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

Porous Organic Polymers for CO2 Capture and Catalytic Conversion

Overuse of fossil fuels and anthropogenic activities have led to excessive emissions of carbon dioxide, leading to global warming, and measures to reduce atmospheric carbon dioxide concentrations are needed to overcome this global challenge. Therefore, exploring an environmentally friendly strategy for capturing airborne CO2 and converting it into high-value-added chemicals offers a promising pathway toward "carbon neutrality". In recent years, porous organic polymers have attracted much attention for carbon capture and the catalytic conversion of carbon dioxide because of their high specific surface area, high chemical stability, nanoscale porosity, and structural versatility, which make them easy to functionalize. In this review, we introduce the preparation methods for various POPs, the types of POPs adsorbed during carbon dioxide capture, and the progress in the use of POPs for the photocatalytic and chemicatalytic conversion of carbon dioxide, with a special discussion on the influence of adsorption type on the efficiency of catalytic conversion. Finally, we propose a prospective direction for the subsequent development of this field.

Host-Guest Interactions of Metal-Organic Framework Enable Highly Conductive Quasi-Solid-State Electrolytes for Li-CO2 Batteries

High-energy lithium (Li)-based batteries, especially rechargeable Li-CO2 batteries with CO2 fixation capability and high energy density, are desirable for electrified transportation and other applications. However, the challenges of poor stability, low energy efficiency, and leakage of liquid electrolytes hinder the development of Li-CO2 batteries. Herein, a highly conductive and stable metal-organic framework-encapsulated ionic liquid (IL@MOF) electrolyte system is developed for quasi-solid-state Li-CO2 batteries. Benefiting from the host-guest interaction of MOFs with open micromesopores and internal IL, the optimized IL@MOF electrolytes exhibit a high ionic conductivity of 1.03 mS cm-1 and a high transference number of 0.80 at room temperature. The IL@MOF electrolytes also feature a wide electrochemical stability window (4.71 V versus Li+/Li) and a wide working temperature (-60 °C ∼ 150 °C). The IL@MOF electrolytes also enable Li+ and electrons transport in the carbon nanotubes-IL@MOF (CNT-IL@MOF) solid cathodes in quasi-solid-state Li-CO2 batteries, delivering a high specific capacity of 13,978 mAh g-1 (50 mA g-1), a long cycle life of 441 cycles (500 mA g-1 and 1000 mAh g-1), and a wide operation temperature of -60 to 150 °C. The proposed MOF-encapsulated IL electrolyte system presents a powerful strategy for developing high-energy and highly safe quasi-solid-state batteries.

MIL-101(Cr)/aminoclay nanocomposites for conversion of CO2 into cyclic carbonates

We present the use of an amine functionalized two-dimensional clay i.e., aminoclay (AC), in the chemistry of a three-dimensional metal-organic framework (MOF) i.e., MIL-101(Cr), to prepare MIL-101(Cr)/AC composites, which are exploited as catalysts for efficient conversion of CO2 gas into cyclic carbonates under ambient reaction conditions. Three different MOF nanocomposites, denoted as MIL-101(Cr)/AC-1, MIL-101(Cr)/AC-2, and MIL-101(Cr)/AC-3, were synthesized by an in situ process by adding different amounts of AC to the precursor solutions of the MIL-101(Cr). The composites were characterized by various techniques such as FT-IR, PXRD, FESEM, EDX, TGA, N2 adsorption, as well as CO2 and NH3-TPD measurements. The composites were exploited as heterogeneous catalysts for CO2 cycloaddition reactions with different epoxides and the catalytic activity was investigated at atmospheric pressure under solvent-free conditions. Among all the materials, MIL-101(Cr)/AC-2 shows the best catalytic efficiency under the optimized conditions and exhibits enhanced efficacy compared to various MIL-101(Cr)-based MOF catalysts, which typically need either high temperature and pressure or a longer reaction time or a combination of all the parameters. The present protocol using MIL-101(Cr)/AC-2 as the heterogeneous catalyst gives 99.9% conversion for all the substrates into the products at atmospheric pressure.

