Transient intermediate in the formation of an amorphous metal-organic framework

Amorphous metal-organic frameworks are rarely formed via direct synthesis. Our limited understanding of their atomic assembly in solution prevents full exploitation of their unique structural complexity. Here, we use in situ synchrotron X-ray absorption spectroscopy with sub-second time resolution to probe the formation of the amorphous Fe-BTC framework. Using a combination of spectral fingerprinting, linear combination analysis, and principal component analysis coupled with kinetic analyses, we reveal a multi-stage formation mechanism that, crucially, proceeds via the generation of a transient intermediate species.

Metal-organic frameworks (MOFs) as effectual diagnostic and therapeutic tools for cancer

Metal-organic frameworks (MOFs) are a class of multifunctional organometallic compounds that include metal ions combined with assorted organic linkers. Recently, these compounds have received widespread attention in medicine, due to their exceptional qualities, including a wide surface area, high porosity, outstanding biocompatibility, non-toxicity, etc. Such characteristic qualities make MOFs superb candidates for biosensing, molecular imaging, drug delivery, and enhanced cancer therapies. This review illustrates the key attributes of MOFs and their importance in cancer research. The structural and synthetic aspects of MOFs are briefly discussed with primary emphasis on diagnostic and therapeutic features, as well as their performance and significance in modern therapeutic methods and synergistic theranostic strategies including biocompatibility. This review offers cumulative scrutiny of the widespread appeal of MOFs in modern-day oncological research, which may stimulate further explorations.

Asymmetric Supercapacitors Using Porous Carbons and Iron Oxide Electrodes Derived from a Single Fe Metal-Organic Framework (MIL-100 (Fe))

MOF-derived carbon (MDC) and metal oxide (MDMO) are superior materials for supercapacitor electrodes due to their high specific capacitances, which can be attributed to their high porosity, specific surface area (SSA), and pore volume. To improve the electrochemical performance, the environmentally friendly and industrially producible MIL-100 (Fe) was prepared using three different Fe sources through hydrothermal synthesis. MDC-A with micro- and mesopores and MDC-B with micropores were synthesized through carbonization and an HCl washing process, and MDMO (α-Fe₂O₃) was obtained by a simple sintering in air. The electrochemical properties in a three-electrode system using a 6 M KOH electrolyte were investigated. These novel MDC and MDMO were applied to an asymmetric supercapacitor (ASC) system to overcome the disadvantages of traditional supercapacitors, enhancing energy density, power density, and cyclic performance. High SSA materials (MDC-A nitrate and MDMO iron) were selected for negative and positive electrode material to fabricate ASC with KOH/PVP gel electrolyte. As-fabricated ASC resulted in high specific capacitance 127.4 Fg^-1 at 0.1 Ag^-1 and 48.0 Fg^-1 at 3 Ag^-1, respectively, and delivered superior energy density (25.5 Wh/kg) at a power density 60 W/kg. The charging/discharging cycling test was also conducted, indicating 90.1% stability after 5000 cycles. These results indicate that ASC with MDC and MDMO derived from MIL-100 (Fe) has promising potential in high-performance energy storage devices.

Trends in monoliths: Packings, stationary phases and nanoparticles

Monoliths media are gaining interest as excellent substitutes to conventional particle-packed columns. Monolithic columns show higher permeability and lower flow resistance than conventional liquid chromatography columns, providing high-throughput performance, resolution and separation in short run times. Monolithic columns with longer length, smaller inner diameter and specific selectivity to peptides or enantiomers have been played important role in hyphenated system. Monolithic stationary phases possess great efficiency, resolution, selectivity and sensitivity in the separation of complex biological samples, such as the complex mixtures of peptides for proteome analysis. The development of monolithic stationary phases has opened the new avenue in chromatographic separation science and is in turn playing much more important roles in the wide application area. Monolithic stationary phases have been widely used in fast and high efficiency one- and multi-dimensional separation systems, miniaturized devices, and hyphenated system coupled with mass spectrometers. The developing technology for preparation of monolithic stationary phases is revolutionizing the column technology for the separation of complex biological samples. These techniques using porous monoliths offer several advantages, including miniaturization and on-line coupling with analytical instruments. Additionally, monoliths are ideal support media for imprinting template-specific sites, resulting in the so-called molecularly-imprinted monoliths, with ultra-high selectivity. In this review, the origin of the concept, the differences between their characteristics and those of traditional packings, their advantages and drawbacks, theory of separations, the methods for the monoliths preparation of different forms, nanoparticle monoliths and metal-organic framework are discussed. Two application areas of monolithic metal-organic framework and nanoparticle monoliths are provided. The review article discusses the results reported in a total of 218 references. Other older references were included to illustrate the historical development of monoliths, both in preparation and types, as well as separation mechanism.

