Structure modulation of periodic mesoporous organosilicas with organic salts

The design of the hierarchical structure and geometry of nanomaterials at the molecular and macroscopic level are crucial to determine their properties and applications. In this work, we describe a facile and effective method to control over the mesostructure and morphology of ethane-bridged PMOs with the assistance of various organic salts under basic conditions. It is demonstrated that the specific interaction between the surfactant and organic salts is responsible for the shape of surfactant micelles and the formation of ethane-bridged PMOs. Specifically, the structure and the hydrophobicity of the organic salts play a major role. The addition of organic salts with more hydrophobic organic moieties, such as sodium salicylate, sodium succinate and sodium benzoate, will increase the surfactant packing parameter more effectively, leading to the mesophase change from cubic Pm3n to 2-D hexagonal P6mm structure, whereas the addition of organic salts with lower hydrophobicity and larger polar head, like sodium oxalate, will result in the mesophase transformation from cubic Pm3n to 3-D hexagonal P6₃/mmc structure. Moreover, the addition of organic salts will not only affect the micellar formation, but also influence the charge matching at the surfactant/silicate interface as well as the condensation and aggregation kinetics of silica species. The addition of large amount of any organic salts will eventually lead to the formation of PMOs with disordered mesoporous structure.