Imaging defects and their evolution in a metal–organic framework at sub-unit-cell resolution

Yttrium-based metal-organic frameworks built on hexanuclear clusters

Yttrium-based metal-organic frameworks built on hexanuclear clusters (Y6-MOFs) represent an important subgroup of MOFs that are assembled from Y6 clusters and diverse organic linkers, featuring a variety of topologies. Due to the robust Y-O bonds and high connectivity of hexanuclear SBUs, Y6-MOFs are generally thermally stable and resistant to water. Additionally, their pore structures are highly tunable through the practice of the reticular chemistry strategy, resulting in excellent performance in gas adsorption and separation related applications. Y6-MOFs are structurally analogous to Zr6-MOFs; however, the existence of charge-balancing cations in Y6-MOFs serves as an additional pore structure regulator, enhancing their tailorability with respect to pore shape and dimensions. In this Frontier article, we summarize the main advances in the design and synthesis of Y6-MOFs, with a particular focus on the precise engineering of their pore structure for gas separation. Future directions of research efforts in this field are also discussed.

Dihydrotetrazine-Functionalized Zirconium-Based Metal-Organic Frameworks for High-Capacity Oil Denitrogenation

High structural stability, dual organic-inorganic nature, and tunability in chemical functionality are promising characteristics of zirconium-based metal-organic frameworks (Zr-MOFs). These properties assist Zr-MOFs in extending their applications in various fields, especially adsorptive removal of pollutants. In this work, two well-known Zr-MOFs (UiO-66(Zr) and MIL-140(Zr) with the formula Zr6O4(OH)4(BDC)6, H2BDC is benzene 1,4-dicarboxylic acid) were synthesized and decorated with a dihydrotetrazine functional group through postsynthesis linker exchange (PSLE). Two dihydrotetrazine (DHTZ)-functionalized frameworks, UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, were applied for the removal of quinoline (Qui) and indole (Ind) from the model oil. The results of adsorption experiments at room temperature display that these functionalized Zr-MOFs have significantly improved removal capacities for Qui (875% for UiO-66(Zr)-DHTZ and 303% for MIL-140(Zr)-DHTZ) and Ind (722% for UiO-66(Zr)-DHTZ and 257% for MIL-140(Zr)-DHTZ). Mechanistic studies based on X-ray photoelectron (XPS) and Fourier-transform infrared (FT-IR) spectroscopies reveal that there is a specific kind of host-guest interaction between dihydrotetrazine and nitrogen-containing compounds (NCCs). UiO-66(Zr)-DHTZ adsorbs 1426 mg·g-1 Qui and 1176 mg·g-1 Ind, while MIL-140(Zr)-DHTZ adsorbs 619 mg·g-1 Qui and 511 mg·g-1 Ind. The lower adsorption capacities of MIL-140(Zr)-DHTZ compared to UiO-66(Zr)-DHTZ are related to its lower surface area (783 m2·g-1 versus 330 m2·g-1). The recyclability of the frameworks goes up to five cycles without any significant decrease in the removal capacity. These results indicate that dihydrotetrazine-functionalized Zr-MOFs are highly stable platforms with superior adsorption capacity compared to basic and neutral NCCs.

Structural engineering in hierarchical nanoarchitectures of metal-organic frameworks and their derivatives

Metal-organic frameworks (MOFs) have attracted much attention owing to their tuneable structures, high surface areas, and good functionalization. Nanoreactors derived from various MOFs are now widely used in heterogeneous catalysis, electrocatalysis and photocatalysis. The nanoarchitectures of MOFs and their derivatives have a great impact on mass and energy transfer pathways, thus affecting the activity and selectivity of the catalysts. In this review, we intend to provide a universal survey of reported methods to synthesize MOF-based core-satellite, core-shell, yolk-shell and hollow-shell structures or their derivatives in recent years and present a continuous evolution among them. We hope that this review could provide some perspectives for exploring new facile methods to prepare different hierarchical nanoarchitectures of MOFs or their derivatives.

Exploring porous structures without crystals: advancements with pair distribution function in metal- and covalent organic frameworks

The pair distribution function (PDF) is a versatile characterisation tool in materials science, capable of retrieving atom-atom distances on a continuous scale (from a few angstroms to nanometres), without being restricted to crystalline samples. Typically, total scattering experiments are performed using high-energy synchrotron X-rays, neutrons or electrons to achieve a high atomic resolution in a short time. Recently, PDF analysis provides a powerful approach to target current characterisation challenges in the field of metal- and covalent organic frameworks. By identifying molecular interactions on the pore surfaces, tracking complex structural transformations involving disorder states, and elucidating nucleation and growth mechanisms, structural analysis using PDF has provided invaluable insights into these materials. This review article highlights the significance of PDF analysis in advancing our understanding of MOFs and COFs, paving the way for innovative applications and discoveries in porous materials research.

Atomic Imaging of the Pb Precipitation in Lead-Halide Perovskites

The lead iodide (PbI2) in lead-halide perovskite (LHP) is both a positive additive for material properties and a site for the formation of device defects. Therefore, atomic-level detection of PbI2 and its derived Pb structures are crucial for understanding the performance and stability of the LHP material. In this work, the atomic imaging of the LHP, PbI2, and Pb lattices is achieved using low-dose integrated differential phase contrast (iDPC) scanning transmission electron microscopy (STEM). Combining it with the traditional high-angle annular dark field (HAADF)-STEM, the Pb precipitation in different LHPs (CsPbI3, CsPbBr3, and FAPbI3) and under different conditions (light, air, and heat) can be investigated in real space. Then, the features of Pb precipitation (positions and sizes) are visually revealed under different conditions and the stabilities of different LHPs. Meanwhile, the pathway of Pb precipitation is directly imaged and confirmed by the iDPC-STEM during an in situ heating process, supporting the detailed mechanism of Pb precipitation. These results provide the visual evidence for analyzing atomic Pb precipitation in LHPs, which helps better understand the structure-property relation induced by Pb impurity.

Low-dose electron microscopy imaging for beam-sensitive metal-organic frameworks

Metal-organic frameworks (MOFs) have garnered significant attention in recent years owing to their exceptional properties. Understanding the intricate relationship between the structure of a material and its properties is crucial for guiding the synthesis and application of these materials. (Scanning) Transmission electron microscopy (S)TEM imaging stands out as a powerful tool for structural characterization at the nanoscale, capable of detailing both periodic and aperiodic local structures. However, the high electron-beam sensitivity of MOFs presents substantial challenges in their structural characterization using (S)TEM. This paper summarizes the latest advancements in low-dose high-resolution (S)TEM imaging technology and its application in MOF material characterization. It covers aspects such as framework structure, defects, and surface and interface analysis, along with the distribution of guest molecules within MOFs. This review also discusses emerging technologies like electron ptychography and outlines several prospective research directions in this field.

Electron beam and thermal stabilities of MFM-300(M) metal-organic frameworks

This work reports the thermal and electron beam stabilities of a series of isostructural metal-organic frameworks (MOFs) of type MFM-300(M) (M = Al, Ga, In, Cr). MFM-300(Cr) was most stable under the electron beam, having an unusually high critical electron fluence of 1111 e- Å-2 while the Group 13 element MOFs were found to be less stable. Within Group 13, MFM-300(Al) had the highest critical electron fluence of 330 e- Å-2, compared to 189 e- Å-2 and 147 e- Å-2 for the Ga and In MOFs, respectively. For all four MOFs, electron beam-induced structural degradation was independent of crystal size and was highly anisotropic, although both the length and width of the channels decreased during electron beam irradiation. Notably, MFM-300(Cr) was found to retain crystallinity while shrinking up to 10%. Thermal stability was studied using in situ synchrotron X-ray diffraction at elevated temperature, which revealed critical temperatures for crystal degradation to be 605, 570, 490 and 480 °C for Al, Cr, Ga, and In, respectively. The pore channel diameters contracted by ≈0.5% on desorption of solvent species, but thermal degradation at higher temperatures was isotropic. The observed electron stabilities were found to scale with the relative inertness of the cations and correlate well to the measured lifetime of the materials when used as photocatalysts.

