One-Step Room-Temperature Synthesis of Metal(IV) Carboxylate Metal-Organic Frameworks

Engineering the Activity and Stability of the Zn-MOF Catalyst via the Interaction of Doped Zr with Zn

Metallic atoms within metal-organic framework (MOF) materials exhibit a distinctive and adaptable coordination structure. The three-dimensional (3D) pore configuration of MOFs enables the complete exposure of metal active sites, rendering them prevalent in various catalytic reactions. In this study, zinc (Zn) atoms within Zn-based MOF materials, characterized by an abundance of valence electrons, are utilized for the transesterification of dimethyl carbonate (DMC). Additionally, the introduction of zirconium (Zr) effectively addresses the susceptibility of the MOFs' crystal structure to dissolution in organic solvents. The formulated catalyst, Zn-10%Zr-MOF(300), demonstrates remarkable catalytic performance with 91.5% DMC selectivity, 61.9% propylene carbonate (PC) conversion, and 56.6% DMC yield. Impressively, the catalyst maintains its high performance over five cycles. Results indicate that Zr interacts with Zn, forming new coordination bonds and enhancing the catalyst crystal structure stability. Moreover, electron transfer intensifies the alkalinity of the active Zn atoms, enhancing the overall catalyst performance. This research informs the development of transesterification heterogeneous catalysts and broadens the application scope of MOF catalysts.

Unique Hierarchically Structured High-Entropy Alloys with Multiple Adsorption Sites for Rechargeable Li-CO2 Batteries with High Capacity

Lithium-carbon dioxide (Li-CO2) batteries offer the possibility of synchronous implementation of carbon neutrality and the development of advanced energy storage devices. The exploration of low-cost and efficient cathode catalysts is key to the improvement of Li-CO2 batteries. Herein, high-entropy alloys (HEAs)@C hierarchical nanosheet is synthesized from the simulation of the recycling solution of waste batteries to construct a cathode for the first time. Owing to the excellent electrical conductivity of the carbon material, the unique high-entropy effect of the HEAs, and the large number of catalytically active sites exposed by the hierarchical structure, the FeCoNiMnCuAl@C-based battery exhibits a superior discharge capability of 27664 mAh g-1 and outstanding durability of 134 cycles as well as low overpotential with 1.05 V at a discharge/recharge rate of 100 mA g-1. The adsorption capacity of different sites on the HEAs is deeply understood through density functional theory calculations combined with experiments. This work opens up the application of HEAs in Li-CO2 batteries catalytic cathodes and provides unique insights into the study of adsorption active sites in HEAs.

Ultrasmall Functionalized UiO-66 Nanoparticle/Polymer Pebax 1657 Thin-Film Nanocomposite Membranes for Optimal CO2 Separation

Ultrasmall 4 to 6 nm nanoparticles of the metal-organic framework (MOF) UiO-66 (University of Oslo-66) were successfully prepared and embedded into the polymer Pebax 1657 to fabricate thin-film nanocomposite (TFN) membranes for CO2/N2 and CO2/CH4 separations. Furthermore, it has been demonstrated that ligand functionalization with amino (-NH2) and nitro (-NO2) groups significantly enhances the gas separation performance of the membranes. For CO2/N2 separation, 7.5 wt % UiO-66-NH2 nanoparticles provided a 53% improvement in CO2 permeance over the pristine membrane (from 181 to 277 GPU). Regarding the CO2/N2 selectivity, the membranes prepared with 5 wt % UiO-66-NO2 nanoparticles provided an increment of 17% over the membrane without the MOF (from 43.5 to 51.0). However, the CO2 permeance of this membrane dropped to 155 GPU. The addition of 10 wt % ZIF-94 particles with an average particle size of ∼45 nm into the 5 wt % UiO-66-NO2 membrane allowed to increase the CO2 permeance to 192 GPU while maintaining the CO2/N2 selectivity at ca. 51 due to the synergistic interaction between the MOFs and the polymer matrix provided by the hydrophilic nature of ZIF-94. In the case of CO2/CH4 separation, the 7.5 wt % UiO-66-NH2 membrane exhibited the best performance with an increase of the CO2 permeance from 201 to 245 GPU.

