Wide temperature adaptive oxidase-like based on mesoporous manganese based metal-organic framework for detecting total antioxidant capacity

Overcoming the intense variation of enzymatic activity among different temperatures is very critical in catalytic medicine and catalytic biology. Here, Mn-based metal-organic framework-based wide-temperature-adaptive mesoporous artificial enzymes (Mn-TMA-MOF) were designed and synthesized. The oxidase-like Mn-TMA-MOF showed excellent catalytic activity at 0-50 °C and avoided the activity loss and instability due to temperature variation that occurred. The excellent oxidase-like properties of Mn-TMA-MOF with wide temperature adaptativeness are mainly ascribed to the mixed oxidized state (Mn3+/Mn2+) and high substrate affinity (Km = 0.034 mM) of Mn. Moreover, the mesopore-micropores two-level structure of Mn-TMA-MOF provides a large space and surface area for enzyme catalysis. Based on the stability of Mn-TMA-MOF, we developed a colorimetric sensor that can detect total antioxidant capacity in fruits with a limit of detection up to 0.59 μM.

Mixed N,O-donor Directed Blue Emissive Nano-dispersed Mesoporous Mn(II)-MOF: Dual Sensing Probe for Recyclable and Ultrasensitive ppb-Level Recognition of TNP and Cr(VI)-Oxoanions

A new mesoporous Mn(II)-MOF [Mn2(phen)2(nia)2]∞ with 4-c uninodal net topology and reiterating rectangular channels in its cargo-net like extension was synthesized using π-conjugated phenanthroline (phen) and syn-syn bridging 5-nitroisopthalic acid (nia) linkers. The MOF (1) exhibited phase purity, uniform morphology, photo and thermal stability, and robustness; duly triggered by the exceptional framework rigidity via intermolecular H-bonding and interlayer π-π stacking interactions. The bright-blue luminescence of the MOF nano-dispersion was explored for sensitive, specific and ultrafast detection of trinitrophenol (TNP) with extremely low LOD (90.62 nM), high KSV (18.27×104 M-1) and Kq (4×1014 M-1s-1). The vapor-phase TNP sensing was also accomplished. Additionally, 1 served towards discriminatory, aqueous-phase monitoring of Cr(VI)-oxoanions, depicting LODs: 36.08 and 35.70 ppb; KSV: 3.46×104 and 4.87×104 M-1; Kq: 3.26×1013 M-1s-1 and 4.31×1013 M-1s-1; and response time: 32 and 40s for CrO4 2- and Cr2O7 2- respectively. The quenching mechanisms (i. e., RET, PET, IFE, weak interactions, collisional quenching and π⋅⋅⋅π stacking) was explained from several experimental investigations and theoretical DFT calculations. The recyclable sensing events and quantification from complex environmental matrices with admirable recovery rates and high KSV (13.02-22.44×104; ~6.31-10.98×104 and ~6.60-11.42×104 M-1 for TNP, CrO4 2- and Cr2O7 2-) undoubtedly advocated the consistency of the probe.

Transient intermediate in the formation of an amorphous metal-organic framework

Amorphous metal-organic frameworks are rarely formed via direct synthesis. Our limited understanding of their atomic assembly in solution prevents full exploitation of their unique structural complexity. Here, we use in situ synchrotron X-ray absorption spectroscopy with sub-second time resolution to probe the formation of the amorphous Fe-BTC framework. Using a combination of spectral fingerprinting, linear combination analysis, and principal component analysis coupled with kinetic analyses, we reveal a multi-stage formation mechanism that, crucially, proceeds via the generation of a transient intermediate species.

