Adsorption-based characterization of hierarchical metal–organic frameworks

Nitrogen adsorption at 77 K on metal–organic framework (MOF) is investigated by means of molecular simulations. We consider both regular Cu–BTC crystal and a MOF-based hierarchical porous solid consisting of a mesopore carved out of a Cu–BTC crystal. The t-plot method is applied to these solids by using a non-porous Cu–BTC surface as the reference sample. The values of the mesoporous and external surface areas are determined from the t-plot, and the validity of the method for this type of hierarchical solid is discussed.     

Irradiation and isolation of fission products from uranium metal–organic frameworks

Journal of Radioanalytical and Nuclear Chemistry - A customized single-stage cylindrical combined air lift mixer-settler (C-CALMIX) device has been developed and its performance was evaluated by...     

Selective adsorption of potassium and rubidium by metal–organic frameworks supported supramolecular materials

Journal of Radioanalytical and Nuclear Chemistry - A new MOFs-based adsorbent UiO-66@iPCC5 was prepared by hybridization of 25,27-bis(iso-propoxyl)-calix[4]arene-26,28-crown-5 (iPCC5) into the...     

Chiral metal–organic framework used as stationary phases for capillary electrochromatography

Metal–organic frameworks (MOFs) have received great attention as novel media in separation sciences because of their fascinating structures and unusual properties. However, to the best of our knowledge, there has been no attempt to utilize chiral MOFs as stationary phases in capillary electrochromatography (CEC). In this study, a homochiral helical MOF [Zn₂(D-Cam)₂(4,4′-bpy)]_n (D-Cam = D-(+)-camphoric acid, 4,4′-bpy = 4,4′-bipyridine) was explored as the chiral stationary phase in open tubular capillary electrochromatography (OT-CEC) for separation of chiral compounds and isomers. The MOFs coated column has been developed using a simple procedure via MOFs post-coated on the sodium silicate layer. The baseline separations of flavanone and praziquantel were achieved on the MOFs coated column with high resolution of more than 2.10. The influences of pH, organic modifier content and buffer concentration on separation were investigated. Besides, the separations of isomers (nitrophenols and ionones) were evaluated. The relative standard deviations (RSDs) for the retention time of run-to-run, day-to-day and column-to-column were 1.04%, 2.16% and 3.07%, respectively. The results demonstrated that chiral MOFs are promising for enantioseparation in CEC.     

Luminescent nanoscale metal–organic frameworks for chemical sensing

Metal–organic frameworks(MOFs) are a fascinating class of crystalline materials constructed from selfassembly of metal cations/clusters and organic ligands. Both metal and organic components can be used to generate luminescence, and can further interact via antenna effect to increase the quantum yield,providing a versatile platform for chemical sensing based on luminescence emission. Moreover, MOFs can be miniaturized to nanometer scale to form nano-MOF(NMOF) materials, which exhibit many advantages over conventional bulk MOFs in terms of the facile tailorability of compositions, sizes and morphologies, the high dispersity in a wide variety of medium, and the intrinsic biocompatibility. This review will detail the development of NMOF materials as chemical sensors, including the synthetic methodologies for designing NMOF sensory materials, their luminescent properties and potential sensing applications.     

Cobalt imine–pyridine–carbonyl complex functionalized metal–organic frameworks as catalysts for alkene epoxidation

Aerobic epoxidation of alkene is a green and economical route to produce epoxides. For such reaction, transition metal complexes exhibit favorable catalytic activity. In this work, NH₂-MIL-101, a stable metal–organic framework (MOF) material with large surface area and high pore volume, was functionalized with pyridine-2,6-dicarbaldehyde and Co(NO₃)₂, to realize the immobilization of Co(II) via imine–pyridine–carbonyl (N,N,O) tridentate ligands bonding to MOF skeleton. The modified materials were applied as heterogeneous catalysts for the aerobic epoxidation of cyclohexene at ambient temperature, and multiple factors were studied to explore their influences on catalytic effects. Under the optimal reaction conditions, satisfactory substrate conversion and epoxide selectivity were reached. In addition, this catalytic system is suitable for a variety of alkene substrates. Furthermore, recycle experiments and infrared spectroscopy characterization illustrated that the coordination surroundings of Co are altering smoothly during the reaction process, thus having an impact on the performance of catalyst.

