Computational study of adsorption and separation of CO2, CH4, and N2 by an rht-type metal-organic framework

Computational and Machine Learning Methods for CO2 Capture Using Metal-Organic Frameworks

Machine learning (ML) using data sets of atomic and molecular force fields (FFs) has made significant progress and provided benefits in the fields of chemistry and material science. This work examines the interactions between chemistry and materials computational science at the atomic and molecular scales for metal-organic framework (MOF) adsorbent development toward carbon dioxide (CO2) capture. Herein, a connection will be drawn between atomic forces predicted by ML algorithms and the structures of MOFs for CO2 adsorption. Our study also takes into account the successes of atomic computational screening in the field of materials science, especially quantum ML, and its relationship to ML algorithms that clarify advancements in the area of CO2 adsorption by MOFs. Additionally, we reviewed the processes for supplying data to ML algorithms for algorithm training, including text mining from scientific articles, and MOF's formula processing linked to the chemical properties of MOFs. To create ML algorithms for future research, we recommend that the digitization of scientific records can help efficiently synthesize advanced MOFs. Finally, a future vision for developing pioneer MOF synthesis routes for CO2 capture is presented in this review article.

Engineering Insights into Tailored Metal-Organic Frameworks for CO2 Capture in Industrial Processes

Despite the known impacts on climate change of carbon dioxide emissions, the continued use of fossil fuels for energy generation leading to the emission of carbon dioxide (CO2) into the atmosphere is evident. Therefore, innovation to address and reduce CO2 emissions from industrial operations remains an urgent and crucial priority. A viable strategy in the area is postcombustion capture mainly through absorption by aqueous alkanolamines, which focuses on the separation of CO2 from flue gas, despite its limitations. Within this context, porous materials, particularly metal-organic frameworks (MOFs), have arisen as favorable alternatives owing to their significant adsorption capacity, selectivity, and reduced regeneration energy demands. This research evaluates the engineering insights into tailored MOFs for enhanced CO2 capture, focusing on three series of MOFs (ZIF, UiO-66, and BTC) to investigate the effects of organic ligands, functional groups, and metal ions. The evaluation encompassed a range of aspects including adsorption isotherms of pure gases [CO2 and nitrogen (N2)] and mixed gas mixture (CO2 and N2 with 15:85% ratio), along with utilization of the ideal adsorbed solution theory (IAST) to simulate multicomponent gas adsorption isotherms. Moreover, the reliability of IAST for mixed gas adsorption prediction has been investigated in detail. The research offers valuable insights into the correlation between the characteristics of MOFs and their effectiveness in gas separation and how these characteristics contribute to the differences between IAST predictions and experimental results. The findings enhance the understanding of how to enhance MOF characteristics in order to reduce CO2 emissions and also highlight the need for advanced models that consider thermodynamic nonidealities to accurately predict the behavior of mixed gas adsorption in MOFs. As a result, the incorporation of MOFs with enhanced predictability and reliability into CO2 capture industrial processes is facilitated.

Separation of SO2 and NO2 with the Zeolite Membrane: Molecular Simulation Insights into the Advantageous NO2 Dimerization Effect

NO₂ and SO₂, as valuable chemical feedstock, are worth being recycled from flue gases. The separation of NO₂ and SO₂ is a key process step to enable practical deployment. This work proposes SO₂ separation from NO₂ using chabazite zeolite (SSZ-13) membranes and provides insights into the feasibility and advantages of this process using molecular simulation. Grand canonical ensemble Monte Carlo and equilibrium molecular dynamics methods were respectively adopted to simulate the adsorption equilibria and diffusion of SO₂, NO₂, and N₂O₄ on SSZ-13 at varying Si/Al (1, 5, 11, 71, +∞), temperatures (248-348 K), and pressures (0-100 kPa). The adsorption capacity and affinity (SO₂ > N₂O₄ > NO₂) demonstrated strong competitive adsorption of SO₂ based on dual-site interactions and significant reduction in NO₂ adsorption due to dimerization in the ternary gas mixture. The simulated order of diffusivity (NO₂ > SO₂ > N₂O₄) on SSZ-13 demonstrated rapid transport of NO₂, strong temperature dependence of SO₂ diffusion, and the impermeability of SSZ-13 to N₂O₄. The membrane permeability of each component was simulated, rendering a SO₂/NO₂ membrane separation factor of 26.34 which is much higher than adsorption equilibrium (6.9) and kinetic (2.2) counterparts. The key role of NO₂-N₂O₄ dimerization in molecular sieving of SO₂ from NO₂ was addressed, providing a facile membrane separation strategy at room temperature.

