Stepped water isotherm and breakthrough curves on aluminium fumarate metal–organic framework: experimental and modelling study

Adsorption of water vapour on the Al-fumarate metal–organic framework (MOF) was studied in static and dynamic conditions, by performing gravimetric and fixed bed experiments. A two-step, type IV water isotherm is obtained, which reveals the complexity and the duality of the hydrophilic/hydrophobic behaviour of this MOF. Breakthrough experiments with feed conditions corresponding to three different zones in the water adsorption isotherm were performed to study the effect of isotherm shape on the column dynamics. At low partial pressure of water in the feed, a single breakthrough step is observed while a stepped profile is observed at higher partial pressure of water. These breakthrough curves could be described qualitatively with a simple model accounting for the isotherm shape.status: publishe

An aliphatic copper metal-organic framework as versatile shape selective adsorbent in liquid phase separations

© 2016 Published by Elsevier Inc. Shape selective adsorption of organics on the metal-organic framework Cu(CDC) is demonstrated in both organic and aqueous media. Molecular sieving in the one-dimensional channels is responsible for the pronounced para-selectivity observed in the separation of C8 alkylaromatics as well as in the adsorption of dihydroxybenzene isomers from water. This pronounced selectivity for linear compounds in both organic and aqueous media is further proven in the selective adsorption of the linear n-butanol over branched butanol isomers out of water. Moreover, the framework is extremely stable towards water and in a pH range between 2 and 12. This high stability, combined with a facile, multigram scalable room temperature synthesis in water, make Cu(CDC) a very promising adsorbent material for liquid phase separations.publisher: Elsevier articletitle: An aliphatic copper metal-organic framework as versatile shape selective adsorbent in liquid phase separations journaltitle: Microporous and Mesoporous Materials articlelink: http://dx.doi.org/10.1016/j.micromeso.2016.01.044 content_type: article copyright: Copyright © 2016 Elsevier Inc. All rights reserved.status: publishe

Adsorptive desulfurization with CPO-27/MOF-74: an experimental and computational investigation

International audienceBy combining experimental adsorption isotherms, microcalorimetric data, infrared spectroscopy and quantum chemical calculations the adsorption behaviour of the CPO-27/MOF-74 series (Ni, Co, Mg, Cu, and Zn) in the desulfurization of fuels is evaluated. The results show a clear influence of the metal ion on the adsorption capacity and affinity for S-heterocyclic compounds, with CPO-27(Ni) being the best performing material both in terms of capacity and affinity. The microcalorimetric data and infrared spectroscopy confirm the high affinity of CPO-27(Ni) for thiophene and similar compounds, while the computational data reveal that the origin of this outstanding adsorption performance is the strong sulfur-metal interaction

Experimental Study of Adsorptive Interactions of Polar and Nonpolar Adsorbates in the Zeolitic Imidazolate Framework ZIF-68 via Pulse Gas Chromatography

Low coverage adsorptive properties of linear and branched alkanes, 1-alkenes, cycloalkanes, aromatics, and small polar adsorbates on the Zeolitic Imidazolate Framework ZIF-68 were explored by pulse gas chromatographic experiments at temperatures between 413 and 513 K. ZIF-68 has a complex structure with amphiphilic properties due to the presence of two different imidazole linkers (2-nitroimidazolate and benzimidazolate), resulting in small polar and large nonpolar channels. Shape selective properties are absent for linear and branched alkanes (C₅–C₁₂), which is not surprising given the occurrence of large channels in the structure. A specific mechanism for the adsorption of polar adsorbates is proposed via strong interactions with the nitro groups, pointing inward in the small channel. Further, <i>n</i>-alkanes, 1-alkenes, cycloalkanes, and aromatics were used as probe molecules to determine whether or not specific interactions were involved in the framework for nonpolar adsorbates. These experimentally obtained adsorption energy values were linked to a simple model, which relates the adsorption enthalpy to the degree of branching and to the contribution of nonspecific van der Waals (number of hydrogen atoms) and electrostatic (number of double bonds) interactions

