The structure of mesoporous silica obtained by pseudomorphic transformation of SBA-15 and SBA-16

Abstract

Mesoporous silica with bimodal pore size distributions was prepared by pseudomorphic transformation of SBA-15 and SBA-16 in the presence of hexadecyltrimethylammonium ions as a structure-directing agent. The characteristic particle morphology of the starting materials was retained after the transformation. Analysis of the products by gas sorption and small-angle X-ray scattering (SAXS) revealed hybrid pore structures, which featured – depending on the degree of transformation – variable contributions from the original and the newly introduced pore systems. In the case of SBA-15, it was found that a high degree of transformation leads to a seemingly complete conversion of the original pores with a diameter of 7.1 nm to pores with a diameter of 4.0 nm. The SAXS pattern of the product shows additional peaks that can be assigned to the original SBA-15 pore spacing. Similarly, a cubic phase could be observed in the samples prepared by pseudomorphic transformation of SBA-16, despite an almost complete conversion of the SBA-16 cavities. This leads to the conclusion that the pore structure of the starting material significantly affects the outcome of the pseudomorphic transformation, thus opening possibilities for the synthesis of new porous materials with complex pore systems.