Sorption of methane, hydrogen and carbon dioxide on metal-organic framework, iron terephthalate (MOF-235)

Synthesis and utilization of mixed-metal (Zn/Cd) metal-organic frameworks for ultra-trace determination of diazinon and ethion via ion mobility spectrometry

A novel mixed-metal (Zn/Cd) metal-organic framework-based dispersive solid-phase microextraction (MM-MOFs-DSPME) method was developed for the efficient extraction of organophosphorus pesticides, diazinon and ethion, from various environmental matrices. The detection of the extracted analytes was performed using ion mobility spectrometry. The synthesized mixed-metal (Zn/Cd) MOF was characterized using a comprehensive array of analytical techniques: Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), and zeta potential measurement. This comprehensive characterization provided an in-depth understanding of the material's structural and functional properties. Key parameters influencing the efficiency of the dispersive solid-phase microextraction (DSPME) method were optimized, including pH, type of desorption solvent, buffer type and volume, sorbent amount, and adsorption and desorption time. Under these optimal conditions, the linear dynamic ranges obtained were 0.5 to 300 ng mL-1 for diazinon and 1.0 to 300 ng mL-1 for ethion, with limits of detection of 0.15 ng mL-1 and 0.29 ng mL-1, respectively. Preconcentration factors of 74% and 78%, with extraction recoveries of 98.4-104.2% and 96.6-103.4%, were achieved for diazinon and ethion, respectively. The relative standard deviations, calculated based on ten replicate measurements, yielded values of 3.8% for diazinon and 3.9% for ethion at a concentration of 10 ng mL-1, and 2.2% for diazinon, and 1.6% for ethion at a concentration of 150 ng mL-1, respectively. The developed method was successfully applied to the quantification of the target pesticides in soil, water, and apple samples.

Metal-Organic Frameworks (MOFs): Classification, Synthesis, Modification, and Biomedical Applications

Metal-organic frameworks (MOFs) are a new variety of solid crystalline porous functional materials. As an extension of inorganic porous materials, it has made important progress in preparation and application. MOFs are widely used in various fields such as gas adsorption storage, drug delivery, sensing, and biological imaging due to their high specific surface area, porosity, adjustable pore size, abundant active sites, and functional modification by introducing groups. In this paper, the types of MOFs are classified, and the synthesis methods and functional modification mechanisms of MOFs materials are summarized. Finally, the application prospects and challenges of metal-organic framework materials in the biomedical field are discussed, hoping to promote their application in multidisciplinary fields.

Data-Driven and Machine Learning to Screen Metal-Organic Frameworks for the Efficient Separation of Methane

With the rapid growth of the economy, people are increasingly reliant on energy sources. However, in recent years, the energy crisis has gradually intensified. As a clean energy source, methane has garnered widespread attention for its development and utilization. This study employed both large-scale computational screening and machine learning to investigate the adsorption and diffusion properties of thousands of metal-organic frameworks (MOFs) in six gas binary mixtures of CH4 (H2/CH4, N2/CH4, O2/CH4, CO2/CH4, H2S/CH4, He/CH4) for methane purification. Firstly, a univariate analysis was conducted to discuss the relationships between the performance indicators of adsorbents and their characteristic descriptors. Subsequently, four machine learning methods were utilized to predict the diffusivity/selectivity of gas, with the light gradient boosting machine (LGBM) algorithm emerging as the optimal one, yielding R2 values of 0.954 for the diffusivity and 0.931 for the selectivity. Furthermore, the LGBM algorithm was combined with the SHapley Additive exPlanation (SHAP) technique to quantitatively analyze the relative importance of each MOF descriptor, revealing that the pore limiting diameter (PLD) was the most critical structural descriptor affecting molecular diffusivity. Finally, for each system of CH4 mixture, three high-performance MOFs were identified, and the commonalities among high-performance MOFs were analyzed, leading to the proposals of three design principles involving changes only to the metal centers, organic linkers, or topological structures. Thus, this work reveals microscopic insights into the separation mechanisms of CH4 from different binary mixtures in MOFs.

Green synthesis of a hydrophobic metal-organic gel for the capture of trace odorous hexanal from humid air

The development of superhydrophobic adsorbents for the capture of trace volatile organic compounds (VOCs) from humid indoor air is still a challenge. Herein, we reported the formation of a granular zinc-based metal-organic gel, i.e., ZIF-412(gel) by optimizing the synthesis conditions. The thermally stable xerogel exhibited high surface area (1008 m²/g), hydrophobicity, and viscosity for self-depositing on the substrate such as non-woven fibers. Dynamic adsorption experiments under various humidity conditions demonstrated as-synthesized ZIF-412(gel) owned excellent VOC (hexanal) adsorption performance with adsorption capacity higher than commercial activated carbon and some water-stable MOFs including ZIF-8, ZIF-67, MIL-101(Cr) and ZIF-414. ZIF-412(gel) could be regenerated at temperature as low as 358 K without obvious loss in adsorption capacity. The adsorption mechanism of hexanal over ZIF-412(gel) is also simulated by Grand canonical Monte Carlo (GCMC).

