Tom Van Assche

High pressure, high temperature electrochemical synthesis of metal–organic frameworks: films of MIL-100 (Fe) and HKUST-1 in different morphologies

Thanks to a new high temperature electrodeposition setup, MIL-100(Fe) is synthesized and deposited electrochemically for the first time. In comparison to other methods commonly used to produce this MOF, the reported synthesis allows formation of layers, and it takes place under milder conditions. The layers have been tested for anti-fouling, gas adsorption and vapor separation. With the same setup Cu–BTC MOF HKUST-1 has been deposited at different temperatures obtaining different morphologies.

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.

On the electrochemical deposition of metal–organic frameworks

The electrochemical deposition of Metal–Organic Frameworks (MOFs) is an interesting technique to synthesise adherent, microporous layers on top of conductive substrates. The technique can be subdivided in two approaches: anodic and cathodic deposition. While the mechanism of the cathodic approach has already been well investigated, at least for MOF-5, up to now not much is known about the anodic approach. In this paper, a four-step mechanism is proposed to better understand the anodic deposition, and the same MOF used for the investigation, HKUST-1, is also deposited cathodically to compare the two approaches. This study focuses on how nucleation starts and proceeds, on the influence of the potential applied, the stresses in the growing layers, and the origin of defects like delamination and MOF detachment. The study is followed by critical considerations on the methods and on the technique, together with suggestions and guidelines to synthesise new MOF layers.

Prediction of Molecular Separation of Polar–Apolar Mixtures on Heterogeneous Metal–Organic Frameworks: HKUST-1

Due to the combination of metal ions and organic linkers and the presence of different types of cages and channels, metal-organic frameworks often possess a large structural and chemical heterogeneity, complicating their adsorption behavior, especially for polar-apolar adsorbate mixtures. By allocating isotherms to individual subunits in the structure, the ideal adsorbed solution theory (IAST) can be adjusted to cope with this heterogeneity. The binary adsorption of methanol and n-hexane on HKUST-1 is analyzed using this segregated IAST (SIAST) approach and offers a significant improvement over the standard IAST model predictions. It identifies the various HKUST-1 cages to have a pronounced polar or apolar adsorptive behavior.

A micromixer with consistent mixing performance for a wide range of flow rates

A micromixer with consistent mixing performance for a wide range of flow rates is presented. The mixer makes use of internally moving elements, i.e. steel balls that are located in dedicated mixing chambers. Movement is induced by a rotating magnetic field. To get better insight in differences between active and passive mixing, we studied a mixer that can operate in both regimes. A mixing performance study for a range of flow rates along with pressure drop data is presented. The response of the moving elements in regard to the magnetic field is shown experimentally and shows the limitations of earlier modeling studies. Lastly, the estimated power input on the fluids was calculated and allows for a comparison with more well‐known convective‐type mixers.

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.