     

Advanced metal–organic frameworks for aqueous sodium-ion rechargeable batteries

Inexpensive and abundant sodium resources make energy storage systems using sodium chemistry promising replacements for typical lithium-ion rechargeable batteries(LIBs).Fortuitously,aqueous sodium-ion rechargeable batteries(ASIBs),which operate in aqueous electrolytes,are cheaper,safer,and more ionically conductive than batteries that operate in conventional organic electrolytes;furthermore,they are suitable for grid-scale energy storage applications.As electrode materials for storing Na~+ ions in ASIBs,a variety of multifunctional metal-organic frameworks(MOFs) have demonstrated great potential in terms of having porous 3 D crystal structures,compatibility with aqueous solutions,long cycle lives(≥1000 cycles),and ease of synthesis.The present review describes MOF-derived technologies for the successful application of MOFs to ASIBs and suggests future challenges in this area of research based on the current understanding.     

In situ construction of metal–organic sulfur-containing heterocycle frameworks

This review outlines three types of in situ methods used for constructing metal–organic sulfur-containing heterocycle frameworks, viz., in situ S–S function reactions, in situ C–S bond cleavage and in situ thiol-S atom reactions. Each method is described in detail in three respects, namely (i) reaction parameters, (ii) the organic transformation and coordination modes involved, and (iii) fascinating structures and functional properties of those in situ-generated metal-coordination compounds.     

Two-dimensional nanosheets of metal–organic frameworks with tailorable morphologies

The controlled preparation of two-dimensional (2D) nanosheets of metal–organic frameworks (MOFs), with tailorable methodologies, properties, and applications, is of significant importance. Here, in this work, by subtle control of the ultrasonic duration and solvent polarity, the iron(II)-based 2D MOF Fe(pyz)₂Cl₂ (pyz = pyrazine) has been elegantly tailored into 2D nanosheets (lateral size ≥500 nm in aqueous, with ultrasonic duration of 30 min) and one-dimensional (1D) nanoribbons (lateral size ≤100 nm in ethanol solution, with ultrasonic duration of 90 min). The aqueous suspension of 2D nanosheets was featured with thermal-induced spin-state transition at around room temperature and can be used as effective Fenton catalysts for degradation of water-soluble organic dyes, whereas the ethanol suspension of 1D nanoribbons can act as a versatile nanoplatform for trans-to-cis isomerization of 4, 4′-azopyridine. These results may provide a novel strategy for the controlled preparation of layered nanomaterials.     

Alkaline earth metal–organic frameworks supported by ditopic carboxylates

Hydrothermal reactions of alkaline earth metal nitrates with two ditopic carboxylic acids, trans-1,4-cyclohexanedicarboxylic acid (H₂CDC) and 1,4-phenylenedipropionic acid (H₂PDP), generate two 3-D metal–organic frameworks (MOFs) with empirical formulas [Ca(CDC)(H₂O)₂]·H₂O (1) and [Sr(PDP)(H₂O)] (2), respectively. Compound 1 consists of Ca–COO–H₂O chains cross-linked through the –C₆H₁₀– spacers of the CDC anions, showing slightly open 1-D channels along the crystallographic c axis that accommodate the guest water molecules. Compound 2 exhibits a MOF consisting of wavy 2-D Sr–COO–H₂O nets linked by –CH₂CH₂C₆H₄CH₂CH₂– tethers, and the condensed structure appears to arise from conformational flexibility of the ligand spacer.     

