Nearly X-ray amorphous hollow sphere manganese oxides (hollow sphere MnO 2 ) have been synthesized by a carboxylic acid-mediated system containing KMnO 4 and Na 2 S 2 O 4 under ambient conditions for supercapacitor applications. The product was characterized by powder XRD, Raman spectroscopy and thermal analysis. SEM and TEM were used to investigate the morphology of MnO 2 . The as-prepared MnO 2 was X-ray amorphous and had particles in the size range 0.1-1 mm. A mechanism has been proposed for the formation of hollow sphere structures in the micro-emulsion medium. Upon annealing the sample at temperatures greater than 500 C, the amorphous MnO 2 transforms into Mn 2 O 3 . Cyclic voltammetry and galvanostatic charge-discharge cycling were used to evaluate the electrochemical performance. The initial discharge capacities were found to be 283 and 188 F g À1 in 0.1 M Ca(NO 3 ) 2 and 0.1 M Na 2 SO 4 , respectively, at a current density of 0.5 mA cm À2 . The higher specific capacitance in the electrolyte with a bivalent cation is attributed to the reduction of two Mn 4+ to Mn 3+ by each of the bivalent cations present in the electrolyte.

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Bismutite (Bi2O2CO3) possessing diverse morphologies, namely nanosheets, nanodiscs and nanoplatelets, was synthesized by a simple controllable method using bismuth nitrate pentahydrate and urea as precursors in a water/ethylene glycol mixture. The as-synthesized samples showed unique physical and chemical properties, such as varying morphology, phase identification, chemical composition, surface area and surface potential. Bi2O2CO3 nanosheets exhibited excellent adsorption capabilities for anionic dyes (acid orange 7 and methyl orange) and high photocatalytic performance for the decolorization of cationic dyes (rhodamine B and methylene blue) under simulated solar illumination. Furthermore, the electrochemical performance of Bi2O2CO3 nanosheets showed good capacitance properties and hence could be a potential candidate for electrode materials in energy related applications.