H2storage in isostructural UiO-67 and UiO-66 MOFs

Porous ionic liquids for oxidative desulfurization influenced by electrostatic solvent effect

Developing a highly efficient strategy for the stabilization of the solid-liquid interface is a persistent pursuit for researchers. Herein, porous ionic liquids based on UiO-66 (Zr) porous materials were synthesized and applied to the selective desulfurization catalysis, which integrates the permanent pores of porous solids with the exceptional properties of ionic liquids. Results show that porous ionic liquids possess high activity and selectivity for dibenzothiophene. Experimental analysis and density functional theory calculations revealed that the ionic liquids moiety served as an extractant to enrich dibenzothiophene into the porous ionic liquids phase through the π···π and CH···π interactions. Additionally, the electrostatic solvent effect in the porous ionic liquids contributes to the stabilization solid-liquid interface, which was favorable for UiO-66 moiety to catalytically activate hydrogen peroxide (H2O2) to generate ·OH radicals, and subsequently oxidized dibenzothiophene to the corresponding sulfone. It is hoped that the development of porous ionic liquids could pave a new route to the stabilization of the solid-liquid interface for catalytic oxidation.

Enabling a bioinspired N,N,N-copper coordination motif through spatial control in UiO-67: synthesis and reactivity

Metal-organic frameworks (MOFs) featuring zirconium-based clusters are widely used for the development of functionalized materials due to their exceptional stability. In this study, we report the synthesis of a novel N,N,N-ligand compatible with a biphenyl dicarboxylic acid-based MOF. However, the resulting copper(I) complex exhibited unexpected coordination behaviour, lacking the intended trifold coordination motif. Herein, we demonstrate the successful immobilization of a bioinspired ligand within the MOF, which preserved its crystalline and porous nature while generating a well-defined copper site. Comprehensive spectroscopic analyses, including X-ray absorption, UV/Vis, and infrared spectroscopy, were conducted to investigate the copper site and its thermal behaviour. The immobilized ligand exhibited the desired tridentate coordination to copper, providing access to a coordination motif otherwise unattainable. Notably, water molecules were also found to coordinate to copper. Upon heating, the copper centre within the MOF exhibited reversible dehydration, suggesting facile creation of open coordination sites. Furthermore, the copper site displayed reduction at elevated temperatures and subsequent susceptibility to oxidation by molecular oxygen. Lastly, both the molecular complexes and the MOF were evaluated as catalysts for the oxidation of cyclohexane using hydrogen peroxide. This work highlights the successful immobilization of a bioinspired ligand in a zirconium-based MOF, shedding light on the structural features, thermal behaviour, and catalytic potential of the resulting copper sites.

The Promise and Potential of Metal-Organic Frameworks and Covalent Organic Frameworks in Vaccine Nanotechnology

The immune system's complexity and ongoing evolutionary struggle against deleterious pathogens underscore the value of vaccination technologies, which have been bolstering human immunity for over two centuries. Despite noteworthy advancements over these 200 years, three areas remain recalcitrant to improvement owing to the environmental instability of the biomolecules used in vaccines─the challenges of formulating them into controlled release systems, their need for constant refrigeration to avoid loss of efficacy, and the requirement that they be delivered via needle owing to gastrointestinal incompatibility. Nanotechnology, particularly metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), has emerged as a promising avenue for confronting these challenges, presenting a new frontier in vaccine development. Although these materials have been widely explored in the context of drug delivery, imaging, and cancer immunotherapy, their role in immunology and vaccine-related applications is a recent yet rapidly developing field. This review seeks to elucidate the prospective use of MOFs and COFs for biomaterial stabilization, eliminating the necessity for cold chains, enhancing antigen potency as adjuvants, and potentializing needle-free delivery of vaccines. It provides an expansive and critical viewpoint on this rapidly evolving field of research and emphasizes the vital contribution of chemists in driving further advancements.

Recent Progress and Future Prospects of Laccase Immobilization on MOF Supports for Industrial Applications

Laccase is a multicopper oxidoreductase enzyme that can oxidize organics such as phenolic compounds. Laccases appear to be unstable at room temperature, and their conformation often changes in a strongly acidic or alkaline environment, making them less effective. Therefore, rationally linking enzymes with supports can effectively improve the stability and reusability of native enzymes and add important industrial value. However, in the process of immobilization, many factors may lead to a decrease in enzymatic activity. Therefore, the selection of a suitable support can ensure the activity and economic utilization of immobilized catalysts. Metal-organic frameworks (MOFs) are porous and simple hybrid support materials. Moreover, the characteristics of the metal ion ligand of MOFs can enable a potential synergistic effect with the metal ions of the active center of metalloenzymes, enhancing the catalytic activity of such enzymes. Therefore, in addition to summarizing the biological characteristics and enzymatic properties of laccase, this article reviews laccase immobilization using MOF supports, as well as the application prospects of immobilized laccase in many fields.

