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.

Binding of carbon dioxide and acetylene to free carboxylic acid sites in a metal-organic framework

The functionalisation of organic linkers in metal-organic frameworks (MOFs) to improve gas uptake is well-documented. Although the positive role of free carboxylic acid sites in MOFs for binding gas molecules has been proposed in computational studies, relatively little experimental evidence has been reported in support of this. Primarily this is because of the inherent synthetic difficulty to prepare MOF materials bearing free, accessible -COOH moieties which would normally bind to metal ions within the framework structure. Here, we describe the direct binding of CO2 and C2H2 molecules to the free -COOH sites within the pores of MFM-303(Al). MFM-303(Al) exhibits highly selective adsorption of CO2 and C2H2 with a high selectivity for C2H2 over C2H4. In situ synchrotron X-ray diffraction and inelastic neutron scattering, coupled with modelling, highlight the cooperative interactions of adsorbed CO2 and C2H2 molecules with free -COOH and -OH sites within MFM-303(Al), thus rationalising the observed high selectivity for gas separation.

Direct Observation of Enhanced Iodine Binding within a Series of Functionalized Metal-Organic Frameworks with Exceptional Irradiation Stability

Optimization of active sites and stability under irradiation are important targets for sorbent materials that might be used for iodine (I2) storage. Herein, we report the direct observation of I2 binding in a series of Cu(II)-based isostructural metal-organic frameworks, MFM-170, MFM-172, MFM-174, NJU-Bai20, and NJU-Bai21, incorporating various functional groups (-H, -CH3, - NH2, -C≡C-, and -CONH-, respectively). MFM-170 shows a reversible uptake of 3.37 g g-1 and a high packing density of 4.41 g cm-3 for physiosorbed I2. The incorporation of -NH2 and -C≡C- moieties in MFM-174 and NJU-Bai20, respectively, enhances the binding of I2, affording uptakes of up to 3.91 g g-1. In addition, an exceptional I2 packing density of 4.83 g cm-3 is achieved in MFM-174, comparable to that of solid iodine (4.93 g cm-3). In situ crystallographic studies show the formation of a range of supramolecular and chemical interactions [I···N, I···H2N] and [I···C≡C, I-C═C-I] between -NH2, -C≡C- sites, respectively, and adsorbed I2 molecules. These observations have been confirmed via a combination of solid-state nuclear magnetic resonance, X-ray photoelectron, and Raman spectroscopies. Importantly, γ-irradiation confirmed the ultraresistance of MFM-170, MFM-174, and NJU-Bai20 suggesting their potential as efficient sorbents for cleanup of radioactive waste.

One-Pot Synthesis of MOF@MOF: Structural Incompatibility Leads to Core-Shell Structure and Adaptability Control Makes the Sequence

Core-shell metal-organic frameworks (MOF@MOF) are promising materials with sophisticated structures that cannot only enhance the properties of MOFs but also endow them with new functions. The growth of isotopic lcore-shell MOFs is mostly limited to inconvenient stepwise seeding strategies with strict requirements, and by far one-pot synthesis is still of great challenge due to the interference of different components. Through two pairs of isoreticular MOFs, it reveals that the structural incompatibility is a prerequisite for the formation of MOFs@MOFs by one-pot synthesis, as illustrated by PMOF-3@HHU-9. It further unveils that the adaptability of the shell-MOF is a more key factor for nucleation kinetic control. MOFs with flexible linkers has comparably slower nucleation than MOFs with rigid linkers (forming PMOF-3@NJU-Bai21), and structural-flexible MOFs built by flexible linkers show the lowest nucleation and the most adaptability (affording NJU-Bai21@HHU-9). This degree of adaptability variation controls the sequence and further facilitates the synthesis of a first triple-layered core-shell MOF (PMOF-3@NJU-Bai21@HHU-9) by one-pot synthesis. The insight gained from this study will aid in the rational design and synthesis of other multi-shelled structures by one-pot synthesis and the further expansion of their applications.

Optimized Pore Nanospace through the Construction of a Cagelike Metal-Organic Framework for CO2/N2 Separation

The development of metal-organic framework (MOF) adsorbents with a potential molecule sieving effect for CO₂ capture and separation from flue gas is of critical importance for reducing the CO₂ emissions to the atmosphere yet challenging. Herein, a cagelike MOF with a suitable cage window size falling between CO₂ and N₂ and the cavity has been constructed to evaluate its CO₂/N₂ separation performance. It is noteworthy that the introduction of coordinated dimethylamine (DMA) and N,N'-dimethylformamide (DMF) molecules not only significantly reduces the cage window size but also enhances the framework-CO₂ interaction via C-H···O hydrogen bonds, as proven by molecular modeling, thus leading to an improved CO₂ separation performance. Moreover, transient breakthrough experiments corroborate the efficient CO₂/N₂ separation, revealing that the introduction of DMA and DMF molecules plays a vital role in the separation of a CO₂/N₂ gas mixture.

