Creating hierarchical pores in metal-organic frameworks via postsynthetic reactions

Hierarchically porous MOF@COF structures with ultrafast gas diffusion rate for C2H6/C2H4 separation

For ethylene purification, C2H6-selective metal-organic frameworks (MOFs) show great potential to directly produce polymer-grade C2H4 from C2H6/C2H4 mixtures. Most C2H6-traping MOFs are ultra-microporous structures so as to strengthen multiple supramolecular interactions with C2H6. However, the narrowed pore channels of C2H6-traping MOFs cause large guest diffusion barriers, greatly hampering their practical applications. Herein, we present a feasible strategy by precisely constructing hierarchically porous MOF@COF core-shell structures to address this issue. Additional mesoporous diffusion channels were incorporated between MOF crystals through the construction of the COF shell, thereby enhancing the gas adsorption kinetics. Notably, designing a core-shell MOF@COF structure with an optimal coating amount of mesoporous COF shell will further improve the gas diffusion rate. Breakthrough experiments reveal that the tailored MOF@COF composites can effectively achieve C2H6/C2H4 separation and maintain its separation performance over five continuous measurement cycles. This investigation opens up a new avenue to solve the diffusion/transfer issues and provides more opportunities and potentials for MOF@COF composites in practical separation applications.

Mining for Metal-Organic Systems: Chemistry Frontiers of Th-, U-, and Zr-Materials

The conceptual framework presented in this Perspective overviews the design principles of innovative thorium-based materials that could address urgent needs of the medicinal, nuclear energy, and waste remediation sectors from the lens of zirconium and uranium analogs. We survey the intersections of Zr, Th, and U chemistry with a focus on how the intrinsic behavior of each metal translates to broader material properties, including, but not limited to, structural and topological diversity, preferential metal-ligand binding, and reactivity. On the example of several classes of materials, including organometallic complexes, polyoxometalates, and the primary focus of this Perspective, metal-organic frameworks (MOFs), the design principles that govern the preparation of Zr-, Th-, and U-compounds, including oxophilicity, variation in oxidation states, and stable coordination environments have been considered. Further, we highlight how the impact of the mentioned variables may shift throughout the progression from discrete molecular systems to extended structures. We discuss the common assumption that zirconium-organic materials are typically considered a close analog of thorium-based congeners in areas such as material design and preparation. Through consideration of fundamental chemistry principles, we shed light on the relationships between Zr-, Th-, and U-based materials and highlight how a critical analysis of their distinct properties can be used to target a desired material performance. As a result, we provide a detailed understanding of Th-based materials chemistry by anchoring their fundamental properties between two well-studied reference points, zirconium- and uranium-containing analogs.

"Hard" Emulsion-Induced Interface Super-Assembly: A General Strategy for Two-Dimensional Hierarchically Porous Metal-Organic Framework Nanoarchitectures

Two-dimensional (2D) hierarchically porous metal-organic framework (MOF) nanoarchitectures with tailorable meso-/macropores hold great promise for enhancing mass transfer kinetics, augmenting accessible active sites, and thereby boosting performance in heterogeneous catalysis. However, achieving the general synthesis of 2D free-standing MOF nanosheets with controllable hierarchical porosity and thickness remains a challenging task. Herein, we present an ingenious "hard" emulsion-induced interface super-assembly strategy for preparing 2D hierarchically porous UiO-66-NH2 nanosheets with highly accessible pore channels, tunable meso-/macropore sizes, and adjustable thicknesses. The methodology relies on transforming the geometric shape of oil droplet templates within appropriate oil-in-water emulsions from conventional zero-dimensional (0D) "soft" liquid spheres to 2D "hard" solid sheets below the oil's melting/freezing point. Subsequent surfactant exchange on the surface of 2D "hard" emulsions facilitates the heterogeneous nucleation and interfacial super-assembly of in situ formed mesostructured MOF nanocomposites, serving as structural units, in a loosely packed manner to produce 2D MOF nanosheets with multimodal micro/meso-/macroporous systems. Importantly, this strategy can be extended to prepare other 2D hierarchically porous MOF nanosheets by altering metal-oxo clusters and organic ligands. Benefiting from fast mass transfer and highly accessible Lewis acidic sites, the resultant 2D hierarchically porous UiO-66-NH2 nanosheets deliver a fabulous catalytic yield of approximately 96% on the CO2 cycloaddition of glycidyl-2-methylphenyl ether, far exceeding the yield of approximately 29% achieved using conventional UiO-66-NH2 microporous crystals. This "hard" emulsion-induced interface super-assembly strategy paves a new path toward the rational construction of elaborate 2D nanoarchitecture of hierarchical MOFs with tailored physicochemical properties for diverse potential applications.