Reversible solvent interactions with UiO-67 metal-organic frameworks

The utility of UiO-67 Metal-Organic Frameworks (MOFs) for practical applications requires a comprehensive understanding of intermolecular host-guest MOF-analyte interactions. To investigate intermolecular interactions between UiO-67 MOFs and complex molecules, it is useful to evaluate the interactions with simple polar and non-polar analytes. This problem is approached by investigating the interactions of polar (acetone and isopropanol) and non-polar (n-heptane) molecules with functionalized UiO-67 MOFs via temperature programmed desorption mass spectrometry and temperature programmed Fourier transform infrared spectroscopy. We find that isopropanol, acetone, and n-heptane bind reversibly and non-destructively to UiO-67 MOFs, where MOF and analyte functionality influence relative binding strengths (n-heptane ≈ isopropanol > acetone). During heating, all three analytes diffuse into the internal pore environment and directly interact with the μ3-OH groups located within the tetrahedral pores, evidenced by the IR response of ν(μ3-OH). We observe nonlinear changes in the infrared cross sections of the ν(CH) modes of acetone, isopropanol, and n-heptane following diffusion into UiO-67. Similarly, acetone's ν(C=O) infrared cross section increases dramatically when diffused into UiO-67. Ultimately, this in situ investigation provides insights into how individual molecular functional groups interact with UiO MOFs and enables a foundation where MOF interactions with complex molecular systems can be evaluated.

Physiochemical characterization of metal organic framework materials: A mini review

Metal-organic frameworks (MOFs) are promising materials offering exceptional performance across a myriad of applications, attributable to their remarkable physicochemical properties such as regular porosity, crystalline structure, and tailored functional groups. Despite their potential, there is a lack of dedicated reviews that focus on key physicochemical characterizations of MOFs for the beginners and new researchers in the field. This review is written based on our expertise in the synthesis and characterization of MOFs, specifically to provide a right direction for the researcher who is a beginner in this area. In this way, experimental errors can be reduced, and wastage of time and chemicals can be avoided when new researchers conduct a study. In this article, this topic is critically analyzed, and findings and conclusions are presented. We reviewed three well-known XRD techniques, including PXRD, single crystal XRD, and SAXS, which were used for XRD analysis depending on the crystal size and the quality of crystal morphology. The TGA profile was an effective factor for evaluating the quality of the activation process and for ensuring the successful investigation for other characterizations. The BET and pore size were significantly affected by the activation process and selective benzene chain cross-linkers. FTIR is a prominent method that is used to investigate the functional groups on pore surfaces, and this method is successfully used to evaluate the activation process, characterize functionalized MOFs, and estimate their applications. The most significant methods of characterization include the X-ray diffraction, which is utilized for structural identification, and thermogravimetric analysis (TGA), which is used for exploring thermal decomposition. It is important to note that the thermal stability of MOFs is influenced by two main factors: the metal-ligand interaction and the type of functional groups attached to the organic ligand. The textural properties of the MOFs, on the other hand, can be scrutinized through nitrogen adsorption-desorption isotherms experiments at 77 K. However, for smaller pore size, the Argon adsorption-desorption isotherm at 87.3 K is preferred. Furthermore, the CO2 adsorption isotherm at 273 K can be used to measure ultra-micropore sizes and sizes lower than these, which cannot be measured by using the N2 adsorption-desorption isotherm at 77 K. The highest BET was observed in high-valence MOFs that are constructed based on the metal-oxo cluster, which has an excellent ability to control their textural properties. It was found that the synthesis procedure (including the choice of solvent, cross-linker, secondary metal, surface functional groups, and temperature), activation method, and pressure significantly impact the surface area of the MOF and, by extension, its structural integrity. Additionally, Fourier-transform infrared spectroscopy plays a crucial role in identifying active MOF functional groups. Understanding these physicochemical properties and utilizing relevant characterization techniques will enable more precise MOF selection for specific applications.

Strategies to improve adsorption and photocatalytic performance of metal-organic frameworks (MOFs) for perfluoroalkyl and polyfluoroalkyl substances (PFASs) removal from water: A review

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) represent a category of persistent and hazardous organic pollutants extensively prevalent across aquatic environments. The combination of adsorption and photocatalytic degradation has been identified as an effective approach for removing trace amounts of PFASs from water. Among the various materials explored for this purpose, metal-organic frameworks (MOFs) have structural solid tunability, and suitable modification methods could endow them with rich adsorption capabilities and excellent photocatalytic performance, which has potential for applications involving the treatment of trace, multi-chain-length PFASs in water. The research within this realm is currently in its nascent phase, and a holistic knowledge of modification methods can provide a comprehensive framework for future studies. Therefore, this review intends to (1) summarize the mechanism underlying the adsorption and photocatalytic removal of PFASs by MOFs; (2) present various modification methods aimed at enhancing the adsorption and photocatalytic performance of MOFs in alignment with the goal mentioned above; (3) provide an outlook on the prospects of utilizing MOFs for PFASs removal based on current trends and data. Ultimately, the findings from these studies will contribute to advancing knowledge in this area and facilitate the development of effective strategies for addressing PFASs contamination in water systems.

