Quantitative description of silanol cover influence on the 3-aminopropyl silica gel acid-base properties

Abstract

In the present study we reviewed the prediction of the graft on silica 1-aminopropan protolytic properties. The investigation purpose is the searching of correlations between the starting silica silanol cover composition and concentration and the graft aminopropyl protolytic properties. This material was chosen as a model because of synthesis simplicity, a well-established structure, the possibility of a clean surface obtaining.
We used a set of well-known experimental techniques, such as thermogravimetric analysis, nitrogen sorption-desorption, potentiometric titration. To differentiate the active surface sites of the modified silica we used a simple and well-proven method of pK-spectroscopy. The algorithm of method, based on the overdetermined system of equations solution, is implemented in a package Mathematica 10. DTG-curves decomposed into Gaussian using its own algorithm, implemented in VBA.
View of the samples pK-spectra is consistent with the known concept of graft groups insular topography. It was found that the laws of insular graft topography formation depends on the ratio of terminal and related hydrogen-bonded silanol groups number on silica surface. Grafted amine protolytic properties may be described in the using the method of the full content, providing a surface layer as a solution phase The silanol groups mole fraction inside and outside of the islets in the surface layer affects the graft aminopropyl strength as a base. The surface layer of silica as a mesoporous sorbent is limited to a monolayer of the solvent. We found empirical equations to link the starting silica silanol groups concentration and the surface area with corrected coefficients of graft aminopropyl dissociation equilibrium inside and outside of the islets.
For preliminary calculation needs to know the surface area and the silanol groups (including terminal) concentration on the starting silica surface.