Features Of Metal-organic Frameworks Research Articles

Metal Centers and Organic Ligands Determine Electrochemistry of Metal-Organic Frameworks.

The properties and applications of metal-organic frameworks (MOFs) can be tuned by their metal centers and organic ligands. To reveal experimentally and theoretically the influence of metal centers and ligands on electrochemical performance of MOFs, three MOFs with copper or zinc centers and organic ligands of 2-methylimidazole (2MI) or 1,3,5-benzenetricarboxylic acid (H3 BTC) are synthesized and characterized in this study. 2D and porous Cu-2MI exhibits a larger active area, faster electron transfer capability, and stronger adsorption capacity than bulk Cu-BTC and dodecahedron Zn-2MI. Density functional theory calculations of adsorption ability of three MOFs toward xanthine (XA), hypoxanthine (HXA), and malachite green (MG) prove that 2D Cu-2MI has the strongest adsorption energies to three targets. Rotating disk electrode measurements reveal that 2D Cu-2MI features the biggest intrinsic heterogeneous rate constant toward three analytes. On 2D Cu-2MI sensitive and selective monitoring of XA, HXA, and MG is then achieved using differential pulse voltammetry. Their monitoring in real samples on 2D Cu-2MI is accurate and comparable with that using high-performance liquid chromatography. In summary, regulation of electrochemical sensing features of MOFs is realized through defining selected metal centers and organic ligands.

Perspectives of metal-organic framework nanosystem to overcome tumor drug resistance.

Cancer is one of the most harmful diseases in the world, which causes huge numbers of deaths every year. Many drugs have been developed to treat tumors. However, drug resistance usually develops after a period of time, which greatly weakens the therapeutic effect. Tumor drug resistance is characterized by blocking the action of anticancer drugs, resisting apoptosis and DNA repair, and evading immune recognition. To tackle tumor drug resistance, many engineered drug delivery systems (DDS) have been developed. Metal-organic frameworks (MOFs) are one kind of emerging and promising nanocarriers for DDS with high surface area and abundant active sites that make the functionalization simpler and more efficient. These features enable MOFs to achieve advantages easily towards other materials. In this review, we highlight the main mechanisms of tumor drug resistance and the characteristics of MOFs. The applications and opportunities of MOF-based DDS to overcome tumor drug resistance are also discussed, shedding light on the future development of MOFs to address tumor drug resistance.

MOF/COF hybrids as next generation materials for energy and biomedical applications.

The rapid increase in the number and variety of metal organic frameworks (MOFs) and covalent organic frameworks (COFs) has led to groundbreaking applications in the field of materials science and engineering. New MOF/COF hybrids combine the outstanding features of MOF and COF structures, such as high crystallinities, large surface areas, high porosities, the ability to decorate the structures with functional groups, and improved chemical and mechanical stabilities. These new hybrid materials offer promising performances for a wide range of applications including catalysis, energy storage, gas separation, and nanomedicine. In this highlight, we discuss the recent advancements of MOF/COF hybrids as next generation materials for energy and biomedical applications with a special focus on the use of computational tools to address the opportunities and challenges of using MOF/COF hybrids for various applications.

Combining crystal graphs and domain knowledge in machine learning to predict metal-organic frameworks performance in methane adsorption

A novel method capable of efficiently predicting the methane adsorption uptakes by metal-organic frameworks (MOFs) is proposed, which is built on the crystal graph convolutional neural network algorithm. Our method considers certain key physical features of MOFs along with information on secondary building units. Because the general force field fails to reproduce methane–MOF interactions involving the open metal site (OMS) adequately, the new force field parameters for methane are refined specifically for the OMS MOFs using a generic algorithm, which is particularly useful in constructing a more accurate dataset via the high-throughput grand canonical Monte Carlo. Extensive analyses demonstrate that the Pearson correlation coefficient and mean average error can reach as high as 0.973 and 9.98 cm3/cm3 for the newly developed algorithm, respectively. Furthermore, this model acquires information from the adsorption volume as embedding representations. This allows for the application of transfer learning by fine-tuning a pretrained graph network for the different properties. Finally, we predicted the methane adsorption volumes by all the MOFs in a 137953 hypothetical database at 298 K and 65 bar within hours. It is believed that this new method could be a useful tool in the early stages of high-throughput virtual screening of novel porous materials for gas adsorption or separation.