Icing on the Cake: Imidazole-Anchored Strategy To Enhance the Proton Conductivity of Two Isostructural Ce(IV)/Hf(IV) Metal-Organic Frameworks

In the field of proton conduction, the acquisition of crystalline metal-organic frameworks (MOFs) with high stability and ultrahigh proton conductivity has been of great research value and is worth continuous exploration. Here, we greenly synthesized a three-dimensional porous MOF (MOF-801-Ce) by using [(NH4)2Ce(NO3)6 and fumaric acid as starting materials and solvothermally synthesized Hf-UiO-66-NO2 by using HfCl4 and 2-nitroterephthalic acid as starting materials. A series of measurements have shown that both MOFs exhibit good water stability, acid-base stability, and thermal stability and demonstrate outstanding proton conductivity. At 100 °C and 98% relative humidity (RH), the proton conductivities (σ) could be 2.59 × 10-3 S·cm-1 for MOF-801-Ce and 0.89 × 10-3 S·cm-1 for Hf-UiO-66-NO2. To pursue higher proton conductivity, we further adopted the evaporation approach to encapsulate imidazole molecules in the pores of the two compounds, achieving the imidazole-encapsulated MOFs, Im@MOF-801-Ce and Im@Hf-UiO-66-NO2. As expected, their σ values were significantly boosted by almost an order of magnitude up to 10-2 S·cm-1. Finally, their proton-conductive mechanisms were explored in light of the structural information, gas adsorption/desorption, and other tests. The outstanding structural stability of these MOFs and their durability of the proton conduction capability manifested that they have great promise in electrochemical fields.

Detangling electrolyte chemical dynamics in lithium sulfur batteries by operando monitoring with optical resonance combs

Challenges in enabling next-generation rechargeable batteries with lower cost, higher energy density, and longer cycling life stem not only from combining appropriate materials, but from optimally using cell components. One-size-fits-all approaches to operational cycling and monitoring are limited in improving sustainability if they cannot utilize and capture essential chemical dynamics and states of electrodes and electrolytes. Herein we describe and show how the use of tilted fiber Bragg grating (TFBG) sensors to track, via the monitoring of both temperature and refractive index metrics, electrolyte-electrode coupled changes that fundamentally control lithium sulfur batteries. Through quantitative sensing of the sulfur concentration in the electrolyte, we demonstrate that the nucleation pathway and crystallization of Li2S and sulfur govern the cycling performance. With this technique, a critical milestone is achieved, not only towards developing chemistry-wise cells (in terms of smart battery sensing leading to improved safety and health diagnostics), but further towards demonstrating that the coupling of sensing and cycling can revitalize known cell chemistries and break open new directions for their development.

Concentration- and Self-Catalysis-Dominated Rapid Synthesis of Multifunctional UiO-66(Ce) for Dual-Mode Sensing of Tetracycline

Simple and rapid synthesis of multifunctional metal-organic frameworks (MOFs) at room temperature (RT) with their multifunction controllable is still appealing for further expansion of the practical applications of MOFs. Herein, in this work, rapid RT synthesis of a multifunctional UiO-66(Ce) [M-UiO-66(Ce)] with both oxidase-like activity and fluorescence emission properties was facilely achieved within 15 min through a straightforward reactant concentration modulation and self-catalytic postmodification strategy. Appropriate concentrations of cerium ammonium nitrate or 1,4-benzenedicarboxylic acid (BDC) were beneficial for the synthesis of UiO-66(Ce) with better crystallization. During the postmodification process, through regulation of the self-photocatalysis of UiO-66(Ce), a high conversion rate from BDC to BDC-OH of up to 14% can be obtained, resulting in a significantly enhanced fluorescence signal of M-UiO-66(Ce) within 2 min. Moreover, M-UiO-66(Ce) enabled the accurate and reliable detection of tetracycline (TC) in real samples. Besides, the colorimetric and fluorescence modes complemented each other, expanding the linear range of TC detection and exhibiting its great potential for practical applications. This work provides new insights for the convenient and rapid synthesis of multifunctional materials based on MOFs, which is favorable for promoting the large-scale preparation of MOFs and their practical application in on-site environmental pollutant sensing.

