Employing high-throughput methods, the synthesis conditions for a series of six new MOFs based on aluminium ions and the V-shaped linker molecule 1,3-benzene dicarboxylic acid, denoted as CAU-10-X (CAU = Christian-Albrechts-University) with the sum formula [Al(OH)(C 8 H 3 O 4 X)]•solvent, were established (X = functional group in 5-position of the aromatic ring; X = H (1), CH 3 (2), OCH 3 (3) NO 2 (4), NH 2 (5), or OH (6)). Due to the absence of macroscopic crystals, the obtained compounds were structurally characterized employing XRPD-methods. The crystal structures of 1, 2 and 3 were refined using Rietveld methods. Although the described MOFs are isoreticular, they crystallize in several, sometimes non-centrosymmetric space groups (1, 4, 6), due to slight structural changes induced by the functionalization. These space groups were confirmed with second-harmonic generation measurements. All compounds are highly stable as confirmed by temperature-dependent XRPD-and IR-experiments and decompose at temperatures above 350 °C. The stabilities of all compounds in aqueous solutions of varying pH were confirmed by XRPD-measurements and their sorption properties towards nitrogen, hydrogen, carbon dioxide and water vapor at low pressures are reported. A drastic influence of the functional group on affinity, capacity and accessibility of the pores for these gases is observed. These properties depend on the polarity and size of the functional group as well as on subtle structural differences between the CAU-10-X compounds.
Many chemical compositions produce layered solids consisting of extended sheets with thickness not greater than a few nanometers. The layers are weakly bonded together in a crystal and can be modified into various nanoarchitectures including porous hierarchical structures. Several classes of 2-dimensional (2D) materials have been extensively studied and developed because of their potential usefulness as catalysts and sorbents. They are discussed in this review with focus on clays, layered transition metal oxides, silicates, layered double hydroxides, metal(iv) phosphates and phosphonates, especially zirconium, and zeolites. Pillaring and delamination are the primary methods for structural modification and pore tailoring. The reported approaches are described and compared for the different classes of materials. The methods of characterization include identification by X-ray diffraction and microscopy, pore size analysis and activity assessment by IR spectroscopy and catalytic testing. The discovery of layered zeolites was a fundamental breakthrough that created unprecedented opportunities because of (i) inherent strong acid sites that make them very active catalytically, (ii) porosity through the layers and (iii) bridging of 2D and 3D structures. Approximately 16 different types of layered zeolite structures and modifications have been identified as distinct forms. It is also expected that many among the over 200 recognized zeolite frameworks can produce layered precursors. Additional advances enabled by 2D zeolites include synthesis of layered materials by design, hierarchical structures obtained by direct synthesis and top-down preparation of layered materials from 3D frameworks.
A combination of adsorption, microcalorimetry, infra-red spectroscopy and modeling has been implemented to reveal the potential of the H2S resistant amino-functionalized Ti MOF MIL-125 porous solid for the concomitant elimination of CO2 and H2S from biogas and natural gas.
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