Determination of chlorophenoxy acid herbicides by using a zirconium-based metal–organic framework as special sorbent for dispersive micro-solid-phase extraction and high-performance liquid chromatography

This study reports a Zr-based MOF with 2-amino-benzenedicarboxylic acid ligand as an adsorbent for chlorophenoxy acid herbicides from biosamples.

Monodispersed gold nanoparticles supported on a zirconium-based porous metal–organic framework and their high catalytic ability for the reverse water–gas shift reaction

A highly active and selective Au@UIO-67 catalyst has been assembled.

Environmentally benign dry-gel conversions of Zr-based UiO metal–organic frameworks with high yield and the possibility of solvent re-use

UiO-MOFs were synthesized using only 1/6 or upon solvent re-use only 1/30 of the DMF solvent volume compared to the solution synthesis on the same scale.

Hierarchical structure and porosity in UiO-66 polyMOFs

The first polymer–MOF hybrid material (polyMOF) with a UiO-66 architecture is reported, prepared from polymers with varying alkyl spacers, molecular weights, and dispersities.

Cascade catalytic hydrogenation–cyclization of methyl levulinate to form γ-valerolactone over Ru nanoparticles supported on a sulfonic acid-functionalized UiO-66 catalyst

The developed Ru/SO₃H-UiO-66 exhibits a novel synergistic catalysis to upgrade methyl levulinate into γ-valerolactone under mild conditions in water.

The duality of UiO-67-Pt MOFs: connecting treatment conditions and encapsulated Pt species by operando XAS

XAS study of Pt-functionalized UiO-67 MOFs shows that 2 types of catalytically active sites can be formed in MOF cavities isolated Pt-complexes and Pt nanoparticles.

Tuning the stability of bimetallic Ce(iv)/Zr(iv)-based MOFs with UiO-66 and MOF-808 structures

A series of solid solutions of bimetallic Ce/Zr-UiO-66 and -MOF-808 compounds with a varying ratio of Ce⁴⁺ to Zr⁴⁺ were obtained under mild reaction conditions within 15 min. Samples with Ce ≤20 at% exhibit an enhanced thermal stability, better resistance against acids and smaller particle sizes.

Metal–organic frameworks (MOFs) as highly efficient agents for boron removal and boron isotope separation

A variety of MOFs were observed with ZIF-8, to our knowledge, showing the highest boron uptake and MIL-101(Cr) with an unprecedentedly high boron isotope separation factor.

Incorporation of CuO NPs into modified UiO-66-NH2 metal–organic frameworks (MOFs) with melamine for catalytic C–O coupling in the Ullmann condensation

The UiO-66-NH₂ is initially modified with melamine via a post-synthetic approach. CuO NPs are then anchored via the available functional groups on the surface of the modified MOF.

Metal–organic framework incorporated monolithic capillary for selective enrichment of phosphopeptides

Protein phosphorylation is a major post-translational modification, which plays a central role in the cellular signaling of numerous biological processes.

Effective removal of chemical warfare agent simulants using water stable metal–organic frameworks: mechanistic study and structure–property correlation

Water stable zirconium based MOFs are used for the efficient adsorptive removal of chemical warfare agent simulants from aqueous medium.

Trace-doped metal–organic gels with remarkably enhanced luminescence

Novel highly luminescent metal–organic gels with a trace amount of doping (as low as 0.01 mol%) have been fabricated.

A dendritic catiomer with an MOF motif for the construction of safe and efficient gene delivery systems

The dendritic catiomer using biocompatible Zr-MOFs as the core exhibited a markedly higher transfection efficiency and lower cytotoxicity than the commercial gold standard branched PEI_25k in A549 cells.

Microwave-induced fast incorporation of titanium into UiO-66 metal–organic frameworks for enhanced photocatalytic properties

A microwave-assisted method was developed to incorporate Ti into UiO-66(Zr) to obtain a bimetallic MOF with enhanced photocatalytic performance.

Picolinoyl functionalized MOF ligands for an air-promoted secondary alcohol oxidation with CuBr

A novel Zr-derived pyridine MOF ligand was designed and synthesized for an efficient Cu(i)-catalyzed secondary alcohol oxidation.

