Effect of precursors on lithium containing silicate gels studied by 7Li nuclear magnetic resonance

Abstract

Lithium containing silica gels were prepared by hydrolysis of tetraethylorthosilicate (TEOS) with a methanol-water-LiNO 3 or LiOH solution and by infiltration of silica gel with LiOH or LiNO 3 solution. Gels prepared in this way, dried and heat treated between 200 and 850°C were studied by solid state 7Li static and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. There are dramatic differences in the 7Li NMR spectra of the various gels. The lineshape of the NMR spectra for gels prepared from LiOH (both via hydrolysis of TEOS and infiltration of prepared silica gel) is similar to that of crystalline Li 2SiO 3 where the lithium ions are associated with the silica network. The spectra do not change significantly with increasing temperature up to 850°C. For gels prepared from LiNO 3, the 7Li NMR spectra indicate the presence of two different Li species; one of the Li species is attributed to hydrated lithium ions trapped in the pores of the gels, the other Li species is due to crystalline LiNO 3. When the LiNO 3 gels are heat treated above 650°C, the lineshape of the NMR spectra becomes similar to that of Li 2SiO 3.