158 research outputs found
Dynamics of water diffusion in mesoporous zeolites
No full textPulsed field gradient NMR has been applied to investigate water diffusion in Na+-form zeolites beta and LTA if, in addition to the micropores, the intracrystalline space is traversed by a network of mesopores. In zeolite beta, the presence of the mesopores is found to enhance the rate of molecular diffusion by a factor of 3. The measurements with mesoporous zeolite LTA yield diffusivities which reproduce the order of magnitude of the diffusivities found in previous studies with genuine microporous specimens. (C) 2010 Elsevier Inc. All rights reserved.Financial supports by the Ministry of Education, Science and
Technology in Korea through the National Honor Scientist Program
(20100029665) and World Class University Program (R31-2010-
000-10071-0), and the Deutsche Forschungsgemeinschaft and the
Fonds der ChemischenIndustrie in Germany are gratefully
acknowledged
NMR under Confinement: Roots in Retrospect
No full textNuclear magnetic resonance (NMR) has provided us with many beneficial opportunities for science and technology. Its continued use in novel fields has yielded impressive strength and attractiveness for nearly a century. This is particularly true with regards to the topic of this book, the exploration of ‘‘Fluid Transport in Porous Solids and Heterogeneous Materials’’.
Here, the benefit of NMR in being able to look ‘‘from the outside’’ into a system becomes particularly evident. NMR operates as an ‘‘ideal spy’’, providing information without interfering with internally occurring phenomena. NMR is able to give information on pore spaces as well as anything that might happen within them. This wide-range of information that is accessible is illustrated by the examples in this book. The origin of some of these developments can, most remarkably, be traced back over many decades, to the very beginning of NMR research. In this chapter we will
recollect some of the roots of the challenges we face today with applying NMR to studying ‘‘Fluid Transport in Porous Solids and Heterogeneous Materials’’- albeit with some bias by personal experiences and impressions
DIFFUSION IN COMPLEX PORE SPACES
No full textThe diffusion behavior of guest molecules introduced in porous materials has been studied. Diffusion studies in such porous materials may help for elucidating the structural properties, transport mechanism and/or surface barriers of the zeolite structure. The focus of this work is on diffusion in nanoporous materials with complex pore spaces.
First a short introduction in the basics of diffusion and the PFG NMR technique (Pulsed Field Gradient Nuclear Magnetic Resonance) is described.
In the following two chapters the diffusion in hierarchical pore spaces or, to be more precise, zeolites with generated mesopores, which traverse the microporous bulk phase, are investigated. The hierarchical pore spaces consists in the first case of micro- and mesopores and in the second case of micro-, meso- and macropores. The diffusion behavior in these materials has been investigated revealing diffusion acceleration in the mesoporous samples, as compared to the purely microporous material.
In the next chapter the diffusion behavior in glass samples with different porosity and their complementary pore space is investigated. Diffusion with full loaded pore spaces and surface diffusion, where the molecules were only able to diffuse along the pore walls, has been explored. The aim was to find out to what extent the diffusion in two complementary pore spaces is correlated.
In the last chapter, the effect of an inorganic binder on the transport in zeolite pellets has been studied. First the diffusion behavior in binderless zeolite beads in comparison with the zeolite powder employed for their production has been explored. The particular interest was to find out up to which extent the diffusion patterns observed with the powder samples could again be recognized in the beads. In a second study the transport characteristics within binderless molecular sieves have been investigated, with the purpose to reveal differences in the diffusion behavior in comparison with their binder-containing counterparts
Structure-Dynamics Relationships in Complex Fluids and Disordered Porous Solids Assessed using NMR: Structure-Dynamics Relationships in Complex Fluidsand Disordered Porous Solids Assessed using NMR
No full textA NMR study of the structure-dynamics relationships in heterogeneous materials is presented. In the first part, transport in soft-matter systems is studied using the pulsed field gradient NMR technique (PFG NMR). The molecular crowding effect in biological matter has been addressed using polymer solutions as model systems. By performing ensemble-based diffusion studies, the earlier obtained data on anomalous diffusion have been complemented. The transition to normal diffusion on a larger time scale has been shown. Taking advantages of the NMR approach, transport properties of microemulsions consisting of micellar colloids dissolved in liquid crystals have been investigated. The self-diffusivities measured under equilibrium conditions have shown weak correlations with microscopic ordering and macroscopic phase transitions occurring in the systems under study. The formation of micelles is shown to be decisive for macroscopic separation at the isotropic-nematic transition.
The second part of the thesis covers heterogeneous effects in diffusion for fluids in porous solids, as probed using a combination of NMR diffusometry and structure characterization methods. Ionic liquids have been investigated, revealing a complex behavior under confinement. The attempts to correlate the observed characteristics of the ionic liquids with their internal chemical structure were undertaken. Finally, the series of nanoporous glasses with tunable pore structure characteristics were studied. Strong correlations between their structure and the preparation conditions as well as between the resulting transport properties have been shown
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