Metal-organic Frameworks In Water Research Articles

Amino Functionality Enables Aqueous Synthesis of Carboxylic Acid-Based MOFs at Room Temperature by Biomimetic Crystallization.

Enzyme immobilization within metal-organic frameworks (MOFs) is a promising solution to avoid denaturation and thereby utilize the desirable properties of enzymes outside of their native environments. The biomimetic mineralization strategy employs biomacromolecules as nucleation agents to promote the crystallization of MOFs in water at room temperature, thus overcoming pore size limitations presented by traditional postassembly encapsulation. Most biomimetic crystallization studies reported to date have employed zeolitic imidazole frameworks (ZIFs). Herein, we expand the library of MOFs suitable for biomimetic mineralization to include zinc(II) MOFs incorporating functionalized terephthalic acid linkers and study the catalytic performance of the enzyme@MOFs. Amine functionalization of terephthalic acids is shown to accelerate the formation of crystalline MOFs enabling new enzyme@MOFs to be synthesized. The structure and morphology of the enzyme@MOFs were characterized by PXRD, FTIR, and SEM-EDX, and the catalytic potential was evaluated. Increasing the linker length while retaining the amino moiety gave rise to a family of linkers; however, MOFs generated with the 2,2'-aminoterephthalic acid linker displayed the best catalytic performance. Our data also illustrate that the pH of the reaction mixture affects the crystal structure of the MOF and that this structural transformation impacts the catalytic performance of the enzyme@MOF.

Enhancing Drug Delivery Efficacy Through Bilayer Coating of Zirconium-Based Metal-Organic Frameworks: Sustained Release and Improved Chemical Stability and Cellular Uptake for Cancer Therapy.

The development of nanoparticle (NP)-based drug carriers has presented an exciting opportunity to address challenges in oncology. Among the 100,000 available possibilities, zirconium-based metal-organic frameworks (MOFs) have emerged as promising candidates in biomedical applications. Zr-MOFs can be easily synthesized as small-size NPs compatible with intravenous injection, whereas the ease of decorating their external surfaces with functional groups allows for targeted treatment. Despite these benefits, Zr-MOFs suffer degradation and aggregation in real, in vivo conditions, whereas the loaded drugs will suffer the burst effect-i.e., the fast release of drugs in less than 48 h. To tackle these issues, we developed a simple but effective bilayer coating strategy in a generic, two-step process. In this work, bilayer-coated MOF NU-901 remained well dispersed in biologically relevant fluids such as buffers and cell growth media. Additionally, the coating enhances the long-term stability of drug-loaded MOFs in water by simultaneously preventing sustained leakage of the drug and aggregation of the MOF particles. We evaluated our materials for the encapsulation and transport of pemetrexed, the standard-of-care chemotherapy in mesothelioma. The bilayer coating allowed for a slowed release of pemetrexed over 7 days, superior to the typical 48 h release found in bare MOFs. This slow release and the related performance were studied in vitro using both A549 lung cancer and 3T mesothelioma cells. Using high-resolution microscopy, we found the successful uptake of bilayer-coated MOFs by the cells with an accumulation in the lysosomes. The pemetrex-loaded NU-901 was indeed cytotoxic to 3T and A549 cancer cells. Finally, we demonstrated the general approach by extending the coating strategy using two additional lipids and four surfactants. This research highlights how a simple yet effective bilayer coating provides new insights into the design of promising MOF-based drug delivery systems.

Enhanced photocatalytic hydrogen evolution with a Mixed-Valence iron Metal-Organic framework

Fe-oxo cluster-based metal–organic frameworks (MOFs) offer a tunable platform for visible-light-driven catalysis, yet the unmatched energy level and the ease of charge recombination strongly hinder their application in photocatalytic H2 generation. In this work, we report an Fe(II/III) mixed-valence catalyst derived from the transition of an Fe(II)2N2O10 cluster-based MOF in water through a solvent displacement pathway. Both electronic band structure and charge transfer dynamics are effectively optimized via heteroatom coordination and valence mixing in the iron clusters. 25 times the visible-light-induced H2 yield of pristine FeMOF was obtained by Fe(II/III) MOF with platinum as cocatalyst. The Fe MOF catalyst also shows significantly superior performance in comparison with the well-known oxide catalyst α-Fe2O3 and the commonly investigated MOF catalyst NH2-UiO-66. This work provides a direction for the structural engineering of Fe-MOFs for photocatalysts.