Photoselectively modulating main products by changing the wavelength of visible light over D-π-A-D conjugated polymers

The diversity of catalytic products determines the difficulty of selective product modulation, which usually relies on adjusting the catalyst and reaction conditions to obtain different main products selectively. Herein, we synthesized D-π-A-D conjugated organic polymers (TH-COP) using cyclotriphosphonitrile, alkyne, 2H-benzimidazole, and sulfur units as electron donors, π bridges, electron acceptors, and electron donors, respectively. TH-COP exhibited excellent photoinduced carrier separation and redox ability under different visible light wavelengths, and the main products of its CO2 reduction are CH4 (1000.0 μmol g-1) and CO (837.0 μmol g-1) under 400-420 nm and 420-560 nm, respectively. In addition, TH-COP could completely convert phenylmethyl sulfide to methyl phenyl sulfone at 400-420 nm and diphenyl disulfide at 480-485 nm in yields up to 95 %. This study presents a novel strategy for the targeted fabrication of various main products using conjugated polymers by simply changing the wavelength range of visible light.

Precise Distance Control and Functionality Adjustment of Frustrated Lewis Pairs in Metal-Organic Frameworks

We report the construction of frustrated Lewis pairs (FLPs) in a metal-organic framework (MOF), where both Lewis acid (LA) and Lewis base (LB) are fixed to the backbone. The anchoring of a tritopic organoboron linker as LA and a monotopic linker as LB to separate metal oxide clusters in a tetrahedron geometry allows for the precise control of distance between them. As the type of monotopic LB linker varies, pyridine, phenol, aniline, and benzyl alcohol, a series of 11 FLPs were constructed to give fixed distances of 7.1, 5.5, 5.4, and 4.8 Å, respectively, revealed by 11B-1H solid-state nuclear magnetic resonance spectroscopy. Keeping LA and LB apart by a fixed distance makes it possible to investigate the electrostatic effect by changing the functional groups in the monotopic LB linker, while the LA counterpart remains unaffected. This approach offers new chemical environments of the active site for FLP-induced catalysis.

Metal-Organic-Framework-Derived Bromine and Nitrogen Dual-Doped Porous Carbon for CO2 Photocycloaddition Reaction

The cycloaddition of CO2 with epoxides driven by light irradiation is an intriguing approach to preparing cyclic carbonates. However, it remains a great challenge to achieve high photocatalytic efficiency in the absence of a cocatalyst. Herein, we explored a metal-organic-framework (MOF)-templated pyrolysis strategy to prepare uniform bromine ions/nitrogen-codoped carbon materials (Br-CN) as low-cost photocatalysts for CO2 cycloaddition. The optimal catalyst Br-CN-1-550 can be used as a photocatalyst to catalyze CO2 cycloaddition, remarkably reducing the energy consumption. As a result of its benefits of high photothermal efficiency and rich nucleophilic sites (Br ions), BN-CN-1-550 affords a 9 times higher yield of 4-(chloromethyl)-1,3-dioxolan-2-one than that of the ZIF-8-derived CN under cocatalyst-free conditions and light irradiation (300 mW·cm-2 full-spectrum irradiation, 10 h). This strategy provides a cost-effective way to obtain cyclic carbonate under cocatalyst-free conditions.

Facile Construction of Advanced 1D Metal-Organic Coordination Polymer for Efficient Lithium Storage

Recently, coordination polymers (CPs) have been frequently reported in the field of energy storage as electrode materials for lithium-ion batteries (LIBs) due to their highly adjustable architectures, which have a variety of active sites and obviously defined lithium transport routes. A well-designed redox-active organic linker with potential active sites for storing lithium ions, pyrazine-2,3-dicarboxylate (H2PDA), was applied for generating CPs by a simple hydrothermal method. When employed as anode materials in LIBs, those two one-dimensional (1D) CPs with an isomorphic composition, [M(PDA)(H2O)2]n (M = Co for Co-PDA and Ni for Ni-PDA), produced outstanding reversible capacities and stable cycling performance. The Co-PDA displays a substantial reversible capacity of 936 mAh g-1 at 200 mA g-1 after 200 cycles, as well as an excellent cycling life at high currents. According to the ex situ characterizations, the high reversible specific capacity of the post-cycled electrodes was found to be a result of both the transition metal ions and the organic ligands, and Co-PDA and Ni-PDA electrode materials show reversible insertion/extraction processes that are accompanied by crystallization to an amorphous state.