ZIF-95 as a filler for enhanced gas separation performance of polysulfone membrane

Metal-organic frameworks (MOFs) are found to be promising porous crystalline materials for application in gas separation. Considering that mixed matrix membranes usually increase the gas separation performance of a polymer by increasing selectivity, permeability, or both (i.e., perm-selectivity), the zeolitic imidazole framework-95 (ZIF-95) MOF was dispersed for the first time in polysulfone (PSF) polymer to form mixed matrix membranes (MMMs), namely, ZIF-95/PSF. The fabricated ZIF-95/PSF membranes were examined for the separation of various gases. The characterization of solvothermally synthesized ZIF-95 was carried out using different analyses such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), porosity measurements, etc. ZIF-95 was mixed with PSF at 8%, 16%, 24%, and 32% weight percent to form different loading MMMs. SEM analysis of membranes revealed good compatibility/adhesion between the MOF and polymer. The permeability of He, H₂, O₂, CO₂, N₂, and CH₄ were measured for the pure and composite membranes. The ideal selectivity of different gas pairs were calculated and compared with reported mixed matrix membranes. The maximum increases in permeabilities were observed in 32% loaded membrane; nevertheless, these performance/permeability increases were at the expense of a slight decrease of selectivity. In the optimally loaded membrane (i.e., 24 wt% loaded membrane), the permeability of H₂, O₂, and CO₂ increased by 80.2%, 78.0%, and 67.2%, respectively, as compared to the pure membrane. Moreover, the selectivity of H₂/CH₄, O₂/N₂, and H₂/CO₂ gas pairs also increased by 16%, 15%, and 8% in the 24% loaded membrane, respectively.

Understanding the Effect of Water on CO2 Adsorption

Carbon capture from large sources and ambient air is one of the most promising strategies to curb the deleterious effect of greenhouse gases. Among different technologies, CO₂ adsorption has drawn widespread attention mostly because of its low energy requirements. Considering that water vapor is a ubiquitous component in air and almost all CO₂-rich industrial gas streams, understanding its impact on CO₂ adsorption is of critical importance. Owing to the large diversity of adsorbents, water plays many different roles from a severe inhibitor of CO₂ adsorption to an excellent promoter. Water may also increase the rate of CO₂ capture or have the opposite effect. In the presence of amine-containing adsorbents, water is even necessary for their long-term stability. The current contribution is a comprehensive review of the effects of water whether in the gas feed or as adsorbent moisture on CO₂ adsorption. For convenience, we discuss the effect of water vapor on CO₂ adsorption over four broadly defined groups of materials separately, namely (i) physical adsorbents, including carbons, zeolites and MOFs, (ii) amine-functionalized adsorbents, and (iii) reactive adsorbents, including metal carbonates and oxides. For each category, the effects of humidity level on CO₂ uptake, selectivity, and adsorption kinetics under different operational conditions are discussed. Whenever possible, findings from different sources are compared, paying particular attention to both similarities and inconsistencies. For completeness, the effect of water on membrane CO₂ separation is also discussed, albeit briefly.

A new multi-functional Cu(ii)-organic framework as a platform for selective carbon dioxide chemical fixation and separation of organic dyes

A new multi-functional metal–organic framework {[Cu2(HL)(H2O)2]·NMP·2H2O}n was synthesized. It shows efficient catalytic performance for the chemical fixation of CO2 and exhibits selective sorption towards the rhodamine B dye.

Mechano-chemical stability and water effect on gas selectivity in mixed-metal zeolitic imidazolate frameworks: a systematic investigation from van der Waals corrected density functional theory

A series of Zn/Cu Zeolitic Imidazolate Frameworks (ZIFs) ZIF-202, -203, and -204 are systematically investigated by Density Functional Theory (DFT) with and without van der Waals (vdW) corrections.

