Analysis of Distribution and Intraparticle Diffusion of a Fluorescent Dye in Mesoporous Silica Gel by Confocal...

A micrometer-sized spherical silica gel microparticle (pore diameter, ∼7 nm) was injected into an aqueous rhodamine 6G solution using microcapillary manipulation-injection technique, and the dye distribution in the single microparticle was measured as the fluorescence depth profile by confocal fluorescence microspectroscopy. The fluorescence depth profile was simulated by the convolution and deconvolution methods to correct the contribution of the spatial resolution of the experimental system. The dye homogeneously or heterogeneously distributed in the microparticle at the adsorption equilibrium, dependent on the type of silica gel. The intraparticle diffusion coefficient of the dye distributed homogeneously in the silica gel was analyzed by the simulations of the time dependence of the fluorescence depth profile based on the external and intraparticle diffusion model. The results indicated that the intraparticle diffusion of the dye in the silica gel is governed by the pore diffusion.