Metal-Organic Frameworks as a New Platform to Construct Ordered Mesoporous Ce-Based Oxides for Efficient CO2 Fixation under Ambient Conditions

Metal-organic frameworks (MOFs) are proved to be good precursors to derive various nanomaterials with desirable functions, but so far the controllable synthesis of ordered mesoporous derivatives from MOFs has not been achieved. Herein, this work reports, for the first time, the construction of MOF-derived ordered mesoporous (OM) derivatives by developing a facile mesopore-inherited pyrolysis-oxidation strategy. This work demonstrates a particularly elegant example of this strategy, which involves the mesopore-inherited pyrolysis of OM-CeMOF into a OM-CeO2 @C composite, followed by the oxidation removal of its residual carbon, affording the corresponding OM-CeO2 . Furthermore, the good tunability of MOFs helps to allodially introduce zirconium into OM-CeO2 to regulate its acid-base property, thus boosting its catalytic activity for CO2 fixation. Impressively, the optimized Zr-doped OM-CeO2 can achieve above 16 times higher catalytic activity than its solid CeO2 counterpart, representing the first metal oxide-based catalyst to realize the complete cycloaddition of epichlorohydrin with CO2 under ambient temperature and pressure. This study not only develops a new MOF-based platform for enriching the family of ordered mesoporous nanomaterials, but also demonstrates an ambient catalytic system for CO2 fixation.

Ligand-dependent structural diversity and optimizable CO2 chemical fixation activities of Cu-doped polyoxo-titanium clusters

Heterometallic oxo clusters have been attracting intensive interest due to their unique properties originating from the synergistic interactions between different components. Herein, we report the construction and catalytic applications of a family of copper-doped polyoxo-titanium clusters (Cu-PTCs) coordinated with different acetate derivative ligands. The solvothermal reactions of metal salts and trimethylacetic acid or 1,2-phenylenediacetic acid in ethanol produced Ti6Cu3(μ3-O)4(μ2-O)(OEt)16(L1)4 (L1 = trimethyl acetate, PTC-367) and H2Ti8Cu2Br2(μ4-O)2(μ2-O)4(OEt)20(L2)2 (L2 = 1,2-phenylenediacetate, PTC-368), respectively. When smaller acetic acid was introduced as a stabilizing ligand, higher nuclei H2Ti16Cu3(μ4-O)5(μ3-O)15(μ2-O)3(OiPr)18(Ac)8 (Ac = acetate, PTC-369) and H3Ti29Cu3(μ4-O)6(μ3-O)30(μ2-O)8(OiPr)17(Ac)20 (PTC-370) were prepared. The number of metal ions exposed on the surface of the four clusters changes due to variations in the steric hindrance of functionalizing ligands, and theoretically, so does their catalytic activity as Lewis acids. In light of this, we conducted a carbon dioxide cycloaddition reaction in an atmospheric environment and the four obtained compounds displayed increasing catalytic activities from PTC-367 to PTC-370. These results provide a feasible synthetic method for modulating the structures of Cu-doped titanium oxide materials and improving their catalytic activities.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks

Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal-organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble-metal-free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.

Comparative Study of Commercial Silica and Sol-Gel-Derived Porous Silica from Cornhusk for Low-Temperature Catalytic Methane Combustion

The synthesis and characterization of sol-gel-derived cornhusk support for low-temperature catalytic methane combustion (LTCMC) were investigated in this study. The prepared cornhusk support was impregnated with palladium and cerium oxide (Pd/CeO₂) via the classical incipient wetness method. The resulting catalyst was characterized using various techniques, including X-ray diffraction (XRD), N₂ physisorption (BET), transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H₂-TPR). The catalytic performance of the Pd/CeO₂/CHSiO₂ catalyst was evaluated for methane combustion in the temperature range of 150-600 °C using a temperature-controlled catalytic flow reactor, and its performance was compared with a commercial catalyst. The results showed that the Pd/CeO₂ dispersed on SiO₂ from the cornhusk ash support (Pd/CeO₂/CHSiO₂) catalyst exhibited excellent catalytic activity for methane combustion, with a conversion of 50% at 394 °C compared with 593 °C for the commercial silica catalyst (Pd/CeO₂/commercial). Moreover, the Pd/CeO₂/CHSiO₂ catalyst displayed better catalytic stability after 10 h on stream, with a 7% marginal loss in catalytic activity compared with 11% recorded for the Pd/CeO₂/commercial catalyst. The N₂ physisorption and H₂-TPR results indicated that the cornhusk SiO₂ support possessed a higher surface area and strong reducibility than the synthesized commercial catalyst, contributing to the enhanced catalytic activity of the Pd/CeO₂/SiO₂ catalyst. Overall, the SiO₂ generated from cornhusk ash exhibited promising potential as a low-cost and environmentally friendly support for LTCMC catalysts.