High-Entropy Metal-Organic Frameworks (HEMOFs): A New Frontier in Materials Design for CO2 Utilization

High-entropy materials (HEMs) emerged as promising candidates for a diverse array of chemical transformations, including CO2 utilization. However, traditional HEMs catalysts are nonporous, limiting their activity to surface sites. Designing HEMs with intrinsic porosity can open the door toward enhanced reactivity while maintaining the many benefits of high configurational entropy. Here, a synergistic experimental, analytical, and theoretical approach to design the first high-entropy metal-organic frameworks (HEMOFs) derived from polynuclear metal clusters is implemented, a novel class of porous HEMs that is highly active for CO2 fixation under mild conditions and short reaction times, outperforming existing heterogeneous catalysts. HEMOFs with up to 15 distinct metals are synthesized (the highest number of metals ever incorporated into a single MOF) and, for the first time, homogenous metal mixing within individual clusters is directly observed via high-resolution scanning transmission electron microscopy. Importantly, density functional theory studies provide unprecedented insight into the electronic structures of HEMOFs, demonstrating that the density of states in heterometallic clusters is highly sensitive to metal composition. This work dramatically advances HEMOF materials design, paving the way for further exploration of HEMs and offers new avenues for the development of multifunctional materials with tailored properties for a wide range of applications.

Cluster-Cluster Co-Nucleation Induced Defective Polyoxometalate-Based Metal-Organic Frameworks for Efficient Tandem Catalysis

The construction of defective sites is one of the effective strategies to create high-activity Metal-Organic frameworks (MOFs) catalysts. However, traditional synthesis methods usually suffer from cumbersome synthesis steps and disordered defect structures. Herein, a cluster-cluster co-nucleation (CCCN) strategy is presented that involves the in situ introduction of size-matched functional polyoxometalates (H6P2W18O62, {P2W18}) to intervene the nucleation process of cluster-based MOFs (UiO-66), achieving one-step inducement of exposed defective sites without redundant post-processing. POM-induced UiO-66 ({P2W18}-0.1@UiO-66) exhibits a classical reo topology for well-defined cluster defects. Moreover, the defective sites and the interaction between POM and skeletal cluster nodes are directly observed by Integrated Differential Phase Contrast in Scanning Transmission Electron Microscopy (iDPC-STEM). Owing to the molecular-level proximity between defective sites and POM in the same nano-reaction space, {P2W18}-0.1@UiO-66 exhibits efficient tandem catalysis in the preparation of γ-valerolactone (γ-GVL) from laevulinic acid (LA) by the combination of Lewis and Brønsted acids with 11 times higher performance than defective UiO-66 formed by conventional coordination modulation strategy. The CCCN strategy is applicable to different POM and has the potential to be extended to other cluster-based MOFs, which will pave a new way for the construction of functional MOFs with multi-centered synergistic catalysis.

A Zero-Gap Gas Phase Photoelectrolyzer for CO2 Reduction with Porous Carbon Supported Photocathodes

A modified Metal-Organic Framework UiO-66-NH2-based photocathode in a zero-gap gas phase photoelectrolyzer was applied for CO2 reduction. Four types of porous carbon fiber layers with different wettability were employed to tailor the local environment of the cathodic surface reactions, optimizing activity and selectivity towards formate, methanol, and ethanol. Results are explained by mass transport through the different type and arrangement of carbon fiber support layers in the photocathodes and the resulting local environment at the UiO-66-NH2 catalyst. The highest energy-to-fuel conversion efficiency of 1.06 % towards hydrocarbons was achieved with the most hydrophobic carbon fiber (H23C2). The results are a step further in understanding how the design and composition of the photoelectrodes in photoelectrochemical electrolyzers can impact the CO2 reduction efficiency and selectivity.

Defective UiO-66/cellulose nanocomposite aerogel for the adsorption of heterocyclic aromatic amines

Heterocyclic aromatic amines (HAAs), arising as chemical derivatives during the high-temperature culinary treatment of proteinaceous comestibles, exhibit notable carcinogenic potential. In this paper, a composite aerogel (AGD-UiO-66) with high-capacity and fast adsorption of HAAs was made with anchoring defective UiO-66 (D-UiO-66) mediated by lauric acid on the backbone of cellulose nanofibers (CNF). AGD-UiO-66 with hierarchical porosity reduced the mass transfer efficiency for the adsorption of HAAs and achieved high adsorption amount (0.84-1.05 μmol/g) and fast adsorption (15 min). The isothermal adsorption model demonstrated that AGD-UiO-66 belonged to a multilayer adsorption mechanism for HAAs. Furthermore, AGD-UiO-66 was successfully used to adsorb 12 HAAs in different food (roasted beef, roasted pork, roasted salmon and marinade) with high recoveries of 94.65%-104.43%. The intrinsic potential of AGD-UiO-66 demonstrated that it could be widely applicable to the adsorption of HAAs in foods.

In Situ Defect Engineering of Fe-MIL for Self-Enhanced Peroxidase-Like Activity

Defect engineering is an effective strategy to enhance the enzyme-like activity of nanozymes. However, previous efforts have primarily focused on introducing defects via de novo synthesis and post-synthetic treatment, overlooking the dynamic evolution of defects during the catalytic process involving highly reactive oxygen species. Herein, a defect-engineered metal-organic framework (MOF) nanozyme with mixed linkers is reported. Over twofold peroxidase (POD)-like activity enhancement compared with unmodified nanozyme highlights the critical role of in situ defect formation in enhancing the catalytic performance of nanozyme. Experimental results reveal that highly active hydroxyl radical (•OH) generated in the catalytic process etches the 2,5-dihydroxyterephthalic acid ligands, contributing to electronic structure modulation of metal sites and enlarged pore sizes in the framework. The self-enhanced POD-like activity induced by in situ defect engineering promotes the generation of •OH, holding promise in colorimetric sensing for detecting dichlorvos. Utilizing smartphone photography for RGB value extraction, the resultant sensing platform achieves the detection for dichlorvos ranging from 5 to 300 ng mL-1 with a low detection limit of 2.06 ng mL-1. This pioneering work in creating in situ defects in MOFs to improve catalytic activity offers a novel perspective on traditional defect engineering.

Pristine MOF Materials for Separator Application in Lithium-Sulfur Battery

Lithium-sulfur (Li-S) batteries have attracted significant attention in the realm of electronic energy storage and conversion owing to their remarkable theoretical energy density and cost-effectiveness. However, Li-S batteries continue to face significant challenges, primarily the severe polysulfides shuttle effect and sluggish sulfur redox kinetics, which are inherent obstacles to their practical application. Metal-organic frameworks (MOFs), known for their porous structure, high adsorption capacity, structural flexibility, and easy synthesis, have emerged as ideal materials for separator modification. Efficient polysulfides interception/conversion ability and rapid lithium-ion conduction enabled by MOFs modified layers are demonstrated in Li-S batteries. In this perspective, the objective is to present an overview of recent advancements in utilizing pristine MOF materials as modification layers for separators in Li-S batteries. The mechanisms behind the enhanced electrochemical performance resulting from each design strategy are explained. The viewpoints and crucial challenges requiring resolution are also concluded for pristine MOFs separator in Li-S batteries. Moreover, some promising materials and concepts based on MOFs are proposed to enhance electrochemical performance and investigate polysulfides adsorption/conversion mechanisms. These efforts are expected to contribute to the future advancement of MOFs in advanced Li-S batteries.

