The MOF-driven synthesis of supported palladium clusters with catalytic activity for carbene-mediated chemistry

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.

Translocation and Confinement of Tetraamines in Adaptable Microporous Cavities

Metal-Organic Frameworks can be grafted with amines by coordination to metal vacancies to create amine-appended solid adsorbents, which are being considered as an alternative to using aqueous amine solutions for CO2 capture. In this study, we propose an alternative mechanism that does not rely on the use of neutral metal vacancies as binding sites but is enabled by the structural adaptability of heterobimetallic Ti2Ca2 clusters. The combination of hard (Ti4+) and soft (Ca2+) metal centers in the inorganic nodes of the framework enables MUV-10 to adapt its pore windows to the presence of triethylenetetramine molecules. This dynamic cluster response facilitates the translocation and binding of tetraamine inside the microporous cavities to enable the formation of bis-coordinate adducts that are stable in water. The extension of this grafting concept from MUV-10 to larger cavities not restrictive to CO2 diffusion will complement other strategies available for the design of molecular sorbents for decarbonization applications.

Copper-Vit B3 MOF preparation, characterization and catalytic evaluation in a one-pot synthesis of benzoxanthenones with docking validation as anti H. pylori

Copper-Vit B3 MOF was successfully prepared by efficient and eco hydrothermal method. The prepared MOF was characterized as a tetragonal crystal copper-MOF nanoparticles by FTIR, SEM, TEM, EDX and XRD. The prepared nanoparticles were used as an effective, inexpensive and low-toxic catalyst in the one-pot synthesis of some new benzoxanthenone derivatives. As example 4-(9,9-dimethyl-11-oxo-8,10,11,12-tetrahydro-9H-benzo[a]xanthen-12-yl)phenyl benzoate (4h) was synthesized in high yield 92%. The MOF catalyst's role is activating the nucleophilic attack by increasing the carbonyl polarization, and this generally improves the reaction time, which ranges between 20-60 minutes and products' yields ranging between 80-92%. Prepared compounds (4a-4j) undergo molecular docking scanning as Helicobacter pylori type II dehydroquinase inhibitors, and the data obtained showed that there are three promises of the prepared compounds 4d, 4e, 4h and 4j compared with amoxicillin.

Recent advances in atomic cluster synthesis: a perspective from chemical elements

Despite its potential significance, "cluster chemistry" remains a somewhat marginalized topic within the chemistry field. However, atomic clusters with their unusual and unique structures and properties represent a novel material group situated between molecules and nanoparticles or solid matter, judging from both scientific standpoints and historical backgrounds. Surveying an entire material group, including all substances that can be regarded as a cluster, is essential for establishing cluster chemistry as a more prominent chemistry field. This review aims to provide a comprehensive understanding by categorizing, summarizing, and reviewing clusters, focusing on their constituent elements in the periodic table. However, because numerous disparate synthetic processes have been individually developed to date, their straightforward and uniform classification is a challenging task. As such, comprehensively reviewing this field from a chemical composition viewpoint presents significant obstacles. It should be therefore noted that despite adopting a synthetic method-based classification in this review, the discussions presented herein could entail inaccuracies. Nevertheless, this unorthodox viewpoint unfolds a new scientific perspective which accentuates the common ground between different development processes by emphasizing the lack of a definitive border between their synthetic methods and material groups, thus opening new avenues for cementing cluster chemistry as an attractive chemistry field.

Metalation of metal-organic frameworks: fundamentals and applications

Metalation of metal-organic frameworks (MOFs) has been developed as a prominent strategy for materials functionalization for pore chemistry modulation and property optimization. By introducing exotic metal ions/complexes/nanoparticles onto/into the parent framework, many metallized MOFs have exhibited significantly improved performance in a wide range of applications. In this review, we focus on the research progress in the metalation of metal-organic frameworks during the last five years, spanning the design principles, synthetic strategies, and potential applications. Based on the crystal engineering principles, a minor change in the MOF composition through metalation would lead to leveraged variation of properties. This review starts from the general strategies established for the incorporation of metal species within MOFs, followed by the design principles to graft the desired functionality while maintaining the porosity of frameworks. Facile metalation has contributed a great number of bespoke materials with excellent performance, and we summarize their applications in gas adsorption and separation, heterogeneous catalysis, detection and sensing, and energy storage and conversion. The underlying mechanisms are also investigated by state-of-the-art techniques and analyzed for gaining insight into the structure-property relationships, which would in turn facilitate the further development of design principles. Finally, the current challenges and opportunities in MOF metalation have been discussed, and the promising future directions for customizing the next-generation advanced materials have been outlined as well.