Highly Efficient Conversion of Aziridines and CO2 Catalyzed by Microporous [Cu12] Nanocages

The conversion of CO₂ as a C1 source into value-added products is an attractive alternative in view of the green synthesis. Among the reported approaches, the cyclization reaction of aziridines with CO₂ is of great significance since the generated N-containing cyclic skeletons are extensively found in pharmaceutical chemistry and industrial production. However, a low turnover number (TON) and homogeneous catalysts are often involved in this catalytic system. Herein, one novel copper-organic framework {[Cu₂(L^4-)(H₂O)₂]·3DMF·2H₂O}_n (1) (H₄L = 2'-fluoro-[1,1':4',1″-Terphenyl]-3,3″,5,5″-tetracarboxylic acid) assembled by nanosized [Cu₁₂] cages was successfully synthesized and structurally characterized, which exhibits high CO₂/N₂ selectivity due to the strong interactions between CO₂ and open Cu(II) sites and ligands in the framework. Catalytic investigations suggest that 1 as a heterogeneous catalyst can effectively catalyze the cyclization of aziridines with CO₂, and the TON can reach a record value of 90.5. Importantly, 1 displays excellent chemical stability, which can be recycled at least five times. The combination explorations of nuclear magnetic resonance (NMR), ¹³C-isotope labeling experiments, and density functional theory (DFT) clearly uncover the mechanism of this aziridine/CO₂ coupling reaction system, in which 1 and tetrabutylammonium bromide (TBAB) can highly activate the substrate molecule, and the synergistic catalytic effect between them can greatly reduce the reaction energy barrier from 51.7 to 36.2 kcal/mol.

Porous functional metal–organic frameworks (MOFs) constructed from different N-heterocyclic carboxylic ligands for gas adsorption/separation

This review mainly summarizes the recent progress of MOFs composed of N-heterocyclic carboxylate ligands in gas sorption/separation. This work may help to understand the relationship between the structures of MOFs and gas sorption/separation.

Designing Multicomponent Metal-Organic Frameworks with Hierarchical Structure-Mimicking Distribution for High CO2 Capture Performance

By utilizing a mixed-ligand strategy, a novel multicomponent Cu-metal-organic framework (MOF) (JLU-MOF107) has been successfully synthesized. JLU-MOF107 has an unusual hierarchical structure-mimicking distribution structure. The triangular 4,4',4″-benzene-1,3,5-triyl-tribenzoate (BTB) ligand and the binuclear Cu cluster form a threefold interpenetration layer, while the linear ligand 1,4-phenylene-4,4'-bis(1,2,4-triazole) (p-tr₂ph) and tetranuclear Cu cluster form a noninterpenetration pillared-layer structure. Then, the two types of layers are connected by tetranuclear Cu clusters to construct the final sandwichlike framework. JLU-MOF107 exhibits good water and humidity stability. Due to the presence of various active sites and pores, JLU-MOF107 shows an outstanding performance for CO₂ capture (171.0 cm³ g^-1 at 273 K). Density functional theory (DFT)-based calculations further prove the interactions between CO₂ molecules and multiple active sites. The innovative synthesis of this multicomponent structure offers a new perspective on making hierarchical porous materials and multifunctional MOFs.

Recent advances in performance improvement of Metal-organic Frameworks to remove antibiotics: Mechanism and evaluation

Antibiotic pollution is a serious global problem, which may threaten the health of human and ecosystem. Thereinto, water pollution is the most common way. Thus, it is necessary to develop effective methods to remove antibiotics from the natural aqueous environments. Metal-organic Frameworks (MOFs) - based adsorption and photocatalysis strategies have been demonstrated to be efficient, environmental and promising methods to solve antibiotic pollution and repair the environment. In this review, several strategies to improve the properties of MOFs for removal were summarized and discussed. And the removal mechanisms were also discussed. Besides, new and more reliable evaluation methods of MOFs to remove antibiotics were presented, including preferential adsorption (q_p), quantum yields (QY), space time yields (SY) and figure of merit (FOM). This paper provides alternative perspectives for researchers to improve the properties of MOFs and raise analytic efficiency of antibiotic removal.

