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Diffusion in Micropores
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Diffusion in Micropores

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Porous Materials".

Deadline for manuscript submissions: closed (31 January 2012) | Viewed by 43551

Special Issue Editors

Dr. Sergey Vasenkov

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Guest Editor
Department of Chemical Engineering, University of Florida, 423 ChE Bldg., PO Box 116005, Gainesville, FL 32611, USA
Interests: transport in porous materials with hierarchy of pore sizes; dynamics in room temperature ionic liquids; single-file diffusion in nanochannels; separations of greenhouse gases
Special Issues, Collections and Topics in MDPI journals
Dr. Siegfried Fritzsche

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Guest Editor
Department of Molecular Dynamics/Computer Simulation, Faculty of Physics and Geosciences, Institute for Theoretical Physics (ITP),University of Leipzig, Postfach 100920, 04009 Leipzig, Germany
Interests: molecular dynamics computer simulations (MD); diffusion in porous materials; transport processes; surface effects; zeolites; metal - organic frameworks (MOF)

Special Issue Information

Dear Colleagues,

Last decade is characterised by the most remarkable progress in the introduction and further development of advanced microporous materials such as metal-organic framework materials (MOFs), single wall carbon nanotubes, and zeolites. These materials are important for many applications including catalysis, separations, molecular storage and sensor development. The majority of these applications involves transport of molecules and ions in micropore networks of these matarials. Hence, detailed fundamental understanding of transport properties of guest species in micropores is crucial for both applied and basic research related to microporous solids. Recent studies of sorbate diffusion in microporous materials resulted in fascinating discoveries related to normal diffusion, and also anomalous diffusion, such as single-file diffusion in micropores. These discoveries become possible due to most recent development of many new experimental techniques allowing monitoring molecular transport on various length scales of displacements under different experimental conditions and by the further development and application of multiscale computer simulations.

Dr. Siegfried Fritzsche
Prof. Dr. Sergey Vasenkov
Guest Editors

Keywords

  • advanced membranes
  • hybrid materials
  • anomalous transport
  • surface diffusion
  • pore diffusion
  • channel diffusion
  • sorption properties

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Published Papers (6 papers)

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Research

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830 KiB  
Article
“Pore-Like” Effects of Super-Molecular Self-Assembly on Molecular Diffusion of Poly(Ethylene Oxide)-Poly(Propylene Oxide)-Poly(Ethylene Oxide) in Water
by Konstantin Ulrich, Petrik Galvosas, Jörg Kärger and Farida Grinberg
Materials 2012, 5(5), 966-984; https://doi.org/10.3390/ma5050966 - 24 May 2012
Cited by 9 | Viewed by 6442
Abstract
Molecular diffusion of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in water was studied with the help of Pulsed Field Gradient NMR in the broad range of polymer weight fractions from 0.09 to 0.8. Owing to amphiphilic nature of the molecules, these block copolymers [...] Read more.
Molecular diffusion of triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in water was studied with the help of Pulsed Field Gradient NMR in the broad range of polymer weight fractions from 0.09 to 0.8. Owing to amphiphilic nature of the molecules, these block copolymers exhibit rich self-organization properties when mixed with water. In particular, at ambient temperatures they form micelles and three liquid crystalline mesophases: cubic, hexagonal, and lamellar. The corresponding super-molecular structure formations were studied with the same block copolymer and at the same temperature. Self-assembly of molecules was shown to produce “pore-like” effects on their self-diffusion properties by imposing severe constraints on the dimensionality of propagation. Diffusion in the hexagonal phase was shown to be quasi one-dimensional in the direction parallel to the long axis of the ordered molecular rods. In the lamellar phase, diffusion was found to be quasi two-dimensional, in the plane of the lamellar structures. The observed diffusion anisotropy was attributed to the effects of the specific molecular ordering on the mesoscopic length scale. Full article
(This article belongs to the Special Issue Diffusion in Micropores)
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1961 KiB  
Article
X-Nuclei NMR Self-Diffusion Studies in Mesoporous Silica Foam and Microporous MOF CuBTC
by Stefan Schlayer, Anne-Kristin Pusch, Friederike Pielenz, Steffen Beckert, Mikuláš Peksa, Carsten Horch, Lutz Moschkowitz, Wolf-Dietrich Einicke and Frank Stallmach
Materials 2012, 5(4), 617-633; https://doi.org/10.3390/ma5040617 - 12 Apr 2012
Cited by 21 | Viewed by 8004
Abstract
A standard X-observe NMR probe was equipped with a z-gradient coil to enable high-sensitivity pulsed field gradient NMR diffusion studies of Li+ and Cs+ cations of aqueous salt solutions in a high-porosity mesocellular silica foam (MCF) and of CO2 adsorbed [...] Read more.
A standard X-observe NMR probe was equipped with a z-gradient coil to enable high-sensitivity pulsed field gradient NMR diffusion studies of Li+ and Cs+ cations of aqueous salt solutions in a high-porosity mesocellular silica foam (MCF) and of CO2 adsorbed in metal-organic frameworks (MOF). The coil design and the necessary probe modifications, which yield pulsed field gradients of up to ±16.2Tm−1, are introduced. The system was calibrated at 2H resonance frequency and successfully applied for diffusion studies at 7Li, 23Na, 13C and 133Cs frequencies. Significant reductions of the diffusivities of the cations in LiClac and CsClac solution introduced into MCFs are observed. By comparison of the diffusion behavior with the bulk solutions, a tortuosity of the silica foam of 4.5 ± 0.6 was derived. Single component self-diffusion of CO2 and CH4 (measured by 1H NMR) as well as self-diffusion of the individual components in CO2/CH4 mixtures was studied in the MOF CuBTC. The experimental results confirm high mobilities of the adsorbed gases and trends for diffusion separation factors predicted by MD simulations. Full article
(This article belongs to the Special Issue Diffusion in Micropores)
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Review

