Phase Controlled Synthesis of Iron Sulfide Nanocrystals

Abstract

The iron sulfides are the most earth abundant naturally occurring metal sulfides with a wide range of properties and thereby applications. However, relative to other metal chalcogenides, the iron-sulfur system is poorly understood due to its complexity, as numerous phase variations arise from minimal changes in stoichiometry. This thesis demonstrates that organosulfur precursor reactivity tunes the phase of iron sulfide nanocrystals phase between pyrite (FeS2), greigite (Fe3S4), and pyrrhotite (Fe1-XS) in a colloidal hot injection synthesis. Sulfur rich phases were favored when the C-S bond strength was low in the dialkyl disulfides, alkyl thiols, and dialkyl disulfides (allyl, benzyl, t-butyl, and phenyl). Diallyl disulfide alone yielded FeS2, which is noteworthy as a potential source of (S-S) 2- units. Evidence is provided that suggests that FeS2 forms directly without an FeS intermediate, unlike most synthetic procedures to pyrite. FeS2 is of particular interest as a low-cost earth abundant semiconductor for photovoltaics. In addition to phase control, a novel pyrite hybrid nanostructure was synthesized in which an epitaxial layer of isostructural cattierite (CoS2) was grown on the surface of FeS2 nanocubes. The epitaxial layer morphology was tuned between core-frame and core-shell structures based on the cobalt/sulfur precursor ratio and the hybrid nanocrystals demonstrated activity toward the hydrogen evolution reaction (HER). Approved