Room Temperature Synthesis Mediated Porphyrinic NanoMOF Enables Benchmark Electrochemical Biosensing

Leveraging size effects, nanoparticles of metal-organic frameworks, nanoMOFs, have recently gained traction, amplifying their scopes in electrochemical sensing. However, their synthesis, especially under eco-friendly ambient conditions remains an unmet challenge. Herein, an ambient and fast secondary building unit (SBU)-assisted synthesis (SAS) route to afford a prototypal porphyrinic MOF, Fe-MOF-525 is introduced. Albeit the benign room temperature conditions, Fe-MOF-525(SAS) nanocrystallites obtained are of ≈30 nm size, relatively smaller than the ones conventional solvothermal methods elicit. Integrating Fe-MOF-525(SAS) as a thin film on a conductive indium tin oxide (ITO) surface affords Fe-MOF-525(SAS)/ITO, an electrochemical biosensor. Synergistic confluence of modular MOF composition, analyte-specific redox metalloporphyrin sites, and crystal downsizing contribute to its benchmark voltammetric uric acid (UA) sensing. Showcasing a wide linear range of UA detection with high sensitivity and low detection limit, this SAS strategy coalesces ambient condition synthesis and nanoparticle size control, paving a green way to advanced sensors.

In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40-80%). Although the selective capture of VOCs over water is still challenging, metal-organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF₃) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2-6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF₃ present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF₃ was shown to overpass MIL-101(Cr) in terms of AA/H₂O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

Regulating defective sites for pharmaceuticals selective removal: Structure-dependent adsorption over continuously tunable pores

Developing efficient adsorbents with proper pore size for pharmaceutical removal is challenging. Water stable metal-organic frameworks (MOFs) are crystalline materials within the three-dimensional frameworks, which have already aroused increasing attention for their potential advantages with high surface area and abundant channels. However, whether or not the existing ones are performing their full capacities needs to be seriously considered. Herein, we precisely designed a series of fine-tuning hierarchically porous materials based on the water-stable Zr-based MOFs. The adsorption capacity and uptake rate of as-synthesized materials for pharmaceuticals are significantly improved. Fifteen isostructural frameworks with increasing finely tuned pore structures were successfully constructed with seven monocarboxylic modulators of increasing alkyl chain lengths. A strong correlated relationship between the mesoporous proportion and trapping kinetics can be found. Adsorption performance of 17 pharmaceuticals with various typical categories has been systematically studied over these as-synthesized materials. Competitors in natural wastewater were studied systematically. The competitive adsorption can selectively trap the target compounds in HA (humic acid), BSA (bovine serum albumin), and BHB (bovine hemoglobin) by an efficient size exclusion effect. Thus, this study offers helpful guidance for MOF modification to enhance the removal of micropollutants in natural wastewater and a fundamental understanding of the porosity-performance relationships.

Room temperature synthesis of monolithic MIL-100(Fe) in aqueous solution for energy-efficient removal and recovery of aromatic volatile organic compounds

The removal and recovery of volatile organic compounds (VOCs) are widely used in many industrials. Unfortunately, most conventional porous materials not only have low VOCs uptake, but also need to be regenerated at relatively high temperature. Metal-organic frameworks (MOFs) have great potential for the removal and recovery of VOCs as their record-breaking gas adsorption capacity, easy regeneration, tunable pore structure and functional groups. Whereas, powdered MOFs are hardly implemented in industrial fields owing to their low bulk density and high pressure drop. Exploring a green method to prepare granular MOFs for the removal and recovery of VOCs is still a challenge. Herein, we report the room temperature green synthesis of a stable Fe-based MOF monolith by using water as the solvent without applying high pressure and chemical binders. The static and dynamic experiments show that the optimized centimeter-scale monolith has high porosity and mechanical strength, and exhibits much better adsorption performance for representative aromatic VOCs (benzene, toluene and p-xylene), than commercial activated carbon and activated carbon fiber under the same conditions. Remarkably, as-synthesized monolith can be rapidly regenerated at lower temperature. These results clearly demonstrate the advantages of MOF monoliths in removing and recovering VOCs, and also provide new insight into the effects of drying temperature, washing and centrifugation procedures on MOF shaping.

