Multicomponent self-assembly of a nested co(24) @co(48) metal-organic polyhedral framework

A tale of two polyhedra: Two nested Archimedean metal-organic polyhedra, a rhombicuboctahedron (Co(48) cage) and a cuboctahedron (Co(24) cage), have been assembled from two types of cobalt dimers and two complementary ligands. Within the 3D covalent cubic array of outer Co(48) cages and framework lie encapsulated inner Co(24) cages that are linked into a separate "hidden" 3D framework.     

A highly porous metal-organic framework: structural transformations of a guest-free MOF depending on activation method and temperature

A doubly interpenetrating porous metal–organic framework ( SNU‐77 ) has been synthesized from the solvothermal reaction of the extended carboxylic acid tris(4′‐carboxybiphenyl)amine (H₃TCBPA) and Zn(NO₃)₂ ? 6H₂O in N,N‐dimethylacetamide (DMA). SNU‐77 undergoes single‐crystal‐to‐single‐crystal transformations during various activation processes, such as room‐temperature evacuation, supercritical CO₂ drying, and high temperature evacuation, to afford SNU‐77R , SNU‐77S , and SNU‐77H , respectively. These guest‐free MOFs exhibited different fine structures with different window shapes and different effective window sizes at room temperature. Variable‐temperature synchrotron single‐crystal X‐ray analyses reveal that the guest‐free structure is also affected by changes in temperature. Despite the different fine structures, SNU‐77R , SNU‐77S , and SNU‐77H show similar gas sorption properties due to the nonbreathing nature of the framework and an additional structural change upon cooling to cryogenic gas sorption temperature. SNU‐77H exhibits a large surface area (BET, 3670 m² g^?1), a large pore volume (1.52 cm³ g^?1), and exceptionally high uptake capacities for N₂, H₂, O₂, CO₂, and CH₄ gases.     

Photocatalytic Hydrogen Production Coupled with Selective Benzylamine Oxidation over MOF Composites

Photocatalytic water splitting requires separation of the mixed H₂ and O₂ products and is often hampered by the sluggish O₂‐producing half reaction. An approach is now reported to address these issues by coupling the H₂‐producing half reaction with value‐added benzylamine oxidation reaction using metal–organic framework (MOF) composites. Upon MOF photoexcitation, the electrons rapidly reduce the protons to generate H₂ and the holes promote considerable benzylamine oxidation to N‐benzylbenzaldimine with high selectivity. Further experimental characterizations and theoretical calculation reveal that the highly conjugated s‐triazine strut in the MOF structure is crucial to the efficient charge separation and excellent photocatalytic activity.     

HKUST-1 Derived Hollow C-Cu2−xS Nanotube/g-C3N4 Composites for Visible-Light CO2 Photoreduction with H2O Vapor

As the main component of syngas, reducing CO₂ to CO with high selectivity through photocatalysis could provide a sustainable way to alleviate energy shortage issues. Developing a photocatalytic system with low cost and high performance that is environmentally friendly is the ultimate goal towards CO₂ photoreduction. Herein, an efficient and economic three-component heterojunction photocatalyst is designed and fabricated for converting CO₂ to CO in the absence of organic sacrificial agents. The heterojunction is made of Cu_2−xS nanotubes coated with a carbon layer (C-Cu_2−xS) and g-C₃N₄. By using the classical MOF material HKUST-1 as a precursor, hollow tubular-like metal sulfides (C-Cu_2−xS) with carbon coating were synthesized and further loaded on g-C₃N₄, forming a three-component heterojunction C-Cu_2−xS@g-C₃N₄. The carbon coat in C-Cu_2−xS@g-C₃N₄ acts as an electron reservoir, which facilitates electron–hole pair separation. The optimized C-Cu_2−xS@g-C₃N₄ acted as a photocatalyst in CO₂ reduction with a high reactivity of 1062.6 μmol g⁻¹ and selectivity of 97 %. Compared with bare g-C₃N₄ (158.4 μmol g⁻¹) and C-Cu_2−xS, the reactivity is nearly 7 and 23-fold enhanced and this CO generation rate is higher than most of the reported Cu₂S or g-C₃N₄ composites under similar conditions. The prominent activity may result from enhanced light adsorption and effective charge separation. This work might open up an alternative method for the design and fabrication of high-performance and low-cost photocatalysts for efficiently and durably converting CO₂ to CO with high selectivity.     

