New members of MOF-76 family containing Ho(III) and Tm(III) ions: Characterization, stability and gas adsorption properties

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Lanthanide Metal-Organic Frameworks Exhibiting Fluoro-Bridged Extended Chains: Synthesis, Crystal Structures, and Magnetic Properties

Two fluoro-bridged lanthanide-containing metal-organic frameworks (MOFs) were synthesized using 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDC), a fluorinated modulator, and a lanthanide nitrate. The syntheses of MOFs containing Gd3+ or Tb3+ and a closely related MOF structure containing Ho3+, Gd3+, or Tb3+ are presented. The presence of the fluorinated metal chains in these MOFs is shown through single crystal X-ray diffraction, energy dispersion X-ray spectroscopy, 19F nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Magnetic measurements reveal weak antiferromagnetic exchange between the Ln3+ ions mediated by fluoride anions along the zigzag ladder chains present in the crystal structures of these MOFs.

Expanding the Transuranic Metal-Organic Framework Portfolio: The Optical Properties of Americium(III) MOF-76

Reported is the synthesis, crystal structure, and solid-state characterization of a new americium containing metal-organic framework (MOF), [Am(C9H3O6)(H2O)], MOF-76(Am). This material is constructed from Am3+ metal centers and 1,3,5-tricarboxylic acid (BTC) ligands, forming a porous three-dimensional framework that is isostructural with several known trivalent lanthanide (Ln) analogs (e.g., Ce, Nd, and Sm-Lu). The Am3+ ions have seven coordinates and assume a distorted, capped trigonal prismatic geometry with C1 symmetry. The Am3+-O bonds were studied via infrared spectroscopy and compared to several MOF-76(Ln) analogs, where Ln = Nd3+, Eu3+, Tb3+, and Ho3+. The results show that the strength of the ligand carboxylate stretching and bending modes increase with Nd3+ < Eu3+ < Am3+ < Tb3+ < Ho3+, suggesting the metal-oxygen bonds are predominantly ionic. Optical absorbance spectroscopy measurements reveal strong f-f transitions; some exhibit pronounced crystal field splitting. The photoluminescence spectrum contains weak Am3+-based emission that is achieved through direct and indirect metal center excitation. The weak emissive behavior is somewhat surprising given that ligand-to-metal resonance energy transfer is efficient in the isoelectronic Eu3+ (4f6) and related Tb3+ (4f8) analogs. The optical properties were explored further within a series of heterometallic MOF-76(Tb1-xAmx) (x = 0.8, 0.2, and 0.1) samples, and the results reveal enhanced Am3+ photoluminescence.

Holmium-Containing Metal-Organic Frameworks as Modifiers for PEBA-Based Membranes

Recently, there has been an active search for new modifiers to create hybrid polymeric materials for various applications, in particular, membrane technology. One of the topical modifiers is metal-organic frameworks (MOFs), which can significantly alter the characteristics of obtained mixed matrix membranes (MMMs). In this work, new holmium-based MOFs (Ho-MOFs) were synthesized for polyether block amide (PEBA) modification to develop novel MMMs with improved properties. The study of Ho-MOFs, polymers and membranes was carried out by methods of X-ray phase analysis, scanning electron and atomic force microscopies, Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, dynamic and kinematic viscosity, static and dynamic light scattering, gel permeation chromatography, thermogravimetric analysis and contact angle measurements. Synthesized Ho-MOFs had different X-ray structures, particle forms and sizes depending on the ligand used. To study the effect of Ho-MOF modifier on membrane transport properties, PEBA/Ho-MOFs membrane retention capacity was evaluated in vacuum fourth-stage filtration for dye removal (Congo Red, Fuchsin, Glycine thymol blue, Methylene blue, Eriochrome Black T). Modified membranes demonstrated improved flux and rejection coefficients for dyes containing amino groups: Congo Red, Fuchsin (PEBA/Ho-1,3,5-H3btc membrane possessed optimal properties: 81% and 68% rejection coefficients for Congo Red and Fuchsin filtration, respectively, and 0.7 L/(m2s) flux).

