The study of vanadium oxide, in its many forms, has been ongoing for over a century. The varied crystal chemistry of vanadium oxides, with oxidation states of 3+, 4+, and 5+, makes it possible for many interesting morphologies to be formed. Because of their ability to form layered structures, they have many desirable properties that have been harnessed for use in a range of applications in the fields of catalysis and electrochemistry. The hydrothermal synthesis method is useful for creating these layered structures because the low-temperature technique allows for the synthesis of metastable phases. The use of amine and ammonium templates allows even greater structural control over the final product. In this work, several such hydrothermally synthesized, templated materials were studied.
The vanadium oxide nanotube (VONT) morphology, which has been studied for over a decade, was elucidated by the comparative study of two related compounds: the VONT precursor material and the vanadium oxide nano-urchin morphology. Vanadium oxide nanotubes are made up of layers of vanadium oxide intercalated with long-chain amines that roll or scroll to form a tubular morphology with a diameter of approximately 100 nm and lengths up to a micron. Compared to the nano-urchins, which are made up of a radial array of high-quality nanotubes, the vanadium in VONTs was less reduced, while vanadium in the precursor material was almost completely in the 5+ state, indicating that reduction takes place during hydrothermal synthesis. The cytotoxicology of VONTs was tested and cells exposed to the material demonstrated a significant loss in viability after only four hours.
The compound (enH2)V7O16 was synthesized for the first time as a single phase by a new, pH-based synthesis method. Due to the presence of short-chain ethylene diamine between the layers of this material, it is not able to scroll in the manner of the VONTs. Both the VONTs and (enH2)V7O16 have the same V 7O16 wall structure with a mixed V4+/V 5+ oxidation state, though magnetic studies indicate that the non-scrolled (enH2)V7O16 has a larger fraction of V 4+ ions. Studying the characteristics of this material provides structural information that cannot be obtained from VONTs directly, due to the lack of three-dimensional periodicity and long-range order in the curved nanotube walls.
The hydrothermal synthesis of NH4V4O10 was explored, and its structure studied. The double layer of distorted vanadium oxide octahedra has a negative charge that is balanced by NH4 + ions that are present between the layers. The material has shown good reactivity with lithium, with a reversible capacity of 230 mAh/g in lithium-ion batteries. The magnetic properties, which have not been studied previously, reveal the possibility of vanadium vacancies in the structure.
|Advisor:||Whittingham, M. Stanley|
|School:||State University of New York at Binghamton|
|School Location:||United States -- New York|
|Source:||DAI-B 71/09, Dissertation Abstracts International|
|Keywords:||Hydrothermal synthesis, Nanotubes, Vanadium oxides|
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