IAST Selectivity Research Articles

Porous aromatic frameworks as HF resistant adsorbents for SF6 separation at elevated pressure

The public concern about sulfur hexafluoride (SF6) emission has driven the exploration of related removal processes via adsorptive separation technology. Based on task-specific porous materials, the capture of SF6 achieves lower energy consumption and less carbon footprint. Herein, four HF resistant porous aromatic frameworks (PAF-XJTU-1 to PAF-XJTU-4) with robust CC linkage were prepared for the separation of SF6 in semiconductor etching exhaust. Single-component gas adsorption and IAST selectivity confirmed the separation performance of the four PAFs materials under elevated pressure (10 bar). Moreover, DFT studies revealed the nonnegligible SF6 intermolecular interaction in PAFs at elevated pressure. Under the dynamic scenario, breakthrough experiments proved the effective capture of SF6 in PAF-XJTUs.

Highly Efficient Separation of CH4/C2H6/C3H8 from Natural Gas on a Novel Copper-Based Metal–Organic Framework

The separation of light hydrocarbons like methane, ethane, and propane is an important section of the chemical industry. Herein, we reported a novel porous metal–organic framework (MOF) Cu-IPA and investigated its CH4/C2H6/C3H8 separation performance, particularly for efficient capture of C2H6 and C3H8 at low concentrations. Cu-IPA featured 1D hexagonal channels and triangular channels decorated with extensive oxygen atoms. It showed high C2H6 and C3H8 capacities in the low-pressure region, where C3H8 uptake at 5 kPa was 1.62 mmol/g and C2H6 uptake reached 1.33 mmol/g at 10 kPa, suggesting the strong adsorption affinities toward C2H6 and C3H8. For an equimolar C2H6/CH4 mixture, Cu-IPA exhibited a considerable IAST selectivity of 40, exceeding most reported MOF adsorbents. Excellent CH4/C2H6/C3H8 separation performance for Cu-IPA can be attributed to its appropriate pore size and abundant accessible oxygens atoms in the triangular channel. The molecular simulation revealed that Cu-IPA tended to form stronger C–H···O interactions with C2H6 and C3H8 due to the higher polarizabilities, resulting in larger interaction differences between C2H6/CH4 and C3H8/CH4. Breakthrough tests also supported the excellent dynamic separation performance and recyclability of Cu-IPA.

A Structured Ultramicroporous Metal‐Organic Framework for Carbon Dioxide Capture†

Comprehensive SummaryCarbon dioxide (CO2) capture is one of the most important aspects of reducing global warming. In terms of CO2 capture, metal‐organic frameworks (MOFs) have several advantages. However, it isn't easy to shape MOFs while maintaining their performance. Herein, we describe the development of a pellet‐shaped ultramicroporous MOF, Ni(3‐ain)2 (3‐ain = 3‐aminoinoisonicotinic acid), that is capable of selectively adsorbing CO2. Polyvinyl butyral (PVB) is used as a binder during the production of Ni(3‐ain)2 MOF pellets. The adequately shaped material can maintain its crystallinity and exhibit a high CO2 adsorption capacity (3.73 mmol·g–1) at ambient conditions, which is significantly greater than those obtained for N2 (0.63 mmol·g–1) and CO (0.90 mmol·g–1). Consequently, this material displays high IAST selectivities for CO2/N2 (26.3, 15/85, V/V) and CO2/CO (19.2, 1/99, V/V). According to the theoretical calculations, Ni(3‐ain)2 preferentially adsorbs CO2 molecules over N2 molecules and CO molecules. The results of experiments on dynamic breakthrough have demonstrated that Ni(3‐ain)2 pellets are capable of effectively separating CO2/N2 or CO2/CO mixtures under conditions of dynamic flow. Furthermore, the structured MOF materials can be synthesized in one step at kilogram scale. This work provides an avenue for the shaping of MOFs for potential industrial applications in the future.