Synthesis and properties of a novel photochromic metal organic framework for rapid amine selective sensing and Cr2O72− detection

A new photochromic metal organic frameworks (MOFs) have been synthesized by using a viologen ligand, named 1,1′-bis(3,5-carboxylatobenzyl)-(4,4′-bipyridinium) dichloride (H4bdcbpy•2Cl) and Cd(NO3)2·4H2O. This MOF (Cd-bdcbpy) features a three-dimensional (3D) framework structure, exhibiting photochromic properties under the irradiation of white light, blue light, UV light and heat with obvious color change from light yellow to dark green. Meanwhile, Cd-bdcbpy displays a visible color change to the naked eye when exposed to different organic amine molecules (ammonia, aniline, o-methylaniline and diphenylamine). Moreover, the detection of ammonia has been confirmed by the visual color changing phenomenon and luminescence quenching experiment and it can detect ammonia in very low concentrations (10-6 ​M). Attractively, through luminescence quenching, Cd-bdcbpy can be used as a multi response sensor for Cr2O72− anion in aqueous solution.

Metal-Organic Framework Based Gas Sensors.

The ever‐increasing concerns over indoor/outdoor air quality, industrial gas leakage, food freshness, and medical diagnosis require miniaturized gas sensors with excellent sensitivity, selectivity, stability, low power consumption, cost‐effectiveness, and long lifetime. Metal‐organic frameworks (MOFs), featuring structural diversity, large specific surface area, controllable pore size/geometry, and host‐guest interactions, hold great promises for fabricating various MOF‐based devices for diverse applications including gas sensing. Tremendous progress has been made in the past decade on the fabrication of MOF‐based sensors with elevated sensitivity and selectivity toward various analytes due to their preconcentrating and molecule‐sieving effects. Although several reviews have recently summarized different aspects of this field, a comprehensive review focusing on MOF‐based gas sensors is absent. In this review, the latest advance of MOF‐based gas sensors relying on different transduction mechanisms, for example, chemiresistive, capacitive/impedimetric, field‐effect transistor or Kelvin probe‐based, mass‐sensitive, and optical ones are comprehensively summarized. The latest progress for making large‐area MOF films essential to the mass‐production of relevant gas sensors is also included. The structural and compositional features of MOFs are intentionally correlated with the sensing performance. Challenges and opportunities for the further development and practical applications of MOF‐based gas sensors are also given.

MOF-based membranes for pervaporation

Pervaporation competes with conventional separation techniques, such as distillation and adsorption in organic liquid dehydration, removal or recovery of organic compounds from aqueous solutions, and separation of organic-organic mixtures. Pervaporation is a separation technique relying on the concentration gradient, often expressed as partial vapor pressures, across polymeric or polymer-composite membranes. Those membranes often exhibit a strong trade-off between permeability and selectivity of target compounds, making the search for alternative materials with advanced performance characteristics highly desirable. Metal–organic frameworks (MOFs), a sub-group of porous functionalised materials, have recently demonstrated potential to become a valuable building block in the fabrication of future high-performance pervaporation membranes. MOFs feature unique properties, such as molecular sieve effects, preferential adsorption to the target molecular compounds, and thermal and chemical stability, being suitable for direct applications in pervaporation separation of liquid mixtures. This paper comprehensively examines the current design strategies of MOF-based membranes in pervaporation. The main developments of MOF-based membranes in pervaporation are discussed and the performance of pervaporation processes using MOF-based membranes is also analysed. Furthermore, some perspectives for future development of MOF-based membranes in pervaporation are given.