The Promise and Potential of Metal-Organic Frameworks and Covalent Organic Frameworks in Vaccine Nanotechnology

The immune system's complexity and ongoing evolutionary struggle against deleterious pathogens underscore the value of vaccination technologies, which have been bolstering human immunity for over two centuries. Despite noteworthy advancements over these 200 years, three areas remain recalcitrant to improvement owing to the environmental instability of the biomolecules used in vaccines─the challenges of formulating them into controlled release systems, their need for constant refrigeration to avoid loss of efficacy, and the requirement that they be delivered via needle owing to gastrointestinal incompatibility. Nanotechnology, particularly metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), has emerged as a promising avenue for confronting these challenges, presenting a new frontier in vaccine development. Although these materials have been widely explored in the context of drug delivery, imaging, and cancer immunotherapy, their role in immunology and vaccine-related applications is a recent yet rapidly developing field. This review seeks to elucidate the prospective use of MOFs and COFs for biomaterial stabilization, eliminating the necessity for cold chains, enhancing antigen potency as adjuvants, and potentializing needle-free delivery of vaccines. It provides an expansive and critical viewpoint on this rapidly evolving field of research and emphasizes the vital contribution of chemists in driving further advancements.

Rapid and large-capacity adsorption of heterocyclic aromatic amines on heat resistant two-dimensional metal organic layer/cellulose nanofiber aerogels constructed by a thawing cross-linking strategy

Composite aerogels, formed by the combination of nanoscale polymers and highly efficient adsorbents, offer the potential to deploy adsorbent distinct separation properties into a processable matrix. This paper presents a method for the fabrication of low energy bio-aerogels with high ductility, excellent wet strength and favorable heat resistance, based on cellulose nanofibers (CNFs) bound by calcium carbonate particles (CaCO3) via a simple process of ice induction, cross-linking during freezing and freeze-drying. Due to induced defects, two-dimensional metal-organic layers (MOLs) were rich in mesoporous structure and embedded in the aerogel (AGCa-MOL), which exhibited a powerful adsorption capacity. AGCa-MOL could take full advantage of their hierarchical pores and available surface area to obtain high adsorption capacity (0.694-5.470 μmol/g) and rapid adsorption kinetics (5 min) for 14 heterocyclic aromatic amines (HAAs). Moreover, the CaCO3 particles and MOLs gave the AGCa-MOL excellent thermal stability, so that it could maintain excellent adsorption capacity at a high temperature (100 °C) and be applied as an adsorbent to remove HAAs in the boiling marinade. The intrinsic potential of composite aerogels was revealed due to the synergistic properties of the various components in the composite aerogel.

A zero-valent palladium cluster-organic framework

Acquiring spatial control of nanoscopic metal clusters is central to their function as efficient multi-electron catalysts. However, dispersing metal clusters on surfaces or in porous hosts is accompanied by an intrinsic heterogeneity that hampers detailed understanding of the chemical structure and its relation to reactivities. Tethering pre-assembled molecular metal clusters into polymeric, crystalline 2D or 3D networks constitutes an unproven approach to realizing ordered arrays of chemically well-defined metal clusters. Herein, we report the facile synthesis of a {Pd3} cluster-based organometallic framework from a molecular triangulo-Pd3(CNXyl)6 (Xyl = xylyl; Pd3) cluster under chemically mild conditions. The formally zero-valent Pd3 cluster readily engages in a complete ligand exchange when exposed to a similar, ditopic isocyanide ligand, resulting in polymerization into a 2D coordination network (Pd3-MOF). The structure of Pd3-MOF could be unambiguously determined by continuous rotation 3D electron diffraction (3D-ED) experiments to a resolution of ~1.0 Å (>99% completeness), showcasing the applicability of 3D-ED to nanocrystalline, organometallic polymers. Pd3-MOF displays Pd03 cluster nodes, which possess significant thermal and aerobic stability, and activity towards hydrogenation catalysis. Importantly, the realization of Pd3-MOF paves the way for the exploitation of metal clusters as building blocks for rigidly interlocked metal nanoparticles at the molecular limit.

From Simple Palladium(II) Monomers to 2D Heterometallic Sodium-Palladium(II) Coordination Networks with 2-Halonicotinates

The 2D heterometallic sodium-palladium(II) coordination polymers with 2-halonicotinates [2-chloropyridine-3-carboxylate (2-chloronicotinate), 2-Clnic- and 2-bromopyridine-3-carboxylate (2-bromonicotinate), 2-Brnic-], {[Na2(H2O)2(μ-H2O)4PdCl2(μ-2-Clnic-N:O')2]}n (1), and {[Na2(H2O)2(μ-H2O)4PdBr2(μ-2-Brnic-N:O')2]·2H2O}n (2) were prepared in aqueous solutions under the presence of NaHCO3, while palladium(II) monomers with the neutral 2-chloronicotinic and 2-bromonicotinic acid ligands, [PdCl2(2-ClnicH-N)2]·2DMF (3) and [PdCl2(2-BrnicH-N)2]·2DMF (4), were prepared in DMF/water mixtures (DMF = N,N'-dimethylformamide). The zigzag chains of water-bridged sodium ions are in turn bridged by [PdCl2(2-Clnic)2]2- moieties in 1 or by [PdBr2(2-Brnic)2]2- moieties in 2, leading to the formation of the infinite 2D coordination networks of 1 or 2. The DFT calculations showed the halosubstituents type (Cl vs Br) does not have an influence on the formation of either trans or cis isomers. The trans isomers were found in all reported compounds; being more stable for about 10 to 15 kJ mol-1. The 2D coordination networks 1 and 2 are more stabilized by the formation of Na-Ocarboxylate bonds, comparing to the stabilization of palladium(II) monomers 3 and 4 by hydrogen-bonding with DMF molecules. The difference in DFT calculated energy stabilization for 1 and 2 is ascribed to the type of halosubstituents and to the presence/absence of lattice water molecules in 1 and 2. The compounds show no antibacterial activity toward reference strains of Escherichia coli and Staphylococcus aureus bacteria and no antiproliferative activity toward bladder (T24) and lung (A549) cancer cell lines.

