Investigation of drying silica gel by fluorescence methods

Abstract

Results of steady-state and time-resolved fluorescence studies for a model drying process of selected silane gels are discussed in the paper. Gels which contained a fluorescence probe in the form of pyrene, at pH 4.1 and 5.9 were dried in the oxygen-free atmosphere, using a vacuum system. After subsequent stages of the drying process the spectra of fluorescence excitation and emission as well as fluorescence decay curves were recorded using the time-resolution techniques. On this basis micropolarity of the environment of pyrene encapsulated in gel pores and changes in the excimer intensity of a probe during the process were determined. A kinetic model of drying for the tested gels and the value of a drying rate constant were specified on the basis of the determination of the number of moles of water and ethanol evaporated from the gel. The analysis of lifetime distributions of particular pyrene forms led to the conclusions concerning changes in the fluorophore environment during the gel–xerogel transition connected with the evaporation of solvents from gel pores and next with a decrease of the pore sizes.