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 largescale preparation of nanostructures of the interesting and useful materials rutile VO 2 and corundum V 2 O 3 . Vanadium oxide (V 2 O 5-δ ) nanoscrolls, prepared by the hydrothermal treatment of aged suspensions of V 2 O 5 and dodecylamine, were reduced in a furnace in an atmosphere of 5% H 2 :95% N 2 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, N 2 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 VO 2 . These convert to corundum V 2 O 3 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.

Nanothermochromics: Calculations for VO2 nanoparticles in dielectric hosts show much improved luminous transmittance and solar energy transmittance modulation

“…The limitations are not as stringent as they may seem, though, and it should be observed that metallic vanadium can be transformed to VO 2 by controlled oxidation [121][122][123][124] and that insulating V 2 O 5 van be transformed to VO 2 by controlled reduction in films. [125][126][127] There is a tendency that limited dimensions decreases c and widens the hysteresis in nanocrystalline films 46,48,[128][129][130][131][132][133][134][135] and nanorods. 27,28,81,90,118 This may be associated with internal stress in the particles.…”

Spontaneously formed porous and composite materials

“…3). 40,41 These porous structures are formed due to the loss of the amine intercalant, which acts as a sacrificial poreformer during the reduction process which is carried out at elevated temperatures. Fig.…”

Nanothermochromics with VO2-based core-shell structures: Calculated luminous and solar optical properties

“…Hollow nanospheres and microspheres of VO 2 , 6 15 and such coatings on carbon have been prepared chemically. 16 We also note that VO 2 nanoparticle infiltration into ordered polystyrene sphere arrangements have yielded inverse opal nanostructures, 17 that VO 2 "nanoscrolls" have been made from chemically prepared V 2 O 5Àd , 18 and that seaurchinlike nanostructures of VO x ÁyH 2 O have been deposited chemically 19 as well as electrochemically. 20 The mentioned research on VO 2 -based core-shell nanostructures represents examples of a huge endeavor to develop analogous structures of a vast range of materials, and representative recent work on hollow nanospheres-which will be shown below to have the most interesting properties for the case of VO 2 -has been presented for a multitude of other oxides including MgO, 21 SiO 2 , 22 c-MnO 2 , 23 NiO, 24 ZnO, 25 In 2 O 3 , 26,27 and SnO 2 .…”