Application of temperature-programmed oxidation, multinuclear MAS NMR and DRIFT spectroscopy to the surface characterization of modified silica nanoparticles

Abstract

Grafting of organosilane-functionalized substances onto the surface of nano-sized silica particles was studied by temperature-programmed oxidation (TPO), solid-state 13 C and 29 Si MAS NMR and DRIFT spectroscopy. By using 29 Si MAS NMR quantitative data on the proportions of the various grafted structures, grafting yields and the reactivity of the geminal and free silanols towards the coupling agent were obtained. For 3-(trimethoxysilyl)propylmethacrylate as coupling agent and maleic acid as catalyst, the TPO weight loss of about 24 wt.% revealed a hypothetical coverage of about 5.5 graft/nm 2. Compared to the surface concentration of 2-3-OH groups per nm 2, this value can be only explained by grafting precondensed silane molecules onto nano-sized silica, assuming a core shell principle.