Tailoring parameters for QM/MM simulations: accurate modeling of adsorption and catalysis in zirconium-based metal-organic frameworks

Quantum mechanics/molecular mechanics (QM/MM) simulations offer an efficient way to model reactions occurring in complex environments. This study introduces a specialized set of charge and Lennard-Jones parameters tailored for electrostatically embedded QM/MM calculations, aiming to accurately model both adsorption processes and catalytic reactions in zirconium-based metal-organic frameworks (Zr-MOFs). To validate our approach, we compare adsorption energies derived from QM/MM simulations against experimental results and Monte Carlo simulation outcomes. The developed parameters showcase the ability of QM/MM simulations to represent long-range electrostatic and van der Waals interactions faithfully. This capability is evidenced by the prediction of adsorption energies with a low root mean square error of 1.1 kcal mol-1 across a wide range of adsorbates. The practical applicability of our QM/MM model is further illustrated through the study of glucose isomerization and epimerization reactions catalyzed by two structurally distinct Zr-MOF catalysts, UiO-66 and MOF-808. Our QM/MM calculations closely align with experimental activation energies. Importantly, the parameter set introduced here is compatible with the widely used universal force field (UFF). Moreover, we thoroughly explore how the size of the cluster model and the choice of density functional theory (DFT) methodologies influence the simulation outcomes. This work provides an accurate and computationally efficient framework for modeling complex catalytic reactions within Zr-MOFs, contributing valuable insights into their mechanistic behaviors and facilitating further advancements in this dynamic area of research.

Chemistries and materials for atmospheric water harvesting

Atmospheric water harvesting (AWH) is recognized as a crucial strategy to address the global challenge of water scarcity by tapping into the vast reserves of atmospheric moisture for potable water supply. Within this domain, sorbents lie in the core of AWH technologies as they possess broad adaptability across a wide spectrum of humidity levels, underpinned by the cyclic sorption and desorption processes of sorbents, necessitating a multi-scale viewpoint regarding the rational material and chemical selection and design. This Invited Review delves into the essential sorption mechanisms observed across various classes of sorbent systems, emphasizing the water-sorbent interactions and the progression of water networks. A special focus is placed on the insights derived from isotherm profiles, which elucidate sorbent structures and sorption dynamics. From these foundational principles, we derive material and chemical design guidelines and identify key tuning factors from a structural-functional perspective across multiple material systems, addressing their fundamental chemistries and unique attributes. The review further navigates through system-level design considerations to optimize water production efficiency. This review aims to equip researchers in the field of AWH with a thorough understanding of the water-sorbent interactions, material design principles, and system-level considerations essential for advancing this technology.

Operando-reconstructed polyatomic ion layers boost the activity and stability of industrial current-density water splitting

Metal-organic frameworks have garnered attention as highly efficient pre-electrocatalysts for the oxygen evolution reaction (OER). Current structure-activity relationships primarily rely on the assumption that the complete dissolution of organic ligands occurs during electrocatalysis. Herein, modeling based on NiFe Prussian blue analogs (NiFe-PBAs) show that cyanide ligands leach from the matrix and subsequently oxidize to corresponding inorganic ions (ammonium and carbonate) that re-adsorb onto the surface of NiFe OOH during the OER process. Interestingly, the surface-adsorbed inorganic ions induce the OER reaction of NiFe OOH to switch from the adsorbate evolution to the lattice-oxygen-mediated mechanism, thus contributing to the high activity. In addition, this reconstructed inorganic ion layer acting as a versatile protective layer can prevent the dissolution of metal sites to maintain contact between catalytic sites and reactive ions, thus breaking the activity-stability trade-off. Consequently, our constructed NiFe-PBAs exhibit excellent durability for 1250 h with an ultralow overpotential of 253 mV at 100 mA cm-2. The scale-up NiFe-PBAs operated with a low energy consumption of ∼4.18 kWh m-3 H2 in industrial water electrolysis equipment. The economic analysis of the entire life cycle demonstrates that this green hydrogen production is priced at US$2.59/ [Formula: see text] , meeting global targets ( Collapse

Key Words

• Chemical recognition
• Industrial water electrolysis
• Oxygen evolution mechanism

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Affiliation(s)

Yingxia Zhao Guangdong Engineering Technology Research Center of Modern Fine Chemical Engineering, School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China; Analysis and Test Center Guangdong University of Technology, Guangdong University of Technology, Guangzhou 510006, China
Ying Wu Guangdong Engineering Technology Research Center of Modern Fine Chemical Engineering, School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China; Jieyang Branch of Chemistry and Chemical Engineering Guangdong Laboratory (Rongjiang Laboratory), Jieyang 515200, China; School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510641, China
Qunlei Wen State Key Laboratory of Materials Processing and Die & Mould Technology, and School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Danji Huang State Key Laboratory of Advanced Electromagnetic Engineering and Technology, and School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Ruoou Yang State Key Laboratory of Materials Processing and Die & Mould Technology, and School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Haozhi Wang State Key Laboratory of Marine Resource Utilization in South China Sea, School of Materials Science and Engineering, Hainan University, Haikou 570228, China
Yingying Xu Guangdong Engineering Technology Research Center of Modern Fine Chemical Engineering, School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China
Ming Sun Guangdong Engineering Technology Research Center of Modern Fine Chemical Engineering, School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China; Jieyang Branch of Chemistry and Chemical Engineering Guangdong Laboratory (Rongjiang Laboratory), Jieyang 515200, China
Youwen Liu State Key Laboratory of Materials Processing and Die & Mould Technology, and School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
Jiakun Fang State Key Laboratory of Advanced Electromagnetic Engineering and Technology, and School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
Tianyou Zhai State Key Laboratory of Materials Processing and Die & Mould Technology, and School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Lin Yu Guangdong Engineering Technology Research Center of Modern Fine Chemical Engineering, School of Chemical Engineering and Light Industry, Guangdong University of Technology, Guangzhou 510006, China; Jieyang Branch of Chemistry and Chemical Engineering Guangdong Laboratory (Rongjiang Laboratory), Jieyang 515200, China.

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Carboxyl-Decorated UiO-66 Supporting Pd Nanoparticles for Efficient Room-Temperature Hydrodeoxygenation of Lignin Derivatives

Hydrodeoxygenation (HDO) of lignin derivatives at room-temperature (RT) is still of challenge due to the lack of satisfactory activity reported in previous literature. Here, it is successfully designed a Pd/UiO-66-(COOH)2 catalyst by using UiO-66-(COOH)2 as the support with uncoordinated carboxyl groups. This catalyst, featuring a moderate Pd loading, exhibited exceptional activity in RT HDO of vanillin (VAN, a typical model lignin derivative) to 2-methoxyl-4-methylpheonol (MMP), and >99% VAN conversion with >99% MMP yield is achieved, which is the first metal-organic framework (MOF)-based catalyst realizing the goal of RT HDO of lignin derivatives, surpassing previous reports in the literature. Detailed investigations reveal a linear relationship between the amount of uncoordinated carboxyl group and MMP yield. These uncoordinated carboxyl groups accelerate the conversion of intermediate such as vanillyl alcohol (VAL), ultimately leading to a higher yield of MMP over Pd/UiO-66-(COOH)2 catalyst. Furthermore, Pd/UiO-66-(COOH)2 catalyst also exhibits exceptional reusability and excellent substrate generality, highlighting its promising potential for further biomass utilization.