Highly scalable acid-base resistant Cu-Prussian blue metal-organic framework for C2H2/C2H4, biogas, and flue gas separations

One of the emerging problems plaguing the chemical industry today is the selective capture and separation of gases from their mixtures in an efficient and cost-effective manner. MOFs are new-age physisorbent materials extensively investigated for various gas mixture separations (such as biogas, flue gas, olefin/paraffin etc.); however, face the challenge of separations in a realistic environment. Here, we have investigated one of the Prussian blue analogues (Cu-PSB) to explore its potential as energy-efficient gas separation material. Cu-PSB can easily be scaled up at room temperature from water and is highly robust under harsh acidic, basic environments (pH = 1–11, 6 M HCl, 18 M H2SO4), exhibiting excellent separation of C2H2/C2H4, biogas (CO2:CH4 = 50:50), and flue gas (CO2:N2 = 15:85) mixtures. The IAST selectivity at ambient conditions (295 K, 50:50 mixture) could reach up to 5.2 for C2H2/C2H4, 14.7 for CO2/CH4, and 60.5 for the CO2/N2 (15:85 mixture). Such high C2H2 and CO2 uptake capacity and separation selectivity could be attributed to the synergistic effect of open CuII sites and the multiple H-bonding interactions within the functional pore channels of optimal pore size. Further, breakthrough simulation confirmed the complete separations from their binary mixtures, thus proving to be highly useful for the C2H2/C2H4 separation and CO2 capture from the bio and post-combustion flue gas mixtures. Cu-PSB was found to be even a more robust framework than ZIF-8 and UiO-66 MOFs.

Synthesis of grape-seed derived carbon with high specific surface area for CO2 selective adsorption

Nitrogen-doped porous carbons with BET surface area of 1068.2–3314.5 m2/g and nitrogen contents of 3.2–6.5% were prepared with solid waste grape-seed as raw material, NaNH2 as activator and nitrogen source at low activation temperature. Super The activation mechanism of NaNH2 on hydrothermal carbon precursors was first explored by thermodynamic analysis and TG-IR, which provided theoretical support for pore forming of carbon materials. Maximum CO2 and CH4 adsorption capacity at 273 K and pressure of 101 kPa was 5.42 and 1.76 mmol g−1 respectively, which are higher than those of majority of carbon derived from most solid wastes reported in literature. IAST selectivities of GS-3-450 with the largest BET surface area for CO2/CH4 (40v/60v), CO2/N2 (15v/85v), CH4/N2 (50v/50v) were found to be 20.3, 71.4, 6.0 under 101 kPa and 298 K respectively. The competitive adsorption of GS-3-450 for CO2/CH4 (40v/60v), CO2/N2 (15v/85v), CH4/N2 (50v/50v) gases mixture were examined through breakthrough experiments, and the results showed that the breakthrough time of CO2 was longer than that of CH4 and N2, which was beneficial to the separation of CO2 from gases mixture. Eight cycles of CH4 adsorption–desorption studies revealed that the material exhibited excellent recycling stability. Low temperature preparation method, excellent BET specific surface area and total pore volume, as well as excellent adsorption ability of CO2 and CH4 make it have a very great potential for the capture of CO2 and CH4.

Concurrent Enhancement of Acetylene Uptake Capacity and Selectivity by Progressive Core Expansion and Extra-Framework Anions in Pore-Space-Partitioned Metal-Organic Frameworks.

A multi-stage core-expansion method is proposed here as one component of the integrative binding-site/extender/core-expansion (BEC) strategy. The conceptual deconstruction of the partitioning ligand into three editable parts draws our focus onto progressive core expansion and allows the optimization of both acetylene uptake and selectivity. The effectiveness of this strategy is shown through a family of eight cationic pore-partitioned materials containing three different partitioning ligands and various counter anions. The optimized structure, Co3 -cpt-tph-Cl (Hcpt=4-(p-carboxyphenyl)-1,2,4-triazole, H-tph=(2,5,8-tri-(4-pyridyl)-1,3,4,6,7,9-hexaazaphenalene) with the largest surface area and highest C2 H2 uptake capacity (200 cm3 /g at 298 K), also exhibits (desirably) the lowest CO2 uptake and hence the highest C2 H2 /CO2 selectivity. The successful boost in both C2 H2 capacity and IAST selectivity allows Co3 -cpt-tph-Cl to rank among the best crystalline porous materials, ionic MOFs in particular, for C2 H2 uptake and C2 H2 /CO2 experimental breakthrough separation.

