Microspectroscopic Studies on Ionic Dye Diffusion in Single Ion-Exchange Beads.

控制离子交换过程的一个重要因素是离子在离子交换树脂中的扩散（粒子扩散）。由于缺乏实验方法，对粒子扩散过程的直接观察是非常困难的。空间分辨微光谱技术的最新进展，如激光捕获微光谱技术，为研究微粒子中发生的各种现象提供了强有力的手段。在这里，我们报告了使用激光捕获微光谱和共聚焦荧光微光谱技术直接观察粒子扩散过程。采用两种不同的方法测定了离子染料在单离子交换树脂中的浓度分布。一种是共聚焦荧光微光谱学，它提供了沿3d轴的荧光强度分布的信息。测定了罗丹明B （Rhodamine B, RhB）沿粒径方向的荧光强度谱，与树脂中染料的浓度谱相对应。根据RhB在树脂中的扩散曲线变化，确定了RhB在树脂中的扩散系数。还采用了能量传递淬火方法。最初，RhB被预均匀吸附在离子交换树脂上。然后将孔雀石绿作为能量受体吸附在树脂上。由于MG从树脂表面扩散到内部，RhB荧光只在MG扩散层中淬灭。淬火效率对应于MG在树脂中扩散层与非扩散层的体积比，因此该值给出了MG在树脂中的渗透深度。根据MG扩散过程中RhB荧光强度的变化或渗透深度的变化，我们直接确定了MG在离子交换树脂中的扩散系数。基于单粒子的光谱技术为离子交换的动态过程提供了有用的信息，可以进一步应用于研究单个微粒子的光化学过程。少

One of the important factors governing ion-exchange processes is diffusion of an ion in an ion-exchange resin (particle diffusion). Because of a lack of experimental methods, a direct observation of the particle diffusion process is very difficult. Recent progresses in spatially-resolved microspectroscopic techniques such as laser trapping-micro-spectroscopy have provided a powerful means to study various phenomena occurring in microparticles. Here we report direct observation of the particle diffusion process by using laser trapping-microspectroscopy and confocal fluorescence micro-spectroscopy techniques.Two different methods were applied to determine concentration profiles of ionic dyes in single ion-exchange resins. One was confocal fluorescence microspectroscopy, which provided an information on fluorescence intensity profiles along 3D-axs. The fluorescence intensity profile of Rhodamine B (RhB) along the particle diameter, corresponding to the concentration profile of the dye in … More the resin, was measured. From the change in the profile during RhB diffusion, we determined the diffusion coefficient of RhB in the resin. An energy transfer quenching method was also applied. Initially, RhB was pre-adsorbed homogeneously on the ion-exchange resin. Then, Malachite green (MG) as an energy acceptor was adsorbed on the resin. Since MG diffuses from the resin surface to the inside, the RhB fluorescence is quenched only in a MG-diffused layr. The quenching efficiency corresponds to the volume ratio of the MG-diffused layr to the non-diffused layr in the resin, so that the value gives the penetration depth of MG in the resin. On the basis of the change in the fluorescence intensity of RhB during MG diffusion or that in the penetration depth, we determined directly the diffusion coefficient of MG in the ion-exchange resin.The single-particles based spectroscopic techniques provide a useful information on the dynamic processes of the ion-exchange and can e further applied to study photochemical processes in single microparticles. Less