Higher Symmetry Multinuclear Clusters of Metal–Organic Frameworks for Highly Selective CO2 Capture

Solvent-Induced In(III)-MOFs with Controllable Interpenetration Degree Performing High-Efficiency Separation of CO2/N2 and CO2/CH4

Herein, three In(III)-based metal-organic frameworks (In-MOFs) with different degrees of interpenetration (DOI), namely In-MOF-1, In-MOF-2, and In-MOF-3, constructed by In3+ and Y-shaped ligands 4,4',4″-s-triazine-2,4,6-triyltribenzoate (H3TATB), are successfully synthesized through the ionothermal/solvothermal method. Subsequently, three novel In-MOFs, including noninterpenetration polycatenation, 2-fold interpenetrated, and 4-fold interpenetrated structure, are employed as the platform for systematically investigating the separation efficiency of CO2/N2, CO2/CH4, and CO2/CH4/N2 mixture gas system. Among them, In-MOF-2 shows the highest CO2 uptake capacities at 298 K and simultaneously possesses the low adsorption enthalpy of CO2 (26.4 kJ/mol at low coverage), a feature desirable for low-energy-cost adsorbent regeneration. The CO2/N2 (v: v = 15/85) selectivity of In-MOF-2 reaches 37.6 (at 298 K and 1 bar), also revealing outstanding selective separation ability from flue gases and purifying natural gas, affording a unique robust separation material as it has moderate DOI and pore size. In-MOF-2 shows exceptional stability and feasibility to achieve reproducibility. Aperture adjustment makes In-MOF-2 a versatile platform for selectively capturing CO2 from flue gases or purifying natural gas.

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) modified metal-organic frameworks boosting carbon dots electrochemiluminescence emission for sensitive miRNA detection

Highly efficient luminescent materials play an important role in electrochemiluminescence (ECL) biosensing systems. Herein, the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) modified carbon dots (CDs)/zeolitic imidazolate framework-8 (ZIF-8) compositing metal-organic frameworks (MOFs) materials with excellent luminescence performance were prepared as the ECL emitters for biosensing application. In this novel ternary composites, CDs were used as emitters, ZIF-8 was used as a carrier, and the luminescent performance was finally improved by introducing PEDOT:PSS to improve the conductivity of the nanomaterials. As a result, CDs/PEDOT:PSS/ZIF-8 exhibited an approximately 8 times ECL intensity compared to CDs alone. By further modifying with AuNPs, the enhancement factor reached ≈10 in reference to the individual CDs. After combining with a DNAzyme-based two-cycle target amplification principle, an ECL biosensor was constructed to achieve high-sensitivity detection of miRNA-21 with a detection limit of 50 aM. The biosensor also demonstrated desirable selectivity, excellent stability, and quantitative ability for human serum target detection. Overall, these findings not only provide a promising pathway for high luminous efficiency ECL emitters synthesis, but also provide a platform for ultrasensitive miRNA sensing.

Finely Tuning Metal Ion Valences of [Fe3-xMx(μ3-OH)(Carboxyl)6(pyridyl)2] Cluster-Based ant-MOFs for Highly Improved CO2 Capture Performances

Solvothermal reactions of different trinuclear precursors and 5-(pyridin-4-yl)isophthalic acid (H2L) successfully led to four anionic ant topological MOFs as Fe3-xMx(μ3-OH)(CH3COO)2(L)2·(DMA+)·DMF [M = Mn(II), Fe(II), Co(II), x = 0, 1, 2 and 3], namely, NJTU-Bai79 [NJTU-Bai = Nanjing Tech University Bai's group, Mn3(μ3-OH)], NJTU-Bai80 [Fe2Mn(μ3-OH)], NJTU-Bai81 [Fe3(μ3-OH)], and NJTU-Bai82 [Fe2Co(μ3-OH)], which possess the narrow pores (2.5-6.0 Å). NJTU-Bai80-82 is able to be tuned to the neutral derivatives [NJTU-Bai80-82(-ox), ox = oxidized] with M2+ ions oxidized to M3+ ones in the air and the OH- ions coordinated on M3+ ions. Very interestingly, selective CO2/N2 adsorptions of NJTU-Bai80-82(-ox) are significantly enhanced with the CO2 adsorption uptakes more than about 6 times that of NJTU-Bai79. GCMC simulations further revealed that neutral NJTU-Bai80-82(-ox) supplies more open frameworks around the -CH3 groups at separate spaces to the CO2 gas molecules with relatively more pores available to them after the removal of counterions. For the first time, finely tuning metal ion valences of metal clusters of ionic MOFs and making them from electrostatic to neutral were adopted for greatly improving their CO2 capture properties, and it would provide another promising strategy for the exploration of high-performance CO2 capture materials.