Defect Engineering Strategy for Superior Integration of Metal-Organic Framework and Halide Perovskite as a Fluorescence Sensing Material

Combining halide perovskite quantum dots (QDs) and metal-organic frameworks (MOFs) material is challenging when the QDs' size is larger than the MOFs' nanopores. Here, we adopted a simple defect engineering approach to increase the size of zeolitic imidazolate framework 90 (ZIF-90)'s pores size to better load CH3NH3PbBr3 perovskite QDs. This defect structure effect can be easily achieved by adjusting the metal-to-ligand ratio throughout the ZIF-90 synthesis process. The QDs are then grown in the defective structure, resulting in a hybrid ZIF-90-perovskite (ZP) composite. The QDs in ZP composites occupied the gap of 10-18 nm defective ZIF-90 crystal and interestingly isolated the QDs with high stability in aqueous solution. We also investigated the relationship between defect engineering and fluorescence sensing, finding that the aqueous Cu2+ ion concentration was directly correlated to defective ZIF-90 and ZP composites. We also found that the role of the O-Cu coordination bonds and CH3NHCu+ species formation in the materials when they reacted with Cu2+ was responsible for this relationship. Finally, this strategy was successful in developing Cu2+ ion fluorescence sensing in water with better selectivity and sensitivity.

Defect-enabling zirconium-based metal-organic frameworks for energy and environmental remediation applications

This comprehensive review explores the diverse applications of defective zirconium-based metal-organic frameworks (Zr-MOFs) in energy and environmental remediation. Zr-MOFs have gained significant attention due to their unique properties, and deliberate introduction of defects further enhances their functionality. The review encompasses several areas where defective Zr-MOFs exhibit promise, including environmental remediation, detoxification of chemical warfare agents, photocatalytic energy conversions, and electrochemical applications. Defects play a pivotal role by creating open sites within the framework, facilitating effective adsorption and remediation of pollutants. They also contribute to the catalytic activity of Zr-MOFs, enabling efficient energy conversion processes such as hydrogen production and CO2 reduction. The review underscores the importance of defect manipulation, including control over their distribution and type, to optimize the performance of Zr-MOFs. Through tailored defect engineering and precise selection of functional groups, researchers can enhance the selectivity and efficiency of Zr-MOFs for specific applications. Additionally, pore size manipulation influences the adsorption capacity and transport properties of Zr-MOFs, further expanding their potential in environmental remediation and energy conversion. Defective Zr-MOFs exhibit remarkable stability and synthetic versatility, making them suitable for diverse environmental conditions and allowing for the introduction of missing linkers, cluster defects, or post-synthetic modifications to precisely tailor their properties. Overall, this review highlights the promising prospects of defective Zr-MOFs in addressing energy and environmental challenges, positioning them as versatile tools for sustainable solutions and paving the way for advancements in various sectors toward a cleaner and more sustainable future.

Atomic-level imaging of beam-sensitive COFs and MOFs by low-dose electron microscopy

Electron microscopy, an important technique that allows for the precise determination of structural information with high spatiotemporal resolution, has become indispensable in unravelling the complex relationships between material structure and properties ranging from mesoscale morphology to atomic arrangement. However, beam-sensitive materials, particularly those comprising organic components such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), would suffer catastrophic damage from the high energy electrons, hindering the determination of atomic structures. A low-dose approach has arisen as a possible solution to this problem based on the integration of advancements in several aspects: electron optical system, detector, image processing, and specimen preservation. This article summarizes the transmission electron microscopy characterization of MOFs and COFs, including local structures, host-guest interactions, and interfaces at the atomic level. Revolutions in advanced direct electron detectors, algorithms in image acquisition and processing, and emerging methodology for high quality low-dose imaging are also reviewed. Finally, perspectives on the future development of electron microscopy methodology with the support of computer science are presented.

Engineering Porosity and Functionality in a Robust Twofold Interpenetrated Bismuth-Based MOF: Toward a Porous, Stable, and Photoactive Material

Defect engineering in metal-organic frameworks (MOFs) has gained worldwide research traction, as it offers tools to tune the properties of MOFs. Herein, we report a novel 2-fold interpenetrated Bi-based MOF made of a tritopic flexible organic linker, followed by missing-linker defect engineering. This procedure creates a gradually augmented micro- and mesoporosity in the parent (originally nonporous) network. The resulting MOFs can tolerate a remarkable extent of linker vacancy (with absence of up to 60% of linkers per Bi node) created by altering the crystal-growth rate as a function of synthesis temperature and duration. Owing to the enhanced porosity and availability of the uncoordinated Lewis acidic Bi sites, the defect-engineered MOFs manifested improved surface areas, augmented CO2 and water vapor uptake, and catalytic activity. Parallel to this, the impact of defect engineering on the optoelectronic properties of these MOFs has also been studied, offering avenues for new applications.

Three-Dimensional Crystalline Organic Framework Stabilized by Molecular Mortise-and-Tenon Jointing

Three-dimensional (3D) crystalline organic frameworks with complex topologies, high surface area, and low densities afford a variety of application prospects. However, the design and construction of these frameworks have been largely limited to systems containing polyhedron-shaped building blocks or those relying on component interpenetration. Here, we report the synthesis of a 3D crystalline organic framework based on molecular mortise-and-tenon jointing. This new material takes advantage of tetra(4-pyridylphenyl)ethylene and chlorinated bis(benzodioxaborole)benzene as building blocks and is driven by dative B-N bonds. A single-crystal X-ray diffraction analysis of the framework reveals the presence of two-dimensional (2D) layers with helical channels that are formed presumably during the boron-nitrogen coordination process. The protrusion of dichlorobenzene units from the upper and lower surfaces of the 2D layers facilitates the key mortise-and-tenon connections. These connections enable the interlocking of adjacent layers and the stabilization of an overall 3D framework. The resulting framework is endowed with high porosity and attractive mechanical properties, rendering it potentially suitable for the removal of impurities from acetylene.

Phase Engineering of Zirconium MOFs Enables Efficient Osmotic Energy Conversion: Structural Evolution Unveiled by Direct Imaging

Creating structural defects in a controlled manner within metal-organic frameworks (MOFs) poses a significant challenge for synthesis, and concurrently, identifying the types and distributions of these defects is also a formidable task for characterization. In this study, we demonstrate that by employing 2-sulfonylterephthalic acid as the ligand for synthesizing Zr (or Hf)-based MOFs, a crystal phase transformation from the common fcu topology to the rare jmt topology can be easily facilitated using a straightforward mixed-solvent strategy. The jmt phase, characterized by an extensively open framework, can be considered a derivative of the fcu phase, generated through the introduction of missing-cluster defects. We have explicitly identified both MOF phases, their intermediate states, and the novel core-shell structures they form using ultralow-dose high-resolution transmission electron microscopy. In addition to facilitating phase engineering, the incorporation of sulfonic groups in MOFs imparts ionic selectivity, making them applicable for osmotic energy harvesting through mixed matrix membrane fabrication. The membrane containing the jmt-phase MOF exhibits an exceptionally high peak power density of 10.08 W m-2 under a 50-fold salinity gradient (NaCl: 0.5 M|0.01 M), which surpasses the threshold of 5 W m-2 for commercial applications and can be attributed to the combination of large pore size, extensive porosity, and abundant sulfonic groups in this novel MOF material.

Highly defective ultra-small tetravalent MOF nanocrystals

The size and defects in crystalline inorganic materials are of importance in many applications, particularly catalysis, as it often results in enhanced/emerging properties. So far, applying the strategy of modulation chemistry has been unable to afford high-quality functional Metal-Organic Frameworks (MOFs) nanocrystals with minimized size while exhibiting maximized defects. We report here a general sustainable strategy for the design of highly defective and ultra-small tetravalent MOFs (Zr, Hf) crystals (ca. 35% missing linker, 4-6 nm). Advanced characterizations have been performed to shed light on the main factors governing the crystallization mechanism and to identify the nature of the defects. The ultra-small nanoMOFs showed exceptional performance in peptide hydrolysis reaction, including high reactivity, selectivity, diffusion, stability, and show emerging tailorable reactivity and selectivity towards peptide bond formation simply by changing the reaction solvent. Therefore, these highly defective ultra-small M(IV)-MOFs particles open new perspectives for the development of heterogeneous MOF catalysts with dual functions.