A robust and porous titanium metal-organic framework for gas adsorption, CO2 capture and conversion

A robust and porous titanium metal-organic framework (Ti-MOF; LCU-402) has been hydrothermally synthesized through combining a tetranuclear Ti2Ca2(μ3-O)2(μ2-H2O)1.3(H2O)4(O2C-)8 cluster and a tritopic 1,3,5-benzene(tris)benzoic (BTB) ligand. LCU-402 shows remarkable stability and permanent porosity for CO2, CH4, C2H2, C2H4, and C2H6 gas adsorption. Moreover, LCU-402 as a heterogeneous catalyst can smoothly convert CO2 under a simulated flue atmosphere into organic carbonate molecules by cycloaddition reactions of CO2 and epoxides, indicating that LCU-402 might be a promising catalyst candidate in practical applications. We are confident that the identification of a persistent titanium-oxo building unit would accelerate the development of new porous Ti-MOF materials.

Construction of Macroporous β-Glucosidase@MOFs by a Metal Competitive Coordination and Oxidation Strategy for Efficient Cellulose Conversion at 120 °C

Metal-organic frameworks (MOFs) have become promising accommodation for enzyme immobilization in recent years. However, the microporous nature of MOFs affects the accessibility of large molecules, resulting in a significant decline in biocatalysis efficiency. Herein, a novel strategy is reported to construct macroporous MOFs by metal competitive coordination and oxidation with induced defect structure using a transition metal (Fe²⁺) as a functional site. The feasibility of in situ encapsulating β-glucosidase (β-G) within the developed macroporous MOFs endows an enzyme complex (β-G@MOF-Fe) with remarkably enhanced synergistic catalysis ability. The 24 h hydrolysis rate of β-G@MOF-Fe (with respect to cellobiose) is as high as approximately 99.8%, almost 32.2 times that of free β-G (3.1%). Especially, the macromolecular cellulose conversion rate of β-G@MOF-Fe reached 90% at 64 h, while that of β-G@MOFs (most micropores) was only 50%. This improvement resulting from the expansion of pores (significantly increased at 50-100 nm) can provide enough space for the hosted biomacromolecules and accelerate the diffusion rate of reactants. Furthermore, unexpectedly, the constructed β-G@MOF-Fe showed a superior heat resistance of up to 120 °C, attributing to the new strong coordination bond (Fe²⁺-N) formation through the metal competitive coordination. Therefore, this study offers new insights to solve the problem of the high-temperature macromolecular substrate encountered in the actual reaction.

Functional Porous Ionic Polymers as Efficient Heterogeneous Catalysts for the Chemical Fixation of CO2 under Mild Conditions

The development of efficient and metal-free heterogeneous catalysts for the chemical fixation of CO2 into value-added products is still a challenge. Herein, we reported two kinds of polar group (-COOH, -OH)-functionalized porous ionic polymers (PIPs) that were constructed from the corresponding phosphonium salt monomers (v-PBC and v-PBH) using a solvothermal radical polymerization method. The resulting PIPs (POP-PBC and POP-PBH) can be used as efficient bifunctional heterogeneous catalysts in the cycloaddition reaction of CO2 with epoxides under relatively low temperature, ambient pressure, and metal-free conditions without any additives. It was found that the catalytic activities of the POP-PBC and POP-PBH were comparable with the homogeneous catalysts of Me-PBC and PBH and were higher than that of the POP-PPh3-COOH that was synthesized through a post-modification method, indicating the importance of the high concentration catalytic active sites in the heterogeneous catalysts. Reaction under low CO2 concentration conditions showed that the activity of the POP-PBC (with a conversion of 53.8% and a selectivity of 99.0%) was higher than that of the POP-PBH (with a conversion of 32.3% and a selectivity of 99.0%), verifying the promoting effect of the polar group (-COOH group) in the porous framework. The POP-PBC can also be recycled at least five times without a significant loss of catalytic activity, indicating the high stability and robustness of the PIPs-based heterogeneous catalysts.