Atomic-Scale Elucidation of Unusually Distorted Dimeric Complexes Confined in a Zr-Based Metal-Organic Framework

Nanoconfinement in metal-organic framework (MOF) pores can lead to the isolation of unusual or reactive metal complexes. However, MOFs that support the stabilization and precise structural elucidation of metal complexes and small metal clusters are rare. Here, we report a thermally and chemically stable zirconium-based MOF (University of Adelaide Material-1001, UAM-1001) with a high density of free bis-pyrazolyl units that can confine mono- and dinuclear metal complexes. The precursor MOF, UAM-1000, has a high degree of structural flexibility, but post synthetic modification with a bracing linker, biphenyl-4,4'-dicarboxylic acid, partially rigidifies the MOF (UAM-1001). This allows "matrix isolation" and detailed structural elucidation of postsynthetically added dimeric complexes bound within a tetradentate binding site formed by two linkers. Dimeric species [Co2Cl4], [Cu2Cl4], [Ni2Cl3(H2O)2]Cl, and [Rh2(CO)3Cl2] were successfully isolated in UAM-1001 and characterized by single-crystal X-ray diffraction. Comparison of the UAM-1001 isolated species with similar complexes in the solid state reveals that UAM-1001 can significantly distort the structures and enforce notably shorter metal-metal distances. For example, MOF tethering allows isolation of a [Cu2Cl4] complex that rapidly reacts with water in the solid state. The stability, porosity, and modulated flexibility of UAM-1001 provide an ideal platform material for the isolation and study of new dimeric complexes and their reactivity.

Silver-Exchanged Zeolite Y Catalyzes a Selective Insertion of Carbenes into C-H and O-H Bonds

Commercially available zeolite Y modulates the catalytic activity and selectivity of ultrasmall silver species during the Buchner reaction and the carbene addition to methylene and hydroxyl bonds, by simply exchanging the counter cations of the zeolite framework. The zeolite acts as a macroligand to tune the silver catalytic site, enabling the use of this cheap and recyclable solid catalyst for the in situ formation of carbenes from diazoacetate and selective insertion in different C-H (i.e., cyclohexane) and C-O (i.e., water) bonds. The amount of catalyst in the reaction can be as low as ≤0.1 mol % silver. Besides, this reactivity allows deeply drying the HY zeolite framework by making the strongly adsorbed water molecules react with the in situ formed carbenes.

Advances in heterogeneous single-cluster catalysis

Heterogeneous single-cluster catalysts (SCCs) comprising atomically precise and isolated metal clusters stabilized on appropriately chosen supports offer exciting prospects for enabling novel chemical reactions owing to their broad structural diversity with unparalled opportunities for engineering their properties. Although the pioneering work revealed intriguing performance trends of size-selected metal clusters deposited on supports, synthetic and analytical challenges hindered a thorough understanding of surface chemistry under realistic conditions. This Review underscores the importance of considering the cluster environment in SCCs, encompassing the development of robust metal-support interactions, precise control over the ligand sphere, the influence of reaction media and dynamic behaviour, to uncover new reactivities. Through examples, we illustrate the criticality of tailoring the entire catalytic ensemble in SCCs to achieve stable and selective performance with practically relevant metal coverages. This expansion in application scope transcends from model reactions to complex and technically relevant reactions. Furthermore, we provide a perspective on the opportunities and future directions for SCC design within this rapidly evolving field.

Opportunities and Challenges of Metal-Organic Framework Micro/Nano Reactors for Cascade Reactions

Building bridges among different types of catalysts to construct cascades is a highly worthwhile pursuit, such as chemo-, bio-, and chemo-bio cascade reactions. Cascade reactions can improve the reaction efficiency and selectivity while reducing steps of separation and purification, thereby promoting the development of "green chemistry". However, compatibility issues in cascade reactions pose significant constraints on the development of this field, particularly concerning the compatibility of diverse catalyst types, reaction conditions, and reaction rates. Metal-organic framework micro/nano reactors (MOF-MNRs) are porous crystalline materials formed by the self-assembly coordination of metal sites and organic ligands, possessing a periodic network structure. Due to the uniform pore size with the capability of controlling selective transfer of substances as well as protecting active substances and the organic-inorganic parts providing reactive microenvironment, MOF-MNRs have attracted significant attention in cascade reactions in recent years. In this Perspective, we first discuss how to address compatibility issues in cascade reactions using MOF-MNRs, including structural design and synthetic strategies. Then we summarize the research progress on MOF-MNRs in various cascade reactions. Finally, we analyze the challenges facing MOF-MNRs and potential breakthrough directions and opportunities for the future.

