Adsorption of several gases on flexible metal organic framework [Cu(dhbc)2(4,4'-bpy)]·H2O

The adsorption of ten gases on the flexible metal organic framework material [Cu(dhbc)(2)(4,4'-bpy)]·H(2)O (Cu(db)) has been measured over a wide range of temperatures and pressures. The gate opening condition and driving force behind gate adsorption for Cu(db) were discussed by examining the adsorption isotherms. The adsorption isotherms for each adsorbate can be generalized to a characteristic curve using the adsorption potential energy (ε) and the adsorption volume. The adsorption potential (ε(gate)) at gate opening is almost constant over a wide range of temperatures; thus, the gate pressure at a desired temperature can be deduced using the ε(gate) evaluated from one adsorption isotherm. The gate opening capacity of the gases was arranged in the order: CO(2)≒N(2)O>C(2)H(4)≒Xe>CH(4)>CO>O(2)>Ar≒N(2)>H(2), which is governed by the interaction energy between the outer surface of Cu(db) and the adsorbate. It is suggested that the gate effect is brought about when the integral interaction energy of adsorbates with the Cu(db) surface exceeds a defined limit correlating with the π-π stacking energy of Cu(db) layers.     

Thermal decomposition of inclusion compounds on the base of the metal–organic framework [Zn4(dmf)(ur)2(ndc)4]

Inclusion compounds based on metal–organic frameworks (MOFs) have promising practical applications in gas storage, the separation, and fine purification of substances, and also in catalysis. These MOFs are crystalline compounds consisting of metal ions coordinated by bridging organic ligands with the formation of porous structures. We study the kinetic stability of two inclusion compounds on the base of the new framework: [Zn₄(dmf)(ur)₂(ndc)₄]·6C₆H₆ and [Zn₄(dmf)(ur)₂(ndc)₄]·5C₆H₅CH₃ (ndc^2? = 2,6-naphtalenedicarboxylate, ur = hexamethylentetramin, dmf = N,N′-dimethylformamide). The inclusion compound with benzene is more stable than the compound with toluene. The reduced stability of the toluene compound may be connected with the toluene molecule’s shape: the C₆H₅CH₃ molecule is more bulky and asymmetric than the C₆H₆ molecule; the MOF matrix structure must be greatly distorted to include the toluene molecules and the compound stability decreases.     

Zn–porphyrin metal–organic framework–based photoelectrochemical enzymatic biosensor for hypoxanthine

Journal of Solid State Electrochemistry - The exploitation of metal–organic frameworks as photoactive materials for photoelectrochemical (PEC) sensing is of great importance because of their...     

Adsorption desulfurization of model gasoline by metal–organic framework Ni_3(BTC)_2

This work presented the synthesis of Ni-based metal-organic framework material with a paddle-wheel structure Ni_3(BTC)_2(Ni-BTC) and its application in thiophene(TP) adsorption from gasoline distillate by batch method. Adsorption isotherms of TP, cyclohexene, and toluene in cyclohexane onto Ni-BTC were conducted at 298–308 K to interpret the different effect of cyclohexene and toluene on TP adsorption.The results showed that, compared with cyclohexene, toluene addition in model gasoline led to a more evident decline in sulfur capacity of Ni-BTC, which is opposite to isostructural HKUST-1. The adsorption isotherms of TP, cyclohexene and toluene fit Langmuir model, S-type model and Temkin model well, respectively, indicating that the adsorption mechanisms of TP and the two competitors are different from one another. The adsorption capacities on Ni-BTC followed the order of cyclohexene toluene TP at the same equilibrium concentrations, implying the order of the adsorption affinities, which is in good agreement with the different extent of influence by the two competitors. The enthalpy of TP adsorption on Ni-BTC was estimated to be-80.01 kJ/mol, almost twice that on HKUST-1. The poor reusability of Ni-BTC in batch experiment, which is owing to its sensitivity to the air, can be prevented from regenerating used Ni-BTC in fixed-bed reactor by N_2 flow. The difference between Ni-BTC and HKUST-1 in maximum adsorption capacity(q_0), H of TP adsorption, and stability demonstrates that the central metal in isostructural MOFs plays a key role in adjusting the desulfurization performance, which may open up a potential avenue for the development of MOF-based adsorbents with superior desulfurization performance.     

An updated review of metal–organic framework materials in photo(electro)catalytic applications: From CO2 reduction to wastewater treatments

This review summarizes recent advances in the development of metal–organic framework (MOF) materials, focusing on their photocatalytic and photoelectrocatalytic activities for different applications, such as CO₂ reduction, water splitting, elimination of inorganic contaminants, and degradation of organic pollutants. In each section, the first applications described focus on the photocatalysts developed using MOF materials. Meanwhile, the latest are centered on photoelectrode applications using these materials. The last advances in the synthesis process are discussed in terms of improvement in electron transfer and charge separation, which enhance the activity of the photo (electro)catalysts. Finally, some insights about the upcoming applications of MOF materials are provided.     