Hydrogen generation from sodium borohydride hydrolysis promoted by MOF-derived carbon supported cobalt catalysts

Co-based catalysts represent a kind of low-cost non-noble metal catalysts with attractive performance for catalyzing NaBH4 hydrolysis to produce hydrogen. In the present work, a series of carbon-supported Co catalysts are fabricated through pyrolysis with activated carbon as substrate and metal organic frameworks as Co precursor. Due to the features of metal organic frameworks including well-defined and stable structure and high surface area, Co species is well dispersed in the catalysts with narrow size distribution. The results of NaBH4 hydrolysis experiments indicate that the fabricated catalysts have excellent catalytic activity, especially under alkaline conditions. The catalyzed NaBH4 hydrolysis provides a hydrogen generation rate of 4.9 LH2/(min gCo) at 30 °C, and the activation energy of the reaction is calculated to be 35.09 kJ/mol. Moreover, the good distribution of Co species in the catalysts makes the Co efficiency not decrease significantly even when the Co content in the catalyst increases up to 20.1 wt%, providing possibility to fabricate catalysts with both high metal loading and high metal efficiency. This kind of Co catalyst could provide a very promising choice for controllable hydrogen generation from NaBH4 hydrolysis.

Metal organic frameworks (MOFs) as potential anode materials for improving power generation from algal biophotovoltaic (BPV) platforms

Microalgae based biophotovoltaic (BPV) cells are substantiated as innovative renewable energy generation devices, owing to their ability in mimicking the catalytic activity of microorganisms for water splitting reaction along with an effectual reduction of carbon footprint in our environment. As the direct contact between algal cells and anodic surface effectually governs the electron transfer and overall BPV performance, the development of electrochemically active and stable catalysts is crucial for the evolution of high performance BPVs. Accordingly, the monoclinic structured copper (Cu) metal organic framework (MOF) is prepared through the simple ageing process and the consequent bimetallic (Cu-Nickel(Ni)) MOF is developed via the partial substitution of Cu2+ with Ni2+ nodes without any variation in the chemical structure of Cu-MOF. The as-formulated MOFs loaded indium tin oxides (ITOs) are exploited as BPV anodes and their influences on green energy generation by using the freshwater microalgae Chlorella sp. UMACC 313 as a catalytic system are scrutinized in detail. The electrochemical activeness and robust stability of as-fabricated BPV anodes are enunciated, respectively, from the cyclic voltammetry and chronoamperometry techniques. Cu-Ni MOF/ITO equipped BPV establishes the power density of 40 μWm−2, which is substantially higher than those of Cu-MOF/ITO and ITO. The substantial features of Cu-Ni MOF including the elevated structural integrity, existence of different metallic ions with the rational electrical conductivity, and supplemental functionality accelerate its maximum green energy generation performance. Thus, these verdicts establish a distinctive approach in tailoring the electrochemically active and stable MOF anode materials for the evolution of ecologically benevolent fuel cells.

Synthesis of porous secondary metal-doped MOFs for removal of Rhodamine B from water: Role of secondary metal on efficiency and kinetics

Metal-organic frameworks (MOFs) are newly introduced category of porous compounds reflected as proficient and economic to exclude organic dyes from water. In the present work, a metal doping strategy in MOFs has been introduced to enhance the efficiency of porous MOFs for adsorption of environmentally detrimental rhodamine B (Rh-B). The porous ZIF-67 and metal-doped MOFs (Fe@ZIF-67) having Fe metal composition 1%, 3% and 5% were fabricated by in situ doping strategy during a simple solvothermal synthesis of ZIF-67. The spectroscopic characterization showed that limited metal-doping did not affect the characteristic features of MOFs like structural topology, porosity and surface area. The highest observed adsorption amount of Fe@ZIF-67 (5%) calculated with Langmuir model was 135.14 mg. g−1, considerably higher as compared to pristine ZIF-67 (85.69 mg. g−1) and other synthesized MOFs. The adsorption experiments data was well fitted by Langmuir model (R2 = 0.998) clarified that the adsorption process of Rh-B was monolayer and specified a stronger electrostatic interaction between Rh-B and porous Fe@ZIF-67 with 5% Fe, which was reliable with the observation from the effects of pH and ionic strength. The results showed that 47.71, 64.52 and 79.92% of rhodamine B dye removed by Fe@ZIF-67 (1%), Fe@ZIF-67 (3%) and Fe@ZIF-67 (5%) respectively with 240 minutes contact time. The recycling experiments also disclosed high stability of the Fe-doped MOFs. Up to 92% adsorption efficiency was examined after four regeneration cycles. All of the outcomes shown a pronounced prospective of the synthesized Fe@ZIF-67 nanocomposite in water treatment/purification in the industry.