A highly stable terbium(III) metal-organic framework MOF-76(Tb) for hydrogen storage and humidity sensing

The present study described the synthesis and characterization of MOF-76(Tb) for hydrogen storage and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning, and transmission electron microscopy. The crystal structure of MOF-76(Tb) consists of terbium(III) and benzene-1,3,5-tricarboxylate(-III) ions, one coordinated aqua ligand and one crystallization N,N´-dimethylformamide molecule. The polymeric framework of MOF-76(Tb) contains 1D sinusoidally shaped channels with sizes of 6.6 × 6.6 Å propagating along c crystallographic axis. The thermogravimetric analysis of the prepared material exhibited thermal stability up to 600 °C. At 77 K and pressure up to 20 bar; 0.6 wt.% hydrogen storage capacity for MOF-76(Tb) was observed. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Tb) is not a suitable material for moisture sensing applications.

MFM-300(Sc): a chemically stable Sc(III)-based MOF material for multiple applications

Developing robust multifunctional metal-organic frameworks (MOFs) is the key to advancing the further deployment of MOFs into relevant applications. Since the first report of MFM-300(Sc) (MFM = Manchester Framework Material, formerly known as NOTT-400), the development of applications of this robust microporous MOF has only grown. In this review, a summary of the applications of MFM-300(Sc), as well as some emerging advanced applications, have been discussed. The adsorption properties of MFM-300(Sc) are presented systematically. Particularly, this contribution is focused on acid and corrosive gas adsorption. In addition, recent applications for catalysis based on the outstanding hemilabile Sc-O bond character are highlighted. Finally, some new research areas are introduced, such as host-guest chemistry and biomedical applications. This highlight aims to showcase the recent advances and the potential for developing new applications of this promising material.

Green Ultrasound-Assisted Synthesis of Rare-Earth-Based MOFs

Rare-earth (RE)-based metal organic frameworks (MOFs) are quickly gaining popularity as flexible functional materials in a variety of technological fields. These MOFs are useful for more than just conventional uses like gas sensors and catalyst materials; in fact, they also show significant promise in emerging technologies including photovoltaics, optical, and biomedical applications. Using yttrium and europium as ionic host centres and dopants, respectively, and 1,3,5-benzenetricarboxylic acid (H3-BTC) as an organic linker, we describe a simple and green approach for the fabrication of RE-MOFs. Specifically, Y-BTCs and Eu-doped Y-BTCs MOFs have been synthesised in a single step using an eco-friendly method that makes use of ultrasound technology. To establish a correlation between the morphological and structural properties and reaction conditions, a range of distinct reaction periods has been employed for the synthetic processes. Detailed analyses of the synthesised samples through powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared spectroscopy (FT-IR) have confirmed the phase formation. Furthermore, thermal analyses such as thermogravimetric analysis (TGA) have been employed to evaluate the thermal stability and structural modifications of the Y-BTC and Eu-doped Y-BTC samples. Finally, the luminescent properties of the synthesised samples doped with Eu3+ have been assessed, providing an evaluation of their characteristics. As a proof of concept, an Eu-doped Y-BTC sample has been applied for the sensing of nitrobenzene as a molecule test of nitro derivatives.