NiFe2O4@SiO2@Cu3(BTC)2 nanocomposite as a magnetic metal–organic framework

A new magnetic metal–organic framework (MOF), namely, NiFe₂O₄@SiO₂@Cu₃(BTC)₂, was synthesized via an in situ method using Fe(NO₃)₃, Ni(NO₃)₂, CuN₂O₆, TEOS, (3-aminopropyl)triethoxysilane, and benzene-1,3,5-tricarboxylic acid. Three different samples were fabricated according to a formula; xNiFe₂O₄@(100 − x)SiO₂@Cu₃(BTC)₂, where x = 10, 30, and 50. The integration of the intrinsic characteristic of Cu₃(BTC)₂ as an MOF with strong magnetic properties of NiFe₂O₄ could lead to an exquisite material with specific behaviors. X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and simulated thermal analyzer (STA) were utilized to characterize the mentioned samples. Results approved that the synthesized compounds were composed of SiO₂ and Cu-MOF and NiFe₂O₄ crystalline phases with rod-like morphology. The similarity between the morphology of the synthesized samples and Cu-MOF approved that an appropriate fabrication method has been selected. This fact led to observe mesoporous composites with 38–90 m² g⁻¹ specific surface area. PL spectroscopy confirmed the near bandgap emission, ligand-to-metal charge transfer, and metal-to-ligand charge transfer. Although all the samples had magnetic hysteresis, the highest magnetization was seen in the 50NiFe₂O₄@SiO₂@Cu₃(BTC)₂ sample. This composite compound with a magnetization value of 2 emu g⁻¹ at 8000 Oe and a specific surface area of 90 m² g⁻¹ could be classified as a magnetic MOF (MMOF). STA results suggested that 400°C is the highest operating temperature for this compound.     

Exceptional thermal stability and thermodynamic properties of lithium based metal–organic framework

A three-dimensional lithium-based metal–organic framework Li₂(2,6-NDC) (2,6-NDC = 2,6-naphthalene dicarboxylate) has been synthesized solvothermally and characterized by X-ray powder diffraction, elemental analysis, FT-IR spectroscopy, thermogravimetry and mass spectrometer analysis (TG–MS). The framework has exceptional stability and is stable to 863 K. The thermal decomposition characteristic of this compound was investigated through the TG–MS from 293 to 1250 K. The molar heat capacity of the compound was measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 195 to 670 K for the first time. The thermodynamic parameters such as entropy and enthalpy versus 298.15 K based on the above molar heat capacity were calculated.     

Chemical principles underpinning the performance of the metal–organic framework HKUST-1

A common feature of multi-functional metal–organic frameworks is a metal dimer in the form of a paddlewheel, as found in the structure of Cu₃(btc)₂ (HKUST-1). The HKUST-1 framework demonstrates exceptional gas storage, sensing and separation, catalytic activity and, in recent studies, unprecedented ionic and electrical conductivity. These results are a promising step towards the real-world application of metal–organic materials. In this perspective, we discuss progress in the understanding of the electronic, magnetic and physical properties of HKUST-1, representative of the larger family of Cu···Cu containing metal–organic frameworks. We highlight the chemical interactions that give rise to its favourable properties, and which make this material well suited to a range of technological applications. From this analysis, we postulate key design principles for tailoring novel high-performance hybrid frameworks.     

Cu(I) metal organic framework catalyzed C–C and C–N coupling reactions

DABCO (1,4-diazabicyclo[2.2.2]octane) based Cu(I) metal organic framework (here after represented as Cu(I)-MOF) catalyzed Sonogashira cross-coupling reaction of iodobenzene and phenylacetylene was conducted smoothly to afford diphenylacetylene in excellent yield under N₂ atmosphere. For comparative study, piperidine based Cu(I) clusters were also investigated. Among these catalysts, Cu(I)-MOF exhibited higher activity with good selectivity for the C–C cross-coupled product. Cu(I) catalysts investigated in this study exhibited similar activity in the C–C homo-coupling reaction of phenylacetylene in O₂ atmosphere. Application of these catalysts was extended in the C–N coupling reactions between phenylboronic acid and aromatic/aliphatic/heterocyclic amines. Cu(I)-MOF can be readily recovered from the reaction mixture and reused for several cycles without loss in the catalytic activity.     

Conversion of carbon dioxide to propionaldehyde over cobalt and rhodium nanoparticles supported on MIL-53 (Al) metal–organic framework

The two-step conversion of carbon dioxide to propionic acid and propionaldehyde has been studied in the presence of novel catalysts, cobalt and rhodium nanoparticles supported on MIL-53(Al) microporous metal–organic framework. The first step is hydrogenation of carbon dioxide with formation of synthesis gas over cobalt-containing catalyst Co/MIL-53(Al) (500°C, 1 atm), and the second step is continuous (without separation) Rh/MIL-53 (Al)-catalyzed hydroformylation of ethylene with the synthesis gas formed in the first step.     

