| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 2005: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2004: ¥3,500,000 (Direct Cost: ¥3,500,000)
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| Research Abstract |
Diffusion in zeolites plays an important role in most of the applications of zeolites as adsorbents and catalysts. The concise picture of the diffusion in a group of these microporous crystals is drawn as in the following : adsorbed species migrate among a few adsorption sites within a cage besides a jump to neighboring cages through interconnecting windows, and occasionally travel from one zeolite crystal to another. Various methods have been developed for the measurement of intracrysalline diffusivity of adsorbed species including the NMR spin-lattice relaxation, pulsed field-gradient (PFG) NMR, quasielastic neutron scattering (QENS) and triplet-triplet energy transfer techniques. The results were also discussed on the theoretical basis utilizing molecular dynamics and Monte Carlo simulation methods. In spite of these efforts, their still remains a difficulty in the precise measurement of diffusivity of molecules larger than benzene. Our idea is to apply a relatively new technique, f
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luorescence correlation spectroscopy which has been very successful in the measurement of diffusion coefficients in solution and biological systems (membranes and cells) but so far not been applied to heterogeneous systems such as zeolites. We have constructed a setup based on microscope with an Ar-ion laser as a excitation light source, a Si-avalanche photodiode as a detector and a correlation board as an analyzing system. We confirmed that our setup works properly for solution systems, however, difficulty arises when we applied to the zeolite systems. Because of too slow diffusion in zeolites we could not measure proper correlation, thus we are forced to modify the detection system. We, therefore, applied a single molecule spectroscopy to the problem of diffusion within a single zeolite crystal. We used epi-illumination technique coupled with the image capture by cooled CCD camera. We followed the time course of the fluorescence image of single molecules on a zeolite crystals and analyzed the trajectories of 20-30 molecules. By doing so, we could obtain the diffusion coefficient of adsorbed species. We could establish the methodology for the measurements of diffusivity within zeolites for various molecules, we could not obtain data for many molecules because of time limitation. As a result, we have no solid view for the outcome and this will be our future works. Less
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