TOWARDS RATIONAL SYNTHETIC DESIGN OF TERNARY CHALCOGENIDE NANOPARTICLES THROUGH MECHANISTIC STUDIES OF COPPER TETRASELENOPHOSPHATE

Abstract

The transition to sustainable energy technologies demands the rational design and scalable synthesis of efficient, Earth-abundant materials. Chalcogenide-based ternary nanoparticles (TNPs), such as copper tetraselenophosphate (Cu3PSe4) represent compelling targets for next-generation photovoltaics and energy storage due to their highly tunable electronic structures and high theoretical efficiencies. However, realizing the potential of these multinary systems is fundamentally bottlenecked by classical empirical, trial-and-error synthetic protocols. These traditional approaches typically rely on the dissolution of elemental selenium (Se0) in complex alkylamine or phosphine mixtures, creating a poorly defined "black box" of polyselenide equilibria and reactive solvent byproducts that obscure the balanced reaction stoichiometry and preclude rigorous kinetic modeling. To shift this paradigm from empirical screening toward predictive synthesis, this dissertation establishes a transferable, data-driven methodology that applies the classic mechanistic principles of physical-organic and physical-inorganic chemistry to multinary nanoscale phase spaces. First, a comprehensive structural and statistical analysis, of 127 literature reports spanning 1999–2026 deconstructs selenium precursor behavior across all known I–M–Se (where group I = Cu, Ag; M = group III, IV, V) TNP syntheses is reported. This diagnostic review establishes a strategic roadmap demonstrating how transitioning from ill-defined Se0 to well-defined molecular organodiselenides (e.g,, R2Se2) provides the necessary chemical handles to control selenium delivery rates, isolate metastable phases, and quantify reaction mass balances. Building upon these precursor guidelines, dibenzyl diselenide (Bn2Se2) is deployed as a monitorable, atom-efficient probe to systematically unravel the formation pathway of Cu3PSe4 TNPs from copper phosphide (Cu3-xP) precursors. By introducing the net two-hydrogen-atom donor 9,10-dihydroanthracene, the organic byproducts are restricted to stoichiometric equivalents of toluene (PhCH3) serving as a quantitative solution-phase proxy for net Se02 insertion and establishing a fully mass-balanced reaction stoichiometry. Finally, the underlying non-equilibrium reaction coordinate is mapped via an array of temperature-resolved analytical techniques, including synchrotron X-ray pair distribution function (PDF) analysis, multi-nuclear solid-state MAS NMR, and aberration-corrected electron microscopy. These structural investigations reveal that the transformation does not proceed via idealized thermodynamic self-assembly, but through a sequence of discrete molecular steps. Upon surface coordination of selenium, the initial Cu3-xP NP template fragments and reorganizes into highly disordered, vacancy-rich binary copper selenide (Cu2-xSe and Cu1-xSe) intermediates. Concurrently, P cations migrate to occupy antisite defects within the close-packed selenium sublattice, pre-forming tetrahedral [PSe4]3- building blocks within a transient (Cu,P)–Se matrix (using IUPAC nomenclature) that subsequently crystallizes into phase-pure ternary Cu3PSe4 via a comprehensive 8-electron redox reaction. Ultimately, this body of work delivers a complete set of plausible pseudoelementary steps that capture the structural evolution and chemical complexity of multinary nanoparticle formation. By validating that colloidal nanocrystal growth can be systematically tracked and deconstructed using monitorable molecular handles, this dissertation provides the essential foundational constraints required to guide autonomous synthetic algorithms and accelerate the discovery of next-generation energy technologies from the bottom up. I would like to acknowledge the Analytical Resources Core (RRID: SCR_021758) at Colorado State University for instrument access, training, and assistance with sample preparation. This work was supported by NSF Macromolecular, Supramolecular, and Nanochemistry (MSN #2109141 and MSN #2506142) awarded to A.L.P.