Room temperature design of Ce(iv)-MOFs: from photocatalytic HER and OER to overall water splitting under simulated sunlight irradiation

A new synthetic approach is reported to synthesize redox-active Ce(iv) MOFs at room temperature for efficient and reusable photo-induced overall water splitting.

Defined metal atom aggregates precisely incorporated into metal-organic frameworks

Nanosized metal aggregates (MAs), including metal nanoparticles (NPs) and nanoclusters (NCs), are often the active species in numerous applications. In order to maintain the active form of MAs in "use", they need to be anchored and stabilised, preventing agglomeration. In this context, metal-organic frameworks (MOFs), which exhibit a unique combination of properties, are of particular interest as a tunable and porous matrix to host MAs. A high degree of control in the synthesis towards atom-efficient and application-oriented MA@MOF composites is required to derive specific structure-property relationships and in turn to enable design of functions on the molecular level. Due to the versatility of MA@MOF (derived) materials, their applications are not limited to the obvious field of catalysis, but increasingly include 'out of the box' applications, for example medical diagnostics and theranostics, as well as specialised (bio-)sensoring techniques. This review focuses on recent advances in the controlled synthesis of MA@MOF materials en route to atom-precise MAs. The main synthetic strategies, namely 'ship-in-bottle', 'bottle-around-ship', and approaches to achieve novel hierarchical MA@MOF structures are highlighted and discussed while identifying their potential as well as their limitations. Hereby, an overview of standard characterisation methods that enable a systematic analysis procedure and state-of-art techniques that localise MA within MOF cavities are provided. While the perspectives of MA@MOF materials in general have been reviewed various times in the recent past, few atom-precise MAs inside MOFs have been reported so far, opening opportunities for future investigation.

Synthesis and shaping of metal-organic frameworks: a review

Metal-organic frameworks (MOFs) possess excellent advantages, such as high porosity, large specific surface area, and an adjustable structure, showing good potential for applications in gas adsorption and separation, catalysis, conductivity, sensing, magnetism, etc. However, they still suffer from significant limitations in terms of the scale-up synthesis and shaping, hindering the realization of large-scale commercial applications. Despite some attempts having been devoted to addressing this, challenges remain. In this paper, we outline the advantages and drawbacks of existing synthetic routes such as electrochemistry, microwave, ultrasonic radiation, green solvent reflux, room temperature stirring, steam-assisted transformation, mechanochemistry, and fluid chemistry in terms of scale-up production. Then, the shaping methods of MOFs such as extrusion, mechanical compaction, rolling granulation, spray drying, gel technology, embedded granulation, phase inversion, 3D printing and other shaping methods for the preparation of membranes, coatings and nanoparticles are discussed. Finally, perspectives on the large-scale synthesis and shaping of MOFs are also proposed. This work helps provide in-depth insight into the scale-up production and shaping process of MOFs and boost commercial applications of MOFs.

Acetylenedicarboxylate as a linker in the engineering of coordination polymers and metal-organic frameworks: challenges and potential