Molecular-level Manipulation of Interface Charge Transfer on Plasmonic Metal/MOF Heterostructures

Plasmon-excited hot carriers have drawn great attention for driving various chemical reactions, but the short lifetimes of hot carriers seriously restrict the performance of plasmonic photocatalysis. Constructing plasmonic metal/metal-organic framework (MOF) heterostructures has been proved as an effective strategy to extend the lifetimes of hot carriers. Due to the high molecular tunability of MOFs, the MOF substrate in plasmonic metal/MOF heterostructures is able to capture hot electrons on the conduction band of MOF and hot holes on its valence band, and thus offers an ideal platform to separately study the detailed mechanism of hot electron and hole transfer processes. This review focuses on a molecular-level understanding of both hot-electron and hot-hole transfer at plasmonic metal/MOF interfaces. The enhanced stability and photocatalytic performance by introducing MOF substrates are discussed for plasmonic metal/MOF heterostructures. Additionally, typical characterization technologies are also proposed as powerful tools for tracking hot carrier transfer process.     

Semiconductor Photocatalysis—Mechanistic and Synthetic Aspects

Preceding work on photoelectrochemistry at semiconductor single‐crystal electrodes has formed the basis for the tremendous growth in the three last decades in the field of photocatalysis at semiconductor powders. The reason for this is the unique ability of inorganic semiconductor surfaces to photocatalyze concerted reduction and oxidation reactions of a large variety of electron‐donor and ‐acceptor substrates. Whereas great attention was paid to water splitting and the exhaustive aerobic degradation of pollutants, only a small amount of research also explored synthetic aspects. After introducing the basic mechanistic principles, standard experiments for the preparation and characterization of visible light active photocatalysts as well as the investigation of reaction mechanisms are discussed. Novel atom‐economic C? C and C? N coupling reactions illustrate the relevance of semiconductor photocatalysis for organic synthesis, and demonstrate that the multidisciplinary field combines classical photochemistry with electrochemistry, solid‐state chemistry, and heterogeneous catalysis.     

Selective CO2 adsorption by a triazacyclononane-bridged microporous metal-organic framework

Metal-organic frameworks constructed by self-assembly of metal ions and organic linkers have recently been of great interest in the preparation of porous hybrid materials with a wide variety of functions. Despite much research in this area and the large choice of building blocks used to fine-tune pore size and structure, it remains a challenge to synthesise frameworks composed of polyamines to tailor the porosity and adsorption properties for CO(2). Herein, we describe a rigid and microporous three-dimensional metal-organic framework with the formula [Zn(2)(L)(H(2)O)]Cl (L=1,4,7-tris(4-carboxybenzyl)-1,4,7-triazacyclononane) synthesised in a one-pot solvothermal reaction between zinc ions and a flexible cyclic polyaminocarboxylate. We have demonstrated, for the first time, that a porous rigid framework can be obtained by starting from a flexible amine building block. Sorption measurements revealed that the material exhibited a high surface area (135 m(2) g(-1)) and was the best compromise between capacity and selectivity for CO(2) over CO, CH(4), N(2) and O(2); as such it is a promising new selective adsorbent for CO(2) capture.     

Chromatography in a single metal-organic framework (MOF) crystal

Millimeter-sized single MOF-5 crystals are used as "chromatographic columns" to effectively separate mixtures of organic dyes. Remarkably, owing to the nanoscopic pore dimensions and the molecular-level interactions between the migrating molecules and the MOF scaffold, the separations occur over a distance of only a few hundred micrometers which is unambiguously confirmed by fluorescence confocal microscopy.     

