Hydrothermal Synthesis of Novel Vanadium Oxides

Abstract

Extending our prior work on tungsten and molybdenum oxides, we have found that a wide variety of vanadium oxides can be prepared using hydrothermal methods. These include a number of layer compounds as well as cluster complexes. The starting reaction medium usually contained vanadium pentoxide, an alkali containing compound such as LiOH, an organic template such as tetramethylammonium, and the pH of the whole was controlled by the addition of acid. Reaction temperature was 150°C to 200°C, and time was up to 3 days. A new lithium vanadium oxide, which has the simplest structure of any layered vanadium oxide, was formed. The lithium could be readily removed leading to a new form of vanadium dioxide. This vanadium oxide was also capable of intercalating a variety of other ionic and molecular species. Several other new vanadium oxides containing the TMA cation were also formed; one of these TMAV₃O₇ readily absorbed oxygen to form TMAV₃O₈. Addition of zinc or iron to the reaction medium caused the formation of layer structures containing double V₂O₅ layers; for iron the TMA was retained in the structure whereas for zinc the TMA was excluded. Changing the organic entity resulted in other new structures, for example methylamine and dimethylamine gave tetragonal structures.