Despite its simplicity as a short and rod-like linear linker, acetylenedicarboxylate (ADC) has for a long time been somewhat overlooked in the engineering of coordination polymers (CPs) and especially in the construction of porous metal-organic frameworks (MOFs). This situation seems to be stemming from the thermosensitivity of the free acid (H₂ADC) precursor and its dicarboxylate, which makes the synthesis of their CP- and MOF-derivatives, as well as the evacuation of guest molecules from their pores, challenging. However, an increasing number of publications dealing with the synthesis, structural characterization and properties of ADC-based CPs and MOFs, disclose ways to tackle this obstacle. In this regard, using mostly room temperature solution synthesis or mechanochemical synthesis, and very rarely solvothermal synthesis, the ADC linker has successfully been used to form one-, two-, and three-dimensional CPs with metal cations from almost all groups of the periodic table of the elements, whereby its carboxylate groups adopt mainly all types of known coordination modes. ADC-based CPs feature properties, including negative thermal expansion, formation of non-centrosymmetric networks, long-range magnetic ordering, and solid-state polymerization. The first ADC-based microporous MOFs were obtained with Ce(IV), Hf(IV) and Zr(IV), in which the presence of the -CC- triple-bond within their backbone results in high hydrophilicity, high CO₂ adsorption capacity and enthalpy, as well as the uptake of halogen vapors. This discloses the potential of ADC-MOFs for gas storage/separation and water adsorption-based applications. Furthermore, H₂ADC/ADC was discovered to undergo facile in situ hydrohalogenation to yield halogen-functionalized fumarate-based CPs/MOFs. This review surveys investigations on ADC-based coordination polymers and metal-organic frameworks, and is intended to stimulate interest on this linker in chemists working in the fields of crystal chemistry or materials science.

Comparative Studies on the Proton Conductivities of Hafnium-Based Metal-Organic Frameworks and Related Chitosan or Nafion Composite Membranes

Hafnium (Hf)-based UiO-66 series metal-organic frameworks (MOFs) have been widely studied on gas storage, gas separation, reduction reaction, and other aspects since they were first prepared in 2012, but there are few studies on proton conductivity. In this work, one Hf-based MOF, Hf-UiO-66-fum showing UiO-66 structure, also known as MOF-801-Hf, was synthesized at room temperature using cheap fumaric acid as the bridging ligand, and then imidazole units were successfully introduced into MOF-801-Hf to obatin a doped product, Im@MOF-801-Hf. Note that both MOF-801-Hf and Im@MOF-801-Hf demonstrate excellent thermal, water, and acid-base stabilities. Expectedly, the maximum proton conductivity (σ) of Im@MOF-801-Hf (1.46 × 10^-2 S·cm^-1) is nearly 4 times greater than that of MOF-801-Hf (3.98 × 10^-3 S·cm^-1) under 100 °C and 98% relative humidity (RH). To explore their possible practical application value, we doped them into chitosan (CS) or Nafion membranes as fillers, namely, CS/MOF-801-Hf-X, CS/Im@MOF-801-Hf-Y, and Nafion/MOF-801-Hf-Z (X, Y, and Z are the doping percentages of MOF in the membrane, respectively). Intriguingly, it was found that CS/MOF-801-Hf-6 and CS/Im@MOF-801-Hf-4 indicated the highest σ values of 1.73 × 10^-2 and 2.14 × 10^-2 S·cm^-1, respectively, under 100 °C and 98% RH and Nafion/MOF-801-Hf-9 also revealed a high σ value of 4.87 × 10^-2 S·cm^-1 under 80 °C and 98% RH, which showed varying degrees of enhancement compared to the original MOFs or pure CS and Nafion membranes. Our study illustrates that these Hf-based MOFs and related composite membranes offer great potential in electrochemical fields.

Construction and application of base-stable MOFs: a critical review

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials constructed from organic ligands and metal ions/clusters. Owing to their unique advantages, they have attracted more and more attention in recent years and numerous studies have revealed their great potential in various applications. Many important applications of MOFs inevitably involve harsh alkaline operational environments. To achieve high performance and long cycling life in these applications, high stability of MOFs against bases is necessary. Therefore, the construction of base-stable MOFs has become a critical research direction in the MOF field. This review gives a historic summary of the development of base-stable MOFs in the last few years. The key factors that can determine the robustness of MOFs under basic conditions are analyzed. We also demonstrate the exciting achievements that have been made by utilizing base-stable MOFs in different applications. In the end, we discuss major challenges for the further development of base-stable MOFs. Some possible methods to address these problems are presented.