Unlocking Efficiency: Minimizing Energy Loss in Electrocatalysts for Water Splitting

Catalysts play a crucial role in water electrolysis by reducing the energy barriers for hydrogen and oxygen evolution reactions (HER and OER). Research aims to enhance the intrinsic activities of potential catalysts through material selection, microstructure design, and various engineering techniques. However, the energy consumption of catalysts has often been overlooked due to the intricate interplay among catalyst microstructure, dimensionality, catalyst-electrolyte-gas dynamics, surface chemistry, electron transport within electrodes, and electron transfer among electrode components. Efficient catalyst development for high-current-density applications is essential to meet the increasing demand for green hydrogen. This involves transforming catalysts with high intrinsic activities into electrodes capable of sustaining high current densities. This review focuses on current improvement strategies of mass exchange, charge transfer, and reducing electrode resistance to decrease energy consumption. It aims to bridge the gap between laboratory-developed, highly efficient catalysts and industrial applications regarding catalyst structural design, surface chemistry, and catalyst-electrode interplay, outlining the development roadmap of hierarchically structured electrode-based water electrolysis for minimizing energy loss in electrocatalysts for water splitting.

One-Step Butadiene Purification in a Sulfonate-Functionalized Metal-Organic Framework through Synergistic Separation Mechanism

Porous materials that could recognize specific molecules from complex mixtures are of great potential in improving the current energy-intensive multistep separation processes. However, due to the highly similar structures and properties of the mixtures, the design of desired porous materials remains challenging. Herein, a sulfonate-functionalized metal-organic framework ZU-609 with suitable pore size and pore chemistry is designed for 1,3-butadiene (C4H6) purification from complex C4 mixtures. The sulfonate anions decorated in the channel achieve selective recognition of C4H6 from other C4 olefins with subtle polarity differences through C-H⋅⋅⋅O-S interactions, affording recorded C4H6/trans-2-C4H8 selectivity (4.4). Meanwhile, the shrunken mouth of the channel with a suitable pore size (4.6 Å) exhibits exclusion effect to the larger molecules cis-2-C4H8, iso-C4H8, n-C4H10 and iso-C4H10. Benefiting from the moderate C4 olefins binding affinity exhibited by sulfonate anions, the adsorbed C4H6 could be easily regenerated near ambient conditions. Polymer-grade 1,3-butadiene (99.5 %) is firstly obtained from 7-component C4 mixtures via one adsorption-desorption cycle. The work demonstrates the great potential of synergistic recognition of size-sieving and thermodynamically equilibrium in dealing with complex mixtures.

Deep learning and big data mining for Metal-Organic frameworks with high performance for simultaneous desulfurization and carbon capture

Carbon capture and desulfurization of flue gases are crucial for the achievement of carbon neutrality and sustainable development. In this work, the "one-step" adsorption technology with high-performance metal-organic frameworks (MOFs) was proposed to simultaneously capture the SO2 and CO2. Four machine learning algorithms were used to predict the performance indicators (NCO2+SO2, SCO2+SO2/N2, and TSN) of MOFs, with Multi-Layer Perceptron Regression (MLPR) showing better performance (R2 = 0.93). To address sparse data of MOF chemical descriptors, we introduced the Deep Factorization Machines (DeepFM) model, outperforming MLPR with a higher R2 of 0.95. Then, sensitivity analysis was employed to find that the adsorption heat and porosity were the key factors for SO2 and CO2 capture performance of MOF, while the influence of open alkali metal sites also stood out. Furthermore, we established a kinetic model to batch simulate the breakthrough curves of TOP 1000 MOFs to investigate their dynamic adsorption separation performance for SO2/CO2/N2. The TOP 20 MOFs screened by the dynamic performance highly overlap with those screened by the static performance, with 76 % containing open alkali metal sites. This integrated approach of computational screening, machine learning, and dynamic analysis significantly advances the development of efficient MOF adsorbents for flue gas treatment.

