence of hydrolyzed rice husk assisted by microwave. Batch adsorption experiments were carried out to evaluate the adsorbent dosage, pH₀ solution effect, contact time, adsorbate concentration, and temperature effect. The results demonstrated that a maximum adsorption capacity of 296.95 mg g^-1, at pH₀ 4 with a ratio of 0.04 g MIL-53(Al)@RH/50 mL of solution, was achieved in 30 min. The Avrami and pseudo-second order models appropriately described the adsorption kinetics and the equilibrium by Langmuir and Sips models. The enthalpy changes (ΔH°) determined propose an endothermic reaction governed by chemisorption, corroborating the kinetic and equilibrium settings. Hydrogen bonds, π*-π interactions, and complexation between the metal centers of MIL-53(Al) and the anionic groups of glyphosate were postulated to be involved as adsorption mechanisms. Finally, for practical application, MIL-53(Al)@RH was packed in a column for a fixed-bed test which revealed that the hybrid can remove glyphosate with an adsorption capacity of 76.304 mg L^-1, utilizing 90% of the bed.

Water-Harvesting Metal-Organic Frameworks with Gigantic Al24 Units and their Deconstruction into Molecular Clusters

In contrast to the vast Al-oxo molecular cluster chemistry, Al-based building units for metal-organic framework (MOF) construction are limited in structural diversity and complexity. Synthesis of single crystalline MOFs based on this "hard" metal is further complicated by the poor reversibility of the Al-organic coordination linkages. Here, a strategy to employ two kinds of linkages with distinct strength-strong Al-carboxylate linkage and weak Cu-pyrazol N linkage-gives FDM-91 (FDM=Fudan Materials) with gigantic Al₂₄ -based units. After replacing the weak moieties with organic linkers post-synthetically, two new stable MOFs with exceptional water harvesting capacity (up to 0.53 g g^-1 ) and outstanding cycling performance are developed. Linkage-selective dissociation of FDM-91 further leads to the isolation of the Al₂₄ molecular clusters. The versatile chemistry performed here to reinforce or deconstruct MOFs provides a new way to make important extended and discrete structures.

Ligand-Functional Groups Induced Tuning MOFs' 2D into 1D Pore Channels for Pipeline Natural Gas Purification

The solvothermal reactions of CoCl₂  ⋅ 6H₂ O, 3,5-pyridinedicarboxylic acid (H₂ L) and isonicotinic acid (HL₁ )/3-amino isonicotinic acid (HL₂ )/3-chloro isonicotinic acid (HL₃ ) successfully led to three tfz-d topological pillar-layer [Co₄ (μ-F)₂ (COO)₆ (NC₅ H₄ )₄ ] cluster-based MOFs, namely, [Co₄ (μ-F)₂ (L)₂ (L₁ )₂  ⋅ 2DMA] ⋅ DMA ⋅ 2H₂ O (SNNU-Bai76, SNNU-Bai=Shaanxi Normal University Bai's group), [Co₄ (μ-F)₂ (L)₂ (L₂ )₂  ⋅ 2H₂ O] ⋅ 2DMA ⋅ 2H₂ O (SNNU-Bai77) and [Co₄ (μ-F)₂ (L)₂ (L₃ )₂  ⋅ 2H₂ O] ⋅ 2DMF ⋅ 2H₂ O (SNNU-Bai78). With the 2D pore channels in SNNU-Bai76 and SNNU-Bai77 being tuned to the 1D pore channel in SNNU-Bai78, C₃ H₈ and C₂ H₆ adsorption uptakes are apparently improved and the IAST selectivities of C₃ H₈ /CH₄ and C₂ H₆ /CH₄ almost remain, which indicate that SNNU-Bai78 may be one potential separation material for the pipeline natural gas purification. These were further confirmed by the breakthrough experiments for the simulated pipeline natural gas (C₃ H₈ /C₂ H₆ /CH₄  : 5/10/85 gas mixture) of three isostructural MOFs. Furthermore, GCMC simulations revealed that due to one of the pore channels blocked by Cl atoms in a couple of 3-chloro isonicotinic acid with the changed conformation as the pillar, the pore wall of the formed 1D pore channel in SNNU-Bai78 may interact with the adsorbed C₃ H₈ or C₂ H₆ molecule more strongly, for which more atoms of framework at the new adsorption site will interact with the adsorbed gas molecule by more intermolecular interactions. This was also evidenced by the increased binding energies, being consistent with the tuning of adsorption enthalpies for C₃ H₈ and C₂ H₆ gas molecules, and the reduced C₃ H₈ and C₂ H₆ gas diffusion coefficients in SNNU-Bai78. Very interestingly, this work is the first example of finely tuning the pore connectivity of MOFs toward strengthened host-guest interactions for the gas adsorption and separation.

