As-prepared Metal-organic Frameworks Research Articles

Defective Metal-Organic Frameworks As Unpyrolyzed Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) represent core electrocatalytic processes in unitized regenerative fuel cells and rechargeable metal-air batteries catalyzed by the costly platinum group metals (PGMs) materials. Finding highly efficient yet durable ORR/OER catalysts using earth-abundant, low-cost materials represents a critical path in lowering cost barrier for widespread commercialization of the devices. We herein report two approaches to construct defective metal-organic frameworks (MOFs) to remove PGM usage for oxygen electrocatalysis.In approach 1, we prepared a coordinately unsaturated Co-MOF as a bifunctional ORR/OER electrocatalyst in an alkaline electrolyte. The Co-MOF possessed great π-π stacking and hydrogen bonding interactions, giving rise to excellent structural and catalytic stabilities. Structure characterizations demonstrated that the coordination of Co(II) was largely unsaturated. Modeling simulations further confirmed that the unsaturated coordination significantly promoted the interactions with molecular water and oxygen and improved the electronic conductivity, leading to enhanced mass and charge transfer properties.In approach 2, we developed a partial ligand removal (or ligand-defect) approach to create mesopores and unsaturated coordination in a Cu-MOF. Since the micropores typically limit the mass-transfer properties (and the capability to store insoluble discharge product for aprotic metal-air battery), the mesopores of the as-prepared MOF showed less steric hindrance, and the unsaturated Cu coordination also boosted electronic conductivity and auxiliary reactant affinity, leading to high Li-air battery capacity.The defective MOFs may open up a new venue for developing effective electrocatalysts with enhanced intrinsic activity towards oxygen electrocatalysis.

Carbon paste electrode modified with fern leave-like MIL-47(as) for electrochemical simultaneous detection of Pb(II), Cu(II) and Hg(II)

A fern leave-like structure metal-organic frameworks (MOFs), MIL-47(as) has been fabricated by a simple one-pot hydrothermal reaction and characterized by a variety of means, such as X-ray diffraction, Fourier transform infrared spectroscopy, micro-morphology analysis, X-ray photoelectron spectroscopy and specific surface area and pore size distribution. The as-prepared MOFs were found to be an effective material for the selective electrochemical detection of microgram levels of Pb(II), Cu(II) and Hg(II) in aqueous solution performed by differential pulse voltammetry. The electrochemical properties and applications of the modified electrode were also studied, in which operational parameters such as pH, deposition potential, and deposition time, were optimized to detect trace amounts of Pb(II), Cu(II) and Hg(II) ions. The as-prepared electrode not only has good stability and repeatability, but also has good practical detection ability.

Porous Membranes with Special Wettabilities: Designed Fabrication and Emerging Application

Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Re...

Facile synthesis of Ni-, Co-, Cu-metal organic frameworks electrocatalyst boosting for hydrogen evolution reaction

The conductive metal-organic frameworks (MOFs) are suggested as the ideal electrocatalysts for hydrogen evolution reaction (HER) because of the high utilization of metal atoms. Rational design and facile synthesis of MOFs with large specific surface area, proper metals as center, and tunable chemical components is still full of challenges. Herein, we report the facile synthesis three types of porous MOFs by regulating metal center using benzene-1,3,5-tricarboxylic acid (H3BTC) as organic ligand and have successfully synthesized the rhombic octahedral Cu-BTC, rod-shaped Co-BTC and spherical Ni-BTC materials with large specific surface area ranged in 350-500 m2 g−1. These as-prepared MOFs materials exhibit high performance of HER in 0.5 M H2SO4. Ni-BTC material exhibits the lowest overpotential of 53 mV at 10 mA cm-2 and the smallest Tafel slope of 62 mV dec−1 than those of Cu-BTC (270 mV, 155 mV dec−1) and Co-BTC (123 mV, 100 mV dec−1), which are much superior to these previously reported MOFs catalysts. In addition, the fast catalytic kinetic of Ni-BTC was confirmed by the smaller charge transfer resistance (Rct) value of 0.9 Ω and larger electrochemical active surface area (ECSA) of 35.5 cm2 than those of Cu-BTC (8.2 Ω, 22.5 cm2) and Co-BTC (1.9 Ω, 27.7 cm2). Because of the structural advantage and large ECSA, the turnover frequency (TOF) value of Ni-BTC reaches up to 0.041 s−1 at 120 mV overpotential, which is 20.5 and 2.6 times greater than that of Cu-BTC (0.002 s−1) and Co-BTC (0.016 s−1). Besides, these three types of MOFs exhibited excellent durability over 12 h. This study unfolds diverse insights into the design and facile synthesis of MOFs for electrochemical energy conversion system.