Efficient one-pot synthesis of magnetic MIL-100(Fe) using nitric acid without additional Fe ion addition and adsorption behavior of charged organic compounds

Metal organic frameworks (MOFs) are attracting attention as high-performance adsorbents because of their high specific surface area and porosity. In particular, magnetic MIL-100(Fe) has the both characteristics of Fe₃O₄ and MIL-100(Fe), which are magnetic characteristics, high specific surface area and open metal sites. However, multiple synthetic steps are required for synthesis of magnetic MOF, and there is limitation that the residual organic linker and unreacted Fe center ions can be discharged, and they cause water pollution. In this study, magnetic MIL-100(Fe) was synthesized within 4 h without the addition of Fe ions by using nitric acid for the surface modification of Fe₃O₄. Magnetic MIL-100(Fe) was confirmed through XRD, FTIR, and TEM surface analysis, and the optimal conditions for nitric acid addition were selected through magnetization measurements and BET analysis of synthesized magnetic MIL-100(Fe). Thereafter, adsorption evaluation was performed using MB and MO, which are representative cationic and anionic dyes, respectively. The pseudo-second-order Langmuir model showed a relatively high correlation compared to the other models. This shows that the adsorption mechanism depends on both the amount of adsorbent and adsorbate, and Fe₃O₄ modification with nitric acid does not cause any change in the adsorption mechanism. In the case of adsorption selectivity between the MB and MO, removal rates of 93.27% and 58.73% were obtained, respectively. The above results can contribute to the simplification of the manufacturing of magnetic metal organic frameworks for removing ionic organic compounds and the minimization of water pollution in the manufacturing process.

Ultrasonic-Assisted Fabrication of MIL-100(Fe) Metal-Organic Frameworks as a Carrier for the Controlled Delivery of the Chloroquine Drug

Metal-organic framework materials (MOFs) are materials with an ordered crystalline structure and high porosity that have been intensively investigated for many applications, such as gas adsorption, catalysis, sensors, drug delivery, and so on. Among them, the MOF-based drug delivery system has received increasing interest from scientists worldwide. This work presented the preparation of the MIL-100(Fe) metal-organic framework from the organic ligand of trimesic acid and iron ions with ultrasonic assistance. Scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area (BET), X-ray diffraction (XRD), infrared spectroscopy (FTIR), and Raman spectroscopy were employed to characterize the prepared MIL-100(Fe) material. MIL-100(Fe) materials synthesized by the ultrasonic method have uniform particle morphology ranging from 100 to 300 nm with a surface area of 1033 m²/g. The prepared MIL-100(Fe) was employed as a carrier for delivering chloroquine drug with a maximal loading capacity of 220 mg/g. The MIL-100(Fe)@chloroquine system was also characterized in detail. The delivery system's slow drug release was studied, showing that nearly 80% of chloroquine molecules were released after 7.5 h of immersing time in PBS and simulated gastric solutions and completely detached from the MIL-100(Fe)@chloroquine system only after approximately 80 h. This result shows the ability to control chloroquine drug release of the material, reducing the possibility of drug shock.

Nanomaterials and metal-organic frameworks for biosensing applications of mutations of the emerging viruses

The world today lives in a state of terrible fear due to the mutation of the emerging COVID-19. With the continuation of this pandemic, there is an urgent need for fast, accurate testing devices to detect the emerging SARS-CoV-2 pandemic in terms of biosensors and point-of-care testing. Besides, the urgent development in personal defense tools, anti-viral surfaces and wearables, and smartphones open the door for simplifying the self-diagnosis process everywhere. This review introduces a quick COVID-19 overview: definition, transmission, pathophysiology, the identification and diagnosis, mutation and transformation, and the global situation. It also focuses on an overview of the rapidly advanced technologies based on nanomaterials and MOFs for biosensing, diagnosing, and viral control of the SARS-CoV-2 pandemic. Finally, highlight the latest technologies, applications, existing achievements, and preventive diagnostic strategies to control this epidemic and combat the emerging coronavirus. This humble effort aims to provide a helpful survey that can be used to develop a creative solution and to lay down the future vision of diagnosis against COVID-19.

