A New Microporous Lanthanide Metal–Organic Framework with a Wide Range of pH Linear Response

Lanthanide metal–organic frameworks (Ln-MOFs) have attracted extensive attention because of their structural adjustability and wide optical function applications. However, MOFs with a wide linear pH response and stable framework structures in acidic or alkaline solutions are rare to date. Here, we used 4,4′,4″-s-triazine-2,4,6-triyltribenzoate (H₃TATB) as an organic ligand, coordinated with lanthanide ions (Eu³⁺/Tb³⁺), and synthesized a new metal–organic framework material. The material has a porous three-dimensional square framework structure and emits bright red or green fluorescence under 365 nm UV light. The carboxyl group of the ligand is prone to protonation in an acidic environment, and negatively charged OH⁻ and ligand (TATB³⁻) have a competitive effect in an alkaline environment, which could affect the coordination ability of ligand. The luminescence degree of the framework decreases with the increase in the degree of acid and base. In particular, such fluorescence changes have a wide linear response (pH = 0–14), which can be used as a potential fluorescence sensing material for pH detection.     

Preparation and Characterization of Magnetic Metal–Organic Frameworks Functionalized by Ionic Liquid as Supports for Immobilization of Pancreatic Lipase

Enzymes are difficult to recycle, which limits their large-scale industrial applications. In this work, an ionic liquid-modified magnetic metal–organic framework composite, IL-Fe₃O₄@UiO-66-NH₂, was prepared and used as a support for enzyme immobilization. The properties of the support were characterized with X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectra, transmission electron microscopy (TEM), scanning electronic microscopy (SEM), and so on. The catalytic performance of the immobilized enzyme was also investigated in the hydrolysis reaction of glyceryl triacetate. Compared with soluble porcine pancreatic lipase (PPL), immobilized lipase (PPL-IL-Fe₃O₄@UiO-66-NH₂) had greater catalytic activity under reaction conditions. It also showed better thermal stability and anti-denaturant properties. The specific activity of PPL-IL-Fe₃O₄@UiO-66-NH₂ was 2.3 times higher than that of soluble PPL. After 10 repeated catalytic cycles, the residual activity of PPL-IL-Fe₃O₄@UiO-66-NH₂ reached 74.4%, which was higher than that of PPL-Fe₃O₄@UiO-66-NH₂ (62.3%). In addition, kinetic parameter tests revealed that PPL-IL-Fe₃O₄@UiO-66-NH₂ had a stronger affinity to the substrate and, thus, exhibited higher catalytic efficiency. The results demonstrated that Fe₃O₄@UiO-66-NH₂ modified by ionic liquids has great potential for immobilized enzymes.     

A Paradigmatic Approach to Find the Valency-Based K-Banhatti and Redefined Zagreb Entropy for Niobium Oxide and a Metal–Organic Framework

Entropy is a thermodynamic function in chemistry that reflects the randomness and disorder of molecules in a particular system or process based on the number of alternative configurations accessible to them. Distance-based entropy is used to solve a variety of difficulties in biology, chemical graph theory, organic and inorganic chemistry, and other fields. In this article, the characterization of the crystal structure of niobium oxide and a metal–organic framework is investigated. We also use the information function to compute entropies by building these structures with degree-based indices including the K-Banhatti indices, the first redefined Zagreb index, the second redefined Zagreb index, the third redefined Zagreb index, and the atom-bond sum connectivity index.     

Beyond Pristine Metal–Organic Frameworks: Preparation of Hollow MOFs and Their Composites for Catalysis,Sensing, and Adsorption Removal Applications

Metal–organic frameworks (MOFs) have been broadly applied to numerous domains with a substantial surface area, tunable pore size, and multiple unsaturated metal sites. Recently, hollow MOFs have greatly attracted the scientific community due to their internal cavities and gradient pore structures. Hollow MOFs have a higher tunability, faster mass-transfer rates, and more accessible active sites when compared to traditional, solid MOFs. Hollow MOFs are also considered to be candidates for some functional material carriers. For example, composite materials such as hollow MOFs and metal nanoparticles, metal oxides, and enzymes have been prepared. These composite materials integrate the characteristics of hollow MOFs with functional materials and are broadly used in many aspects. This review describes the preparation strategies of hollow MOFs and their composites as well as their applications in organic catalysis, electrochemical sensing, and adsorption separation. Finally, we hope that this review provides meaningful knowledge about hollow-MOF composites and their derivatives and offers many valuable references to develop hollow-MOF-based applied materials.     

