Overcoming the Trade-Off between C2H2 Sorption and Separation Performance by Regulating Metal-Alkyne Chemical Interaction in Metal-Organic Frameworks

Designing porous materials for C₂H₂ purification and safe storage is essential research for industrial utilization. We emphatically regulate the metal-alkyne interaction of Pd^II and Pt^II on C₂H₂ sorption and C₂H₂/CO₂ separation in two isostructural NbO metal–organic frameworks (MOFs), Pd/Cu-PDA and Pt/Cu-PDA . The experimental investigations and systematic theoretical calculations reveal that Pd^II in Pd/Cu-PDA undergoes spontaneous chemical reaction with C₂H₂, leading to irreversible structural collapse and loss of C₂H₂/CO₂ sorption and separation. Contrarily, Pt^II in Pt/Cu-PDA shows strong di-σ bond interaction with C₂H₂ to form specific π-complexation, contributing to high C₂H₂ capture (28.7 cm³ g⁻¹ at 0.01 bar and 153 cm³ g⁻¹ at 1 bar). The reusable Pt/Cu-PDA efficiently separates C₂H₂ from C₂H₂/CO₂ mixtures with satisfying selectivity and C₂H₂ capacity (37 min g⁻¹). This research provides valuable insight into designing high-performance MOFs for gas sorption and separation.     

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B . Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H₂S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.     

Defect Engineered Metal–Organic Framework with Accelerated Structural Transformation for Efficient Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) have been increasingly applied in oxygen evolution reaction (OER), and the surface of MOFs usually undergoes structural transformation to form metal oxyhydroxides to serve as catalytically active sites. However, the controllable regulation of the reconstruction process of MOFs remains as a great challenge. Here we report a defect engineering strategy to facilitate the structural transformation of MOFs to metal oxyhydroxides during OER with enhanced activity. Defective MOFs (denoted as NiFc′_xFc_1-x) with abundant unsaturated metal sites are constructed by mixing ligands of 1,1′-ferrocene dicarboxylic acid (Fc′) and defective ferrocene carboxylic acid (Fc). NiFc′_xFc_1-x series are more prone to be transformed to metal oxyhydroxides compared with the non-defective MOFs (NiFc′). Moreover, the as-formed metal oxyhydroxides derived from defective MOFs contain more oxygen vacancies. NiFc′Fc grown on nickel foam exhibits excellent OER catalytic activity with an overpotential of 213 mV at the current density of 100 mA cm⁻², superior to that of undefective NiFc′. Experimental results and theoretical calculations suggest that the abundant oxygen vacancies in the derived metal oxyhydroxides facilitate the adsorption of oxygen-containing intermediates on active centers, thus significantly improving the OER activity.     

Single-Crystal Transformation Engineering the Spin Change of Metal–Organic Frameworks via Cluster Deconstruction

Spin crossover (SCO) materials with new architectures will expand and enrich the research in the SCO field. Here, we report two metal–organic frameworks (MOFs) containing tetradentate organic ligands and hexatopic linkers [Ag₈X₈(CN)₆]⁶⁻ (X=Br and I), which represents the first SCO MOF with clusters as building blocks. The silver halide cluster can be further removed after reacting with lithium tetracyanoquinodimethan (LiTCNQ). Such post-synthetic modification (PSM) is realized via single-crystal to single-crystal (SCSC) transformation from urk to nbo topology. Accordingly, the spin state and fluorescence properties are greatly modified by cluster deconstruction. Therefore, these achievements will provide new ideas for the design of new SCO systems and the development of PSM methods.     

Reticular Chemistry-Enabled Sonodynamic Activity of Covalent Organic Frameworks for Nanodynamic Cancer Therapy

The development of covalent organic framework (COF) sonosensitizers with intrinsic sonodynamic effects is highly desirable. However, such COFs are generally constructed using small-molecule photosensitizers. Herein, we report that the reticular chemistry-based synthesis of COFs from two inert monomers yields a COF-based sonosensitizer (TPE-NN) with inherent sonodynamic activity. Subsequently, a nanoscale COF TPE-NN is fabricated and embedded with copper (Cu)-coordinated sites to obtain TPE-NN-Cu. Results show that Cu coordination can enhance the sonodynamic effect of TPE-NN, whereas ultrasound (US) irradiation for sonodynamic therapy can augment the chemodynamic efficacy of TPE-NN-Cu. Consequently, TPE-NN-Cu upon US irradiation shows high-performance anticancer effects based on mutually reinforced sono-/chemo-nanodynamic therapy. This study reveals the backbone-originated sonodynamic activity of COFs and proposes a paradigm of intrinsic COF sonosensitizers for nanodynamic therapy.     

Integrated Cascade Nanozymes with Antisenescence Activities for Atherosclerosis Therapy

Senescent cells are the critical drivers of atherosclerosis formation and maturation. Mitigating senescent cells holds promise for the treatment of atherosclerosis. In an atherosclerotic plaque microenvironment, senescent cells interact with reactive oxygen species (ROS), promoting the disease development. Here, we hypothesize that a cascade nanozyme with antisenescence and antioxidant activities can serve as an effective therapeutic for atherosclerosis. An integrated cascade nanozyme with superoxide dismutase- and glutathione peroxidase-like activities, named MSe₁, is developed in this work. The obtained cascade nanozyme can attenuate human umbilical vein endothelial cell (HUVEC) senescence by protecting DNA from damage. It significantly weakens inflammation in macrophages and HUVECs by eliminating overproduced intracellular ROS. Additionally, the MSe₁ nanozyme effectively inhibits foam cell formation in macrophages and HUVECs by decreasing the internalization of oxidized low-density lipoprotein. After intravenous administration, the MSe₁ nanozyme significantly inhibits the formation of atherosclerosis in apolipoprotein E-deficient (ApoE^−/−) mice by reducing oxidative stress and inflammation and then decreases the infiltration of inflammatory cells and senescent cells in atherosclerotic plaques. This study not only provides a cascade nanozyme but also suggests that the combination of antisenescence and antioxidative stress holds considerable promise for treating atherosclerosis.     

