Isoreticular Contraction of Cage-like Metal-Organic Frameworks with Optimized Pore Space for Enhanced C2H2/CO2 and C2H2/C2H4 Separations.

The C2H2 separation from CO2 and C2H4 is of great importance yet highly challenging in the petrochemical industry, owing to their similar physical and chemical properties. Herein, the pore nanospace engineering of cage-like mixed-ligand MFOF-1 has been accomplished via contracting the size of the pyridine- and carboxylic acid-functionalized linkers and introducing a fluoride- and sulfate-bridging cobalt cluster, based on a reticular chemistry strategy. Compared with the prototypical MFOF-1, the constructed FJUT-1 with the same topology presents significantly improved C2H2 adsorption capacity, and selective C2H2 separation performance due to the reduced cage cavity size, functionalized pore surface, and appropriate pore volume. The introduction of fluoride- and sulfate-bridging cubane-type tetranuclear cobalt clusters bestows FJUT-1 with exceptional chemical stability under harsh conditions while providing multiple potential C2H2 binding sites, thus rendering the adequate ability for practical C2H2 separation application as confirmed by the dynamic breakthrough experiments under dry and humid conditions. Additionally, the distinct binding mechanism is suggested by theoretical calculations in which the multiple supramolecular interactions involving C-H···O, C-H···F, and other van der Waals forces play a critical role in the selective C2H2 separation.

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.

Implanting Colloidal Nanoparticles into Single-Crystalline Zeolites for Catalytic Dehydration.

The encapsulation of functional colloidal nanoparticles (100 nm) into single-crystalline ZSM-5 zeolites, aiming to create uniform core-shell structures, is a highly sought-after yet formidable objective due to significant lattice mismatch and distinct crystallization properties. In this study, we demonstrate the fabrication of a core-shell structured single-crystal zeolite encompassing an Fe3O4 colloidal core via a novel confinement stepwise crystallization methodology. By engineering a confined nanocavity, anchoring nucleation sites, and executing stepwise crystallization, we have successfully encapsulated colloidal nanoparticles (CN) within single-crystal zeolites. These grafted sites, alongside the controlled crystallization process, compel the zeolite seed to nucleate and expand along the Fe3O4 colloidal nanoparticle surface, within a meticulously defined volume (1.5×107≤V≤1.3×108 nm3). Our strategy exhibits versatility and adaptability to an array of zeolites, including but not restricted to ZSM-5, NaA, ZSM-11, and TS-1 with polycrystalline zeolite shell. We highlight the uniformly structured magnetic-nucleus single-crystalline zeolite, which displays pronounced superparamagnetism (14 emu/g) and robust acidity (~0.83 mmol/g). This innovative material has been effectively utilized in a magnetically stabilized bed (MSB) reactor for the dehydration of ethanol, delivering an exceptional conversion rate (98 %), supreme ethylene selectivity (98 %), and superior catalytic endurance (in excess of 100 hours).

Introducing Frustrated Lewis Pairs to Metal-Organic Framework for Selective Hydrogenation of N-Heterocycles.

Hydrogenated nitrogen heterocyclic compounds play a critical role in the pharmaceutical, polymer, and agrochemical industries. Recent studies on partial hydrogenation of nitrogen heterocyclic compounds have focused on costly and toxic precious metal catalysts. As an important class of main-group catalysts, frustrated Lewis pairs (FLPs) have been widely applied in catalytic hydrogenation reactions. In principle, the combination of FLPs and metal-organic framework (MOF) is anticipated to efficiently enhance the recyclability performance of FLPs; however, the previously studied MOF-FLPs showed low reactivity in the hydrogenation of N-heterocycles compounds. Herein, we offer a novel P/B type MOF-FLP catalyst that was achieved via a solvent-assisted linker incorporation approach to boost catalytic hydrogenation reactions. Using hydrogen gas under moderate pressure, the proposed P/B type MOF-FLP can serve as a highly efficient heterogeneous catalyst for selective hydrogenation of quinoline and indole to tetrahydroquinoline and indoline-type drug compounds in high yield and excellent recyclability.

Chiral Frustrated Lewis Pair@Metal-Organic Framework as a New Platform for Heterogeneous Asymmetric Hydrogenation.