Sulfonate Functional Ultramicroporous Materials with Suitable Pore Size and Layer-Stacked Structure for C4 Olefins Purification

Selective recognition of 1,3-butadiene from complex olefin isomers is vital for 1,3-butadiene purification, but the lack of porous materials with suitable pore structures results in poor selectivity and low capacity in C4 olefin separation. Herein, two sulfonate-functionalized organic frameworks, ZU-601 and ZU-602, are designed and show impressive separation performance toward C4 olefins. Benefiting from the suitable aperture size caused by the flexibility of coordinated organic ligand, ZU-601, ZU-602 that are pillared with different sulfonate anions could discriminate C4 olefin isomers with high uptake ratio: 1,3-butadiene/1-butene (207), 1,3-butadiene/trans-2-butene (10.1). Meanwhile, their layer-stacked structure enables the utilization of both intra- and interlayer space, enhancing the accommodation of guest molecules. ZU-601 exhibits record high 1,3-butadiene adsorption capacity of 2.90 mmol g-1 (0.5 bar, 298 K) among the reported flexible porous materials with high 1,3-butadiene/1-butene selectivity. The breakthrough experiments confirm their superior separation ability even for all five C4 olefin isomers, and the molecular-level structural change is well elucidated via powder, crystal analysis, and simulation studies. The work provides ideas toward advanced materials design with simultaneous high separation capacity and high separation selectivity for challenging separations.

UiO-66 nanoparticles combat influenza A virus in mice by activating the RIG-I-like receptor signaling pathway

The Influenza A virus (IAV) is a zoonotic pathogen that infects humans and various animal species. Infection with IAV can cause fever, anorexia, and dyspnea and is often accompanied by pneumonia characterized by an excessive release of cytokines (i.e., cytokine storm). Nanodrug delivery systems and nanoparticles are a novel approach to address IAV infections. Herein, UiO-66 nanoparticles (NPs) are synthesized using a high-temperature melting reaction. The in vitro and in vivo optimal concentrations of UiO-66 NPs for antiviral activity are 200 μg mL-1 and 60 mg kg-1, respectively. Transcriptome analysis revealed that UiO-66 NPs can activate the RIG-I-like receptor signaling pathway, thereby enhancing the downstream type I interferon antiviral effect. These NPs suppress inflammation-related pathways, including the FOXO, HIF, and AMPK signaling pathways. The inhibitory effect of UiO-66 NPs on the adsorption and entry of IAV into A549 cells is significant. This study presents novel findings that demonstrate the effective inhibition of IAV adsorption and entry into cells via UiO-66 NPs and highlights their ability to activate the cellular RIG-I-like receptor signaling pathway, thereby exerting an anti-IAV effect in vitro or in mice. These results provide valuable insights into the mechanism of action of UiO-66 NPs against IAV and substantial data for advancing innovative antiviral nanomedicine.

Copper-decorated strategy based on defect-rich NH2-MIL-125(Ti) boosts efficient photocatalytic degradation of methyl mercaptan under sunlight

Photocatalysis has received significant attention as a technology that can solve environmental problems. Metal-organic frameworks are currently being used as novel photocatalysts but are still limited by the rapid recombination of photogenerated carriers, low photogenerated electron migration efficiency and poor solar light utilization rate. In this work, a novel photocatalyst was successfully constructed by introducing Cu species into thermal activated mixed-ligand NH2-MIL-125 (Ti) via defect engineering strategy. The constructed defect structure not only provided 3D-interconnected gas transfer channels, but also offered suitable space to accommodate introduced Cu species. For the most effective photocatalyst 0.2Cu/80%NH2-MIL-125 (300 °C) with optimized Cu content, the photocatalytic degradation rate of CH3SH achieved 4.65 times higher than that of pristine NH2-MIL-125 under visible light (λ > 420 nm). At the same time, it showed great degradation efficiency under natural sunlight, 100 ppm CH3SH was completely removed within 25 min in full solar light illumination. The improved catalytic efficiency is mainly due to the synergistic effect of the integrated Schottky junction and rich-defective NH2-MIL-125, which improved the bandgap and band position, and thus facilitated the separation and transfer of the photo-generated carriers. This work provided a facile way to integrate Schottky junctions and rich-defective MOFs with high stability. Due to its excellent degradation performance under sunlight, it also offered a prospective strategy for rational design of high-efficiency catalysts applied in environmental technologies.