Zeolitic imidazolate framework [Zn(2)(IM)(4)·(DMF)] for UV-white light-emitting diodes

A polymorph of a [Zn(2)(IM)(4)·(DMF)] (IM: imidazolate; DMF: dimethyl formamide) framework was synthesized using a DMF template. The topology of a ZnN(4) framework is similar to that of zeolites with a chain of connected SiO(4) tetrahedra. This polymorph has a zeolite-like structure and a wave shape topology in the [010] direction. The main chain is connected to an imidazolate ligand. The structure has excellent chemical and thermal stability. This framework also exhibits broad range near-UV excitation from 350 nm to 430 nm and broadened photoluminescence emission at 445 nm. It has great potential as a phosphor in applications of near-UV or UV white light-emitting diodes.     

Solid-state NMR studies of the acidity of functionalized metal–organic framework UiO-66 materials

The acid strength of metal–organic frameworks plays a key role in their catalytic performance such as activity and selectivity during catalytic reactions. Solid-state nuclear magnetic resonance in combination with probe molecules including 2-¹³C-acetone and pyridine-d₅ was employed to characterize the acid strength of UiO-66-X (X = -H, -2COOH, -SO₃H). It was found that after introduction of the functional groups, the acid strength of UiO-66-2COOH and UiO-66-SO₃H is considerably enhanced compared with that of parent UiO-66, with that of the former being similar to that of zeolite H-ZSM-5, and with that of the latter being slightly stronger than that of the former. Even though the acid density can efficiently be modified through changing the relative ratio in multivariate functionalized UiO-66-X, no significant alternation for the acid strength could be discerned in the MTV-UiO-66-X compared with acidic same-link counterpart. Theoretical calculations were employed to further confirm the acid strength of UiO-66-SO₃H and UiO-66-2COOH.     

Construction of visible-light-responsive metal–organic framework with pillared structure for dye degradation and Cr(VI) reduction

A water-stable mixed-linker metal–organic framework (MOF) was rationally synthesized using a controllable pillared-layer method. The prepared Co(II)–MOF shows wide-range absorption in the visible light region due to the incorporation of highly conjugated anthracene-based bipyridine ligand. Experiments suggest that the MOF is highly efficient for the photoreduction of toxic Cr(VI) ions in water under visible light. Important issues affecting photocatalytic performance, such as the influence of pH and the control of electron–hole separation by scavenger, were carefully examined. Beyond Cr(VI) ions, we also explored the photocatalytic degradation performance of the MOF using a persistent azo dye as a model substrate, where H₂O₂-involved advanced oxidation process was applied. Control experiments suggest that the introduction of environmentally benign H₂O₂ significantly enhances the degradation performance due to the generation of reactive hydroxyl radicals. The study not only demonstrates the great feasibility of the preparation of a new MOF photocatalyst through a controllable pillared-layer method, but also reveals that rational functionalization of ligand in the MOF is convenient for achieving desirable applications.     

Shaping metal–organic framework (MOF) powder materials for CO2 capture applications—a thermogravimetric study

Journal of Thermal Analysis and Calorimetry - The paper presents the effect of the tabletting pressure and time on the chemical structure and crystallinity of the CuBTC and MIL-53(Al)...     

Solvothermal synthesis and structural characterization of a three-dimensional metal–organic polymer [NaZn(1,2,4-BTC)] (1,2,4-BTC=1,2,4-benzenetricarboxylate)

A new three-dimensional metal–organic polymer, [NaZn(1,2,4-BTC)] (where 1,2,4-BTC=1,2,4-benzenetricarboxylate), has been prepared under solvothermal conditions and characterized by single crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2₁/c, with cell parameters: a=9.7706(4) Å, b=12.3549(5) Å, c=6.8897(3) Å, β=91.640(2)°, V=831.35(6) Å³ and Z=4. In the three-dimensional structure of the compound, each Zn atom is five-coordinated in distorted trigonal bipyramidal geometry, while the sixfold coordination of Na corresponds to a slightly distorted triangular prism. The organic ligand, 1,2,4-BTC, shows a novel and unprecedented coordination mode: 11 bonds to 10 metals with each carboxylate function exhibiting different linkages. It remains stable when desolvated and when heated up to 410 °C.     

Heterogeneous oxidation of alcohols with hydrogen peroxide catalyzed by polyoxometalate metal–organic framework

HSiW-MOF, PMo-MOF, HPMo-MOF and PW-MOF were synthesized and characterized by elemental analysis, UV–Vis, FT-IR, cyclic voltammetry and XRD. These compounds were used as catalyst for the selective oxidation of alcohols by hydrogen peroxide. Within them, PW-MOF showed a higher catalytic activity compared to other catalysts in a similar reaction condition. Therefore, PW-MOF catalyst system was successfully used for the selective oxidation of the benzylic, linear and secondary alcohols to the corresponding aldehydes and ketones. Also, allylic alcohols were converted to the corresponding aldehydes with high conversion and significant selectivity. Moreover, PW-MOF was stable to leaching, behaved as true heterogeneous catalysts, easily recovered by filtration, and reused four times with the preserve of the catalytic performance.