Asymmetric hydrogenation, a seminal strategy for the synthesis of chiral molecules, remains largely unmet in terms of activation by non-metal sites of heterogeneous catalysts. Herein, as demonstrated by combined computational and experimental studies, we present a general strategy for integrating rationally designed molecular chiral frustrated Lewis pair (CFLP) with porous metal-organic framework (MOF) to construct the catalyst CFLP@MOF that can efficiently promote the asymmetric hydrogenation in a heterogeneous manner, which for the first time extends the concept of chiral frustrated Lewis pair from homogeneous system to heterogeneous catalysis. Significantly, the developed CFLP@MOF, inherits the merits of both homogeneous and heterogeneous catalysts, with high activity/enantio-selectivity and excellent recyclability/regenerability. Our work not only advances CFLP@MOF as a new platform for heterogeneous asymmetric hydrogenation, but also opens a new avenue for the design and preparation of advanced catalysts for asymmetric catalysis.

Kinetic Control via Binding Sites within the Confined Space of Metal Metalloporphyrin-Frameworks for Enhanced Shape-Selectivity Catalysis.

One striking feature of enzyme is its controllable ability to trap substrates via synergistic or cooperative binding in the enzymatic pocket, which renders the shape-selectivity of product by the confined spatial environment. The success of shape-selective catalysis relies on the ability of enzyme to tune the thermodynamics and kinetics for chemical reactions. In emulation of enzyme's ability, we showcase herein a targeting strategy with the substrate being anchored on the internal pore wall of metal-organic frameworks (MOFs), taking full advantage of the sterically kinetic control to achieve shape-selectivity for the reactions. For this purpose, a series of binding site-accessible metal metalloporphyrin-frameworks (MMPFs) have been investigated to shed light on the nature of enzyme-mimic catalysis. They exhibit a different density of binding sites that are well arranged into the nanospace with corresponding distances of opposite binding sites. Such a structural specificity results in a facile switch in selectivity from an exclusive formation of the thermodynamically stable product to the kinetic product. Thus, the proposed targeting strategy, based on the combination of porous materials and binding events, paves a new way to develop highly efficient heterogeneous catalysts for shifting selectivity.

A Microporous Metal-Organic Framework with Unique Aromatic Pore Surfaces for High Performance C2 H6 /C2 H4 Separation.

Developing adsorptive separation processes based on C2 H6 -selective sorbents to replace energy-intensive cryogenic distillation is a promising alternative for C2 H4 purification from C2 H4 /C2 H6 mixtures, which however remains challenging. During our studies on two isostructural metal-organic frameworks (Ni-MOF 1 and Ni-MOF 2), we found that Ni-MOF 2 exhibited significantly higher performance for C2 H6 /C2 H4 separation than Ni-MOF-1, as clearly established by gas sorption isotherms and breakthrough experiments. Density-Functional Theory (DFT) studies showed that the unblocked unique aromatic pore surfaces within Ni-MOF 2 induce more and stronger C-H⋅⋅⋅π with C2 H6 over C2 H4 while the suitable pore spaces enforce its high C2 H6 uptake capacity, featuring Ni-MOF 2 as one of the best porous materials for this very important gas separation. It generates 12 L kg-1 of polymer-grade C2 H4 product from equimolar C2 H6 /C2 H4 mixtures at ambient conditions.

Observation of General Entropy-Enthalpy Compensation Effect in the Relaxation of Wrinkled Polymer Nanocomposite Films.

Surface-textured polymer nanocomposite (PNC) films are utilized in many device applications, and therefore understanding the relaxation behavior of such films is important. By extending an in situ wrinkle relaxation method, we observed that the thermal stability of wrinkled PNC films, both above and below the glass transition temperature (Tg), is proportional to a film's nanoparticle (polymer grafted and bare) concentration, with a slope that changes sign at a compensation temperature (Tcomp) that is determined to be in the vicinity of the film's Tg. This provides unambiguous confirmation of entropy-enthalpy compensation (EEC) as a general feature of PNC films, implying that the stability of PNC films changes from being enhanced to becoming diminished by simply passing through this characteristic temperature, a phenomenon having evident practical ramifications. We suggest EEC will also arise in films where residual stresses are associated with the film fabrication process, which is relevant to nanotech device applications.

Self-Adjusting Metal-Organic Framework for Efficient Capture of Trace Xenon and Krypton.

The capture of the xenon and krypton from nuclear reprocessing off-gas is essential to the treatment of radioactive waste. Although various porous materials have been employed to capture Xe and Kr, the development of high-performance adsorbents capable of trapping Xe/Kr at very low partial pressure as in the nuclear reprocessing off-gas conditions remains challenging. Herein, we report a self-adjusting metal-organic framework based on multiple weak binding interactions to capture trace Xe and Kr from the nuclear reprocessing off-gas. The self-adjusting behavior of ATC-Cu and its mechanism have been visualized by the in-situ single-crystal X-ray diffraction studies and theoretical calculations. The self-adjusting behavior endows ATC-Cu unprecedented uptake capacities of 2.65 and 0.52 mmol g-1 for Xe and Kr respectively at 0.1 bar and 298 K, as well as the record Xe capture capability from the nuclear reprocessing off-gas. Our work not only provides a benchmark Xe adsorbent but proposes a new route to construct smart materials for efficient separations.