Green synthesis of DOX-loaded hollow MIL-100 (Fe) nanoparticles for anticancer treatment by targeting mitochondria

Fe-based Metal-Organic Frameworks (MOFs) are promising drug delivery materials due to their large surface area, high stability, and biocompatibility. However, their drug loading capacity is constrained by their small pore size, and a further improvement in their drug capacity is needed. In this work, we report an effective and green structural modification strategy to improve drug loading capacity for Fe-based MOFs. Our strategy is to grow MIL-100 (Fe) on carboxylate-terminated polystyrene (PS-COOH) via a sustainable route, which creates a large inner cavity as well as exposure of more functional groups that benefit drug loading capacity. We perform the scanning electron microscope and transmission electron microscope to confirm the hollow structure of MIL-100 (Fe). Up to 30% of drug loading capacity has been demonstrated in our study. We also conduct cell viability tests to investigate its therapeutic effects on breast cancer cells (MDA-MB-231). Confocal laser scanning microscopy imaging confirms cellular uptake and mitochondrial targeting function of doxorubicin-loaded H-M (DOX@H-M) nanoparticles. JC-1 staining of cancer cells reveals a significant change in the mitochondrial membrane potential, indicating the mitochondrial dysfunction and apoptosis of tumor cells. Our study paves the way for facile synthesis of hollow structural MOFs, and demonstrates the potential of applying Fe-based MOFs in breast cancer treatment.

Insights into the mechanism of enhanced peroxymonosulfate degraded tetracycline using metal organic framework derived carbonyl modified carbon-coated Fe0

Tetracycline (TC) is a commonly used antibiotic that has gained wide spread notoriety owing to its high environmental risks. In this study, rich carbonyl-modified carbon-coated Fe⁰ was obtained by pyrolysis of MIL-100(Fe) in an Ar atmosphere, and used to activate peroxymonosulfate (PMS) for the degradation of tetracycline in water. The roles of Fe⁰, carbon and surface carbonyl on PMS activation were investigated. Fe⁰ continuously activated PMS, acted as a sustained-release source of Fe²⁺, and could effectively activate PMS to produce SO₄^•-, O₂^•- and •OH. Carbon was found to do responsible for electron transportation during the activation of PMS and slow down the oxidation of Fe⁰. The carbonyl group on the carbon surface layer was the active site of ¹O₂, which explains the enhanced performance for TC degradation. When Ca = 0.1 g/L and C₀ = 0.4 mM, TC degradation rate reached 96%, which was attributed to the synergistic effect of radicals (i.e., SO₄^•-, O₂^•-, •OH) and non-radical (i.e., ¹O₂). Finally, the degradation pathway was proposed by combining density functional theory (DFT) calculations with liquid chromatography-mass spectrometry (LC-MS), toxicities of the intermediate products were also evaluated. All results show that carbonyl-modified carbon-coated Fe⁰ possesses promising capacity for the removal of antibiotics from water.

Iron-based metal-organic framework: Synthesis, structure and current technologies for water reclamation with deep insight into framework integrity

Water is a supreme requirement for the existence of life, the contamination from the point and non-point sources are creating a great threat to the water ecosystem. Advance tools and techniques are required to restore the water quality and metal-organic framework (MOFs) with a tunable porous structure, striking physical and chemical properties are an excellent candidate for it. Fe-based MOFs, which developed rapidly in recent years, are foreseen as most promising to overcome the disadvantages of traditional water depolluting practices. Fe-MOFs with low toxicity and preferable stability possess excellent performance potential for almost all water remedying techniques in contrast to other MOF structures, especially visible light photocatalysis, Fenton, and Fenton-like heterogeneous catalysis. Fe-MOFs become essential tool for water treatment due to their high catalytic activity, abundant active site and pollutant-specific adsorption. However, the structural degradation under external chemical, photolytic, mechanical, and thermal stimuli is impeding Fe-MOFs from further improvement in activity and their commercialization. Understanding the shortcomings of structural integrity is crucial for large-scale synthesis and commercial implementation of Fe-MOFs-based water treatment techniques. Herein we summarize the synthesis, structure and recent advancements in water remediation methods using Fe-MOFs in particular more attention is paid for adsorption, heterogeneous catalysis and photocatalysis with clear insight into the mechanisms involved. For ease of analysis, the pollutants have been classified into two major classes; inorganic pollutants and organic pollutants. In this review, we present for the first time a detailed insight into the challenges in employing Fe-MOFs for water remediation due to structural instability.