Effects of Intrinsic Flexibility on Adsorption Properties of Metal-Organic Frameworks at Dilute and Nondilute Loadings

Molecular simulation of adsorption in nanoporous materials has become a valuable complement to experimental studies of these materials. In almost all cases, these simulations treat the adsorbing material as rigid. We use molecular simulations to examine the validity of this approximation for the adsorption in metal-organic frameworks (MOFs) that have framework flexibility without change in their unit cells because of thermal vibrations. All nanoporous materials are subject to this kind of framework flexibility. We examine the adsorption of nine molecules (CO₂, CH₄, ethane, ethene, propane, propene, butane, Xe, and Kr) and four molecular mixtures (CO₂/CH₄, ethane/ethene, propane/propene/butane, and Xe/Kr) in 100 MOFs at dilute and nondilute adsorption conditions. Our results show that single-component adsorption uptakes at nondilute conditions are only weakly affected by framework flexibility, but adsorption selectivities at both dilute and nondilute conditions can be significantly affected by flexibility. The most dramatic impacts of framework flexibility occur for adsorption uptake in the limit of dilute adsorption. These results suggest that the importance of including framework flexibility when attempting to make quantitative predictions of adsorption selectivity in MOFs and similar materials may have been underestimated in the past.

Two microporous CoII-MOFs with dual active sites for highly selective adsorption of CO2/CH4 and CO2/N2

Two microporous Co^II-MOFs exhibit highly CO₂/CH₄ and CO₂/N₂ selective adsorption owing to abundant dual active sites. GCMC theoretical simulations further verify the experimental results.

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.

Acidity and Cd2+ fluorescent sensing and selective CO2 adsorption by a water-stable Eu-MOF

A new luminescent Eu-MOF from an amino-group modified tetracarboxylic acid ligand was designed, which could perform as an efficient pH acidity and Cd²⁺ PL sensor and CO₂ selector.

Rational Synthesis of Chabazite (CHA) Zeolites with Controlled Si/Al Ratio and Their CO2 /CH4 /N2 Adsorptive Separation Performances

Separation of CO₂ from CH₄ and N₂ is of great significance from the perspectives of energy production and environment protection. In this work, we report the rational synthesis of chabazite (CHA) zeolites with controlled Si/Al ratio by using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as an organic structure-directing agent, wherein the dependence of TMAdaOH consumption on the initial Si/Al ratio was investigated systematically. More TMAdaOH is required to direct the crystallization of CHA with higher Si/Al ratio. Once the product Si/Al ratio is larger than 24, the amount of TMAdaOH consumption remains nearly constant. CHA zeolites with different Si/Al ratios and charge-compensating cations were then applied for the separation of CO₂ /CH₄ /N₂ mixtures. The equilibrium selectivities predicted by ideal adsorbed solution theory (IAST) and ideal selectivities calculated from the ratio of Henry's constants for both CO₂ /CH₄ and CO₂ /N₂ decrease with the zeolite Si/Al ratio increasing, whereas the percentage regenerability of CO₂ presents the opposite trend. Therefore, there is a trade-off between adsorption selectivity and regenerability for the adsorbents. There is a weaker interaction between CO₂ molecules and the H-type zeolites than that on the Na-type ones, thus a higher regenerability can be achieved. This study indicates that it is possible to design CHA zeolites with different physicochemical properties to meet various adsorptive separation requirements.

Simulations of hydrogen, carbon dioxide, and small hydrocarbon sorption in a nitrogen-rich rht-metal–organic framework

Detailed theoretical insights into the gas-sorption mechanism of Cu-TDPAH are presented for the first time.

Five transition metal coordination polymers driven by a semirigid trifunctional nicotinic acid ligand: selective adsorption and magnetic properties

Five coordination polymers have been synthesized by a new organic linker containing three distinct types of functional groups together with the mixed 2,2′-bipy or 4,4′-bipy co-ligand, revealing various framework structures and selective gas adsorption and magnetic properties.

Investigating gas sorption in an rht-metal-organic framework with 1,2,3-triazole groups