Structural diversity of metal–organic frameworks via employment of azamacrocycles as a building block

Research on incorporating macrocycles into metal–organic frameworks (MOFs) has been performed intensively due to the opportunities afforded by merging a merit of macrocycles with MOF chemistry, which lead to novel hybrid materials for potential application. Among the numerous kinds of macrocycles, azamacrocycles are used as traditional and popular chelating agents in supramolecular coordination chemistry, because they are very easily functionalized by joining pendant arms and possess a strong propensity to complex metal cations, accounting for the amine functionalities. With this as background, many types of azamacrocyclic MOFs have been synthesized, granting compositionally and topologically new MOFs. The macrocyclic rings can serve as additional adsorption sites or catalytic sites, and the pendant arms on the macrocycles can also play versatile roles such as structure-directing agents, pore-decorating moieties, or rotatable molecular gates for opening/closing pores. In this review, we comprehensively discuss the syntheses, structures, and features of azamacrocyclic MOFs reported to date. Based on representative studies, advantages of these compounds are described, such as how the azamacrocycles increase the structural diversity and complexity of the MOFs and induce novel structural properties within the architectures.     

The application of Bimetallic metal–organic frameworks for antibiotics adsorption

Fe/Zr-base metal–organic frameworks(Fe/Zr-MOFs) were prepared using a solvothermal method from 1,3,5-phthalic acid (H₃BTC, 98 %) as the organic chain and ferrous heptahydrate (FeSO₄·7H₂O) and zirconium acetate Zr(CH₃COO)₄] as the metal ions. The resulting material was used to remove Doxycycline hydrochloride (DC). The experimental results showed that when the concentration of DC was 10 ppm and the mass of Zr/Fe-MOFs was 100 mg, the maximum removal rate after 5 h was 87.5 %. The results showed that the correlation coefficients (R²) of the pseudo-second-order kinetics model and Freundlich isotherm model of Zr/Fe-MOFs adsorption of DC were greater than 0.99, indicating good consistency. The results showed that the adsorption process of DC by Zr/Fe-MOFs was endothermic and spontaneous. Fe/Zr-MOFs had a high adsorption capacity for DC removal and good application prospects.     

Investigation of inorganic–organic hybrid materials containing polyoxometalate cluster anions and organic dye cations

Two new ionic-pair salts containing an organic dye cation, i.e. New Fuchsin or Pararosaniline cation, with Keggin-type POMs, [SiW₁₂O₄₀]^4? and [BW₁₂O₄₀]^6?, have been isolated under hydrothermal conditions. [(C₂₂H₂₄N₃)₄][SiW₁₂O₄₀] (1) and [(C₁₉H₁₈N₃)₆][BW₁₂O₄₀] (2) have been characterized by elemental analyses, FT-IR and single crystal X-ray crystallography. Both of these complexes have strong absorption in the visible-light range due to the involvement of the organic dye and both show weak fluorescence emission.     

An integrated supramolecular fungicide nanoplatform based on pH-sensitive metal–organic frameworks

The construction of an integrated nanoplatform with controlled fungicide delivery features in the specific microenvironment produced by fungal pathogens is a highly desirable strategy to improve the utilization of fungicides. Herein, we report a supramolecular fungicide delivery system based on benzimidazole-modified NH₂-MIL-101(Fe) metal–organic frameworks (B-MIL-101(Fe) MOFs) as carriers loaded with osthole (OS), and β-cyclodextrin (β-CD) as nanovalves to form β-CD@B-MIL-101(Fe)-OS. The nanoplatform can release the loaded OS for fungus control through self-degradation of the MOFs skeleton in an oxalic acid microenvironment produced by Botrytis cinerea. The experimental results exhibit that the constructed supramolecular fungicide delivery system could effectively inhibit mycelial growth and protect the tomatoes from infection by B. cinerea during the ripening stage. This strategy constructs a facile and integrated supramolecular drug delivery system for B. cinerea control and opens up a new avenue for the sustainable development of modern agriculture.     

Structural identification of multidimensional metal–organic frameworks using soft x-ray tomography

This paper mainly discusses the applicability of using soft x-ray tomography technology to examine the multidimensional structure of metal–organic frameworks, such as their core-shell and hollow framework, by visually observing their corresponding images in different energy bands by different excitation energies for different elements. The results show that the use of soft x-ray tomography (SXT) can effectively observe the distribution of metals in the structure, as well as observe the type of hollow pores the metal – organic framework (MOF) possesses. This pioneering evaluation of MOFs via SXT shows excellent performance in the structure identification of multidimensional metal–organic frameworks.