A facile synthesis of CeO2 from the GO@Ce-MOF precursor and its efficient performance in the oxygen evolution reaction

Electrochemical water splitting has enticed fascinating consideration as a key conduit for the advancement of renewable energy systems. Fabricating adequate electrocatalysts for water splitting is fervently preferred to curtail their overpotentials and hasten practical utilizations. In this work, a series of Ce-MOF, GO@Ce-MOF, calcinated Ce-MOF, and calcinated GO@Ce-MOF were synthesized and used as high-proficient electrocatalysts for the oxygen evolution reaction. The physicochemical characteristics of the prepared samples were measured by diverse analytical techniques including SEM, HRTEM, FTIR, BET, XPS, XRD, and EDX. All materials underwent cyclic voltammetry tests and were evaluated by electrochemical impedance spectroscopy and oxygen evolution reaction. Ce-MOF, GO@Ce-MOF, calcinated Ce-MOF, and calcinated GO@Ce-MOF have remarkable properties such as enhanced specific surface area, improved catalytic performance, and outstanding permanency in the alkaline solution (KOH). These factors upsurge ECSA and intensify the OER performance of the prepared materials. More exposed surface active-sites present in calcinated GO@Ce-MOF could be the logic for superior electrocatalytic activity. Chronoamperometry of the catalyst for 15°h divulges long-term stability of Ce-MOF during OER. Impedance measurements indicate higher conductivity of synthesized catalysts, facilitating the charge transfer reaction during electrochemical water splitting. This study will open up a new itinerary for conspiring highly ordered MOF-based surface active resources for distinct electrochemical energy applications.

Gd(III) metal-organic framework as an effective humidity sensor and its hydrogen adsorption properties

Metal-organic frameworks (MOFs) represent a class of nanoporous materials built up by metal ions and organic linkers with several interesting potential applications. The present study described the synthesis and characterization of Gd(III)-based MOF with the chemical composition [Gd(BTC)(H₂O)]·DMF (BTC - trimesate, DMF = N,N'-dimethylformamide), known as MOF-76(Gd) for hydrogen adsorption/desorption capacity and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning and transmission electron microscopy. The crystal structure of MOF-76(Gd) consists of gadolinium (III) and benzene-1,3,5-tricarboxylate ions, one coordinated aqua ligand and one crystallization DMF molecule. The polymeric framework of MOF-76(Gd) contains 1D sinusoidally shaped channels with sizes of 6.7 × 6.7 Å propagating along c crystallographic axis. The thermogravimetric analysis, heating infrared spectroscopy and in-situ heating powder X-ray diffraction experiments of the prepared framework exhibited thermal stability up to 550 °C. Nitrogen adsorption/desorption measurement at -196 °C showed a BET surface area of 605 m² g^-1 and pore volume of 0.24 cm³ g^-1. The maximal hydrogen storage capacity of MOF-76(Gd) was 1.66 wt % and 1.34 wt % -196 °C and -186 °C and pressure up to 1 bar, respectively. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Gd) is a suitable material for moisture sensing application with a fast response (11 s) and recovery time (2 s) in the relative humidity range of 11-98%.

Investigation of Intermetallic Energy Transfers in Lanthanide Coordination Polymers Molecular Alloys: Case Study of Trimesate-Based Compounds

Reactions in water at ambient temperature and pressure between a lanthanide ion and benzene-1,3,5-tricarboxylate (or trimesate) lead to two series of iso-structural coordination polymers. Their general chemical formula is [Ln(tma)(H₂O)₆]_∞ for the lightest lanthanide ions (Ln = La-Dy except Pm), while it is [Ln(tma)(H₂O)₅·3.5H₂O]_∞ for the heaviest ones (Ho-Lu plus Y). For the heaviest lanthanide ions, reactions at 50 °C lead to a third structural family with the general chemical formula [Ln(tma)(H₂O)₃·1.5H₂O]_∞ with Ln = Ho-Lu plus Y. Homo-lanthanide coordination polymers that belong to the latter two families do not exhibit luminescence in the visible region. Therefore, we used a phase induction strategy to obtain molecular alloys that belong to these structural families and show sizeable emission. The random distribution of the lanthanide ions over the metallic sites has been investigated using ⁸⁹Y and ¹³⁹La solid-state NMR spectroscopy experiments. Luminescent properties of homo- and hetero-nuclear coordination polymers based on Eu³⁺ and Tb³⁺ have been studied in detail and compared. As a result, this study strongly suggests that exchange-based intermetallic energy transfer mechanisms play an important role in these systems. It also suggests the presence of an intermetallic exchange pathway through π-stacking interactions.