Single-Pore versus Dual-Pore Bipyridine-Based Covalent-Organic Frameworks: An Insight into the Heterogeneous Catalytic Activity for Selective CH Functionalization.

Exponential growth in the field of covalent-organic frameworks (COFs) is emanating from the direct correlation between designing principles and desired properties. The comparison of catalytic activity between single-pore and dual-pore COFs is of importance to establish structure-function relationship. Herein, the synthesis of imine-linked dual-pore [(BPyDC)]x % -ETTA COFs (x = 0%, 25%, 50%, 75%, 100%) with controllable bipyridine content is fulfilled by three-component condensation of 4,4',4″,4'″-(ethene-1,1,2,2-tetrayl)tetraaniline (ETTA), 4,4'-biphenyldialdehyde, and 2,2'-bipyridyl-5,5'-dialdehyde in different stoichiometric ratio. The strong coordination of bipyridine moieties of [(BPyDC)]x % -ETTA COFs with palladium imparts efficient catalytic active sites for selective functionalization of sp2 CH bond to CX (X = Br, Cl) or CO bonds in good yield. To broaden the scope of regioselective CH functionalization, a wide range of electronically and sterically substituted substrates under optimized catalytic condition are investigated. A comparison of the catalytic activity of palladium decorated dual-pore frameworks with single-pore imine-linked Pd(II) @ Py-2,2'-BPyDC framework  is undertaken. The finding of this work provides a sporadic example of chelation-assisted CH functionalization and disclosed an in-depth comparison of the relationship between superior catalytic activity and core properties of rationally designed imine linked frameworks.

3D Cationic Polymeric Network Nanotrap for Efficient Collection of Perrhenate Anion from Wastewater.

Rhenium is one of the most valuable elements found in nature, and its capture and recycle are highly desirable for resource recovery. However, the effective and efficient collection of this material from industrial waste remains quite challenging. Herein, a tetraphenylmethane-based cationic polymeric network (CPN-tpm) nanotrap is designed, synthesized, and evaluated for ReO4- recovery. 3D building units are used to construct imidazolium salt-based polymers with positive charges, which yields a record maximum uptake capacity of 1133 mg g-1 for ReO4- collection as well as fast kinetics ReO4- uptake. The sorption equilibrium is reached within 20 min and a kd value of 8.5 × 105 mL g-1 is obtained. The sorption capacity of CPN-tpm remains stable over a wide range of pH values and the removal efficiency exceeds 60% for pH levels below 2. Moreover, CPN-tpm exhibits good recyclability for at least five cycles of the sorption-desorption process. This work provides a new route for constructing a kind of new high-performance polymeric material for rhenium recovery and rhenium-contained industrial wastewater treatment.

Efficient Electron Transfer from Electron-Sponge Polyoxometalate to Single-Metal Site Metal-Organic Frameworks for Highly Selective Electroreduction of Carbon Dioxide.

In this work, by combining the superiority of polyoxometalates (POMs) and catalytic single-metal site Co of metalloporphyrin, a series of mixed-valence POM-based metal-organic frameworks (MOFs) composites is synthesized by a post-modification method. The electron-transfer property of POM@PCN-222(Co) composite is significantly enhanced owing to the directional electron-transfer from POM to single-metal site Co in PCN-222(Co). In particular, H-POM@PCN-222(Co) gives a high Faradaic efficiency of 96.2% for electroreduction of CO2 into CO and good stability over 10 h. DFT calculations confirm that the directional electron transfer, which accelerates the multi-electron transfer from the electrode to active single-metal site Co, enriches the electron density of the Co center, and ultimately reduces the energy of the rate-determining step, thus increasing the catalytic activity of CO2 reduction reaction (CO2 RR). This work therefore suggests some new insight for the design of efficient electrocatalysts for CO2 RR.

Recent developments in the synthesis of chemically modified nanomaterials for use in dielectric and electronics applications.

