Controlled Reduction of Vanadium Oxide Nanoscrolls: Crystal Structure, Morphology, and Electrical Properties

Abstract

The systematic and controlled reduction of vanadium oxide nanoscrolls results in routes to the large-scale preparation of nanostructures of the interesting and useful materials rutile VO2 and corundum V2O3. Vanadium oxide (V2O5−δ) nanoscrolls, prepared by the hydrothermal treatment of aged suspensions of V2O5 and dodecylamine, were reduced in a furnace in an atmosphere of 5% H2:95% N2 under different time and temperature conditions to monitor systematic trends in the structure and morphology of the resulting oxides. The products were characterized by X-ray diffraction (XRD), electron microscopy, N2 sorption measurements, and electrical transport studies. We find that the reduction conditions (time and temperature) play a significant role in determining the crystal structure and morphology of the products. At short times and low temperatures, the reduction products are rutile VO2. These convert to corundum V2O3 when temperatures are increased. In all cases, the appearance of crystalline Bragg peaks in XRD is associated with the breaking up of the starting high-aspect nanostructures into small, dense crystallites. Under certain reduction conditions, porous materials with ill-defined X-ray structures are obtained as intermediates.