Use Of Metal-organic Frameworks Research Articles

Encoding Metal-Cation Arrangements in Metal-Organic Frameworks for Programming the Composition of Electrocatalytically Active Multimetal Oxides.

In the present contribution, we report how through the use of metal-organic frameworks (MOFs) composed of addressable combinations of up to four different metal elements it is possible to program the composition of multimetal oxides, which are not attainable by other synthetic methodologies. Thus, due to the ability to distribute multiple metal cations at specific locations in the MOF secondary building units it is possible to code and transfer selected metal ratios to multimetal oxides with novel, desired compositions through a simple calcination process. The demonstration of an enhancement in the electrocatalytic activity of new oxides by preadjusting the metal ratios is here reported for the oxygen reduction reaction, for which activity values comparable to commercial Pt/C catalysts are reached, while showing long stability and methanol tolerance.

Colorimetric detection of heavy metal ions in water via metal-organic framework

Interest in the design and use of metal-organic frameworks (MOFs) for the selective detection of heavy metal ions is increasing rapidly. Herein, a new SALI-MAA-3eq MOF was synthesized by incorporating mercaptoacetic acid into NU-1000 via a solvent-assisted ligand incorporation (SALI) approach. SALI-MAA-3eq was fully characterized by common analytical techniques and further tested for sensing applications. SALI-MAA-3eq was found to selectively detect Hg2+ over a range of metal ions in an aqueous environment. Its selectivity was further confirmed by fluorescence and X-ray photoelectron spectroscopy (XPS) studies.

Immobilization of Metal–Organic Frameworks on Supports for Sample Preparation and Chromatographic Separation

Metal–organic frameworks (MOFs) are porous crystalline materials with large surface areas, uniform pore size, and tunable selectivity. In the last few years, the number of analytical applications of MOFs has been growing constantly. However, the direct use of as-synthesized MOFs in packed column format is rather limited for analytical separations because of the small size and non-spherical shape of MOF crystals. In this review, we outline and critically discuss the advantages and limitations of the different methods described to immobilize MOFs into functional supports for analytical separations, including beads, monoliths, and fibers. These methods are based on embedding MOF crystals into functional supports, in situ MOF growth, controlled layer-by-layer MOF growth, or the in situ conversion of immobilized MOF metal oxide precursors. Representative examples of immobilized MOFs for sample preparation and chromatographic separation are overviewed. We also overview recent progress on the use of MOFs as precursors to obtain other functional materials such as layered double hydroxides or porous carbons.

Propylene Enrichment via Kinetic Vacuum Pressure Swing Adsorption Using ZIF-8 Fiber Sorbents.

This work presents the synthesis, characterization, and implementation of ZIF-8/cellulose acetate fiber sorbents for the cyclic kinetic adsorption separation of an equimolar propane/propylene feed. These fiber sorbents are packed as structured mass-transfer contactors and employed in a two-bed vacuum pressure swing adsorption cycle without propylene product purge. The unoptimized adsorption cycle process produces a high-pressure product of up to 81% propane purity at 31% recovery at 0 °C. The effects of adsorption step time, temperature, and feed rate are investigated and presented as a purity/recovery trade-off. This work represents the first successful demonstration of a metal-organic framework fiber sorbent in a pressure swing adsorption cycle and the first use of metal-organic frameworks in a kinetic separation cycle.

Robust photocatalytic reduction of Cr(VI) on UiO-66-NH2(Zr/Hf) metal-organic framework membrane under sunlight irradiation

The removal of toxic hexavalent chromium (Cr(VI)) ions from surface and ground water is highly demanded. While photocatalytic reduction of Cr(VI) to Cr(III) by traditional powder photocatalysts is a promising method, the difficult in the separation of the photocatalysts from the water hinders their wide practical applications. Herein we present the use of metal-organic framework (MOF) UiO-66-NH2(Zr/Hf) membrane as photocatalysts to reduce Cr(VI) ions with high efficiency and easy separation from the treated waste water. The UiO-66-NH2(Zr/Hf) MOF membrane photocatalysts were fabricated via a reactive seeding method on a α-Al2O3 substrate. It was found that the UiO-66-NH2(Zr/Hf) membranes exhibited excellent photocatalytic Cr(VI) reduction performance under both simulated and real sunlight irradiation. The UiO-66-NH2(Zr) membrane can maintain more than 94% Cr(VI) reduction efficiency after 20 cycles because of its exceptional chemical and water stability. The influences of foreign ions on Cr(VI) reduction were investigated to mimic real lake water, which revealed that no obvious adverse effects can be found with the presence of common foreign ions in surface water. The MOF membrane photocatalysts provide a new approach to carry out efficiently photocatalytic removal of pollutants in wastewater.