Polymer nanocomposites (PNC) have attracted enormous scientific and technological interest due to their applications in energy storage, electronics, biosensing, drug delivery, cosmetics and packaging industry. Nanomaterials (platelet, fibers, spheroids, whiskers, rods) dispersed in different types of polymer matrices constitute such PNC. The degree of dispersion of the inorganic nanomaterials in the polymer matrix, as well as the structured arrangement of the nanomaterials, are some of the key factors influencing the overall performance of the nanocomposite. To this end, the surface functionalization of the nanomaterials determines its state of dispersion within the polymer matrix. For energy storage and electronics, these nanomaterials are usually chosen for their dielectric properties for enhancing the performance of device applications. Although several reviews on surface modification of nanomaterials have been reported, a review on the surface functionalization of nanomaterials as it pertains to polymer dielectrics is currently lacking. This review summarizes the recent developments in the surface modification of important metal oxide dielectric nanomaterials including Silicon dioxide (SiO2), titanium dioxide (TiO2), barium titanate (BaTiO3), and aluminum oxide (Al2O3) by chemical agents such as silanes, phosphonic acids, and dopamine. We report the impact of chemical modification of the nanomaterial on the dielectric performance (dielectric constant, breakdown strength, and energy density) of the nanocomposite. Aside from bringing novice and experts up to speed in the area of polymer dielectric nanocomposites, this review will serve as an intellectual resource in the selection of appropriate chemical agents for functionalizing nanomaterials for use in specific polymer matrix so as to potentially tune the final performance of nanocomposite.

A MOF-based Ultra-Strong Acetylene Nano-trap for Highly Efficient C2 H2 /CO2 Separation.

Porous materials with open metal sites have been investigated to separate various gas mixtures. However, open metal sites show the limitation in the separation of some challenging gas mixtures, such as C2 H2 /CO2 . Herein, we propose a new type of ultra-strong C2 H2 nano-trap based on multiple binding interactions to efficiently capture C2 H2 molecules and separate C2 H2 /CO2 mixture. The ultra-strong acetylene nano-trap shows a benchmark Qst of 79.1 kJ mol-1 for C2 H2 , a record high pure C2 H2 uptake of 2.54 mmol g-1 at 1×10-2  bar, and the highest C2 H2 /CO2 selectivity (53.6), making it as a new benchmark material for the capture of C2 H2 and the separation of C2 H2 /CO2 . The locations of C2 H2 molecules within the MOF-based nanotrap have been visualized by the in situ single-crystal X-ray diffraction studies, which also identify the multiple binding sites accountable for the strong interactions with C2 H2 .

Nanospace Engineering of Metal-Organic Frameworks through Dynamic Spacer Installation of Multifunctionalities for Efficient Separation of Ethane from Ethane/Ethylene Mixtures.

Herein, a dynamic spacer installation (DSI) strategy has been implemented to construct a series of multifunctional metal-organic frameworks (MOFs), LIFM-61/31/62/63, with optimized pore space and pore environment for ethane/ethylene separation. In this respect, a series of linear dicarboxylic acids were deliberately installed in the prototype MOF, LIFM-28, leading to a dramatically increased pore volume (from 0.41 to 0.82 cm3 g-1 ) and reduced pore size (from 11.1×11.1 Å2 to 5.6×5.6 Å2 ). The increased pore volume endows the multifunctional MOFs with much higher ethane adsorption capacity, especially for LIFM-63 (4.8 mmol g-1 ), representing nearly three times as much ethane as the prototypical counterpart (1.7 mmol g-1 ) at 273 K and 1 bar. Meanwhile, the reduced pore size imparts enhanced ethane/ethylene selectivity of the multifunctional MOFs. Theoretical calculations and dynamic breakthrough experiments confirm that the DSI is a promising approach for the rational design of multifunctional MOFs for this challenging task.

Investigation of the Anticancer Activity of Coordination-Driven Self-AssembledTwo-Dimensional Ruthenium Metalla-Rectangle.

Coordination-driven self-assembly is an effective synthetic tool for the construction of spatially and electronically tunable supramolecular coordination complexes (SCCs), which are useful in various applications. Herein, we report the synthesis of a two-dimensional discrete metalla-rectangle [(η6-p-cymene)4Ru4(C6H2O4)2(2)2](CF3SO3)4 (3) by the reaction of a dinuclear half-sandwich ruthenium (II) complex [Ru2(η6-p-cymene)2(C6H2O4)Cl2] (1) and bis-pyridyl amide linker (2) in the presence of AgO3SCF3. This cationic ruthenium metalla-rectangle (3) has been isolated as its triflate salt and characterized by analytical techniques including elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H-NMR), carbon nuclear magnetic resonance spectroscopy (13C-NMR), 1H-1H correlation spectroscopy (COSY), 1H-1H nuclear Overhauser effect spectroscopy (NOESY), diffusion ordered spectroscopy (DOSY), and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). Significantly, the 2D cationic ruthenium metalla-rectangle showed better anticancer activity towards three different cell lines (A549, Caki-1 and Lovo) as compared with the parent ruthenium complex (1) and the commercially used drug, cisplatin.

