Solvothermal synthesis of VO₂ nanoparticles with locally patched V₂O₅ surface layer and their morphology-dependent catalytic properties for the oxidation of alcohols

Vanadium oxides are promising oxidation catalysts because of their rich redox chemistry. We report the synthesis of VO₂ nanocrystals with VO₂(B) crystal structure. By varying the mixing ratio of the components of a binary ethanol/water mixture, different VO₂ nanocrystal morphologies (nanorods, -urchins, and -sheets) could be made selectively in pure form. Polydisperse VO₂(B) nanorods with lengths between 150 nm and a few micrometers were formed at large water : ethanol ratios between 4 : 1 and 3 : 2. At a water : ethanol ratio of 1 : 9 VO₂ nanosheets with diameters of ∼50-70 nm were formed, which aggregated to nano-urchins with diameters of ∼200 nm in pure ethanol. The catalytic activity of VO₂ nanocrystals for the oxidation of alcohols was studied as a function of nanocrystal morphology. VO₂ nanocrystals with all morphologies were catalytically active. The activity for the oxidation of benzyl alcohol to benzaldehyde was about 30% higher than that for the oxidation of furfuryl alcohol to furfural. This is due to the substrate structure. The oxidation activity of VO₂ nanostructures decreases in the order of nanourchins > nanosheets > nanorods.