Double-Walled Zn36@Zn104 Multicomponent Senary Metal-Organic Polyhedral Framework and Its Isoreticular Evolution

Metal-organic polyhedral frameworks are attractive in gas storage and separation due to large voids with windows that can serve as traps for guest molecules. Introducing multivariant/multicomponent functionalities in them are ways of improving performances for certain targets. The high compatibility of organic linkers can generate multivariant MOFs, but by far, the diversity of secondary building units (SBUs) in a single metal-organic framework is still limited (no more than two in most cases). Here we report a new double-walled Zn₃₆@Zn₁₀₄ metal-organic polyhedral framework (HHU-8) with five types of topologically distinct SBUs and its isoreticular evolution to the Zn₃₆@Zn₁₃₆ counterpart (HHU-8s). Both MOFs are the first to be constructed with such high numbers of topologically distinct SBUs as well as topologically distinct nodes, and their formation and evolution provide new insight into SBU's controllability.

Efficient Gas and VOC Separation and Pesticide Detection in a Highly Stable Interpenetrated Indium-Organic Framework

The new indium-based organic framework {(Me₂NH₂)[In(BDPO)]·DMF·2H₂O}_n (1) was successfully constructed by using the oxalamide group modified ligand N,N'-bis(isophthalic acid)oxalamide (H₄BDPO). This framework presents a 2-fold interpenetrating structural characteristic, and the unique polar pore environment leads to a high capture ability for CO₂, C₂H_n and CH₃OH and good separation ability for CO₂ and C₂H_n over CH₄ as well as for CH₃OH over C₂H₅OH, which was further verified by an ideal adsorbed solution theory (IAST) calculation. Theoretical simulations pointed out the possible adsorption sites of different adsorbed gases in 1. In addition, the excellent chemical stability and strong luminescence of 1 give it an effective selective detection ability for 2,6-dichloro-4-nitroaniline (DCN) in water with a low detection limit of 3.85 ppm, and the detection mechanism is discussed in detail.

Precise Pore Space Partitions Combined with High-Density Hydrogen-Bonding Acceptors within Metal-Organic Frameworks for Highly Efficient Acetylene Storage and Separation

The high storage capacity versus high selectivity trade-off barrier presents a daunting challenge to practical application as an acetylene (C₂ H₂ ) adsorbent. A structure-performance relationship screening for sixty-two high-performance metal-organic framework adsorbents reveals that a moderate pore size distribution around 5.0-7.5 Å is critical to fulfill this task. A precise pore space partition approach was involved to partition 1D hexagonal channels of typical MIL-88 architecture into finite segments with pore sizes varying from 4.5 Å (SNNU-26) to 6.4 Å (SNNU-27), 7.1 Å (SNNU-28), and 8.1 Å (SNNU-29). Coupled with bare tetrazole N sites (6 or 12 bare N sites within one cage) as high-density H-bonding acceptors for C₂ H₂ , the target MOFs offer a good combination of high C₂ H₂ /CO₂ adsorption selectivity and high C₂ H₂ uptake capacity in addition to good stability. The optimized SNNU-27-Fe material demonstrates a C₂ H₂ uptake of 182.4 cm³  g^-1 and an extraordinary C₂ H₂ /CO₂ dynamic breakthrough time up to 91 min g^-1 under ambient conditions.

Reversible coordinative binding and separation of sulfur dioxide in a robust metal-organic framework with open copper sites

Emissions of SO₂ from flue gas and marine transport have detrimental impacts on the environment and human health, but SO₂ is also an important industrial feedstock if it can be recovered, stored and transported efficiently. Here we report the exceptional adsorption and separation of SO₂ in a porous material, [Cu₂(L)] (H₄L = 4',4‴-(pyridine-3,5-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid)), MFM-170. MFM-170 exhibits fully reversible SO₂ uptake of 17.5 mmol g^-1 at 298 K and 1.0 bar, and the SO₂ binding domains for trapped molecules within MFM-170 have been determined. We report the reversible coordination of SO₂ to open Cu(II) sites, which contributes to excellent adsorption thermodynamics and selectivities for SO₂ binding and facile regeneration of MFM-170 after desorption. MFM-170 is stable to water, acid and base and shows great promise for the dynamic separation of SO₂ from simulated flue gas mixtures, as confirmed by breakthrough experiments.