Cooperativity in the Aldol Condensation Using Bifunctional Mesoporous Silica-Poly(styrene) MCM-41 Organic/Inorganic Hybrid Catalysts

This work explores the efficacy of silica/organic hybrid catalysts, where the organic component is built from linear aminopolymers appended to the silica support within the support mesopores. Specifically, the role of molecular weight and polymer chain composition in amine-bearing atom transfer radical polymerization-synthesized poly(styrene-co-2-(4-vinylbenzyl)isoindoline-1,3-dione) copolymers is probed in the aldol condensation of 4-nitrobenzaldehyde and acetone. Controlled polymerization produces protected amine-containing poly(styrene) chains of controlled molecular weight and dispersity, and a grafting-to thiol-ene coupling approach followed by a phthalimide deprotection step are used to covalently tether and activate the polymer hybrid catalysts prior to the catalytic reactions. Site-normalized batch kinetics are used to assess the role of polymer molecular weight and chain composition in the cooperative catalysis. Lower-molecular-weight copolymers are demonstrated to be more active than catalysts built from only molecular organic components or from higher-molecular-weight chains. Molecular dynamics simulations are used to probe the role of polymer flexibility and morphology, whereby it is determined that higher-molecular-weight hybrid structures result in congested pores that inhibit active site cooperativity and the diffusivity of reagents, thus resulting in lower rates during the reaction.

Imidazolium-based poly(ionic liquid)s@MIL-101 for CO2 adsorption and subsequent catalytic cycloaddition without additional cocatalyst and solvent

Poly(ionic liquid)@MIL-101 incorporates an ionic liquid in a MOF and can be used in CO2 capture and conversion.

Optimizing the mobility of active species in ionic liquid/MIL-101 composites for boosting carbon dioxide conversion

The mobility of active species has been optimized based on ionic liquid/metal–organic framework (MOF) composites for efficient CO2 chemical fixation.

Tailoring Heterogeneous Catalysts at the Atomic Level: In Memoriam, Prof. Chia-Kuang (Frank) Tsung

Professor Chia-Kuang (Frank) Tsung made his scientific impact primarily through the atomic-level design of nanoscale materials for application in heterogeneous catalysis. He approached this challenge from two directions: above and below the material surface. Below the surface, Prof. Tsung synthesized finely controlled nanoparticles, primarily of noble metals and metal oxides, tailoring their composition and surface structure for efficient catalysis. Above the surface, he was among the first to leverage the tunability and stability of metal-organic frameworks (MOFs) to improve heterogeneous, molecular, and biocatalysts. This article, written by his former students, seeks first to commemorate Prof. Tsung's scientific accomplishments in three parts: (1) rationally designing nanocrystal surfaces to promote catalytic activity; (2) encapsulating nanocrystals in MOFs to improve catalyst selectivity; and (3) tuning the host-guest interaction between MOFs and guest molecules to inhibit catalyst degradation. The subsequent discussion focuses on building on the foundation laid by Prof. Tsung and on his considerable influence on his former group members and collaborators, both inside and outside of the lab.

Amino and triazole-containing metal-organic frameworks for highly efficient CO2 fixation

In this study, a novel porous metal-organic framework (MOF) functionalized with amino and triazole moieties has been synthesized. Attributed to the high affinity to CO₂ and unsaturated zinc centers, the MOF exhibits high catalytic activity for the CO₂ to epoxide cycloaddition reaction, with a turnover number value of up to 10 000 per cycle, and can be reused at least for 20 cycles.

Porous Organic Polymers for Catalytic Conversion of Carbon Dioxide

To overcome the challenges of global warming and environmental pollution, it is necessary to reduce the concentration of carbon dioxide (CO₂ ) in the atmosphere, which is mainly accumulated in the air through the burning of fossil fuels. Therefore, the development of environmentally friendly strategies to capture carbon dioxide and convert it into value-added products offers a promising way forward for reducing carbon dioxide concentration in the atmosphere. In this context, POPs (porous organic polymers) have shown great potential as CO₂ selective adsorbents due to their high specific surface area, chemical stability, nanoscale porosity and structural diversity, as well as POPs based heterogeneous catalysts for CO₂ conversion. This review provides a concise account of preparation methods of various POPs, challenges and current development trends of POPs in photocatalytic CO₂ reduction, electrocatalytic CO₂ reduction and chemical CO₂ conversion.

