DISSERTATION DEFENSE
Andrey A. Shults, Chemistry
*under the direction of Janet Macdonald
“Exploring mechanisms behind phase formations of metal chalcogenide nanoparticles”
03.06.25 | 1:00PM | 5211 Stevenson Center | Zoom
Our understanding of nanoparticle phase control is currently limited by our knowledge of the mechanisms responsible. How molecular precursors interact with each other, the solvent, and the ligand, and how they decompose thermally can all have an effect on the resulting phase of the product. Through the use of various analytical techniques like nuclear magnetic resonance (NMR), in-situ gas phase Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM), we shed light on the interactions that can occur between ubiquitous reagents in nanosynthesis. In the first project, we demonstrate that thiourea can interact with oleic acid during the synthesis of metal sulfide nanoparticles to produce ammonium thiocyanate, a more reluctant sulfur source, leading to the formation of metastable and sulfur poor nanoparticles, a trend seen across four different metals (Cu2+, Ni2+, Co2+, and Fe3+). In the second project, we use selenourea for the synthesis of iron selenides, and, for the first time, show that chalcogen allotropes can act as phase-determining intermediates in the synthesis of metal chalcogenides. In the presence of oleylamine, selenourea can decompose into red selenium, leading to the formation of Fe7Se8. In the presence of oleic acid, grey selenium forms instead and leads to the formation of FeSe2. In the third project, we make progress towards the synthesis of colloidal chromium telluride nanoparticles. With the use of the fast reacting didodecyl ditelluride, we show that commonly used chromium (III) halide precursors yield only unreactive Te(0). We attempt to overcome this synthetic challenge with the synthesis of a more reactive chromium (II) iodide. Finally, in the fourth project, we use the steric effects of N-heterocyclic derived selenoureas to influence not only the phase of iron selenide nanoparticles but also their morphology. We find that as the sterics of the N-heterocyclic derived selenourea increase, the nanoparticle size decreases, and the shape becomes more irregular. With these reports, we hope to deconvolute the mechanisms affecting phase control and to add onto our synthetic tool-box for repeatable and reliable synthesis of nanoparticles.