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Membranes from metal-organic frameworks (MOFs) are highly interesting for industrial gas separation applications. Strongly improved performances for carbon capture and H₂ purification tasks in MOF membranes are obtained by using highly reproducable and very accuratly, hierarchically grown ZIF-8-on-ZIF-67 (ZIF-8@ZIF-67) nanostructures. To forgo hardly controllable solvothermal synthesis, particles and layers are prepared by self-assembling methods. It was possible for the first time to confirm ZIF-8-on-ZIF-67 membrane growth on rough and porous ceramic supports using the layer-by-layer deposition. Additionally, hierarchical particles are made in a fast RT synthesis with high monodispersity. Characterization of the hierarchical and epitaxial grown layers and particles is performed by SEM, TEM, EDXM and gas permeation. The system ZIF-8@ZIF-67 shows a nearly doubled H₂/CO₂ separation factor, regardless of whether neat membrane or mixed-matrix-membrane in comparison to other MOF materials.

MOF-on-MOF: Hierarchical nanostructures were fabricated by highly tunable and accurately adjustable self-assembly techniques. The ZIF-8-on-ZIF-67, either applied as mixed-matrix membrane or as neat MOF layer, shows highly increased performance in hydrogen separation tasks. They outperform the single ZIF-8 and ZIF-67 materials and other MOF materials in gas separation membranes, because of their additive adsorption effects originating from stacking of the frameworks.

Selective anion extraction is useful for the recovery and purification of valuable chemicals, and in the removal of pollutants from the environment. Here we report that Fe^II₄L₄ cage 1 is able to extract an equimolar amount of ReO₄⁻, a high-value anion and a nonradioactive surrogate of TcO₄⁻, from water into nitromethane. Importantly, the extraction was efficiently performed even in the presence of 10 other common anions in water, highlighting the high selectivity of 1 for ReO₄⁻. The extracted guest could be released into water as the cage disassembled in ethyl acetate, and then 1 could be recycled by switching the solvent to acetonitrile. The versatile solubility of the cage also enabled complete extraction of ReO₄⁻ (as the tetrabutylammonium salt) from an organic phase into water by using the sulfate salt of 1 as the extractant.

A Fe^II₄L₄ coordination cage enabled complete extraction of ReO₄⁻, a nonradioactive surrogate of TcO₄⁻, from water into an organic phase. In the presence of 10 other anions, 97 % of ReO₄⁻ was selectively removed. The extracted ReO₄⁻ could be released and the cage extractant recycled by a solvent-switching strategy. Rendering the cage water-soluble also allowed complete extraction of ReO₄⁻ from an organic phase into water.

Biologically relevant hydrophilic molecules rarely interact with hydrophobic compounds and surfaces in water owing to effective hydration. Nevertheless, herein we report that the hydrophobic cavity of a polyaromatic capsule, formed through coordination-driven self-assembly, can encapsulate hydrophilic oligo(lactic acid)s in water with relatively high binding constants (up to K_a=3×10⁵ m⁻¹). X-ray crystallographic and ITC analyses revealed that the unusual host–guest behavior is caused by enthalpic stabilization through multiple CH–π and hydrogen-bonding interactions. The polyaromatic cavity stabilizes hydrolyzable cyclic di(lactic acid) and captures tetra(lactic acid) preferentially from a mixture of oligo(lactic acid)s even in water.

Incompatible interactions: The hydrophobic cavity of a polyaromatic capsule efficiently encapsulated hydrophilic oligo(lactic acid)s in water (see scheme). The X-ray crystallographic and ITC analyses revealed that the unusual host–guest behavior is caused by enthalpic stabilization through multiple CH–π and hydrogen bonding interactions.

The influence of reaction parameters like molar ratio of methanol to oleic acid, catalyst amount, and reaction temperatures for oleic acid esterification with methanol by using Zr(SO₄)₂ as a heterogeneous catalyst was investigated. Nearly complete conversion was obtained when the esterification reaction was carried out under optimized reaction conditions in terms of molar ratio of methanol to oleic acid, catalyst amount, reflux temperature of methanol, and reaction time. Furthermore, the kinetics of the esterification reaction was also investigated. The experimental data supported the validity of the suggested Eley-Rideal model.

The catalytic performance of the Zr(SO₄)₂ catalyst was investigated for esterification of oleic acid with methanol. The effects of relevant reaction parameters like methanol-to-oleic acid molar ratio, reaction temperature, and catalyst amount versus reaction time were examined. The kinetics of esterification was studied by applying pseudo-homogeneous and Eley-Rideal models to experimental data.