Characterisation of the grafting of (3-aminoethyl)aminopropyltrimethoxy silane on precipitated silica

Abstract

In this study, we have investigated the reaction between (3-aminoethyl)amino-propyltrimethoxysilane (AEPTS) and a precipitated silica in organic solvents. Solid-state ²⁹Si NMR and Karl Fischer titration have been used to produce useful information on the grafted silica samples. AEPTS was chosen in order to characterise the distribution of alkoxysilanes at the silica surface. Indeed, this alkoxysilane has an ethylene diamine function that can form coloured and paramagnetic complexes with copper in 1 ∶ 1 and 2 ∶ 1 molar ratios ([Cu(AEP-Si)]²⁺ and [Cu(AEP-Si)₂]²⁺). These species have been further identified and quantified by UV-visible and ESR spectroscopies, and the proximity of the alkoxysilanes at the surface was thus traced back through the detection of the 2 ∶ 1 complex [Cu(AEP-Si)₂]²⁺.