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.     

A two-dimensional microporous metal–organic framework for highly selective adsorption of carbon dioxide and acetylene

Solvothermal reaction of 3-aminoisonicotinic acid(Haina) and Cu(NO_3)_2·2.5H_2O gave a novel twodimensional(2D) microporous metal–organic framework, [Cu(aina)_2(DMF)]·DMF(1, DMF = N,N-dimethylformamide). Single-crystal X-ray crystallographic study of compound 1 revealed that Cu(II)ions are linked by ainaàligands forming square grid-like layers, which stack together via multiple hydrogen bonding interactions. The solvent-free framework of 1a displayed considerable porosity(void = 46.5%) with one-dimensional(1D) open channels(4.7 ? ? 4.8 ?) functionalized by amino groups.Gas sorption measurements of 1 revealed selective carbon dioxide(CO_2) and acetylene(C_2H_2) adsorption over methane(CH_4) and nitrogen(N_2) at ambient temperature.     

ZrIV metal–organic framework based on terephthalic acid and 1,10-phenanthroline as an adsorbent for solid phase extraction of tetracycline antibiotics

Zr^IV metal–organic framework based on terephthalic acid and 1,10-phenanthroline has been prepared by solvothermal method. The product represents an effective adsorbent for solid phase extraction of tetracycline antibiotics from aqueous media.     

Copper-based metal–organic framework decorated by CuO hair-like nanostructures: Electrocatalyst for oxygen evolution reaction

We report a Cu-based metal–organic framework (MOF) decorated by CuO nanostructures as an efficient catalyst for the oxygen evolution reaction (OER). MIL-53(Cu) was synthesized by a hydrothermal approach using 1,4-bezenedicarboxylic acid as organic precursor and further annealed at 300°C to form CuO nanostructures on its surface. The produced electrocatalyst, CuO@MIL-53(Cu), was characterized using various techniques. Under alkaline conditions, the developed electrocatalyst exhibited an overpotential of 801 and 336 mV versus RHE at 10 and 1 mA cm⁻², respectively. The reproducibility of the catalytic performance was validated using several electrodes. It was confirmed that the CuO hair-like nanostructures grown on MIL-53(Cu) using thermal treatment exhibit high OER activity, good kinetics and durability. CuO@MIL-53(Cu) is an economic noble-metal-free OER electrocatalyst. It has potential for application as anode material for sustainable energy technologies like batteries, fuel cells and water electrolysis.     

Introducing lanthanide metal–organic framework and perovskite onto pulp fibers for fluorescent anti-counterfeiting and encryption

The research of anti-counterfeiting and encryption has always been a subject of universal concern all over the world. Herein, lanthanide metal–organic framework (Eu-MOF) and CH₃NH₃PbBr₃ (MAPbBr₃) perovskite were introduced onto pulp fibers (PFs) to prepare fluorescent anti-counterfeiting and encryption papers. Eu-MOF@PFs paper emitted red fluorescence at 254 nm UV excitation. The optimum preparation conditions of Eu-MOF@PFs were 2.5 mmol of Eu(NO₃)₃, 4 h of reaction time and room temperature. When MABr ink was written on Pb/Eu-MOF@PFs paper, the green fluorescent handwriting and red fluorescent paper were observed under 365 nm and 254 nm UV excitation, respectively. The appropriate addition amount of lead nitrate was 0.6 mmol. Pb/Eu-MOF@PFs paper was immersed in MABr solution to prepare MAPbBr₃@Pb/Eu-MOF@PFs paper. Under 254 nm and 365 nm UV irradiations, MAPbBr₃@Pb/Eu-MOF@PFs paper emitted red-green double fluorescence and the quantum yields of which were 3.11% and 2.48%, respectively. The crystal structure of MAPbBr₃ was easily destroyed by polar solution, which realized on/off switching of the luminescence signal for multistage information encryption. The above paper-based fluorescence materials were potential for advanced anti-counterfeiting and encryption applications.

     

A surface architectured metal–organic framework for targeting delivery: Suppresses cancer growth and metastasis

Porous nanosized metal–organic frameworks (MOFs) are becoming possible candidates as drug-delivery nanocarriers for their versatile porous structures and large loadings of drugs. However, controlling synthesis of MOFs with uniform morphology, good biocompatibility and targeting drug delivery is still a challenge, which greatly limits their clinical applications. Herein, a multifunctional nano-sized drug-delivery material MIL-101(Fe)@FU@FA with a uniform particle size about 500 nm was successfully synthesized for targeting therapeutic purposes. The targeting reagent folic acid (FA) molecules are connected on the surface of 5-FU-loaded nanoparticle MIL-101(Fe)-NH₂ by a covalent conjugation. Cytotoxicity tests showed that the synthesized nanoparticles are biocompatible and can significantly inhibit cell proliferation on SMMC-7721 cells compared with MIL-101(Fe)@FU and free 5-FU. The cell metastasis and invasion experiments proved that the nanoparticles had a good anti-metastasis ability to tumor cells. Mechanistically, MIL-101(Fe)@FU@FA induces apoptosis of SMMC-7721 cells and block cell cycle progression in the G2/M phase. Taken together, the drug-loaded nanoparticles MIL-101(Fe)@FU@FA have the effect of targeting and sustained release to achieve the therapeutic effect.     