Seed-aided green synthesis of metal-organic frameworks in water

Green synthesis of metal-organic frameworks (MOFs) in water with alleviated environmental influence and reduced cost is an essential step to transfer laboratory MOFs research to industrial application. Switching from the commonly used organic solvents to pure water encounters challenges of the poor solubility of organic linkers, slow reaction kinetics, and the formation of polymorphic products. So far, a universal MOFs synthetic strategy in water system has yet to be developed. This study reports the seed-aided synthesis of eleven MOFs with diverse compositions and structures while pure water serving as solvent. The corresponding reaction temperature and time of using this new strategy were reduced compared with original synthetic approaches, while the products maintain porous structure and high crystallinity. The success of this strategy relies on the addition of parent MOFs as seeds which could promote crystallization process by skipping the time-consuming induction period and avoiding the formation of polymorphic impurities.

Self-assembly of three-dimensional zeolite imidazolate framework/anionic polyacrylamide network with enhanced hydrophilicity and water dispersibility for highly efficient water purification

Metal-organic frameworks (MOFs) have attracted widespread attention in recent years due to their high surface area and adjustable porosity. However, some MOFs such as ZIF-8 have strong hydrophobicity, which is not conducive to the purification of pollutants in water. Herein, we adopted a simple in-situ growth method to incorporate typical MOFs (ZIF-8, ZIF-67) to a low-cost hydrophilic anionic polyacrylamide (APAM) matrix to facilitate the dispersion of MOFs in water. The successful synthesis of ZIFs@APAM were verified by the comprehensive characterization of the synthesized material. The contact angle test proved the hydrophilicity of MOFs@APAM, indicating that MOFs@APAM composite materials were more prone to contact with pollutants in aqueous solutions. To test the potential of this material as a water treatment agent, the ability of ZIF-8 @APAMs to adsorb tetracycline from the water was evaluated, and the adsorption and removal reached 63.80% in 4 h, which had a 25.41% higher removal rate than pure ZIF-8. Also, ZIF-67 @APAM was evaluated to degrade rhodamine B by advanced oxidation in water, and the degradation reached 97.8% in 60 min and it can be looped multiple times.

Research Progress on the Water Stability of a Metal-Organic Framework in Advanced Oxidation Processes

Metal-organic frameworks (MOFs) are a new class of organic-inorganic hybrid materials that are self-assembled metal clusters and organic ligands. Because MOFs have an ultrahigh surface area, a controllable size, and adjustable chemical properties, which are not available in other porous materials, it has broad application potential in chemical sensing, gas storage, and catalysis. However, the stability of MOFs in water is poor. The presence of water molecules changes the structures and properties of MOFs, which limits their industrial application in advanced oxidation process. In this paper, the definition of water stability is introduced in detail, and the damage mechanism of water molecules on MOFs is analyzed from the perspective of thermodynamic stability and kinetic stability. According to varying factors that affect MOFs’ water stability, corresponding methods to improve MOFs water stability are proposed, and research trends on the stability of MOFs in water are speculated.