An Effective Hybrid Heterogeneous Catalyst to Desulfurize Diesel: Peroxotungstate@Metal–Organic Framework

A peroxotungstate composite comprising the chromium terephthalate metal–organic framework MIL-101(Cr) and the Venturello peroxotungstate [PO₄{WO(O₂)₂}₄]³⁻ (PW₄) has been prepared by the impregnation method. The PW₄@MIL-101(Cr) composite presents high catalytic efficiency for oxidative desulfurization of a multicomponent model diesel containing the most refractory sulfur compounds present in real fuels (2000 ppm of total S). The catalytic performance of this heterogeneous catalyst is similar to the corresponding homogeneous PW₄ active center. Desulfurization efficiency of 99.7% was achieved after only 40 min at 70 °C using H₂O₂ as an oxidant and an ionic liquid as an extraction solvent ([BMIM]PF₆, 2:1 model diesel/[BMIM]PF₆). High recycling and reusing capacity was also found for PW₄@MIL-101(Cr), maintaining its activity for consecutive oxidative desulfurization cycles. A comparison of the catalytic performance of this peroxotungstate composite with others previously reported tungstate@MIL-101(Cr) catalysts indicates that the presence of active oxygen atoms from the peroxo groups promotes a higher oxidative catalytic efficiency in a shorter reaction time.     

Metal–Organic Frameworks–Based Memristors: Materials,Devices, and Applications

Facing the explosive growth of data, a number of new micro-nano devices with simple structure, low power consumption, and size scalability have emerged in recent years, such as neuromorphic computing based on memristor. The selection of resistive switching layer materials is extremely important for fabricating of high performance memristors. As an organic-inorganic hybrid material, metal-organic frameworks (MOFs) have the advantages of both inorganic and organic materials, which makes the memristors using it as a resistive switching layer show the characteristics of fast erasing speed, outstanding cycling stability, conspicuous mechanical flexibility, good biocompatibility, etc. Herein, the recent advances of MOFs-based memristors in materials, devices, and applications are summarized, especially the potential applications of MOFs-based memristors in data storage and neuromorphic computing. There also are discussions and analyses of the challenges of the current research to provide valuable insights for the development of MOFs-based memristors.     

Synthesis and Biomedical Applications of Highly Porous Metal–Organic Frameworks

In this review, aspects of the synthesis, framework topologies, and biomedical applications of highly porous metal–organic frameworks are discussed. The term “highly porous metal–organic frameworks” (HPMOFs) is used to denote MOFs with a surface area larger than 4000 m² g⁻¹. Such compounds are suitable for the encapsulation of a variety of large guest molecules, ranging from organic dyes to drugs and proteins, and hence they can address major contemporary challenges in the environmental and biomedical field. Numerous synthetic approaches towards HPMOFs have been developed and discussed herein. Attempts are made to categorise the most successful synthetic strategies; however, these are often not independent from each other, and a combination of different parameters is required to be thoroughly considered for the synthesis of stable HPMOFs. The majority of the HPMOFs in this review are of special interest not only because of their high porosity and fascinating structures, but also due to their capability to encapsulate and deliver drugs, proteins, enzymes, genes, or cells; hence, they are excellent candidates in biomedical applications that involve drug delivery, enzyme immobilisation, gene targeting, etc. The encapsulation strategies are described, and the MOFs are categorised according to the type of biomolecule they are able to encapsulate. The research field of HPMOFs has witnessed tremendous development recently. Their intriguing features and potential applications attract researchers’ interest and promise an auspicious future for this class of highly porous materials.     