Conformational Control of Organocatalyst in Strongly Brønsted-Acidic Metal-Organic Frameworks for Enantioselective Catalysis

Chiral imidodiphosphates (IDPs) have emerged as strong Brønsted acid catalysts for many enantioselective processes. However, the dynamic transformation between O,O-syn and O,O-anti conformers typically results in low enantioselectivity. Here we demonstrate that topologies of metal-organic frameworks (MOFs) can be exploited to control IDP conformations and local chiral microenvironments for enantioselective catalysis. Two porous Dy-MOFs with different topologies are obtained from an enantiopure 1,1'-biphenol IDP-based tetracarboxylate ligand. While the ligand adopts a 4- or 3-connected (c) binding mode, all IDPs are rigidified to get only a single O,O-syn conformation and display greatly enhanced Brønsted acidity relative to the free IDP. The MOF with the 4-c IDP that has a relatively less compact shape than the 3-c IDP can be an efficient and recyclable heterogeneous Brønsted acid catalysing the challenging asymmetric O,O-acetalization reaction with up to 96 % enantiomeric excess.

Ultrathin Metal-Organic Framework Nanosheets Exhibiting Exceptional Catalytic Activity

Two-dimensional (2D) metal-organic framework nanosheets (MONs) or membranes are classes of periodic, crystalline polymeric materials that may show unprecedented physicochemical properties due to their modular structures, high surface areas, and high aspect ratios. Yet preparing 2D MONs from multiple components and two different types of polymerization reaction remains challenging and less explored. Here, we report the synthesis of MOF films via interfacial polymerization, which involves three active monomers for simultaneous polycondensation and polycoordination taking place in a confined interface. The well-defined lamellar structure of the MOF films allowed feasible and scalable exfoliation to produce free-standing 2D MONs with high aspect ratio up to 2000:1 and ultrathin thickness (∼1.7 nm). The pore structure was revealed by high-resolution TEM images with near-atomic precision. The imide-linkage of MONs provided superior thermal (up to 530 °C) and good chemical stability in the pH range from 3 to 12. More importantly, the MONs exhibited exceptional catalytic activity and superior reusability for the hydroboration reactions of alkynes, in which the turnover frequency (TOF) reached 41734 h^-1, which is 2-4 orders of magnitude greater than that reported for homogeneous and heterogeneous catalysts.

Partial Linker Substitution Strategy to Construct a Quaternary HKUST-like MOF for Efficient Acetylene Storage and Separation

Multicomponent metal-organic frameworks (MOFs) have received much attention as emerging materials capable of precisely programing exquisite structures and specific functions. Here, we applied a partial linker substitution strategy to compile an HKUST-1-like quaternary MOF by introducing a bifunctional ligand into the well-known HKUST-1 structure. FUT-1, a new HKUST-like tbo topology MOF, was assembled with paddlewheel [Cu₂(COO)₄], triangular metallocycle pyrazole cluster Cu₃(μ₃-OH) (NN)₃ building blocks, and two distinct linkers. FUT-1 exhibited good mechanical stability, water stability, and chemical stability (pH = 3-12) in aqueous solutions. Moreover, the porous environments created by this multicomponent primitive endow FUT-1 with high C₂H₂ storage and significantly selective separation performance of C₂H₂/CO₂. Dynamic breakthrough experiments and ideal adsorbed solution theory calculations further demonstrate that FUT-1 can selectively capture C₂H₂ from C₂H₂/CO₂ mixtures under ambient conditions. Based on grand canonical Monte Carlo simulations, the high C₂H₂ separation performance of FUT-1 is attributed to the π-complex formed between the C₂H₂ molecule and the trinuclear metallocycle clusters on the wall, which provides stronger affinity for C₂H₂ recognition than the CO₂ molecule.