Manganese-oxide-supported gold catalyst derived from metal-organic frameworks for trace PCl3 oxidation in an organic system

Polysilicon is widely used in the field of semiconductors and solar energy. Trichlorosilane feedstocks that are used to produce polysilicon in the mainstream production process contain PCl3 impurities that have adverse effects on the quality of the polysilicon. Traditional methods for dephosphorization cannot achieve the effect of complete removal, whereas oxidizing PCl3 to POCl3 in the presence of oxygen for removal via adsorption is a promising and appealing route for establishing a dephosphorization process; it has a high phosphorous removal rate due to the strong Lewis-base property of POCl3 in comparison with PCl3. In this work, we synthesized an active catalyst with an active interface between Au nanoparticles (NPs) and a manganese-oxide support (Mn3O4) by calcination of a corresponding composite, where Au NPs were embedded uniformly in a metal-organic framework (MOF). The catalyst shows a significantly active catalytic performance for trace PCl3 oxidation in an organic system that is an imitation of a trichlorosilane system, with a 99.13% yield of POCl3 in an 80 °C and 0.6 MPa reaction environment. The structure-performance-mechanism analysis shows that the possible reaction and catalytic mechanism is PCl3 oxidation by interface lattice oxygens, which bridge the Au NPs and the support, in a Mars van Krevelen (MvK) process; this process was promoted by the interaction between the Au NPs and Mn3O4 in terms of charge transfer and chemical potential changes. This work provides an effective way to dephosphorize trichlorosilane feedstocks in the polysilicon industry and gives guidance for constructing an efficient catalyst via the study of the structure and mechanism.

Transformation of ZIF-67 Nanocubes to ZIF-L Nanoframes

Investigating the process of crystalline transformation in metal-organic frameworks (MOFs) has significant implications in advancing our understanding of the growth mechanisms and design of innovative materials. This study achieves a theoretically impossible transformation direction from three-dimensional (3D) zeolitic imidazolate nanocubes (ZIF) to two-dimensional (2D) ZIF nanoframes through the Marangoni effect in droplets. This transformation challenges the established belief that only a transition from 2D ZIF-L to 3D ZIF-67 is possible, which neglects the reverse process. Finite element analysis indicates that the conversion from 3D ZIF to 2D ZIF is feasible when uniform mass distribution and heat transport are guaranteed under Marangoni flow. This research not only demonstrates an alternative pathway for MOF crystalline transformation but also provides a fresh perspective on the construction of MOF nanoframes.

Freestanding MOF-Derived Honeycomb-Shape Porous MnOC@CC as an Electrocatalyst for Reversible LiOH Chemistry in Li-O2 Batteries

In rechargeable Li-O₂ batteries, the electrolyte and the electrode are prone to be attacked by aggressive intermediates (O₂^- and LiO₂) and products (Li₂O₂), resulting in low energy efficiency. It has been reported that in the presence of water, the formation of low-activity LiOH is more stable for electrolyte and electrode, effectively reducing the production of parasitic products. However, the reversible formation and decomposition of LiOH catalyzed by solid catalysts is still a challenge. Here, a freestanding metal-organic framework (MOF)-derived honeycomb-shape porous MnOC@CC cathode was prepared for Li-O₂ batteries by in situ growth of urchin-like Mn-MOFs on carbon cloth (CC) and carbonization. The battery with the MnOC@CC cathode exhibits an ultrahigh practical discharge specific capacity of 22,838 mAh g^-1 at 200 mA g^-1, high-rate capability, and more stable cycling, which is superior to the MnOC powder cathode. X-ray diffraction and Fourier transform infrared results identify that the discharge product of the batteries is LiOH rather than highly active Li₂O₂, and no parasitic products were found during operation. The MnOC@CC cathode can induce the formation of flower-like LiOH in the presence of water due to its unique porous structure and directional alignment of Mn-O centers. This work achieves the reversible formation and decomposition of LiOH in the presence of water, offering some insights into the practical application of semiopen Li-O₂ batteries.