Syntheses, Structures and Sorption Properties of Three Isoreticular Trinuclear Indium-Based Amide-Functionalized Metal-Organic Frameworks

Amide-functionalized metal-organic frameworks (AFMOFs) as a subclass of MOF materials have received great interest recently because of their intriguing structures and diverse potential applications. In this work, solvothermal reactions between indium nitrate and two mixed-linkers afforded two new isoreticular 8-connected trinuclear indium-based AFMOFs of [(In₃ O)(OH)(L2)₂ (IN)₂ ]⋅(solv)_x (2-In) and [(In₃ O)(OH)(L2)₂ (AIN)₂ ]⋅(solv)_x (NH₂ -2-In) (H₂ L2=4,4'-(carbonylimino)dibenzoic acid and HIN=isonicotinic acid or HAIN=3-aminoisonicotinic acid), respectively. Moreover, by means of reticular chemistry, an extended network of [(In₃ O)(OH)(L3)₂ (PB)₂ ]⋅(solv)_x (3-In) (H₂ L3=4,4'-(terephthaloylbis(azanediyl))dibenzoic acid, HPB=4-(4-pyridyl)benzoic acid) was also successfully realized after prolongation of the former dicarboxylate linker and HIN, resulting in a truly 8-connected isoreticular AFMOF platform. These frameworks were structurally determined by single-crystal X-ray diffraction (SCXRD). Sorption studies further demonstrate that 2-In and NH₂ -2-In exhibit not only high surface areas and pore volumes but also relatively high carbon capture capabilities (the CO₂ uptakes reach 60.0 and 75.5 cm³  g^-1 at 298 K and 760 torr, respectively) due to the presences of amide and/or amine functional groups. The selectivity of CO₂ /N₂ and CO₂ /CH₄ calculated by IAST are 10.18 and 12.43, 4.20 and 4.23 for 2-In and NH₂ -2-In, respectively, which were additionally evaluated by mixed-gases dynamic breakthrough experiments. In addition, high-pressure gas sorption measurements show that both materials could take up moderate amounts of natural gas.

Trends in Solid Adsorbent Materials Development for CO2 Capture

A recent report from the United Nations has warned about the excessive CO₂ emissions and the necessity of making efforts to keep the increase in global temperature below 2 °C. Current CO₂ capture technologies are inadequate for reaching that goal, and effective mitigation strategies must be pursued. In this work, we summarize trends in materials development for CO₂ adsorption with focus on recent studies. We put adsorbent materials into four main groups: (I) carbon-based materials, (II) silica/alumina/zeolites, (III) porous crystalline solids, and (IV) metal oxides. Trends in computational investigations along with experimental findings are covered to find promising candidates in light of practical challenges imposed by process economics.

Rapid room temperature conversion of hydroxy double salt to MOF-505 for CO2 capture

Given the fact that solvothermal synthesis is the most common synthetic method to obtain metal–organic frameworks (MOFs) on a gram scale, it still remains a great challenge to produce MOFs in a scalable and sustainable synthetic process.

Incorporation of bifunctional aminopyridine into an NbO-type MOF for the markedly enhanced adsorption of CO2 and C2H2 over CH4

An NbO-type MOF based on an aminopyridine-heterobifunctionalized diisophthalate linker was synthesized, displaying markedly enhanced C₂H₂ and CO₂ adsorption over CH₄ compared to its parent compound.

A lactam-functionalized copper bent diisophthalate framework displaying significantly enhanced adsorption of CO2 and C2H2 over CH4

The first lactam-functionalized MOF based on a bent diisophthalate ligand was constructed, displaying significantly enhanced uptake and selectivity for C₂H₂ and CO₂ over CH₄.

A heterometallic metal–organic framework based on multi-nuclear clusters exhibiting high stability and selective gas adsorption

Porous In/Tb-CBDA has been successfully synthesized in the light of the heterometallic cooperative crystallization (HCC) approach. In/Tb-CBDA with high thermal and chemical stability exhibited high performance for gas storage and separation.

Tailoring the structures and gas adsorption properties of copper–bent diisophthalate frameworks by a substituent-driven ligand conformation regulation strategy

A substituent-induced ligand conformation regulation strategy was employed to tailor the structures and gas adsorption properties of copper-bent diisophthalate frameworks.