3D Metallo-organic coordination assembly-based anion-enriched supramolecular material for fast and efficient removal of Cr2O72−

Chromium(VI), especially dichromate (Cr2O72−) contamination in wastewater due to rapid industrialization with uncontrolled effluent management is still a serious concern which needs focused attention. Multiprong approaches are practiced such as chemical precipitation, reverse osmosis, ion-exchange, adsorption by granular activated carbon etc. to capture and separate this “Group A” human carcinogenic effluent from water. However, low capture capacity, non-reusability, poor selectivity, pH-limited performance are some major limitations of these techniques. Recently, metal organic frameworks (MOFs), metal organic cages (MOCs), porous organic polymers (POPs) or covalent organic frameworks (COFs), covalent organic networks (CONs) etc. emerged as new-generation materials to overcome such limitations. However, the development is still in initial stage and issues related to structural stability and integrity of many MOFs in water and in wide pH range, as well as reusability need to be addressed. At this juncture, herein we report a novel [Zn(terpyridine)2]2+-templated trisimidazolium-based highly cationic three-dimensional metal-organic coordination assembly (3D MOCA), serving as a new class of efficient, fast, robust and recyclable dichromate-removal material. Not only the highly cationic assembly is enriched with a high density of Br− anions, but its three-dimensional propagation and flexibility also exposes the exchangeable Br− ions for facile anion-metathesis with Cr2O72−. By virtue of the benefits of these attributes, the presented supramolecular material exhibits a high capture capacity (469 mg g−1), fast exchange kinetics (0.028 g mg−1 min−1), wide working pH range (pH 2–12) and reusability up to a minimum of 10 cycles without much loss of efficiency. Key mechanistic examinations highlight the evidences in favor of ion-exchange-based chemistry to be responsible for dichromate removal with the present material.

Ultrasound-assisted exfoliation of a layered 2D coordination polymer with HER electrocatalytic activity

Large blue rectangular crystals of the 2D layered coordination polymer 1 have been obtained. The interest for this complex is two-fold. First, complex 1 is made of 2D layers packing along the (0–11) direction favored by the presence of lattice and coordinated water molecules. And second, nanostructures that could be derived by delamination are potentially suitable for catalytic purposes. Therefore it represents an excellent example to study the role of interlayer solvent molecules on the ultrasound-assisted delamination of functionally-active 2D metal-organic frameworks in water, a field of growing interest. With this aim, ultrasound-assisted delamination of the crystals was optimized with time, leading to stable nanosheet colloidal water suspensions with very homogeneous dimensions. Alternative bottom-up synthesis of related nanocrystals under ultrasound sonication yielded similar shaped crystals with much higher size dispersions. Finally, experimental results evidence that the nanostructures have higher catalytic activities in comparison to their bulk counterparts, due to larger metallic center exposition. These outcomes confirm that the combination of liquid phase exfoliation and a suitable synthetic design of 2D coordination polymers represents a very fruitful approach for the synthesis of functional nanosheets with an enhancement of catalytic active sites, and in general, with boosted functional properties.

A Water-Stable Luminescent Metal-Organic Framework for Rapid and Visible Sensing of Organophosphorus Pesticides.

Metal-organic frameworks (MOFs) have shown considerable prospects for sensing pesticide residues. However, the low stability of MOFs in water hinders them from testing food and environmental samples. Herein, we report an easy and cost-efficient synthesis of a water-stable zirconium luminescent MOF (Zr-LMOF) and its application for rapid, sensitive, and in situ detection of organophosphorous pesticides (OPPs). The Zr-MOF is prepared using Zr(IV) and 1,2,4,5-tetrakis(4-carboxyphenyl)benzene. The synthesized Zr-LMOF rapidly absorbs trace amounts of OPP parathion-methyl and indicates its presence. A low limit of detection of 0.115 μg kg-1 (0.438 nM) with a wide linear range from 70 μg kg-1 to 5.0 mg kg-1 was achieved. Satisfactory recoveries ranging from 78% to 107% were obtained for spiked food and environmental samples. Further, the Zr-LMOF was applied to imitate rapid and in situ imaging detection of pesticide residue on fresh produce nondestructively; visual signals appeared under ultraviolet light within 5 min. These results suggest that the Zr-LMOF has the potential for low-cost, rapid, and in situ imaging detection of OPPs contamination via easy-to-read visual signal.