Catalytic Activation of Hydrogen Peroxide Using Highly Porous Hydrothermally Modified Manganese Catalysts for Removal of Azithromycin Antibiotic from Aqueous Solution

Hydrogen peroxide catalytic activation holds great promise in the treatment of persistent pollutants. In this study, the novel Mn-Acacair/Al, Mn-Acacarg/Al and Mn-BTCarg/Al catalysts, supported on Al2O3, were applied for rapid hydrogen peroxide activation and azithromycin antibiotic removal. The catalysts were prepared by the calcination-hydrothermal method under air or argon atmosphere. The characterization confirmed that the modification of manganese with acetylacetonate and benzene-1,3,5-tricarboxylic acid (H3BTC) O-donor ligands highly improves the catalyst porosity, amorphousity, and abundance of coordinately unsaturated sites, which facilitate the generation of reactive oxygen species. The hydrogen peroxide activation and azithromycin removal reached 98.4% and 99.3% after 40 min using the Mn-BTCarg/Al catalyst with incredible stability and reusability. Only a 5.2% decrease in activity and less than 2% manganese releasing in solutions were detected after five regeneration cycles under the optimum operating conditions. The removal intermediates were identified by LC-MS/MS analysis, and the pathways were proposed. The hydroxylation and decarboxylation reactions play a key role in the degradation reaction.

Different degradation mechanisms of low-concentration ozone for MIL-100(Fe) and MIL-100(Mn) over wide humidity fluctuation

The synergistic control of ozone and fine particulate matter is a research hotspot in the current environmental fields. Among the ozone removal, wide humidity fluctuation and low concentration dynamic adsorption are two thorny problems. In this work, MIL-100(Fe) and MIL-100(Mn), synthesized by hydrothermal and solvothermal methods respectively, were selected to investigate the degradation of flowing ozone pollutants. The samples showed different ozone degradation mechanisms, namely photocatalytic degradation and normal temperature degradation. Notably, MIL-100(Fe) exhibited more outstanding photocatalytic activity than MIL-100(Mn), while the normal temperature catalytic efficiency of MIL-100(Mn) was much superior to MIL-100(Fe). For different humidity conditions, MIL-100(Fe) has the optimal photocatalytic performance at 10% humidity, which is 38%, while MIL-100(Mn) has basically no change in normal temperature catalytic degradation efficiency at different humidity levels of 10-90%. Furthermore, the degradation mechanism was proposed by in-situ DRIFTS and ESR, which was significantly correlated with oxygen vacancy and photogenerated electron efficiency. By the aid of Temperature Programmed Desorption (TPD), a large quantity of Lewis acid sites was detected in MIL-100(Mn), which was the critical factor that the selected materials could maintain excellent normal temperature degradation performance under high humidity. This work will expand the practical application of ozone removal and improve the degradation efficiency.

MOF-Derived MnO/C Nanocomposites for High-Performance Supercapacitors

As ordered porous materials, metal-organic frameworks (MOFs) have attracted tremendous attention in the field of energy conversion and storage due to their high specific surface area, permanent porosity, and tunable pore sizes. Here, MOF-derived MnO/C nanocomposites with regular octahedral shape were synthesized using a Mn-based analogue of the MIL-100 framework (Mn-MIL-100, MIL: Matérial Institut Lavoisier) as the precursor. Using aberration-corrected environmental transmission electron microscopy (ETEM), MnO nanocages with a diameter of approximately 20 nm were recognized in the MnO/C nanocomposites fabricated, dispersed in a microporous carbon matrix homogeneously. The nanocages are composed of MnO nanoparticles with a diameter of approximately 2 nm and with a single crystal structure. The specific surface area of the as-prepared MnO/C octahedra decreases to 256 m² g^-1 from 507 m² g^-1 of the Mn-MIL-100 precursor, whereas the total pore volume increases to 0.245 cm³ g^-1, which is approximately 29% higher than that of the precursor (0.190 cm³ g^-1). Additionally, when utilized as an electrode for supercapacitors, the MOF-derived MnO/C nanocomposite demonstrates a towering specific capacitance of 421 F g^-1 at 0.5 A g^-1 and good cycle stability (94%) after 5000 cycles. Our work reveals that the MnO nanoparticles in MOF-derived MnO/C nanocomposites exhibit nanocage structure characteristics, which might be inherited from the Mn-MIL-100 precursor with analogous supertetrahedron units.