Linker Functionalization Strategy for Water Adsorption in Metal–Organic Frameworks

Water adsorption in metal–organic frameworks has gained a lot of scientific attention recently due to the potential to be used in adsorption-based water capture. Functionalization of their organic linkers can tune water adsorption properties by increasing the hydrophilicity, thus altering the shape of the water adsorption isotherms and the overall water uptake. In this work, a large set of functional groups is screened for their interaction with water using ab initio calculations. The functional groups with the highest water affinities form two hydrogen bonds with the water molecule, acting as H-bond donor and H-bond acceptor simultaneously. Notably, the highest binding energy was calculated to be −12.7 Kcal/mol for the -OSO₃H group at the RI-MP2/def2-TZVPP-level of theory, which is three times larger than the reference value. Subsequently, the effect of the functionalization strategy on the water uptake is examined on a selected set of functionalized MOF-74-III by performing Monte Carlo simulations. It was found that the specific groups can increase the hydrophilicity of the MOF and enhance the water uptake with respect to the parent MOF-74-III for relative humidity (RH) values up to 30%. The saturation water uptake exceeded 800 cm³/cm³ for all candidates, classifying them among the top performing materials for water harvesting.     

Metalloporphyrin Metal–Organic Frameworks: Eminent Synthetic Strategies and Recent Practical Exploitations

The emergence of metal–organic frameworks (MOFs) in recent years has stimulated the interest of scientists working in this area as one of the most applicable archetypes of three-dimensional structures that can be used as promising materials in several applications including but not limited to (photo-)catalysis, sensing, separation, adsorption, biological and electrochemical efficiencies and so on. Not only do MOFs have their own specific versatile structures, tunable cavities, and remarkably high surface areas, but they also present many alternative procedures to overcome emerging obstacles. Since the discovery of such highly effective materials, they have been employed for multiple uses; additionally, the efforts towards the synthesis of MOFs with specific properties based on planned (template) synthesis have led to the construction of several promising types of MOFs possessing large biological or bioinspired ligands. Specifically, metalloporphyrin-based MOFs have been created where the porphyrin moieties are either incorporated as struts within the framework to form porphyrinic MOFs or encapsulated inside the cavities to construct porphyrin@MOFs which can combine the peerless properties of porphyrins and porous MOFs simultaneously. In this context, the main aim of this review was to highlight their structure, characteristics, and some of their prominent present-day applications.     

Tunable Ammonia Adsorption within Metal–Organic Frameworks with Different Unsaturated Metal Sites

Ammonia (NH₃) emissions during agricultural production can cause serious consequences on animal and human health, and it is quite vital to develop high-efficiency adsorbents for NH₃ removal from emission sources or air. Porous metal–organic frameworks (MOFs), as the most promising candidates for the capture of NH₃, offer a unique solid adsorbent design platform. In this work, a series of MOFs with different metal centers, ZnBTC, FeBTC and CuBTC, were proposed for NH₃ adsorption. The metal centers of the three MOFs are coordinated in a different manner and can be attacked by NH₃ with different strengths, resulting in different adsorption capacities of 11.33, 9.5, and 23.88 mmol/g, respectively. In addition, theoretical calculations, powder XRD patterns, FTIR, and BET for the three materials before and after absorption of ammonia were investigated to elucidate their distinctively different ammonia absorption mechanisms. Overall, the study will absolutely provide an important step in designing promising MOFs with appropriate central metals for the capture of NH₃.     

A Novel Turn-On Fluorescence Probe Based on Cu(II) Functionalized Metal–Organic Frameworks for Visual Detection of Uric Acid

As an important biomarker in urine, the level of uric acid is of importance for human health. In this work, a Cu(II) functionalized metal–organic framework (Cu²⁺@Tb-MOFs) is designed and developed as a novel fluorescence probe for wide-range uric acid detection in human urine. The study shows that this fluorescence platform demonstrated excellent pH-independent stability, high water tolerance, and good thermal stability. Based on the strong interaction between metal ions and uric acid, the designed Cu²⁺@Tb-MOFs can be employed as efficient turn-on fluorescent probes for the detection of uric acid with wide detection range (0~10⁴ µM) and high sensitivity (LOD = 0.65 µM). This probe also demonstrates an anti-interference property, as other species coexisted, and the possibility for recycling. The sensing mechanisms are further discussed at length. More importantly, we experimentally constructed a molecular logic gate operation based on this fluorescence probe for intelligent detection of uric acid. These results suggest the Cu(II) functionalized metal–organic framework can act as a prominent candidate for personalized monitoring of the concentration of uric acid in the human urine system.     

