Mesoporous organosilicas containing disulfide moiety: Synthesis and generation of sulfonic acid functionality through chemical transformation in the pore wall

Mesoporous organosilicas with disulfide moiety bridged in the pore wall have been synthesized by co-condensation of bis[3-(triethoxysilyl)propyl]disulfide (BTPDS) and tetramethoxysilane (TMOS) in acetic acid/sodium acetate buffer solution (HAc–NaAc, pH 4.4), using nonionic surfactant P123 as the template. With the molar percent of BTPDS increasing, the mesostructure of the resultant material transforms from highly ordered 2-D hexagonal structure to cellular foam structure. The disulfide moiety could be transferred to sulfonic acid functionality by a simple post-oxidation method. The structural characterizations show that the mesostructure changes during the oxidation step especially for the materials with high content of disulfide moiety. In the esterification of aliphatic acid and ethanol, the oxidized materials show higher yield than the conventional heterogeneous solid acids such as zeolites and sulfonic acid resin. Comparisons of the structural properties and the catalytic results of the materials show that a large pore diameter and low surface hydrophilicity are required to obtain high catalytic activity.