Exploring the Effect of Iron Metal-Organic Framework Particles in Polylactic Acid Membranes for the Azeotropic Separation of Organic/Organic Mixtures by Pervaporation

A microporous carboxylate metal-organic framework MIL-100 Fe was prepared as submicron particles by microwave-assisted hydrothermal synthesis (Fe-MOF-MW). This product was explored, for the first time, for the preparation of polylactic acid (PLA) mixed matrix membranes. The produced MOF was characterised by powder X-ray diffraction (PXRD), environmental scanning electron microscopy (ESEM) as well as by thermogravimetric analysis (TGA) and nitrogen adsorption/desorption. The effect of different Fe-MOF-MW concentrations (0.1 and 0.5 wt%) on the membrane properties and performance were evaluated. These membranes were used in the pervaporation process for the separation of methanol/methyl tert-butyl-ether mixtures at the azeotropic point. The influence of the feed temperature and vacuum pressure on the membrane performance was evaluated and the results were compared with PLA pristine membranes. Moreover, the produced membranes have been characterised in terms of morphology, MOF dispersion in the polymeric membrane matrix, wettability, thickness, mechanical resistance and swelling propensity. The presence of Fe-MOF-MW was found to have a beneficial effect in improving the selectivity of mixed matrix membranes towards methanol at both concentrations. The highest selectivity was obtained for the PLA membranes embedded with 0.5 wt% of Fe-MOF-MW and tested at the temperature of 25 °C and vacuum pressure of 0.09 mbar.

Biocompatibility and biodegradability of metal organic frameworks for biomedical applications

Metal organic frameworks (MOFs) are a unique class of smart hybrid materials that have recently attracted significant interest for catalysis, separation and biomedical applications. Different strategies have been developed to overcome the limitations of MOFs for bio-applications in order to produce a system with high biocompatibility and biodegradability. In this review, we outline the chemical and physical factors that dictate the biocompatibility and biodegradability characteristics of MOFs including the nature of the metal ions and organic ligands, size, surface properties and colloidal stability. This review includes the in vitro biodegradation and in vivo biodistribution studies of MOFs to better understand their pharmacokinetics, organ toxicity and immune response. Such studies can guide the design of future bio-friendly systems that bring us closer to safely translating these platforms into the pharmaceutical consumer market.

Highly Porous MIL-100(Fe) for the Hydrogen Evolution Reaction (HER) in Acidic and Basic Media

The present study reports the synthesis of a porous Fe-based MOF named MIL-100(Fe) by a modified hydrothermal method without the HF process. The synthesis gave a high surface area with the specific surface area calculated to be 2551 m² g^-1 and a pore volume of 1.407 cm³ g^-1 with an average pore size of 1.103 nm. The synthesized electrocatalyst having a high surface area is demonstrated as an excellent electrocatalyst for the hydrogen evolution reaction investigated in both acidic and alkaline media. As desired, the electrochemical results showed low Tafel slopes (53.59 and 56.65 mV dec^-1), high exchange current densities (76.44 and 72.75 mA cm^-2), low overpotentials (148.29 and 150.57 mV), and long-term stability in both media, respectively. The high activity is ascribed to the large surface area of the synthesized Fe-based metal-organic framework with porous nature.