Functionalization of polyethylene with hydrolytically-stable ester groups

Low-density (LD) and high-density polyethylene (HDPE), recycled or not, incorporates up to 7 wt% of ester groups after reacting either with ethyl diazoacetate (EDA) under catalytic and solvent free-reaction conditions, or with maleic anhydride (MA) and acrylates (AC) under catalytic radical conditions. The resulting upcycled polyethylene esters are hydrolytically stable at extreme pH (0-14) and can be further transformed into carboxylic acids, carboxylates, other esters and amides.

Tuning hydrogenation chemistry of Pd-based heterogeneous catalysts by introducing homogeneous-like ligands

Noble metals have been extensively employed in a variety of hydrotreating catalyst systems for their featured functionality of hydrogen activation but may also bring side reactions such as undesired deep hydrogenation. It is crucial to develop a viable approach to selectively inhibit side reactions while preserving beneficial functionalities. Herein, we present modifying Pd with alkenyl-type ligands that forms homogeneous-like Pd-alkene metallacycle structure on the heterogeneous Pd catalyst to achieve the selective hydrogenolysis and hydrogenation. Particularly, a doped alkenyl-type carbon ligand on Pd-Fe catalyst is demonstrated to donate electrons to Pd, creating an electron-rich environment that elongates the distance and weakens the electronic interaction between Pd and unsaturated C of the reactants/products to control the hydrogenation chemistry. Moreover, high H₂ activation capability is maintained over Pd and the activated H is transferred to Fe to facilitate C-O bond cleavage or directly participate in the reaction on Pd. The modified Pd-Fe catalyst displays comparable C-O bond cleavage rate but much higher selectivity (>90%) than the bare Pd-Fe (<50%) in hydrotreating of diphenyl ether (DPE, modelling the strongest C-O linkage in lignin) and enhanced ethene selectivity (>90%) in acetylene hydrogenation. This work sheds light on the controlled synthesis of selective hydrotreating catalysts via mimicking homogeneous analogues.

Ag2(0) dimers within a thioether-functionalized MOF catalyze the CO2 to CH4 hydrogenation reaction

Ultrasmall silver clusters in reduced state are difficult to synthesize since silver atoms tend to rapidly aggregate into bigger entities. Here, we show that dimers of reduced silver (Ag₂) are formed within the framework of a metal-organic framework provided with thioether arms in their walls (methioMOF), after reduction with NaBH₄ of the corresponding Ag⁺-methioMOF precursor. The resulting Ag₂-methioMOF catalyzes the methanation reaction of carbon dioxide (CO₂ to CH₄ hydrogenation reaction) under mild reaction conditions (1 atm CO₂, 4 atm H₂, 140 °C), with production rates much higher than Ag on alumina and even comparable to the state-of-the-art Ru on alumina catalyst (Ru-Al₂O₃) under these reaction conditions, according to literature results.

MOF-Triggered Synthesis of Subnanometer Ag02 Clusters and Fe3+ Single Atoms: Heterogenization Led to Efficient and Synergetic One-Pot Catalytic Reactions

The combination of well-defined Fe³⁺ isolated single-metal atoms and Ag₂ subnanometer metal clusters within the channels of a metal-organic framework (MOF) is reported and characterized by single-crystal X-ray diffraction for the first time. The resulting hybrid material, with the formula [Ag⁰₂(Ag⁰)_1.34Fe^III_0.66]@Na^I₂{Ni^II₄[Cu^II₂(Me₃mpba)₂]₃}·63H₂O (Fe³⁺Ag⁰₂@MOF), is capable of catalyzing the unprecedented direct conversion of styrene to phenylacetylene in one pot. In particular, Fe³⁺Ag⁰₂@MOF─which can easily be obtained in a gram scale─exhibits superior catalytic activity for the TEMPO-free oxidative cross-coupling of styrenes with phenyl sulfone to give vinyl sulfones in yields up to >99%, which are ultimately transformed, in situ, to the corresponding phenylacetylene product. The results presented here constitute a paradigmatic example of how the synthesis of different metal species in well-defined solid catalysts, combined with speciation of the true metal catalyst of an organic reaction in solution, allows the design of a new challenging reaction.

Covalent Organic Frameworks: Recent Progress in Biomedical Applications

Covalent organic frameworks (COFs) are a type of crystalline organic porous material with specific features and interesting structures, including porosity, large surface area, and biocompatibility. These features enable COFs to be considered as excellent candidates for applications in various fields. Recently, COFs have been widely demonstrated as promising materials for biomedical applications because of their excellent physicochemical properties and ultrathin structures. In this review, we cover the recent progress of COF materials for applications in photodynamic therapy, gene delivery, photothermal therapy, drug delivery, bioimaging, biosensing, and combined therapies. Moreover, the critical challenges and further perspectives with regards to COFs for future biology-facing applications are also discussed.