Construction of a 3D Metal-Organic Framework and Its Composite for Water Remediation via Selective Adsorption and Photocatalytic Degradation of Hazardous Dye

In this work, a new bimetallic Na(I)-Zn(II) metal-organic framework (MOF), formulated as [Na₂Zn₃(btc)₂(μ-HCOO)₂(μ-H₂O)₈] _n (1) (H₃btc = benzene tricarboxylic acid), and its composite (ZnO@1) have been successfully synthesized using solvothermal and mechanochemical solid grinding methods. 1 and ZnO@1 were characterized by diffraction [single-crystal X-ray diffraction (XRD) and powder XRD], spectroscopic (ultraviolet-visible diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy), microscopic (transmission electron microscopy), and thermal (thermogravimetric analysis) methods. The surface area and porosity of 1 were determined using a Brunauer-Emmett-Teller analyzer. Single-crystal diffraction of 1 confirms that Na1 and Zn2 have octahedral coordination environments, whereas Zn1 has a tetrahedral coordination geometry. Topological simplification of 1 shows a 3,6-connected kgd net. Na(I)-Zn(II) MOF (1) is crystallized with slight porosity and exhibits good tendency toward the encapsulation of zinc oxide nanoparticles (ZnO NPs). The photocatalytic behaviors of 1 and its composite (ZnO@1) were investigated over MB dye under sunlight illumination with promising degradation efficiencies of 93.69% for 1 and 97.53% for ZnO@1 in 80 min.

A novel core@double-shell three-layer structure with dendritic fibrous morphology based on Fe3O4@TEA@Ni-organic framework: a highly efficient magnetic catalyst in the microwave-assisted Sonogashira coupling reaction

In synthetic organic chemistry, the formation of carbon-carbon bonds is a significant and substantial reaction. As a result, developing a highly active magnetic heterogeneous catalyst with excellent performance is a very appealing technique for constructing C-C bonds in organic chemistry. The present study describes the fabrication of a novel and readily recoverable nickel-based metal-organic framework (MOF) for C-C bond formation through the Sonogashira coupling reaction. The efficient magnetic core-shell structure (Fe₃O₄@TEA@MOF) with a 3D dendritic fibrous morphology was successfully synthesized using a hydrothermal approach by immobilizing Ni-based MOF onto the Fe₃O₄@TEA core-shell structure. The fabrication of Fe₃O₄@TEA@MOF was confirmed by various analyses; Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDS), and elemental mapping confirmed the stepwise fabrication of catalyst. X-ray diffraction analysis (XRD) showed the crystalline nature of the catalyst. Field-emission scanning electron microscopy (FE-SEM) displayed the 3D dendritic fibrous morphology. Thermogravimetric analysis (TGA) and vibrating sample magnetometer analysis (VSM) showed the excellent thermal stability and magnetic properties of Fe₃O₄@TEA@MOF. The Brunauer-Emmett-Teller analysis (BET) found that the fabricated catalyst with a surface area of 36.2 m² g^-1, pore volume of 0.18 cm³ g^-1, and mean pore diameter of 20.38 nm belongs to mesoporous structures. In addition, the information from the inductively coupled plasma-optical emission spectroscopy (ICP-OES) about fresh and reused catalysts showed that the metal leaching amount is slight and about 1.98%. Other advantages of the Fe₃O₄@TEA@MOF catalyst can be mentioned as easily reusable for four runs and high performance (above 98%) in synthesizing diphenylacetylene from phenylacetylene, aryl halide, and cesium carbonate (as the base) under solvent-free and microwave conditions.

Reactive organic radical-doped Ag(I)-based coordination compounds for highly efficient antibacterial wound therapy

Antibiotics, being critical antimicrobial agents, have been widely used for treating bacterial infections. However, prolonged use of antibiotics can induce drug resistance resulting in "superbug" that threatens human health. Therefore, developing antibiotic-free materials with intrinsic antibacterial properties is the key to the "superbug" challenge. In this study, two highly efficient metal-organic frameworks (MOFs) were successfully assembled through synergistic use of the antibacterial properties of reactive organic radicals and silver (Ag) cations. These hybrid Ag-based materials possessed radical-doped characteristics, continuously releasing Ag⁺, which significantly inhibited the growth of four common Gram-negative and Gram-positive human pathogens (Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus), and particularly two multi-drug-resistance bacteria (MRSA and MDR-PA). Furthermore, in vivo assays indicated that the synergistic antibacterial effect of these compounds could significantly accelerate the healing rate of infected wounds in mice. Blood biochemistry and histological analyses of main organs in treated mice also exhibited negligible cytotoxicity. This study unveiled the promising potential of Ag-MOFs for anti-infective therapies and future clinical applications.