Synthesis, Structure, and Thermal Stability of a Mesoporous Titanium(III) Amine-Containing MOF

The first mesoporous bimetallic Ti^III/Al metal-organic framework (MOF) containing amine functionalities on its linkers has been selectively obtained by converting the cheap commercially available (TiCl₃)₃AlCl₃ into Ti_3-xAl_xCl₃(THF)₃ and reacting this complex with 2-aminoterephthalic acid in dimethylformamide (DMF) under soft solvothermal conditions. This compound is structurally related to the previously described NH₂-MIL-101(M) (M = Cr, Al, and Fe) MOFs. Thermal gravimetric analyses and in situ powder X-ray diffraction (PXRD) measurements demonstrated that this highly air-sensitive Ti^III-containing MOF is structurally stable up to 200 °C. Nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and inductively coupled plasma (ICP) revealed that NH₂-MIL-101(Ti^III) contains trinuclear Ti₃(μ₃-O)Cl(DMF)₂(RCOO)₆ clusters with strongly bound DMF molecules and a small amount of aluminum. Sorption experiments revealed a higher affinity of this MOF for hydrogen compared to the previously described monometallic unfunctionalized MIL-101(Ti^III) MOF.

In Situ Construction of MIL-100@NiMn-LDH Hierarchical Architectures for Highly Selective Photoreduction of CO2 to CH4

Layered double hydroxides (LDHs) are considered a promising catalyst for photocatalytic CO₂ reduction due to their broad photoresponse, facile channels for electron transfer, and the presence of abundant defects. Herein, we reported for the first time the fabrication of a novel photocatalyst MIL-100@NiMn-LDH with a hierarchical architecture by selecting MIL-100 (Mn) as a template to provide Mn³⁺ for the in situ growth of ultrathin NiMn-LDH nanosheets. Moreover, the in situ growth strategy exhibited excellent universality toward constructing MIL-100@LDH hierarchical architectures. When applied in the photocatalytic CO₂ reduction reaction, the as-prepared MIL-100@NiMn-LDH exhibited excellent CH₄ selectivity of 88.8% (2.84 μmol h^-1), while the selectivity of H₂ was reduced to 1.8% under visible light irradiation (λ > 500 nm). Such excellent catalytic performance can be attributed to the fact that (a) the MIL-100@NiMn-LDH hierarchical architectures with exposed catalytic active sites helped to enhance the CO₂ adsorption and activation and (b) the presence of rich oxygen vacancies and coordinately unsaturated metal sites in MIL-100@NiMn-LDH that optimized the band gap and accelerated the separation/transport of photoinduced charges.

The missing MIL-101(Mn): geometrically guided synthesis and topologically correlated valence states

Through a geometrically guided approach, i.e. with the aid of pyridyl modulators, the long-sought MIL-101(Mn) structure is finally achieved, which features emergent topologically correlated mixed-valence states that are apt for enzymatic catalysis.

Rational Design and General Synthesis of Multimetallic Metal-Organic Framework Nano-Octahedra for Enhanced Li-S Battery

Metal-organic frameworks (MOFs), which consist of central metal nodes and organic linkers, constitute a fast growing class of crystalline porous materials with excellent application potential. Herein, a series of Mn-based multimetallic MOF (bimetallic and trimetallic MIL-100) nano-octahedra are prepared by a facile one-pot synthetic strategy. The types and proportions of the incorporated elements can be tuned while retaining the original topological structure. The introduction of other metal ions is verified at the atomic level by combining X-ray absorption fine structure experiments and theoretical calculations. Furthermore, these multimetallic Mn-based MIL-100 nano-octahedra are utilized as sulfur hosts to prepare cathodes for Li-S batteries. The MnNi-MIL-100@S cathode exhibits the best Li-S battery performance among all reported MIL-100@S composite cathode materials, with a reversible capacity of ≈708.8 mAh g^-1 after 200 cycles. The synthetic strategy described herein is utilized to incorporate metal ions into the MOF architecture, of which the parent monometallic MOF nano-octahedra cannot be prepared directly, thus rationally generating novel multimetallic MOFs. Importantly, the strategy also allows for the general synthesis and study of various micro-/nanoscale MOFs in the energy storage field.