Fabrication of highly uniform ultra-small zeolite T nanocrystals

Ultra-Small Nanosized zeolite T crystals with an average size of about 16 nm were successfully obtained from freshly prepared NaAlO2 using Al powder at a low crystallization temperature of 60 °C, while the commercial NaAlO2 led to the amorphous product. The nanocrystals prepared from Al powder were pure and uniform, evidenced by XRD, SEM, and TEM. The prepared zeolite T crystals showed highest CO2 adsorption capacity (73.19 cm3/g STP) and high CO2/N2 IAST selectivity (47.62) at 1 bar at 25 °C, indicating its high CO2 adsorption potential. The freshly prepared NaAlO2 by Al powder led to much smaller crystals than commercial NaAlO2 at a higher crystallization temperature. This work demonstrates a simple and effective approach for the achievement of ultra-small zeolite T nanocrystal, providing the possibility for manipulation of ultrathin zeolite membrane or film.

Aromatic Amine-Functionalized Covalent Organic Frameworks (COFs) for CO2/N2 Separation.

CO2 is a prominent example for an exhaust gas, and it is known for its high impact on global warming. Therefore, carbon capture from CO2 emissions of industrial processes is increasingly important to halt and prevent the disruptive consequences of global warming. Covalent organic frameworks (COFs) as porous nanomaterials have been shown to selectively adsorb CO2 in high quantities and with high CO2/N2 selectivity. Interactions with amines are recognized to selectively adsorb CO2 and help capture it from exhaust emissions. Herein, a novel COF (Me3TFB-(NH2)2BD), which was not accessible via a direct condensation reaction, was synthetized by dynamic linker exchange starting with Me3TFB-BD. Despite the linker exchange, the porosity of the COF was largely maintained, resulting in a high BET surface area of 1624 ± 89 m2/g. The CO2 and N2 adsorption isotherms at 273 and 295 K were studied to determine the performance in carbon capture at flue gas conditions. Me3TFB-(NH2)2BD adsorbs 1.12 ± 0.26 and 0.72 ± 0.07 mmol/g of CO2 at 1 bar and 273 and 295 K, respectively. The COF shows a high CO2/N2 IAST selectivity under flue gas conditions (273 K:83 ± 11, 295 K: 47 ± 11). The interaction of the aromatic amine groups with CO2 is based on physisorption, which is expected to make the regeneration of the material energy efficient.

Tailoring zeolite ERI aperture for efficient separation of CO2 from gas mixtures

Constructing the metal cation-mediated low-cost inorganic sorbent with high separation efficiency in CO2, N2, and CH4 remains a major challenge. Herein, we developed a series of alkali metal cations (Na+, K+, Rb+, Cs+)-exchanged ERI zeolites and adopted in the separation process of CO2 among the gas mixture. Among the ion-exchanged zeolites, the zeolite K-ERI showed a high adsorption volume of 70.84 cm3g−1 and an IAST selectivity of CO2/CH4: 6254, CO2/N2: 2872 at 298 K, respectively, far outweighed the reported metal cation exchanged zeolites. Combining powder X-ray diffraction crystallography and density functional theory calculations, we unequivocally unveiled that the metal cations located at s8r effectively tailored zeolite aperture, and metal cation-gas molecules interactions synergically restrained the pass-through capacity of CO2 in ion-exchanged ERI framework. Such a unique host–guest interaction governed by metal cations in aluminosilicate zeolite ERI affords a general strategy for gas separation.

