Studies on sorption properties of ordered mesoporous silica MCM- 41 and SBA-15 toward non-polar α-tocopherol. Part 1. Kinetics of sorption

Abstract The sorption kinetics of α-tocopherol (TP) was studied on nanostructured silica materials such as MCM-41 and SBA-15. A significant influence of the pore size on the type of kinetics was noted. In case of MCM-41 (pore size 2.7-3.0 nm), the pseudo-second-order model has the best correlation with the kinetic data. The kinetic coefficients are 1-1.5 orders of magnitude higher than those for SBA-15 (pore size 6.0-6.5 nm). Consequently, the sorption equilibrium is established much faster. For the description of the adsorption behavior of TP on SBA-15 intraparticle diffusion models were applied. In comparison with the Boyd and Weber-Morrison model, the Vermeulen approach describes the best fit with the experimental data. The filling of the large mesopores of SBA-15 results in a higher adsorption capacity of TP compared with MCM-41. It is noted, that increase of temperature in the range 273-318 K leads to decrease of the sorption capacity for both silicas. Raise of the temperature during sorption on MCM-41 results in the increase of the contribution of diffusion inside mesopores in comparison with surface diffusion.