Efficient CO2 Capture and Separation in MOFs: Effect from Isoreticular Double Interpenetration

Severe CO2 emissions has posed an increasingly alarming threat, motivating the development of efficient CO2 capture materials, one of the key parts of carbon capture, utilization, and storage (CCUS). In this study, a series of metal-organic frameworks (MOFs) named Sc-X (X = S, M, L) were constructed inspired by recorded MOFs, Zn-BPZ-SA and MFU-4l-Li. The corresponding isoreticular double-interpenetrating MOFs (Sc-X-IDI) were subsequently constructed via the introduction of isoreticular double interpenetration. Grand canonical Monte Carlo (GCMC) simulations were adopted at 298 K and 0.1-1.0 bar to comprehensively evaluate the CO2 capture and separation performances in Sc-X and Sc-X-IDI, with gas distribution, isothermal adsorption heat (Qst), and van der Waals (vdW)/Coulomb interactions. It is showed that isoreticular double interpenetration significantly improved the interactions between adsorbed gases and frameworks by precisely modulating pore sizes, particularly observed in Sc-M and Sc-M-IDI. Specifically, the Qst and Coulomb interactions exhibited a substantial increase, rising from 28.38 and 22.19 kJ mol-1 in Sc-M to 43.52 and 38.04 kJ mol-1 in Sc-M-IDI, respectively, at 298 K and 1.0 bar. Besides, the selectivity of CO2 over CH4/N2 was enhanced from 55.36/107.28 in Sc-M to 3308.61/7021.48 in Sc-M-IDI. However, the CO2 capture capacity is significantly influenced by the pore size. Sc-M, with a favorable pore size, exhibits the highest capture capacity of 15.86 mmol g-1 at 298 K and 1.0 bar. This study elucidated the impact of isoreticular double interpenetration on the CO2 capture performance in MOFs.

Enhanced CO2 capture in partially interpenetrated MOFs: Synergistic effects from functional group, pore size, and steric-hindrance

Excessive CO2 emissions have contributed to global environmental issues, driving the development of CO2 capture adsorbents. Among various candidates, metal-organic frameworks (MOFs) are considered the most promising due to their unique microporous structure. Herein, a series of partially interpenetrated MOFs named UPC-XX were built to investigate the continuous enhancement in CO2 capture performance via synergistic effects from functional group, pore size, and steric-hindrance using theoretical calculations. It's showed that the introduction of functional groups improved the structure polarity and created more adsorption sites, thus, enhanced CO2 capture capacity. The pore size modification augments the exposure of adsorption sites to mitigate the negative impact of pore space and surface area reduction caused by the introduction of functional groups, thereby further increasing the CO2 capture capacity. The steric-hindrance effect optimized the adsorption sites distribution, which hasn't been considered in the previous two regulation strategies, thus, further increased the CO2 capture capacity. The results underscore UPC-MOFs as outstanding adsorbent materials, among the UPC-MOFs, UPC-OSO3-steric exhibited the highest CO2 capture capacity of 12.69 mmol/g with selectivities of 1142.41 (CO2 over N2) and 507.42 (CO2 over CH4) at 1.0 bar, 298 K. And the synergistic effect mechanisms of functional group, structure size, and steric hindrance were elucidated through theoretical calculations analyzing pore characteristics, gas distribution, isosteric heat, and van der Waals/Coulomb interactions.

Optimizing Sieving Effect for CO2 Capture from Humid Air Using an Adaptive Ultramicroporous Framework

Excessive CO2 in the air can not only lead to serious climate problems but also cause serious damage to humans in confined spaces. Here, a novel metal-organic framework (FJI-H38) with adaptive ultramicropores and multiple active sites is prepared. It can sieve CO2 from air with the very high adsorption capacity/selectivity but the lowest adsorption enthalpy among the reported physical adsorbents. Such excellent adsorption performances can be retained even at high humidity. Mechanistic studies show that the polar ultramicropore is very suitable for molecular sieving of CO2 from N2 , and the distinguishable adsorption sites for H2 O and CO2 enable them to be co-adsorbed. Notably, the adsorbed-CO2 -driven pore shrinkage can further promote CO2 capture while the adsorbed-H2 O-induced phase transitions in turn inhibit H2 O adsorption. Moreover, FJI-H38 has excellent stability and recyclability and can be synthesized on a large scale, making it a practical trace CO2 adsorbent. This will provide a new strategy for developing practical adsorbents for CO2 capture from the air.

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.

Stepwise Engineering the Pore Aperture of a Cage-like MOF for the Efficient Separation of Isomeric C4 Paraffins under Humid Conditions

The separation of isomeric C4 paraffins is an important task in the petrochemical industry, while current adsorbents undergo a trade-off relationship between selectivity and adsorption capacity. In this work, the pore aperture of a cage-like Zn-bzc (bzc=pyrazole-4-carboxylic acid) is tuned by the stepwise installation methyl groups on its narrow aperture to achieve both molecular-sieving separation and high n-C₄ H₁₀ uptake. Notably, the resulting Zn-bzc-2CH₃ (bzc-2CH₃ =3,5-dimethylpyrazole-4-carboxylic acid) can sensitively capture n-C₄ H₁₀ and exclude iso-C₄ H₁₀ , affording molecular-sieving for n-C₄ H₁₀ /iso-C₄ H₁₀ separation and high n-C₄ H₁₀ adsorption capacity (54.3 cm³  g^-1 ). Breakthrough tests prove n-C₄ H₁₀ /iso-C₄ H₁₀ can be efficiently separated and high-purity iso-C₄ H₁₀ (99.99 %) can be collected. Importantly, the hydrophobic microenvironment created by the introduced methyl groups greatly improves the stability of Zn-bzc and significantly eliminates the negative effect of water vapor on gas separation under humid conditions, indicating Zn-bzc-2CH₃ is a new benchmark adsorbent for n-C₄ H₁₀ /iso-C₄ H₁₀ separation.

