The interaction of Mn2+ with porous silica xerogels and the hydration-dehydration processes in the xerogels

The electron paramagnetic resonance (EPR) spectra of Mn2+ have been used to investigate the structure of silica xerogels prepared from tetraethylorthosilicate. The measurements were made at similar to 9.8 GHz. The probe was introduced during preparation of a sol and the EPR spectra of subsequent xerogels were measured following calcination at various temperatures (120 degrees C less than or equal to T-T less than or equal to 1000 degrees C). The spectra after adsorption of NH3 or H2O were measured. Adsorption of NH3 showed a quasi non-reversible effect whereas there was a modification of the spectra which depended on the water vapor pressure. Adsorption and desorption of water were ascribed to surface effects and simulation of the spectra showed that two different sites are involved. An EPR method of determination of pore diameter is proposed. (C) 1997 Elsevier Science B.V.