Spectroscopic investigations of gamma-ray irradiation effects on metal organic framework

The chemical and physical features of metal organic frameworks (MOFs) at a molecular level are of great merit to understand structure–property relationships and, consequently, to aid in the design of improved high value products. This paper reports on the processing of one MOF-type material, namely MIL-101(Cr), by γ-ray irradiation at low doses up to 30 kGy. The optimum dose is determined to be 15 kGy, at which an increase in the adsorption of iodine of more than 40% is achieved in comparison with thermally activated un-irradiated MIL-101(Cr). Scanning electron microscopy, X-ray diffraction and the Brunauer−Emmett−Teller (BET) isotherms indicate a significant particle agglomeration and a preservation of both the unit cell topology as well as the mesoporous structure of MOF. Two-dimensional correlation Fourier transformation infrared and X-ray diffraction reveals that orientation is the driving force for structural alterations including water type, bonding and contents. These effects account for the increasing adsorption capacity of MOF after irradiation and suggest further exploitation of irradiation as a promising method for MOFs activation.

Multiple functional groups in metal–organic frameworks and their positional regioisomerism

Abstract Metal-organic frameworks (MOFs) have been considered an emerging material for various applications. The fine tunability of both their inorganic nodes and organic ligands make MOFs a good platform for target-specific utilization. Generally, two coordinating groups (e.g., carboxylate) are necessary for MOF formations in case of representative, benzene-dicarboxylic acid type MOFs, and the additional functional groups could be installed in the remaining sites of organic ligands. Various functional groups could be introduced on the ligands such as amino-, halo-, hydroxy-, ether, thiol, and etc. In addition, multiple functional groups could be installed at specific position on the ligand by implementing positional regioisomerism, which helps elucidate the individual effects that each substituent imposes on the organic linkers. Therefore, deliberate structural and functional features can be introduced into a pristine framework. Indeed, this relatively ease functionalizations and positional isomerism of functional groups are the unique features of MOFs compare to other porous materials. In this review, we systematically categorized and described positional regioisomerism with multiple functional groups in MOF organic linkers. Specifically, regioisomeric MOFs bearing two identical groups, two different groups, more than three dissimilar groups, or miscellaneous moieties were discussed in terms of their structures and functions. A comprehensive overview of studies investigating the structures and properties triggered by the different positioning of functional groups in MOF frameworks could provide a base for the molecular design of desirable materials with advanced functionality.

XGBoost: An Optimal Machine Learning Model with Just Structural Features to Discover MOF Adsorbents of Xe/Kr.

The inert gases Xe and Kr mainly exist in the used nuclear fuel (UNF) with the Xe/Kr ratio of 20:80, which it is difficult to separate. In this work, based on the G-MOFs database, high-throughput computational screening for metal–organic frameworks (MOFs) with high Xe/Kr adsorption selectivity was performed by combining grand canonical Monte Carlo (GCMC) simulations and machine learning (ML) technique for the first time. From the comparison of eight classical ML models, it is found that the XGBoost model with seven structural descriptors has superior accuracy in predicting the adsorption and separation performance of MOFs to Xe/Kr. Compared with energetic or electronic descriptors, structural descriptors are easier to obtain. Note that the determination coefficients R2 of the generalized model for the Xe adsorption and Xe/Kr selectivity are very close to 1, at 0.951 and 0.973, respectively. In addition, 888 and 896 MOFs have been successfully predicted by the XGBoost model among the top 1000 MOFs in adsorption capacity and selectivity by GCMC simulation, respectively. According to the feature engineering of the XGBoost model, it is shown that the density (ρ), porosity (ϕ), pore volume (Vol), and pore limiting diameter (PLD) of MOFs are the key features that affect the Xe/Kr adsorption property. To test the generalization ability of the XGBoost model, we also tried to screen MOF adsorbents on the CO2/CH4 mixture, it is found that the prediction performance of XGBoost is also much better than that of the traditional machine learning models although with the unbalanced data. Note that the dimension of features of MOFs is low while the quantity of MOF samples in database is very large, which is suitable for the prediction by model such as XGBoost to search the global minimum of cost function rather than the model involving feature creation. The present study represents the first report using the XGBoost algorithm to discover the MOF adsorbates.