Transmission Porosimetry Study on High-quality Zr-fum-MOF Thin Films

Crystalline Zr-fum-MOF (MOF-801) thin films of high quality are prepared on glass and silicon substrates by direct growth under solvothermal conditions. The synthesis is described in detail and the influence of different synthesis parameters such as temperature, precursor concentration, and the substrate type on the quality of the coatings is illustrated. Zr-fum-MOF thin films are characterized in terms of crystallinity, porosity, and homogeneity. Dense films of optical quality are obtained. The sorption behavior of the thin films is studied with various adsorptives. It can be easily monitored by measuring the transmission of the films in gas flows of different compositions. This simple transmission measurement at only one wavelength allows a very fast evaluation of the adsorption properties of thin films as compared to traditional sorption methods. The sorption behavior of the thin films is compared with the sorption properties of Zr-fum-MOF powder samples.

MOF-Based Chemiresistive Gas Sensors: Toward New Functionalities

The sensing performances of gas sensors must be improved and diversified to enhance quality of life by ensuring health, safety, and convenience. Metal-organic frameworks (MOFs), which exhibit an extremely high surface area, abundant porosity, and unique surface chemistry, provide a promising framework for facilitating gas-sensor innovations. Enhanced understanding of conduction mechanisms of MOFs has facilitated their use as gas-sensing materials, and various types of MOFs have been developed by examining the compositional and morphological dependences and implementing catalyst incorporation and light activation. Owing to their inherent separation and absorption properties and catalytic activity, MOFs are applied as molecular sieves, absorptive filtering layers, and heterogeneous catalysts. In addition, oxide- or carbon-based sensing materials with complex structures or catalytic composites can be derived by the appropriate post-treatment of MOFs. This review discusses the effective techniques to design optimal MOFs, in terms of computational screening and synthesis methods. Moreover, the mechanisms through which the distinctive functionalities of MOFs as sensing materials, heterostructures, and derivatives can be incorporated in gas-sensor applications are presented.

Water-assisted hydrogen spillover in Pt nanoparticle-based metal-organic framework composites

Hydrogen spillover is the migration of activated hydrogen atoms from a metal particle onto the surface of catalyst support, which has made significant progress in heterogeneous catalysis. The phenomenon has been well researched on oxide supports, yet its occurrence, detection method and mechanism on non-oxide supports such as metal-organic frameworks (MOFs) remain controversial. Herein, we develop a facile strategy for efficiency enhancement of hydrogen spillover on various MOFs with the aid of water molecules. By encapsulating platinum (Pt) nanoparticles in MOF-801 for activating hydrogen and hydrogenation of C=C in the MOF ligand as activated hydrogen detector, a research platform is built with Pt@MOF-801 to measure the hydrogenation region for quantifying the efficiency and spatial extent of hydrogen spillover. A water-assisted hydrogen spillover path is found with lower migration energy barrier than the traditional spillover path via ligand. The synergy of the two paths explains a significant boost of hydrogen spillover in MOF-801 from imperceptible existence to spanning at least 100-nm-diameter region. Moreover, such strategy shows universality in different MOF and covalent organic framework materials for efficiency promotion of hydrogen spillover and improvement of catalytic activity and antitoxicity, opening up new horizons for catalyst design in porous crystalline materials.

MOFs as Versatile Catalysts: Synthesis Strategies and Applications in Value-Added Compound Production

Catalysts played a crucial role in advancing modern human civilization, from ancient times to the industrial revolution. Due to high cost and limited availability of traditional catalysts, there is a need to develop cost-effective, high-activity, and nonprecious metal-based electrocatalysts. Metal-organic frameworks (MOFs) have emerged as an ideal candidate for heterogeneous catalysis due to their physicochemical properties, hybrid inorganic/organic structures, uncoordinated metal sites, and accessible organic sections. MOFs are high nanoporous crystalline materials that can be used as catalysts to facilitate polymerization reactions. Their chemical and structural diversity make them effective for various reactions compared to traditional catalysts. MOFs have been applied in gas storage and separation, ion-exchange, drug delivery, luminescence, sensing, nanofilters, water purification, and catalysis. The review focuses on MOF-enabled heterogeneous catalysis for value-added compound production, including alcohol oxidation, olefin oligomerization, and polymerization reactions. MOFs offer tunable porosity, high spatial density, and single-crystal XRD control over catalyst properties. In this review, MOFs were focused on reactions of CO2 fixation, CO2 reduction, and photoelectrochemical water splitting. Overall, MOFs have great potential as versatile catalysts for diverse applications in the future.

In Situ FTIR Spectroscopy for Scanning Accessible Active Sites in Defect-Engineered UiO-66

Three UiO-66 samples were prepared by solvothermal synthesis using the defect engineering approach with benzoic acid as a modulator. They were characterized by different techniques and their acidic properties were assessed by FTIR spectroscopy of adsorbed CO and CD₃CN. All samples evacuated at room temperature contained bridging μ₃-OH groups that interacted with both probe molecules. Evacuation at 250 °C leads to the dehydroxylation and disappearance of the μ₃-OH groups. Modulator-free synthesis resulted in a material with open Zr sites. They were detected by low-temperature CO adsorption on a sample evacuated at 200 °C and by CD₃CN even on a sample evacuated at RT. However, these sites were lacking in the two samples obtained with a modulator. IR and Raman spectra revealed that in these cases, the Zr⁴⁺ defect sites were saturated by benzoates, which prevented their interaction with probe molecules. Finally, the dehydroxylation of all samples produced another kind of bare Zr sites that did not interact with CO but formed complexes with acetonitrile, probably due to structural rearrangement. The results showed that FTIR spectroscopy is a powerful tool for investigating the presence and availability of acid sites in UiO-66, which is crucial for its application in adsorption and catalysis.

