Photochemical reaction dynamics of molecules adsorbed into zeolites as revealed by time-resolved spectroscopic techniques.

时间分辨光谱技术揭示了吸附到沸石中的分子的光化学反应动力学。

基本信息

批准号：
10640502
负责人：
HASHIMOTO Shuichi
金额：
$ 2.18万
依托单位：
Gunma College of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

1. Flurescence Spectroscopic Investigation of the Interaction of aromatics with ZeolitesThe fluorescence spectroscopic results revealed a remarkable behavior of anthracene adsorbed into zeolites depending on the loading level and the state of hydration of the zeolites as well as the chemical composition of the zeolites. Anthracene molecules are suggested to be complexed with Na^+ ions in the zeolite frameworks of dehydrated NaX and NaY, and at high loading levels. they form dimers under the influence of Na^+ ion. Additionally, our fluorescence spectroscopic investigation revealed the formation of anthracene crystals at relatively high loadings in the presence of a large amount of water and other solvent molecules. Thus we found that the dynamic behavior of the guest aromatic molecules within the zeolite supercages are critically dependent upon the balance of interactions among the zeolite frameworks, guest species and coadsorbates. especially coadsorbed water.2. Effect of Coadsorbed So … More lventsWe found that at a sufficiently low loading level of anthracene the decay rate is dependent on the amount of water, methanol and pyridine but scarcely affected by n-hexane. The enhanced triplet decay rate was found to be ascribable to a self-quenching event, i.e. the triplet quenching by ground-state anthracene. Thus a picture was given that anthracene molecules are highly mobile when the zeolite cavities are loaded with the coadsorbed solvents in quantities sufficient to shield the cationic sites at which anthracene is supposed to be adsorbed. The high mobility of the guest species is presumably caused by the liberation of adsorption interaction of anthracene with the zeolite walls by the action of small quantities of the solvent molecules with strong affinity towards the zeolite frameworks. On the contrary, large quantities of the coadsorbed solvens are expected to interfere with the movement of anthracene in the cage networks because they are so crowded enough to fill the interconnecting windows between cages as well as a large portion of the cage volume.3. Molecular Diffusivity in ZeolitesWe present a new experimental technique based on photochemistry for acquiring diffusion constants of aromatic species adsorbed in zeolites. The technique basically observes the quenching kinetics of excited probes produced by the pulsed-laser irradiation. The probe molecules are expected either to deactivate or to undergo quenching by another molecule (a quencher) migrating within the cage networks. The quenching kinetics were analyzed by applying the CTRW (continuous time random walk) model. In addition to the estimation of the diffusion coefficient for anthracene and azulene in NaY, the present study showed the indication of the long-range reaction between molecules residing in the neighboring cages, reflecting open structure of the cage network. Less

1.芳烃与沸石相互作用的荧光光谱研究荧光光谱结果揭示了蒽吸附到沸石中的显着行为，这取决于沸石的负载水平和水合状态以及蒽分子的化学组成。建议在脱水 NaX 和 NaY 的沸石骨架中与 Na^+ 离子络合，并且在高负载水平下它们。此外，我们的荧光光谱研究揭示了在大量水和其他溶剂分子存在下，蒽晶体的形成。沸石超笼内的客体芳香分子很大程度上取决于沸石骨架、客体物种和共吸附物之间的相互作用的平衡，特别是共吸附水的影响。2。我们发现，在蒽的负载水平足够低的情况下，衰变速率取决于水、甲醇和吡啶的量，但几乎不受正己烷的影响，发现增强的三重态衰变速率可归因于自猝灭事件，即基态蒽的三线态猝灭因此给出了当沸石空腔装载有蒽分子时具有高度流动性的图。共吸附溶剂的量足以屏蔽蒽被吸附的阳离子位点，客体物质的高迁移率可能是由于少量溶剂的作用而释放了蒽与沸石壁的吸附相互作用。相反，大量的共吸附溶剂预计会干扰笼网络中的蒽的运动，因为它们非常拥挤，无法容纳。填充笼之间的互连窗口以及大部分笼体积。3.沸石中的分子扩散性我们提出了一种基于光化学的新实验技术，用于获取吸附在沸石中的芳香族物质的扩散常数。脉冲激光照射产生的激发探针分子预计会失活或被另一个分子（a）猝灭。除了估算 NaY 中蒽和甘菊的扩散系数外，还通过应用 CTRW（连续时间随机游走）模型分析了猝灭动力学。相邻笼中分子之间的范围反应，反映了笼网络的开放结构。