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1649 KiB  
Review
Micro-Imaging by Interference Microscopy: A Case Study of Orientation-Dependent Guest Diffusion in MFI-Type Zeolite Host Crystals
by Laurent Gueudré, Tomas Binder, Christian Chmelik, Florian Hibbe, Douglas M. Ruthven and Jörg Kärger
Materials 2012, 5(4), 721-740; https://doi.org/10.3390/ma5040721 - 24 Apr 2012
Cited by 21 | Viewed by 6600
Abstract
Because of the small particle size, orientation-dependent diffusion measurements in microporous materials remains a challenging task. We highlight here the potential of micro-imaging by interference microscopy in a case study with MFI-type crystals in which, although with different accuracies, transient concentration profiles in [...] Read more.
Because of the small particle size, orientation-dependent diffusion measurements in microporous materials remains a challenging task. We highlight here the potential of micro-imaging by interference microscopy in a case study with MFI-type crystals in which, although with different accuracies, transient concentration profiles in all three directions can be observed. The measurements, which were performed with “rounded-boat” shaped crystals, reproduce the evolution patterns of the guest profiles recorded in previous studies with the more common “coffin-shaped” MFI crystals. The uptake and release patterns through the four principal faces (which in the coffin-shaped crystals extend in the longitudinal direction) are essentially coincident and there is no perceptible mass transfer in the direction of the long axis. The surface resistances of the four crystal faces through which mass transfer occurs are relatively small and have only a minor effect on the mass transfer rate. As a result of the pore structure, diffusion in the crystallographic c direction (which corresponds to the direction of the long axis) is expected to be much slower than in the transverse directions. This could explain the very low rate of mass transfer observed in the direction of the long axis, but it is also possible that the small end faces of the crystal may have high surface resistance. It is not possible to distinguish unequivocally between these two possibilities. All guest molecules studied (methyl-butane, benzene and 4-methyl-2-pentyne) show the same orientation dependence of mass transfer. The long 4-methyl-2-pentyne molecules would be expected to propagate at very different rates through the straight and sinusoidal channels. The coinciding patterns for uptake through the mutually perpendicular crystal faces therefore provide clear evidence that both the coffin shaped crystals and the rounded-boat-shaped crystals considered in this study, must be intergrowths rather than pure single crystals. Full article
(This article belongs to the Special Issue Diffusion in Micropores)
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613 KiB  
Review
Exploring Mass Transfer in Mesoporous Zeolites by NMR Diffusometry
by Dirk Mehlhorn, Rustem Valiullin, Jörg Kärger, Kanghee Cho and Ryong Ryoo
Materials 2012, 5(4), 699-720; https://doi.org/10.3390/ma5040699 - 20 Apr 2012
Cited by 18 | Viewed by 7048
Abstract
With the advent of mesoporous zeolites, the exploration of their transport properties has become a task of primary importance for the auspicious application of such materials in separation technology and heterogeneous catalysis. After reviewing the potential of the pulsed field gradient method of [...] Read more.
With the advent of mesoporous zeolites, the exploration of their transport properties has become a task of primary importance for the auspicious application of such materials in separation technology and heterogeneous catalysis. After reviewing the potential of the pulsed field gradient method of NMR (PFG NMR) for this purpose in general, in a case study using a specially prepared mesoporous zeolite NaCaA as a host system and propane as a guest molecule, examples of the attainable information are provided. Full article