Simulations of CO₂ and H₂ sorption were performed in an rht-metal-organic framework (MOF) that consists of Cu²⁺ ions coordinated to 5,5',5''-(4,4',4''-(benzene-1,3,5-triyl)tris(1H-1,2,3-triazole-4,1-diyl))triisophthalate (BTTI) linkers; it is referred to as Cu-BTTI herein. This MOF was previously synthesized and reported by three different experimental groups [Zhao et al., Sci. Rep., 2013, 3, 1149; Schröder et al., Chem. Sci., 2013, 4, 1731-1736; Hupp et al., Energy Environ. Sci., 2013, 6, 1158-1163]. This MOF is notable for the presence of open-metal sites and nitrogen-rich regions through the copper paddlewheel ([Cu₂(O₂CR)₄]) clusters and 1,2,3-triazole groups, respectively, which allows this material to display remarkable CO₂ and H₂ sorption properties. All three groups report distinct experimental and theoretical gas sorption results for the MOF. In contrast to the force fields utilized in the aforementioned studies, our simulations include explicit many-body polarization interactions, which was important to reproduce sorption onto the open-metal sites. Simulations using polarizable potentials for the MOF and sorbates generated sorption isotherms and isosteric heat of adsorption (Q_st) values that are outstanding agreement with the corresponding experimental data for all three groups; this is in contrast to the theoretical results presented in the respective original references. The simulations carried out in the previous studies often looked reasonable but they missed a key feature of the sorption process that lead to unreliable results. Analysis of the radial distribution function (g(r)) about the open-metal sites and examination of the modeled structure reveal that the CO₂ and H₂ molecules prefer to sorb onto two unique types of Cu²⁺ ions that exhibit the highest partial positive charges. Sorption was also observed within the corners of the truncated tetrahedral (T-T_d) cages and onto the 1,2,3-triazole groups of the linkers for both sorbates. Overall, this study demonstrates how utilizing a classical polarizable force field led to the reproduction of experimental observables and allowed for an accurate description of the sorption mechanism in this MOF that is an important member of the rht-MOF family.

Two Analogous Polyhedron-Based MOFs with High Density of Lewis Basic Sites and Open Metal Sites: Significant CO2 Capture and Gas Selectivity Performance

By means of modulating the axial ligand and adopting supermolecular building blocks (SBBs) strategy, two polyhedron-based metal-organic frameworks (PMOFs) have been successfully synthesized [Cu₆(C₁₇O₉N₂H₈)₃(C₆H₁₂N₂)(H₂O)₂(DMF)₂]·3DMF·8H₂O (JLU-Liu46) and [Cu₆(C₁₇O₉N₂H₈)₃(C₄H₄N₂)(H₂O)₂(DMF)₂]·3DMF·8H₂O (JLU-Liu47), which possess a high density of Lewis basic sites (LBSs) and open metal sites (OMSs). Since the size of axial ligand in JLU-Liu47 is smaller than that in JLU-Liu46, JLU-Liu47 shows larger pore volume and higher BET surface area. Then, the adsorption ability of JLU-Liu47 for some small gases is better than JLU-Liu46. It is worthwhile to mention that both of the two compounds exhibit outstanding adsorption capability for CO₂ ascribed to the introducing of urea groups. In addition, the theoretical ideal adsorbed solution theory (IAST) calculation and transient breakthrough simulation indicate that JLU-Liu46 and JLU-Liu47 should be potential materials for gas storage and separation, particularly for CO₂/N₂, CO₂/CH₄, and C₃H₈/CH₄ separation.

Porous MOF with Highly Efficient Selectivity and Chemical Conversion for CO2

A new Co(II)-based MOF, {[Co₂(tzpa)(OH)(H₂O)₂]·DMF}_n (1) (H₃tzpa = 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid), was constructed by employing a tetrazolyl-carboxyl ligand H₃tzpa. 1 possesses 1D tubular channels that are decorated by μ₃-OH groups, uncoordinated carboxylate O atoms, and open metal centers generated by the removal of coordinated water molecules, leading to high CO₂ adsorption capacity and significantly selective capture for CO₂ over CH₄ and CO in the temperature range of 298-333 K. Moreover, 1 shows the chemical stability in acidic and basic aqueous solutions. Grand canonical Monte Carlo simulations identified multiple CO₂-philic sites in 1. In addition, the activated 1 as the heterogeneous Lewis and Brønsted acid bifunctional catalyst facilitates the chemical fixation of CO₂ coupling with epoxides into cyclic carbonates under ambient conditions.

CO2 Capture and Separations Using MOFs: Computational and Experimental Studies

This Review focuses on research oriented toward elucidation of the various aspects that determine adsorption of CO₂ in metal-organic frameworks and its separation from gas mixtures found in industrial processes. It includes theoretical, experimental, and combined approaches able to characterize the materials, investigate the adsorption/desorption/reaction properties of the adsorbates inside such environments, screen and design new materials, and analyze additional factors such as material regenerability, stability, effects of impurities, and cost among several factors that influence the effectiveness of the separations. CO₂ adsorption, separations, and membranes are reviewed followed by an analysis of the effects of stability, impurities, and process operation conditions on practical applications.