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Experimental investigations into the irregular synthesis of iron(iii) terephthalate metal-organic frameworks MOF-235 and MIL-101

MOF-235(Fe) and MIL-101(Fe) are two well-studied metal-organic frameworks (MOFs) with dissimilar crystal structures and topologies. Previously reported syntheses of the former show that it has greatly varying surface areas, indicating a lack of phase purity of the products, i.e. the possible presence of both MOFs in the same sample. To find the reason for this, we have tested and modified the commonly used synthesis protocol of MOF-235(Fe), where a 3 : 5 molar ratio of iron(iii) ions and a terephthalic acid linker is heated in a 1 : 1 DMF : ethanol solvent at 80 °C for 24 h. Using XRD and BET surface area (SA_BET) measurements, we found that it is difficult to obtain a pure phase of MOF-235, as MIL-101 also appears to form during the solvothermal treatment. Comparison of the XRD peak height ratios of the synthesis products revealed a direct correlation between the MOF-235/MIL-101 content and surface area; more MOF-235 yields a lower surface area and vice versa. In general, using a larger (3 : 1) DMF : ethanol ratio than that reported in the literature and a stoichiometric (4 : 3) Fe(iii) : TPA ratio yields a nearly pure MOF-235 product (SA_BET = 295 m² g^-1, 67% yield). An optimized synthesis procedure was developed to obtain high-surface area MIL-101(Fe) (SA_BET > 2400 m² g^-1) in a large yield and at a previously unreported temperature (80 °C vs. previously used 110-150 °C). In situ X-ray scattering was utilized to investigate the crystallization of MOF-235 and MIL-101. At 80 °C, only MOF-235 formed and at 85 and 90 °C, only MIL-101 formed.

Design and evaluation of novel MOF-polymer core-shell composite as mixed-mode stationary phase for high performance liquid chromatography

A general method was developed for preparing a metal-organic framework-polymer composite coated silica core-shell stationary phase. Silica microspheres were comodified with metal-organic framework and polyvinylpyrrolidone rather than the in situ method of silica modification by original metal-organic framework particles. Metal-organic framework particles and polyvinylpyrrolidone on silica surface were beneficial to suppress silanol activity and enhance composite material tolerance, as well as increasing the water compatibility of the original metal-organic framework-based stationary phases. The stationary phase exhibited superior hydrophilic and hydrophobic performance in terms of separation for various analytes including seven alkaloids, six sulfonamides, five antibiotics, and five polycyclic aromatic hydrocarbons. Moreover, the composite material also showed excellent stability with the relative standard deviation of the retention time of 0.4 to 0.7%. The separation performance with real samples proved that the column has good practical application potential. In summary, the poposed method provides a general way for preparing metal-organic framework-polymer composite material and changed the current status of original metal-organic framework particles modified silica as a single mode chromatographic stationary phase.

Engineered Fe3 triangle for the rapid and selective removal of aromatic cationic pollutants: complexity is not a necessity

In this study, a low-cost oxo-bridged {Fe3} triangular cluster was constructed based on a benzoate ligand via slow evaporation. The cluster was thoroughly characterized by FTIR and UV-visible spectroscopy, TGA, and PXRD, and the exact structure was elucidated by single-crystal XRD. The formation of C-H⋯π and π-π interactions is responsible for the extra stability of {Fe3} clusters, which further enhances the dye adsorption property. The dye adsorption experiments performed on cationic [methylene blue (MB) and rhodamine-B (Rh-B)] as well as anionic [methyl orange (MO) and congo red (CR)] dyes revealed the ultimate selectivity of the present cluster towards the cationic ones. The {Fe3} cluster exclusively adsorbs the cationic dyes, i.e., MB and Rh-B even in the presence of anionic dyes, i.e., CR and MO. The extra stability, reusability and high efficiency of the {Fe3} molecular ensemble make it an attractive and fascinating material of importance. The kinetics analysis was evaluated employing different kinetics models. Furthermore, the plausible adsorption mechanism was also proposed, which suggests the interplay of cation-π and π-π interactions consolidating the efficient adsorption. Thus, the present work opens new doors for coordination chemists to further tune the structural features to modulate the adsorption/separation capacities of simple low-cost clusters for environmental protection for future efforts.