Preparation of Superhydrophobic Metal-Organic Framework/Polymer Composites as Stable and Efficient Catalysts

Metal-organic frameworks (MOFs), as a chemical platform, combined with multifunctional polymers are of interest in catalytic applications, which can not only inherit the outstanding properties of the two components but also lead to unique synergistic effects. Nonetheless, most MOFs possess varying degrees of water instability, which limits their real application. Herein, we fabricated highly hydrophobic MOF/polymer composites via a universal post-synthetic polymerization strategy as efficient catalysts. Polyaniline (PANI) was first hybridized with MOFs by vapor deposition polymerization, and then, hydrophobic molecules were grafted to the PANI by a covalent linking process, thereby forming a superhydrophobic MOF/PANI hybrid material (MOF/PANI-shp). The resultant MOF/PANI-shp not only obtains superior moisture/water resistance without significantly disturbing the original features but also exhibits a novel catalytic selectivity in styrene oxidation because of the accessible sites and synergistic effects. Such a synthetic strategy for the MOF/polymer catalyst opens a new avenue for the design of a unique catalyst with outstanding catalytic efficiency, selectivity, and stability.

Bioinspired Construction of Uranium Ion Trap with Abundant Phosphate Functional Groups

Highly efficient extraction of radioactive uranium from aqueous solution remains a serious task in the nuclear energy field. To address this, we here create an effective uranium ion trap by using a novel and facile strategy that introduces bioinspired moiety phytic acid (PA) into highly robust PCN-222. The resultant metal-organic framework (MOF)-based uranium ion trap (PCN-222-PA) with a high density of accessible phosphate groups exhibits a remarkable U(VI) uptake capacity (401.6 mg·g^-1), surpassing most of the reported phosphorus-modified MOFs and various other MOF adsorbents. Kinetics study reveals that PCN-222-PA can reduce the uranium concentration from 10 mg L^-1 to 21 μg L^-1, below the acceptable limit defined by the US Environmental Protection Agency. In addition, PCN-222-PA also shows good selectivity and high stability as well as excellent recyclability toward uranium capture. Our work demonstrates a new strategy to design functional MOFs with abundant phosphate groups and provides a new perspective for extracting uranium from aqueous solution.

Defect Engineering of Nanoscale Hf-Based Metal-Organic Frameworks for Highly Efficient Iodine Capture

With the rapid development of the nuclear industry, how to deal with radioactive iodine waste in a timely and effective manner has become an important issue to be solved urgently. Herein, the defect-engineering strategy has been applied to develop a metal-organic framework (MOF)-based solid adsorbent by using the classical UiO-type Hf-UiO-66 as an example. After simple acid treatment, the produced defect-containing Hf-UiO-66 (DHUN) not only retains its topological structure, high crystallization, and regular shape but also shows a great increase in the Brunauer-Emmett-Teller value and pore size in comparison with the original Hf-UiO (HUN). These formed defects within DHUN have been demonstrated to be important for the great enhancement of the iodine capture and following application in computed tomography imaging in vitro. This present work gives a new insight into the control and formation of defect sites, and this simple and efficient defect-engineering strategy also shows great promise for the development of novel solid adsorbents and other functional MOF materials.

Selective Implantation of Diamines for Cooperative Catalysis in Isoreticular Heterometallic Titanium-Organic Frameworks

We introduce the first example of isoreticular titanium-organic frameworks, MUV-10 and MUV-12, to show how the different affinity of hard Ti(IV) and soft Ca(II) metal sites can be used to direct selective grafting of amines. This enables the combination of Lewis acid titanium centers and available -NH₂ sites in two sizeable pores for cooperative cycloaddition of CO₂ to epoxides at room temperature and atmospheric pressure. The selective grafting of molecules to heterometallic clusters adds up to the pool of methodologies available for controlling the positioning and distribution of chemical functions in precise positions of the framework required for definitive control of pore chemistry.