Metal-organic frameworks as chemical nanoreactors for the preparation of catalytically active metal compounds

Since the emergence of metal-organic frameworks (MOFs), a myriad of thrilling properties and applications, in a wide range of fields, have been reported for these materials, which mainly arise from their porous nature and rich host-guest chemistry. However, other important features of MOFs that offer great potential rewards have been only barely explored. For instance, despite the fact that MOFs are suitable candidates to be used as chemical nanoreactors for the preparation, stabilization and characterization of unique functional species, that would be hardly accessible outside the functional constrained space offered by MOF channels, only very few examples have been reported so far. In particular, we outline in this feature recent advances in the use of highly robust and crystalline oxamato- and oxamidato-based MOFs as reactors for the in situ preparation of well-defined catalytically active single atom catalysts (SACS), subnanometer metal nanoclusters (SNMCs) and supramolecular coordination complexes (SCCs). The robustness of selected MOFs permits the post-synthetic (PS) in situ preparation of the desired catalytically active metal species, which can be characterised by single-crystal X-ray diffraction (SC-XRD) taking advantage of its high crystallinity. The strategy highlighted here permits the always challenging large-scale preparation of stable and well-defined SACs, SNMCs and SCCs, exhibiting outstanding catalytic activities.

Parts-Per-Million of Soluble Pd0 Catalyze the Semi-Hydrogenation Reaction of Alkynes to Alkenes

The synthesis of cis-alkenes is industrially carried out by selective semi-hydrogenation of alkynes with complex Pd catalysts, which include the Lindlar catalyst (PdPb on CaCO₃) and c-Pd/TiS (colloidal ligand-protected Pd nanoparticles), among others. Here, we show that Pd⁰ atoms are generated from primary Pd salts (PdCl₂, PdSO₄, Pd(OH)₂, PdO) with H₂ in alcohol solutions, independently of the alkyne, to catalyze the semi-hydrogenation reaction with extraordinarily high efficiency (up to 735 s^-1), yield (up to 99%), and selectivity (up to 99%). The easy-to-prepare Pd⁰ species hold other potential catalytic applications.

Heterometallic palladium-iron metal-organic framework as a highly active catalyst for cross-coupling reactions

Palladium-based metal-organic frameworks (Pd-MOFs) are an emerging class of heterogeneous catalysts extremely challenging to achieve due to the facile leaching of palladium and its tendency to be reduced. Herein, Pd(ii) was successfully incorporated in the framework of a MOF denoted as MUV-22 using a solvent assisted reaction. This stable MOF, with square-octahedron (soc) topology as MIL-127, and a porosity of 710 m² g^-1, is highly active, selective, and recyclable for the Suzuki-Miyaura allylation of aryl and alkyl boronates as exemplified with the coupling between cinnamyl bromide and Me-Bpin, a typically reluctant reagent in cross-coupling reactions.

Defined metal atom aggregates precisely incorporated into metal-organic frameworks

Nanosized metal aggregates (MAs), including metal nanoparticles (NPs) and nanoclusters (NCs), are often the active species in numerous applications. In order to maintain the active form of MAs in "use", they need to be anchored and stabilised, preventing agglomeration. In this context, metal-organic frameworks (MOFs), which exhibit a unique combination of properties, are of particular interest as a tunable and porous matrix to host MAs. A high degree of control in the synthesis towards atom-efficient and application-oriented MA@MOF composites is required to derive specific structure-property relationships and in turn to enable design of functions on the molecular level. Due to the versatility of MA@MOF (derived) materials, their applications are not limited to the obvious field of catalysis, but increasingly include 'out of the box' applications, for example medical diagnostics and theranostics, as well as specialised (bio-)sensoring techniques. This review focuses on recent advances in the controlled synthesis of MA@MOF materials en route to atom-precise MAs. The main synthetic strategies, namely 'ship-in-bottle', 'bottle-around-ship', and approaches to achieve novel hierarchical MA@MOF structures are highlighted and discussed while identifying their potential as well as their limitations. Hereby, an overview of standard characterisation methods that enable a systematic analysis procedure and state-of-art techniques that localise MA within MOF cavities are provided. While the perspectives of MA@MOF materials in general have been reviewed various times in the recent past, few atom-precise MAs inside MOFs have been reported so far, opening opportunities for future investigation.

Advances in the Electrocatalytic Hydrogen Evolution Reaction by Metal Nanoclusters-based Materials

With the development of renewable energy systems, clean hydrogen is burgeoning as an optimal alternative to fossil fuels, in which its application is promising to retarding the global energy and environmental crisis. The hydrogen evolution reaction (HER), capable of producing high-purity hydrogen rapidly in electrocatalytic water splitting, has received much attention. Abundant research about HER has been done, focusing on advanced electrocatalyst design with high efficiency and robust stability. As potential HER catalysts, metal nanoclusters (MNCs) have been studied extensively. They are composed of several to a hundred metal atoms, with sizes being comparable to the Fermi wavelength of electrons, that is, < 2.0 nm. Different from metal atoms/nanoparticles, they exhibit unique catalytic properties due to their quantum size effect and low-coordination environment. In this review, the activity-enhancing approaches of MNCs applied in HER electrocatalysis are mainly summarized. Furthermore, recent progress in MNCs classified with different stabilization strategies, that is, the freestanding MNCs, MNCs with organic, metal and carbon supports, are introduced. Finally, the current challenges and deficiencies of these MNCs for HER are prospected.