Hexahydric Components Metal Organic Frameworks Constructed by Multiple Ligands and Mixed-Valence Ions

In this work, we report two multi-component MOFs [CH3NH2CH3]2[FeIII2MII10(tz)11(HCO2)12(btc)5/3] (MII10 = FeII10 for 1 and MII10 = FeII2CoII8 for 2) obtained by solvothermal assembling formate, benzene-1,3,5-tricarboxylate (btc) and 1,2,4 triazole...

Synthesis, Structure and Highly Selective C3H8/CH4 and C2H6/CH4 Adsorptions of a (4,8)-c Ternary flu-Metal-organic Framework based upon both [Sc4O2(COO)8] and [Cu4OCl6] Clusters

A new ternary flu topological metal-organic framework based upon the torsional cubic 8-connected [Sc4O2(COO)8] cluster and the tetrahedral 4-connected [Cu4OCl6] cluster, namely, [Sc4O2(Cu4Cl6O)2(L)8•5H2O]•xGuest (SNNU-Bai69; SNNU-Bai = Shaanxi Normal University, Bai’s...

Full-Color Emission in Multicomponent Metal-Organic Frameworks via Linker Installation

Herein, we demonstrate that linker installation (LI) through postsynthesis is an effective strategy to insert emissive second linkers into single-linker-based metal-organic frameworks (MOFs) to tune the emission properties of multicomponent MOFs. Full-color emission, including white-light emission, can be achieved via such a LI process.

Double-Walled Zn36@Zn104 Multicomponent Senary Metal-Organic Polyhedral Framework and Its Isoreticular Evolution

Metal-organic polyhedral frameworks are attractive in gas storage and separation due to large voids with windows that can serve as traps for guest molecules. Introducing multivariant/multicomponent functionalities in them are ways of improving performances for certain targets. The high compatibility of organic linkers can generate multivariant MOFs, but by far, the diversity of secondary building units (SBUs) in a single metal-organic framework is still limited (no more than two in most cases). Here we report a new double-walled Zn₃₆@Zn₁₀₄ metal-organic polyhedral framework (HHU-8) with five types of topologically distinct SBUs and its isoreticular evolution to the Zn₃₆@Zn₁₃₆ counterpart (HHU-8s). Both MOFs are the first to be constructed with such high numbers of topologically distinct SBUs as well as topologically distinct nodes, and their formation and evolution provide new insight into SBU's controllability.

Ligand-Conformer-Induced Formation of Zirconium-Organic Framework for Methane Storage and MTO Product Separation

In pursuit of novel adsorbents with efficient adsorptive gas storage and separation capabilities remains highly desired and challenging. Although the documented zirconium-tricarboxylate-based metal-organic frameworks (MOFs) have displayed a variety of topologies encompassing underlying and geometry mismatch ones, the employed organic linkers are exclusively rigid and poorly presenting one type of conformation in the resultant structures. Herein, a used and semirigid tricarboxylate ligand of H₃ TATAB was judiciously selected to isolate a zirconium-based spe-MOF after the preliminary discovery of srl-MOF. Single-crystal X-ray diffraction reveals that the fully deprotonated TATAB linker in spe-MOF exhibits two distinct conformers, concomitant with popular O_h and rare S₆ symmetrical Zr₆ molecular building blocks, generating an unprecedented (3,3,12,12)-c nondefault topology. Specifically, the spe-MOF exhibits structurally higher complexity, hierarchical micropores, open metal sites free and rich electronegative groups on the pore surfaces, leading to relatively high methane storage capacity without considering the missing-linker defects and efficient MTO product separation performance.