A new strategy for the preparation of core-shell MOF/Polymer composite material as the mixed-mode stationary phase for hydrophilic interaction/ reversed-phase chromatography

A facile method for efficient synthesis of core-shell composite material was proposed. In this method, the silica microspheres were co-modified with metal organic framework (MOF-235) and polyethylene glycol polymer (PEG) and used as mixed-mode stationary phase (MOF-235@PEG@silica) for high-performance liquid chromatography. Elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Brunauer-Emmett-Teller etc. methods were used to investigate the properties of the core-shell composite material. The MOF-235@PEG@silica stationary phase showed flexible selectivity for the separation of both hydrophilic and hydrophobic compounds especially for the separation of nine alkaloids, which showed superior hydrophilic separation performance than previous MOF-based composite stationary phases. Some factors including the pH of buffer salt, the ratio of organic phase and water phase in the mobile phase have been investigated, suggesting that the chromatographic retention mechanism of the column was a mixed mode of hydrophilic and reversed phase. The composite material also showed excellent chromatographic repeatability with the RSDs of the retention time found to be 0.2%-0.6% (n = 10) and the standard addition test in the actual sample proved that it can be used for practical sample analysis. In short, it provided a general way for preparing MOFs-based composites as mixed-mode chromatographic stationary phases, and changed the current status of MOF-based composite materials as single mode chromatographic stationary phases.

Fe-based metal-organic frameworks as heterogeneous catalysts for highly efficient degradation of wastewater in plasma/Fenton-like systems

Fe-based metal organic frameworks (Fe-MOFs) were successfully synthesized with the dielectric barrier discharge (DBD) plasma method and FeSO4·7H2O as the Fe precursor. Fe-MOFs were used as Fenton-like catalysts in DBD plasma/Fenton-like technology to treat wastewater, which addressed the issues with iron solubility. Since the valence state of iron will affect the catalytic performance, the Fe precursor FeSO4·7H2O was added to regulate the valence state and adjust the catalytic performance by improving the availability of active sites. The influences of discharge voltage, catalyst addition amount, H2O2 addition amount and pH on the degradation efficiency of methyl orange (MO) were systematically examined. Through free radical capture experiments, the reaction mechanism of the plasma/Fenton-like catalytic degradation process was deduced primarily as the coordinated oxidation process of hydroxyl radicals (·OH), photo-generated holes (h+) and superoxide radicals (·O2 -). The reusability experiments proved that the catalyst was stable and reusable. The possible degradation pathways were proposed based on the identification of intermediate products generated in the degradation process by liquid chromatography-mass spectrometry (LC-MS) analyses.

Some aspects of the formation and structural features of low nuclearity heterometallic carboxylates

Heterometallic carboxylate complexes are of paramount interest in pure and applied coordination chemistry. Despite that plurality of such type compounds have been published to date, synthetic aspects of their chemistry often remain in the shadow of intriguing physical properties manifesting by these species. Present review summarizes reliable data on direct synthesis of low nuclearity molecular compounds as well as coordination polymers on their base with carboxylate-bridged {M2Mg} (M = Co2+, Ni2+, Cd2+), {M2Li2} (M = Co2+, Ni2+, Zn2+, VO2+), {M2Ln2} and {M2Ln} (M = Cu2+, Zn2+, Co2+) metal cores. Structural features and stabilization factors are considered and principal outcomes are confirmed by quantum-chemical calculations. Particular attention is paid to consideration of ligand-exchange reactions that allow controllable modification of heterometallic metal core under mild conditions giving diverse molecular complexes with modified ligand environment or Metal-Organic Frameworks with permanent porosity.

Engineering Metal-Organic Framework Catalysts for C-C and C-X Coupling Reactions: Advances in Reticular Approaches from 2014-2018

Metal-organic frameworks (MOFs) are a class of crystalline porous materials that have been actively used for several industrial and synthetic applications. MOFs are spatially and geometrically extrapolated coordination polymers with intriguing properties such as tunable porosity and dimensionality. In terms of their catalytic efficiency, MOFs combine the easy recoverability of heterogeneous catalysts with the increased selectivity of biological catalysts. It is therefore not surprising that a lot of work on optimizing MOF catalysts for organic transformations has been carried out over the past decade. In this review, recent developments in MOF catalysis are summarized, with special attention being paid to C-C, C-N, and C-O coupling reactions. The influence of pore size, pore environment, and load on catalytic activity is described. Post-synthetic stabilization techniques and host-guest interactions in caged MOF scaffolds are detailed. Mechanistic aspects pertaining to the use of MOFs in asymmetric heterogeneous catalysis are highlighted and categorized.