Stabilizing the titanium-based metal organic frameworks in water by metal cations with empty or partially-filled d orbitals

Though titanium-based metal-organic frameworks (MOFs) are declared to be relatively water stable, their framework gradually collapses in water within days due to the attack of OH− to OTiO bond. For practical applications of titanium-based MOFs, it is crucial to solve their instability problem in water. We searched for a simple and efficient method to enhance the stability of titanium-based MOFs in water by using Ti-ATA (ATA = 2-aminoterephthallate ion) as a representative titanium-based MOF. Here, we show that the stability of Ti-ATA in water is greatly improved nearly without affecting its porosity and photocatalytic activity by treating it with aqueous solutions containing metal ions of empty d orbitals (Y3+, La3+, Ce3+, Nd3+ and Tm3+) or partially-filled d orbitals (Cr3+).

Adsorption of Cr(VI) on nano Uio-66-NH2 MOFs in water

ABSTRACTAn efficient adsorbent, nano Uio-66-NH2 Metal-organic frameworks (MOFs), for the high efficiency removal of Cr(VI) from aqueous solution was successfully synthesized. The adsorbent was characterized and its performance in Cr(VI) removal was evaluated for the first time. Kinetic data reveal that the Cr(VI) adsorption is rapid in the beginning followed by a slower adsorption process; The Cr(VI) adsorption kinetics were well described by the pseudo-second-order kinetics model. The calculated adsorption capacity of this adsorbent for Cr(VI) by Langmuir model was 32.36 mg/g at pH 6.5. The temperature-dependent isotherms indicated that the adsorption reaction of Cr(VI) on the MOFs was a spontaneous process. Filtration experiments revealed that the membranes fabricated by the MOFs could quickly remove Cr(VI) ions from the aqueous solutions. Electrostatic attraction between Uio-66-NH2 and Cr(VI) should be the mechanism for Cr(VI) adsorption by Uio-66-NH2.

Adsorption of fluoride to UiO-66-NH2 in water: Stability, kinetic, isotherm and thermodynamic studies

To provide safe drinking water, fluoride in water must be removed and adsorption processes appear to be the most widely used method. Metal organic frameworks (MOFs) represent a new class of adsorbents that have been used in various adsorption applications. To study the adsorption mechanism of fluoride to MOFs in water and obtain related adsorption parameters, we synthesized a zirconium-based MOF with a primary amine group on its ligand, named UiO-66-NH2. The kinetics, adsorption isotherm and thermodynamics of fluoride adsorption to UiO-66-NH2 were investigated. The crystalline structure of UiO-66-NH2 remained intact and the local structure of zirconium in UiO-66-NH2 did not change significantly after being exposed to fluoride. The kinetics of the fluoride adsorption in UiO-66-NH2 could be well represented by the pseudo second order rate law. The enthalpy of the adsorption indicates that the F− adsorption to UiO-66-NH2 was classified as a physical adsorption. However, the comparison between the adsorption capacities of UiO-66-NH2 and UiO-66 suggests that the fluoride adsorption to UiO-66-NH2 might primarily involve a strong interaction between F− and the metal site. The fluoride adsorption capacity of UiO-66-NH2 was found to decrease when pH>7. While the presence of chloride/bromide ions did not noticeably change the adsorption capacity of UiO-66-NH2, the ionic surfactants slightly affected the adsorption capacity of UiO-66-NH2. These findings provide insights to further optimize the adsorption process for removal of fluoride using zirconium-based MOFs.

Salt metathesis in three dimensional metal–organic frameworks (MOFs) with unprecedented hydrolytic regenerability

Eight Zn-based porous (1.2 nm) homochiral MOFs (ValZnX, AlaZnX, X = Cl(-), Br(-), HCO2(-) and CH3CO2(-)) were synthesized which possess extremely rare zeolitic (unh) topology. These MOFs show an unprecedented hydrolytic regenerability. Salt metathesis reaction performed on these 3D MOFs in water resulted in 2D coordination polymers (CPs).