Indirect quantitative IR assessment of maximal monomolecular deposition of 3-aminopropyltrimethoxysilane on silica gel surface

Abstract

Quantification of the amount of maximum loaded 3-aminopropyltrimethoxysylil (APS) on a thermally pretreated silica gel (600 ºC) was performed using IR spectroscopy. A possibility to find the maximum load through a construction of a Langmuir isotherm was not possible due to the irreversibility of the chemisorption reaction. The method used in this work was based on the analysis of the toluene solution on the quantity of the non-reacted APTMS after the saturation of the silica gel surface with APS. The process of chemisorption was monitored via the increasing band intensity of CH₂ and NH­₂ modes of the adsorbent and decreasing band intensity characteristic for the free isolated OH groups of silica gel using DRIFT spectroscopy. The obtained results on maximum adsorption are in line with the previously obtained, using carbon elemental analysis and a direct DRIFT method.