A Rigid Nested Metal–Organic Framework Featuring a Thermoresponsive Gating Effect Dominated by Counterions

We herein report a rigid nested metal–organic framework (MOF) featuring a unique thermoresponsive gating adsorption behavior, which, in contrast to any known flexibility modes for stimuli‐responsive MOFs, depends on the thermal motion of the extra‐framework counterions. In addition, this MOF also exhibits adsorption selectivity of CO₂ over N₂, H₂, and Ar at 273 K, thus enabling a strategic separation and encapsulation of CO₂.     

The Surge of Metal–Organic-Framework (MOFs)-Based Electrodes as Key Elements in Electrochemically Driven Processes for the Environment

Metal–organic-frameworks (MOFs) are emerging materials used in the environmental electrochemistry community for Faradaic and non-Faradaic water remediation technologies. It has been concluded that MOF-based materials show improvement in performance compared to traditional (non-)faradaic materials. In particular, this review outlines MOF synthesis and their application in the fields of electron- and photoelectron-Fenton degradation reactions, photoelectrocatalytic degradations, and capacitive deionization physical separations. This work overviews the main electrode materials used for the different environmental remediation processes, discusses the main performance enhancements achieved via the utilization of MOFs compared to traditional materials, and provides perspective and insights for the further development of the utilization of MOF-derived materials in electrified water treatment.     

Flexible and Hierarchical Metal–Organic Framework Composites for High‐Performance Catalysis

The development of porous composite materials is of great significance for their potentially improved performance over those of individual components and extensive applications in separation, energy storage, and heterogeneous catalysis. Now mesoporous metal–organic frameworks (MOFs) with macroporous melamine foam (MF) have been integrated using a one‐pot process, generating a series of MOF/MF composite materials with preserved crystallinity, hierarchical porosity, and increased stability over that of melamine foam. The MOF nanocrystals were threaded by the melamine foam networks, resembling a ball‐and‐stick model overall. The resulting MOF/MF composite materials were employed as an effective heterogeneous catalyst for the epoxidation of cholesteryl esters. Combining the advantages of interpenetrative mesoporous and macroporous structures, the MOF/melamine foam composite has higher dispersibility and more accessibility of catalytic sites, exhibiting excellent catalytic performance.     

Synthesis and the Crystal Structure of a New Chiral 1D Metal–Organic Coordination Polymer Based on L-Prolineamide-Substituted Diarylacetylenedicarboxylic Acid Derivative

The new homochiral 1D metal–organic coordination polymer [Cu₂(EDPB)•H₂O]_n was synthesized starting from the original 3,3′-ethyne-1,2-diylbis[6-(L-prolylamino)benzoic acid] (H₄EDPB). The unique crystal structure of the new compound was established by powder X-ray diffraction. The [Cu₂(EDPB)•H₂O]_n system shows catalytic activity and enantioselectivity in a Henry reaction of p-nitrobenzaldehyde with nitromethane.     

A Metal–Organic Framework/DNA Hybrid System as a Novel Fluorescent Biosensor for Mercury(II) Ion Detection

Mercury(II) ions have emerged as a widespread environmental hazard in recent decades. Despite different kinds of detection methods reported to sense Hg²⁺, it still remains a challenging task to develop new sensing molecules to replenish the fluorescence‐based apparatus for Hg²⁺ detection. This communication demonstrates a novel fluorescent sensor using UiO‐66‐NH₂ and a T‐rich FAM‐labeled ssDNA as a hybrid system to detect Hg²⁺ sensitively and selectively. To the best of our knowledge, it has rarely been reported that a MOF is utilized as the biosensing platform for Hg²⁺ assay.