Reimpregnation of Disordered Mesopores by Ionic Liquids

The reimpregnation, i.e., replacement of the soft-templating ionic liquid (IL, BMIM-TFSI) that forms the porosity during the synthesis of disordered mesoporous silica-based (ionosilica) materials, has been studied by an original combination of small-angle X-ray scattering (SAXS), thermogravimetric analysis, and nitrogen sorption. The architecture of the mesoporous scaffold was identified by SAXS after IL extraction using ethanol. Subsequently, the same ionic liquid, or IL-ethanol mixtures, were reintroduced into the ionosilica after a vacuum treatment, allowing controlled IL filling up to total reimpregnation of the mesopores. By confronting SAXS, where the intensity is a direct function of the degree of filling, with BET giving access to filling-dependent mesopore surface areas, a striking convergence of results shows that macroscopic and microscopic techniques target the same physical characteristics. In particular, the mesopores are shown to fill in a controlled way, one after the other, up to high degrees of filling.