Advances in Matrix-Supported Palladium Nanocatalysts for Water Treatment

Advanced catalysts are crucial for a wide range of chemical, pharmaceutical, energy, and environmental applications. They can reduce energy barriers and increase reaction rates for desirable transformations, making many critical large-scale processes feasible, eco-friendly, energy-efficient, and affordable. Advances in nanotechnology have ushered in a new era for heterogeneous catalysis. Nanoscale catalytic materials are known to surpass their conventional macro-sized counterparts in performance and precision, owing it to their ultra-high surface activities and unique size-dependent quantum properties. In water treatment, nanocatalysts can offer significant promise for novel and ecofriendly pollutant degradation technologies that can be tailored for customer-specific needs. In particular, nano-palladium catalysts have shown promise in degrading larger molecules, making them attractive for mitigating emerging contaminants. However, the applicability of nanomaterials, including nanocatalysts, in practical deployable and ecofriendly devices, is severely limited due to their easy proliferation into the service environment, which raises concerns of toxicity, material retrieval, reusability, and related cost and safety issues. To overcome this limitation, matrix-supported hybrid nanostructures, where nanocatalysts are integrated with other solids for stability and durability, can be employed. The interaction between the support and nanocatalysts becomes important in these materials and needs to be well investigated to better understand their physical, chemical, and catalytic behavior. This review paper presents an overview of recent studies on matrix-supported Pd-nanocatalysts and highlights some of the novel emerging concepts. The focus is on suitable approaches to integrate nanocatalysts in water treatment applications to mitigate emerging contaminants including halogenated molecules. The state-of-the-art supports for palladium nanocatalysts that can be deployed in water treatment systems are reviewed. In addition, research opportunities are emphasized to design robust, reusable, and ecofriendly nanocatalyst architecture.

Isolating Single and Few Atoms for Enhanced Catalysis

Atomically dispersed metal catalysts have triggered great interest in the field of catalysis owing to their unique features. Isolated single or few metal atoms can be anchored on substrates via chemical bonding or space confinement to maximize atom utilization efficiency. The key challenge lies in precisely regulating the geometric and electronic structure of the active metal centers, thus significantly influencing the catalytic properties. Although several reviews have been published on the preparation, characterization, and application of single-atom catalysts (SACs), the comprehensive understanding of SACs, dual-atom catalysts (DACs), and atomic clusters has never been systematically summarized. Here, recent advances in the engineering of local environments of state-of-the-art SACs, DACs, and atomic clusters for enhanced catalytic performance are highlighted. Firstly, various synthesis approaches for SACs, DACs, and atomic clusters are presented. Then, special attention is focused on the elucidation of local environments in terms of electronic state and coordination structure. Furthermore, a comprehensive summary of isolated single and few atoms for the applications of thermocatalysis, electrocatalysis, and photocatalysis is provided. Finally, the potential challenges and future opportunities in this emerging field are presented. This review will pave the way to regulate the microenvironment of the active site for boosting catalytic processes.

Highly Efficient MOF-Driven Silver Subnanometer Clusters for the Catalytic Buchner Ring Expansion Reaction

The preparation of novel efficient catalysts—that could be applicable in industrially important chemical processes—has attracted great interest. Small subnanometer metal clusters can exhibit outstanding catalytic capabilities, and thus, research efforts have been devoted, recently, to synthesize novel catalysts bearing such active sites. Here, we report the gram-scale preparation of Ag₂⁰ subnanometer clusters within the channels of a highly crystalline three-dimensional anionic metal–organic framework, with the formula [Ag₂⁰]@Ag^I₂Na^I₂{Ni^II₄[Cu^II₂(Me₃mpba)₂]₃}·48H₂O [Me₃mpba^4– = N,N′-2,4,6-trimethyl-1,3-phenylenebis(oxamate)]. The resulting crystalline solid catalyst—fully characterized with the help of single-crystal X-ray diffraction—exhibits high catalytic activity for the catalytic Buchner ring expansion reaction.

The present work describes the MOF-driven preparation of well-defined ligand-free Ag₂⁰ nanoclusters, which are efficiently stabilized by the MOF channels. The small Ag₂⁰ nanoclusters, prepared in the gram scale, are used as efficient and recoverable catalysts for the Buchner ring expansion reaction. These results expand the toolkit of readily affordable Ag species for heterogeneous catalysis in organic synthesis.

Epoxidation vs. dehydrogenation of allylic alcohols: heterogenization of the VO(acac)2 catalyst in a metal-organic framework

Allylic alcohol epoxidation and dehydrogenation reactivity is distinguished when VO(acac)₂ is used in solution or anchored in a metal-organic framework (MOF). The chemical mechanism depends on the electronic profile of alkene substituents when the vanadyl complex is used in the homogenous phase. However, confinement effects imparted by MOF channels allow gaining control of the chemoselectivity toward the dehydrogenation product.