Systematic study of the impact of MOF densification into tablets on textural and mechanical properties

Densification process of MOF powders (HKUST-1, UiO-66, UiO-66-NH₂, and UiO-67) into mechanically resistant pellets with maintained microporosity and enhanced volumetric uptake.

Dual-Metal Centered Zirconium-Organic Framework: A Metal-Affinity Probe for Highly Specific Interaction with Phosphopeptides

The highly specific affinity between probes and phosphopeptides is the fundamental interaction for selective identification of phosphoproteomes that uncover the mechanisms of signal transduction, cell cycle, enzymatic regulation, and gene expression in biological systems. In this study, a metal-affinity probe possessing both interactions of metal oxide affinity chromatography (MOAC) and immobilized metal ion affinity chromatography (IMAC) was facilely prepared by immobilizing zirconium(IV) on a zirconium-organic framework of UiO-66-NH₂, which holds dual-metal centers of not only the inherent Zr-O cluster but also the immobilized Zr(IV) center. This dual-metal centered zirconium-organic framework (DZMOF) demonstrates as a highly specific metal-affinity probe toward the extraction of phosphopeptides due to the metal-affinity interactions of MOAC and IMAC toward either mono-phosphorylated or multi-phosphorylated peptides. The binding energies of zirconium 3d_5/2 and 3d_3/2 in this DZMOF are 183.07 and 185.47 eV, respectively, which are higher than those of the intact UiO-66-NH₂ (182.84 and 185.17 eV, respectively), confirming the higher metal-affinity interaction between the DZMOF and phosphopeptides. This high metal-affinity probe presents an unprecedented strong performance in anti-nonspecific interference during the capturing of phosphopeptides of β-casein with the molar ratio of β-casein vs bovine serum albumin up to ca. 1:5000. The enrichment of phosphopeptides from a human saliva sample by DZMOF further confirms the great potential of DZMOF in the extraction of low-abundance phosphopeptides for real complex biological samples.

Assessing the Surface Area of Porous Solids: Limitations, Probe Molecules, and Methods

In this modeling study, the uses of nitrogen (77.3 K), probe molecule of choice for decades, and argon, opted as alternative in the 2015 IUPAC report on adsorptive characterization, as probe molecules for geometric surface area determination are compared. Graphene sheets possessing slit-shaped pores with varying size (width) are chosen as model porous solids, and different methods for the determination of specific surface areas are investigated. The BET method, which is the most commonly applied analysis, is compared to the Langmuir and relatively recently proposed ESW (excess sorption work) method. We show that either using argon or nitrogen as adsorptive, the physical meaningfulness of adsorption-derived surface areas highly depends on the pore size. When less than two full layers of adsorbate molecules can be formed within slitlike pores of a graphitic material (D_pore < 5.8 Å for Ar/N₂), adsorption-derived surface areas are about half that of the geometric surface area. Between two and four layers (6.8 < D_pore < 12.8 Å), adsorption surface areas can be significantly larger (up to 75%) than the geometric surface area because monolayer-multilayer formation and pore filling cannot be distinguished. For four or more layers of adsorbate molecules (D_pore > 12.8 Å), adsorption-derived surface areas are comparable to their geometrically accessible counterparts. Note that for the Langmuir method this only holds if pore-filling effects are excluded during determination. This occurs in activated carbon materials as well. In the literature, this indistinguishability issue has been largely overlooked, and erroneous claims of materials with extremely large surface areas have been made. Both the BET and Langmuir areas, for D_pore > 12.8 Å, correspond to geometric surface areas, whereas the ESW method yields significantly lower values. For the 6.8 Å < D_pore < 12.8 Å range, all methods erroneously overestimate the specific surface area. For the energetically homogeneous graphene sheets, differences between argon and nitrogen for the assessment of surface areas are minor.

