The effect of the hydrophobicity of aromatic swelling agents on pore size and shape of mesoporous silicas

Benzene and four trisubstituted aromatic compounds were used as swelling agents for mixed hexadecyl- and dodecyltrimethylammonium micelles. These micelles served as templates for the synthesis of mesoporous M41S materials. By varying the amount and the nature of the aromatic swelling agent, M41S materials with any pore diameter between 3 and 11 nm could be synthesized. All materials exhibited specific surface areas around 1000 m2/g and large specific pore volumes as it is characteristic for the M41S family. Phases with layered, rod-like, and globular building units were obtained by varying the nature and/or the amount of aromatic swelling agent. A detailed analysis of the trends showed that the hydrophobicity of the swelling agents determines the size and shape of the pores: with the more hydrophobic swelling agents smaller pores with higher curvature are obtained.