Exploring the Parameter Space of p-Cresyl Sulfate Adsorption in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have high porosity and surface area, making them ideal candidates for adsorption-mediated applications. One high-value application is the removal of uremic toxins from solution for dialysis. Previous studies have reported adsorptive removal of the uremic toxin p-cresyl sulfate from solution via zirconium-based MOFs, but a specific analysis of parameters contributing to adsorptive uptake is needed to clarify differences in uptake performance between MOFs. We synthesized zirconium 1,3,5-benzenetricarboxylate (MOF-808) and an iron-based analog, MIL-100(Fe), and compared their adsorptive uptake with previously reported values of other zirconium-based MOFs. MIL-100(Fe) adsorbed three times more p-cresyl sulfate from solution on a per mass basis than MOF-808 and had a greater adsorption efficiency than 75% of previously reported Zr-based MOFs. We compared p-cresyl sulfate uptake by MOFs as a function of BET surface area, number of aromatic carbons in the organic linker, internal cage diameter, and pore window diameter. There is poor correlation between p-cresyl sulfate uptake and each of the variables considered, but the number of aromatic carbons of the MOF linker was a better predictor of uptake than BET surface area (R² = 0.7034 and 0.1430, respectively), and pore window aperture was a better predictor of uptake than the pore cage diameter (R² = 0.4780 and 0.0383, respectively). We hypothesize that the greater adsorptive capacity of MIL-100(Fe) compared to MOF-808 results from direct coordination of p-cresyl sulfate to vacant metal sites in the MOF, and the total adsorption may be accounted for by some combination of adsorptive interactions occurring at both metal and organic linker sites near to the exterior particle surface. The adsorptive uptake of p-cresyl sulfate by MIL-100(Fe) was observed to increase with p-cresyl sulfate content, mass of MIL-100(Fe), and volume of p-cresyl sulfate solution; the mass of MIL-100(Fe) had the greatest effect on total adsorption.

MIL-100(Fe) and its derivatives: from synthesis to application for wastewater decontamination

MIL-100(Fe), an environmental-friendly and water-stable metal-organic framework (MOF), has caught increasing research and application attention in the recent decade. Thanks to its mesoporous structure and eximious surface area, MIL-100(Fe) has been utilized as precursors for synthesizing various porous materials under high thermolysis temperature, which makes the derivatives of MIL-100(Fe) pretty promising candidates for the decontamination of wastewater. Herein, this review systematically summarizes the versatile synthetic methods and conditions for optimizing the properties of MIL-100(Fe) and its derivatives. Then, diverse environmental applications (i.e., adsorption, photocatalysis, and Fenton-like reaction) of MIL-100(Fe) and its derivatives and the corresponding removal mechanisms are detailed in the discussion. Finally, existing knowledge gaps related to fabrications and applications are discussed to close and promote the future development of MIL-100(Fe) and its derivatives toward environmental applications. Graphical abstract.

Green synthesis of a large series of bimetallic MIL-100(Fe,M) MOFs

Here we present a scalable and green methodology to synthesize a large variety of MIL-100(Fe,M), metal-doped iron-based MOFs with high thermal stability and surface areas.

Hydrothermal Synthesize of HF-Free MIL-100(Fe) for Isoniazid-Drug Delivery

Sustainable development of drug delivery materials with good biocompatibility and controlled-release is a popular topic among researchers. In this research study, we demonstrated the potential of the metal-organic framework, that is MIL-100(Fe), as a drug delivery platform for isoniazid (INH). The MIL-100(Fe) was prepared by using the hydrofluoric acid-free hydrothermal method. Several physical measurements were conducted to characterize the MIL-100(Fe), including x-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen sorption, and thermal-gravimetric (TG). The synthesized MIL-100(Fe) has octahedron-shaped particles with superior properties, that is large surface area (1456.10 m2/g) and pore volume (1.25 cm3/g). The drug loading rate and capacity were determined by means of adsorption kinetic and isotherm. The studied INH@MIL-100(Fe) adsorption system kinetics follow the pseudo-first-order model, while the isotherm system follows the Langmuir model with the maximum adsorption capacity of 128.5 mg/g at 30 °C. MIL-100(Fe) shows adequate biocompatibility, also exhibits a reasonable and controlled drug release kinetics. The results obtained show that MIL-100 (Fe) can be a good choice of drug delivery platform among other available platforms.

Robust synthesis routes and porosity of the Al-based metal–organic frameworks Al-fumarate, CAU-10-H and MIL-160

We confirm that the investigated Al-MOFs are robust with respect to reproducible synthesis and concomitant porosity as a prerequisite for applications.

Microwave-assisted dry-gel conversion-a new sustainable route for the rapid synthesis of metal–organic frameworks with solvent re-use

Microwave-assisted dry-gel conversion (MW-DGC) combines the advantages of concentrated reactants in DGC with fast heating by microwave irradiation.

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.