Co3(HCOO)6 microporous metal-organic framework membrane for separation of CO2/CH4 mixtures

Continuous metal–organic framework‐type Co₃(HCOO)₆ intergrown films with a one‐dimensional zigzag channel system and pore aperture of 5.5 Å are prepared by secondary growth on preseeded macroporous glass‐frit disks and silicon wafers. The adsorption behavior of CO₂ or CH₄ single gases on the Co₃(HCOO)₆ membrane is investigated by in situ IR spectroscopy. It is shown that the isosteric heats of adsorption for CO₂ (17.7 kJ mol^?1) and CH₄ (14.4 kJ mol^?1) do not vary with increasing amount of adsorbed gases. The higher value of isosteric heat for CO₂ is an indication of the stronger interaction between the CO₂ and the Co₃(HCOO)₆ membrane. The Co₃(HCOO)₆ membrane is studied by binary gas permeation of CO₂ and CH₄ at different temperatures (0, 25, and 60 °C). The membrane has CO₂/CH₄ selectivity with a separation factor higher than 10, which is due to the unique structure and molecular sieving effect. Upon increasing the temperature from 0 to 60 °C, the preferred permeance of CO₂ over CH₄ is increased from 1.70×10^?6 to 2.09×10^?6 mol m^?2 s^?1 Pa^?1, while the separation factor for CO₂/CH₄ shows a corresponding decrease from 15.95 to 10.37. The effective pore size of the Co₃(HCOO)₆ material combined with the pore shape do not allow the two molecules to pass simultaneously, and once the CO₂ molecules are diffused in the micropores, the CH₄ is blocked. The supported Co₃(HCOO)₆ membrane retains high mechanical stability after a number of thermal cycles.     

Enhanced Charge Transfer Process and Photocatalytic Activity over a Phosphonate-based MOF via Amorphization Strategy

Recently, amorphous materials have gained great attention as an emerging kind of functional material, and their characteristics such as isotropy, absence of grain boundaries, and abundant defects are very likely to outrun the disadvantages of crystalline counterparts, such as low conductivity, and ultimately lead to improved charge transfer efficiency. Herein, we investigated the effect of amorphization on the charge transfer process and photocatalytic performance with a phosphonate-based metal–organic framework (FePPA) as the research object. Comprehensive experimental results suggest that compared to crystalline FePPA, amorphous FePPA has more distorted metal nodes, which affects the electron distribution and consequently improves the photogenerated charge separation efficiency. Meanwhile, the distorted metal nodes in amorphous FePPA also greatly promote the adsorption and activation of O₂. Hence, amorphous FePPA exhibits a better performance of photocatalytic C(sp³)−H bond activation for selective oxidation of toluene to benzaldehyde. This work illustrates the advantages of amorphous MOFs in the charge transfer process, which is conducive to the further development of high performance MOFs-based photocatalysts.     

Evaluation of copper-1,3,5-benzenetricarboxylate metal-organic framework (Cu-MOF) as a selective sorbent for Lewis-base analytes

The metal-organic framework copper-1,3,5-benzenetricarboxylate (Cu-BTC) was evaluated for its ability to selectively interact with Lewis-base analytes by examining retention on gas-chromatographic columns packed with Chromosorb W HP that contained 3.0% SE-30 along with various loadings of Cu-BTC. Scanning electron microscopy images of the support material showed the characteristic Cu-BTC crystals embedded in the SE-30 coating on the diatomaceous support. The results indicated that the Cu-BTC-containing stationary phase had limited thermal stability (220 °C) and strong general retention for analytes. Kováts index calculations showed selective retention (amounting to about 300 Kováts units) relative to n-alkanes for many small Lewis-base analytes on a column that contained 0.75% Cu-BTC compared with an SE-30 control. Short columns that contained lower loadings of Cu-BTC (0.10%) allowed elution of nitroaromatics; however, selectivity was not observed for aromatic compounds (including nitroaromatics) or nitroalkanes. Observed retention characteristics are discussed.