NH2-Modified UiO-66: Structural Characteristics and Functional Properties

The development of new functional materials based on metal-organic frameworks (MOFs) for adsorption and catalytic applications is one of the promising trends of modern materials science. The Zr-based MOFs, specifically UiO-66, are considered as the supports for metallic catalysts for the 5-hydroxymethylfurfural platform molecule reduction into valuable products. The present work focused on the effect of NH₂ modification of UiO-66 on its structure and functional properties. The samples were prepared by a solvothermal method. The structure of the obtained materials was studied by X-ray diffraction, IR spectroscopy, UV-visible spectroscopy, and low-temperature nitrogen adsorption. Basic properties were investigated by HCl and CH₃COOH adsorption, and electrokinetic properties were studied by electrophoretic light scattering. UiO-66-NH₂ samples with different contents of aminoterephthalate linkers were successfully prepared. A gradual decrease in the specific surface area and the fraction of micropores with a diameter of ~0.9 nm was observed with an increase in the aminoterephthalate content. A proportional increase in the total number of basic sites in UiO-66-NH₂ samples was established with an increase in the aminoterephthalate content up to 75%. At the same time, a noticeable decrease in the total number of basic sites and an increase in their strength with higher aminoterephthalate content was observed.

Exploring ionic liquid-laden metal-organic framework composite materials as hybrid electrolytes in metal (ion) batteries

This review focuses on the combination of metal-organic frameworks (MOFs) and ionic liquids (ILs) to obtain composite materials to be used as solid electrolytes in metal-ion battery applications. Benefiting from the controllable chemical composition, tunable pore structure and surface functionality, MOFs offer great opportunities for synthesizing high-performance electrolytes. Moreover, the encapsulation of ILs into porous materials can provide environmentally benign solid-state electrolytes for electrochemical devices. Due to the versatility of MOF-based materials, in this review we also explore their use as anodes and cathodes in Li- and Na-ion batteries. Finally, solid IL@MOF electrolytes and their implementation into Li and Na batteries have been analyzed, as well as the design and advanced manufacturing of solid IL@MOF electrolytes embedded on polymeric matrices.

Controlling the Mobility of Ionic Liquids in the Nanopores of MOFs by Adjusting the Pore Size: From Conduction Collapse by Mutual Pore Blocking to Unhindered Ion Transport

Ionic liquids (ILs) in nanoporous confinement are the core of many supercapacitors and batteries, where the mobility of the nanoconfined ILs is crucial. Here, by combining experiments based on impedance spectroscopy with molecular dynamics simulations, the mobility of a prototype IL in the nanopores of an isoreticular metal-organic framework (MOF)-series with different pore sizes is explored, where an external electric field is applied. It has been found that the conduction behavior changes tremendously depend on the pore size. For small-pore apertures, the IL cations and anions cannot pass the pore window simultaneously, causing the ions to mutually block the pores. This results in a strong concentration dependence of the ionic conduction, where the conduction drops by two orders of magnitude when filling the pores. For large-pore MOFs, the mutual hindrance of the ions in the pores is small, causing only a small concentration dependence. The cutoff between the large-pore and small-pore behavior is approximately the size of a cation-anion-dimer and increasing the pore diameter by only 0.2 nm changes the conduction behavior fundamentally. This study shows that the pore aperture size has a substantial effect on the mobility of ions in nanoporous confinement and has to be carefully optimized for realizing highly-mobile nanoconfined ILs.

Regulated synthesis of Zr-metal-organic frameworks with variable hole size and its influence on the performance of novel MOF-based heterogeneous amino acid-thiourea catalysts

We present an efficient and easy synthesis method for incorporating organocatalytic moieties into Zr-metal organic frameworks (Zr-MOFs). The catalytic activity and selectivity of the new chiral catalysts were improved by adjusting the aperture of the MOF cavities. The hole size of the Zr-MOF was modulated by adding acid and replacing bridge ligands during synthesis. The difunctional chiral units of amino acid-thiourea are anchored onto the Zr-MOF by a mild synthesis method from an isothiocyanate intermediate which could effectively avoid the racemization of chiral moieties in the synthesis process. By means of specific surface area measurement (BET), scanning electron microscopy (SEM) and powder X-ray Diffraction (PXRD), it was confirmed that Zr-MOFs with different pore sizes were synthesized without breaking the basic octahedral structure of the MOF. Finally, good yields (up to 83%) and ee values (up to 73%) were achieved with the new heterogeneous catalysts in 48 hours for the aldol reaction of 4-nitrobenzaldehyde with acetone. By contrast, using the catalyst support without modulating the synthesis, the yield (30%) and the ee-value (26%) were both low. Experiments have confirmed the important influence on the reaction selectivity of providing a suitable reaction environment by controlling the aperture of MOF cavities.

