On the completeness of three-dimensional electron diffraction data for structural analysis of metal-organic frameworks.

Metal-organic frameworks (MOFs) have attracted considerable interest due to their well-defined pore architecture and structural tunability on molecular dimensions. While single-crystal X-ray diffraction (SCXRD) has been widely used to elucidate the structures of MOFs at the atomic scale, the formation of large and well-ordered crystals is still a crucial bottleneck for structure determination. To alleviate this challenge, three-dimensional electron diffraction (3D ED) has been developed for structure determination of nano- (submicron-)sized crystals. Such 3D ED data are collected from each single crystal using transmission electron microscopy. In this protocol, we introduce the entire workflow for structural analysis of MOFs by 3D ED, from sample preparation, data acquisition and data processing to structure determination. We describe methods for crystal screening and handling of crystal agglomerates, which are crucial steps in sample preparation for single-crystal 3D ED data collection. We further present how to set up a transmission electron microscope for 3D ED data acquisition and, more importantly, offer suggestions for the optimization of data acquisition conditions. For data processing, including unit cell and space group determination, and intensity integration, we provide guidelines on how to use electron and X-ray crystallography software to process 3D ED data. Finally, we present structure determination from 3D ED data and discuss the important features associated with 3D ED data that need to be considered. We believe that this protocol provides critical details for implementing and utilizing 3D ED as a structure determination platform for nano- (submicron-)sized MOFs as well as other crystalline materials.

The ORR kinetics of ZIF-derived Fe[sbnd]N[sbnd]C electrocatalysts

A pair of metal organic framework (MOF)-derived oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts for zinc-air batteries

Chapter 8 - Effect of structural modifications on the oxygen reduction reaction properties of metal-organic framework-based catalysts

Two-Dimensional Metal–Organic Frameworks with Unique Oriented Layers for Oxygen Reduction Reaction: Tailoring the Activity through Exposed Crystal Facets

Removal of low Sb(V) concentrations from mining wastewater using zeolitic imidazolate framework-8

The in situ solvothermal conversion of metal-organic gels (MOGs) to crystalline metal-organic frameworks (MOFs) represents a versatile and ingenious strategy that has been employed for the synthesis of MOF materials with specific morphologies, high yield, and improved functional properties. Herein, we have adopted an in situ solvothermal conversion of bimetallic MOGs to crystalline bimetallic MOFs with the aim of introducing a redox-active metal heterogeneity into the monometallic counterpart. The formation of bimetallic NiZn-MOF and CoZn-MOF via in situ solvothermal sol-gel-crystal and sol-crystal transformation is found to depend on the solvent systems used. The sol-to-gel-to-crystal transformation of NiZn-MOF via the formation of NiZn-MOG is found to occur through the gradual disruption of gel fibers leading to subsequent formation of microcrystals and single crystals of NiZn-MOF. These bimetallic MOFs and MOGs serve as promising electrocatalysts for oxygen reduction reaction (ORR) with an excellent methanol tolerance property, which can be attributed to the enhanced mass and charge transfer, higher oxygen vacancies, and bimetallic synergistic interactions among the heterometals. This work demonstrates a convenient strategy for producing bimetallic MOGs to MOFs through the introduction of a redox-active metal heterogeneity in the inorganic hybrid functional materials for fundamental and applied research. Our results connect MOGs and MOFs which have been regarded as having opposite physical states, that is, soft vs hard, and provide promising structural correlation between MOGs and MOFs at the molecular level.

Improvement of solubility of sparingly water-soluble drug triggered by metal-organic framework

Recent prospects and trends on zeolitic imidazolate frameworks for microwave absorption and EMI shielding applications

Noble metal nanoparticles exhibit unique surface plasmon resonance dependent optical properties. On this basis, gold nanoparticles (AuNPs) encapsulated in metal–organic frameworks (MOFs) can form AuNPs@MOFs composites to modulate the optical properties of fluorescent molecules, which is less reported. In this paper, based on the fluorescence enhancement effect of AuNPs on 2-(2-hydroxyphenyl)-1H-benzimidazole (HPBI) molecules, zeolitic imidazolate framework-8 (ZIF-8) crystals with structural stability were introduced. AuNPs@ZIF-8 exhibited a significantly pronounced fluorescence enhancement of the HPBI molecules. In addition, by comparing the fluorescence characteristics of the HPBI molecules adsorbed on AuNPs@ZIF-8 and those captured in AuNPs@ZIF-8, we found that the ZIF-8 can act as a spacer layer with highly effective near-field enhancement. All our preliminary results shed light on future research on the composite structures of noble metal particles and MOFs for fluorescent probes and sensing applications.