Functional UiO-66 Series Membranes with High Perm Selectivity of Monovalent and Bivalent Anions for Electrodialysis Applications

Metal–organic frameworks (MOFs) have a good separation potential due to their uniform pore size, easy functionalization, and adjustable structure. Therefore, we make use of this feature of MOFs for the separation of Cl–/SO₄²– systems with different charges and sizes. In this work, two kinds of UiO-66 membranes with different functional groups were synthesized and applied to the monovalent perm-selective separation of the Cl–/SO₄²– system in electrodialysis (ED). UiO-66-NH₂ membranes were used to investigate the influence of current density and initial solution concentration on perm selectivity. A layer of UiO-66-NH₂ was first grown on the anodic alumina oxide (AAO) disks. After that, short chains containing sulfonic acid groups were grafted onto the amino groups by the ring-opening reaction of 1,3-propanesulfonate. The structural stability of the MOF layer was confirmed by XRD analysis of the membrane surface after the ED test. Ion exchange capacity (IEC) and elemental mapping were used to confirm the comparison changes in the degree of sulfonation. It was found that UiO-66-NH₂ membranes exhibited a higher monovalent anion perm selectivity with a peak value of 36.23 (initial mixture solution of 0.05 M NaCl and 0.05 M Na₂SO₄) at lower current density (2.5 mA·cm–²). The perm selectivity of UiO-66-SO₃H membranes increased with running time under 24 h of sulfonation time. In particular, with low IEC value of 0.10–0.16, it still showed a good performance on perm selectivity. Compared with published polymer ion exchange membranes (perm selectivity < 5) for ED, it has higher perm selectivity, more convenient functionalization, and resistance to organic solvents.

Turn‐On Circularly Polarized Luminescence in Metal–Organic Frameworks

AbstractThe fabrication of circularly polarized luminescence (CPL) active materials by self‐assembly is still in its challenge. In this work, a family of homochiral metal–organic frameworks (MOFs) and metal–organic cages (MOCs) are constructed by solvothermal subcomponent self‐assembly. These MOFs feature an eta topology with trifold helical chains, while the MOCs adopt a cubic cage structure. The chiral ligands show two distinct types of conformations: “opened” and “closed” in MOFs and MOCs, respectively. Although homochiral MOFs and MOCs show similar spectra of circular dichroism and photoluminescence with similar quantum yields and lifetimes, the MOFs yield clear CPL signals and the CPL of MOCs are silent. The turn‐on CPL in MOFs achieved by tuning the conformation of ligands and controlling self‐assembly provides a new approach for development of CPL‐active MOF materials.

Analyzing acetylene adsorption of metal–organic frameworks based on machine learning

Metal–organic frameworks (MOFs) containing open metal sites are important materials for acetylene (C2H2) adsorption. However, it is inefficient or even impossible to search suitable MOFs by molecular simulation method in nearly infinite MOFs space. Therefore, machine learning (ML) methods are adopted in the material screening and prediction of high-performance MOFs. In this paper, architecture, chemical and structural features are used to analyze the C2H2 adsorption performance of the MOFs. Different ML algorithms are applied to perform classification and regression analysis to the factors affecting material adsorption. By decision tree (DT) algorithm, it is found that only PV, GSA, and Cu-OMS are sufficient to determine the high adsorption of the MOFs. Furthermore, the influence of topology on the performance of MOFs is obtained. Gradient Boosting Decision Tree (GBDT), Support Vector Machine (SVM), and Back Propagation Neural Network (BPNN), are introduced to analyze the quantitative structure–property relationship (QSPR) between C2H2 adsorption and the features of MOFs. The prediction of the GBDT model is found to have the highest accuracy, with R2 as 0.93 and RMSE as 11.58. In addition, the GBDT model is used for feature analysis, and the contribution of each feature to the performance is obtained, which is of great significance for the design and analysis of MOFs. The successful application of ML to MOFs screening greatly reduce the calculation time and provides important reference for the design and synthesis of new MOFs.