CO2 Hydrogenation on Metal-Organic Frameworks-Based Catalysts: A Mini Review

Conversion of carbon dioxide (CO₂) into value-added fuels and chemicals can not only reduce the emission amount of CO₂ in the atmosphere and alleviate the greenhouse effect but also realize carbon recycling. Through hydrogenation with renewable hydrogen (H₂), CO₂ can be transformed into various hydrocarbons and oxygenates, including methanol, ethanol, methane and light olefins, etc. Recently, metal-organic frameworks (MOFs) have attracted extensive attention in the fields of adsorption, gas separation, and catalysis due to their high surface area, abundant metal sites, and tunable metal-support interface interaction. In CO₂ hydrogenation, MOFs are regarded as important supports or sacrificed precursors for the preparation of high-efficient catalysts, which can uniformly disperse metal nanoparticles (NPs) and enhance the interaction between metal and support to prevent sintering and aggregation of active metal species. This work summarizes the recent process on hydrogenation of CO₂ to methanol, methane and other C₂₊ products over various MOFs-based catalysts, and it will provide some dues for the design of MOFs materials in energy-efficient conversion and utilization.

Iodine Uptake by Zr-/Hf-Based UiO-66 Materials: The Influence of Metal Substitution on Iodine Evolution

Many works reported the encapsulation of iodine in metal-organic frameworks as well as the I₂ → I₃^- chemical conversion. This transformation has been examined by adsorbing gaseous iodine on a series of UiO-66 materials and the different Hf/Zr metal ratios (0-100% Hf) were evaluated during the evolution of I₂ into I₃^-. The influence of the hafnium content on the UiO-66 structure was highlighted by PXRD, SEM images, and gas sorption tests. The UiO-66(Hf) presented smaller lattice parameter (a = 20.7232 Å), higher crystallite size (0.18 ≤ Φ ≤ 3.33 μm), and smaller SSA_BET (818 m²·g^-1) when compared to its parent UiO-66(Zr) ─ a = 20.7696 Å, 100 ≤ Φ ≤ 250 nm, and SSA_BET = 1262 m²·g^-1. The effect of replacing Zr atoms by Hf in the physical properties of the UiO-66 was deeply evaluated by a spectroscopic study using UV-vis, FTIR, and Raman characterizations. In this case, the Hf presence reduced the band gap of the UiO-66, from 4.07 eV in UiO-66(Zr) to 3.98 eV in UiO-66(Hf). Furthermore, the UiO-66(Hf) showed a blue shift for several FTIR and Raman bands, indicating a stiffening on the implied interatomic bonds when comparing to UiO-66(Zr) spectra. Hafnium was found to clearly favor the capture of iodine [285 g·mol^-1, against 230 g·mol^-1 for UiO-66(Zr)] and the kinetic evolution of I₂ into I₃^- after 16 h of I₂ filtration. Three iodine species were typically identified by Raman spectroscopy and chemometric analysis. These species are as follows: "free" I₂ (206 cm^-1), "perturbed" I₂ (173 cm^-1), and I₃^- (115 and 141 cm^-1). It was also verified, by FTIR spectroscopy, that the oxo and hydroxyl groups of the inorganic [M₆O₄(OH)₄] (M = Zr, Hf) cluster were perturbed after the adsorption of I₂ into UiO-66(Hf), which was ascribed to the higher acid character of Hf. Finally, with that in mind and considering that the EPR results discard the possibility of a redox phenomenon involving the tetravalent cations (Hf⁴⁺ or Zr⁴⁺), a mechanism was proposed for the conversion of I₂ into I₃^- in UiO-66─based on an electron donor-acceptor complex between the aromatic ring of the BDC linker and the I₂ molecule.

Insights into the Solid-State Synthesis of Defect-Rich Zr-UiO-66

Metal-organic frameworks (MOFs), a new type of porous material, have shown many possible applications in gas storage and separation, biomedicine, catalysis, and so on. While most MOFs are synthesized through solvothermal synthesis where a large quantity of organic solvent is used, the green synthetic approach using a minimized amount of solvent is important to prevent irreversible environmental compacts. In this study, we successfully synthesized Zr-MOFs with SBUs (e.g., UiO-66 and MIL-140A) using a simple metal source and investigated the role of organic modulators in modulating the MOF structures during solid-state synthesis. Meanwhile, UiO-66 rich in defects synthesized via a solid-state conversion strategy shows good catalytic performance for the ring-opening of epoxides with alcohols. This work contributes to the understanding of the role of organic modulators in the solid-state synthesis of MOFs.

