Characterization of the porous structure of SBA-15

Abstract

SBA-15 ordered mesoporous silicas were synthesized using the method reported by Zhao et al, The structures of these materials were characterized using powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nitrogen adsorption. The samples were found to exhibit structural properties similar to those reported earlier. Our study confirmed that the size of primary mesopores of SBA-15 can be tailored by the choice of synthesis temperature and that SBA-15 exhibits a significant amount of disordered micropores and small mesopores, The volume and size of these complementary pores were found to be dependent to some extent on the synthesis/aging temperature. It was shown that the washing of as-synthesized SBA-15 in water or ethanol was accompanied by an appreciable structural shrinkage and led to the removal of a significant part of the polymeric template. Therefore, washing needs to be avoided if one wants to isolate SBA-15 without appreciable loss of the template. It was confirmed that water-washed SBA-15 samples have fully accessible primary mesopores. Ethanol-washed samples also were found to exhibit accessible porosity. Despite an appreciable content of the template in the water- and ethanol-washed samples, their pore sizes were usually larger than those of the calcined materials. The observed structural properties of SBA-15 and their dependence on the synthesis temperature and washing were attributed to the changes in the degree of penetration of the poly(ethylene oxide) chains of the triblock copolymer template within the siliceous walls of SBA-15.