A "bottle-around-ship" like method synthesized yolk-shell Ag3PO4@MIL-53(Fe) Z-scheme photocatalysts for enhanced tetracycline removal

A novel yolk-shell Ag₃PO₄@MIL-53(Fe) Z-scheme photocatalyst was fabricated via a "bottle-around-ship" like method. Experiments on the treatment of tetracycline upon visible light irradiation showed that the as-prepared photocatalyst possessed excellent photocatalytic performance. Experimental results showed that tetracycline removal efficiency of the yolk-shell Ag₃PO₄@MIL-53(Fe) Z-scheme photocatalyst was almost 3 times higher than that of MIL-53(Fe). The enhanced photocatalytic performance of Ag₃PO₄@MIL-53(Fe) nanocomposite could be contributed to its higher surface area, better absorption capability, and greater charge separation efficiency. In addition, the H₂O₂ concentration detection results for Ag₃PO₄ (154 μmol/L) and Ag₃PO₄@MIL-53(Fe) (52 μmol/L) indicated that a big part of generated H₂O₂ on the Ag₃PO₄ core would be quickly decomposed by the MIL-53(Fe) shell and generated more reactive species through the photo-Fenton-like reaction, which is beneficial for the improvement of photocatalytic performance. This is a promising approach to fabricate yolk-shell structure photocatalyst and a different aspect to design multiple semiconductor composites heterojunction for environmental remediation.

Fe-MOFs prepared with the DBD plasma method for efficient Fenton catalysis

Fe-MOFs were successfully synthesized with the dielectric barrier discharge (DBD) plasma method, and applied for degradation of methyl orange by the Fenton process. Fe-MOFs were characterized by XRD, SEM, EDS, BET and FT-IR. A systematic study was carried out to optimize the synthesis conditions, taking into account the Fenton capacity performance for degradation of methyl orange. The optimal synthesis conditions were a discharge time of 100 min, discharge voltage of 18 kV, reactant concentration of 14 g L⁻¹ and reactant mass ratio (TA : FeCl₃·6H₂O) of 1 : 5, with influence on the crystallization, morphologies and particle size. The degradation rate of methyl orange could reach 85% within 40 min with the MO concentration of 50 mg L⁻¹, Fe-MOF dosage of 0.12 g L⁻¹, pH of 5 and H₂O₂ at 1 mL L⁻¹. Meanwhile, the Fenton catalytic process was conducted covering a range of catalyst concentrations, initial MO concentrations, pH and H₂O₂ amounts. Higher catalyst concentration, lower MO initial concentration, pH of 3 and H₂O₂ amount of 1 mL L⁻¹ were conducive to the degradation efficiency.

Fe-MOFs were successfully synthesized with the dielectric barrier discharge (DBD) plasma method, and applied for degradation of methyl orange by the Fenton process.

Synthesis of magnetic metal–organic framework composites, Fe3O4-NH2@MOF-235, for the magnetic solid-phase extraction of benzoylurea insecticides from honey, fruit juice and tap water samples

Herein, a novel, fusiform-like magnetic metal–organic framework material (Fe₃O₄-NH₂@MOF-235) was fabricated by a facile two-step solvothermal approach.

Iron-based metal–organic framework as an effective sorbent for the rapid and efficient removal of illegal dyes

A metal organic framework (MOF-235) was fabricated by a simple solvothermal method and utilized as an adsorbent for the selective removal of electron-rich conjugated dyes.

Direct arylation of benzoazoles with aldehydes utilizing metal–organic framework Fe3O(BDC)3 as a recyclable heterogeneous catalyst

Aryl-substituted azoles were effectively produced via the direct arylation of azoles with benzaldehydes under metal–organic framework catalysis.

Facile synthesis of MOF 235 and its superior photocatalytic capability under visible light irradiation

MOF 235 was fabricated by a facile microwave-assisted method. It showed excellent visible-light photocatalytic activity in the presence of H₂O₂. It displays a high chemical stability for repeated RhB degradation reactions.

Adsorption behavior of one-dimensional coordination polymers [Cu(bipy)X]n (X = 2Cl− and SO42−) toward acid orange 7 and methyl orange

A kind of one-dimensional coordination polymer, [Cu(bipy)X]_n (X = 2Cl⁻ or SO₄²⁻), was prepared by Cu²⁺ and 4,4′-bipyridine (bipy) through a facile method, and used as the adsorbent for removal of acid orange 7 (AO7) and methyl orange (MO) from water.