Confinement of all-inorganic perovskite quantum dots assembled in metal-organic frameworks for ultrafast scintillator application

Nucleation and growth of quantum dots (QDs) are thermodynamic processes driven by the total Gibbs free energy change (ΔG). We discuss the nucleation and growth theory of perovskite quantum dots (PeQDs) inside a metal-organic framework (MOF) as a strong constraint framework, which can effectively confine the size of QDs below 3 nm and achieve a scintillator with an ultra-fast transient lifetime of fluorescence. Therefore, based on the requirements for the optical properties of ultra-fast scintillation materials, two kinds of suitable MOFs (UiO-67-bpy and MIL-101(Cr)) were selected for synthesis. The method of 'ship-in-bottle' was adopted to embed perovskite quantum dots CsPbBrCl₂ into MOF cages to form PeQDs@MOF composite materials, which is different from the one-pot method. In order to further improve the stability of PeQDs@MOF, polystyrene was used to cure the composite scintillator, which can resist exposure to UV light and withstand the ISO level 4 test, with the fastest transient lifetime of 2.13 ns and a fluorescence emission wavelength of 445 nm.

Immobilization of Lewis Basic Sites into a Stable Ethane-Selective MOF Enabling One-Step Separation of Ethylene from a Ternary Mixture

Purification of C₂H₄ from a ternary C₂H₂/C₂H₆/C₂H₄ mixture by one-step adsorption separation is of prime importance but challenging in the petrochemical industry; however, effective strategies to design high-performance adsorbents are lacking. We herein report for the first time the incorporation of Lewis basic sites into a C₂H₆-selective MOF, enabling efficient one-step production of polymer-grade C₂H₄ from ternary mixtures. Introduction of amino groups into highly stable C₂H₆-selective UiO-67 can not only partition large pores into smaller cagelike pockets to provide suitable pore confinement but also offer additional binding sites to simultaneously enhance C₂H₂ and C₂H₆ adsorption capacities over C₂H₄. The amino-functionalized UiO-67-(NH₂)₂ thus exhibits exceptionally high C₂H₂ and C₂H₆ uptakes as well as benchmark C₂H₂/C₂H₄ and C₂H₆/C₂H₄ selectivities, surpassing all of the C₂H₂/C₂H₆-selective materials reported so far. Theoretical calculations combined with in situ infrared spectroscopy indicate that the synergetic effect of suitable pore confinement and functional surfaces decorated with amino groups provides overall stronger multipoint van der Waals interactions with C₂H₂ and C₂H₆ over C₂H₄. The exceptional performance of UiO-67-(NH₂)₂ was evidenced by breakthrough experiments for C₂H₂/C₂H₆/C₂H₄ mixtures under dry and wet conditions, providing a remarkable C₂H₄ productivity of 0.55 mmol g^-1 at ambient conditions.

A facile and sustainable one-pot approach to the aqueous and low-temperature PET-to-UiO-66(Zr) upcycling

Accelerating waste management requires the conversion of polymer waste to value-added materials through sustainable approaches. While depolymerised PET has been used as feedstock to produce metal-organic frameworks, this is the first report of the successful one-pot hydrothermal synthesis of the desirable UiO-66 topology through the judicious choice of reactants, modulators and reaction conditions.

Selective ligand removal to improve accessibility of active sites in hierarchical MOFs for heterogeneous photocatalysis

Metal-organic frameworks (MOFs) are commended as photocatalysts for H2 evolution and CO2 reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis. Here we report photoactive MOFs of the MIL-125-Ti family with two distinct mesopore architectures resembling either large cavities or branching fractures. The ligand removal is highly selective and follows a 2-step process tunable by temperature and time. The introduction of mesopores and the associated formation of new active sites have improved the HER rates of the MOFs by up to 500%. We envision that this strategy will allow the purposeful engineering of hierarchical MOFs and advance their applicability in environmental and energy technologies.

Experimental Volumetric Hydrogen Uptake Determination at 77 K of Commercially Available Metal-Organic Framework Materials

Storage is still limiting the implementation of hydrogen as an energy carrier to integrate the intermittent operation of renewable energy sources. Among different solutions to the currently used compressed or liquified hydrogen systems, physical adsorption at cryogenic temperature in porous materials is an attractive alternative due to its fast and reversible operation and the resulting reduction in storage pressure. The feasibility of cryoadsorption for hydrogen storage depends mainly on the performance of the used materials for the specific application, where metal-organic frameworks or MOFs are remarkable candidates. In this work, gravimetric and volumetric hydrogen uptakes at 77 K and up to 100 bar of commercially available MOFs were measured since these materials are made from relatively cheap and accessible building blocks. These materials also show relatively high porous properties and are currently near to large-scale production. The measuring device was calibrated at different room temperatures to calculate an average correction factor and standard deviation so that the correction deviation is included in the measurement error for better comparability with different measurements. The influence of measurement conditions was also studied, concluding that the available adsorbing area of material and the occupied volume of the sample are the most critical factors for a reproducible measurement, apart from the samples’ preparation before measurement. Finally, the actual volumetric storage density of the used powders was calculated by directly measuring their volume in the analysis cell, comparing that value with the maximum volumetric uptake considering the measured density of crystals. From this selection of commercial MOFs, the materials HKUST-1, PCN-250(Fe), MOF-177, and MOF-5 show true potential to fulfill a volumetric requirement of 40 g·L−1 on a material basis for hydrogen storage systems without further packing of the powders.