Ingenious Modulation of Third-Order Nonlinear Optical Response of Zr-MOFs through Defect Engineering Based on a Mixed-Linker Strategy

Defect engineering plays a pivotal role in regulating electronic structure and facilitating charge transfer, yielding captivating effects on third-order nonlinear optical (NLO) properties. In this work, we utilized a mixed-linker strategy to intentionally disrupt the initial periodic arrangement of UiO-66 and construct defects. Specifically, we incorporated tetrakis(4-carboxyphenyl)porphyrin (TCPP) with an exceptionally electron-rich delocalization system into the framework of UiO-66 using a one-pot solvothermal method, ingeniously occupying the partial distribution sites of the Zr6 clusters. Compared to UiO-66, the NLO absorption and refraction performance of TCPP/UiO-66 were significantly improved. Additionally, due to the presence of nitrogen-rich sites that can accommodate metal ions in the porphyrin ring of TCPP, Co(II), Ni(II), Cu(II), and Zn(II) are introduced into TCPP/UiO-66, extending the d-π conjugation effect to further regulate the defects. The NLO absorption behavior transforms saturation absorption (SA) to reverse saturation absorption (RSA), while the refraction behavior shifts from self-defocusing to self-focusing. This work shows that defects can effectively regulate the electronic structure, while TCPP plays a crucial role in significantly enhancing electron delocalization.

Metal-Organic Framework as a New Type of Magnetothermally-Triggered On-Demand Release Carrier

The development of external stimuli-controlled payload systems has been sought after with increasing interest toward magnetothermally-triggered drug release (MTDR) carriers due to their non-invasive features. However, current MTDR carriers present several limitations, such as poor heating efficiency caused by the aggregation of iron oxide nanoparticles (IONPs) or the presence of antiferromagnetic phases which affect their efficiency. Herein, a novel MTDR carrier is developed using a controlled encapsulation method that fully fixes and confines IONPs of various sizes within the metal-organic frameworks (MOFs). This novel carrier preserves the MOF's morphology, porosity, and IONP segregation, while enhances heating efficiency through the oxidation of antiferromagnetic phases in IONPs during encapsulation. It also features a magnetothermally-responsive nanobrush that is stimulated by an alternating magnetic field to enable on-demand drug release. The novel carrier shows improved heating, which has potential applications as contrast agents and for combined chemo and magnetic hyperthermia therapy. It holds a great promise for magneto-thermally modulated drug dosing at tumor sites, making it an exciting avenue for cancer treatment.

In Situ Multicolor Imaging of Photocatalytic Degradation Process of Permanganate on Single Bismuth-Based Metal-Organic Frameworks

Bismuth-based metal-organic frameworks (Bi-MOFs) have emerged as important photocatalysts for pollutant degradation applications. Understanding the photocatalytic degradation mechanism is key to achieving technological advantage. Herein, we apply dark-field optical microscopy (DFM) to realize in situ multicolor imaging of the photocatalytic degradation process of permanganate (MnO4-) on single CAU-17 Bi-MOFs. Three reaction kinetic processes such as surface adsorption, photocatalytic reduction, and disproportionation are revealed by combining the time-lapsed DFM images with optical absorption spectra, indicating that the photocatalytic reduction of purple MnO4- first produces beige red MnO42- through a one-electron pathway, and then MnO42- disproportionates into yellow MnO2 on CAU-17. Meanwhile, we observe that the deposition of MnO2 cocatalysts enhances the surface adsorption reaction and the photocatalytic reduction of MnO4- to MnO42-. Unexpectedly, it is found that isopropanol as a typical hole scavenger can stabilize MnO42-, avoiding disproportionation and causing the alteration of the photocatalytic reaction pathway from a one-electron avenue to a three-electron (1 + 2) process for producing MnO2 on CAU-17. This research opens up the possibility of comprehensively tracking and understanding the photocatalytic degradation reaction at the single MOF particle level.

Janus Quasi-Solid Electrolyte Membranes with Asymmetric Porous Structure for High-Performance Lithium-Metal Batteries

Quasi-solid electrolytes (QSEs) based on nanoporous materials are promising candidates to construct high-performance Li-metal batteries (LMBs). However, simultaneously boosting the ionic conductivity (σ) and lithium-ion transference number (t+) of liquid electrolyte confined in porous matrix remains challenging. Herein, we report a novel Janus MOFLi/MSLi QSEs with asymmetric porous structure to inherit the benefits of both mesoporous and microporous hosts. This Janus QSE composed of mesoporous silica and microporous MOF exhibits a neat Li+ conductivity of 1.5 × 10-4 S cm-1 with t+ of 0.71. A partially de-solvated structure and preference distribution of Li+ near the Lewis base O atoms were depicted by MD simulations. Meanwhile, the nanoporous structure enabled efficient ion flux regulation, promoting the homogenous deposition of Li+. When incorporated in Li||Cu cells, the MOFLi/MSLi QSEs demonstrated a high Coulombic efficiency of 98.1%, surpassing that of liquid electrolytes (96.3%). Additionally, NCM 622||Li batteries equipped with MOFLi/MSLi QSEs exhibited promising rate performance and could operate stably for over 200 cycles at 1 C. These results highlight the potential of Janus MOFLi/MSLi QSEs as promising candidates for next-generation LMBs.

Effective Strategy toward Obtaining Reliable Breakthrough Curves of Solid Adsorbents

Metal-organic frameworks (MOFs) have demonstrated their versatility in a wide range of applications, including chemical separation, gas capture, and storage. In industrial adsorption processes, MOFs are integral to the creation of selective gas adsorption fixed beds. In this context, the assessment of their separation performance under relevant conditions often relies on breakthrough experiments. One aspect frequently overlooked in these experiments is the shaping of MOF powders, which can significantly impact the accuracy of breakthrough results. In this study, we present an approach for immobilizing MOF particles on the surface of glass beads (GBs) utilizing trimethylolpropane triglycidyl ether (TMPTGE) as a binder, leading to the creation of MOF@GB materials. We successfully synthesized five targeted MOF composites, namely, SIFSIX-3-Ni@GB, CALF-20@GB, UiO-66@GB, HKUST-1@GB, and MOF-808@GB, each possessing distinct pore sizes and structural topologies. Characterization studies employing powder X-ray diffraction and adsorption isotherm analyses demonstrated that MOFs@GB retained their crystallinity and 73-90% of the Brunauer-Emmett-Teller area of their parent MOFs. Dynamic breakthrough experiments revealed that, in comparison to their parent MOFs, MOF@GB configurations enhanced the accuracy of breakthrough measurements by mitigating pressure buildup and minimizing reductions in the gas flow rate. This work underscores the significance of meticulous experimental design, specifically in shaping MOF powders, to optimize the efficacy of breakthrough experiments. Our proposed strategy aims to provide a versatile platform for MOF powder processing, thereby facilitating more reliable breakthrough experiments.

Production of eco friendly DME fuel over sonochemically synthesized UiO66 catalyst

The ultrasound-assisted preparation of UiO-66 was carried out at T = 80-220 °C, and the catalytic performances were evaluated in methanol conversion. Also, physicochemical properties were assessed by XRD, SEM, PSD, FTIR, N2 adsorption-desorption, TG-DTG, and NH3-TPD analysis. The characterization proved that increasing the synthesis temperature positively affected the crystallinity, specific surface area, thermal stability, and acidity of the catalysts. Besides, the catalysts' performance was investigated in the methanol conversion reaction (T = 350-450 °C, P = 1 atm, and WHSV = 5 h-1), leading to the DME (Dimethyl Ether) production. Rising reaction temperature increased the methanol conversion and DME yield. The synthesized sample at 220 °C had the best properties and performance with conversion and yield of about 38% and 51%, respectively. The stability test for the UiO-66-220 (University of Oslo 66) catalyst was performed at 450 °C for 12 h, and the activity remained stable for about 5 h. Furthermore, the used catalyst was characterized via XRD and TG analysis.

