12 research outputs found
Stepped water isotherm and breakthrough curves on aluminium fumarate metalâorganic framework: experimental and modelling study
Adsorption of water vapour on the Al-fumarate metalâorganic 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 (C<sub>5</sub>âC<sub>12</sub>), 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)]
International audienc
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 C1âC6 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 âŒ25%
Conformation-Controlled Sorption Properties and Breathing of the Aliphatic Al-MOF [Al(OH)(CDC)]
The Al-MOF CAU-13 ([AlÂ(OH)Â(<i>trans</i>-CDC)]; <i>trans</i>-H<sub>2</sub>CDC = <i>trans</i>-1,4-cyclohexanedicarboxylic
acid) is structurally related to the MIL-53 compounds that are well-known
for their âbreathingâ 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 N<sub>2</sub>, H<sub>2</sub>, CH<sub>4</sub>, CO, CO<sub>2</sub>, and water were recorded, and the adsorption
enthalpies for the gases were determined by microcalorimetry. The
structural changes upon adsorption of CO<sub>2</sub> 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 CO<sub>2</sub> 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-13Â(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<sup>2â</sup> 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 âbreathingâ