S. Ashoka

Morphological Evolution of (NH4)0.5V2O5·mH2O Fibers into Belts, Triangles, and Rings

In this contribution, single-crystalline (NH(4))(0.5)V(2)O(5)·mH(2)O 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 (NH(4))(0.5)V(2)O(5)·mH(2)O rings, triangles, and ovals have been formed by connecting two ends of the vanadium oxide sheet made of edge and corner sharing VO(5) square pyramids. The as-prepared (NH(4))(0.5)V(2)O(5)·mH(2)O 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 V(2)O(5) was obtained on calcination of (NH(4))(0.5)V(2)O(5)·mH(2)O at 350 °C for 2 h. The SEM image of this V(2)O(5) 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.

Synthesis and characterisation of microstructural α-Mn2O3 materials

Low-dimensional α-Mn2O3 materials with novel surface morphologies have been prepared by thermal decomposition of hydrothermal-derived MnCO3. The powder X-ray diffraction pattern reveals that the Mn2O3 microstructures are of cubic phase structure. From Fourier transform infrared spectroscopy results, the peaks around 600–450 cm−1 correspond to Mn–O bending vibrations. From the TGA results, the observed major weight loss ∼31% between 350 and 540°C is due to the decomposition of MnCO3 into Mn2O3. The X-ray photoelectron spectroscopy results showed that Mn is in +3 oxidation state. The peaks at 641.2 and 652.73 eV are assigned to the Mn2p3/2 and Mn2p1/2 of Mn+3 states, respectively. The scanning electron microscope images showed that the α-Mn2O3 products exhibit spheres, dumbbell- and peanut-shaped microstructure. These microstructures are mainly composed of wires/rods and particles. The scanning electron microscope results also revealed that the obtained α-Mn2O3 maintains the frame structure of the precursor MnCO3.