An efficient modulated synthesis of zirconium metal–organic framework UiO-66

The use of large amounts of deleterious solvents in the synthesis of metal–organic frameworks (MOFs) is one of the important factors limiting their application in industry.

Metal–organic framework-based solid-state electrolytes for all solid-state lithium metal batteries: a review

This work systematically reviewed recent progress of MOF-based solid electrolytes in all solid-state metal batteries which has rarely been summarized.

UiO-67-derived bithiophene and bithiazole MIXMOFs for luminescence sensing and removal of contaminants of emerging concern in wastewater

The UiO-67-type MIXMOF [Zr6O4(OH)4(PhPh)5(TzTz)], containing a blue-emitting bithiazole linker, is a potential multifunctional material for environmental remediation, being both a luminescent sensor and an adsorbent for diclofenac in aqueous solutions.

Thermal degradation of defective high-surface-area UiO-66 in different gaseous environments

UiO-66 is a versatile zirconium-based MOF, which is thermally stable up to 500 °C. In the present work, the thermal degradation of UiO-66 with a high number of defects has been studied in inert, oxidative and reductive environments. A sample of UiO-66 with a high BET surface area of 1827 m² g^-1 was prepared, which contains 2.3 missing linkers per hexa-zirconium node, as calculated by the thermogravimetric curve. The crystalline framework of this UiO-66 sample collapses at 250 °C, while thermal decomposition starts at 450 °C in the oxidative environment and at 500 °C in the reductive and inert environments. The BET surface area of the MOF is affected variably by heating under different gaseous conditions. Under inert conditions, porosity is maintained up to 711 m² g^-1, which is quite high when compared to that under reductive (527 m² g^-1) or oxidative (489 m² g^-1) conditions. Upon complete thermal decomposition at 600 °C, the MOF produces predominantly tetragonal zirconia. TEM images of the thermally decomposed samples show that the shape of the original MOF crystal is maintained during the heating process in the inert and reductive environments, whereas under oxidative conditions, all of the carbon is burnt to carbon dioxide, leaving no carbon matrix as the support.

Surface Charge Regulation of MIL-100(Fe) by Anion Exchange for Demulsifying the Cationic Surfactant-Stabilized O/W Emulsion

Demulsifying ionic surfactant-stabilized emulsions remains an emerging issue due to the stringent electrostatic barriers. In this work, a phosphate-mediated anion exchange strategy was proposed to fabricate a metal-organic framework, MIL-100(Fe), with adjustable surface charge for effective demulsification toward a cationic surfactant-stabilized emulsion. By adjusting the pH of the phosphate precursor solution, the surface charge of MIL-100(Fe) can be fine-tuned. At pH 3.0, the phosphate-exchanged MIL-100(Fe) with the zeta potential decreasing from 21.4 to 6.1 mV exhibited a significant enhancement of the demulsification efficiency (DE) from 35 to 91%. Further elevating the pH to 9.0 results in the zeta potential of the phosphate-exchanged MIL-100(Fe) to be reversed to -2.0 mV, and the DE can be optimized to 96% within 5 min. The demulsification mechanism was systematically explored based on the zeta potential, distribution of the surfactant, viscoelastic modulus evaluation, and morphological characterization of the emulsion in combination with monitoring of the dynamics process of demulsification. It was found that the phosphate-exchanged MIL-100(Fe) captured by the emulsion can lead to the release of the surfactant and heterogenization of the interfacial film, causing the elasticity of the emulsion to decrease and the irreversible deformation of emulsion droplets. Consequently, the destabilized emulsion could be subjected to the effective demulsification either by the fusion pathway mediated by the phosphate-exchanged MIL-100(Fe) or direct rupture. This work emphasized a facile and promising approach to deal with the cationic surfactant-emulsified oily wastewater and disclosed the fundamental demulsification process.

Computational Investigation of Adsorptive Removal of Pb

Adsorption using metal–organic frameworks (MOFs) such as UiO-66 has shown great promise in remediating water sources contaminated with toxic heavy metals such as Pb2+, but detailed information about the adsorption process remains limited. In this article, we gained mechanistic insights into Pb2+ adsorption using both functionalised and defective UiO-66 by performing density functional theory calculations using cluster models. Our benchmarked approach led to a computational model of solvated Pb2+ (a hemidirected Pb(H2O)62+ complex) fully consistent with experimental reports. The analysis of Pb2+ adsorption using functionalised UiO-66 determined that factors such as electrostatic attraction, chelation, and limited constraints on the Pb2+ coordination geometry lead to enhanced binding affinity. For these reasons, UiO-66-COO– was identified as the most promising functionalised MOF, consistent with experimental literature. We additionally explored a novel aspect of Pb2+ adsorption by UiO-66: the role of missing linker defects that often characterise this MOF. We found that the defects expected to form in an aqueous environment can act as excellent adsorption sites for Pb2+ and the preferred adsorption geometry is again determined by electrostatic attraction, chelation, and constraints on the Pb2+ coordination geometry. Overall, we conclude that functional groups and defect sites can both contribute to Pb2+ adsorption and our study provides crucial design principles for improving the UiO-66 MOF performance in toxic Pb2+ removal from water.