Quest for an Efficient 2-in-1 MOF-Based Catalytic System for Cycloaddition of CO2 to Epoxides under Mild Conditions

We have devised a straightforward tandem postsynthetic modification strategy for Zr-based metal-organic framework (MOF) materials, which resulted in a series of well-defined 2-in-1 heterogeneous catalysts, cat1-cat8, exhibiting high catalytic activity in the synthesis of cyclic carbonates under solvent-free and co-catalyst-free conditions. The materials feature precisely located co-catalyst moieties decorating the metal nodes throughout the bulk of the MOF and yield cyclic carbonates with up to 99% efficiency at room temperature. We use diffuse reflectance infrared Fourier transform (DRIFT) and solid-state nuclear magnetic resonance (NMR) measurements to elucidate the role of each component in this model catalytic reaction. Establishing a method to precisely control the co-catalyst loading allowed us to observe the cooperativity between Lewis acid sites and the co-catalyst in the 2-in-1 heterogeneous system.

Aminoethylimidazole ionic liquid-grafted MIL-101-NH2 heterogeneous catalyst for the conversion of CO2 and epoxide without solvent and cocatalyst

An aminoethylimidazole IL-functionalized MIL-101-NHIM-NH₂ catalyst efficiently catalyzes the cycloaddition reaction of CO₂ and epoxide without solvent and cocatalyst, owing to the synergistic effects of Cr, –NH₂ and Br⁻ active sites.

Rational Design of a ZnII MOF with Multiple Functional Sites for Highly Efficient Fixation of CO2 under Mild Conditions: Combined Experimental and Theoretical Investigation

The development of efficient heterogeneous catalysts suitable for carbon capture and utilization (CCU) under mild conditions is a promising step towards mitigating the growing concentration of CO₂ in the atmosphere. Herein, we report the construction of a hydrogen-bonded 3D framework, {[Zn(hfipbba)(MA)]⋅3 DMF}_n (hfipbba=4,4'-(hexaflouroisopropylene)bis(benzoic acid)) (HbMOF1) utilizing Zn^II center, a partially fluorinated, long-chain dicarboxylate ligand (hfipbba), and an amine-rich melamine (MA) co-ligand. Interestingly, the framework possesses two types of 1D channels decorated with CO₂ -philic (-NH₂ and -CF₃ ) groups that promote the highly selective CO₂ adsorption by the framework, which was supported by computational simulations. Further, the synergistic involvement of both Lewis acidic and basic sites exposed in the confined 1D channels along with high thermal and chemical stability rendered HbMOF1 a good heterogeneous catalyst for the highly efficient fixation of CO₂ in a reaction with terminal/internal epoxides at mild conditions (RT and 1 bar CO₂ ). Moreover, in-depth theoretical studies were carried out using periodic DFT to obtain the relative energies for each stage involved in the catalytic reaction and an insight mechanistic details of the reaction is presented. Overall, this work represents a rare demonstration of rational design of a porous Zn^II MOF incorporating multiple functional sites suitable for highly efficient fixation of CO₂ with terminal/internal epoxides at mild conditions supported by comprehensive theoretical studies.

Optimizing Strategy for Enhancing the Stability and 99TcO4 - Sequestration of Poly(ionic liquids)@MOFs Composites

Metal-organic frameworks (MOFs) are a class of promising sorbents for effective sequestration of radioactive ⁹⁹TcO₄ ^- anions. However, their poor stability and slow sorption kinetics in the industrial condition pose a great challenge. Herein, we demonstrate an optimizing strategy via in situ polymerization of ionic liquids (ILs) encapsulated in the pores of MOFs, forming polyILs@MOFs composites with greatly enhanced TcO₄ ^- sequestration compared with the pristine MOFs. Notably, the cross-linked polymerization of ILs facilitates the formation of both the inside ionic filler as the active sites and outside coating as the protective layers of MOFs, which is significantly beneficial to obtain the optimized sorption materials of exceptional stability under extreme conditions (e.g., in 6 M HNO₃). The final optimized composite shows fast sorption kinetics (<30 s), good regeneration (>30 cycles), and superior uptake performance for TcO₄ ^- in highly acidic conditions and simulated recycle stream. This strategy opens up a new opportunity to construct the highly stable MOF-based composites and extend their applicability in different fields.