Multi-Component Metal-Organic Frameworks Significantly Boost Visible-Light-Driven Hydrogen Production Coupled with Selective Organic Oxidation

Visible-light-driven hydrogen production coupled with selective organic oxidation has attracted increasing attention, as it not only provides clean and renewable energy, but also utilizes the other half reaction to achieve some value-added organic chemicals. Metal-organic frameworks based on metal clusters and organic ligands self-assembly give a perspective on the formation of multifunctional heterogeneous photocatalyst to significantly boost visible-light photocatalytic activities under mild conditions. By incorporating two types of photoactive units, tricarboxytriphenylamine (H₃ TCA) and tris(4-(pyridinyl)phenyl)amine (NPy₃ ), into a single metal-organic frameworks, a multi-component MOF Co-MIX was obtained. With the redox active metal centers enabling the photoexcitation reduction of protons into hydrogen and the photogenerated holes promoting considerable oxidation of substrates, the resulting Co-MIX exhibits high catalytic activity for the photocatalytic hydrogen production coupled with selective oxidation of benzylamine or 1,2,3,4-tetrahydroisoquinoline. Importantly, the photocatalytic experiments of single-component Co-TCA and Co-NPy₃ verified the positive synergistic effects on stability and photocatalytic ability of the two ligands (H₃ TCA and NPy₃ ) in one single MOF, revealing that the multi-component strategy is very important for the efficient charge separation and excellent photocatalytic activity of the catalyst.

An Imine-Linked Metal-Organic Framework as a Reactive Oxygen Species Generator

A new metal-organic framework (MOF) with both coordination linkages and covalent linkages is prepared by coordinating Cu^I with pyrazolate for an aldehyde-functionalized trinuclear complex, and subsequent imine condensation with p-phenylenediamine, a reaction typical for covalent organic framework (COF) synthesis. This MOF×COF collaboration yields FDM-71 with honeycomb layers stacked in eclipsed fashion. After dissociating the Cu^I -pyrazolate coordination in FDM-71, the obtained organic components carry the information of structural defects, and thus vacancy identity (aldehyde-based unit vacancy and amine-based unit vacancy) and concentration are definitely resolved. Further to the redox catalytic activity inherited from the complex, FDM-71 features effective photosensitizing activity. The two functions integrated in one well-defined structure is demonstrated by its high efficiency in decomposing H₂ O₂ and consequent excitation of O₂ to reactive oxygen species.

Increasing the Complexity in the MIL-53 Structure: The Combination of the Mixed-Metal and the Mixed-Linker Concepts

The isoreticular mixed-component concept is a promising approach to tailor the material properties of metal-organic frameworks. While isoreticular mixed-metal or mixed-linker materials are commonly synthesized, the combination of both concepts for the development of isoreticular materials featuring both two metals and two linkers is still rarely investigated. Herein, we present the development of mixed-metal/mixed-linker MIL-53 materials that contain different metal combinations (Al/Sc, Al/V, Al/Cr, Al/Fe) and different linker ratios (terephthalate/2-aminoterephthalate). The possibility of changing the metal combination and the linker ratio independently from each other enables a large variety of modifications. A thorough characterization (PXRD, ATR-IR, TGA, 1 H NMR, ICP-OES) confirmed that all components were incorporated into the framework structure with a statistical distribution. Nitrogen physisorption measurements showed that the breathing behavior can be tailored by adjusting the linker ratio for all metal combinations. All materials were successfully used for post-synthetic modification reactions with maleic anhydride.

Recent developments in the synthesis of polysubstituted pyridines via multicomponent reactions using nanocatalysts

This review describes the evolution and application of active metal-based and heterometallic NPs as efficient heterogeneous catalysts for the synthesis of pyridine derivatives by multicomponent reactions in the last decade (2010–2020).

Luminescence response mode and chemical sensing mechanism for lanthanide-functionalized metal–organic framework hybrids

This comprehensive review systematically summarizes the luminescence response mode and chemical sensing mechanism for lanthanide-functionalized MOF hybrids (abbreviated as LnFMOFH).

Adsorption of dicamba and MCPA onto MIL-53(Al) metal-organic framework: response surface methodology and artificial neural network model studies

