²⁹Si and ¹²⁹Xe NMR of Mn²⁺ doped silica xerogels

Paramagnetic Mn²⁺ ions were incorporated in silica gel during the preparation of the sol. Doped silica xerogels were obtained by heat treatment at different temperatures and studied by ²⁹Si and ¹²⁹Xe nuclear magnetic resonance (NMR) experiments. Comparison between ²⁹Si NMR magic angle spinning (MAS) spectra of doped and undoped xerogels showed that there is a significant effect of the paramagnetic probe on Q², Q³ and Q⁴ peaks. Reduction of the ²⁹Si-T₁ relaxation time in the presence of the Mn²⁺ probe was observed. ¹²⁹Xe NMR spectra were recorded on the xerogels at variable Xe pressures. Results were consistent with ²⁹Si NMR data and confirmed the localization of the paramagnetic probe in surface sites as shown by electron paramagnetic resonance (EPR) of Mn²⁺.