Metal-Organic Frameworks as a Potential Platform for Selective Treatment of Gaseous Sulfur Compounds

The release of various anthropogenic pollutants such as gaseous sulfur compounds into the environment has been accelerated as globalization has promoted the production of high-quality products at lower prices. Because of strict enforcement of mitigation technologies, advanced materials have been developed to efficiently remove gaseous sulfur compounds released from various source processes. Metal-organic frameworks (MOFs) are promising materials to treat sulfur compounds via adsorption, catalysis, or separation. Nonetheless, the practical applicability of MOFs is limited by a number of factors including loss of structural integrity after use, limited reusability of spent MOFs, and low stability toward omnipresent molecules (e.g., H₂O). Here, we provide a comprehensive assessment of MOF technology for the effective control of gaseous sulfur compounds. This review will thus help expand the fields of real-world application for MOFs with a roadmap for this highly challenging area of research.

UiO-66-Type Metal-Organic Framework with Free Carboxylic Acid: Versatile Adsorbents via H-bond for Both Aqueous and Nonaqueous Phases

The metal-organic framework (MOF) UiO-66 was synthesized in one step from zirconium chloride and isophthalic acid (IPA), together with the usual link material, terephthalic acid (TPA). UiO-66 with free -COOH can be obtained in a facile way by replacing up to 30% of the TPA with IPA. However, the chemical and thermal stability of the synthesized MOFs decreased with increasing IPA content used in the syntheses, suggesting an increase in the population of imperfect bonds in the MOFs because of the asymmetrical structure of IPA. The obtained MOFs with free -COOH were applied in liquid-phase adsorptions from both water and model fuel to not only estimate the potential applications but also confirm the presence of -COOH in the MOFs. The adsorbed amounts of several organics (triclosan and oxybenzone from water and indole and pyrrole from fuel) increased monotonously with increasing IPA content applied in MOF synthesis (or -COOH in the MOFs). The favorable contribution of free -COOH to adsorption can be explained by H-bonding, and the direction of H-bonds (adsorbates: H donor; MOFs: H acceptor) was confirmed by the adsorption of oxybenzone in a wide pH range. The versatile applications of the MOFs with -COOH in adsorptions from both polar and nonpolar phases are remarkable considering that hydrophobic and hydrophilic adsorbents are generally required for water and fuel purification, respectively. Finally, the presence of free -COOH in the MOFs was confirmed by liquid-phase adsorptions together with general Fourier transform infrared analyses and decreased chemical and thermal stability.

Endocytosis Mechanism of Nano Metal-Organic Frameworks for Drug Delivery

The pathway of internalization and final fate of a specific metal-organic framework (MOF) in cells has been investigated for the first time. This study is based on two calcein-loaded UiO-66 samples with particle sizes of 150 and 260 nm (i.e., cal@150 UiO-66 and cal@260 UiO-66, respectively), and shows that the active trafficking of cal@150 UiO-66 is done almost exclusively through clathrin-mediated endocytosis, whereas the uptake of cal@260 UiO-66 is a combination of both clathrin and caveolae-mediated endocytosis. Colocalization studies with a lysosomal marker showed that cal@150 UiO-66 is located mostly in lysosomes for further degradation, whereas cal@260 UiO-66 seems to avoid the lysosomal degradation and potentially deliver the cargo molecules in the cytosol, allowing their distribution to different cellular organelles. This study reveals the importance of the internalization processes of MOFs, particularly the relevance of their particle size, and also the critical significance of their final fate to become an efficient drug delivery system. Based on these results, it is possible that extremely small particle-sized MOFs are not the most efficient carriers and instead relatively medium-sized particles are required.

Determining the structural stability of UiO-67 with respect to time: a solid-state NMR investigation

The stability of UiO-67 has been questioned for some time. We have used solid-state NMR to investigate the temporal stability of this MOF. Proper activation is necessary to achieve optimal surface area. However, even with proper activation, the long-term (30+ days) fate of UiO-67 is hydrolysis of the linker-metal bonds and, ultimately, pore collapse.