Modulating Pt-O-Pt atomic clusters with isolated cobalt atoms for enhanced hydrogen evolution catalysis

Platinum is the most efficient catalyst for hydrogen evolution reaction in acidic conditions, but its widespread use has been impeded by scarcity and high cost. Herein, Pt atomic clusters (Pt ACs) containing Pt-O-Pt units were prepared using Co/N co-doped carbon (CoNC) as support. Pt ACs are anchored to single Co atoms on CoNC by forming strong interactions. Pt-ACs/CoNC exhibits only 24 mV overpotential at 10 mA cm⁻² and a high mass activity of 28.6 A mg⁻¹ at 50 mV, which is more than 6 times higher than commercial Pt/C with any Pt loadings. Spectroscopic measurements and computational modeling reveal the enhanced hydrogen generation activity attributes to the charge redistribution between Pt and O atoms in Pt-O-Pt units, making Pt atoms the main active sites and O linkers the assistants, thus optimizing the proton adsorption and hydrogen desorption. This work opens an avenue to fabricate noble-metal-based ACs stabilized by single-atom catalysts with desired properties for electrocatalysis.

Modulating single-metal sites at the atomic level can boost the intrinsic catalytic activity. Here, the authors describe the design of Pt atomic clusters containing Pt-O-Pt units supported on Co single atoms and N co-doped carbon for enhanced hydrogen evolution catalysis.

Metal-Organic Frameworks as Unique Platforms to Gain Insight of σ-Hole Interactions for the Removal of Organic Dyes from Aquatic Ecosystems

The combination of high crystallinity and rich host-guest chemistry in metal-organic frameworks (MOFs), have situated them in an advantageous position, with respect to traditional porous materials, to gain insight on specific weak noncovalent supramolecular interactions. In particular, sulfur σ-hole interactions are known to play a key role in the biological activity of living beings as well as on relevant molecular recognitions processes. However, so far, they have been barely explored. Here, we describe both how the combination of the intrinsic features of MOFs, especially the possibility of using single-crystal X-ray crystallography (SCXRD), can be an extremely valuable tool to gain insight on sulfur σ-hole interactions, and how their rational exploitation can be enormously useful in the efficient removal of harmful organic molecules from aquatic ecosystems. Thus, we have used a MOF, prepared from the amino acid L-methionine and possessing channels decorated with -CH2 CH2 SCH3 thioalkyl chains, to remove a family of organic dyes at very low concentrations (10 ppm) from water. This MOF is able to efficiently capture the four dyes in a very fast manner, reaching within five minutes nearly the maximum removal. Remarkably, the crystal structure of the different organic dyes within MOFs channels could be determined by SCXRD. This has enabled us to directly visualize the important role sulfur σ-hole interactions play on the removal of organic dyes from aqueous solutions, representing one of the first studies on the rational exploitation of σ-hole interactions for water remediation.

Metal-Organic Framework-Based Nanoheater with Photo-Triggered Cascade Effects for On-Demand Suppression of Cellular Thermoresistance and Synergistic Cancer Therapy

Nanomedicine with stable light-heat conversion and spatiotemporally controllable drug activation is crucial for the success of photothermal therapy (PTT). Herein, a metal-organic framework (MOF)-based nanoheater with light-triggered multi-responsiveness is engineered to in-situ and on-demand sensitize cancer cells to local hyperthermia. Well-dispersed platinum nanoparticles synthesized inside nanospaces of the MOF are employed as the near-infrared (NIR)-harvesting unit with stable and high light-heat conversion performance. A conformation switchable polymer shell is constructed as a secondary light-responding unit to gate the targeted activation of a molecular inhibitor against thermoresistance. By cascade transformation of light stimuli to downstream signals, the nanoheater enables inhibitor release to go with local heating at the same time restricted in lesion sites to maximize efficacy and minimize systemic toxicity. The efficient photothermal conversion and the blockage of cellular heat-protective pathways provide a dual-mode of action which selectively sensitizes cancer cells to hyperthermia in a spatiotemporally controlled manner. With NIR as the remote switch, the MOF-based nanosystem demonstrates localized and boosted PTT efficacy against cancer both in vitro and in vivo. These results present nanosized MOFs as tailorable and versatile platforms for synergistic and precise cancer therapy.

Confinement synthesis in porous molecule-based materials: a new opportunity for ultrafine nanostructures

A balance between activity and stability is greatly challenging in designing efficient metal nanoparticles (MNPs) for heterogeneous catalysis. Generally, reducing the size of MNPs to the atomic scale can provide high atom utilization, abundant active sites, and special electronic/band structures, for vastly enhancing their catalytic activity. Nevertheless, due to the dramatically increased surface free energy, such ultrafine nanostructures often suffer from severe aggregation and/or structural degradation during synthesis and catalysis, greatly weakening their reactivities, selectivities and stabilities. Porous molecule-based materials (PMMs), mainly including metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and porous organic polymers (POPs) or cages (POCs), exhibit high specific surface areas, high porosity, and tunable molecular confined space, being promising carriers or precursors to construct ultrafine nanostructures. The confinement effects of their nano/sub-nanopores or specific binding sites can not only effectively limit the agglomeration and growth of MNPs during reduction or pyrolysis processes, but also stabilize the resultant ultrafine nanostructures and modulate their electronic structures and stereochemistry in catalysis. In this review, we highlight the latest advancements in the confinement synthesis in PMMs for constructing atomic-scale nanostructures, such as ultrafine MNPs, nanoclusters, and single atoms. Firstly, we illustrated the typical confinement methods for synthesis. Secondly, we discussed different confinement strategies, including PMM-confinement strategy and PMM-confinement pyrolysis strategy, for synthesizing ultrafine nanostructures. Finally, we put forward the challenges and new opportunities for further applications of confinement synthesis in PMMs.