High Speed Mass Measurement of a Single Metal-Organic Framework Nanocrystal in a Paul Trap

Mass spectrometry (MS) has emerged as an excellent tool for the characterization of metal-organic frameworks (MOFs) based on the characteristic metal ions and organic ligands. Mass measurement of intact MOF nanocrystals, however, remains a challenge for MS technology. Here, we reported the development of a probe particles based charge detection-quadrupole ion trap mass spectrometry (probe CD-QIT MS) method, where charge detection and mass measurement of a single MOF nanocrystal were achieved under the assistance of probe particles of micrometer size. As a validation of the method, the masses of a series of polystyrene (PS) size standards from 493 nm to 1.6 μm were measured with 3 μm PS particles as probes, and the measured masses were found to match well with their certified masses. Then, charge detections and mass analysis of single ZIF-8 and GOx@ZIF-8 with a size around 600 nm were achieved successfully. The method presented here demonstrates simplicity, high speed, and accuracy. Notably, it allows quantitative measurement of the amount of immobilized GOx enzyme by using the mass difference between ZIF-8 and GOx@ZIF-8. In addition, based on the determined mass, the size analysis of these MOF particles with irregular shape was carried out and demonstrated to be complementary to transmission electron microscopy (TEM).

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Aqueous degradation of artificial sweeteners saccharin and neotame by metal organic framework material

The artificial sweeteners (ASs) saccharin (SAC) and neotame (NEO) are widely used across the globe and are considered as emerging contaminants in surface, ground, and drinking waters. To degrade SAC and NEO, the metal organic framework material Co-based bio-MOF-11 was prepared by hydrothermal reaction and used with peroxymonosulfate (PMS) activator. The effects of the initial concentration of SAC and NEO, bio-MOF-11-Co dosage, PMS concentration, initial pH, temperature, and competitive anions were determined. The results revealed that bio-MOF-11-Co effectively catalyzed the degradation of SAC and NEO and possessed good stability and recycling efficiency. The degradation reaction was effective from pH 3.6-9.8 and followed quasi-first-order kinetics with degradation rate constants of 0.001-0.013 min^-1 for SAC and 0.03-0.52 min^-1 for NEO. Increased temperature was conducive to the degradation of both artificial sweeteners. The presence of Cl^- inhibited the degradation of SAC and NEO, while the presence of CO₃^2- promoted their degradation. Electron paramagnetic resonance (EPR) and free radical quenching demonstrated that the primary free radicals were sulfate radicals ( [Formula: see text] ) and hydroxyl radicals (HO). The change of cobalt oxidation state and electron transfer in bio-MOF-11-Co mainly induces the production of [Formula: see text] . A plausible mechanism for degradation is [Formula: see text] and HO attack on CS bonds, NS bonds, and benzene rings.

Tuning dimensionality between 2D and 1D MOFs by lanthanide contraction and ligand-to-metal ratio

2D/1D dimensionality tuning in LnMOFs is related to both (i) ligand-to-metal ratio and (ii) lanthanide contraction, this is only possible with Er/Tm, lighter lanthanides e.g. Pr only produced 2D MOFs, despite different ligand-to-metal ratios were used.

