Diffusion of protons in silica hydrogel

The effect of preparation pH of silica hydrogel on the effective diffusion coefficient of protons in silica hydrogel (D_e, m²/s), on surface area of silica gel (S, m²/s) and on particle size of silica gel (D_p, mm) was studied. Silica hydrosols were obtained by adding water glass to sulfuric acid. The effective diffusion coefficient of proton in silica hydrogel was determined by the method of diffusion from silica hydrogel plane sheet to a stirred solution of a limited volume. A numerical solution was obtained for the diffusion equation using the Regula Falsi method. Regression analyses of experimental data were conducted.Diffusion of protons in silica hydrogel is a complicated process due to a decelerating effect of the porous structure of silica hydrogel and to the accelerating effects of slow ions such as Na⁺ and surface diffusion. The effective diffusion coefficient increased with surface area of silica gel, indicating the diffusion of protons on the surface of the silica particles.