Insights into the thermodynamic-kinetic synergistic separation of propyne/propylene in anion pillared cage MOFs with entropy-enthalpy balanced adsorption sites.

Propyne/propylene (C3H4/C3H6) separation is an important industrial process yet challenged by the trade-off of selectivity and capacity due to the molecular similarity. Herein, record C3H4/C3H6 separation performance is achieved by fine tuning the pore structure in anion pillared MOFs. SIFSIX-Cu-TPA (ZNU-2-Si) displays a benchmark C3H4 capacity (106/188 cm3 g-1 at 0.01/1 bar and 298 K), excellent C3H4/C3H6 IAST selectivity (14.6-19.3) and kinetic selectivity, and record high C3H4/C3H6 (10/90) separation potential (36.2 mol kg-1). The practical C3H4/C3H6 separation performance is fully demonstrated by breakthroughs under various conditions. 37.8 and 52.9 mol kg-1 of polymer grade C3H6 can be produced from 10/90 and 1/99 C3H4/C3H6 mixtures. 4.7 mol kg-1 of >99% purity C3H4 can be recovered by a stepped desorption process. Based on the in situ single crystal analysis and DFT calculation, an unprecedented entropy-enthalpy balanced adsorption pathway is discovered. MD simulation further confirmed the thermodynamic-kinetic synergistic separation of C3H4/C3H6 in ZNU-2-Si.

Highly Selective Separation of C2H2/CO2 and C2H2/C2H4 in an N-Rich Cage-Based Microporous Metal-Organic Framework

The separation of acetylene (C2H2) from carbon dioxide (CO2) and the purification of ethylene (C2H4) from C2H2 are quite essential processes for the chemical industry. However, these processes are challenging due to their similar physical properties, including molecule sizes and boiling points. Herein, we report an N-rich cage-based microporous metal-organic framework (MOF), [Cd5(Tz)9](NO3) (termed as Cd-TZ, TZ stands for tetrazole), and its highly efficient separation of C2H2/CO2 and C2H2/C2H4. Single-component gas adsorption isotherms reveal that Cd-TZ exhibits high C2H2 adsorption capacity (3.10 mmol g-1 at 298 K and 1 bar). The N-rich cages in Cd-TZ can trap C2H2 with a higher isosteric heat of adsorption (40.8 kJ mol-1) than CO2 and C2H4 owing to the robust host-guest interactions between the noncoordinated N atoms and C2H2, which has been verified by molecular modeling studies. Cd-TZ shows a high IAST selectivity for C2H2/CO2 (8.3) and C2H2/C2H4 (13.3). The breakthrough simulations confirm the potential for separating C2H2/CO2 and the purification of C2H4 from C2H2.

Phenoxazine-based COFs for CO2/N2 separation and organic dye adsorption

CO2 adsorption IAST selectivities of phenoxazine-cored YCOF1 up to 70.97 (237 K) and 30.05 (298 K) under simulated flue gas conditions. High adsorption capacities of 650.14 (YCOF1) and 572.95 (YCOF2) mg g−1 for the dye MG in the aqueous solution.

A dense 3d–4f metal–organic framework with “gas pockets” for highly efficient CH4/N2separation

A pillar-layered dense 3d–4f MOF shows high IAST selectivity for CH4/N2owing to the enhancement of the interactions between the MOF and CH4by the heteroatoms of the pillars.

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.