Screening the Effect of Water Vapour on Gas Adsorption Performance: Application to CO2 Capture from Flue Gas in Metal-Organic Frameworks

A simple laboratory-scale protocol that enables the evaluation of the effect of adsorbed water on CO₂ uptake is proposed. 45 metal-organic frameworks (MOFs) were compared against reference zeolites and active carbons. It is possible to classify materials with different trends in CO₂ uptake with varying amounts of pre-adsorbed water, including cases in which an increase in CO₂ uptake is observed for samples with a given amount of pre-adsorbed water. Comparing loss in CO₂ uptake between "wet" and "dry" samples with the Henry constant calculated from the water adsorption isotherm results in a semi-logarithmic trend for the majority of samples allowing predictions to be made. Outliers from this trend may be of particular interest and an explanation for the behaviour for each of the outliers is proposed. This thus leads to propositions for designing or choosing MOFs for CO₂ capture in applications where humidity is present.

Isostructural functionalization by –OH and –NH2: different contributions to CO2 adsorption

Amino- and hydroxyl-functionalized mfj-type MOFs were successfully synthesized, and gas-adsorption results demonstrated amino groups contribute more to CO₂ adsorption.

Two microporous Fe-based MOFs with multiple active sites for selective gas adsorption

Two Fe-based porous MOFs have been constructed from dimeric Fe-clusters and rod-shaped heterobimetallic Fe/Na-chains as SBUs, respectively. Notably, both of them exhibit highly selective CO₂ uptake over CH₄ and N₂ owing to abundant multiple active sites.

Two metal–organic frameworks based on a flexible benzimidazole carboxylic acid ligand: selective gas sorption and luminescence

Two new 3D frameworks with a novel (3,4,7)-connected trinodal net and (3,6)-connected binodal net were obtained by using a flexible ligand, showing significant adsorption selectivity for CO₂ over CH₄ as well as strong luminescence.

Experimental and theoretical investigations of the gas adsorption sites in rht-metal–organic frameworks

This highlight article reviews the experimental and theoretical studies that have been implemented to investigate the sorption sites for gases in rht-metal–organic frameworks.

Multiscale Computational Study on the Adsorption and Separation of CO2 /CH4 and CO2 /H2 on Li+ -Doped Mixed-Ligand Metal-Organic Framework Zn2 (NDC)2 (diPyNI)

The quantum mechanics (QM) method and grand canonical Monte Carlo (GCMC) simulations are used to study the effect of lithium cation doping on the adsorption and separation of CO₂ , CH₄ , and H₂ on a twofold interwoven metal-organic framework (MOF), Zn₂ (NDC)₂ (diPyNI) (NDC=2,6-naphthalenedicarboxylate; diPyNI=N,N'-di-(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide). Second-order Moller-Plesset (MP2) calculations on the (Li⁺ -diPyNI) cluster model show that the energetically most favorable lithium binding site is above the pyridine ring side at a distance of 1.817 Å from the oxygen atom. The results reveal that the adsorption capacity of Zn₂ (NDC)₂ (diPyNI) for carbon dioxide is higher than those of hydrogen and methane at room temperature. Furthermore, GCMC simulations on the structures obtained from QM calculations predict that the Li⁺ -doped MOF has higher adsorption capacities than the nondoped MOF, especially at low pressures. In addition, the probability density distribution plots reveal that CO₂ , CH₄ , and H₂ molecules accumulate close to the Li cation site. The selectivity results indicate that CO₂ /H₂ selectivity values in Zn₂ (NDC)₂ (diPyNI) are higher than those of CO₂ /CH₄ . The selectivity of CO₂ over CH₄ on Li⁺ -doped Zn₂ (NDC)₂ (diPyNI) is improved relative to the nondoped MOF.

A comprehensive study of methane/carbon dioxide adsorptive selectivity in different bundle nanotubes

We have investigated methane/carbon dioxide adsorptive selectivity in carbon nanotube (CNT) and silicon carbide nanotube (SiCNT) bundlesviaMD simulations.

