Compositional Effects and Hydrothermal Reorganization of Mesoporous Silicates Synthesized in Surfactant Solutions

Abstract

Surfactant aggregates play a key role in aqueous condensation polymerization reactions of silicate species to form mesoporous siliceous solids. The effects of surfactant (cetyltrimethylammonium chloride, CTAC) concentration and silicate/surfactant ratio on the synthesis of mesoporous silicates were studied. The subsequent hydrothermal reorganization of the surfactant−silicate mesophases during drying was also investigated. At low CTAC concentration (<10 wt %) and low Si/CTAC molar ratio (<2.6), the CTAC micellar aggregates and bound silicate counterions have sufficient mobility to form hexagonal arrangements through the intermicellar silicate condensation. At higher CTAC concentration and higher Si/CTAC ratio, the hexagonal arrangement is considerably hindered due to the increased contour length of the micelles and the reduced intermicellar distance, resulting in cross-linking of micelles that disrupts formation of hexagonal pore structures. During drying, hydrothermal reorganizations of lamellar silicate...