Metal-Organic-Framework Based Functional Materials for Uranium Recovery: Performance Optimization and Structure/Functionality-Activity Relationships

Uranium recovery has profound significance in both uranium resource acquisition and pollution treatment. In recent years, metal-organic frameworks (MOFs) have attracted much attention as potential uranium adsorbents owing to their tunable structural topology and designable functionalities. This review explores the research progress in representative classic MOFs (MIL-101, UiO-66, ZIF-8/ZIF-67) and other advanced MOF-based materials for efficient uranium extraction in aqueous or seawater environments. The uranium uptake mechanism of the MOF-based materials is refined, and the structure/functionality-property relationship is further systematically elucidated. By summarizing the typical functionalization and structure design methods, the performance improvement strategies for MOF-based adsorbents are emphasized. Finally, the present challenges and potential opportunities are proposed for the breakthrough of high-performance MOF-based materials in uranium extraction.

Enhancing Demulsification Performance for Oil-Water Separation through Encapsulating Ionic Liquids in the Pore of MIL-100(Fe)

Emulsion poses a greater challenge for the remediation of oily wastewater, which can be effectively resolved by the metal-organic framework of MIL-100(Fe). The formula Fe₃O(H₂O)₂(OH) (BTC)₂ pronounces that MIL-100(Fe) suffers from an intrinsic defect of less charged atoms, which limits its demulsification performance for oil-water separation. Herein, cations of the ionic liquid (1-allyl-3-methylimidazolium, Amim⁺) were encapsulated in the micropore of MIL-100(Fe) in situ to increase the positive charge density of MIL-100(Fe). Zeta potential demonstrated that the encapsulation of Amim⁺ increased the positive charge amount of MIL-100(Fe). N₂ probe isothermal adsorption/desorption and spectral measurements (X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflection spectroscopy, and attenuated total-reflectance infrared spectroscopy) revealed the host-guest interactions of π···Fe complexation and π···cation electrostatic attraction between Amim⁺ and MIL-100(Fe) for the composite materials. Amim⁺ encapsulation greatly enhanced the demulsification performance of MIL-100(Fe) for oil-in-water (O/W) emulsion stabilized by sodium dodecyl sulfate. Amim⁺-encapsulated MIL-100(Fe) with an Amim⁺/Fe³⁺ molar ratio of 1:1 [Amim@MIL-100(Fe)-3:3] showed a demulsification efficiency (DE) of 94% within 30 s, compared with MIL-100(Fe) within 30 min. The maximum DE of Amim@MIL-100(Fe)-3:3 was found to be more than 98% within 5 min. The DE lost by MIL-100(Fe) at the third run decreased from 36 to 17% after encapsulating Amim⁺. The analysis of surface charge and interfacial tension implied a demulsification mechanism of capturing-fusion, which could be promoted by the greater electrostatic attraction. Finally, the role of Amim⁺ on the outstanding demulsification performance by Amim⁺-encapsulated MIL-100(Fe) could be explained by the enhanced nonbonded interaction of electrostatic attraction and van der Waals based on the molecular dynamics simulation.

Factors Affecting Hydrogen Adsorption in Metal-Organic Frameworks: A Short Review

Metal–organic frameworks (MOFs) have significant potential for hydrogen storage. The main benefit of MOFs is their reversible and high-rate hydrogen adsorption process, whereas their biggest disadvantage is related to their operation at very low temperatures. In this study, we describe selected examples of MOF structures studied for hydrogen adsorption and different factors affecting hydrogen adsorption in MOFs. Approaches to improving hydrogen uptake are reviewed, including surface area and pore volume, in addition to the value of isosteric enthalpy of hydrogen adsorption. Nanoconfinement of metal hydrides inside MOFs is proposed as a new approach to hydrogen storage. Conclusions regarding MOFs with incorporated metal nanoparticles, which may be used as nanoscaffolds and/or H₂ sorbents, are summarized as prospects for the near future.

Ionic Liquid (IL) Laden Metal-Organic Framework (IL-MOF) Electrolyte for Quasi-Solid-State Sodium Batteries

An ionic liquid (IL) laden metal-organic framework (MOF) sodium-ion electrolyte has been developed for ambient-temperature quasi-solid-state sodium batteries. The MOF skeleton is designed according to a UIO-66 (Universitetet i Oslo) structure. A sodium sulfonic (-SO₃Na) group grafted to the UIO-based MOF ligand improves the Na⁺-ion conductivity. Upon lading with a sodium-based ionic liquid (Na-IL), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) in 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Bmpyr-TFSI), the Na-IL laden sulfonated UIO-66 (UIOSNa) quasi-solid electrolyte exhibits a Na⁺-ion conductivity of 3.6 × 10^-4 S cm^-1 at ambient temperature. Quasi-solid-state sodium batteries with the Na-IL/UIOSNa electrolyte are demonstrated with a layered Na₃Ni_1.5TeO₆ cathode and sodium-metal anode. The quasi-solid-state Na∥Na-IL/UIOSNa∥Na₃Ni_1.5TeO₆ cells show remarkable cycling performance.