Asymmetric Supercapacitors Based on Hierarchically Nanoporous Carbon and ZnCo2O4 From a Single Biometallic Metal-Organic Frameworks (Zn/Co-MOF).

Metal-organic framework (MOF)-derived nanoporous carbons (NPCs) and porous metal oxide nanostructures or nanocomposites have gathered considerable interest due to their potential use in supercapacitor (SCs) applications, owing to their precise control over porous architectures, pore volumes, and surface area. Bimetallic MOFs could provide rich redox reactions deriving from improved charge transfer between different metal ions, so their supercapacitor performance could be further greatly enhanced. In this study, “One-for-All” strategy is adopted to synthesize both positive and negative electrodes for hybrid asymmetric SCs (ASCs) from a single bimetallic MOF. The bimetallic Zn/Co-MOF with cuboid-like structures were synthesized by a simple method. The MOF-derived nanoporous carbons (NPC) were then obtained by post-heat treatment of the as-synthesized Zn/Co-MOF and rinsing with HCl, and bimetallic oxides (ZnCo2O4) were achieved by sintering the Zn/Co-MOF in air. The as-prepared MOF-derived NPC and bimetallic oxides were utilized as negative and positive materials to assemble hybrid ASCs with 6 M KOH as an electrolyte. Owing to the matchable voltage window and specific capacitance between the negative (NPC) and positive (ZnCo2O4), the as-assembled ASCs delivered high specific capacitance of 94.4 F/g (cell), excellent energy density of 28.6 Wh/kg at a power density of 100 W/kg, and high cycling stability of 87.2% after 5,000 charge-discharge cycles. This strategy is promising in producing high-energy-density electrode materials in supercapacitors.

RETRACTED ARTICLE: A Heterometallic MOF for Highly Selective Al3+ Ion Detection and Protective Effect Against Periodontitis by Reducing P. gingivalis CFU and Inflammatory Cytokines Levels

By employment of an amide-functionalized tetracarboxylic ligand 5,5′-(carbonylbis(azanediyl))-diisophthalic acid (H4cbab), a new polyhedral metal–organic framework (MOF) with the chemical formula of {[InZn2(cbda)2(H2O)2](NMF)3}n (1, NMF = N-methylformamide) has been synthesized under the solvothermal reaction condition. The structural feature was studied via the single crystal X-ray diffraction along with ultimate analysis. This as-prepared MOF shows excellent luminescence performance which can be able to detect Al3+ ions selectively. In aqueous solutions, the detection limitation for Al3+ ion is 0.56 µM, which is significantly below the highest standard of 7.41 µM for Al3+ ion in drinking water that is defined by the World Health Organization (WHO). The protective effect of compound against periodontitis was further explored. The viable cell counts (CFU) number was counted to evaluate the inhibitory effect of compound on bacterial growth. The enzyme linked immunosorbent assay (ELISA) was carried on in order to measure accurately the proportion of inflammatory cytokines in gingival fluid around the implant. The potential binding modes of the synthesized compounds as well as the targeted protein was explored by calculating docking with high accuracy as well as pose scoring process.