Enhanced Adsorption Selectivity of Carbon Dioxide and Ethane on Porous Metal–Organic Framework Functionalized by a Sulfur-Rich Heterocycle

Porous metal-organic framework [Zn2(ttdc)2(bpy)] (1) based on thieno [3,2-b]thiophenedicarboxylate (ttdc) was synthesized and characterized. The structure contains intersected zig-zag channels with an average aperture of 4 × 6 Å and a 49% (v/v) guest-accessible pore volume. Gas adsorption studies confirmed the microporous nature of 1 with a specific surface area (BET model) of 952 m2·g-1 and a pore volume of 0.37 cm3·g-1. Extensive CO2, N2, O2, CO, CH4, C2H2, C2H4 and C2H6 gas adsorption experiments at 273 K and 298 K were carried out, which revealed the great adsorption selectivity of C2H6 over CH4 (IAST selectivity factor 14.8 at 298 K). The sulfur-rich ligands and double framework interpenetration in 1 result in a dense decoration of the inner surface by thiophene heterocyclic moieties, which are known to be effective secondary adsorption sites for carbon dioxide. As a result, remarkable CO2 adsorption selectivities were obtained for CO2/CH4 (11.7) and CO2/N2 (27.2 for CO2:N2 = 1:1, 56.4 for CO2:N2 = 15:85 gas mixtures). The computational DFT calculations revealed the decisive role of the sulfur-containing heterocycle moieties in the adsorption of CO2 and C2H6. High CO2 adsorption selectivity values and a relatively low isosteric heat of CO2 adsorption (31.4 kJ·mol-1) make the porous material 1 a promising candidate for practical separation of biogas as well as for CO2 sequestration from flue gas or natural gas.

Vapor sorption behavior in heptazine-based MOF featuring a brick-shaped framework

A new porous MOF, [Mg1.5(HTB)2]·2Me2NH2·3DMF·12MeOH, (1) (HTB ​= ​s-heptazine tribenzoate) was successfully synthesized by employing a π-conjugated organic ligand possessing a brick-shaped framework. The activated 1a was investigated as an adsorbent towards a series of vapors (H2O, MeOH, EtOH, n-PrOH and CH2Cl2). The H2O vapor adsorption capacity of 1a can reach 533.9 ​cm3 ​g−1. Interesting, the absorption isotherm of MeOH shows an obvious stepwise sorption phenomenon with the saturated adsorption capacity of 300.8 ​cm3 ​g−1, whereas the bulker EtOH, n-PrOH and CH2Cl2 present hardly any uptakes. Moreover, the IAST selectivities of equimolar H2O/MeOH and H2O/EtOH vapor mixtures was calculated, GCMC simulations were performed to locate the framework-vapor binding sites.

Functionalized modulators in imine-linked covalent organic frameworks (COFs)

Covalent Organic Frameworks (COFs) are porous materials with high surface areas, making them interesting for a large variety of applications including energy storage, chemical sensing, and gas separation. In gas separation and sensing, functionalization beyond the COF linkage can result in selective COF-gas interactions, tailoring the properties for the desired application. However, not all functional groups are compatible with the synthetic conditions needed for COF formation. Modulators, which are typically monovalent building blocks that would terminate the reaction, have been shown to maintain or even improve the COF porosity by slowing down the reaction kinetics. Herein, we report on a series of several para-functionalized (OMe, Me, F, Cl, CF3, NO2) amine modulators to introduce additional functionality into the framework to study the selective CO2/N2 gas separation under flue gas conditions. Thorough characterization of the modulated COFs showed that the modulators are located on the outside of the polymeric sheet and get replaced by benzidine molecules, favoring a regular network formation over a homogeneous modulator distribution. The fractions of eventually incorporated modulator vary per functional group between 2.1% (NO2-modulated COF) and 8.9% (Me-modulated COF) while maintaining high BET surface areas (>1800 m2/g). It was found that all modulated COFs adsorb moderate quantities of CO2 and show comparable CO2/N2 IAST selectivity values under flue gas conditions. A higher number of functional groups in the framework was shown to enhance the IAST selectivity.