Ligand-Functional Groups Induced Tuning MOFs' 2D into 1D Pore Channels for Pipeline Natural Gas Purification

The solvothermal reactions of CoCl₂  ⋅ 6H₂ O, 3,5-pyridinedicarboxylic acid (H₂ L) and isonicotinic acid (HL₁ )/3-amino isonicotinic acid (HL₂ )/3-chloro isonicotinic acid (HL₃ ) successfully led to three tfz-d topological pillar-layer [Co₄ (μ-F)₂ (COO)₆ (NC₅ H₄ )₄ ] cluster-based MOFs, namely, [Co₄ (μ-F)₂ (L)₂ (L₁ )₂  ⋅ 2DMA] ⋅ DMA ⋅ 2H₂ O (SNNU-Bai76, SNNU-Bai=Shaanxi Normal University Bai's group), [Co₄ (μ-F)₂ (L)₂ (L₂ )₂  ⋅ 2H₂ O] ⋅ 2DMA ⋅ 2H₂ O (SNNU-Bai77) and [Co₄ (μ-F)₂ (L)₂ (L₃ )₂  ⋅ 2H₂ O] ⋅ 2DMF ⋅ 2H₂ O (SNNU-Bai78). With the 2D pore channels in SNNU-Bai76 and SNNU-Bai77 being tuned to the 1D pore channel in SNNU-Bai78, C₃ H₈ and C₂ H₆ adsorption uptakes are apparently improved and the IAST selectivities of C₃ H₈ /CH₄ and C₂ H₆ /CH₄ almost remain, which indicate that SNNU-Bai78 may be one potential separation material for the pipeline natural gas purification. These were further confirmed by the breakthrough experiments for the simulated pipeline natural gas (C₃ H₈ /C₂ H₆ /CH₄  : 5/10/85 gas mixture) of three isostructural MOFs. Furthermore, GCMC simulations revealed that due to one of the pore channels blocked by Cl atoms in a couple of 3-chloro isonicotinic acid with the changed conformation as the pillar, the pore wall of the formed 1D pore channel in SNNU-Bai78 may interact with the adsorbed C₃ H₈ or C₂ H₆ molecule more strongly, for which more atoms of framework at the new adsorption site will interact with the adsorbed gas molecule by more intermolecular interactions. This was also evidenced by the increased binding energies, being consistent with the tuning of adsorption enthalpies for C₃ H₈ and C₂ H₆ gas molecules, and the reduced C₃ H₈ and C₂ H₆ gas diffusion coefficients in SNNU-Bai78. Very interestingly, this work is the first example of finely tuning the pore connectivity of MOFs toward strengthened host-guest interactions for the gas adsorption and separation.

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.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Energetic Systematics of Metal-Organic Frameworks: A Case Study of Al(III)-Trimesate MOF Isomers

Thermal stability and thermodynamic properties of aluminum(III)-1,3,5-benzenetricarboxylate (Al-BTC) metal-organic frameworks (MOFs), including MIL-96, MIL-100, and MIL-110, have been investigated through a suite of calorimetric and X-ray techniques. In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC) revealed that these MOFs undergo thermal amorphization prior to ligand combustion. Thermal stabilities of Al-BTC MOFs follow the increasing order MIL-110 < MIL-96 < MIL-100, based on estimated amorphization temperatures. Their thermodynamic stabilities were directly measured by high-temperature drop combustion calorimetry. Normalized (per mole of Al) enthalpies of formation (ΔH*_f) of MIL-96, MIL-100, and MIL-110 from Al₂O_3, H₃BTC, and H₂O (only Al₂O₃ and H₃BTC for MIL-100) were determined to be -56.9 ± 13.7, -36.2 ± 17.9, and 62.8 ± 11.6 kJ/mol·Al, respectively. Our results demonstrate that MIL-96 and MIL-100 are thermodynamically favorable, while MIL-110 is metastable, in agreement with thermal and hydrothermal stability trends. The enthalpic preferences of MIL-96 and MIL-100 may be attributed to their shared trinuclear μ³-oxo-bridged (Al₃(μ₃-O)) secondary building units (SBUs) promoting stabilization of Al polyhedra by the ligands within these frameworks, in comparison to the sterically strained Al₈ octamer cluster cores formed in MIL-110. Furthermore, similar ΔH*_f of MIL-96 and MIL-100 explain their concurrent formation as physical mixtures often encountered during synthesis, implying the importance of kinetic factors that may facilitate the formation of Al-BTC framework isomers. More importantly, the normalized formation enthalpies of Al-BTC MOF isomers follow a negative correlation with the ratio of charged coordinated substituents to linkers (normalized per mole of Al within the MOF formula unit), with enthalpic preference given to systems with smaller (O^2- + OH^-)/ligand ratios. This trend has been successfully extended to the previously measured ΔH*_f of several Zn₄O-based frameworks (e.g., MOF-5, MOF-5(DEF), MOF-177, UMCM-1), all of which have been found to be metastable with respect to their dense phases (ZnO, H₂O, and ligands). The result suggests that carboxylate MOFs with higher metal coordination environments attain more enthalpic stabilization from the coordinated ligands. Thus, the formation of some lanthanide/actinide, transition metal, and main group carboxylate frameworks may be energetically more favored, which, however, requires further studies.