Ultrathin MOF nanosheet assembled highly oriented microporous membrane as an interlayer for lithium-sulfur batteries

Lithium sulfur (Li-S) batteries are attracting increasing attentions as promising next-generation rechargeable batteries. However, the rapid capacity fading of sulfur cathodes caused by the shuttling of polysulfide intermediates between the cathodes and anodes restricts the application of Li-S batteries. In this work, a facile wet-chemistry method is developed for the direct synthesis of few-molecular-layer thin metal-organic framework (MOF) nanosheets without using surfactant. By assembling these ultrathin MOF nanosheets with a facile vacuum filtration method, a highly oriented and flexible MOF membrane with favorable mechanical properties is achieved for the first time. The excellent features make the as-prepared MOF nanosheets ideal to fabricate lightweight interlayer modified separators for suppressing the polysulfide shuttling of Li-S batteries. When using the MOF membrane modified separator, the Li-S batteries made from commercial carbon materials exhibits the significantly enhanced cycling stabilities. This work brings new opportunities for the synthesis and application of MOF materials.

Stable Layered Semiconductive Cu(I)-Organic Framework for Efficient Visible-Light-Driven Cr(VI) Reduction and H2 Evolution.

Metal-organic frameworks (MOFs) have gained tremendous attention in the fields of environmental restoration and sustainable energy for their potential use as photocatalyst. Herein, a new two-dimensional (2D) Cu(I)-based MOF material showing a narrow forbidden-band of 2.13 eV was successfully constructed using a visible-light-harvesting anthracene-based bipyridine ligand. The as-prepared MOF demonstrates high chemical stability and could be stable in the pH range 2-13, which is favorable for its potential application in photocatalysis. Photocatalytic experiments demonstrate that this Cu(I)-MOF exhibits high reactivity for reduction of Cr(VI) in water, with 95% Cr(VI) converting to Cr(III) in 10 min by using MeOH as scavenger under visible-light illumination. Furthermore, this MOF could behave as a highly active photocatalyst for H2 evolution without additional photosensitizers and cocatalyst. Remarkably, the as-prepared MOF shows enhanced photocatalytic Cr(VI) reduction and H2 evolution performances compared with the pristine light-harvesting ligand under the same conditions. In connection to these, the photocatalytic reaction mechanism has also been probed.

Designed synthesis of ultra-hydrophilic sulfo-functionalized metal-organic frameworks with a magnetic core for highly efficient enrichment of the N-linked glycopeptides

Highly efficient extraction and enrichment of the N-linked glycopeptides from complex biological samples before mass spectrometry analysis remains important but challenging, due to the low abundance and suppression by proteins and salts. Herein, a facile route to an ultra-hydrophilic metal-organic frameworks (MOFs)-functionalized magnetic nanoparticle (Fe3O4@PDA@Zr-SO3H) was proposed. The as-prepared MOFs was endowed with excellent and unique properties, such as excellent hydrophilicity, ultrahigh surface area, and strong magnetic responsiveness. By virtue of these properties and based on hydrophilic interaction, Fe3O4@PDA@Zr-SO3H exhibited outstanding sensitivity and selectivity, remarkable recyclability and stability towards N-linked glycopeptide enrichment. In deep, a total of 177 N-linked glycopeptides, assigned to 85 different glycoproteins, were identified from the healthy human serum after treated with the Fe3O4@PDA@Zr-SO3H. These results confirmed that our strategy offered a promising platform for preparing hydrophilic metal-organic framework-functionalized magnetic nanoparticles for glycosylation analysis by mass spectrometry analysis.