The catalyst support materials demonstrate great influence on the performance and durability of oxygen reduction reaction (ORR) electrocatalysts. Metal organic frameworks (MOFs) have been the focus of many Pt alloyed catalyst supports due to their large surface areas and well-defined pore structures. MOF-based carbon supports and a special class of MOFs that have a zeolite-type structure, and Zeolitic imidazolate frameworks (ZIFs) offer high ORR activity and enhanced stability of Pt-alloyed catalysts due to their porous structure, large surface area, and good electrical conductivity. In this study, we used two different MOF-based supports, Mn-NC and ZIF-67 derived Co-NC, to synthesize a nitrogen (N)-doped intermetallic PtNi catalyst. The synthesized material exhibits enhanced ORR activity and stability in an acidic electrolyte that is superior to commercial Pt/C catalyst. The rotating disk electrode (RDE) measurements of the PtNi/Co-NC catalyst demonstrated that the mass activity (MA) and specific activity (SA) are 0.9 A mgPt -1 and 1.8 mA cm-2, respectively at 0.9 V. The synthesized PtNi/Mn-NC catalyst demonstrated 1.4 A mgPt -1 and 2.1 mA cm-2 at 0.9 V, which are higher than those achieved with the commercial Pt/C. The MEA performance of the MOF-based PtNi catalysts will also be discussed. The mechanism of the enhanced performance of the catalysts is being formulated, based on in situ X-ray absorption spectroscopy (XAS) analysis. This work provides a promising approach to improve the activity and stability of binary and ternary Pt-based electrocatalysts for ORR by the use of MOF-based supports.

Metal–organic frameworks (MOFs) have gained significant attention as potential supercapacitor electrodes due to their high surface area, tunability, and well-defined porosity. However, their application is often limited by low capacity, poor electrical conductivity, and weak substrate adhesion, as observed in zeolitic imidazolate framework-67 (ZIF-67). To address these limitations, this study investigates the effect of nickel incorporation into ZIF-67, aiming to enhance its electrochemical performance. A series of hybrid-MOFs, denoted as ZIF-67 : Ni (1 : X), were synthesized via a simple solution-phase method at room temperature by varying the nickel content. Nickel was introduced to facilitate faster redox reactions and improve ion transport, thereby enhancing charge storage capability. The optimized ZIF-67 : Ni (1 : 2) electrode exhibited a high specific capacity of 161.2 mA h g−1 at 1 A g−1, with a capacity retention of 74.6% after 5000 charge–discharge cycles, outperforming pristine ZIF-67 and other nickel-mixture variants. The improved electrochemical performance is attributed to the enhanced porous structure, which increased active site accessibility and reduced charge transfer resistance. Furthermore, an asymmetric supercapacitor device assembled using ZIF-67 : Ni (1 : 2) as the positive electrode and activated carbon (AC) as the negative electrode (ZIF-67 : Ni (1 : 2)//AC) demonstrated a cell capacity of 44.6 mA h g−1, a specific energy of 36.97 W h kg−1, and a specific power of 416.3 W kg−1 at 0.5 A g−1. Notably, the device exhibited excellent cycling stability, retaining 99.8% of its capacity after 10 000 cycles at 10 A g−1. These findings highlight the potential of multi-metallic interactions in enhancing the electrochemical performance of ZIF-67-based MOFs, offering valuable insights for the development of high-performance supercapacitor electrodes.

Metal-organic frameworks (MOFs) have settled in the scientific community over the last decades as versatile materials with several applications. Among those, zeolitic imidazolate framework 8 (ZIF-8) is a well-known MOF that has been applied in various and diverse fields, from drug-delivery platforms to microelectronics. However, the complex role played by the reaction parameters in controlling the size and morphology of ZIF-8 particles is still not fully understood. Even further, many individual reports propose different nucleation and growth mechanisms for ZIF-8, thus creating a fragmented view for the behavior of the system. To provide a unified view, we have generated a comprehensive data set of synthetic conditions and their final outputs and applied machine learning techniques to analyze the data. Our approach has enabled us to identify the nucleation and growth mechanisms operating for ZIF-8 in a given sub-space of synthetic variables space (chemical space) and to reveal their impact on important features such as final particle size and morphology. By doing so, we draw connections and establish a hierarchy for the role of each synthetic variable and provide with rule of thumb for attaining control on the final particle size. Our results provide a unified roadmap for the nucleation and growth mechanisms of ZIF-8 in agreement with mainstream reported trends, which can guide the rational design of ZIF-8 particles which ultimately determine their suitability for any given targeted application. Altogether, our work represents a step forward in seeking control of the properties of MOFs through a deeper understanding of the rationale behind the synthesis procedures employed for their synthesis.

Evaluation of defect induced surface heterogeneity in Metal-Organic Framework materials with alkali dopants employing adsorption isotherm modelling

Background: Dye removal from effluents is one of the major problems faced in the world. It is a very important environmental issue and it is crucial to solve this problem. In this sense, ZIFs are increasingly becoming important in the environmental area. Objective: This work presents the synthesis of metalorganic framework Zeolitic Imidazolate Framework- 8 (ZIF-8) nanoparticles, characterization, and then determines the potential to remove Rhodamine B (RhB) from an aqueous solution. Methods: ZIF-8 was synthesized under solvothermal treatment at 25°C and it was characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, and infrared spectroscopy. To evaluate the capacity of the RhB, pH-influence and kinetic studies were carried out. The pseudo first- and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. Results: ZIF-8 had an average particle size of 47 ± 4.6 nm. The removal percentage increased significantly when the pH was in the range of 7.0-9.0. A pseudo-second-order kinetic of 13.00 mg/g was found for the RhB removal. The adsorption capacity at equilibrium was found to be 11.8 mg/g. Conclusion: According to the characterization results, the ZIF-8 synthesis was effective and produced a crystalline material. The ZIF-8 presented an affinity to the RhB dye. A pseudo-second- order kinetic model represented well the mechanism of interaction involved during RhB adsorption and ZIF-8.