Cobalt-Based Metal Organic Frameworks as Solids Catalysts for Oxidation Reactions

Metal organic frameworks (MOFs) are porous crystalline solids whose frameworks are constituted by metal ions/nodes with rigid organic linkers leading to the formation of materials having high surface area and pore volume. One of the unique features of MOFs is the presence of coordinatively unsaturated metal sites in their crystalline lattice that can act as Lewis acid sites promoting organic transformations, including aerobic oxidation reactions of various substrates such as hydrocarbons, alcohols, and sulfides. This review article summarizes the existing Co-based MOFs for oxidation reactions organized according to the nature of substrates like hydrocarbon, alcohol, olefin, and water. Both aerobic conditions and peroxide oxidants are discussed. Emphasis is placed on comparing the advantages of using MOFs as solid catalysts with respect to homogeneous salts in terms of product selectivity and long-term stability. The final section provides our view on future developments in this field.

Sensitive impedimetric detection of E. coli with metal-organic framework (MIL-53) / polymer (PEDOT) composite modified screen-printed electrodes

Present work details the development of an electrochemical biosensing system for E. coli. A composite of a metal-organic framework (MOF), i.e. MIL-53 (Fe) (MIL = Materials of Institut Lavoisier) with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been prepared and used to modify the carbon-screen printed electrodes (cSPE). Due to the addition of PEDOT:PSS, the composite has exhibited electrochemical conductivity along with several other known beneficial features of MOF. The composite modified cSPE has been functionalized with anti-E. coli antibodies to guarantee the specificity of the detection. The present electrochemical sensor, based on the measurement of electrochemical impedance spectroscopic and different pulse voltammetry signals, has allowed the detection of E. coli over a wide concentration range of 2.1 × 102 to 2.1 × 108 cfu/mL, with the best detection limit of 4 cfu/mL. The sensor could also tolerate the co-presence of other possibly interfering species, such as S. aureus and S. arlettae. The results obtained from the present system have been validated against standard techniques.

Porphyrin-Based Metal-Organic Frameworks for Biomedical Applications.

Porphyrins and porphyrin derivatives have been widely explored for various applications owing to their excellent photophysical and electrochemical properties. However, inherent shortcomings, such as instability and self‐quenching under physiological conditions, limit their biomedical applications. In recent years, metal–organic frameworks (MOFs) have received increasing attention. The construction of porphyrin‐based MOFs by introducing porphyrin molecules into MOFs or using porphyrins as organic linkers to form MOFs can combine the unique features of porphyrins and MOFs as well as overcome the limitations of porphyrins. This Review summarizes important synthesis strategies for porphyrin‐based MOFs including porphyrin@MOFs, porphyrinic MOFs, and composite porphyrinic MOFs, and highlights recent achievements and progress in the development of porphyrin‐based MOFs for biomedical applications in tumor therapy and biosensing. Finally, the challenges and prospects presented by this class of emerging materials for biomedical applications are discussed.

Iontronics Using V2CTx MXene-Derived Metal-Organic Framework Solid Electrolytes.

Electronic applications of porous metal–organic frameworks (MOFs) have recently emerged as an important research area. However, there is still no report on using MOF solid electrolytes in iontronics, which could take advantage of the porous feature of MOFs in the ionic transport. In this article, MXene-derived two-dimensional porphyrinic MOF (MX-MOF) films are demonstrated as an electronic-grade proton-conducting electrolyte. Meanwhile, the MX-MOF film shows high quality, chemical stability, and capability of standard device patterning processes (e.g., dry etching and optical and electron beam lithography). Using the commercialized nanofabrication processes, an electric double-layer (EDL) transistor is demonstrated using the MX-MOF film (derived from V2CTx MXene) as an ionic gate and MoS2 film as a semiconducting channel layer. The EDL transistor, operated by applying an electric field to control the interaction between ions and electrons, is the core device platform in the emerging iontronics field. Therefore, The MX-MOF, confirmed as a solid electrolyte for EDL transistor devices, could have a significant impact on iontronics research and development.