A microporous chromium-organic framework fabricated via solvent-assisted metal metathesis for C2H2/CO2 separation

Removal of CO₂ or C₂H₄ from C₂H₂ is still a challenging task due to their similar physical-chemical properties. Here, a bifunctional ligand decorated with amino and sulfoxide groups, 5',5''''-sulfonylbis (2'-amino-[1,1':3',1''-terphenyl]-4,4''-dicarboxylic acid) (H₄L), was employed to construct a new microporous iron-organic framework (Fe-MOF) with the formula [(Fe₃O)(L)_1.5(H₂O)₃]_n. This MOF can serve as a parent structure to obtain the isostructural Cr-MOF by solvent-assisted metal metathesis. Furthermore, the gas adsorption and separation performance of these two MOFs were systematically investigated. Compared to Fe-MOF, Cr-MOF shows a moderately higher CO₂, C₂H₂ and C₂H₄ uptake capacity. Additionally, Cr-MOF can selectively adsorb C₂H₂ over CO₂ and C₂H₄. The separation potential towards C₂H₂/C₂H₄ and C₂H₂/CO₂ was further established via IAST calculations of mixture adsorption equilibrium. IAST selectivity values of Cr-MOF are 3.4 for C₂H₂/C₂H₄ and 6.9 for C₂H₂/CO₂ at 298 K and initial pressure, indicating its potential C₂H₂ separation ability.

Size exclusion propyne/propylene separation in a ultramicroporous yet hydrophobic metal-organic framework

Propyne/propylene separation is important in the petrochemical industry but challenging resulting from their similar physical properties and close molecular sizes. Herein, we present two isoreticular ultramicroporous Zn(Ⅱ)-MOFs, Zn2(ATZ)2(TPDC) (BUT-305, H2TPDC...

Synthesis, Structure and Highly Selective C3H8/CH4 and C2H6/CH4 Adsorptions of a (4,8)-c Ternary flu-Metal-organic Framework based upon both [Sc4O2(COO)8] and [Cu4OCl6] Clusters

A new ternary flu topological metal-organic framework based upon the torsional cubic 8-connected [Sc4O2(COO)8] cluster and the tetrahedral 4-connected [Cu4OCl6] cluster, namely, [Sc4O2(Cu4Cl6O)2(L)8•5H2O]•xGuest (SNNU-Bai69; SNNU-Bai = Shaanxi Normal University, Bai’s...

pH-Dependent formation of three porous In(III)-MOFs: framework diversity and selective gas adsorption

pH-Dependent self-assembly and structural transformation have been observed in a series of porous In(III)-MOFs, H₃O[In₃(pta)₄(OH)₂]·10H₂O (NXU-1), [In(pta)₂]·C₃H₁₀N (NXU-2) and [In(pta)₂]·C₃H₁₀N (NXU-3) (H₂pta = 2-(4-pyridyl)-terephthalic acid). The structural diversities of NXU-1-3 reveal that the pH value of the reaction plays a key role in the assembly of In-MOFs. NXU-1 with excellent stability exhibits highly selective CO₂ adsorption over CH₄ as compared to NXU-2 and NXU-3, owing to the presence of abundant multiple active sites unveiled by theoretical calculations.

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.

B-Doped 2D-InSe as a bifunctional catalyst for CO2/CH4 separation under the regulation of an external electric field

The separation of CO₂ or CH₄ from a CO₂/CH₄ mixture has drawn great attention in relation to solving air pollution and energy shortage issues. However, research into using bifunctional catalysts to separate CO₂ and CH₄ under different conditions is absent. We have herein designed a novel B-doped two-dimensional InSe (B@2DInSe) catalyst, which can chemically adsorb CO₂ with covalent bonds. B@2DInSe can separate CO₂ and CH₄ in different electric fields, which originates from different regulation mechanisms by an electric field (EF) on the electric properties. The hybridization states between CO₂ and B@2DInSe near the Fermi level have experienced gradual localization and eventually merged into a single narrow peak under an increased EF. As the EF further increased, the merged peak shifted towards higher energy states around the Fermi level. In contrast, the EF mainly alters the degree of hybridization between CH₄ and B@2DInSe at states far below the Fermi level, which is different from the CO₂ situation. These characteristics can also lead to perfect linear relationships between the adsorption energies of CO₂/CH₄ and the electric field, which may be beneficial for the prediction of the required EF without large volumes of calculations. Our results have not only provided novel clues for catalyst design, but they have also provided deep understanding into the mechanisms of bifunctional catalysts.