Sulfonated vitamin K3 mediated bimetallic metal-organic framework for multistage augmented cancer therapy

Chemodynamic therapy (CDT) relying on Fenton reaction has emerged as a promising strategy for tumor treatment. However, its clinical efficacy is hindered by the inadequate reactive oxygen species (ROS) and the potential cytotoxicity towards normal cells. To address these challenges, we have successfully developed a multistage augmented cancer therapy system based on bimetallic metal-organic framework (BMOF) that amplifies ROS and facilitates tumor-specific therapeutic effects. By employing a simple one-pot self-assembly approach, we synthesized SVK3@ZnCo-ZIF in which sulfonated vitamin K3 (SVK3) was encapsulated within ZnCo-ZIF BMOF. The results revealed that the incorporation of Zn atoms significantly diluted the Fenton activity of Co atoms towards normal cells. Notably, SVK3@ZnCo-ZIF underwent pH-controlled decomposition triggered by the tumor microenvironment (TME), thus releasing SVK3, Co2+ and Zn2+. Specifically, the H2O2 levels in tumors was effectively elevated by the interaction of SVK3 with NAD(P)H quinone oxidoreductase-1 (NQO-1). It thus enhanced the Fenton activity of Co2+. Moreover, the release of Zn2+ ions can induce cellular dysfunction and mitochondrial damage, thereby promoting the generation of ROS and subsequent cell death. The synergistic combination of CDT, SVK3 chemotherapy, and Zn2+-interfered therapy greatly facilitated apoptosis of tumor cells. Collectively, our investigations demonstrate the efficacy of such system in selectively inducing toxicity in cancer cells while minimizing detrimental effects on normal cells.

A facile dual-template-directed successive assembly approach to hollow multi-shell mesoporous metal-organic framework particles

Hollow multi-shell mesoporous metal-organic framework (MOF) particles with accessible compartmentalization environments, plentiful heterogeneous interfaces, and abundant framework diversity are expected to hold great potential for catalysis, energy conversion, and biotechnology. However, their synthetic methodology has not yet been established. In this work, a facile dual-template-directed successive assembly approach has been developed for the preparation of monodisperse hollow multi-shell mesoporous MOF (UiO-66-NH2) particles through one-step selective etching of successively grown multi-layer MOFs with alternating two types of mesostructured layers. This strategy enables the preparation of hollow multi-shell mesoporous UiO-66-NH2 nanostructures with controllable shell numbers, accessible mesochannels, large pore volume, tunable shell thickness and chamber sizes. The methodology relies on creating multiple alternating layers of two different mesostructured MOFs via dual-template-directed successive assembly and their difference in framework stability upon chemical etching. Benefiting from the highly accessible Lewis acidic sites and the accumulation of reactants within the multi-compartment architecture, the resultant hollow multi-shell mesoporous UiO-66-NH2 particles exhibit enhanced catalytic activity for CO2 cycloaddition reaction. The dual-template-directed successive assembly strategy paves the way toward the rational construction of elaborate hierarchical MOF nanoarchitectures with specific physical and chemical features for different applications.

Breaking the photoswitch speed limit

The forthcoming generation of materials, including artificial muscles, recyclable and healable systems, photochromic heterogeneous catalysts, or tailorable supercapacitors, relies on the fundamental concept of rapid switching between two or more discrete forms in the solid state. Herein, we report a breakthrough in the "speed limit" of photochromic molecules on the example of sterically-demanding spiropyran derivatives through their integration within solvent-free confined space, allowing for engineering of the photoresponsive moiety environment and tailoring their photoisomerization rates. The presented conceptual approach realized through construction of the spiropyran environment results in ~1000 times switching enhancement even in the solid state compared to its behavior in solution, setting a record in the field of photochromic compounds. Moreover, integration of two distinct photochromic moieties in the same framework provided access to a dynamic range of rates as well as complementary switching in the material's optical profile, uncovering a previously inaccessible pathway for interstate rapid photoisomerization.

A general large-scale synthesis approach for crystalline porous materials

Crystalline porous materials such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs) and porous organic cages (POCs) have been widely applied in various fields with outstanding performances. However, the lack of general and effective methodology for large-scale production limits their further industrial applications. In this work, we developed a general approach comprising high pressure homogenization (HPH), which can realize large-scale synthesis of crystalline porous materials including COFs, MOFs, and POCs under benign conditions. This universal strategy, as illustrated in the proof of principle studies, has prepared 4 COFs, 4 MOFs, and 2 POCs. It can circumvent some drawbacks of existing approaches including low yield, high energy consumption, low efficiency, weak mass/thermal transfer, tedious procedures, poor reproducibility, and high cost. On the basis of this approach, an industrial homogenizer can produce 0.96 ~ 580.48 ton of high-performance COFs, MOFs, and POCs per day, which is unachievable via other methods.