Excellent Mercury Removal in High Sulfur Atmosphere Using a Novel CuS-BDC-2D Derived by Metal-Organic Frame

To effectively remove high concentrations of mercury in a high sulfur atmosphere of nonferrous smelting flue gas, a novel two-dimensional CuS-MOF (CuS-BDC-2D) material is synthesized by anchoring S to Cu sites in the Cu-BDC MOF. The highly dispersed CuS active sites and MOF framework structural properties in CuS-BDC-2D enable efficiently collaborate in capturing mercury. CuS-BDC-2D exhibits a layered floral structure with high specific surface area and thermal stability, with poor crystallinity. Compared to CuS and the three-dimensional CuS-MOF (CuS-BDC-3D) structure, CuS-BDC-2D demonstrates significantly higher mercury capture capacity due to the high exposure of active sites and defects sites in the two-dimensional material. Moreover, CuS-BDC-2D exhibits excellent resistance to sulfur, maintaining its high efficiency in removing Hg0 even at high levels of sulfur dioxide (SO2), such as 5000-20,000 ppm. The superior performance of CuS-BDC-2D makes it suitable for controlling mercury emissions in actual nonferrous smelting flue gas. This discovery also paves the way for the development of new mercury adsorbents, which can guide future advancements in this field.

Revolutionizing the structural design and determination of covalent-organic frameworks: principles, methods, and techniques

Covalent organic frameworks (COFs) represent an important class of crystalline porous materials with designable structures and functions. The interconnected organic monomers, featuring pre-designed symmetries and connectivities, dictate the structures of COFs, endowing them with high thermal and chemical stability, large surface area, and tunable micropores. Furthermore, by utilizing pre-functionalization or post-synthetic functionalization strategies, COFs can acquire multifunctionalities, leading to their versatile applications in gas separation/storage, catalysis, and optoelectronic devices. Our review provides a comprehensive account of the latest advancements in the principles, methods, and techniques for structural design and determination of COFs. These cutting-edge approaches enable the rational design and precise elucidation of COF structures, addressing fundamental physicochemical challenges associated with host-guest interactions, topological transformations, network interpenetration, and defect-mediated catalysis.

Reactivity of metal-oxo clusters towards biomolecules: from discrete polyoxometalates to metal-organic frameworks

Metal-oxo clusters hold great potential in several fields such as catalysis, materials science, energy storage, medicine, and biotechnology. These nanoclusters of transition metals with oxygen-based ligands have also shown promising reactivity towards several classes of biomolecules, including proteins, nucleic acids, nucleotides, sugars, and lipids. This reactivity can be leveraged to address some of the most pressing challenges we face today, from fighting various diseases, such as cancer and viral infections, to the development of sustainable and environmentally friendly energy sources. For instance, metal-oxo clusters and related materials have been shown to be effective catalysts for biomass conversion into renewable fuels and platform chemicals. Furthermore, their reactivity towards biomolecules has also attracted interest in the development of inorganic drugs and bioanalytical tools. Additionally, the structural versatility of metal-oxo clusters allows for the efficiency and selectivity of the biomolecular reactions they promote to be readily tuned, thereby providing a pathway towards reaction optimization. The properties of the catalyst can also be improved through incorporation into solid supports or by linking metal-oxo clusters together to form Metal-Organic Frameworks (MOFs), which have been demonstrated to be powerful heterogeneous catalysts. Therefore, this review aims to provide a comprehensive and critical analysis of the state of the art on biomolecular transformations promoted by metal-oxo clusters and their applications, with a particular focus on structure-activity relationships.

Tuning the Fluorometric Sensing of Phosphate on UiO-66-NH2(Zr, Ce, Hf) Metal Nodes

Metal-organic frameworks (MOFs) with intrinsic luminescent properties, modular structure, and tunable electronic properties, provide unique opportunities for designing target-specific molecular sensors by systematically choosing their constituent building blocks. We report a simple one-step MOF-based sensing platform for phosphate (P) detection that combines the luminescent properties of 2-aminoterephthalic acid (ATA) with the affinity of rationally selected nodes in UiO-66-NH2 to bind with P. This MOF possesses an electron-donating amine group that controls the light-harvesting characteristics of the linkers. Substituting Zr6 node with Ce6 or Hf6 results in a series of isostructural MOFs with distinct optical properties that are nonexistent in the unsubstituted MOF. We have utilized these MOFs to quantitatively measure P, using its ability to bind strongly to metal nodes inhibiting the LMCT process and altering the linker's photon emission. Using this system, detection limits of 4.5, 7.2 and 10.5 μM were obtained for the UiO-66-NH2(Ce), UiO-66-NH2, and UiO-66-NH2(Hf) respectively, adopting a straightforward single step procedure. These results demonstrate that the selection of metal nodes in a series of isostructural MOFs can be used to modulate their electronic properties and create sensing probes possessing the desired characteristics needed for the detection of environmental contaminants.

Versatile Structural Engineering of Metal-Organic Frameworks Enabling Switchable Catalytic Selectivity

The structure engineering of metal-organic frameworks (MOFs) forms the cornerstone of their applications. Nonetheless, realizing the simultaneous versatile structure engineering of MOFs remains a significant challenge. Herein, a dynamically mediated synthesis strategy to simultaneously engineer the crystal structure, defect structure, and nanostructure of MOFs is proposed. These include amorphous Zr-ODB nanoparticles, crystalline Zr-ODB-hz (ODB = 4,4'-oxalyldibenzoate, hz = hydrazine) nanosheets, and defective d-Zr-ODB-hz nanosheets. Aberration-corrected scanning transmission electron microscopy combined with low-dose high-angle annular dark-field imaging technique vividly portrays these engineered structures. Concurrently, the introduced hydrazine moieties confer self-reduction properties to the respective MOF structures, allowing the in situ installation of catalytic Pd nanoparticles. Remarkably, in the hydrogenation of vanillin-like biomass derivatives, Pd/Zr-ODB-hz yields partially hydrogenated alcohols as the primary products, whereas Pd/d-Zr-ODB-hz exclusively produces fully hydrogenated alkanes. Density functional theory calculations, coupled with experimental evidence, uncover the catalytic selectivity switch triggered by the change in structure type. The proposed strategy of versatile structure engineering of MOFs introduces an innovative pathway for the development of high-performance MOF-based catalysts for various reactions.

Modulated Ultrathin NiCo-LDH Nanosheet-Decorated Zr3+-Rich Defective NH2-UiO-66 Nanostructure for Efficient Photocatalytic Hydrogen Evolution

Defect engineering through modification of their surface linkage is found to be an effective pathway to escalate the solar energy conversion efficiency of metal-organic frameworks (MOFs). Herein, defect engineering using controlled decarboxylation on the NH2-UiO-66 surface and integration of ultrathin NiCo-LDH nanosheets synergizes the hydrogen evolution reaction (HER) under a broad visible light regime. Diversified analytical methods including positron annihilation lifetime spectroscopy were employed to investigate the role of Zr3+-rich defects by analyzing the annihilation characteristics of positrons in NH2-UiO-66, which provides a deep insight into the effects of structural defects on the electronic properties. The progressively tuned photophysical properties of the NiCo-LDH@NH2-UiO-66-D-heterostructured nanocatalyst led to an impressive rate of HER (∼2458 μmol h-1 g-1), with an apparent quantum yield of ∼6.02%. The ultrathin NiCo-LDH nanosheet structure was found to be highly favored toward electrostatic self-assembly in the heterostructure for efficient charge separation. Coordination of Zr3+ on the surface of the NiCo-LDH nanosheet support through NH2-UiO-66 was confirmed by X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy techniques. Femtosecond transient absorption spectroscopy studies unveiled a photoexcited charge migration process from MOF to NiCo-LDH which favorably occurred on a picosecond time scale to boost the catalytic activity of the composite system. Furthermore, the experimental finding and HER activity are validated by density functional theory studies and evaluation of the free energy pathway which reveals the strong hydrogen binding over the surface and infers the anchoring effect of the ultrathin layered double hydroxide (LDH) in the vicinity of the Zr cluster with a strong host-guest interaction. This work provided a novel insight into efficient photocatalysis via defect engineering at the linker modulation in MOFs.