An electrochemical immunosensor based on an etched zeolitic imidazolate framework for detection of avian leukosis virus subgroup J.

A novel sandwich-type electrochemical immunosensor for avian leukosis virus subgroup J (ALV-J) is described. The immunosensor was prepared by first modifying a glassy carbon electrode (GCE) with reduced graphene oxide that was functionalized with tannic acid and magnetite nanoparticles (rGO-TA-Fe3O4). Primary antibodies (Ab1) were then deposited on the modified GCE. Hollow zeolitic imidazolate framework (eZIF) crystals functionalized with tannic acid and carrying secondary antibodies (Ab2) and horseradish peroxidase (HRP) were used for signal amplification. The hollow eZIF crystals were found to be an excellent carrier for both Ab2 and HRP, prompting the wider use of metal organic frameworks in electrochemical sensing. Under optimal conditions, the immunoassay afforded a detection range from 152 to 10,000 TCID50 mL-1 (where TCID50 is the 50% tissue culture infective dose) and a low detection limit of 140 TCID50 mL-1 (at S/N= 3). The immunoassay is highly selective for ALV-J, and itdemonstrates excellent reproducibility and operational stability. The practicability of the immunoassay for the fast detection of ALV-J was confirmed in experiments with spiked avian serum samples. Graphical abstract Schematic of a sandwich-type electrochemical immunosensor for avian leukosis virus subgroup J (ALV-J). It consists of reduced graphene oxide, tannic acid and magnetite as the sensing platform, and an etched zeolitic imidazolate framework carrying horseradish peroxidase for signal amplification.

Advances of metal–organic frameworks for gas sensing

Gas sensing is of crucial importance to environmental monitoring, control of chemical processes, agricultural, and medical applications. Particularly, the detection of harmful and toxic gases such as H2S, NH3, CO, and volatile organic chemicals (VOCs) released from various industries is very necessary to avoid serious threat to human health. Sensing materials which can concentrate and adsorb gases onto the surface of the sensors, and then generate a signal for detection play a vital role in the sensing identification of gases. Among various sensing materials, metal–organic frameworks (MOFs) which consist of metal cations and organic ligands by self-assembly process have great advantages in constructing chemical sensors with high sensing selectivity and sensitivity due to their good features such as high surface area, porosity and tunable pore sizes. This review intends to provide an update on recent progress in MOFs for gas sensing. It firstly summarizes the signal transduction manners of MOFs in sensing and detection of gases, including optical (vapochromism, luminescence, interferometry, localized surface plasmon resonance (LSPR)), mechanical (quartz crystal microbalance (QCM), surface acoustic wave sensors (SAWS), microcantilevers (MCL)), and electrical manners. Examples of the use of MOFs in the detection of water vapour, oxygen, hydrogen, hydrogen sulfide, ammonia, carbon monoxide, carbon dioxide, and volatile organic compounds are then detailed.

Water stable metal-organic framework as adsorbent from aqueous solution: A mini-review

Abstract Metal-organic framework (MOF) is a porous material that is made of metal clusters coordinated with organic linkers to generate a large Langmuir surface area and small-to-medium-sized pores. This mini-review provides an overview of current research and development efforts in water-stable MOFs that have the potential to be used as adsorbents of aqueous solutions. The use of MOFs to adsorb anions and cations and potential obstacles to their industrial use are discussed.

