Synthesis of SBA-15 type mesoporous organosilicas with diethylenebenzene in the framework and post-synthetic framework modification

Abstract

The SBA-15 type periodic mesoporous organosilicas (PMOs) containing different fraction of 1,4-diethylenebenzene groups in the framework were synthesized by co-condensation of 1,4-bis(trimethoxysilylethyl)benzene with tetramethoxysilane under acidic conditions using triblock copolymer Pluronic P123 as structural directing agent. The results of X-ray diffraction pattern (XRD), nitrogen sorption isotherm, and transmission electron microscopy (TEM) show that all materials have well-ordered mesoporous structure with uniform pore size distributions. The acidic sites were incorporated in the mesoporous framework by post-synthetic framework modification of 1,4-diethylenebenzene by sulfonation. The framework composition of the mesoporous organosilicas before and after modification was fully characterized by UV Raman spectroscopy, and 13C CP-MAS and 29Si MAS NMR. From elemental analysis, it can be estimated that about 40% of the organic group within the mesoporous framework is available for further chemical reaction. The PMOs with aryl sulfonaic acid groups in the framework are efficient solid acids for the esterification of ethanol with aliphatic acid. With the alkyl chain of the aliphatic acid increasing, the activity of the material is enhanced by more amounts of 1,4-diethylenebenzene incorporated in the mesoporous framework. The post-synthetic modification is a facile approach for the generation of new functional groups in the mesoporous framewrok of PMOs.