Radiation-Induced De Novo Defects in Metal-Organic Frameworks Boost CO2 Sorption

Defects in metal-organic frameworks (MOFs) can significantly change their local microstructures, thus notably leading to an alteration-induced performance in sorption or catalysis. However, achieving de novo defect engineering in MOFs under ambient conditions without the scarification of their crystallinity remains a challenge. Herein, we successfully synthesize defective ZIF-7 through 60Co gamma ray radiation under ambient conditions. The obtained ZIF-7 is defect-rich but also has excellent crystallinity, enhanced BET surface area, and hierarchical pore structure. Moreover, the amount and structure of these defects within ZIF-7 were determined from the two-dimensional (2D) 13C-1H frequency-switched Lee-Goldburg heteronuclear correlation (FSLG-HETCOR) spectra, continuous rotation electron diffraction (cRED), and high-resolution transmission electron microscopy (HRTEM). Interestingly, the defects in ZIF-7 all strongly bind to CO2, leading to a remarkable enhancement of the CO2 sorption capability compared with that synthesized by the solvothermal method.

Formic Acid-Regulated Defect Engineering in Zr-Based Metal-Organic Frameworks toward Fluorescence Sensor for Sensitive Detection of Chlortetracycline

The elaborate defect-engineering of luminescent metal-organic frameworks (MOFs) allows them with enhanced sensing performance. A modulator-induced defect formation strategy is adopted in this paper, and the impact of the open-metal sites on sensing process is rationalized. It is demonstrated that the defect level can be tuned to a remarkable extent by controlling the amount of modulator. When a particular defect concentration is reached, the UiO-66-xFA can be acted as highly sensitive ratiometric fluorescence probes for chlortetracycline (CTE) determination with an ultralow detection limit of 9.9 nm. Furthermore, by virtue of the obvious variation in fluorescence chromaticity of probes from blue to yellow, a sensory hydrogels-based smartphone platform is proposed for visible quantitation of CTE by identifying the RGB values. A delicate device integrated with UV lamp and dark cavity has been developed for avoiding inconsistencies of ambient light and visual errors. Finally, the sensor obtains satisfactory results in the detection of actual seafood samples, with no significant differences from those of liquid chromatography-mass spectrometry. This approach anticipates a novel route to sensitize optical sensors through the design and synthesis of moderate defects in luminescent MOFs.

Synthetic control of correlated disorder in UiO-66 frameworks

Changing the perception of defects as imperfections in crystalline frameworks into correlated domains amenable to chemical control and targeted design might offer opportunities for the design of porous materials with superior performance or distinctive behavior in catalysis, separation, storage, or guest recognition. From a chemical standpoint, the establishment of synthetic protocols adapted to control the generation and growth of correlated disorder is crucial to consider defect engineering a practicable route towards adjusting framework function. By using UiO-66 as experimental platform, we systematically explored the framework chemical space of the corresponding defective materials. Periodic disorder arising from controlled generation and growth of missing cluster vacancies can be chemically controlled by the relative concentration of linker and modulator, which has been used to isolate a crystallographically pure "disordered" reo phase. Cs-corrected scanning transmission electron microscopy is used to proof the coexistence of correlated domains of missing linker and cluster vacancies, whose relative sizes are fixed by the linker concentration. The relative distribution of correlated disorder in the porosity and catalytic activity of the material reveals that, contrarily to the common belief, surpassing a certain defect concentration threshold can have a detrimental effect.

Controllable Synthesis of Defective UiO-66 for Efficient Degradation and Detection of Ozone

Metal-organic framework (MOF) structures have gained significant attention for their exceptional catalytic performance in ozone degradation, even under high humidity conditions, which is attributed to the presence of unsaturated metal sites (MOF defects). However, the correlation between MOF defects and catalytic ozone remains ambiguous, and a general approach for the controllable synthesis of high-performance MOF structures is currently lacking. Herein, different defective UiO-66 materials with cluster or ligand defects were obtained by precisely controlling small molecular acid modulators. Their catalytic performance can be analyzed in real time through the specific cataluminescence (CTL) signal of ozone at the interface. The presence of ligand defects was found to be crucial for both catalytic degradation and luminescence of ozone, and the CTL signal exhibited a positive correlation with the endogenous hydroxyl group content in the material (R2 = 0.982), while external humidity further supplemented internal water molecules within the material. Furthermore, theoretical calculations were conducted to compare the adsorption behaviors of ozone on the defective UiO-66 under dry/wet conditions, leading to the proposal of two potential reaction pathways. Subsequently, UiO-66-DA with superior catalytic performance was employed to develop a highly efficient CTL sensor capable of accurately detecting ozone (LOD = 23.3 ppb). This study held significant value in elucidating the reaction site of ozone on MOFs and achieving optimal catalytic effects through the careful selection of modulators and humidity levels.

Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic Framework-based Catalysts

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li-S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li-S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal-organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S8 →Li2 S4 , while the missing cluster defects can catalyze the reaction of Li2 S4 →Li2 S, so as to effectively inhibit the shuttle effect. Hence, the Li-S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g-1 delivers a capacity of 1087 mAh g-1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm-2 and E/S=3.9 mL g-1 , an areal capacity of 10.4 mAh cm-2 for 45 cycles can still be obtained.

Growth and Local Structures of Single Crystalline Flakes of Three-Dimensional Covalent Organic Frameworks in Water

Due to the enormous chemical and structural diversities and designable properties and functionalities, covalent organic frameworks (COFs) hold great promise as tailored materials for industrial applications in electronics, biology, and energy technologies. They were typically obtained as partially crystalline materials, although a few single-crystal three-dimensional (3D) COFs have been obtained recently with structures probed by diffraction techniques. However, it remains challenging to grow single-crystal COFs with controlled morphology and to elucidate the local structures of 3D COFs, imposing severe limitations on the applications and understanding of the local structure-property correlations. Herein, we develop a method for designed growth of five types of single crystalline flakes of 3D COFs with controlled morphology, front crystal facets, and defined edge structures as well as surface chemistry using surfactants that can be self-assembled into layered structures to confine crystal growth in water. The flakes enable direct observation of local structures including monomer units, pore structure, edge structure, grain boundary, and lattice distortion of 3D COFs as well as gradually curved surfaces in kinked but single crystalline 3D COFs with a resolution of up to ∼1.7 Å. In comparison with flakes of two-dimensional crystals, the synthesized flakes show much higher chemical, mechanical, and thermal stability.