Selective Styrene Oxidation to Benzaldehyde over Recently Developed Heterogeneous Catalysts

The selective oxidation of styrene under heterogeneous catalyzed conditions delivers environmentally friendly paths for the production of benzaldehyde, an important intermediate for the synthesis of several products. The present review explores heterogeneous catalysts for styrene oxidation using a variety of metal catalysts over the last decade. The use of several classes of supports is discussed, including metal-organic frameworks, zeolites, carbon materials and silicas, among others. The studied catalytic systems propose as most used oxidants tert-butyl hydroperoxide, and hydrogen peroxide and mild reaction conditions. The reaction mechanism proceeds through the generation of an intermediate reactive metal-oxygen species by catalyst-oxidant interactions. Overall, most of the studies highlight the synergetic effects among the metal and support for the activity and selectivity enhancement.

In Situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated CeIV -Based Metal-Organic Frameworks with UiO-66 and MIL-140 Architectures*

We report on the results of an in situ synchrotron powder X-ray diffraction study of the crystallisation in aqueous medium of two recently discovered perfluorinated Ce^IV -based metal-organic frameworks (MOFs), analogues of the already well investigated Zr^IV -based UiO-66 and MIL-140A, namely, F4_UiO-66(Ce) and F4_MIL-140A(Ce). The two MOFs were originally obtained in pure form in similar conditions, using ammonium cerium nitrate and tetrafluoroterephthalic acid as reagents, and small variations of the reaction parameters were found to yield mixed phases. Here, we investigate the crystallisation of these compounds, varying parameters such as temperature, amount of the protonation modulator nitric acid and amount of the coordination modulator acetic acid. When only HNO₃ is present in the reaction environment, only F4_MIL-140A(Ce) is obtained. Heating preferentially accelerates nucleation, which becomes rate determining below 57 °C. Upon addition of AcOH to the system, alongside HNO₃ , mixed-phased products are obtained. F4_UiO-66(Ce) is always formed faster, and no interconversion between the two phases occurs. In the case of F4_UiO-66(Ce), crystal growth is always the rate-determining step. A higher amount of HNO₃ favours the formation of F4_MIL-140A(Ce), whereas increasing the amount of AcOH favours the formation of F4_UiO-66(Ce). Based on the in situ results, a new optimised route to achieving a pure, high-quality F4_MIL-140A(Ce) phase in mild conditions (60 °C, 1 h) is also identified.

MOF-derived manganese oxide/carbon nanocomposites with raised capacitance for stable asymmetric supercapacitor

Owing to immense application potentials in electrochemical energy storages, metal organic framework (MOF)-derived metal oxide/carbon nanocomposites have attracted extensive interest of research. Although thermolysis has been widely employed to convert MOFs into various active materials, a large set of in situ changes in chemical composition, phase(s) and morphology requires delicate control over heating parameters. Through an innovative two-stage process, Mn-MIL-100 is first transformed into MnO@C by annealing at 700 °C under N2 flow, which is then transformed into Mn3O4@C at 200 °C in air, while retaining a high surface area. The appropriate retention of carbon content for Mn3O4@C can also be easily obtained with the control of heating time. In contrast, thermolysis of MnO@C at higher temperatures gives rise to manganese oxides with negligible carbon content and a greatly reduced surface area. The optimized Mn3O4@C-2 h, derived from MnO@C at 200 °C for 2 hours, showed the highest capacitance, far exceeding that of MnO@C and other derivatives. When combined with graphene oxide (GO) nanosheets to form a flexible Mn3O4@C/rGO paper electrode, it demonstrated a capacitance of 328.4 F cm-3. The Mn3O4@C/rGO-based asymmetric supercapacitor thus assembled also shows favorable performance. The present work demonstrates the excellent controllability afforded by the innovative two-stage thermolysis in optimizing the electrochemical performance of MOF-derived active materials as electrode materials in supercapacitors.