Designed synthesis of a \u201cOne for Two\u201d hydrophilic magnetic amino-functionalized metal-organic framework for highly efficient enrichment of glycopeptides and phosphopeptides

Highly efficient enrichment of glycopeptides or phosphopeptides from complex biological samples is indispensable for high-throughput mass spectrometry analysis. In this study, for the first time, a “one for two” hydrophilic magnetic amino-functionalized metal-organic framework (MOF) was designed and synthesized for selective enrichment of both glycopeptides and phosphopeptides. A well-known solvo-thermal reaction was adopted to prepare a magnetic core Fe3O4, followed by self- polymerization of dopamine, creating a polydopamine (PDA) onto Fe3O4. Thanks to the hydroxyl and amino group of PDA, Zr3+ was easily adhered to the surface, inducing the following one-pot MOF reaction with amino ligand. After characterization of the as-prepared MOFs (denoted as Fe3O4@PDA@UiO-66-NH2), its ultrahigh surface area, excellent hydrophilicity and strong magnetic responsiveness were highly confirmed. Based on hydrophilic interaction, it was applied to glycopeptide enrichment, while based on strong binding between Zr and phosphopeptides, it was applied to phosphopeptide enrichment, both exhibiting excellent performance in standard proteins and human serum with high sensitivity and selectivity. These results showed the as-prepared MOFs had great potential in proteomics research.

Mesoporous Metal–Organic Framework with Well-Defined Cruciate Flower-Like Morphology for Enzyme Immobilization

Metal-organic frameworks (MOFs) have recently emerged as a promising candidates for the immobilization of enzymes due to their diversified structures and porosity. However, a lack of good size and morphological control over the as-prepared MOFs has limited their practical applications in some cases. Herein, instead of zeolitic imidazolate framework-8 (ZIF-8) with the standard rhombic dodecahedral morphology, we successfully synthesize a novel mesoporous catalase@ZIF composite with cruciate flower-like morphology by embedding catalase molecules into uniformly sized ZIF crystals. With extraordinarily large mesopore size and high protein loading capacity, the catalase@ZIF composites with cruciate flower-like morphology exhibit 400% higher activity than that of catalase@ZIF composites with conventional rhombic dodecahedral morphology, and show higher reusability than conventional rhombic dodecahedral morphology. More importantly, we demonstrate for the first time that the biomacromolecules (proteins) can not directly regulate the crystal size, morphology, and crystallinity of ZIF-8. Moreover, the crystal morphology of ZIF has primary dependence on concentrations of 2-methylimidazole and Zn2+ ions, and can be directly controlled by adjusting concentrations of Zn2+ ions while keeping the high concentration of 2-methylimidazole.

Template-Directed Synthesis of Porous and Protective Core-Shell Bionanoparticles.

Metal-organic frameworks (MOFs) are promising high surface area coordination polymers with tunable pore structures and functionality; however, a lack of good size and morphological control over the as-prepared MOFs has persisted as an issue in their application. Herein, we show how a robust protein template, tobacco mosaic virus (TMV), can be used to regulate the size and shape of as-fabricated MOF materials. We were able to obtain discrete rod-shaped TMV@MOF core-shell hybrids with good uniformity, and their diameters could be tuned by adjusting the synthetic conditions, which can also significantly impact the stability of the core-shell composite. More interestingly, the virus particle underneath the MOF shell can be chemically modified using a standard bioconjugation reaction, showing mass transportation within the MOF shell.

Simple fabrication of flake-like NH2-MIL-53(Cr) and its application as an electrochemical sensor for the detection of Pb2+

A novel metal-organic framework (MOF) material, flake-like NH2-MIL-53(Cr), was prepared by a simple reflux method and then characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The as-prepared MOF was found to be an effective material for the selective electrochemical detection of microgram levels of Pb2+ in aqueous solution. Detection was performed by square wave anodic stripping voltammetry. The NH2-MIL-53(Cr)-modified electrode showed excellent selectivity and stability for Pb2+ detection. The electrochemical properties and applications of the modified electrode were studied. Operational parameters such as pH, deposition potential, and deposition time, were also optimized to detect trace amounts of metal ions. This method offers a new strategy for heavy metal detection using MOF materials.

Charge Transfer-Induced Molecular Hole Doping into Thin Film of Metal-Organic Frameworks.