Turning on Asymmetric Catalysis of Achiral Metal-Organic Frameworks by Imparting Chiral Microenvironment

The development of heterogeneous asymmetric catalysts has attracted increasing interest in synthetic chemistry but mostly relies on the immobilization of homogeneous chiral catalysts. Herein, a series of chiral metal-organic frameworks (MOFs) have been fabricated by anchoring similar chiral hydroxylated molecules (catalytically inactive) with different lengths onto Zr-oxo clusters in achiral PCN-222(Cu). The resulting chiral MOFs exhibit regulated enantioselectivity up to 83 % ee in the asymmetric ring-opening of cyclohexene oxide. The chiral molecules furnished onto the catalytic Lewis sites in the MOF create multilevel microenvironment, including the hydrogen interaction between the substrate and the chiral -OH group, the steric hindrance endowed by the benzene ring on the chiral molecules, and the proximity between the catalytic sites and chiral molecules confined in the MOF pores, which play crucial roles and synergistically promote chiral catalysis. This work nicely achieves heterogeneous enantioselective catalysis by chiral microenvironment modulation around Lewis acid sites.

Controlled Partial Linker Thermolysis in Metal-Organic Framework UiO-66-NH2 to Give a Single-Site Copper Photocatalyst for the Functionalization of Terminal Alkynes

Metal-organic frameworks (MOFs) with expanding porosity and tailored pore environments are intriguing for catalytic applications. We report herein a straightforward method of controlled partial linker thermolysis to introduce desirable mesopores into mono-ligand MOFs, which is different from the classical thermolyzing method that starts from mixed-linker MOFs. UiO-66-NH2 , after partial ligand thermolysis, exhibits significant mesoporosity, retained crystal structure, improved charge photogeneration and abundant anchoring sites, which is ideal to explore single-site photocatalysis. Atomically dispersed Cu is then accommodated in the tailored pore. The resulting single-site Cu catalyst exhibits excellent performance for photocatalytic alkylation and oxidation coupling for the functionalization of terminal alkynes. The study highlights the advantage of controlled partial linker thermolysis to synthesize hierarchical MOFs to achieve the advanced single-site photocatalysis.

Tailoring the Nanoporosity and Photoactivity of Metal-Organic Frameworks With Rigid Dye Modulators for Toluene Purification

Facile synthesis of hierarchically porous metal-organic frameworks (MOFs) with adjustable porosity and high crystallinity attracts great attention yet remains challenging. Herein, a micromolar amount of dye-based modulator (Rhodamine B (RhB)) is employed to easily and controllably tailor the pore size of a Ti-based metal-organic framework (MIL-125-NH2 ). The RhB used in this method is easily removed by washing or photodegradation, avoiding secondary posttreatment. It is demonstrated that the carboxyl functional group and the steric effects of RhB are indispensable for enlarging the pore size of the MIL-125-NH2 . The resulting hierarchically porous MIL-125-NH2 (RH-MIL-125-NH2 ) exhibits optimized adsorption and photocatalytic activity because the newly formed mesopore with defects concurrently facilitates mass transport of guest molecules (toluene) and photogenerated charge separation. This work offers a meaningful basis for the construction of hierarchically porous MOFs and demonstrates the superiority of the hierarchical pore structure for adsorption and heterogeneous catalysis.

Metal-Organic Frameworks for Greenhouse Gas Applications

Using petrol to supply energy for a car or burning coal to heat a building generates plenty of greenhouse gas (GHG) emissions, including carbon dioxide (CO₂ ), water vapor (H₂ O), methane (CH₄ ), nitrous oxide (N₂ O), ozone (O₃ ), fluorinated gases. These up-and-coming metal-organic frameworks (MOFs) are structurally endowed with rigid inorganic nodes and versatile organic linkers, which have been extensively used in the GHG-related applications to improve the lives and protect the environment. Porous MOF materials and their derivatives have been demonstrated to be competitive and promising candidates for GHG separation, storage and conversions as they shows facile preparation, large porosity, adjustable nanostructure, abundant topology, and tunable physicochemical property. Enormous progress has been made in GHG storage and separation intrinsically stemmed from the different interaction between guest molecule and host framework from MOF itself in the recent five years. Meanwhile, the use of porous MOF materials to transform GHG and the influence of external conditions on the adsorption performance of MOFs for GHG are also enclosed. In this review, it is also highlighted that the existing challenges and future directions are discussed and envisioned in the rational design, facile synthesis and comprehensive utilization of MOFs and their derivatives for practical applications.