Analysis and Refinement of Host-Guest Interactions in Metal-Organic Frameworks

ConspectusMetal-organic frameworks (MOFs) are a class of hybrid porous materials characterized by their periodic assembly using metal ions and organic ligands through coordination bonds. Their high crystallinity, extensive surface area, and adjustable pore sizes make them promising candidates for a wide array of applications. These include gas adsorption and separation, substrate binding, and catalysis, of relevance to tackling pressing global issues such as climate change, energy challenges, and pollution. In comparison to traditional porous materials such as zeolites and activated carbons, the design flexibility of organic ligands in MOFs, coupled with their orderly arrangement with associated metal centers, allows for the precise engineering of uniform pore environments. This unique feature enables a rich variety of interactions between the MOF host and adsorbed gas molecules, which are fundamental to understanding the observed uptake capacity and selectivity for target gas molecules and thus the overall performance of the material.In this Account, a data set for three-dimensional MOFs has been constructed based upon the structural analysis of host-guest interactions using the largest experimental database, the Cambridge Structural Database (CSD). A full screening was performed on structures with guest molecules of H2, C2H2, CO2, and SO2, and the relationship between the primary binding site, the isosteric heats of adsorption (Qst), and the adsorption uptake was extracted and established. We review the methodologies to refine host-guest interactions based primarily on our studies on the host-guest chemistry of MOFs. The methods include ligand functionalization, variation of metal centers, formation of defects, addition of single atom sites, and control of pore size and structure. In situ structural and dynamic investigations using diffraction and spectroscopic techniques are powerful tools to visualize the details of host-guest interactions upon the above modifications, affording key insights into functional performance at a molecular level. Finally, we give an outlook of future research priorities in the study of host-guest chemistry in MOF materials. We hope this Account will encourage the rational development and improvement of future MOF-based sorbents for applications in challenging gas adsorption, separations, and catalysis.

Metal-organic framework template-guided electrochemical lithography on substrates for SERS sensing applications

The templating method holds great promise for fabricating surface nanopatterns. To enhance the manufacturing capabilities of complex surface nanopatterns, it is important to explore new modes of the templates beyond their conventional masking and molding modes. Here, we employed the metal-organic framework (MOF) microparticles assembled monolayer films as templates for metal electrodeposition and revealed a previously unidentified guiding growth mode enabling the precise growth of metallic films exclusively underneath the MOF microparticles. The guiding growth mode was induced by the fast ion transportation within the nanochannels of the MOF templates. The MOF template could be repeatedly used, allowing for the creation of identical metallic surface nanopatterns for multiple times on different substrates. The MOF template-guided electrochemical growth mode provided a robust route towards cost-effective fabrication of complex metallic surface nanopatterns with promising applications in metamaterials, plasmonics, and surface-enhanced Raman spectroscopy (SERS) sensing fields.

Applications of Transmission Electron Microscopy in Phase Engineering of Nanomaterials

Phase engineering of nanomaterials (PEN) is an emerging field that aims to tailor the physicochemical properties of nanomaterials by precisely manipulating their crystal phases. To advance PEN effectively, it is vital to possess the capability of characterizing the structures and compositions of nanomaterials with precision. Transmission electron microscopy (TEM) is a versatile tool that combines reciprocal-space diffraction, real-space imaging, and spectroscopic techniques, allowing for comprehensive characterization with exceptional resolution in the domains of time, space, momentum, and, increasingly, even energy. In this Review, we first introduce the fundamental mechanisms behind various TEM-related techniques, along with their respective application scopes and limitations. Subsequently, we review notable applications of TEM in PEN research, including applications in fields such as metallic nanostructures, carbon allotropes, low-dimensional materials, and nanoporous materials. Specifically, we underscore its efficacy in phase identification, composition and chemical state analysis, in situ observations of phase evolution, as well as the challenges encountered when dealing with beam-sensitive materials. Furthermore, we discuss the potential generation of artifacts during TEM imaging, particularly in scanning modes, and propose methods to minimize their occurrence. Finally, we offer our insights into the present state and future trends of this field, discussing emerging technologies including four-dimensional scanning TEM, three-dimensional atomic-resolution imaging, and electron microscopy automation while highlighting the significance and feasibility of these advancements.

Intraparticle ripening to create hierarchically porous Ti-MOF single crystals for deep oxidative desulfurization

The catalytic oxidative desulfurization (ODS) technique is able to remove sulfur compounds from fuels, conducive to achieving deep desulfurization for the good of the ecological environment. Ti-based metal-organic frameworks (Ti-MOFs) possessing good affinity to organic reactants and considerable numbers of Ti active sites are promising catalysts for ODS. However, current Ti-MOFs suffer from severe diffusion limitations caused by the size mismatch between sole micropores and bulky sulfur compounds, leading to poor ODS performance. Here, a facile method of intraparticle ripening without any additive is developed to obtain hierarchically meso-microporous Ti-MIL-125 single crystals (Meso-Ti-MIL-125) for the first time. Such Meso-Ti-MIL-125 shows a BET surface area of 1401 m2 g-1 and a mesoporous volume that is 1.7 times as high as that of the conventional Ti-MIL-125. Our novel Meso-Ti-MIL-125 exhibits excellent catalytic performance in the ODS of a series of bulky thiophenic sulfur compounds, completely removing benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (DMDBT) from model fuels, which is, respectively, 2.4 times, 1.5 times, and 6.7 times higher than the removal achieved with conventional Ti-MIL-125. Such a facile synthetic strategy is envisioned to be applied in many kinds of crystalline materials, such as zeolites, for industrial production.

Anisotropic flexibility and rigidification in a TPE-based Zr-MOFs with scu topology

Tetraphenylethylene (TPE)-based ligands are appealing for constructing metal-organic frameworks (MOFs) with new functions and responsiveness. Here, we report a non-interpenetrated TPE-based scu Zr-MOF with anisotropic flexibility, that is, Zr-TCPE (H4TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene), remaining two anisotropic pockets. The framework flexibility is further anisotropically rigidified by installing linkers individually at specific pockets. By individually installing dicarboxylic acid L1 or L2 at pocket A or B, the framework flexibility along the b-axis or c-axis is rigidified, and the intermolecular or intramolecular motions of organic ligands are restricted, respectively. Synergistically, with dual linker installation, the flexibility is completely rigidified with the restriction of ligand motion, resulting in MOFs with enhanced stability and improved separation ability. Furthermore, in situ observation of the flipping of the phenyl ring and its rigidification process is made by 2H solid-state NMR. The anisotropic rigidification of flexibility in scu Zr-MOFs guides the directional control of ligand motion for designing stimuli-responsive emitting or efficient separation materials.

Geometric phase correction: A direct phase correction method to register low contrast noisy TEM images

A major challenge in the emerging field of low-dose electron microscopy lies in the development of drift correction algorithms against beam-induced specimen motion and compatible with highly noisy transmission electron microscopy (TEM) images. We report here a new drift correction method, namely geometric phase correlation (GPC), to correlate the specimen motion in real space by directly measuring the unwrapped geometric phase shift in the spatial frequency domain of the TEM image (especially from the intensive Bragg spots for crystalline materials) with sub-pixel precision. The GPC method outperforms cross-correlation-based methods in both accuracy of specimen motion prediction from highly noisy TEM movies and computational efficiency of drift calculation from abundant image frames, which holds great promise for diverse applications in low-dose TEM imaging of beam-sensitive materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs).

Rational design of stable functional metal-organic frameworks

Functional porous metal-organic frameworks (MOFs) have been explored for a number of potential applications in catalysis, chemical sensing, water capture, gas storage, and separation. MOFs are among the most promising candidates to address challenges facing our society related to energy and environment, but the successful implementation of functional porous MOF materials are contingent on their stability; therefore, the rational design of stable MOFs plays an important role towards the development of functional porous MOFs. In this Focus article, we summarize progress in the rational design and synthesis of stable MOFs with controllable pores and functionalities. The implementation of reticular chemistry allows for the rational top-down design of stable porous MOFs with targeted topological networks and pore structures from the pre-selected building blocks. We highlight the reticular synthesis and applications of stable MOFs: (1) MOFs based on high valent metal ions (e.g., Al3+, Cr3+, Fe3+, Ti4+ and Zr4+) and carboxylate ligands; (2) MOFs based on low valent metal ions (e.g., Ni2+, Cu2+, and Zn2+) and azolate linkers. We envision that the synthetic strategies, including modulated synthesis and post-synthetic modification, can potentially be extended to other more complex systems like metal-phosphonate framework materials.