Valence State-Controlled Synthesis of Vanadium Oxide Nanocrystals

We report a valence state-controlled synthesis of vanadium oxide nanocrystalline particles via a non-hydrothermal process using an alcohol and an amine ligand. A non-stoichiometric V3O5 (V4+V3+2O5), which is known for its difficulty of formation due to the narrow allowances in the vanadium-to-oxygen ratio, was obtained for the first time as nanocrystals in the anosovite phase─a rare phase discovered only recently in bulk form. The time course of the nanocrystal formation revealed a slow seeded growth process, separated from a subsequent fast growth via Ostwald ripening. We highlight the role of vanadium precursor-to-alcohol-to-ligand ratios in precisely controlling the reduction of V5+. Polyvalence of metals, particularly the unusual stability of vanadium(II)–(V), has been considered a negative factor in achieving the targeted oxidation state in nanocrystal syntheses. In the present system, the polyvalence allowed formations of different oxide nanocrystals in a parameter-controlled manner, including anosovite V3O5 (V4+ + 2V3+) and corundum V2O3 (V3+). Such control is unprecedented in metal oxide nanocrystal syntheses.