Reaction Environment Modification in Covalent Organic Frameworks for Catalytic Performance Enhancement.

Herein, we show how the spatial environment in the functional pores of covalent organic frameworks (COFs) can be manipulated in order to exert control in catalysis. The underlying mechanism of this strategy relies on the placement of linear polymers in the pore channels that are anchored with catalytic species, analogous to outer-sphere residue cooperativity within the active sites of enzymes. This approach benefits from the flexibility and enriched concentration of the functional moieties on the linear polymers, enabling the desired reaction environment in close proximity to the active sites, thereby impacting the reaction outcomes. Specifically, in the representative dehydration of fructose to produce 5-hydroxymethylfurfural, dramatic activity and selectivity improvements have been achieved for the active center of sulfonic acid groups in COFs after encapsulation of polymeric solvent analogues 1-methyl-2-pyrrolidinone and ionic liquid.

In-Situ Synthesis of Amorphous Co Nanoparticles Supported onto TiO2 Nanofibers as a Catalyst for Hydrogen Generation from the Hydrolysis of Ammonia Borane.

Co0 nanoparticles supported on TiO2 nanofibers (nanocomposite) were prepared using a simple electrospinning technique and In-Situ chemical reduction. The synthesized nanocomposite was used to generate hydrogen from ammonia borane (AB). Standard characterization techniques revealed dense distribution of Co0 nanoparticles (Co NPs) onto the TiO2 nanofibers (TiO2 NFs) in the prepared nanocomposite. The introduced nanocomposite has been showed a good catalytic activity as compared to those unsupported Co NPs. As, the hydrogen evolutions for the nanocomposite and Co NPs were 3 mol in 23 min and 47 min, respectively. Furthermore, both the nanocomposite concentration and the temperature have a significant catalytic activity in the AB dehydrogenation. The nanocomposite also showed low effective activation energy of ~26.03 KJ · mol-1.

Lower Activation Energy for Catalytic Reactions through Host-Guest Cooperation within Metal-Organic Frameworks.

Industrial synthesis is driven by a delicate balance of the value of the product against the cost of production. Catalysts are often employed to ensure product turnover is economically favorable by ensuring energy use is minimized. One method, which is gaining attention, involves cooperative catalytic systems. By inserting a flexible polymer into a metal-organic framework (MOF) host, the advantages of both components work synergistically to create a composite that efficiently fixes carbon dioxide to transform various epoxides into cyclic carbonates. The resulting material retains high yields under mild conditions with full reusability. By quantitatively studying the kinetic rates, the activation energy was calculated, for a physical mixture of the catalyst components to be about 50 % higher than that of the composite. Through the unification of two catalytically active components, a new opportunity opens up for the development of synergistic systems in multiple applications.

New Insight into the Synthesis of Large-Pore Ordered Mesoporous Materials.

Ordered mesoporous materials (OMMs) have received increasing interest due to their uniform pore size, high surface area, various compositions and wide applications in energy conversion and storage, biomedicine and environmental remediation, etc. The soft templating synthesis using surfactants or amphiphilic block copolymers is the most efficient method to produce OMMs with tailorable pore structure and surface property. However, due to the limited choice of commercially available soft templates, the common OMMs usually show small pore size and amorphous (or semicrystalline) frameworks. Tailor-made amphiphilic block copolymers with controllable molecular weights and compositions have recently emerged as alternative soft templates for synthesis of new OMMs with many unique features including adjustable mesostructures and framework compositions, ultralarge pores, thick pore walls, high thermal stability and crystalline frameworks. In this Perspective, recent progresses and some new insights into the coassembly process about the synthesis of OMMs based on these tailor-made copolymers as templates are summarized, and typical newly developed synthesis methods and strategies are discussed in depth, including solvent evaporation induced aggregation, ligand-assisted coassembly, solvent evaporation induced micelle fusion-aggregation assembly, homopolymer assisted pore expanding and carbon-supported crystallization strategy. Then, the applications of the obtained large-pore OMMs in catalysis, sensor, energy conversion and storage, and biomedicine by loading large-size guest molecules (e.g., protein and RNA), precious metal nanoparticles and quantum dots, are discussed. At last, the outlook on the prospects and challenges of future research about the synthesis of large-pore OMMs by using tailor-made amphiphilic block copolymers are included.