Study on intra-zeolite diffusional motion by fluorescence correlation spectroscopy

在沸石作为吸附剂和催化剂的大多数应用中，沸石中的扩散起着重要的作用。一组微孔晶体中扩散的简图如下所示：除了通过相互连接的窗口跳到相邻的笼外，被吸附的物质在笼内的几个吸附位点之间迁移，偶尔也会从一个沸石晶体迁移到另一个沸石晶体。各种测量吸附物质晶体内扩散率的方法已经发展起来，包括核磁共振自旋晶格弛豫、脉冲场梯度（PFG）核磁共振、准弹性中子散射（QENS）和三重态能量传递技术。利用分子动力学和蒙特卡罗模拟方法，在理论基础上对所得结果进行了讨论。尽管作出了这些努力，但在精确测量比苯大的分子的扩散率方面仍然存在困难。我们的想法是应用一种相对较新的技术，更多的荧光相关光谱，它在测量溶液和生物系统（膜和细胞）的扩散系数方面非常成功，但到目前为止还没有应用于沸石等非均相系统。我们构建了一个基于显微镜的装置，以ar离子激光器作为激发光源，硅雪崩光电二极管作为探测器，相关板作为分析系统。我们确认我们的设置适用于溶液系统，但是，当我们应用于沸石系统时，会出现困难。由于沸石中的扩散太慢，我们无法测量出适当的相关性，因此我们不得不修改检测系统。因此，我们将单分子光谱应用于单个沸石晶体内的扩散问题。我们采用外延照明技术结合冷却CCD相机的图像采集。我们跟踪了沸石晶体上单分子荧光图像的时间过程，并分析了20-30个分子的荧光轨迹。由此，我们可以得到吸附物质的扩散系数。我们可以建立各种分子的沸石内部扩散系数的测量方法，但由于时间的限制，我们无法获得许多分子的数据。因此，我们对结果没有明确的看法，这将是我们未来的工作。少

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 … More 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