Solid-state transformation of single precursor vanadium complex nanostructures to V2O5 and VO2: catalytic activity of V2O5 for oxidative coupling of 2-naphthol

A vanadium complex, [(C5H5N)(2)V2O3 center dot H2O], of different morphologies has been obtained via a modified hydrothermal procedure using pyridine and VOSO4 salt as the starting material. The evolved [(C5H5N)(2)V2O3 center dot H2O] nanobelts are of 50-200 nm in width and of a length up to several millimeters. At higher temperatures (600 degrees C), the solid [(C5H5N)(2)V2O3 center dot H2O] nanostructures are converted to vanadium pentoxide (V2O5) and vanadium dioxide (VO2) when heated in air and nitrogen atmosphere, respectively. During growth, the mechanism of the evolution of octahedra, truncated octahedra, and hollow truncated octahedra of [(C5H5N)(2)V2O3 center dot H2O] are reported for the first time. These types of well-structured morphology are also isolated while V2O5 and VO2 are evolved. The as-grown belt-like and octahedral morphologies of [(C5H5N)(2)V2O3 center dot H2O] are retained during the solid-state transformation, suggesting a route to evolve crystalline nanomaterials. Again, the morphological evolution of the [(C5H5N)(2)V2O3 center dot H2O] nanostructures has been examined to be pyridine and precursor vanadyl sulfate (VS) concentration dependent. Thus, we are able to isolate truncated octahedra as an intermediate during the formation of [(C5H5N)(2)V2O3 center dot H2O] nanobelts and nanoflowers with a high pyridine (Py) concentration. Interestingly, longer reaction times successively featured the transformation of truncated octahedra into nanobelts. Nanobelt evolution is not observed at low pyridine concentrations. However, the formation of octahedral morphology takes place at low pyridine concentration. All of the nanostructures were critically examined and characterized thoroughly by various physical techniques to ascertain their purity, structure and composition. An interesting, thermodynamically stable, single crystalline product from DMF soluble [(C5H5N)(2)V2O3 center dot H2O] has been characterized, which indirectly supports the composition of [(C5H5N)(2)V2O3 center dot H2O]. Selectively, vanadium pentoxide nanobelts have been found to be an efficient catalyst for the oxidative coupling of 2-naphthol to binaphthols under a molecular oxygen atmosphere.