New rht-Type Metal-Organic Frameworks Decorated with Acylamide Groups for Efficient Carbon Dioxide Capture and Chemical Fixation from Raw Power Plant Flue Gas

Highly efficient CO2 capture and chemical fixation of a microporous (3, 36)-connected txt-type Cu(II)-MOF with multifunctional sites

Incorporating multiple functional sites in porous frameworks to enormously enhance the host-guest interactions is an effective strategy to obtain high-performance CO2 capture and chemical fixation MOF materials. Herein, we designed and constructed a microporous (3, 36)-connected txt-type Cu(II)-based MOF (HNUST-17) from dicopper(II)-paddlewheel clusters and a novel pyridine-based acylamide-linking V-shape diisophthalate ligand with amino groups. Interestingly, with a high density of multiple strong CO2-philic sites (open metal sites, acylamide and amino functionalities) integrated in the framework, which have been identified by GCMC (Grand canonical Monte Carlo) simulations and DFT (Density functional theory) calculations, HNUST-17 exhibits high and selective capture for CO2 over CH4 and N2 at ambient temperature. Moreover, HNUST-17 possesses efficiently catalytic activity and recyclability for chemical fixation of CO2 coupling with epoxides into cyclic carbonates in the presence of tetrabutylammonium bromide as the cocatalyst under mild, solvent-free conditions.

Study on Selected Metal-Organic Framework-Based Catalysts for Cycloaddition Reaction of CO2 with Epoxides: A Highly Economic Solution for Carbon Capture and Utilization

The level of carbon dioxide in the atmosphere is growing rapidly due to fossil fuel combustion processes, heavy oil, coal, oil shelter, and exhausts from automobiles for energy generation, which lead to depletion of the ozone layer and consequently result in global warming. The realization of a carbon-neutral environment is the main focus of science and academic researchers of today. Several processes were employed to minimize carbon dioxide in the air, some of which include the utilization of non-fossil sources of energy like solar, nuclear, and biomass-based fuels. Consequently, these sources were reported to have a relatively high cost of production and maintenance. The applications of both homogeneous and heterogeneous processes in carbon capture and storage were investigated in recent years and the focus now is on the conversion of CO2 into useful chemicals and compounds. It was established that CO2 can undergo cycloaddition reaction with epoxides under the influence of special catalysts to give cyclic carbonates, which can be used as value-added chemicals at a different level of pharmaceutical and industrial applications. Among the various catalysts studied for this reaction, metal-organic frameworks are now on the frontline as a potential catalyst due to their special features and easy synthesis. Several metal-organic framework (MOF)-based catalysts were studied for their application in transforming CO2 to organic carbonates using epoxides. Here, we report some recent studies of porous MOF materials and an in-depth discussion of two repeatedly used metal-organic frameworks as a catalyst in the conversion of CO2 to organic carbonates.

Nanochannel {InZn}-Organic Framework with a High Catalytic Performance on CO2 Chemical Fixation and Deacetalization-Knoevenagel Condensation

The rare combination of In^III 5p and Zn^II 3d in the presence of a structure-oriented TDP^6- ligand led to a robust hybrid material of {(Me₂NH₂)[InZn(TDP)(OH₂)]·4DMF·4H₂O}_n (NUC-42) with the interlaced hierarchical nanochannels (hexagonal and cylindrical) shaped by six rows of undocumented [InZn(CO₂)₆(OH₂)] clusters, which represented the first 5p-3d nanochannel-based heterometallic metal-organic framework. With respect to the multifarious symbiotic Lewis acid-base and Brønsted acid sites in the high porous framework, the catalytic performance of activated NUC-42a upon CO₂ cycloaddition with styrene oxide was evaluated under solvent-free conditions with 1 atm of CO₂ pressure, which exhibited that the reaction could be well completed at ambient temperature within 48 h or at 60 °C within 4 h with high yield and selectivity. Moreover, because of the acidic function of metal sites and a central free pyridine in the TDP^6- ligand, deacetalization-Knoevenagel condensation of acetals and malononitrile could be efficiently facilitated by an activated sample of NUC-42a under lukewarm conditions.

A pyridyl-decorated Zr-organic framework for enhanced gas separation and CO2 transformation

A Zr-based MOF with UiO-66 topology, which was defined as Py-UiO-66, has been synthesized by modifying the ligand of p-phthalic acid with a pyridine group. Py-UiO-66 possesses excellent chemical stability in aqueous solutions of pH = 0-13, especially when the pore structure is functionalized by hanging bare Lewis basic pyridine groups. Results of gas adsorption experiment show that Py-UiO-66 has the ability to selectively absorb C₂H₂ and CO₂ rather than CH₄. More importantly, Py-UiO-66 has an efficient catalytic effect in CO₂ cycloaddition.