Formation of a N/O/F-Rich and Rooflike Cluster-Based Highly Stable Cu(I/II)-MOF for Promising Pipeline Natural Gas Upgrading by the Recovery of Individual C3H8 and C2H6 Gases

Due to the ultralow amounts of C₃H₈ and C₂H₆ gases, to design and synthesize water-stable MOFs that are promising for real-world efficient pipeline natural gas (NG) upgrading by the recovery of individual C₃H₈ and C₂H₆ gases is still a great challenge. Here, a N/O/F heteroatom-rich and rooflike [Cu(II)₄Cu(I)₂(COO)₄(tetrazolyl)₆] cluster-based ultra-microporous tsi-MOF (SNNU-Bai68) was afforded as a multiple heteroatom-rich and curved-surface-shaped cluster-based ultra-microporous MOF and the first porous MOF based upon such rooflike [Cu(II)_xCu(I)_y(tetrazolyl)_z]^(2x+y-z)+ cluster. In SNNU-Bai68, the rooflike cluster was further assembled into a 1D chain secondary building block (SBB), which led to a high density of accessible potential adsorptive sites. Very interestingly, it exhibited the most promising balance of high gas adsorption uptakes at 0.01, 0.03, and 0.05 bar, high C₃H₈/CH₄, C₃H₈/C₂H₆, and C₂H₆/CH₄ adsorption selectivities, moderate adsorption enthalpies, and high water and chemical stability for pipeline natural gas upgrading by the recovery of individual C₃H₈ and C₂H₆ gases, which was further confirmed by the breakthrough experiments of the gas mixtures with/without 74% RH. Furthermore, the SC-XRD and GCMC studies revealed that the successful separation of C₃H₈, C₂H₆, and CH₄ gases in SNNU-Bai68 is due to different synergistic effects of H-bonds between the frameworks at three adsorptive sites around each rooflike cluster and those different gas molecules, which were initially described systematically by the number of H atoms from the gas molecules, the total number of H-bonds within the synergistic H-bonds, and the binding energy of the framework at an adsorption site toward the gas molecules. In addition, this work may provide a method for the construction of a multiple heteroatom-rich and curved-surface-shaped cluster-based ultra-microporous MOF as a novel approach to build MOFs with polar pore surfaces, suitable pore sizes, and unique pore shapes to maximize the synergistic H-bonds between the framework and guests.

Molecular engineering in a family of pillared-layered metal-organic frameworks for tuning gas adsorption behavior

In this work, inspired by a water-assisted three-dimensional supramolecular structure 1, we use a mixed-ligand strategy to form a 3D pillared-layered matrix by the introduction of linear ligands to compete against the water molecules. The resulting analogue microporous MOFs of 2-H, 2-F and 2-N, decorated with different functional groups, similarly show the CO2 uptake. Thanks to the negligible N2 adsorption capacity, enhanced selective adsorption towards CO2 is achieved in compound 2-N. That is, we present here an alternative plan for the high CO2 selective adsorption performance. In addition, the structure stability and moderate affinity for CO2 of these microporous MOFs endow them with excellent reusability.

Modifying a partial corn-sql layer-based (3,3,3,3,4,4)-c topological MOF by substitution of OH- with Cl- and its highly selective adsorption of C2 hydrocarbons over CH4

Modifying VNU-18 (a MOF with a partial cone-sql layer pillared by the chains of pillars decorated with OH^-) by substitution of OH^- with Cl^-, a new isoreticular structure, [Cu₆(L)₅·(Cl^-)₂·H₂O·4DMF]·4DMF·6(H₂O) (SNNU-Bai67, SNNU-Bai = Shaanxi Normal University Bai's group), has been successfully synthesized. Furthermore, we deeply investigated the selective C2 hydrocarbon separation properties of SNNU-Bai67 and VNU-18 by single-component gas adsorption experiments, breakthrough experiments and simulation studies. They exhibit highly selective adsorption for C2 hydrocarbons over CH₄ compared to many reported MOFs for the separation of C2 hydrocarbons from CH₄, due to the suitable pore sizes of the partial corn sql-layer built from the isophthalic acid analogy and Cu-paddlewheel units. Interestingly, with the counterion of OH^- in VNU-18 tuned by Cl^- in SNNU-Bai67, the adsorption uptake values of C2 hydrocarbons were apparently improved by 15.0% for C₂H₂, 20.4% for C₂H₄ and 25.3% for C₂H₆, respectively, while the IAST selectivities of C2 hydrocarbons/CH₄ were still nearly the same, which may be because the synergistic effect of interactions of H_C2/1O_COO, H_C2/1N/C_Py, H_PyC_C2, ππ or H_C2C_C2 between the gas molecules and the framework is enhanced by the weaker polarity of Cl^- decorating the framework.

Efficient and Highly Selective CO2 Capture, Separation, and Chemical Conversion under Ambient Conditions by a Polar-Group-Appended Copper(II) Metal-Organic Framework

A polar sulfone-appended copper(II) metal-organic framework (MOF; 1) has been synthesized from the dual-ligand approach comprised of tetrakis(4-pyridyloxymethylene)methane and dibenzothiophene-5,5'-dioxide-3,7-dicarboxylic acid under solvothermal conditions. This has been studied by different techniques that included single-crystal X-ray diffractometry, based on which the presence of Lewis acidic open-metal sites as well as polar sulfone groups aligned on the pore walls is identified. MOF 1 displays a high uptake of CO₂ over N₂ and CH₄ with an excellent selectivity (S = 883) for CO₂/N₂ (15:85) at 298 K under flue gas combustion conditions. Additionally, the presence of Lewis acidic metal centers facilitates an efficient size-selective catalytic performance at ambient conditions for the conversion of CO₂ into industrially valuable cyclic carbonates. The experimental investigations for this functional solvent-free heterogeneous catalyst are also found to be in good correlation with the computational studies provided by configurational bias Monte Carlo simulation for both CO₂ capture and its conversion.