Reticular Nanoscience: Bottom-Up Assembly Nanotechnology

The chemistry of metal-organic and covalent organic frameworks (MOFs and COFs) is perhaps the most diverse and inclusive among the chemical sciences, and yet it can be radically expanded by blending it with nanotechnology. The result is reticular nanoscience, an area of reticular chemistry that has an immense potential in virtually any technological field. In this perspective, we explore the extension of such an interdisciplinary reach by surveying the explored and unexplored possibilities that framework nanoparticles can offer. We localize these unique nanosized reticular materials at the juncture between the molecular and the macroscopic worlds, and describe the resulting synthetic and analytical chemistry, which is fundamentally different from conventional frameworks. Such differences are mirrored in the properties that reticular nanoparticles exhibit, which we described while referring to the present state-of-the-art and future promising applications in medicine, catalysis, energy-related applications, and sensors. Finally, the bottom-up approach of reticular nanoscience, inspired by nature, is brought to its full extension by introducing the concept of augmented reticular chemistry. Its approach departs from a single-particle scale to reach higher mesoscopic and even macroscopic dimensions, where framework nanoparticles become building units themselves and the resulting supermaterials approach new levels of sophistication of structures and properties.

Biomedical Applications of Metal-Organic Frameworks for Disease Diagnosis and Drug Delivery: A Review

Metal-organic frameworks (MOFs) are a novel class of porous hybrid organic-inorganic materials that have attracted increasing attention over the past decade. MOFs can be used in chemical engineering, materials science, and chemistry applications. Recently, these structures have been thoroughly studied as promising platforms for biomedical applications. Due to their unique physical and chemical properties, they are regarded as promising candidates for disease diagnosis and drug delivery. Their well-defined structure, high porosity, tunable frameworks, wide range of pore shapes, ultrahigh surface area, relatively low toxicity, and easy chemical functionalization have made them the focus of extensive research. This review highlights the up-to-date progress of MOFs as potential platforms for disease diagnosis and drug delivery for a wide range of diseases such as cancer, diabetes, neurological disorders, and ocular diseases. A brief description of the synthesis methods of MOFs is first presented. Various examples of MOF-based sensors and DDSs are introduced for the different diseases. Finally, the challenges and perspectives are discussed to provide context for the future development of MOFs as efficient platforms for disease diagnosis and drug delivery systems.

Composite SPE Paper Membrane Based on the Functional Superstructure of Metal-Organic Frameworks and Ionic Liquids for Detection of Tetracycline-like Antibiotics

Composite adsorbents based on metal-organic frameworks (MOFs) are excellent candidates for solid-phase extraction (SPE) due to their diverse chemical functionality and multilevel porosity. MOF superstructures based on self-assembly at room temperature (RT) could have less energy consumption and easier manipulation due to the larger complex geometry. The π-π stacking of the benzene ring could not only enhance the interaction toward hydrophobic or plane-structured targets but also be expected to promote the formation of the MOF superstructure. In this work, in the established RT self-assembly synthesis system, several factors were investigated to see how to obtain functional MOF superstructures with a regular geometry, among which the number of benzene rings in the ligand was mainly tested for its impact on self-assembly and adsorption capacity. By means of adsorption experiments and computational fluid dynamics (CFD) simulation, the relationship between structure and activity (SARs) was further explored. Interestingly, the MOF unit with the lowest specific surface area performed the best in adsorption. Then, the selected functional MOF superstructure and ionic liquid were used to produce the composite paper membrane facilely applied in the SPE device. After optimization of the preparation conditions and operation parameters, the established SPE-HPLC-UV method could selectively analyze tetracycline-like antibiotics in the range of 16.6-833.3 ng/g (ppb) in a meat sample. This work provided an RT synthesis method to produce a microsize MOF superstructure, with experimental and theoretical insights into the SARs, which could be expanded in the design of other MOF-based SPE composite membranes toward one group of analogues.

The chemistry behind room temperature synthesis of hafnium and cerium UiO-66 derivatives

RT formation of Hf and Ce UiO-66 derivatives is investigated using a one-step method where the linker and metal salt are simply combined, and a two-step method where the inorganic component is pre-heated to form metal clusters.

