Doping Ru on FeNi LDH/FeII/III-MOF heterogeneous core-shell structure for efficient oxygen evolution

Noble metal-based catalysts such as RuO2 and IrO2 are widely used in the catalysis of the OER. However, because of their high price and poor stability, it is urgent to develop transition metal-based electrocatalysts with low precious metal doping as an alternative. Layered double hydroxides (LDHs) grown on 3D metal-organic frameworks (MOFs) are ideal for doping precious metals owing to abundant defects at the heterointerface, large surface area, and intrinsic oxygen evolution activity. In this study, a novel FeNi LDH/MOF heterostructure was prepared via a two-step solvothermal method using Fe-soc-MOFs as the substrate. Subsequently, Ru was introduced through a hydrothermal process. The as-synthesized Ru@FeNi LDH/MOF has an overpotential of only 242 mV at a current density of 10 mA cm-2 and can be used in continuous electrolysis for 48 h. Its unique nanocubic core-shell structure and flower-like LDHs on its surface provide a large number of active sites, which become the key to ensuring high activity and stability. With the doping of Ru, the electronic structure was adjusted and electron transfer was accelerated, further improving electrochemical activity. This study provides a new idea for developing transition metal-based catalysts with low noble metal loading.

Lewis Acid Catalyzed Amide Bond Formation in Covalent Graphene-MOF Hybrids

Covalent hybrids of graphene and metal-organic frameworks (MOFs) hold immense potential in various technologies, particularly catalysis and energy applications, due to the advantageous combination of conductivity and porosity. The formation of an amide bond between carboxylate-functionalized graphene acid (GA) and amine-functionalized UiO-66-NH2 MOF (Zr6O4(OH)4(NH2-bdc)6, with NH2-bdc2- = 2-amino-1,4-benzenedicarboxylate and UiO = Universitetet i Oslo) is a highly efficient strategy for creating such covalent hybrids. Previous experimental studies have demonstrated exceptional properties of these conductive networks, including significant surface area and functionalized hierarchical pores, showing promise as a chemiresistive CO2 sensor and electrode materials for asymmetric supercapacitors. However, the molecular-level origin of the covalent linkages between pristine MOF and GA layers remains unclear. In this study, density functional theory (DFT) calculations were conducted to elucidate the mechanism of amide bond formation between GA and UiO-66-NH2. The theoretical calculations emphasize the crucial role of zirconium within UiO-66, which acts as a catalyst in the reaction cycle. Both commonly observed hexa-coordinated and less common hepta-coordinated zirconium complexes are considered as intermediates. By gaining detailed insights into the binding interactions between graphene derivatives and MOFs, strategies for tailored syntheses of such nanocomposite materials can be developed.

Real-Space Imaging of the Molecular Changes in Metal-Organic Frameworks under Electron Irradiation

Electron-induced structural changes influence the characterizations of the local structure of various materials by electron microscope. However, for beam-sensitive materials, it is still challenging to detect such changes by electron microscopy, which may help us quantitatively reveal how electrons interact with materials under electron irradiation. Here, we use an emergent phase contrast technique in electron microscopy to clearly image a metal-organic framework, UiO-66 (Zr), at an ultralow electron dose and dose rate. The effects of both the dose and dose rate on the UiO-66 (Zr) structure are visualized, which induce obvious missing organic linkers. The kinetics of the missing linker based on the radiolysis mechanism are semiquantitatively expressed by the different intensities of the imaged organic linkers. Deformation of the UiO-66 (Zr) lattice after the missing linker is also observed. These observations make it possible to visually investigate the electron-induced chemistry in various beam-sensitive materials and avoid electron damage to them.

One-dimensional alignment of defects in a flexible metal-organic framework

Crystalline materials are often considered to have rigid periodic lattices, while soft materials are associated with flexibility and nonperiodicity. The continuous evolution of metal-organic frameworks (MOFs) has erased the boundaries between these two distinct conceptions. Flexibility, disorder, and defects have been found to be abundant in MOF materials with imperfect crystallinity, and their intricate interplay is poorly understood because of the limited strategies for characterizing disordered structures. Here, we apply advanced nuclear magnetic resonance spectroscopy to elucidate the mesoscale structures in a defective MOF with a semicrystalline lattice. We show that engineered defects can tune the degree of lattice flexibility by combining both ordered and disordered compartments. The one-dimensional alignment of correlated defects is the key for the reversible topological transition. The unique matrix is featured with both rigid framework of nanoporosity and flexible linkage of high swellability.

Elucidating correlated defects in metal organic frameworks using theory-guided inelastic neutron scattering spectroscopy

Metal organic frameworks (MOFs) that incorporate metal oxide cluster nodes, exemplified by UiO-66, have been widely studied, especially in terms of their deviations from the ideal, defect-free crystalline structures. Although defects such as missing linkers, missing nodes, and the presence of adventitious synthesis-derived node ligands (such as acetates and formates) have been proposed, their exact structures remain unknown. Previously, it was demonstrated that defects are correlated and span multiple unit cells. The highly specialized techniques used in these studies are not easily applicable to other MOFs. Thus, there is a need to develop new experimental and computational approaches to understand the structure and properties of defects in a wider variety of MOFs. Here, we show how low-frequency phonon modes measured by inelastic neutron scattering (INS) spectroscopy can be combined with density functional theory (DFT) simulations to provide unprecedented insights into the defect structure of UiO-66. We are able to identify and assign peaks in the fingerprint region (<100 cm^-1) which correspond to phonon modes only present in certain defective topologies. Specifically, this analysis suggests that our sample of UiO-66 consists of predominantly defect-free fcu regions with smaller domains corresponding to a defective bcu topology with 4 and 2 acetate ligands bound to the Zr₆O₈ nodes. Importantly, the INS/DFT approach provides detailed structural insights (e.g., relative positions and numbers of acetate ligands) that are not accessible with microscopy-based techniques. The quantitative agreement between DFT simulations and the experimental INS spectrum combined with the relative simplicity of sample preparation, suggests that this methodology may become part of the standard and preferred protocol for the characterization of MOFs, and, in particular, for elucidating the structure defects in these materials.

Atomically Dispersed Iron Sites on the Hollow Nitrogen-Doped Carbon Framework with a Highly Efficient Performance on Carbon Dioxide Cycloaddition

The exploration of efficient and low-consumption catalysts for carbon dioxide (CO₂) conversion is desirable yet remains a great challenge. Herein, a novel catalyst composed of a hollow nitrogen-doped carbon framework (HNF) enriched with high-loading (9.8 wt %) atomically dispersed iron sites (defined as Fe_SAs/HNF) has been fabricated by a polymer-assisted strategy. As a result, Fe_SAs/HNF has an excellent performance on the cycloaddition reactions of CO₂ with epoxides (the conversion >96%) under milder conditions because of its ultrahigh loading of atomically dispersed iron sites. This study not only provides an advanced catalyst for driving CO₂ cycloaddition but also furnishes a novel perspective on the rational design of superior catalysts with high-loading active sites for diverse heterogeneous catalytic reactions.

Anions-induced two stable isostructural Cd(II) LMOFs based on benzotriazole with highly selective detection of Fe3+ ion

Two new title LMOFs, [Cd9(BTA)6(5-tbuip)6O2]n (LMOF-1), [Cd3(BTA)2(5-tbuip)2]n (LMOF-2) (BTA=1H-Benzotriazole, 5-tbuip=5-tert-Butylisophthalic Acid) have been synthesized by solvothermal method. The different anions of cadium salts lead to isostructural two LMOFs. Fe3+ could...