Ultrathin Reduced Graphene Oxide/Organosilica Hybrid Membrane for Gas Separation

Here, reduced graphene oxide (r-GO) nanosheets were embedded in an organosilica network to assemble an ultrathin hybrid membrane on the tubular ceramic substrate. With the organosilica nanocompartments inside the r-GO stacks and the intensified polymerization, r-GO sheets endow the as-prepared hybrid membranes with high H₂ and CO₂ separation performance. The resulting selectivities of H₂/CH₄ and CO₂/CH₄ are found to be 223 and 55, respectively, together with gas permeance of approximately 2.5 × 10^-7 mol·m^-2·s^-1·Pa^-1 for H₂ and 6.1 × 10^-8 mol·m^-2·s^-1·Pa^-1 for CO₂ at room temperature and 0.2 MPa. To separate larger molecules from H₂, the H₂/C₃H₈ and H₂/i-C₄H₁₀ selectivities are as high as 1775 and 2548, respectively. Moreover, at 150 °C and 0.2 MPa, the hybrid membrane retains high separation performances with ideal selectivities higher than 200 and 30 for H₂/CH₄ and CO₂/CH₄, respectively, which are attractive for gas separation and purification of practical applications.

Catalyst-free development of N-doped microporous carbons for selective CO2 separation

Owing to their catalyst-free development, high yield, notable CO₂ uptake performance, and excellent CO₂/CH₄ selectivity, the fabricated N-doped microporous carbons (NMCs) are highly suitable for selective CO₂ separation.

Selective adsorption of CO2 from gas mixture by P-decorated C24N24 fullerene assisted by an electric field: A DFT approach

Selective, reversible and tailored adsorption of CO₂ from gas mixture is always demanded to control global warming. We for the first time used P-decorated C₂₄N₂₄ fullerene for selective separation of CO₂ from N₂/CO₂ mixture in the presence of an electric field by using density functional theory methods. The computed geometrical parameters evince that the binding distances and bond angles (OCO) are remarkably reduced in electric field and that transformed the physisorption to chemisorption by increasing the field from 0.012 to 0.013 au. The adsorption/desorption of CO₂ over the substrate can be easily controlled by switching on and off the electric field. This study reveals that P@C₂₄N₂₄ is a selective adsorbent of CO₂ from N₂/CO₂ mixture and will help the future synthesis of selective, controllable and regenerable adsorbent for the CO₂ separation from gas mixture in presence of electric field.

A Rational Design of Microporous Nitrogen-Rich Lanthanide Metal-Organic Frameworks for CO2/CH4 Separation

Three new lanthanide metal-organic frameworks IRHs-(1-3) supported by cyamelurate linkers have been synthesized and structurally characterized. The incorporation of numerous heteroatoms (N and O) into the pore walls and the relatively small microchannels of these porous solids enhance bonding force of the host-guest interactions, thus promoting the adsorption of carbon dioxide (CO₂) over methane (CH₄). The nonpolar covalent bonds in methane also favor the less uptake due to the hydrophilic walls of these frameworks. Grand canonical Monte Carlo simulations were performed to determine the origin of the adsorption. The density isocontour surfaces show that CO₂ is mainly adsorbed on the walls composed of organic linkers and around the metal sites, whereas no specific adsorption site is observed for CH₄, which indicates weak interactions between the framework and the adsorbed gas. As expected, the simulations show that CH₄ is not observed around the metal center due to the presence of H₂O molecules. The excellent selectivity of CO₂/CH₄ binary mixture was predicted by the ideal adsorbed solution theory (IAST) via correlating pure component adsorption isotherms with the Toth model. At 25 °C and 1 bar, the CO₂ and CH₄ uptakes for IRH-3 were 2.7 and 0.07 mol/kg, respectively, and the IAST predicated selectivity for CO₂/CH₄ (1:1) reached 27, which is among the best value for MOF materials.

The synthetic strategies for single atomic site catalysts based on metal-organic frameworks

Metal-organic frameworks (MOFs) are a good platform for the fabrication of single atomic site catalysts (SACs) due to their large specific surface area, rich pore structure, large number of unsaturated coordination metal sites and their intriguing and controllable structures. The influencing factors of each strategy used to synthesize SACs based on MOFs, such as the finetuning ligand strategy, heteroatom doping (N, P, S) strategy, space restriction strategy, bimetallic strategy, metal cluster defect strategy, substrate to capture strategy, and various post-treatment strategies have not been discussed. Here, we will discuss the influencing factors of each strategy and the relationship between the different methods, which are used to synthesize SACs based on MOFs.

