Applications of two-dimensional solid state nuclear magnetic resonance in silicates

Nuclear magnetic resonance (NMR) is a powerful technique and has been routinely applied in many fields. In this study, we have used high resolution two-dimensional (2D) solid state NMR techniques to study the dynamic process of Li diffusion, the kinetic process of oxygen isotope exchange, and the structural characterization of hydrous and anhydrous silicate glasses at atomic level.; In the Li diffusion study, we first established the correlation between the {dollar}sp6{dollar}Li chemical shifts and the lithium coordination environments in lithium containing silicates. Then, we assigned the {dollar}sp6{dollar}Li magic angle spinning (MAS) spectrum and applied 1D, 2D variable temperature exchange NMR to observe Li{dollar}sp+{dollar} diffusion in lithium orthosilicate. For the first time, our result revealed a detailed picture of the hopping rates of Li{dollar}sp+{dollar} ions among structurally distinct sites and helped to define the diffusion pathway. We have shown that Li{dollar}sp+{dollar} ions hopping rates and activation energies depend on site geometry. NMR measurements on Li ionic hopping frequencies was used to accurately predict the bulk conductivity.; In the site-specific oxygen isotope exchange study, we first developed a method to obtain quantitative {dollar}sp{lcub}17{rcub}{dollar}O NMR spectra. Then, we applied the method to stilbite, a natural zeolite. We have shown for the first time that framework oxygens in Al-O-Si sites react faster with oxygens in the channel water than oxygens in Si-O-Si sites. Such an observation has partially proved the quantum ab initio calculation on water adsorption onto silicates. Our measured kinetics results agreed well with bulk isotopic measurements.; Water dissolution mechanism in silicates glasses, especially aluminosilicate glasses, has been a long-standing controversy. We have used the {dollar}sp{lcub}17{rcub}{dollar}O spectra for hydrous and anhydrous sodium tetrasilicate glasses and albite glasses to study the structural role of hydrogen-containing species. For the first time, we have observed the oxygen peak for SiOH in hydrous sodium tetrasilicate glass. Such a component might also be present in hydrous albite glasses. We also detected the oxygen signal for molecular H{dollar}sb2{dollar}O in all the hydrous silicate and aluminosilicate glasses. Our results tend to support one of the water dissolution models.