Electrochemical Properties of Controlled Size Mn3O4 Nanoparticles for Supercapacitor Applications.

A simple and controlled strategy has been used to synthesise Mn3O4 nanoparticles (NPs) via hydrothermal method. The Mn3O4 nanoparticles were further applied for supercapacitor electrode materials. The unique squared-shape Mn3O4 nanoparticles exhibited excellent electrochemical performance due to the small size and porous architecture. After electrochemical testing, the Mn3O4 NPs based electrode showed a large specific capacitance (380 F g-1, 1.0 mAcm-2) and good cycling stability (88.6%) of the initial capacitance after 5000 cycles in 1.0 M Na2SO4 solution. These results may provide useful guidelines for materials selection, synthesis, size and configuration designs for the novel energy storage devices based on transitional metal oxides.

Influence of SiO2 on the structure-controlled synthesis and magnetic properties of prismatic MnO2 nanorods.

Silicon dioxide-doped tetragonal MnO2 single crystalline prismatic nanorods have been successfully synthesized through a facile hydrothermal route at a temperature of 250 ° C with a reaction time as quick as 5 h. The synthesized MnO2 prismatic nanorods were characterized by x-ray diffraction, field emission scanning electron microscopy, energy dispersive x-ray analysis, transmission electron microscopy, high resolution transmission electron microscopy with selected area electron diffraction and Raman spectroscopy. Experimental results show that single crystalline tetragonal MnO2 nanorods have been successfully synthesized at all doping concentrations and that nanorods with a prismatic surface morphology have been obtained at 20 mass% of SiO2. The diameter of as-prepared MnO2 nanorods increases from 125 to 250 nm on increasing the dopant concentration. X-ray photoelectron spectroscopy analysis confirms the presence of valence Si (2p) of SiO2 in the as-prepared MnO2 nanostructures. The intensity of Raman modes clearly increases with increasing doping concentration, indicating an improvement in the structural aspects of the MnO2 nanorods. The magnetic properties of the products have been evaluated using a vibrating sample magnetometer, revealing that the as-prepared MnO2 nanorods exhibit weak ferromagnetic behavior at room temperature. The Néel temperature of the as-obtained products is calculated as 97 K. On the basis of the structural information, a growth mechanism is proposed for the formation of prismatic-like 1D MnO2 nanorods.

Controlled synthesis, characterizations and structural-properties of micro-flowers, pine-cone, core-shell and liver-like micro-architecture of crystalline ZnMn2O4.

The conspicuous ZnMn2O4 micro-structures have been synthesized by hydrothermal method by using Mn3O4 and Zn powder as precursors. The micro-structures of the ZnMn2O4 could be tuned by changing the reaction time only in the reaction system. The final products have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and the Raman spectroscopy. Room temperature Raman spectroscopy investigation indicates that the synthesized micro-structures have strong fundamental vibrational modes. The intensity of the vibrational modes varied with change in the reaction time in the synthesized products of ZnMn2O4. The mechanism of this peculiar Raman property was analyzed.

Effect of atomic percentage of Zn on the size and optical properties of porous ZnMn2O4 nanoparticles.

The porous ZnMn2O4 nanostructures have been synthesized by hydrothermal method by using Mn3O4 and Zn powder as precursors. The morphology of the nanoparticles could be tuned by changing the molar ratio of Zn in the reaction system. The final products have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, UV-visible spectroscopy and the florescence spectrometer. Room temperature photoluminescence investigation indicates that the nanostructures have strong band-gap emission at yellow and orange bands. Absorption properties of ZnMn2O4 nanostructures indicated that the band gap energy varied with change in the atomic percentage of Zn in hetaerolite ZnMn2O4. The mechanism of this peculiar optical property was analyzed.

Preparation, characterizations and optical property of single crystalline ZnMn2O4 nanoflowers via template-free hydrothermal synthesis.

In this work, we have reported a template-free hydrothermal approach to fabricate highly pure single phase ZnMn2O4 pen-type nano needles assembled with flower type nanostructures. The X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy, Raman Spectroscopy, Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, Selected Area Electron Diffraction and UV-visible spectroscopy techniques were used to study the structural and optical properties of Pen-type nanoneedles assembled with flower like nanostrucutres. Single crystalline hetaerolite ZnMn2O4 pen type nanoneedles of flower like nanostructures have an average diameter of 250 nm. Room temperature Raman spectroscopy reveals the four fundamental vibrational modes. Room temperature UV-vis spectrometer was used to determine the transmittance behaviour pen type nanoneedles of flower like nanostructures. Direct optical band gap of 2.19 eV was acquired by using Davis-Mott model. The UV-visible spectrum points out that the absorption is prominent in visible region and transparency is more than 80% in UV region.

Synthesis, characterization and optical property of shrimps-like nanostructures of MnO2 by hydrothermal route.

Hexagonal MnO2 shrimps like nanostructures have been successfully synthesized through a facile hydrothermal route at a temperature of 175 degrees C. The synthesized MnO2 nanostructures were characterized by the X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy, Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, Selected Area Electron Diffraction and UV-visible spectroscopy. UV-vis spectrophotometer was used to determine the absorption behaviour of shrimps like nanostructures. Direct optical band gap of 1.65 eV was acquired by using Davis-Mott model. The UV-visible spectrum exhibited the prominent absorption in visible region.