An NH2-modified {EuIII2}–organic framework for the efficient chemical fixation of CO2 and highly selective sensing of 2,4,6-trinitrophenol

An amino-functionalized microporous material of {(Me2NH2)4[Eu4(DDAC)3(HCO2)(OH2)2]·8DMF·9H2O}n with hierarchical pore voids displays efficient chemical fixation of CO2 and highly selective sensing of 2,4,6-trinitrophenol.

In situ cleavage and rearrangement synthesis of an easy-to-obtain and highly stable Cu(ii)-based MOF for efficient heterogeneous catalysis of carbon dioxide conversion

A Cu(ii)-based MOF has been synthesized by the in situ cleavage and rearrangement solvothermal synthesis. This material exhibits highly stabilities and CO2 adsorption ability to catalyze cycloaddition of CO2 with epoxides efficiently.

Highly Robust 3s-3d {CaZn}-Organic Framework for Excellent Catalytic Performance on Chemical Fixation of CO2 and Knoevenagel Condensation Reaction

In terms of ligand-directed synthetic strategy, multifunctional metal-organic frameworks (MOFs) could be assembled by employing organic ligands with nitrogen-containing heterocycles, which could serve as Lewis base sites in crystallized porous frameworks. Here, the acidic one-pot hydrothermal reaction of CaCl₂, Zn(NO₃)₂, and 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H₆TDP) generates one robust honeycomb-shaped double-walled material of {[(CH₃)₂NH₂]₂[CaZn(TDP)(H₂O)]·3DMF·3H₂O}_n (NUC-21), which has the excellent physicochemical characteristics of nanoscopic channels, high porosity (58.3%), large specific surface area, and high heat/water-resisting property. To the best of our knowledge, this is the first 3s-3d dinuclear [CaZn(CO₂)₆(OH₂)]-based nanoporous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including four-coordinated Zn²⁺ ions, four-coordinated Ca²⁺ ions, uncoordinated carboxyl oxygen atoms, and N_pyridine atoms. As expected, because of the coexistence of Lewis acid-base nature, desolvated NUC-21 displays satisfactory catalytic activity on the chemical cycloaddition of various epoxides with CO₂ into the corresponding alkyl carbonates under comparatively mild conditions. Furthermore, the efficient conversion of benzaldehydes and malononitrile confirms that NUC-21 is simultaneously a bifunctional heterogeneous catalyst for Knoevenagel condensation reactions. Hence, the achievements broaden the way for assembling nanoporous multifunctional MOFs by employing ligand-directed synthetic strategy, which can accelerate the transformation from simple structural research to socially demanding applications.

Imidazolium-Functionalized Ionic Hypercrosslinked Porous Polymers for Efficient Synthesis of Cyclic Carbonates from Simulated Flue Gas

The rapid growth of CO₂ emissions, especially from power plants, has led to the urgent need to directly capture and fix CO₂ in the flue gas after simple purification rather than energy-intensive gas separation. Herein, imidazolium-functionalized ionic hypercrosslinked porous polymers (HCPs) bearing adjustable surface groups were straightforwardly synthesized through co-hypercrosslinking of benzylimidazole salts and crosslinker through Friedel-Crafts alkylation. Abundant microporosity and relatively high ionic moieties were obtainable in the ethyl-group-tethered ionic HCP, giving a remarkably selective CO₂ capture performance with a CO₂ uptake of 3.05 mmol g^-1 and an ideal adsorbed solution theory (IAST) CO₂ /N₂ selectivity as high as 363 (273 K, 1 bar). This ionic polymer demonstrated high efficiency in the synthesis of cyclic carbonates from the coupling of various epoxides with the simulated flue gas (15 % CO₂ and 85 % N₂ ), giving high yields, large turnover numbers (up to 4800), and stable reusability under additive- and solvent-free conditions.