Tailor-Made Stable Zr(IV)-Based Metal-Organic Frameworks for Laser Desorption/Ionization Mass Spectrometry Analysis of Small Molecules and Simultaneous Enrichment of Phosphopeptides

Although thousands of metal-organic frameworks (MOFs) have been fabricated and widely applied in gas storage/separations, adsorption, catalysis, and so on, few kinds of MOFs have been used as adsorption materials while simultaneously serving as matrixes to analyze small molecules for laser desorption/ionization mass spectrometry (LDI-MS). Herein, a new concept is introduced to design and synthesize MOFs as both adsorption materials and matrixes according to the structure of ligands and common matrixes. The proof of concept design was demonstrated by selection of 2,5-pyridinedicarboxylic acid (PDC) and 2,5-dihydroxyterephthalic acid (DHT) as ligands for synthesis of MOFs. Two Zr(IV)-based MOFs of UiO-66-PDC and UiO-66-(OH)2 were synthesized and applied for the first time as new matrixes for analysis of small molecules by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Both of them showed low matrix interferences, high ionization efficiency, and good reproducibility when used as matrixes. A variety of small molecules, including saccharides, amino acids, nucleosides, peptides, alkaline drugs, and natural products, were analyzed. In addition, UiO-66-(OH)2 exhibited potential for application in the quantitative determination of glucose and pyridoxal 5'-phosphate. Furthermore, thanks to its intrinsically large surface area and highly ordered pores, UiO-66-(OH)2 also showed sensitive and specific enrichment of phosphopeptides prior to MS analysis. These results demonstrated that this strategy can be used to efficiently screen tailor-made MOFs as matrixes to analyze small molecules by MALDI-TOF-MS.

Dynamic acidity in defective UiO-66

The metal-organic framework (MOF) material UiO-66 has emerged as one of the most promising MOF materials due to its thermal and chemical stability and its potential for catalytic applications. Typically, as-synthesised UiO-66 has a relatively high concentration of missing linker defects. The presence of these defects has been correlated with catalytic activity but characterisation of defect structure has proved elusive. We refine a recent experimental determination of defect structure using static and dynamic first principles approaches, which reveals a dynamic and labile acid centre that could be tailored for functional applications in catalysis.

The dual capture of AsV and AsIII by UiO-66 and analogues

UiO-66 and analogues were successfully tailored to chemoselectively capture As^V oxyanions at the hydroxylated node and neutral As^III species with the thiolated organic linkers. More efficient and faster uptake of As^V can be achieved with increasing defect densities, increasing pore aperture sizes, and decreasing particle sizes.

UiO-66 and analogues were successfully tailored to chemoselectively capture As^V oxyanions at the hydroxylated node and neutral As^III species with the thiolated organic linkers. More efficient and faster uptake can be achieved with increasing defect densities, increasing pore aperture sizes, and decreasing particle sizes.

Evidence for a chemical clock in oscillatory formation of UiO-66

Chemical clocks are often used as exciting classroom experiments, where an induction time is followed by rapidly changing colours that expose oscillating concentration patterns. This type of reaction belongs to a class of nonlinear chemical kinetics also linked to chaos, wave propagation and Turing patterns. Despite its vastness in occurrence and applicability, the clock reaction is only well understood for liquid-state processes. Here we report a chemical clock reaction, in which a solidifying entity, metal–organic framework UiO-66, displays oscillations in crystal dimension and number, as shown by X-ray scattering. In rationalizing this result, we introduce a computational approach, the metal–organic molecular orbital methodology, to pinpoint interaction between the tectonic building blocks that construct the metal–organic framework material. In this way, we show that hydrochloric acid plays the role of autocatalyst, bridging separate processes of condensation and crystallization.

Reactions with non-linear kinetics, such as chemical clocks, are reasonably common but only well understood in the liquid phase. Here, the authors report and rationalize a chemical clock reaction taking place in a solidifying metal-organic framework.