Design of N-doped carbon materials using self-template strategy for high-performance supercapacitor electrodes and CO2 capture

Hierarchical N-doped porous carbons were synthesized using a self-templated and solvent-free assembly approach via directly heating green polyaspartic acid potassium. The samples prepared under different calcining temperatures were characterized, which exhibited the structural features of high pore volume (0.88–1.75 cm 3 /g) and large specific surface area (1592–3133 m 2 /g). Subsequently, these samples were applied for selective CO 2 capture and supercapacitor electrodes. The N-PCM-900 prepared at 900 °C afforded superb electrochemical performance, including extremely large specific capacitance (346 F/g at 1 A/g), high-rate capability (charge-discharge profiles at 20 A/g), and excellent cycle stability (96.86 % retention after 1000 cycles) in KOH electrolyte (6 M). Moreover, N-PCM-900 simultaneously provided high CO 2 adsorption ability (4.63 mmol/g) at 273 K, and high ideal adsorption solution theoretical value (25) for capturing CO 2 /N 2 at 298 K. The multifunctional porous carbon presented herein exhibited great potential for electrochemical energy storage and gas adsorption/separation. • A self-templated and solvent-free assembly approach was developed for the synthesis of hierarchical N-doped porous carbon. • The samples exhibited the structural features of high pore volume (1.75 m 3 g) and large specific surface area (3133 m 2 g). • High specific capacitance (161 F/g) and stability (99.4 % after 1000 cycles) are obtained. • Excellent CO 2 adsorption capacity (4.21 mmol/g) at 273 K and IAST selectivity (25) are gave.

A novel IL/MOF nanocomposite tailored for trace SO2 efficient capture based on synergistic effects

AbstractDue to its toxicity and corrosiveness, it is of enormous significance to efficiently capture and recover sulfur dioxide (SO2) from flue gas and natural gas. Herein, a new type of IL/MIL‐0.7 composite was precisely designed to meet this challenge, which exhibits a high adsorption capacity for SO2 (13.17 mmol g−1) at 298 K and 1.0 bar while excludes almost completely carbon dioxide (CO2, 0.27 mmol g−1) and nitrogen (N2, 0.07 mmol g−1). The high IAST selectivity (at least 11,925) of IL/MIL‐0.7 for SO2/CO2 can be achieved within the whole test pressure range. In addition, the breakthrough experiment also confirmed the excellent performance of the composite for deep removal of 2000 ppm SO2. Furthermore, the IL/MIL‐0.7 composites can maintain excellent performance after four adsorption/desorption cycles and the thermostability can up to ~450 K. Therefore, this stable IL/MOF composite has the potential application as an effective adsorbent for SO2 removal from flue gas and natural gas.

The Complexity of Comparative Adsorption of C6 Hydrocarbons (Benzene, Cyclohexane, n-Hexane) at Metal-Organic Frameworks.

The relatively stable MOFs Alfum, MIL-160, DUT-4, DUT-5, MIL-53-TDC, MIL-53, UiO-66, UiO-66-NH2, UiO-66(F)4, UiO-67, DUT-67, NH2-MIL-125, MIL-125, MIL-101(Cr), ZIF-8, ZIF-11 and ZIF-7 were studied for their C6 sorption properties. An understanding of the uptake of the larger C6 molecules cannot simply be achieved with surface area and pore volume (from N2 sorption) but involves the complex micropore structure of the MOF. The maximum adsorption capacity at p p0−1 = 0.9 was shown by DUT-4 for benzene, MIL-101(Cr) for cyclohexane and DUT-5 for n-hexane. In the low-pressure range from p p0−1 = 0.1 down to 0.05 the highest benzene uptake is given by DUT-5, DUT-67/UiO-67 and MIL-101(Cr), for cyclohexane and n-hexane by DUT-5, UiO-67 and MIL-101(Cr). The highest uptake capacity at p p0−1 = 0.02 was seen with MIL-53 for benzene, MIL-125 for cyclohexane and DUT-5 for n-hexane. DUT-5 and MIL-101(Cr) are the MOFs with the widest pore window openings/cross sections but the low-pressure uptake seems to be controlled by a complex combination of ligand and pore-size effect. IAST selectivities between the three binary mixtures show a finely tuned and difficult to predict interplay of pore window size with (critical) adsorptive size and possibly a role of electrostatics through functional groups such as NH2.