Speciation of Silanol Groups in Precipitated Silica Nanoparticles by ¹H MAS NMR Spectroscopy

Speciation of the various proton species present in precipitated silica samples by 1 H high-spinning frequency magic-angle spinning (MAS) NMR (25 kHz) is achieved. External standards are used for the calibration of the absolute amount of protons, the relevance of the proton spin counting being checked by comparison with the data deduced from classical thermogravimetric (TG) and 29 Si MAS NMR experiments. The method also allows to follow postsynthesis modifications of silica, corresponding for instance to fluorination or deuteration treatments. In particular, a 1 H resonance occurring at 1.1 ppm/TMS and corresponding to a constant proton amount whatever the applied treatment is tentatively assigned for the first time to inaccessible isolated silanol groups.