Adaptation of silanol groups in mesoporous silica to be silylated and their evaluation by ftir

Abstract

Procedures reported in the literature to modify the silanol content of mesoporous silica are applied to a material prepared with the triblock copolymer Pluronic F127 in acidic medium under quiescent conditions, in order to adapt it for silylation reaction. These include: calcination at relatively high temperature and rehydroxylation in presence of NH4OH. The nature and content of silanol groups in these materials is measured by following the pyridine interaction with them through the infrared specific absorptions at 1595 and 1446 cm−1 assigned to pyridine interacting with hydrogen-bonded and free silanol groups respectively. In order to render these SBA-16-type mesoporous silica hydrophobic, a silylation reaction is effected in which its efficiency depends mainly on the nature and concentration of silanol groups. To follow the degree of silylation a method based on infrared transmission spectroscopy (FTIR) is designed in this work. With this method, unlike solid state 29Si-NMR, it is possible to measure the relative concentrations of the organic groups bonded to silica when two silylating reagents are used, and to qualify in an indirect way how the weak silanol groups change during the different post synthesis treatments of a mesoporous silica.