Structured Growth of Metal–Organic Framework MIL-53(Al) from Solid Aluminum Carbide Precursor

The conventional synthesis of metal-organic frameworks (MOFs) through soluble metal-salt precursors provides little control over the growth of MOF crystals. The use of alternative metal precursors would provide a more flexible and cost-effective strategy for direction- and shape-controlled MOF synthesis. Here, we demonstrate for the first time the use of insoluble metal-carbon matrices to foster directed growth of MOFs. Aluminum carbide was implemented as both the metal precursor and growth-directing agent for the generation of MIL-53(Al). A unique needle-like morphology of the MOF was grown parallel to the bulk surface in a layer-by-layer manner. Importantly, the synthesis scheme was found to be transferrable to the production of different linker analogues of the MOF and other topologies. Given the variety of metal carbides available, these findings can be used as a blueprint for controlled, efficient, and economical MOF syntheses and set a new milestone toward the industrial use of MOFs at large-scale.

The Carbonation of Wollastonite: A Model Reaction to Test Natural and Biomimetic Catalysts for Enhanced CO2 Sequestration

One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its slow kinetics is a handicap for the implementation of silicate mineral carbonation as an effective method for CO2 capture and storage (CCS). Here, we studied the different steps of wollastonite (CaSiO3) carbonation (silicate dissolution → carbonate precipitation) as a model CCS system for the screening of natural and biomimetic catalysts for this reaction. Tested catalysts included carbonic anhydrase (CA), a natural enzyme that catalyzes the reversible hydration of CO2(aq), and biomimetic metal-organic frameworks (MOFs). Our results show that dissolution is the rate-limiting step for wollastonite carbonation. The overall reaction progresses anisotropically along different [hkl] directions via a pseudomorphic interface-coupled dissolution–precipitation mechanism, leading to partial passivation via secondary surface precipitation of amorphous silica and calcite, which in both cases is anisotropic (i.e., (hkl)-specific). CA accelerates the final carbonate precipitation step but hinders the overall carbonation of wollastonite. Remarkably, one of the tested Zr-based MOFs accelerates the dissolution of the silicate. The use of MOFs for enhanced silicate dissolution alone or in combination with other natural or biomimetic catalysts for accelerated carbonation could represent a potentially effective strategy for enhanced mineral CCS.

Metal organic frameworks as catalysts in solvent-free or ionic liquid assisted conditions

This Critical Review describes the use of Metal Organic Frameworks as Solid Catalysts under Solvent-Free or Ionic Liquid Assisted conditions.

Enhancing porphyrin photostability when locked in metal-organic frameworks.

Porphyrins have been widely used in many optical devices given their unique photochemical properties. Their poor photostability has, however, limited their wide applications in bioimaging and biosensing schemes. Herein, we report the remarkable photostability enhancement of the porphyrin, carboxyphenyl porphyrin (TCPP-H2) when locked in a zirconium based metal-organic framework (MOF-525). Steady-state ensemble fluorescence spectroscopy experiments showed minimal changes (2%) in the recorded signal when MOF-525 was continuously illuminated as compared to a 16% decrease for free porphyrins. Single particle fluorescence imaging revealed bright microparticles with exceptional photostability and no-blinking within the experiment window. This study highlights the use of metal-organic frameworks for preparing photostable microstructures by leveraging on their unique self-assembly properties.

Semi-crystalline Fe-BTC MOF material as an efficient support for enzyme immobilization

Metal-organic frameworks (MOFs) have revolutionized the potential applications of nanoporous materials. One of the most recent and promising applications of these materials is their use as supports for enzyme immobilization. In this context, the in-situ (one-step) methodologies, which do not require the use of MOFs with pores larger than the enzyme to be immobilized, seem to be particularly encouraging. This work presents a systematic study of the semi-crystalline Fe-BTC MOF material (commercialized as Basolite F300) employed as support of the enzymes laccase and lipase through either in-situ or post-synthesis methodology. The presence of the enzyme in the resultant solid biocatalysts was proved by CHNS chemical analysis, thermogravimetric analysis, Bradford assays and by SDS-PAGE electrophoresis. The enzymatic activity of the resultant Fe-BTC-based biocatalysts was also tested. The in-situ approach is particularly relevant due to various reasons: (i) the enzyme immobilization is given in one step; (ii) it is rapid (10min); (iii) it is very efficient in terms of encapsulation capacity (≥98% for laccase and ≥87% for lipase); (iv) the enzymes are fully retained and no leaching is observed after an initial release of only around 10% of the enzyme molecules weakly immobilized; and (v) the activity of the retained enzyme can be substantially maintained (97% with respect to the free enzyme in the case of lipase). Any of these parameters systematically improves these given by the post-synthesis (two-step) approach. Moreover, Fe-BTC widely surpasses the benefits given by other MOF-based supports either by in-situ or post-synthesis approaches.