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.     

A multi-responsive luminescent sensor towards Fe_(3+) and acetone based on a Cd-containing metal–organic framework

A Cd-containing metal–organic framework(Cd L), formula as {[Cd_3(L)_2(H_2O)_6] 1.5DMF}, has been synthesized under solvothermal condition by the reaction of 4,40,400-(methylsilanetriyl)tribenzoic acid(H_3L) and Cd~(2+)ion. Single-crystal X-ray diffraction reveals that Cd L displays a three-dimensional framework with 2-fold interpenetration and DMF molecules locate in the void space of the channels. A topological analysis of the framework indicates Cd L is a 3,4-connected pto net. The photoluminescence properties of Cd L are systematically studied in detail. Impressively, Cd L shows excellent detection performance towards Fe~(3+)ion and acetone in the sensing experiments, which undoubtedly demonstrates the great potential of Cd Lasa highly selective multi-responsive luminescent sensor for the detection of organic solvents and metal ions.     

Copper-doped sulfonic acid-functionalized MIL-101(Cr) metal–organic framework for efficient aerobic oxidation reactions

A series of Cr-based metal–organic framework MIL-101-SO₃H bearing sulfonic acid functional groups were utilized for the immobilization of catalytically active copper species via a post-synthetic metalation method. The novel materials were fully characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), the Brunauer–Emmett–Teller method, and thermogravimetric analysis. XPS and the EDX element map both suggested that Cu²⁺ is coordinately bonded to the MIL-101-SO₃H, which forms the MIL-101-SO₃@Cu structure. The obtained copper-doped MIL-101-SO₃@Cu-1, MIL-101-SO₃@Cu-2, and MIL-101-SO₃@Cu-3 catalysts were utilized in the selective oxidation of alcohols and epoxidation of olefins using molecular oxygen as an oxidant. Catalytic aerobic oxidation optimization showed that MIL-101-SO₃@Cu-1 is the optimal catalyst and it can be reused ten times without compromising the yield and selectivity.     

Embedding antimony nanoparticles into metal–organic framework derived TiO2@carbon nanotablets for high-performance sodium storage

Titanium dioxide (TiO₂) has been widely investigated as a candidate for anode materials of sodium-ion batteries (SIBs) due to its low cost and high abundance. However, the intrinsic sluggish ion/electron transfer rate hinders its practical applications for high energy density storage devices. In contrast, antimony (Sb) shows high specific theoretical capacity (660 mAh/g) as well as excellent electron conductivity, but the large volume variation upon cycling usually leads to severe capacity fading. Herein, with the objective of achieving high-performance sodium storage anode materials, TiO₂@C-Sb nanotablets with a small amount of Sb content (6.4 wt%) are developed through calcination Ti-metal–organic framework (MIL-125) derived TiO₂@C/SbCl₃ mixture under reductive atmosphere. Benefitting from the synergetic effect of well-dispersed Sb nanoparticles as well as robust porous TiO₂@C substrate, the TiO₂@C-Sb shows enhanced electron/ion transfer rate and predominantly pseudocapacitive sodium storage behavior, delivering a reversible capacity of 219 mAh/g at 0.5 A/g even after 1000 cycles. More significantly, this method may be commonly used to incorporate other alloy-based high-theoretical materials into MIL-125-derived TiO₂@C, which is promising for developing high-energy-density TiO₂-based energy storage devices.     

Crystalline γ-cyclodextrin metal organic framework nano-containers for encapsulation of benzaldehyde and their host–guest interactions

Journal of Inclusion Phenomena and Macrocyclic Chemistry - The nano-porous crystals of γ-cyclodextrin MOF (CDMOF) were synthesized and encapsulated with benzaldehyde. The host–guest...     

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.     