Enhancing the Catalytic Activity of MOF-808 Towards Peptide Bond Hydrolysis through Synthetic Modulations

The performance of MOFs in catalysis is largely derived from structural features, and much work has focused on introducing structural changes such as defects or ligand functionalisation to boost the reactivity of the MOF. However, the effects of different parameters chosen for the synthesis on the catalytic reactivity of the resulting MOF remains poorly understood. Here, we evaluate the role of metal precursor on the reactivity of Zr-based MOF-808 towards hydrolysis of the peptide bond in the glycylglycine model substrate. In addition, the effect of synthesis temperature and duration has been investigated. Surprisingly, the metal precursor was found to have a large influence on the reactivity of the MOF, surpassing the effect of particle size or number of defects. Additionally, we show that by careful selection of the Zr-salt precursor and temperature used in MOF syntheses, equally active MOF catalysts could be obtained after a 20 minute synthesis compared to 24 h synthesis.

"Shake 'n Bake" Route to Functionalized Zr-UiO-66 Metal-Organic Frameworks

We report a novel synthetic procedure for the high-yield synthesis of metal-organic frameworks (MOFs) with fcu topology with a UiO-66-like structure starting from a range of commercial ZrIV precursors and various substituted dicarboxylic linkers. The syntheses are carried out by grinding in a ball mill the starting reagents, namely, Zr salts and the dicarboxylic linkers, in the presence of a small amount of acetic acid and water (1 mL total volume for 1 mmol of each reagent), followed by incubation at either room temperature or 120 °C. Such a simple "shake 'n bake" procedure, inspired by the solid-state reaction of inorganic materials, such as oxides, avoids the use of large amounts of solvents generally used for the syntheses of Zr-MOF. Acidity of the linkers and the amount of water are found to be crucial factors in affording materials of quality comparable to that of products obtained under solvo- or hydrothermal conditions.

Metalloenzyme-Inspired Ce-MOF Catalyst for Oxidative Halogenation Reactions

The structure of UiO-66(Ce) is formed by CeO_2-x defective nanoclusters connected by terephthalate ligands. The initial presence of accessible Ce³⁺ sites in the as-synthesized UiO-66(Ce) has been determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR)-CO analyses. Moreover, linear scan voltammetric measurements reveal a reversible Ce⁴⁺/Ce³⁺ interconversion within the UiO-66(Ce) material, while nanocrystalline ceria shows an irreversible voltammetric response. This suggests that terephthalic acid ligands facilitate charge transfer between subnanometric metallic nodes, explaining the higher oxidase-like activity of UiO-66(Ce) compared to nanoceria for the mild oxidation of organic dyes under aerobic conditions. Based on these results, we propose the use of Ce-based metal-organic frameworks (MOFs) as efficient catalysts for the halogenation of activated arenes, as 1,3,5-trimethoxybenzene (TMB), using oxygen as a green oxidant. Kinetic studies demonstrate that UiO-66(Ce) is at least three times more active than nanoceria under the same reaction conditions. In addition, the UiO-66(Ce) catalyst shows an excellent stability and can be reused after proper washing treatments. Finally, a general mechanism for the oxidative halogenation reaction is proposed when using Ce-MOF as a catalyst, which mimics the mechanistic pathway described for metalloenzymes. The superb control in the generation of subnanometric CeO_2-x defective clusters connected by adequate organic ligands in MOFs offers exciting opportunities in the design of Ce-based redox catalysts.

A Showcase of Green Chemistry: Sustainable Synthetic Approach of Zirconium-Based MOF Materials

Zirconium-based metal-organic framework materials (Zr-MOFs) have more practical usage over most conventional benchmark porous materials and even many other MOFs due to the excellent structural stability, rich coordination forms, and various active sites. However, their mass-production and application are restricted by the high-cost raw materials, complex synthesis procedures, harsh reaction conditions, and unexpected environmental impact. Based on the principles of "Green Chemistry", considerable efforts have been done for breaking through the limitations, and significant progress has been made in the sustainable synthesis of Zr-MOFs over the past decade. In this review, the advancements of green raw materials and green synthesis methods in the synthesis of Zr-MOFs are reviewed, along with the corresponding drawbacks. The challenges and prospects are discussed and outlooked, expecting to provide guidance for the acceleration of the industrialization and commercialization of Zr-MOFs.