Dual-Mode Light-Emitting Lanthanide Metal-Organic Frameworks with High Water and Thermal Stability and Their Application in White LEDs

It is well known that the upconversion luminescence from lanthanide metal-organic frameworks (Ln-MOFs) is difficult to achieve, and thus, there are few reports on dual luminescence-based MOFs. Here, dual-mode light-emitting Ln-MOFs are synthesized using a low-cost hydrothermal method. Our results show that the obtained Ln-MOFs not only have high thermal stability (up to 420°) but also are stable in deionized water. The dual-mode up- and downconversion luminescence is simultaneously observed from Er-Eu-MOFs. The temperature-dependent fluorescence decay time is calculated to be ranging from 0.46 to 0.36 ms for temperatures from 100 to 300 K. We suggested that this phenomenon was because the number of phonons participating in the MOF matrix increases with temperature during the luminescence process, and the phonons interact with the electrons in the material. The values of the J-O parameters calculated from the emission spectra indicated that the symmetry around Eu³⁺ ions in Eu-MOF is the highest, which was also higher than that of Er-Eu-MOF. To explore the potential applications of Eu-MOFs in white light-emitting diodes (LEDs), red emission from Eu-MOFs was combined with blue, green, and yellow emissions from metal halide perovskites to achieve white light emission. White light with excellent color quality and vision performance was obtained. These findings demonstrate that Ln-MOFs are potentially successful materials for applications in white LEDs.

Large and tunable magnetocaloric effect in gadolinium-organic framework: tuning by solvent exchange

Magnetic properties of three variants of MOF-76(Gd), {[Gd(BTC)(H2O)]·G}n (BTC = benzene-1,3,5-tricarboxylate, G = guest molecules) were investigated by static susceptibility, isothermal magnetization and specific heat capacity measurements. In the study we used as synthesized MOF-76(Gd)-DMF (1) (G = DMF = dimethylformamide), containing DMF molecules in the cavity system, compound MOF-76(Gd) (2), activated complex without solvents in the cavities and water exchanged sample MOF-76(Gd)-H2O (3). A pronounced change in the magnetic entropy was found near the critical temperature for all three compounds. It was shown, that magnetic entropy change depends on the solvatation of the MOF. The highest value entropy change, ΔSMpk(T) was observed for compound 2 (ΔSMpk(T) = 42 J kg-1 K-1 at 1.8 K for ΔH = 5 T). The ΔSMpk(T) for the compounds 1, 2 and 3 reached 81.8, 88.4 and 100% of the theoretical values, respectively. This suggests that in compound 3 Gd3+···Gd3+ antiferromagnetic interactions are decoupled gradually, and higher fields promote a larger decoupling between the individual spin centers. The observed entropy changes of compounds were comparable with other magnetic refrigerants proposed for low-temperature applications. To study the magnetothermal effect of 2 (the sample with largest -ΔSMpk), the temperature-dependent heat capacities (C) at different fields were measured. The value of magnetic entropy S obtained from heat capacities (39.5 J kg-1 K-1 at 1.8 K for an applied magnetic field change of 5 T) was in good agreement with that derived from the magnetization data (42 J kg-1 K-1 at 1.8 K).

Submicron sized water-stable metal organic framework (bio-MOF-11) for catalytic degradation of pharmaceuticals and personal care products

Water-stable and active metal organic frameworks (MOFs) are important materials for mitigation of water contaminants via adsorption and catalytic reactions. In this study, a highly water-stable Co-based MOF, namely bio-MOF-11-Co, was synthesized by a simplified benign method. Moreover, it was used as a catalyst in successful activation of peroxymonsulfate for catalytic degradation of sulfachloropyradazine (SCP) and para-hydroxybenzoic acid (p-HBA) as representatives of pharmaceuticals and personal care products, respectively. The bio-MOF-11-Co showed rapid degradation of both p-HBA and SCP and could be reused multiple times without losing the activity by simply water washing. The effects of catalyst and PMS loadings as well as temperature were further studied, showing that high catalyst and PMS loadings as well as temperature produced faster kinetic degradation of p-HBA and SCP. The generation of highly reactive and HO radicals during the degradation was investigated by quenching tests and electron paramagnetic resonance. A plausible degradation mechanism was proposed based on the functionalities in the bio-MOF-11-Co. The availability of electron rich nucleobase adenine reinforced the reaction kinetics by electron donation along with cobalt atoms in the bio-MOF-11-Co structure.