A low symmetry cluster meets a low symmetry ligand to sharply boost MOF thermal stability

A new approach in which a low symmetry cluster meets a low symmetry ligand to sharply boost the thermal stability of a MOF via additional inter-linker interactions is presented for the first time, leading to the successful synthesis of a novel binuclear Co-based MOF, {[Co₂(L₁)₂DMF]·1.5DMF·0.75MeOH·1.5H₂O}_∞ (H₂L₁ = 5-(pyridin-3-yl) isophthalic acid, NJU-Bai62: NJU-Bai for Nanjing University Bai group), with exceptional thermal stability of up to 450 °C. This work may open up a new avenue for constructing robust MOFs from abundant, unstable, and low symmetry binuclear clusters, which have usually been ignored by most MOF chemists.

Highly Robust Tetranuclear Cobalt-Based 3D Framework for Efficient C2H2/CO2 and C2H2/C2H4Separations

A novel noninterpenetrated tetranuclear cobalt(II)-based metal-organic framework, (NH₄)₂·[Co₄(μ₃-OH)₂(ina)₂(pip)₃]·4EtOH·H₂O (simplified as NbU-10·S), constructed by mix linkers was synthesized by a hydrothermal method. Interestingly, the presence of a hydrophobic benzene ring in the organic linker makes NbU-10·S exhibit high stability in high temperature and even in aqueous solution over a wide pH range of about 4-13. Magnetic studies showed that the tetranuclear cobalt(II) units in NbU-10·S show dominant antiferromangetic properties. However, in the absence of Lewis basic functional sites and open metal sites in the material, NbU-10 still displays high C₂H₂/CO₂ and C₂H₂/C₂H₄ selectivity in ideal adsorbed solution theory calculations and dynamic breakthrough experiments. Moreover, density functional theory calculations were performed to identify the adsorption characteristics of different gas molecules.

Immobilization of a Polar Sulfone Moiety onto the Pore Surface of a Humid-Stable MOF for Highly Efficient CO2 Separation under Dry and Wet Environments through Direct CO2-Sulfone Interactions

The stability of microporous metal-organic frameworks (MOFs) in moist environments must be taken into consideration for their practical implementations, which has been largely ignored thus far. Herein, we synthesized a new moisture-stable Zn-MOF, {[Zn₂(SDB)₂(L)₂]·2DMA}_n, IITKGP-12, by utilizing a bent organic linker 4,4'-sulfonyldibenzoic acid (H₂SDB) containing a polar sulfone group (-SO₂) and a N, N-donor spacer (L) with a Brunauer-Emmett-Teller surface area of 216 m² g^-1. This material displays greater CO₂ adsorption capacity over N₂ and CH₄ with high IAST selectivity, which is also validated by breakthrough experiments with longer breakthrough times for CO₂. Most importantly, the separation performance is largely unaffected in the presence of moisture of simulated flue gas stream. Temperature-programmed desorption (TPD) analysis shows the ease of the regeneration process, and the performance was verified for multiple cycles. In order to understand the structure-function relationship at the atomistic level, grand canonical Monte Carlo (GCMC) calculation was performed, indicating that the primary binding site for CO₂ is between the sulfone moieties in IITKGP-12. CO₂ is attracted to the bonded structure (V-shape) of the sulfone moieties in a perpendicular fashion, where C_CO2 is aligned with S, and the CO₂ axis bisects the SO₂ axis. Thus, the strategic approach to immobilize the polar sulfone moiety with a high number of inherent stronger M-N coordination and the absence of coordination unsaturation made this MOF potential toward practical CO₂ separation applications.

A Highly Connected Trinuclear Cluster Based Metal-Organic Framework for Efficient Separation of C2H2/C2H4 and C2H2/CO2

One of the barriers for efficient gas separation is the trade-off between the selectivity and adsorption capacity. To address this issue, we synthesized an anionic trinuclear Co^II based 3D MOF (NbU-8), which is characterized by an ultramicroporous building unit (UBU) and Lewis basic binding sites on the pore surfaces. Remarkably, the combination of the two strategies can synergistically enhance the C₂H₂ adsorption capacity (182.9 cm³/g at 298 K) and simultaneously achieve a high separation performance toward C₂H₂/C₂H₄ and C₂H₂/CO₂ mixtures. Besides theoretical calculations, the separation efficiencies of C₂H₂/C₂H₄ and C₂H₂/CO₂ are also demonstrated using breakthrough experiments. Density functional theory calculations have further confirmed the -OH groups and ultramicroporous building units play an important synergistic effect in efficiently capturing acetylene molecules.

A Green-Emission Metal-Organic Framework-Based Nanoprobe for Imaging Dual Tumor Biomarkers in Living Cells

The modular nature of metal-organic frameworks (MOFs) permits their tunable structure and function for target application, such as in biomedicine. Herein, a green-emission Zr(IV)-MOF (BUT-88) was constructed from a customized luminescent carbazolyl ligand. BUT-88 represents the first bcu-type MOF with both organic linker and metal node in eight connections and shows medium-sized pores, rich accessible linking sites, and good water stability and biocompatibility. In virtue of these merits, BUT-88 was then fabricated into a MOF-based fluorescent nanoprobe, drDNA-BUT-88. Using it, the live-cell imaging of dual tumor biomarkers was achieved for the first time upon a MOF-based probe, offering enhanced detection precision in early cancer diagnosis. Particularly, the probe showed efficient ratiometric fluorescent sensing toward the cytoplasmic biomarker microRNA-21, further improving the detection accuracy at the cellular level. In this work, the elaborate combination of MOF engineering and the fluorescent detection technique has contributed a facile biosensing platform, unlocking more possibilities of MOF chemistry.

