Molybdenum Vanadium Oxides Low-Dimensional Nanomaterials: Hydrothermal Fabrication, Their Structures And Physical Properties

This doctoral dissertation is aimed at synthesizing hydrothermally low-dimensional nanomaterials of transition-metal oxides. In the context, MoO₃ nanobelts, H_xMoO₃ nanobelts, V_0.13Mo_0.87O_2.935 nanowires, V₂O₅·nH₂O nanosheets, and V₂O₅ nanowires are prepared by polymerization reactions from acided peromolybdate or/and perovanadate solutions.Chapter 1.An overview of nanomaterials includes structure, properties, and potential applications. A variety of synthetic approaches, such as high-temperature vapor transportation, decomposition of metallic organic compounds, are introduced in this part. Special emphasis is placed on hydrothermal / solvothermal routes to nanomaterials.Chapter 2.MoO₃ nanobelts are synthesized hydrothermally at 140℃for 12 h with the acided peromolybdate solution, which is first obtained by reacting metallic molybdenum powder with hydrogen peroxide solution. The introduction of ethanol can lead to H_xMoO₃ nanobelts. The blue H_xMoO₃ nanobelts retain the crystalline structure and morphology of MoO₃ nanobelts, but they display different PL spectrum.Chapter 3.MoO₃ nanobelts can be reduced by N₂H₄·H₂O-HCl solution to blue and dark blue H_xMoO₃ nanobelts. By means of XRD, Raman, XPS and HRTEM, the three nanobelts are compared specifically in terms of crystalline and electronic structure. It can be concluded that with the intercalation of hydrogen, H_xMoO₃ nanobelts expand in lattice parameters and increase in crystal defects, and the delocalized electrons present in layered structure increase in concentration as well. Electric measurements show the resistance of dark blue H_xMoO₃ nanobelts is less than 1/50,000 that of MoO₃ nanobelts. Temperature dependent measurement of the electric resistance of dark blue H_xMoO₃ nanobelts indicates that the conduction complies with the behavior of the doped semiconductor (exponential correlation), and the thermally activated energy of electrons is calculated to be 0.19 eV.Chapter 4.The nanowires of ternary V_0.13Mo_0.87O_2.935 are synthesized hydrothermally at 220℃for 48 h with the acided peromolybdate and perovanadate solutions, which are prepared by reactions among Mo, H₂O₂ and NH₄VO₃. Besides, the microprisms and microrods of V_0.13Mo_0.87O_2.935 as well as V₂O₅·xH₂O nanobelts are also obtained by adjusting molar ratio of Mo to NH₄VO₃. V_0.13Mo_0.87O_2.935 nanowires tend to change from the crystalline state to amorphous state under the strong electron illumination. Photoluminescence measurements indicate that V_0.13Mo_0.87O_2.935 nanowires display strong blue-light emission, which is probably related to intrinsic oxygen vacancies.Chapter 5.V₂O₅·nH₂O nanosheets can be available hydrothermally at 200℃for 12 h with the acidified perovanadate solutions, which are prepared using V₂O₅, H₂O₂ and HCl as starting reagents. The controlled hydrothermal experiments indicate that as-fabricated V₂O₅·nH₂O nanosheets are the intermediate products between V₂O₅·nH₂O nanobelts and V₂O₅ nanowires. What's more, the dehydration process and structure evolution of V₂O₅·nH₂O nanosheets are studied in detail when they are heated in air.