Direct Assembly of Metal-Phenolic Network Nanoparticles for Biomedical Applications

Coordination assembly offers a versatile means to developing advanced materials for various applications. However, current strategies for assembling metal-organic networks into nanoparticles (NPs) often face challenges such as the use of toxic organic solvents, cytotoxicity because of synthetic organic ligands, and complex synthesis procedures. Herein, we directly assemble metal-organic networks into NPs using metal ions and polyphenols (i.e., metal-phenolic networks (MPNs)) in aqueous solutions without templating or seeding agents. We demonstrate the role of buffers (e.g., phosphate buffer) in governing NP formation and the engineering of the NP physicochemical properties (e.g., tunable sizes from 50 to 270 nm) by altering the assembly conditions. A library of MPN NPs is prepared using natural polyphenols and various metal ions. Diverse functional cargos, including anticancer drugs and proteins with different molecular weights and isoelectric points, are readily loaded within the NPs for various applications (e.g., biocatalysis, therapeutic delivery) by direct mixing, without surface modification, owing to the strong affinity of polyphenols to various guest molecules. This study provides insights into the assembly mechanism of metal-organic complexes into NPs and offers a simple strategy to engineer nanosized materials with desired properties for diverse biotechnological applications.     

Solar-to-H2O2 Catalyzed by Covalent Organic Frameworks

Benefiting from the excellent structural tunability, robust framework, ultrahigh porosity, and rich active sites, covalent organic frameworks (COFs) are widely recognized as promising photocatalysts in chemical conversions, and emerged in the hydrogen peroxide (H₂O₂) photosynthesis in 2020. H₂O₂, serving as an environmental-friendly oxidant and a promising liquid fuel, has attracted increasing researchers to explore its potential. Over the past few years, numerous COFs-based photocatalysts are developed with encouraging achievements in H₂O₂ production, whereas no comprehensive review articles exist to summarize this specific and significant area. Herein we provide a systematic overview of the advances and challenges of COFs in photocatalytic H₂O₂ production. We first introduce the priorities of COFs in H₂O₂ photosynthesis. Then, various strategies to improve COFs photocatalytic efficiency are discussed. The perspective and outlook for future advances of COFs in this emerging field are finally offered. This timely review will pave the way for the development of highly efficient COFs photocatalysts for practical production of value-added chemicals not limited to H₂O₂.     

Selectivity Control in the Direct CO Esterification over Pd@UiO-66: The Pd Location Matters

The selectivity control of Pd nanoparticles (NPs) in the direct CO esterification with methyl nitrite toward dimethyl oxalate (DMO) or dimethyl carbonate (DMC) remains a grand challenge. Herein, Pd NPs are incorporated into isoreticular metal–organic frameworks (MOFs), namely UiO-66-X (X=-H, -NO₂, -NH₂), affording Pd@UiO-66-X, which unexpectedly exhibit high selectivity (up to 99 %) to DMC and regulated activity in the direct CO esterification. In sharp contrast, the Pd NPs supported on the MOF, yielding Pd/UiO-66, displays high selectivity (89 %) to DMO as always reported with Pd NPs. Both experimental and DFT calculation results prove that the Pd location relative to UiO-66 gives rise to discriminated microenvironment of different amounts of interface between Zr-oxo clusters and Pd NPs in Pd@UiO-66 and Pd/UiO-66, resulting in their distinctly different selectivity. This is an unprecedented finding on the production of DMC by Pd NPs, which was previously achieved by Pd(II) only, in the direct CO esterification.     

Embedding Hydrogen Atom Transfer Moieties in Covalent Organic Frameworks for Efficient Photocatalytic C−H Functionalization

Covalent organic frameworks (COFs) have emerged as efficient heterogeneous photocatalysts for a wide range of relatively simple organic reactions, whereas their application in complex organic transformations, like site-selective functionalization of unactivated C−H bonds, is underexplored, which can be mainly attributed to the lack of highly active organophotocatalytic cores. Herein through bonding oxygen atoms at the N-terminus of quinolines in nonsubstituted quinoline-linked COFs (NQ−COFs), we successfully realized the embedding of active hydrogen atom transfer (HAT) moieties into the skeleton of COFs. This novel designed COF (NQ−COF_E5−O), serving as both an excellent photosensitizer and HAT catalyst, exhibited much higher efficiency in C−H functionalization than the corresponding NQ−COF_E5. Specially, we evaluated the photocatalytic performance of NQ−COF_E5−O on ten different substrates, including quinolines, benzothiazole, and benzoxazole, all of which were transferred to desired products in moderate to high yields (up to 93 %). Furthermore, the as-synthesized NQ−COF_E5−O displayed excellent photostability and could be reused with negligible loss of activity for five catalytic cycles.