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.