A chiral metal–organic framework with polar channels: unique interweaving six-fold helices and high CO2/CH4 separation

A chiral Cu(ii) metal–organic framework, possesses interesting polar channels based on interweaving heterochiral [4 + 2] helices, exhibiting multiple CO₂ binding sites and highly selective capture for CO₂ over CH₄.

Adsorptive Separation of Methanol-Acetone on Isostructural Series of Metal-Organic Frameworks M-BTC (M = Ti, Fe, Cu, Co, Ru, Mo): A Computational Study of Adsorption Mechanisms and Metal-Substitution Impacts

The adsorptive separation properties of M-BTC isostructural series (M = Ti, Fe, Cu, Co, Ru, Mo) for methanol-acetone mixtures were investigated by using various computational procedures of grand canonical Monte Carlo simulations (GCMC), density functional theory (DFT), and ideal adsorbed solution theory (IAST), following with comprehensive understanding of adsorbate-metal interactions on the adsorptive separation behaviors. The obtained results showed that the single component adsorptions were driven by adsorbate-framework interactions at low pressures and by framework structures at high pressures, among which the mass effects, electrostatics, and geometric accessibility of the metal sites also played roles. In the case of methanol-acetone separation, the selectivity of methanol on M-BTCs decreased with rising pressures due to the pressure-dependent separation mechanisms: the cooperative effects between methanol and acetone hindered the separation at low pressures, whereas the competitive effects of acetone further resulted in the lower selectivity at high pressures. Among these M-BTCs, Ti and Fe analogues exhibited the highest thermodynamic methanol/acetone selectivity, making them promising for adsorptive methanol/acetone separation processes. The investigation provides mechanistic insights on how the nature of metal centers affects the adsorption properties of MOFs, and will further promote the rational design of new MOF materials for effective gas mixture separation.

Selective and Regenerative Carbon Dioxide Capture by Highly Polarizing Porous Carbon Nitride

Energy-efficient CO2 capture is a stringent demand for green and sustainable energy supply. Strong adsorption is desirable for high capacity and selective capture at ambient conditions but unfavorable for regeneration of adsorbents by a simple pressure control process. Here we present highly regenerative and selective CO2 capture by carbon nitride functionalized porous reduced graphene oxide aerogel surface. The resultant structure demonstrates large CO2 adsorption capacity at ambient conditions (0.43 mmol·g(-1)) and high CO2 selectivity against N2 yet retains regenerability to desorb 98% CO2 by simple pressure swing. First-principles thermodynamics calculations revealed that microporous edges of graphitic carbon nitride offer the optimal CO2 adsorption by induced dipole interaction and allows excellent CO2 selectivity as well as facile regenerability. This work identifies a customized route to reversible gas capture using metal-free, two-dimensional carbonaceous materials, which can be extended to other useful applications.

Effective ligand functionalization of zirconium-based metal-organic frameworks for the adsorption and separation of benzene and toluene: a multiscale computational study

The adsorption and separation properties of benzene and toluene on the zirconium-based frameworks UiO-66, -67, -68, and their functional analogues UiO-Phe and UiO-Me2 were studied using grand canonical Monte Carlo simulations, density functional theory, and ideal adsorbed solution theory. Remarkable higher adsorption uptakes of benzene and toluene at low pressures on UiO-Phe and -Me2 were found compared to their parent framework UiO-67. It can be ascribed to the presence of functional groups (aromatic rings and methyl groups) that significantly intensified the adsorption, majorly by reducing the effective pore size and increasing the interaction strength with the adsorbates. At high pressures, the pore volumes and accessible surfaces of the frameworks turned out to be the dominant factors governing the adsorption. In the case of toluene/benzene separation, toluene selectivities of UiOs showed a two-stage separation behavior at the measured pressure range, resulting from the greater interaction affinities of toluene at low pressures and steric hindrance effects at high pressures. Additionally, the counterbalancing factors of enhanced π delocalization and suitable pore size of UiO-Phe gave rise to the highest toluene selectivity, suggesting the ligand functionalization strategy could reach both high adsorption capacity and separation selectivity from aromatic mixtures at low concentrations.

Two microporous MOFs constructed from different metal cluster SBUs for selective gas adsorption

Two microporous MOFs have been constructed from different metal cluster SBUs. Both PMOFs exhibit highly selective uptake for CO₂over CH₄and N₂owing to abundant active sites.