Assembly of mesoporous silica molecular sieves based on nonionic ethoxylated sorbitan esters as structure directors

A new family of mesoporous silica molecular sieves with micelle-templated structures (MTS) has been synthesized using nonionic ethoxylated sorbitan esters, namely, Tween-20, -40, -60, or -80, as structure-directing agents. These MTS materials possess a wormhole-like framework typical of MSU-X mesostructures, with intraparticle (framework) pore sizes in the 3.0-4.0 nm range. Unlike previously reported MSU-X silicas, these new derivatives form monodispersed small particles in the 30-60 nm range, depending on the nature of the surfactant, and exhibit substantial interparticle (textural) porosity in the 9-20 nm range. The sorbitan surfactants are nontoxic, biodegradable, and biocompatible when solvent free, making them attractive structure directors for the synthesis of mesoporous materials. The combination of complementary framework and textural pore distributions should be advantageous in the use of the mesostructures as heterogeneous catalysts, particularly for reactions that are normally diffusion limited.