Prediction of MOF Performance in Vacuum Swing Adsorption Systems for Postcombustion CO2 Capture Based on Integrated Molecular Simulations, Process Optimizations, and Machine Learning Models

Postcombustion CO₂ capture and storage (CCS) is a key technological approach to reducing greenhouse gas emission while we transition to carbon-free energy production. However, current solvent-based CO₂ capture processes are considered too energetically expensive for widespread deployment. Vacuum swing adsorption (VSA) is a low-energy CCS that has the potential for industrial implementation if the right sorbents can be found. Metal-organic framework (MOF) materials are often promoted as sorbents for low-energy CCS by highlighting select adsorption properties without a clear understanding of how they perform in real-world VSA processes. In this work, atomistic simulations have been fully integrated with a detailed VSA simulator, validated at the pilot scale, to screen 1632 experimentally characterized MOFs. A total of 482 materials were found to meet the 95% CO₂ purity and 90% CO₂ recovery targets (95/90-PRTs)-365 of which have parasitic energies below that of solvent-based capture (∼290 kWh_e/MT CO₂) with a low value of 217 kWh_e/MT CO₂. Machine learning models were developed using common adsorption metrics to predict a material's ability to meet the 95/90-PRT with an overall prediction accuracy of 91%. It was found that accurate parasitic energy and productivity estimates of a VSA process require full process simulations.

Accelerated C2H2/CO2 Separation by a Se-Functionalized Porous Coordination Polymer with Low Binding Energy

High-quality pure acetylene (C₂H₂) is a kind of crucial starting material for various value-added products. However, selective capture of C₂H₂ from the main impurity of CO₂ via porous absorbents is a great challenge, as they possess extremely similar kinetic diameters and boiling points, as well as the explosive and reactive properties of C₂H₂. Herein, we report a porous coordination polymer (PCP), (NTU-55), which assembled from the coordination between a Cu dimer and a newly designed ligand with a nonmetal selenium (Se) site. Static single-component adsorption and dynamic breakthrough experiments reveal that desolvated NTU-55 can completely adsorb C₂H₂ from the C₂H₂/CO₂ mixture (1/4, v/v) at 298 K, along with higher C₂H₂ capacity and much lower binding energy. The origin of this separation, as comprehensively revealed by density functional theory (DFT) calculations, is derived from the interaction discriminatory of C₂H₂ and CO₂ toward accessible Se and Cu adsorption sites. To the best of our knowledge, this is the first time to find the positive effect of nonmetal Se sites for selective C₂H₂ capture.

Syntheses of four porous 3-D Cd(ii) metal–organic frameworks from a new multidentate ligand 5-(imidazol-1-yl)-N′-(pyridin-4-ylmethylene) nicotinohydrazide and their characterization and adsorption properties

Herein, a new multidentate ligand, 5-(imidazol-1-yl)-N′-(pyridin-4-ylmethylene) nicotinohydrazide (L), with an acylhydrazone group was synthesized and characterized. Subsequently, four porous Cd(ii)-MOFs, i.e. [Cd(L)(NO₃)]_n (1), [Cd(L)Cl]_n (2), [Cd(L)Br]_n (3), and [Cd(L)I]_n (4), were assembled using the ligand L by a solvothermal method and characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Structural analysis shows that the coordination environments around Cd(ii) in all the four compounds are different due to the different coordinated anions. Among them, the coordination geometries and the arrangement of five-coordinated groups of the compound 1 containing the coordinated NO₃⁻ anions are significantly different from those of the other three compounds containing halides. However, all the four MOFs have similar one-dimensional rhombic channels. In these channels, both the nitrate ions and the halide ions are attached to the inner walls of the pores. The CO₂ adsorption properties of 1–4 were studied at 273 K, and the results showed that these compounds exhibit different adsorption capacities for CO₂ due to the presence of different ions in their pores.

Herein, four stable 3D porous Cd(ii)-MOFs were constructed from the multidentate acylhydrazone ligand, and their CO₂ adsorption properties revealed that the anions have an obvious effect on the adsorption capacities of these MOFs.

A multi-responsive chemosensor for highly sensitive and selective detection of Fe3+, Cu2+, Cr2O72− and nitrobenzene based on a luminescent lanthanide metal–organic framework

Six Ln-MOFs have been synthesized. Eu-MOF behaves a multi-responsive luminescent chemosensor toward Fe³⁺, Cu²⁺, Cr₂O₇²⁻ and nitrobenzene with high sensitivity, selectivity and anti-interference ability. Sensing mechanisms are discussed in detail.

Selective CO2 or CH4 adsorption of two anionic bcu-MOFs with two different counterions: experimental and simulation studies

Two new bcu-MOFs with counterions tuned from Li(H₂O)₄⁺ to DMA⁺ have been successfully synthesized and their selective CO₂ or CH₄ adsorption over N₂ gas has been systematically investigated in-depth by both experimental and simulation studies.