An aluminium-based metal–organic framework ((MOF), MIL-53(Al)), was hydrothermally synthesized, characterized and applied for the remediation of the herbicides dicamba (3,6-dichloro-2-methoxy benzoic acid) and 4-chloro-2-methylphenoxyacetic acid (MCPA) in aqueous medium. Response surface methodology (RSM) and artificial neural network (ANN) were used to design, optimize and predict the non-linear relationships between the independent and dependent variables. The shared interaction of the effects of key response parameters on the adsorption capacity were assessed using the central composite design-RSM and ANN optimization models. The optimum adsorption capacities for dicamba and MCPA are 228.5 and 231.9 mg g⁻¹, respectively. The RSM ANOVA results showed significant p-values, with coefficients of determination (R²) = 0.988 and 0.987 and R² adjusted = 0.974 and 0.976 for dicamba and MCPA, respectively. The ANN prediction model gave R² = 0.999 and 0.999, R² adjusted = 0.997 and 0.995 and root mean square errors (RMSEs) of 0.001 and 0.004 for dicamba and MCPA, respectively. In each set of experimental conditions used for the study, the ANN gave better prediction than the RSM, with high accuracy and minimal error. The rapid removal (∼25 min), reusability (5 times) and good agreement between the experimental findings and simulation results suggest the great potential of MIL-53(Al) for the remediation of dicamba and MCPA from water matrices.

Rapid equilibration within a short time, high adsorption capacity, optimization, multivariate interaction of adsorption parameters and artificial neural network prediction model.

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments

Metal-organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn-Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H₂/CO₂ separation ability of bMOF-200. We examine the H₂/CO₂ separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H₂/CO₂ separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H₂ and CO₂ and a significantly improved H₂/CO₂ separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H₂/CO₂ separations.

Evolution of a Metal-Organic Framework into a Brønsted Acid Catalyst for Glycerol Dehydration to Acrolein

Metal-organic frameworks (MOFs) as solid acid catalysts provide active sites with definite structures. Here, Zr₆ -based MOF-808 and its derivatives were studied as catalysts for glycerol dehydration, the products of which (acrolein vs. acetol) are very sensitive to the nature of the catalytic acid sites. Evolving MOF-808 into MOF-808-S with a 120 % increase in the number of Brønsted OH^- /H₂ O coordinated to Zr^IV and a vanished Lewis acidity by steam treatment, the post-synthetically modified catalyst presented 100 % conversion of glycerol, 91 % selectivity to acrolein, and 0 % selectivity to acetol within the active window. Real-time analysis of the product composition indicated the in situ MOF structural evolution. Overall, the specific MOF-substrate interaction characterized by the probe reaction provides more understandings on the structural evolution of the MOFs and their impact on the performance as solid acid catalysts.

Applications of Dynamic Covalent Chemistry Concept towards Tailored Covalent Organic Framework Nanomaterials: A Review

Covalent organic frameworks (COFs) are a rapidly developing class of materials that has been of immense research interest during the last ten years. Numerous reviews have been devoted to summarizing the synthesis and applications of COFs. However, the underlying dynamic covalent chemistry (DCC), which is the foundation of COFs synthesis, has never been systematically reviewed in this context. Dynamic covalent chemistry is the practice of using thermodynamic equilibriums to molecular assemblies. This Critical Review will cover the state-of-the-art use of DCC to both synthesize COFs and expand the applications of COFs. Five synthetic strategies for COF synthesis are rationalized, namely: modulation, mixed linker/linkage, sub-stoichiometric reaction, framework isomerism, and linker exchange, which highlight the dynamic covalent chemistry to regulate the growth and to modify the properties of COFs. Furthermore, the challenges in these approaches and potential future perspectives in the field of COF chemistry are also provided.

A Heterometallic Three-Dimensional Metal-Organic Framework Bearing an Unprecedented One-Dimensional Branched-Chain Secondary Building Unit

A heterometallic metal−organic framework (MOF) of [Cd₆Ca₄(BTB)₆(HCOO)₂(DEF)₂(H₂O)₁₂]∙DEF∙xSol (1, H₃BTB = benzene-1,3,5-tribenzoic acid; DEF = N,N′-diethylformamide; xSol. = undefined solvates within the pore) was prepared by solvothermal reaction of Cd(NO₃)₂·4H₂O, CaO and H₃BTB in a mixed solvent of DEF/H₂O/HNO₃. The compatibility of these two divalent cations from different blocks of the periodic table results in a solid-state structure consisting of an unusual combination of a discrete V-shaped heptanuclear cluster of [Cd₂Ca]₂Ca′ and an infinite one-dimensional (1D) chain of [Cd₂CaCa′]_n that are orthogonally linked via a corner-shared Ca²⁺ ion (denoted as Ca′), giving rise to an unprecedented branched-chain secondary building unit (SBU). These SBUs propagate via tridentate BTB to yield a three-dimensional (3D) structure featuring a corner-truncated P4₁ helix in MOF 1. This outcome highlights the unique topologies possible via the combination of carefully chosen s- and d-block metal ions with polydentate ligands.

