Donnan Electric Potential Dependence of Intraparticle Diffusion of Malachite Green in Single Cation Exchange Resin Particles: A Laser Trapping-Microspectroscopy Study

Abstract

A laser trapping-microspectroscopy technique combined with excitation energy transfer from a fluorescent cationic dye (Rhodamine B, RB +) to a non-fluorescent cationic dye (Malachite Green, MG +) was employed to study pH effects on the diffusion coefficients of MG + (D(MG +)) in single cation-exchange resin microparticles with the diameters of 16 μm. When RB +-pre-adsorbed resin particles were soaked in an aqueous MG + solution, the RB + fluorescence was quenched gradually with the soaking time. The time course of the quenching efficiency of RB + by MG + was then used to evaluate the D(MG +) value in the particle. The D(MG +) value increased from 1.1 × 10-11 to 4.3 × 10-11 cm 2 ·s-1 on going the solution pH value from 9 to 4. The results were explained reasonably by a Donnan electric potential model.