Highly Porous MIL-100(Fe) for the Hydrogen Evolution Reaction (HER) in Acidic and Basic Media

The present study reports the synthesis of a porous Fe-based MOF named MIL-100(Fe) by a modified hydrothermal method without the HF process. The synthesis gave a high surface area with the specific surface area calculated to be 2551 m² g^-1 and a pore volume of 1.407 cm³ g^-1 with an average pore size of 1.103 nm. The synthesized electrocatalyst having a high surface area is demonstrated as an excellent electrocatalyst for the hydrogen evolution reaction investigated in both acidic and alkaline media. As desired, the electrochemical results showed low Tafel slopes (53.59 and 56.65 mV dec^-1), high exchange current densities (76.44 and 72.75 mA cm^-2), low overpotentials (148.29 and 150.57 mV), and long-term stability in both media, respectively. The high activity is ascribed to the large surface area of the synthesized Fe-based metal-organic framework with porous nature.

Pd/APN-Mn(BTC) as novel, highly efficient, and recyclable catalyst for Suzuki–Miyaura cross coupling reaction

A novel, heterogeneous, and bifunctional metal organic framework containing palladium and manganese, Pd/APN-Mn(BTC), has been prepared and completely characterized using FTIR, XRD, SEM-EDS, N2 adsorption–desorption, TG-DTG, NH3-TPD, and ICP analytical techniques. The APN-Mn(BTC) framework has been shown to be a useful platform for the stabilization and support of palladium nanoparticles (Pd NPs). Very effective catalytic activity has been exhibited by the highly dispersed Pd particles, Pd-NPs/APN-Mn(BTC), in the Suzuki–Miyaura cross-coupling reaction with reasonable to excellent reaction yields under mild conditions in H2O–ethanol solvent.

Spectroscopy, microscopy, diffraction and scattering of archetypal MOFs: formation, metal sites in catalysis and thin films

A comprehensive overview of characterization tools for the analysis of well-known metal–organic frameworks and physico-chemical phenomena associated to their applications.

Interfacing Manganese Oxide and Cobalt in Porous Graphitic Carbon Polyhedrons Boosts Oxygen Electrocatalysis for Zn-Air Batteries

Rational design and synthesis of highly active and robust bifunctional non-noble electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for efficient rechargeable metal-air batteries. Herein, abundant MnO/Co heterointerfaces are engineered in porous graphitic carbon (MnO/Co/PGC) polyhedrons via a facile hydrothermal-calcination route with a bimetal-organic framework as the precursor. The in situ generated Co nanocrystals not only create well-defined heterointerfaces with high conductivity to overcome the poor OER activity but also promote the formation of robust graphitic carbon. Owing to the desired composition and formation of the heterostructures, the resulting MnO/Co/PGC exhibits superior activity and stability toward both OER and ORR, which makes it an efficient air cathode for the rechargeable Zn-air battery. Importantly, the homemade Zn-air battery is able to deliver excellent performance including a peak power density of 172 mW cm^-2 and a specific capacity of 872 mAh g^-1 , as well as excellent cycling stability (350 cycles), outperforming commercial mixed Pt/C||RuO₂ catalysts. This work highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal-air cathode materials.

Structure, characterization, and catalytic properties of open-metal sites in metal organic frameworks

This review provides an overview of the current understanding of structure–catalytic properties of open-metal sites in metal organic framework materials.

