Kellie Morgan

From Grey Lab Page

My research focuses on minerals commonly encountered as constituents of soils and as mineral coatings. There is great interest in understanding the structure and surface chemistry of these compounds due to their propensity for sorbing cations, particularly those for which anthropogenic sources of these cations necessitate environmental remediation.

My work thus far has been with a synthetic analogue of a naturally occurring manganese oxide known as birnessite. This mineral was chosen due to results of previous studies indicating the expansive interlayer surface area of birnessite was the source of its superior sorption capacity when compared to other natural and synthetic manganese oxides and iron oxides. The synthetic birnessite structure consists of sheets of mixed valency (Mn⁴⁺/Mn³⁺) manganese octahedra sandwiching interlayer sodium cations and water. While the sodium can be exchanged with other cations of interest, this sodium form is a useful model to begin understanding how cations are bound within the layers via solid state MAS NMR. I am utilizing ²H and ²³Na soild state MAS NMR to shed some light on the interactions of the water and cations in these interlayers.

There are very few studies involving ²³Na MAS NMR in paramagnetic systems, and no systematic studies from which to draw any meaningful conclusions from the ²³Na NMR spectra of birnessite. As a result, a study of a variety model sodium manganese oxides was done. These model compounds were chosen with a variety of Mn³⁺/Mn⁴⁺ ratios in order to help draw correlations between Mn³⁺/Mn⁴⁺ ratios and observed shifts in the NMR spectra. Synthetic analogues and natural samples of other manganese oxides (cryptomelane and todorokite) are also being investigated by ²³Na NMR.