Exploring the Effect of Ligand-Originated MOF Isomerism and Methoxy Group Functionalization on Selective Acetylene/Methane and Carbon Dioxide/Methane Adsorption Properties in Two NbO-Type MOFs

Investigation of the impact of ligand-originated MOF (metal-organic framework) isomerism and ligand functionalization on gas adsorption is of vital importance because a study in this aspect provides valuable guidance for future fabrication of new MOFs exhibiting better performance. For the abovementioned purpose, two NbO-type ligand-originated MOF isomers based on methoxy-functionalized diisophthalate ligands were solvothermally constructed in this work. Their gas adsorption properties toward acetylene, carbon dioxide, and methane were systematically investigated, revealing their promising potential for the adsorptive separation of both acetylene/methane and carbon dioxide/methane gas mixtures, which are involved in the industrial processes of acetylene production and natural gas sweetening. In particular, compared to its isomer ZJNU-58, ZJNU-59 displays larger acetylene and carbon dioxide uptake capacities as well as higher acetylene/methane and carbon dioxide/methane adsorption selectivities despite its lower pore volume and surface area, demonstrating a very crucial role that the effect of pore size plays in acetylene and carbon dioxide adsorption. In addition, the impact of ligand modification with a methoxy group on gas adsorption was also evaluated. ZJNU-58 exhibits slightly lower acetylene and carbon dioxide uptake capacities but higher acetylene/methane and carbon dioxide/methane adsorption selectivities as compared to its parent compound NOTT-103. By contrast, enhanced adsorption selectivities and uptake capacities were observed for ZJNU-59 as compared to its parent compound ZJNU-73. The results demonstrated that the impact of ligand functionalization with a methoxy group on gas adsorption might vary from MOF to MOF, depending on the chosen parent compound. The results might shed some light on understanding the impact of both ligand-originated MOF isomerism and methoxy group functionalization on gas adsorption.

A metal-organic framework based on a custom-designed diisophthalate ligand exhibiting excellent hydrostability and highly selective adsorption of C2H2 and CO2 over CH4

The ligand truncation strategy provides facile access to a wide variety of linkers for the construction of MOFs bearing diverse structures and intriguing properties. In this work, we employed this strategy to design and prepare a novel bent diisophthalate ligand, and used it to successfully construct a copper-based MOF ZJNU-51 with the formula of [Cu2L(H2O)2]·5DMF (H4L = 5,5'-(triphenylamine-4,4'-diyl) diisophthalic acid), which was thoroughly characterized by various techniques including FTIR, TGA, PXRD and single-crystal X-ray diffraction. ZJNU-51 is a two-fold interpenetrated network in which the single network consists of dicopper paddlewheel units connected by the organic ligands and contains open channels as well as six distinct types of metal-organic cages. Furthermore, gas adsorption properties with respect to C2H2, CO2, and CH4 were systematically investigated, demonstrating that ZJNU-51 is a highly promising material for C2H2/CH4 and CO2/CH4 separations. Specifically, the IAST adsorption selectivity at 298 K and 1 atm reaches 35.6 and 5.4 for the equimolar C2H2/CH4 and CO2/CH4 gas mixtures, respectively. More significantly, as revealed by PXRD and N2 adsorption measurements, ZJNU-51 exhibits excellent chemical stability, which lays a good foundation for its practical application.

Three isoreticular MOFs derived from nitrogen-functionalized diisophthalate ligands: exploring the positional effect of nitrogen functional sites on the structural stabilities and selective C2H2/CH4 and CO2/CH4 adsorption properties

The positional effect of nitrogen functional sites on the structural stability and gas adsorption property was explored in a family of ssa-type MOFs.

A highly porous acylamide decorated MOF-505 analogue exhibiting high and selective CO2 gas uptake capability

A highly porous acylamide decorated MOF-505 analogue with optimized pores, open copper sites and acylamide groups exhibits large and selective CO₂ adsorption over CH₄ and N₂ under ambient conditions.

Rational construction of an ssa-type of MOF through pre-organizing the ligand's conformation and its exceptional gas adsorption properties

A ligand conformation-controlled assembly strategy has been successfully employed to construct a copper-based MOF with the desired ssa-type topology, which exhibits exceptional C₂H₂ and CO₂ adsorption properties.

An unprecedented water stable acylamide-functionalized metal–organic framework for highly efficient CH4/CO2 gas storage/separation and acid–base cooperative catalytic activity

HNUST-8 exhibits water stable, efficient CH₄/CO₂ storage and separation, acid–base cooperative catalytic activity in a tandem deacetalization Knoevenagel densation.

A pair of polymorphous metal–organic frameworks based on an angular diisophthalate linker: synthesis, characterization and gas adsorption properties

A pair of polymorphous MOFs derived from a bent diisophthalate ligand were synthesized by modulating solvothermal conditions, exhibiting comparable gas adsorption properties with respect to C₂H₂, CO₂ and CH₄.

Three ligand-originated MOF isomers: the positional effect of the methyl group on structures and selective C2H2/CH4 and CO2/CH4 adsorption properties

The positional effect of the methyl group on structures and gas adsorption properties was explored in a copper-based MOF platform constructed from bent diisophthalate ligands bearing the methyl group at different positions.