Inorganic Salt Assisted Self-Assembly of Periodic Mesoporous Organosilicas with Various Structures under Alkaline Conditions

Ethylene-bridged PMOs have been prepared with the assistance of inorganic salts using CTACl as surfactant under alkaline conditions. The effects of various sodium salts on the formation of ethylene-bridged PMOs was thoroughly investigated. It was found that the self-assembly of PMOs is not profoundly affected by the concentration of salts, but to be controlled predominantly by the types of anions that contained in the salts. The addition of NaCl during the synthesis can lead to PMOs with mixed mesophases (cubic Pm3n and 2-D hexagonal P6mm), while a pure 2-D hexagonal and lamellar mesophase can be obtained by adding NaBr and NaI respectively. The effects of inorganic salts can be roughly predicted through the binding strengths of counterions to the surface of surfactant micelles. Additionally, the pore wall thickness and degree of cross-linking of PMOs will be increased with the addition of inorganic salts, thus leading to mesoporous materials with improved hydrothermal stability. The study contributes fundamental understanding of the formation of PMOs with the assistance of inorganic salts, providing a facile method to prepare ordered mesoporous materials with more diversified structures and morphologies.