Tuning the Endocytosis Mechanism of Zr-Based Metal-Organic Frameworks through Linker Functionalization.

A critical bottleneck for the use of metal–organic frameworks (MOFs) as drug delivery systems has been allowing them to reach their intracellular targets without being degraded in the acidic environment of the lysosomes. Cells take up particles by endocytosis through multiple biochemical pathways, and the fate of these particles depends on these routes of entry. Here, we show the effect of functional group incorporation into a series of Zr-based MOFs on their endocytosis mechanisms, allowing us to design an efficient drug delivery system. In particular, naphthalene-2,6-dicarboxylic acid and 4,4′-biphenyldicarboxylic acid ligands promote entry through the caveolin-pathway, allowing the particles to avoid lysosomal degradation and be delivered into the cytosol and enhancing their therapeutic activity when loaded with drugs.

Novel nano-conjugate materials for effective arsenic(V) and phosphate capturing in aqueous media

In this study, the ligand functionalized nano-conjugate material was developed for the sensitive and selective detection and removal of toxic arsenic(V) and phosphate ions in aqueous media. The nano-conjugate material was fabricated based on the use of metal-organic frameworks with exhibited of high surface area, pore morphology, and tuneable shape. The newly design nano-conjugate material was exhibited the naked eye monitoring of the ultra-trace arsenic(V) and phosphate in a simple, fast, cost-effective and easy-to-use approach. The data clarified that the arsenic(V) and phosphate adsorption process were found to be relatively fast. The adsorption isotherms of arsenic(V) and phosphate from aqueous solutions to the nano-conjugate material were measured, and the results showed that the Langmuir isotherm was found to be the best represent the measured adsorption data. The maximum adsorption capacity was 82.40 and 70.47mg/g for arsenic(V) and phosphate, respectively. The arsenic(V) and phosphate detection and removal were not affected in the presence of co-existing divers ions. Calibration curves were demonstrated by using UV–Vis spectrophotometric and digital image-based colorimetric analysis. The linear correlation obtained from the two methods, and the detection limit of arsenic(V) and phosphate were 0.15 and 0.13μg/L, respectively. In addition, the nano-conjugate material was regenerated by 0.20M NaOH treatment the arsenic(V) and phosphate detection or removal efficiency was retained almost as that of the original performance. In addition, the nano-conjugate material was applied to the determination and removal of arsenic(V) and phosphate in natural and industrial water samples. Therefore, the newly developed nanomaterial has potentiality for efficient detection and removal of arsenic(V) and phosphate in the real wastewater samples.

Greening the Processes of Metal–Organic Framework Synthesis and their Use in Sustainable Catalysis

Given the shortage of sustainable resources and the increasingly serious environmental issues in recent decades, the demand for clean technologies and sustainable feedstocks is of great interest to researchers worldwide. With regard to the fields of energy saving and environmental remediation, the key point is the development of efficient catalysts, not only in terms of facile synthesis methods, but also the benign utilization of such catalysts. This work reviews the use of metal-organic frameworks (MOFs) and MOF-based materials in these fields. The definition of MOFs and MOF-based materials will be primarily introduced followed by a brief description of the characterization and stability of MOF-related materials under the applied conditions. The greening of MOF synthesis processes will then be discussed and catalogued by benign solvents and conditions and green precursors of MOFs. Furthermore, their suitable application in sustainable catalysis will be summarized, focusing on several typical atom-economic reactions, such as the direct introduction of H2 or O2 and C-C bond formation. Approaches towards reducing CO2 emission by MOF-based catalysts will be described with special emphasis on CO2 fixation and CO2 reduction. In addition, driven by the explosive growth of energy consumption in the last century, much research has gone into biomass, which represents a renewable alternative to fossil fuels and a sustainable carbon feedstock for chemical production. The advanced progress of biomass-related transformations is also illustrated herein. Fundamental insights into the nature of MOF-based materials as constitutionally easily recoverable heterogeneous catalysts and as supports for various active sites is thoroughly discussed. Finally, challenges facing the development of this field and the outlook for future research are presented.

