Intercalation and exfoliation of layered materials to produce nanoplatelets and nanoscrolls

Layered compounds can be intercalated and exfoliated to create low dimensional materials with interesting properties. Sonication of the exfoliated sheets can induce a scrolling mechanism that leads to tubular structures. Bismuth telluride and its p- and n-type alloys are five atom thick layered materials that are currently the best thermoelectric materials at room temperature. Theoretical calculations predict that low dimensionality should enhance the thermoelectric figure-of-merit. This dissertation illustrates how intercalation of bismuth tellurides and selenides with lithium using liquid ammonia, followed by exfoliation in water, produces two-dimensional platelets. These platelets can restack to produce highly c-axis oriented materials. Nitric acid treatment of exfoliated bismuth selenide followed by sonication produces selenium nanorods. One-dimensional thermoelectric materials should exhibit an even higher thermoelectric figure-of-merit than two-dimensional platelets.; This synthetic route can be extended to other layered materials including transition metal dichalcogenides. Molybdenum diselenide was intercalated with lithium using liquid ammonia and exfoliated with water to produce platelets. Sonication of the MoSe2 platelets produces nanoscrolls.; Graphite is a one atom thick layered structure. It can be intercalated with potassium metal to form the first stage intercalation compound, KC 8. Upon the addition of aqueous solvents, the potassium metal is solvated and hydrogen gas evolution aids in separating the layers to form a dispersion of graphitic sheets. These graphite nanoplatelets offer promise as reinforcements for high-strength carbon-carbon composites if the aspect ratio is at least 500. High power sonication of the carbon nanoplatelets results in carbon nanoscrolls, a material analogous to multi-walled carbon nanotubes. As observed by transmission electron microscopy, the carbon nanoscrolls are comprised of sheets of graphite which are 40 +/- 15 layers thick, based on an interlayer spacing of 3.34 A. The carbon nanoscrolls occupy over six times the volume of the original graphite powder. They are stable in air to 450°C, about 200°C lower than pure graphite, consistent with nanoscale materials.