(This article belongs to the Special Issue Diffusion in Micropores)
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1096 KiB  
Review
Magnetic Resonance Characterization of Porous Media Using Diffusion through Internal Magnetic Fields
by Hyung Joon Cho, Eric E. Sigmund and Yiqiao Song
Materials 2012, 5(4), 590-616; https://doi.org/10.3390/ma5040590 - 12 Apr 2012
Cited by 16 | Viewed by 6708
Abstract
When a porous material is inserted into a uniform magnetic field, spatially varying fields typically arise inside the pore space due to susceptibility contrast between the solid matrix and the surrounding fluid. As a result, direct measurement of the field variation may provide [...] Read more.
When a porous material is inserted into a uniform magnetic field, spatially varying fields typically arise inside the pore space due to susceptibility contrast between the solid matrix and the surrounding fluid. As a result, direct measurement of the field variation may provide a unique opportunity to characterize the pore geometry. The sensitivity of nuclear magnetic resonance (NMR) to inhomogeneous field variations through their dephasing effects on diffusing spins is unique and powerful. Recent theoretical and experimental research sheds new light on how to utilize susceptibility-induced internal field gradients to quantitatively probe the microstructure of porous materials. This article reviews ongoing developments based on the stimulated echo-pulse sequence to extend the characterization of porous media using both spatially resolved and unresolved susceptibility-induced internal gradients that operate on a diffusing-spin ensemble. Full article
(This article belongs to the Special Issue Diffusion in Micropores)
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421 KiB  
Review
Sorbate Transport in Carbon Molecular Sieve Membranes and FAU/EMT Intergrowth by Diffusion NMR
by Robert Mueller, Rohit Kanungo, Amrish Menjoge, Mayumi Kiyono-Shimobe, William J. Koros, Steven A. Bradley, Douglas B. Galloway, John J. Low, Sesh Prabhakar and Sergey Vasenkov
Materials 2012, 5(2), 302-316; https://doi.org/10.3390/ma5020302 - 14 Feb 2012
Cited by 3 | Viewed by 7747
Abstract
In this paper we present and discuss selected results of our recent studies of sorbate self-diffusion in microporous materials. The main focus is given to transport properties of carbon molecular sieve (CMS) membranes as well as of the intergrowth of FAU-type and EMT-type [...] Read more.
In this paper we present and discuss selected results of our recent studies of sorbate self-diffusion in microporous materials. The main focus is given to transport properties of carbon molecular sieve (CMS) membranes as well as of the intergrowth of FAU-type and EMT-type zeolites. CMS membranes show promise for applications in separations of mixtures of small gas molecules, while FAU/EMT intergrowth can be used as an active and selective cracking catalyst. For both types of applications diffusion of guest molecules in the micropore networks of these materials is expected to play an important role. Diffusion studies were performed by a pulsed field gradient (PFG) NMR technique that combines advantages of high field (17.6 T) NMR and high magnetic field gradients (up to 30 T/m). This technique has been recently introduced at the University of Florida in collaboration with the National Magnet Lab. In addition to a more conventional proton PFG NMR, also carbon-13 PFG NMR was used. Full article
(This article belongs to the Special Issue Diffusion in Micropores)
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