Photoswitchable Cu(ii)/Cu(i) catalyses assisted by enzyme-like non-covalent interactions in Cu(ii)–melamine coordination polymers for installing CO2/CS2 and CF3 groups in heterocycles

This study describes photoswitchable Cu(ii)/Cu(i) catalyses and enzyme-like interactions in Cu–TDPAT for installing CO₂/CS₂ and CF₃ groups in heterocycles.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks

Transformation of CO₂ based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO₂ . In fact, it is the formation of new covalent bonds between CO₂ and substrate molecules that successfully result in CO₂ solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO₂ conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO₂ , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Highly efficient CO2 capture and conversion of a microporous acylamide functionalized rht-type metal–organic framework

A microporous acylamide functionalized rht-type MOF (HNUST-9) with Lewis acidic open copper sites and CO₂-philic acylamide groups exhibits high performance for CO₂ capture, separation and chemical conversion.

A novel synthesis of new antibacterial nanostructures based on Zn-MOF compound: design, characterization and a high performance application

In this study, the novel zinc metal-organic frameworks (MOF) nanostructure has been employed, which was developed using an affordable, environmental friendly, efficient and fast method of ultrasound-assisted reverse micelle (UARM). These nanostructures were identified with various techniques such as FT-IR, XRD, BET, SEM, TG-DSC, TEM and EDS. It was found that the Zn-MOF samples have favorable physicochemical properties. The impact of experimental parameters of the UARM method is effective on the resulting properties, such as high surface area of the products that increases the interactions between the Zn-MOF nanostructure and bacteria.Their antibacterial activities were investigated using diffusion methods in agar and also with dilutions of Zn-MOF samples. Antibiotics (tetracycline and ampicillin) and their anti-biofilm effects were evaluated using microplate method. Obtained results revealed that the Zn-MOF nanostructures have high antibacterial properties which, could be due to the nature of the applied Zn-MOF as well as the optimization process. The Zn- MOF nanostructures could be a novel antibacterial material as biocatalyst processes.

Carbon dioxide capture and efficient fixation in a dynamic porous coordination polymer

Direct structural information of confined CO₂ in a micropore is important for elucidating its specific binding or activation mechanism. However, weak gas-binding ability and/or poor sample crystallinity after guest exchange hindered the development of efficient materials for CO₂ incorporation, activation and conversion. Here, we present a dynamic porous coordination polymer (PCP) material with local flexibility, in which the propeller-like ligands rotate to permit CO₂ trapping. This process can be characterized by X-ray structural analysis. Owing to its high affinity towards CO₂ and the confinement effect, the PCP exhibits high catalytic activity, rapid transformation dynamics, even high size selectivity to different substrates. Together with an excellent stability with turnover numbers (TON) of up to 39,000 per Zn_1.5 cluster of catalyst after 10 cycles for CO₂ cycloaddition to form value-added cyclic carbonates, these results demonstrate that such distinctive structure is responsible for visual CO₂ capture and size-selective conversion.

Efficient Conversion of CO2 via Grafting Urea Group into a [Cu2(COO)4]-Based Metal-Organic Framework with Hierarchical Porosity

The assembly of mixed [1,1';3',1'']terphenyl-4,5',4''-tricarboxylic acid (H₃TPTC) and [1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂BPDC), 2,2'-diamino-[1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂BPDC-NH₂), or 6-oxo-6,7-dihydro-5H-dibenzo[ d, f][1,3]diazepine-3,9-dicarboxylic acid (H₂BPDC-Urea) with Cu²⁺ ion generated the corresponding copper-paddlewheel-based metal-organic framework (MOF) [Cu₅(TPTC)₃(BPDC)_0.5(H₂O)₅] (1), [Cu₅(TPTC)₃(BPDC-NH₂)_0.5(H₂O)₅] (1-NH₂), or [Cu₅(TPTC)₃(BPDC-Urea)_0.5(H₂O)₅] (1-Urea). They are isostructural with hierarchical porosity, consisting of zero-dimensional cage (19.2 Å × 18.9 Å) and one-dimensional pillar channel (29.7 Å × 15.1 Å) in a manner of face sharing. Platon analyses revealed the porous volume ratios are 80.2%, 80.0%, and 77.8% for 1, 1-NH₂, and for 1-Urea, respectively. Thermogravimetric measurements suggested 53, 51, and 48 wt % guest molecules in 1, 1-NH₂, and 1-Urea, respectively. 1-NH₂ and 1-Urea were precisely functionalized via the introduction of amino and urea functional groups into the pillar channels. The constructed MOF 1-Urea, incorporating both exposed copper active sites and accessible urea functional groups to substrates, presents high efficiency on catalytic CO₂ cycloaddition with propene oxide to produce cyclic carbonate in the yield of 98% with a TOF value of 136 h^-1 at 1 atm and room temperature. This synergic effect provides a new strategy for designing high-efficient catalysts for CO₂ chemical conversion under ambient conditions.