Electrochemical sensor based on super-magnetic metal–organic framework@molecularly imprinted polymer for Sarcosine detection in urine

Accurate determination of Sarcosine (SAR) in urine with high sensitivity and selectivity is important, because it was recently recommended as a prospective biomarker for prostate cancer (PCa) and significant for the early identification of PCa. In this study, an electrochemical sensor based on Fe₃O₄ incorporated metal–organic frameworks (MOFs) @molecularly imprinted polymer (MIP) was constructed for SAR detection. Magnetic Fe₃O₄ nanoparticles embedded zeolitic imidazolate framework-8 (ZIF-8) was used as the support of MIP. MIP provides specific recognition sites for template molecules SAR and MOFs increase the rate of mass transfer and adsorption capacity due to the porous structure. The synthesized super-magnetic Fe₃O₄@ZIF-8@MIP was self-assembled onto an Au electrode in magnetic field and used as the sensing unit of electrochemical sensor. Cyclic voltammetry was used to monitor the electrochemical behavior, and the binding of SAR resulted in a reduction in the measured current. The results revealed a wide linear range from 1 to 100 pM towards trace SAR determination, with extremely low limit of detection down to 0.4 pM. In conclusion, the Fe₃O₄@ZIF-8@MIP based sensor provides a selective, sensitive, and convenient method for SAR diagnosis and other cancer marker detection.     

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.     

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.     

Sorption of benzene vapors to flexible metal–organic framework [Zn2(bdc)2(dabco)]

The isotherms of benzene sorption by the metal–organic coordination polymer [Zn₂(bdc)₂(dabco)] were studied within the temperature range 25–90 °C at pressures up to 75 torr. The maximal benzene content in [Zn₂(bdc)₂(dabco)] at room temperature was demonstrated to correspond to the composition [Zn₂(bdc)₂(dabco)]·3.8C₆H₆. It was established that the process of benzene desorption from the substance under investigation occurs in three stages. (1) Evaporation of benzene from the phase of variable composition (phase C) with compression and distortion of the unit cell (the composition of the phase C varies from [Zn₂(bdc)₂(dabco)]·3.8C₆H₆ to [Zn₂(bdc)₂(dabco)]·3.2C₆H₆). (2) The transformation of the phase C into phase P. The phase P has the same unit cell geometry as that for the empty framework. The maximal benzene content is [Zn₂(bdc)₂(dabco)]·1.0C₆H₆. (3) Benzene evaporation from the phase P of variable composition. We studied the temperature dependences of the equilibrium vapor pressure of benzene for the samples with compositions [Zn₂(bdc)₂(dabco)]·3.0(3)C₆H₆ and [Zn₂(bdc)₂(dabco)]·2.0(3)C₆H₆ within the temperature range 290–370 K. The thermodynamic parameters of benzene vaporization were determined for the latter compound ( $ \Updelta {\text{H}}_{{{\text{av}} .}}^{o} = 49\left( 1 \right) \,{\text{kJ }}\left( {{\text{moleC}}_{6} {\text{H}}_{6} } \right)^{ - 1} $ ; $ \Updelta {\text{S}}_{{{\text{av}} .}}^{^\circ } = 100\left( 3 \right)\, {\text{J}}\left( {{\text{moleC}}_{6} {\text{H}}_{6} {\text{K}}} \right)^{ - 1} $ ; $ \Updelta {\text{G}}_{298}^{^\circ } = 19.0\left( 2 \right)\, {\text{kJ}}\left( {{\text{moleC}}_{6} {\text{H}}_{6} } \right)^{ - 1} $ ).     

Determination of diuretics in human urine using HPLC coupled with magnetic solid-phase extraction based on a metal–organic framework

Magnetic solid-phase extraction (MSPE) employing a metal–organic framework (Fe₃O₄@UiO-66-OH) combined with high-performance liquid chromatography was developed for the determination of trace diuretics in urine. The structure and properties of Fe₃O₄@UiO-66-OH were investigated using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and vibrating sample magnetometry. Magnetic solid-phase extraction conditions, such as adsorbent amount and solution pH, were optimized using response surface methodology. Under the optimal conditions, the method resulted in excellent linearity with a high correlation coefficient (r > 0.99), satisfactory intraday repeatability (1.78–2.99%), low limits of detection (0.08–0.23 ng/ml), and good recoveries in urine samples (between 93.5 and 103%). Fe₃O₄@UiO-66-OH based on MSPE is a novel pretreatment technique for the detection of trace diuretics in urine.     

Palladium supported on metal–organic framework as a catalyst for the hydrogenation of nitroarenes under mild conditions

Sustainable development demands an environmentally friendly and efficient method for the hydrogenation of organic molecules, including the hydrogenation of functionalized nitroarenes. In this study, a highly active and selective metal–organic framework-supported palladium catalyst was prepared for the catalytic hydrogenation of nitroarenes. High selectivity (>99%) and excellent yield (98%) of aniline were realized after 2 hours in ethanol under hydrogen (1 atm) at room temperature. The reductions were successfully carried out in the presence of a wide range of other reducible functional groups. More importantly, the catalyst was very stable without the loss of its catalytic activity after five cycles.     

CuO/NiOx thin film–based photocathodes for photoelectrochemical water splitting

Journal of Solid State Electrochemistry - Copper oxides are considered to be very promising materials for promoting a hydrogen evolution reaction (HER). However, some CuO features, such as the...     

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.