Despite the highly porous nature with significantly large surface area, metal-organic frameworks (MOFs) can be hardly used in electronic and optoelectronic devices due to their extremely poor electrical conductivity. Therefore, the study of MOF thin films that require electron transport or conductivity in combination with the everlasting porosity is highly desirable. In the present work, thin films of Co3(NDC)3DMF4 MOFs with improved electronic conductivity are synthesized using layer-by-layer and doctor blade coating techniques followed by iodine doping. The as-prepared and doped films are characterized using FE-SEM, EDX, UV/visible spectroscopy, XPS, current-voltage measurement, photoluminescence spectroscopy, cyclic voltammetry, and incident photon to current efficiency measurements. In addition, the electronic and semiconductor properties of the MOF films are characterized using Hall Effect measurement, which reveals that, in contrast to the insulator behavior of the as-prepared MOFs, the iodine doped MOFs behave as a p-type semiconductor. This is caused by charge transfer-induced hole doping into the frameworks. The observed charge transfer-induced hole doping phenomenon is also confirmed by calculating the densities of states of the as-prepared and iodine doped MOFs based on density functional theory. Photoluminescence spectroscopy demonstrates an efficient interfacial charge transfer between TiO2 and iodine doped MOFs, which can be applied to harvest solar radiations.

Tunable Anisotropic Thermal Expansion of a Porous Zinc(II) Metal–Organic Framework

A novel three-dimensional metal-organic framework (MOF) that displays anisotropic thermal expansion has been prepared and characterized by single-crystal X-ray diffraction (SCD) and thermal analysis. The as-prepared MOF has one-dimensional channels containing guest molecules that can be removed and/or exchanged for other guest molecules in a single-crystal to single-crystal fashion. When the original guest molecules are replaced there is a noticeable effect on the host mechanics, altering the thermal expansion properties of the material. This study of the thermal expansion coefficients of different inclusion complexes of the host MOF involved systematic alteration of guest size, i.e., methanol, ethanol, n-propanol, and isopropanol, showing that fine control over the thermal expansion coefficients can be achieved and that the coefficients can be correlated with the size of the guest. As a proof of concept, this study demonstrates the realizable principle that a single-crystal material with an exchangeable guest component (as opposed to a composite) may be used to achieve a tunable thermal expansion coefficient. In addition, this study demonstrates that greater variance in the absolute dimensions of a crystal can be achieved when one has two variables that affect it, i.e., the host-guest interactions and temperature.

Lanthanide-Porphyrin Hybrids: from Layered Structures to Metal–Organic Frameworks with Photophysical Properties

Rare-earth layered hydroxides with intercalated tetrasulfonated porphyrins and corresponding to the chemical formula Ln2(OH)4.7(Por)0.33·2H2O (Ln = Eu(3+), Tb(3+); Por = 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and PdTPPS) have been prepared to investigate their photophysical properties. A slight variation of the synthetic procedure led to the metal-organic framework (MOF) assembled from a distorted octahedral oxometalate clusters [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+). These secondary building units (SBUs) are linked together by six distorted porphyrin units. During activation, the original SBU loses not only water molecules from the coordination sphere but also the central μ6-O atom. The loss of the central atom results in the distortion of the octahedral [Eu6(μ6-O)(μ3-OH)8(H2O)14](8+) SBU into a trigonal antiprismatic [Eu6(μ3-OH)8(H2O)2](10+) SBU with two μ3-OH groups nearly in plane with the europium atoms and the reduction of pores to approximately 2 × 3 Å. As a result, the MOF has no accessible porosity. This transformation was thoroughly characterized by means of single-crystal X-ray crystallographic analysis of both phases. Solid-state photophysical investigations suggest that the MOF material is fluorescent; however, in contrast to the prepared layered hydroxides, the as-prepared MOF is an effective sensitizer of singlet oxygen, O2((1)Δg), with a relatively long lifetime of 23 ± 1 μs. The transition is also accompanied by variation in photophysical properties of the coordinated TPPS. The alteration of the fluorescence properties and of the O2((1)Δg) lifetime presents an opportunity for preparation of MOFs with oxygen-sensing ability or with oxidation potential toward organic molecules by O2((1)Δg).

