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Polyoxovanadates as Precursors for the Synthesis of Colloidal Multi-Metal Oxide Nanocrystals



Adam Biacchi, Lucas Johnson, Ashley Sweet, Eric Cal, Angela R. Hight Walker, Matthew Buck, Luke Barrante


Colloidal multi-metal oxide nanocrystals that contain the element vanadium are attractive materials for enabling diverse technologies. Few nanocrystal systems are synthetically well-developed, however, which is attributable to a scarcity of molecular precursors that enable facile incorporation of vanadium. Here, we demonstrate the viability of polyoxovanadates as precursors for colloidal nanocrystal synthesis, which are compelling because they contain polyhedral VOn (n = 4, 5, 6) units that are often also present in the multi-metal oxides of interest. First, we discovered that a commercial tetraalkylammonium halide phase transfer reagent extracts aqueous metavanadate ions into organic solvent, conferring solubility to the resulting polyoxovanadates required for nanocrystal synthesis. We then studied the thermal decomposition of iron oleate complex mixed with phase-transferred polyoxovanadate precursor, which yielded previously inaccessible colloidal ternary oxide nanocrystals in high yield, including triclinic FeVO4 and spinel-type vanadium-doped magnetite (Fe3-xVxO4) phases. The crystal structure, composition, and morphology of the nanocrystals, which were characterized using X-ray diffraction, Raman scattering, X-ray photoelectron spectroscopy, and transmission electron microscopy, were found to depend strongly on the iron-to-vanadium precursor ratio. The magnetic properties of these colloidal nanocrystals were also investigated, and correlated strongly to the phase of vanadium iron oxide as FeVO4 displayed antiferromagnetic behavior and a Néel temperature of 21 K while Fe3-xVxO4 showed a superparamagnetic-like response with a ferrimagnetic blocking temperature at 162 K. The emergence of polyoxovanadates as precursors to ternary metal oxide nanocrystals that contain vanadium is a significant synthetic advance that may be extensible to other important multi-metal oxide systems.
Chemistry of Materials


Biacchi, A. , Johnson, L. , Sweet, A. , Cal, E. , Hight Walker, A. , Buck, M. and Barrante, L. (2022), Polyoxovanadates as Precursors for the Synthesis of Colloidal Multi-Metal Oxide Nanocrystals, Chemistry of Materials, [online],, (Accessed April 24, 2024)
Created March 31, 2022, Updated November 29, 2022