MIL-100Cr with open Cr sites for a record N2O capture

Nitrous oxide (N2O) is considered as the third most important greenhouse gas after carbon dioxide and methane and needs to be removed from air. Herein, we reported the metal-organic framework MIL-100Cr with open Cr sites for record N2O capture capacities of 5.78 mmol g-1 at 298 K and 8.25 mmol g-1 at 273 K, respectively. DFT calculations showed that the static binding energy of N2O on the open-Cr site is notably higher than that of N2, 72.5 kJ mol-1vs. 51.6 kJ mol-1, which enforces MIL-100Cr to exhibit extremely high N2O/N2 ideal adsorbed solution theory (IAST) gas separation selectivity up to 1000.

Restricted self-diffusion of adsorbed water in MIL-100(Al)

An extended two-site exchange model is presented, which is used to evaluate pulsed field gradient (PFG) nuclear magnetic resonance (NMR) measurements of water in the nanoporous metal-organic framework MIL-100(Al). Here the water molecules exchange between the inter- and the intracrystalline space during the observation time, but are also restricted in their movement by the crystal surface. The evaluation of temperature and loading dependent PFG NMR data yields information about the intracrystalline diffusion process, the radius of the restricting geometry and the time constants of the exchange process. The intracrystalline mean residence time is found to decrease with increasing temperature, which allows an estimate of the heat of adsorption under the equilibrium conditions of the NMR measurements.

Formation of a new type of uranium(iv) poly-oxo cluster {U38} based on a controlled release of water via esterification reaction

A new strategy for the synthesis of large poly-oxo clusters bearing 38 tetravalent uranium atoms {U38} has been developed by controlling the water release from the esterification reaction between a carboxylic acid and an alcohol. The molecular entity [U38O56Cl40(H2O)2(ipa)20]·(ipa) x (ipa = isopropanol) was crystallized from the solvothermal reaction of a mixture of UCl4 and benzoic acid in isopropanol at temperature ranging from 70 to 130 °C. Its crystal structure reveals the molecular assembly of the UO2 fluorite-like inner core {U14} with oxo groups bridging the uranium centers. The {U14} core is further surrounded by six tetrameric sub-units of {U4} to form the {U38} cluster. Its surface is decorated by either bridging- and terminal chloride anions or terminal isopropanol molecules. Another synthesis using the same reactant mixture at room temperature resulted in the crystallization of a discrete dinuclear complex [U2Cl4(bz)4(ipa)4]·(ipa)0.5 (bz = benzoate), in which each uranium center is coordinated by two chlorine atoms, four oxygen atoms from carboxylate groups and two additional oxygen atoms from isopropanol. The slow production of water released from the esterification of isopropanol allows the formation of the giant cluster with oxo bridges linking the uranium atoms at a temperature above 70 °C, whereas no such oxo groups are present in the dinuclear complex formed at room temperature. The kinetics of {U38} crystallization as well as the ester formation are analyzed and discussed. SAXS experiments indicate that the {U38} species are not dominant in the supernatant, but hexanuclear entities which are closely related to the [U6O8] type are formed.

Metal organic frameworks as a catalyst for oxygen reduction: an unexpected outcome of a highly active Mn-MOF-based catalyst incorporated in activated carbon

Owing to their unique chemistry and physical properties, metal-organic frameworks (MOFs) are an interesting class of materials which can be utilized for a wide array of applications. MOFs have been proposed to be used as catalysts for fuel cells, but their low intrinsic electronic conductivity hampered their utilization as is. In this work, we present the synthesis and application of MOF-based precious-metal-group-free (PGM-free) catalysts for oxygen reduction based on a unique metal-organic framework-carbon composite material. Benzene tricarboxylic acid-based MOFs were synthesized inside activated carbon (AC) with four different, first row transition metals: Mn, Fe, Co, and Cu. The MOFs@AC were analyzed electrochemically to measure their catalytic activity. Further physical and chemical characterization studies are performed to measure the material properties. The MOFs@AC are found to be conductive and active catalysts for the oxygen reduction reaction in an alkaline environment. Surprisingly, the Mn-MOF-based@AC exhibits the best performance with an onset potential of 0.9 V vs. RHE and the almost four-electron mechanism, as opposed to most other known PGM-free catalysts, which show Fe and Co as the most active metals.