Facile synthesis of highly luminescent nanowires of a terbium-based metal–organic framework by an ultrasonic-assisted method and their application as a luminescent probe for selective sensing of organoamines

In this paper, we report on a facile and environmentally friendly large-scale synthesis of metal–organic framework (MOF) nanowires by using an ultrasonic method without the introduction of any seeds, polymers, or surfactants. Highly luminescent nanowires of a one-dimensional terbium benzenetricarboxylate MOF, [Tb(1,3,5-btc)(H 2 O) 6 ] n (1,3,5-btc = benzene-1,3,5-tricarboxylate), with an average diameter of 50 nm and lengths of up to a few micrometers can be easily obtained in a relatively high yield under ultrasound irradiation at 70 °C and under atmospheric pressure. The structure and morphology of the as-synthesized MOF nanowires were characterized by powder X-ray diffractometry (PXRD) and field emmision scanning electron microscopy (FE-SEM), respectively. The [Tb(1,3,5-btc)(H 2 O) 6 ] n nanowires obtained show strong luminescence emission at 548 and 492 nm, and exhibit high selectivity for sensing of aromatic amines, such as aniline and p -phenylenediamine, in comparison with alkylamines (e.g. methylamine, ethylamine, n -propylamine, n -butylamine and triethylamine). Such a significantly selective luminescence quenching effect of [Tb(1,3,5-btc)(H 2 O) 6 ] n nanowires for aromatic amines makes the nanostructured Tb-MOF-based sensing materials potential for sensing of aromatic amines in a mixture solution of organoamines. Highly luminescent nanowires of a lanthanide metal–organic framework (MOF), [Tb(1,3,5-btc)(H 2 O) 6 ] n , have been successfully fabricated by an ultrasonic method, and the as-prepared MOF nanowires exhibit significantly high selectivity for sensing of aromatic amines. ► Highly luminescent nanowires of a lanthanide metal–organic framework (MOF). ► Rapid synthesis of MOF nanocrystals under ultrasonic irradiation. ► High sensitivity of the [Tb(btc)(H 2 O) 6 ] n MOF nanowires to aromatic amines.

Characterization of a New Porous Pt-Containing Metal-Organic Framework Containing Potentially Catalytically Active Sites: Local Electronic Structure at the Metal Centers

A crystalline and thermally stable metal-organic framework (MOF) with PtII and GdIII sites incorporated in the structure has been recently reported. This material has been synthesized with the aim to develop a heterogeneous PtII counterpart to homogeneous metal-organic complexes having C−H activating properties. The first account focused on the MOF synthesis and on structural and stability characterization of the material. In the present work, a multitechnique approach has been adopted to investigate the effect of solvent removal and the reversibility of this process. Structural features have been investigated by means of powder X-ray diffraction and extended X-ray absorption fine structure spectroscopy at both Pt and Gd L3-edges. Electronic properties have been studied with diffuse reflectance surface UV−vis and X-ray absorption near-edge spectroscopies. Finally, IR spectroscopy has been used to determine the vibration properties. Thermogravimetric methods have been used to quantify the water loss. X-ray absorption spectroscopy has been used to compare the Pt environment in the periodic MOF structure, in related molecular complexes, and in the linkers. Our results demonstrate that the environment around Pt is more or less unaffected by the incorporation of the Pt centers in the molecular complexes into the 3D extended framework of the Pt−Gd MOF. The principle of using known homogeneous complexes as building blocks for the construction of single-site heterogeneous catalysts therefore seems applicable in the present case. Removal of solvent water molecules from the internal voids of the as-prepared MOF presents an opportunity to attain a porous material with accessible PtII sites. We observe that the structure undergoes a reversible loss of long-range order upon dehydration at ambient temperature. The environment of Gd is somewhat perturbed in the dehydration/hydration process, while that of Pt is almost unaffected. When a total dehydration is achieved, the original structure is only partially recovered upon rehydration.