Visible Light Induced Organic Transformations Using Metal-Organic-Frameworks (MOFs).

With the aim of developing renewable energy based processes, researchers are paying increasing interest to light induced organic transformations. Metal-organic frameworks (MOFs), a class of micro-/mesoporous hybrid materials, are recently emerging as a new type of photoactive materials for organic syntheses due to their unique structural characteristics. In this Review, we summarized the recent applications of MOFs as photocatalysts for light induced organic transformations, including (1) oxidation of alcohols, amines, alkene, alkanes and sulfides; (2) hydroxylation of aromatic compounds like benzene; (3) activation of the C-H bonds to construct new C-C or C-X bonds; (4) atom-transfer radical polymerization (ATRP). This Review starts with general background information of using MOFs in photocatalysis, followed by a description of light induced organic transformations promoted by photoactive inorganic nodes and photocatalytic active ligands in MOFs, respectively. Thereafter, the use of MOFs as multifunctional catalysts for light induced organic transformations via an efficient merge of the metal/ligand/guest based catalysis where the photocatalytic activity of MOFs plays a key role are discussed. Finally, the limitations, challenges and the future perspective of the application of MOFs for light induced organic transformations were addressed. The objective of this Review is to serve as a starting point for other researchers to get into this largely unexplored field. It is also our goal to stimulate intensive research in this field for rational designing of MOF materials to overcome their current limitations in photocatalysis, which can lead to more creative visible-light-induced organic transformations.

Multiple Coordination Exchanges for Room-Temperature Activation of Open-Metal Sites in Metal-Organic Frameworks.

The activation of open coordination sites (OCSs) in metal-organic frameworks (MOFs), i.e., the removal of solvent molecules coordinated at the OCSs, is an essential step that is required prior to the use of MOFs in potential applications such as gas chemisorption, separation, and catalysis because OCSs often serve as key sites in these applications. Recently, we developed a "chemical activation" method involving dichloromethane (DCM) treatment at room temperature, which is considered to be a promising alternative to conventional thermal activation (TA), because it does not require the application of external thermal energy, thereby preserving the structural integrity of the MOFs. However, strongly coordinating solvents such as N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), and dimethyl sulfoxide (DMSO) are difficult to remove solely with the DCM treatment. In this report, we demonstrate a multiple coordination exchange (CE) process executed initially with acetonitrile (MeCN), methanol (MeOH), or ethanol (EtOH) and subsequently with DCM to achieve the complete activation of OCSs that possess strong extracoordination. Thus, this process can serve as an effective "chemical route" to activation at room temperature that does not require applying heat. To the best of our knowledge, no previous study has demonstrated the activation of OCSs using this multiple CE process, although MeOH and/or DCM has been popularly used in pretreatment steps prior to the TA process. Using MOF-74(Ni), we demonstrate that this multiple CE process can safely activate a thermally unstable MOF without inflicting structural damage. Furthermore, on the basis of in situ 1H nuclear magnetic resonance (1H NMR) and Raman studies, we propose a plausible mechanism for the activation behavior of multiple CE.

Metal organic framework MIL-101 for radioiodine capture and storage

we report on the use of metal organic frameworks(MOFs) for radioiodine recovery and storage. One MOF (namely MIL-101) was prepared and investigated in detail to demonstrate the iodine removal efficiency and capacity of MOFs. The typical sorption kinetics and uptake isotherms were measured using radioactive iodine (123 I) for the first time. Our measurements indicate that MOFs can capture and store radioiodine in very high efficiency and fast kinetics.

Metal-Organic Frameworks as Active Materials in Electronic Sensor Devices.

In the past decade, advances in electrically conductive metal–organic frameworks (MOFs) and MOF-based electronic devices have created new opportunities for the development of next-generation sensors. Here we review this rapidly-growing field, with a focus on the different types of device configurations that have allowed for the use of MOFs as active components of electronic sensor devices.