Metal–organic framework (MOF)-, covalent-organic framework (COF)-, and porous-organic polymers (POP)-catalyzed selective C–H bond activation and functionalization reactions

The review summarizes the state-of-the-art of C–H active transformations over crystalline and amorphous porous materials as new emerging heterogeneous (photo)catalysts.

MOF-stabilized perfluorinated palladium cages catalyze the additive-free aerobic oxidation of aliphatic alcohols to acids

Extremely high electrophilic metal complexes, composed by a metal cation and very electron poor σ-donor ancillary ligands, are expected to be privileged catalysts for oxidation reactions in organic chemistry. However, their low lifetime prevents any use in catalysis. Here we show the synthesis of fluorinated pyridine-Pd 2+ coordinate cages within the channels of an anionic tridimensional metal organic framework (MOF), and their use as efficient metal catalysts for the aerobic oxidation of aliphatic alcohols to carboxylic acids without any additive. Mechanistic studies strongly support that the MOF-stabilized coordination cage with perfluorinated ligands unleashes the full electrophilic potential of Pd 2+ to dehydrogenate primary alcohols, without any base, and also to activate O 2 for the radical oxidation to the aldehyde intermediate. This study opens the door to design catalytic perfluorinated complexes for challenging organic transformations, where an extremely high electrophilic metal site is required.

Ultralight and shapeable nanocellulose/metal-organic framework aerogel with hierarchical cellular architecture for highly efficient adsorption of Cu(II) ions

Water contamination by heavy metal pollutants is a global concern due to detrimental effects on the environment and human health. Regenerable, high-performance heavy metal sorbents are urgently demanded for improved water purification. Herein, we present an elegant strategy of interweaving metal-organic framework (MOF-808-ethylene diamine tetraacetic acid) and TEMPO-oxidized cellulose nanofibers (TCNF) to construct freeways in hybrid aerogels for rapid and efficient transport and capture of heavy metal ions. In this strategy, a postsynthetic ligand exchange approach is applied to introduce ordered and high-density accessible binding sites for metal ions. The prepared aerogels show excellent shapeability, ultralow density less than 0.005 g cm^-3, and high hierarchical porosity of 99.82%. Furthermore, benefiting from the abundant chelating groups and accessible surface areas, these aerogels exhibit outstanding uptake capacity of 300 mg g^-1 and rapid adsorption kinetics of 0.031 mg g^-1 h^-1 for Cu(II) ions, significantly better than conventional TCNF aerogels. The aerogels could be easily regenerated at least five cycles without greatly performance loss. These aerogels could effectively remove diverse heavy metal ions from complicated contaminated water. Thus, this work provides a novel method to synthesize environmental-friendly, regenerable, and high-performance adsorption materials for water remediation.

A Biocompatible Aspartic-Decorated Metal-Organic Framework with Tubular Motif Degradable under Physiological Conditions

Achieving a precise control of the final structure of metal-organic frameworks (MOFs) is necessary to obtain desired physical properties. Here, we describe how the use of a metalloligand design strategy and a judicious choice of ligands inspired from nature is a versatile approach to succeed in this challenging task. We report a new porous chiral MOF, with the formula Ca5II{CuII10[(S,S)-aspartamox]5}·160H2O (1), constructed from Cu2+ and Ca2+ ions and aspartic acid-decorated ligands, where biometal Cu2+ ions are bridged by the carboxylate groups of aspartic acid moieties. The structure of MOF 1 reveals an infinite network of basket-like cages, built by 10 crystallographically distinct Cu(II) metal ions and five aspartamox ligands acting as bricks of a tubular motif, composed of seven basket-like cages each. The pillared hepta-packed cages generate pseudo-rhombohedral nanosized channels of ca. 0.7 and 0.4 nm along the b and a crystallographic axes. This intricate porous 3D network is anionic and chiral, each cage displaying receptor properties toward three-nuclear [Ca3(μ-H2O)4(H2O)17]6+ entities. 1 represents the first example of an extended porous structure based on essential biometals Cu2+ and Ca2+ ions together with aspartic acid as amino acid. 1 shows good biocompatibility, making it a good candidate to be used as a drug carrier, and hydrolyzes in acid water. The hypothesis has been further supported by an adsorption experiment here reported, as a proof-of-principle study, using dopamine hydrochloride as a model drug to follow the encapsulation process. Results validate the potential ability of 1 to act as a drug carrier. Thus, these make this MOF one of the few examples of biocompatible and degradable porous solid carriers for eventual release of drugs in the stomach stimulated by gastric low pH.