The Swihart research group focuses on synthesizing the transition metal carbides and oxides to explore the growth mechanisms.
For nickel carbides, we present a new type of highly hierarchical but nonporous nanostructure with a unique “dandelion” morphology. Based on the time evolution of these Ni3C nanostructures, we suggest a mechanism for their formation. This type of hierarchical nanocrystal, with high accessible specific surface area in a relatively large (ca. 750 nm overall diameter) stable structure, can be valuable in catalysis and related applications.
For iron oxides, we define and explore synthesis parameters in the system of magnetite (Fe3O4) nanocrystals (MNCs) thoroughly to reveal their effects. We demonstrate the essential role of benzaldehyde and benzyl benzoate produced by oxidation of benzyl ether, the solvent typically used for MNC synthesis, in producing monodisperse MNCs. This insight allowed us to develop stable formulas for producing monodisperse MNCs and propose a model to rationalize MNC size and shape evolution. Solvent polarity controls the MNC size, while short ligands shift the morphology from octahedral to cubic. We demonstrate preparation of specific assemblies with these MNCs. This standardized and reproducible synthesis of MNCs of wellcontrolled size, shape, and magnetic properties demonstrates a rational approach to stabilizing and expanding existing protocols for nanocrystal syntheses and may drive practical advances including enhanced MRI contrast, higher catalytic selectivity, and more accurate magnetic targeting.
For cobalt oxides, we explore a facile method to synthesize the flower-shape Co-O and M-Co-O (M = Fe, Mn, Ni) alloys, that can serve as an autonomous template by all in one step without any preparation. We demonstrate the shape evolution and different growth mechanisms of cobalt oxide and relative alloys. The magnetic properties can also be controlled and tuned by adjusting the sizes and shapes. Large surface area shapes and tunable magnetic properties make these materials wide applications.