Transport in Nanoporous Materials Including MOFs: The Applicability of Fick’s Laws

Titze, Tobias; Lauerer, Alexander; Heinke, Lars; Chmelik, Christian; Zimmermann, Nils; Keil, Frerich J.; Ruthven, Douglas M.; Kärger, Jörg

doi:10.1002/anie.201506954

Cited by 104 publications

(80 citation statements)

References 65 publications

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“…NMR signal attenuation is linear at small gradient (Fig. 5) which is compatible with a Gaussian propagator and then to a Fick's law [59]. This justifies the homogenization approach with a Fick formalism employed in this work.…”

Section: Effective Diffusion From Pfg-nmrsupporting

confidence: 61%

Numerical Simulation of Hindered Diffusion inγ-Alumina Catalyst Supports

Wang

Willot

Moreaud

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-By employing multi-scale random models of c-alumina, we have studied the influence of porosity, grain aspect ratio and aggregation state on the effective diffusion coefficient. Multi-scale Boolean models of platelets were used to produce digital volumes reproducing the alumina porous space. Iterative fast Fourier transform numerical simulation of Fick's diffusion were performed on the volume to obtain the effective diffusion coefficient. The tortuosity factors of the various simulated models show a simple dependence with pore volume fraction with an exponent guided by the platelet aspect ratio and the aggregation state. Comparisons with proton pulsed-field gradient nuclear magnetic resonance spectrometry show a satisfactory agreement.

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Section: Effective Diffusion From Pfg-nmrsupporting

confidence: 61%

Numerical Simulation of Hindered Diffusion inγ-Alumina Catalyst Supports

Wang

Willot

Moreaud

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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“…Despite the substantial progress in obtaining fundamental insight into the diffusion and mass transfer of small molecules with relatively large diffusion coefficients in MOFs, [24] experimentally determining the low diffusion coefficients of large guest molecules remains a challenge. Therefore, a detailed understanding of the diffusion processes is needed.…”

Section: Unique Model System For Diffusion Experimentsmentioning

confidence: 99%

Surface‐Mounted Metal–Organic Frameworks: Crystalline and Porous Molecular Assemblies for Fundamental Insights and Advanced Applications

2019

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with open voids attract significant interest, not only for use in gas storage and separation applications, [1b] but also as model systems used for fundamental investigations on molecular interactions. After being introduced about two decades ago, [2] this new type of crystalline coordination network created considerable excitement and much effort was devoted toward the discovery of new types of these compounds. In early 2017, after 20 years of intense research, the literature contains reports on more than 70 000 structurally characterized examples of this class. [3] Since MOFs can be assembled by combining molecular building blocks, specifically ditopic or higher-topic organic linkers and metal or metal-oxo nodes, a virtually unlimited number of structures can be realized. Moreover, essentially every organic molecule can be modified by the addition of appropriate coupling groups, e.g., carboxylic acid groups or pyridine units, to yield a ditopic linker. Therefore, the number of possible MOF structures is far greater than the number of known structures. In line with this consideration, more than a million of these compounds have been simulated using combinatorial approaches. [4] As MOFs are both crystalline and porous, they have fascinating and often surprising properties. Not only does the immense chemical space spanned by these compounds create enormous potential for advancing materials science, it also provides ideal matrices for reference experiments exploring fundamental spectroscopic and physicochemical properties. The framework provides a well-defined, crystalline, porous environment that can host guest molecules, thus permitting systematic spectroscopic investigations. In contrast to solvents or polymer matrices, MOFs provide a strictly periodic, very well defined structural framework, where the molecular environment is identical for each embedded guest molecule. In this respect, MOFs outperform amorphous noble-gas guest matrices [5] in which the environment surrounding varies from site to site, leading to inhomogeneous broadening of the embedded guest's spectroscopic features, including vibrational bands.Herein, we discuss the use of MOFs and, in particular, of surface-mounted metal-organic frameworks (SURMOFs), to provide well-defined environments for precisely determining Metal-organic frameworks (MOFs) are crystalline coordination polymers, assembled from inorganic nodes connected by organic linker molecules. An enormous surface area, huge compositional variety, regular structure, and favorable mechanical properties are among their outstanding properties. Monolithic MOF thin films, i.e., surface-mounted metalorganic frameworks (SURMOFs), with high degree of structural order and adjustable defect density, can be prepared on solid substrates using layer-by-layer techniques. Recent studies where SURMOFs served as model systems for quantitative studies of molecular interactions in porous media, including diffusion, are reviewed. Moreover, SURMOFs are ideally suited for the incorporation of photoactive mo...

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“…Furthermore, the affinity of the cargo molecules for the internal surface of the porous material (host-guest interaction) is likely to play an important role in determining the kinetics of transport, as well as the loading capacity [48]. Within the diffusion-immobilization model it is conceived that molecules undergo repeated cycles of absorption, desorption, and brief spells of free diffusion before an equilibrium situation is reached [49,50]. In addition, the conditions will change during the course of in vivo delivery.…”

Section: Introductionmentioning

confidence: 99%

Kinetic Analysis of the Uptake and Release of Fluorescein by Metal-Organic Framework Nanoparticles

et al. 2017

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Metal-organic framework nanoparticles (MOF NPs) are promising guest-host materials with applications in separation, storage, catalysis, and drug delivery. However, on-and off-loading of guest molecules by porous MOF nanostructures are still poorly understood. Here we study uptake and release of fluorescein by two representative MOF NPs, MIL-100(Fe) and MIL-101(Cr). Suspensions of these MOF NPs exhibit well-defined size distributions and crystallinity, as verified by electron microscopy, dynamic light scattering, and X-ray diffraction. Using absorbance spectroscopy the equilibrium dissociation constants and maximum numbers of adsorbed fluorescein molecules per NP were determined. Time-resolved fluorescence studies reveal that rates of release and loading are pH dependent. The kinetics observed are compared to theoretical estimates that account for bulk diffusion into NPs, and retarded internal diffusion and adsorption rates. Our study shows that, rather than being simple volumetric carriers, MOF-NPs are dominated by internal surface properties. The findings will help to optimize payload levels and develop release strategies that exploit varying pH for drug delivery.

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Transport in Nanoporous Materials Including MOFs: The Applicability of Fick’s Laws

Cited by 104 publications

References 65 publications

Numerical Simulation of Hindered Diffusion inγ-Alumina Catalyst Supports

Numerical Simulation of Hindered Diffusion inγ-Alumina Catalyst Supports

Surface‐Mounted Metal–Organic Frameworks: Crystalline and Porous Molecular Assemblies for Fundamental Insights and Advanced Applications

Kinetic Analysis of the Uptake and Release of Fluorescein by Metal-Organic Framework Nanoparticles

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