Morphological Evolution of (NH₄)_0.5V₂O₅·mH₂O Fibers into Belts, Triangles, and Rings

In this contribution, single-crystalline (NH₄)_0.5V₂O₅·mH₂O xerogels made of belts, rings, triangles, and ovals have been synthesized using a surfactant-free hydrothermal method. The analytical techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED) have been used to characterize the morphology, composition, and structure of the as-prepared products. On the basis of SEM and TEM observations, we suggested that the as-prepared (NH₄)_0.5V₂O₅·mH₂O rings, triangles, and ovals have been formed by connecting two ends of the vanadium oxide sheet made of edge and corner sharing VO₅ square pyramids. The as-prepared (NH₄)_0.5V₂O₅·mH₂O nanobelts are up to several hundreds of micrometers long, 402–551 nm wide, and 235–305 nm thick. The thickness and width of the rings are respectively ∼454 nm and ∼1 μm. Triangles with three unequal sides having a thickness of ∼143 nm and a width of ∼1 μm were also formed. The crystalline orthorhombic phase of shcherbianite V₂O₅ was obtained on calcination of (NH₄)_0.5V₂O₅·mH₂O at 350 °C for 2 h. The SEM image of this V₂O₅ product retains the parent morphology of the preheated compound. A possible reaction mechanism and the growth process involved in the formation of belts/rings/triangles and ovallike microstructures are discussed.