Application of Metal–Organic Frameworks in CO2 Capture and Conversion

Metal–organic frameworks (MOFs) are promising candidates for CO2 capture and conversion as they possess remarkable properties, including large surface area, open channels and permanent porosity. Through the judicious selection of metal clusters and organic linkers, a framework with a desired topology can be realized. Furthermore, the study of the noncovalent interactions in MOFs provides significant insights into the relationship between the catalytic performance and the framework structure, which will also further promote the development of MOFs as heterogeneous catalysts for CO2 capture and conversion. This chapter is divided into four sections. The first section gives a brief introduction to the structures and chemical features of MOFs. The second section concentrates on MOFs as heterogeneous catalysts for the chemical fixation of CO2 with organic compounds. The third section presents MOFs as photocatalysts for CO2 reduction. The last section covers the application of MOFs in the electrocatalytic reduction of CO2. Particular challenges in the rational design and application of MOF catalysts and research opportunities for further development are highlighted. It is hoped that this chapter will not only serve as a starting point to gain insights into this challenging field but will also stimulate more intensive research on the development of creative MOFs as heterogeneous catalysts towards CO2 capture and conversion.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

This review summarizes recent advances and highlights the structure–property relationship on metal–organic framework-based materials for carbon dioxide capture and conversion.

A tri-functional metal–organic framework heterogeneous catalyst for efficient conversion of CO2 under mild and co-catalyst free conditions

A novel tri-functional MOF catalyst was achieved by PSM method. Because of the synergistic effect of Lewis acid, Brønsted acid and Br⁻ anion, MIL-IMAc-Br⁻ displayed an efficient catalytic performance for CO₂ conversion.

A ligand conformation preorganization approach to construct a copper–hexacarboxylate framework with a novel topology for selective gas adsorption

A ligand conformation preorganization strategy was employed to design a hexacarboxylate ligand, and its corresponding copper-based MOF was constructed, exhibiting a novel topological structure and the potential for the separation and purification of acetylene and natural gas.

Catalytic Space Engineering of Porphyrin Metal-Organic Frameworks for Combined CO2 Capture and Conversion at a Low Concentration

Porous porphyrin metal-organic frameworks (PMOFs) provide promising platforms for studying CO₂ capture and conversion (C3) owing to their versatility in photoelectric, catalytic, and redox activities and porphyrin coordination chemistry. Herein, we report the C3 application of two PMOFs by engineering the coordination space through the introduction of two catalytic metalloporphyrins doped with rhodium or iridium, Rh-PMOF-1 and Ir-PMOF-1, both of which can serve as heterogeneous catalysts for the chemical fixation of CO₂ into cyclic carbonates with yields of up to 99 %. Remarkably, the catalytic reactions can effectively proceed under low CO₂ concentrations and high yields of 83 % and 73 % can be obtained under 5 % CO₂ in the presence of Rh-PMOF-1 and Ir-PMOF-1, respectively. The synergistic effect of the metalloporphyrin ligand and the Zr₆ O₈ cluster, in combination with the CO₂ concentration effect from the pore space, might account for the excellent catalytic performance of Rh-PMOF-1 under low CO₂ concentration. Recycling tests of Rh-PMOF-1 show negligible loss of catalytic activity after 10 runs.

Porous Metal-Organic Polyhedral Framework containing Cuboctahedron Cages as SBUs with High Affinity for H2 and CO2 Sorption: A Heterogeneous Catalyst for Chemical Fixation of CO2

Development of active porous materials that can efficiently adsorb H₂ and CO₂ is needed, due to their practical utilities. Here we present the design and synthesis of an interpenetrated Cu^II metal-organic framework (MOF) that is thermally stable, highly porous and can act as a heterogeneous catalyst. The Cu^II -MOF contains a highly symmetric polyhedral metal cluster (Cu₂₄ ) with cuboctahedron geometry as secondary building unit (SBU). The double interpenetration of such huge cluster-containing nets provides a high density of open metal sites, due to which it exhibits remarkable H₂ storage capacity (313 cm³ g^-1 at 1 bar and 77 K) as well as high CO₂ capture ability (159 cm³ g^-1 at 1 bar and 273 K). Further, its propensity towards CO₂ sorption can be utilized for the heterogeneous catalysis of the chemical conversion of CO₂ into the corresponding cyclic carbonates upon reaction with epoxides, with high turnover number and turnover frequency values.