Date of Award
Doctor of Philosophy
Colloidal nanocrystals with their fascinating properties have found many opportunities in a diverse range of applications including optoelectronic and electronic devices, catalysis, and biomedical applications. Performance of nanomaterials in these applications are directly related to the well-defined properties, phase, composition, size, and morphology, of the nanocrystals. Strategies exist to synthesize colloidal nanocrystals with well-defined properties tailored to desired applications by optimization of several parameters such as concentration and nature of precursors and surfactants, temperature, additives, and multi-step procedures, which can be time consuming and expensive. Using a conceptually simple ‘molecular programming’ bottom up approach, this thesis describes an efficient approach for the phase and composition controlled synthesis of pnictide nanomaterials and group IV Ge-Sn heterostructures. Phase and composition control is achieved through fine-tuning chemical reactivity of group 14 and group 15 molecular precursors, while keeping other reaction conditions constant.
Using a family of organophosphites (P(OR)3) with tunable reactivities as phosphorus precursors, we demonstrated that different organophosphite precursors selectively yield nickel phosphides (Ni12P5 and Ni2P) or metallic nickel and that these phases evolve over the time through separate mechanistic pathways. As a direct result of our study, we built a reactivity scale for organophosphite precursors presenting the ease of these precursors react with nickel precursors to form nickel phosphide nanocrystals. We believe that the organophosphite family is a great addition to the synthetic tool box of pnictides.
Next, fostering our efforts to a controllable synthesis of more complex architectures, we synthesized Ge-Sn heterostructures with different compositions using Ge-Sn molecular precursors (R3GeSnR’3). Sn/Ge core/shell structures with varied shell thickness were observed by varying the Ge-Sn bond strengths of precursors that is tunable through the nature of substituents. This thesis also reports the synthesis of metastable -Ge in ambient pressure conditions, which otherwise existed and reported in high pressure conditions. These group 14 molecular precursors open up new directions for heterostructure synthesis with unique morphologies that offer interesting properties.
As an attempt to discover how different properties of nanocrystals affect potential applications, we explored how different morphologies of nickel phosphide nanocrystals would affect the catalytic properties of the alkyne hydrogenation reaction. Compared to the bimodal (hollow and solid) distribution of Ni2P nanocatalysts, hollow Ni2P nanoparticles are more catalytically active towards the phenylacetylene hydrogenation. These hollow Ni2P catalysts seem to be robust with the ability of recycled up to eight times without losing its catalytic activity while preserving their structural integrity.
Himashi Purnima Andaraarachchi
Andaraarachchi, Himashi Purnima, "Exploring the chemical reactivity of group 14 and group 15 molecular precursors" (2018). Graduate Theses and Dissertations. 17139.