Synthesis of MOFs: a personal view on rationalisation, application and exploration

This perspective highlights some studies and insights in the synthesis of metal-organic frameworks (MOFs) in a brief and comprehensive manner. The understanding of the synthesis procedures investigated by in and ex situ methods is of special interest since knowledge on the nucleation and crystallisation mechanism will ideally lead to an improved control over product formation. The prospective developments associated with the manufacturing of such materials (or devices consisting thereof) are discussed as well. A major challenge is the adjustment of the synthesis conditions to yield quantities suitable for real life applications. Last but not least, vast opportunities are yet to be explored involving the synthesis of both known and novel compounds. Thus the crucial points involving the synthesis of MOFs summarized in this perspective are rationalisation, application and exploration. For each subtopic we have also attempted to anticipate future challenges and developments.

A multi-purpose reaction cell for the investigation of reactions under solvothermal conditions

A new versatile and easy-to-use remote-controlled reactor setup aimed at the analysis of chemical reactions under solvothermal conditions has been constructed. The reactor includes a heating system that can precisely control the temperature inside the reaction vessels in a range between ambient temperature and 180 °C. As reaction vessels, two sizes of commercially available borosilicate vessels (V_max = 5 and 11 ml) can be used. The setup furthermore includes the option of stirring and injecting of up to two liquid additives or one solid during the reaction to initiate very fast reactions, quench reactions, or alter chemical parameters. In addition to a detailed description of the general setup and its functionality, three examples of studies conducted using this setup are presented.

High Anodic Performance of Co 1,3,5-Benzenetricarboxylate Coordination Polymers for Li-Ion Battery

We report the designed synthesis of Co 1,3,5-benzenetricarboxylate coordination polymers (CPs) via a straightforward hydrothermal method, in which three kinds of reaction solvents are selected to form CPs with various morphologies and dimensions. When tested as anode materials in Li-ion battery, the cycling stabilities of the three CoBTC CPs at a current density of 100 mA g(-1) have not evident difference; however, the reversible capacities are widely divergent when the current density is increased to 2 A g(-1). The optimized product CoBTC-EtOH maintains a reversible capacity of 473 mAh g(-1) at a rate of 2 A g(-1) after 500 galvanostatic charging/discharging cycles while retaining a nearly 100% Coulombic efficiency. The hollow microspherical morphology, accessible specific area, and the absence of coordination solvent of CoBTC-EtOH might be responsible for such difference. Furthermore, the ex situ soft X-ray absorption spectroscopy studies of CoBTC-EtOH under different states-of-charge suggest that the Co ions remain in the Co(2+) state during the charging/discharging process. Therefore, Li ions are inserted to the organic moiety (including the carboxylate groups and the benzene ring) of CoBTC without the direct engagement of Co ions during electrochemical cycling.

Improved synthesis of trigone trimer cluster metal organic framework MIL-100Al by a later entry of methyl groups

Later entry of methyl or ethyl groups was carried out for the economical synthesis of trigone trimer cluster MIL-100Al oriented from H3BTC directly. The pure phase MIL-100Al was obtained in a DMF aqueous solution, and equal amounts of methyl and carboxyl groups are the key for the successful synthesis of MIL-100Al.

A thermally activated manganese 1,4-benzenedicarboxylate metal organic framework with high anodic capability for Li-ion batteries

Mn-1,4-BDC@200 was synthesized, with a capacity of 974 mA h g⁻¹after 100 cycles at a rate of 100 mA g⁻¹.