Encapsulation of redox polysulphides via chemical interaction with nitrogen atoms in the organic linkers of metal-organic framework nanocrystals

Lithium polysulphides generated during discharge in the cathode of a lithium-sulphur redox cell are important, but their dissolution into the electrolyte from the cathode during each redox cycle leads to a shortened cycle life. Herein, we use in situ spectroelectrochemical measurements to demonstrate that sp² nitrogen atoms in the organic linkers of nanocrystalline metal-organic framework-867 (nMOF-867) are able to encapsulate lithium polysulphides inside the microcages of nMOF-867, thus helping to prevent their dissolution into the electrolyte during discharge/charge cycles. This encapsulation mechanism of lithiated/delithiated polysulphides was further confirmed by observations of shifted FTIR spectra for the C = N and C-N bonds, the XPS spectra for the Li-N bonds from nMOF-867, and a visualization method, demonstrating that nMOF-867 prevents lithium polysulphides from being dissolved in the electrolyte. Indeed, a cathode fabricated using nMOF-867 exhibited excellent capacity retention over a long cycle life of 500 discharge/charge cycles, with a capacity loss of approximately 0.027% per cycle from a discharge capacity of 788 mAh/g at a high current rate of 835 mA/g.

Free Energy of Ligand Removal in the Metal-Organic Framework UiO-66

We report an investigation of the "missing-linker phenomenon" in the Zr-based metal-organic framework UiO-66 using atomistic force field and quantum chemical methods. For a vacant benzene dicarboxylate ligand, the lowest energy charge-capping mechanism involves acetic acid or Cl^-/H₂O. The calculated defect free energy of formation is remarkably low, consistent with the high defect concentrations reported experimentally. A dynamic structural instability is identified for certain higher defect concentrations. In addition to the changes in material properties upon defect formation, we assess the formation of molecular aggregates, which provide an additional driving force for ligand loss. These results are expected to be of relevance to a wide range of metal-organic frameworks.

Electronic origins of photocatalytic activity in d0 metal organic frameworks

Metal-organic frameworks (MOFs) containing d⁰ metals such as NH₂-MIL-125(Ti), NH₂-UiO-66(Zr) and NH₂-UiO-66(Hf) are among the most studied MOFs for photocatalytic applications. Despite structural similarities, we demonstrate that the electronic properties of these MOFs are markedly different. As revealed by quantum chemistry, EPR measurements and transient absorption spectroscopy, the highest occupied and lowest unoccupied orbitals of NH₂-MIL-125(Ti) promote a long lived ligand-to-metal charge transfer upon photoexcitation, making this material suitable for photocatalytic applications. In contrast, in case of UiO materials, the d-orbitals of Zr and Hf, are too low in binding energy and thus cannot overlap with the π* orbital of the ligand, making both frontier orbitals localized at the organic linker. This electronic reconfiguration results in short exciton lifetimes and diminishes photocatalytic performance. These results highlight the importance of orbital contributions at the band edges and delineate future directions in the development of photo-active hybrid solids.

Stereoselective Halogenation of Integral Unsaturated C-C Bonds in Chemically and Mechanically Robust Zr and Hf MOFs

Metal-organic frameworks (MOFs) containing Zr(IV) -based secondary building units (SBUs), as in the UiO-66 series, are receiving widespread research interest due to their enhanced chemical and mechanical stabilities. We report the synthesis and extensive characterisation, as both bulk microcrystalline and single crystal forms, of extended UiO-66 (Zr and Hf) series MOFs containing integral unsaturated alkene, alkyne and butadiyne units, which serve as reactive sites for postsynthetic modification (PSM) by halogenation. The water stability of a Zr-stilbene MOF allows the dual insertion of both -OH and -Br groups in a single, aqueous bromohydrination step. Quantitative bromination of alkyne- and butadiyne-containing MOFs is demonstrated to be stereoselective, as a consequence of the linker geometry when bound in the MOFs, while the inherent change in hybridisation and geometry of integral linker atoms is facilitated by the high mechanical stabilities of the MOFs, allowing bromination to be characterised in a single-crystal to single-crystal (SCSC) manner. The facile addition of bromine across the unsaturated C-C bonds in the MOFs in solution is extended to irreversible iodine sequestration in the vapour phase. A large-pore interpenetrated Zr MOF demonstrates an I2 storage capacity of 279 % w/w, through a combination of chemisorption and physisorption, which is comparable to the highest reported capacities of benchmark iodine storage materials for radioactive I2 sequestration. We expect this facile PSM process to not only allow trapping of toxic vapours, but also modulate the mechanical properties of the MOFs.