Conformation-Controlled Sorption Properties and Breathing of the Aliphatic Al-MOF [Al(OH)(CDC)]

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Adsorptive Characterization of the ZIF-68 Metal-Organic Framework: A Complex Structure with Amphiphilic Properties

In this experimental study, the adsorption behavior of the ZIF-68 heterolinked zeolitic imidazolate framework has been explored. Vapor phase adsorption isotherms of linear C1–C6 alcohols, C6 alkane isomers, aromatics (benzene, toluene, xylene isomers, 1,3,5-trimethylbenzene, and 1,3,5-triisopropylbenzene), and polar adsorbates (water, acetonitrile, and acetone) are reported and discussed. The complex pore structure of ZIF-68, with two one-dimensional channels, each with a different polarity, displays an overall hydrophobic character. Its two-pore system results in S-shaped isotherms for small polar adsorbates (small alcohols, acetone, and acetonitrile), while longer alcohols and nonpolar molecules, such as aromatics and C6 alkane isomers, lead to type I adsorption isotherms. Bulky molecules, with a kinetic diameter significantly larger than the pore windows, are adsorbed in large amounts, which gave reason to think that this ZIF-68 material has a certain degree of framework flexibility to enlarge the free aperture of the channels. Besides, diffusion coefficients from vapor phase uptake and infrared experiments point to a different adsorption mechanism for polar and nonpolar adsorbates. Liquid phase adsorption experiments demonstrated the separation of alcohol mixtures (ethanol/1-butanol) at low concentration from water, with a clear preference for 1-butanol

Conformation-controlled sorption properties and breathing of the aliphatic Al-MOF [Al(OH)(CDC)]

The sorption properties of the Al-MOF CAU-13 were studied in detail. The adsorption of water and CO2 leads to small structural changes. However, when CAU-13 is exposed to xylene, a drastic change in the crystal structure is observed. In the evacuated form, CAU-13 contains trans-cyclohexanedicarboxylate linkers in the e,e and a,a conformations. After the adsorption of xylene, all of the linker molecules exhibit the e,e conformation, leading to a unit cell increase of ∼25%

Conformation-Controlled Sorption Properties and Breathing of the Aliphatic Al-MOF [Al(OH)(CDC)]

The Al-MOF CAU-13 ([Al­(OH)­(<i>trans</i>-CDC)]; <i>trans</i>-H₂CDC = <i>trans</i>-1,4-cyclohexanedicarboxylic acid) is structurally related to the MIL-53 compounds that are well-known for their “breathing” behavior, i.e., the framework flexibility upon external stimuli such as the presence of adsorbate molecules. The adsorption properties of CAU-13 were investigated in detail. The sorption isotherms of N₂, H₂, CH₄, CO, CO₂, and water were recorded, and the adsorption enthalpies for the gases were determined by microcalorimetry. The structural changes upon adsorption of CO₂ were followed with in situ synchrotron powder X-ray diffraction (PXRD). The patterns were analyzed by parametric unit cell refinement, and the preferential arrangement of the CO₂ molecules was modeled by density functional theory calculations. The adsorption and separation of mixtures of <i>o</i>-, <i>m</i>-, and <i>p</i>-xylene from mesitylene showed a preferred adsorption of <i>o</i>-xylene. The structures of <i>o</i>/<i>m</i>/<i>p</i>-xylene-loaded CAU-13 were determined from PXRD data. The adsorption of xylene isomers induces a larger pore opening than that in the thermal activation of CAU-13. In the crystal structure of the activated sample CAU-13­(empty pore), half of the linkers adopt the a,a confirmation and the other half the e,e conformation, and the presence of a,a-CDC^2– ions hampers the structural flexibility of CAU-13. However, after the adsorption of xylene, all linkers are present in the e,e conformation, allowing for a wider pore opening by this new type of “breathing”