Hydrothermal synthesis and controlled growth of vanadium oxide nanocrystals

Abstract

0-, 1- and 2-dimensional nanocrystals of different vanadium oxides were synthesized using hydrothermal reaction of commercial bulk monoclinic VO2 and V2O3 precursor, which, depending on reaction conditions, produced nanoparticles, nanoribbons and nanosheets of different vanadium oxides. Addition of acetone was used to direct growth and produce two-dimensional nanosheets, whose aspect ratio depends on acetone-to-precursor concentration, while addition of different alcohols as ligands successfully controlled the nanoribbon size. Variation of pH also changes the product dimensionality, allowing production of nanosheets at pH < 3, nanoribbons at 3 < pH < 7 and, through inhibition of reaction, nanoparticles at high pH. Products of different morphology exhibit systematic increase in unit cell volume with decrease in thickness of nanocrystals. The reaction occurs with VO2+ ion as the primary reactant, requiring only a source of VO2+ ions, and not necessarily crystalline VO2(M), allowing use of other precursors, like VOSO4. Calculations indicate that nanoribbon formation is primarily caused by differences in relative stability of individual crystal planes of VO2. Addition of different amounts of hydrogen peroxide changes the oxidation state of vanadium to produce V3O7 and V2O5, without affecting the product morphology, while use of bulk V2O3 as a precursor leads to the formation of V2O3 nanoribbons, nanoleaves and nanoparticles with similar mechanisms of size and shape control.