Sequential Ag+/biothiol and synchronous Ag+/Hg2+ biosensing with zwitterionic Cu2+-based metal-organic frameworks

Zwitterionic metal-organic frameworks (MOFs) of {[Cu(Cbdcp)(Dps)(H₂O)₃]·6H₂O}_n (MOF 1) and [Cu₄(Dcbb)₄(Dps)₂(H₂O)₂]_n (MOF 2) (H₃CbdcpBr = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium bromide; H₂DcbbBr = 1-(3,5-dicarboxybenzyl)-4,4'-bipyridinium bromide; Dps = 4,4'-dipyridyl sulfide) quench the fluorescence of cytosine-rich DNA tagged with 5-carboxytetramethylrhodamine (TAMRA, emission at 582 nm, denoted as C-rich P-DNA-1) and yield the corresponding P-DNA-1@MOF hybrids. Exposure of these hybrids to Ag⁺ results in the release of the P-DNA-1 strands from the MOF surfaces as double-stranded, hairpin-like C-Ag^I-C (ds-DNA-1@Ag⁺) with the restoration of TAMRA fluorescence. The ds-DNA-1@Ag⁺ formed on the surface of 1 can subsequently sense biothiols cysteine (Cys), glutathione (GSH), and homocysteine (Hcy) due to the stronger affinity of mercapto groups for Ag⁺ that serves to unfold the ds-DNA-1@Ag⁺ duplex, reforming P-DNA-1, which is re-adsorbed by MOF 1 accompanied by quenching of TAMRA emission. Meanwhile, MOF 2 is also capable of co-loading a thymine-rich probe DNA tagged with 5-carboxyfluorescein (FAM, emission at 518 nm, denoted as T-rich P-DNA-2) to achieve synchronous sensing of Ag⁺ and Hg²⁺, resulting from the simultaneous yet specific ds-DNA-1@Ag⁺ and T-Hg^II-T duplex (ds-DNA-2@Hg²⁺) formation, as well as the distinctive emission wavelengths of TAMRA and FAM. Detection limits are as low as 5.3 nM (Ag⁺), 14.2 nM (Cys), 13.5 nM (GSH), and 9.1 nM (Hcy) for MOF 1, and 7.5 nM (Ag⁺) and 2.6 nM (Hg²⁺) for MOF 2, respectively. The sequential sensing of Ag⁺ and biothiols by MOF 1, and the synchronous sensing of Ag⁺ and Hg²⁺ by MOF 2 are rapid and specific, even in the presence of other mono- and divalent metal cations or other biothiols at much higher concentrations. Molecular simulation studies provide insights regarding the molecular interactions that underpin these sensing processes.

Metalloporphyrinic metal-organic frameworks: Controlled synthesis for catalytic applications in environmental and biological media

Recently, as a new sub-family of porous coordination polymers (PCPs), porphyrinic-MOFs (Porph-MOFs) with biomimetic features have been developed using porphyrin macrocycles as ligands and/or pillared linkers. The control over the coordination of the porphyrin ligand and its derivatives however remains a challenge for engineering new tunable Porph-MOF frameworks by self-assembly methods. The key challenges exist in the following respects: (i) collapse of the large open pores of Porph-MOFs during synthesis, (ii) deactivation of unsaturated metal-sites (UMCs) by axial coordination, and (iii) the tendency of both coordinated moieties (at peripheral meso- and beta-carbon sites) and the N₄-pyridine core to coordinate with metal cations. In this respect, this review covers the advances in the design of Porph-MOFs relative to their counterpart covalent organic frameworks (Porph-COFs). The potential utility of custom-designed porphyrin/metalloporphyrins ligands is highlighted. Synthesis strategies of Porph-MOFs are also illustrated with modular design of hybrid guest@host composites (either Porph@MOFs or guest@Porph-MOFs) with exceptional topologies and stability. This review summarizes the synergistic benefits of coordinated porphyrin ligands and functional guest molecules in Porph-MOF composites for enhanced catalytic performance in various redox applications. This review shed lights on the engineering of new tunable hetero-metals open active sites within (metallo)porphyrin-MOFs as out-of-the-box platforms for enhanced catalytic processes in chemical and biological media.