Controllable synthesis, characterization, and electrochemical properties of manganese oxide nanoarchitectures
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nta Ooi National Institute of Advanced Industrial Science and Technology, Takamatsu 761-0395, Japan
Zong-Huai Liua) Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an, 710062, People’s Republic of China (Received 11 August 2007; accepted 26 November 2007)
Flowerlike manganese oxide microspheres and cryptomelane-type manganese oxide nanobelts were selectively synthesized by a simple decomposition of KMnO4 under mild hydrothermal conditions without using template or cross-linking reagents. The effect of varying the hydrothermal times and temperatures on the nanostructure, morphology, compositional, and electrochemical properties of the obtained manganese oxides was investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies showed that the flowerlike manganese oxide microspheres could be obtained at relatively low hydrothermal temperatures, while high hydrothermal temperatures were favorable for the formation of cryptomelane-type manganese oxide nanobelts. A morphology and crystalline evolution of the nanostructures was observed as the hydrothermal temperature was increased from 180 to 240 °C. On the basis of changing the temperatures and hydrothermal reaction times, the formation mechanism of cryptomelane-type manganese oxide nanobelts is discussed. Cyclic voltammetry (CV) was used to evaluate the electrochemical properties of the obtained manganese oxide nanostructures, and the results show that the electrochemical properties depend on their shape and crystalline structure. This easily controllable, template-free, and environmentally friendly method has the potential for being used in syntheses of manganese oxide nanomaterials with uniform morphologies and crystal structures.
I. INTRODUCTION
In recent years, nanostructures have received steadily growing interest not only for their fundamental scientific significance but also for the many technological applications that derive from their superior electrical, optical, magnetic, and mechanical properties. In fabricating the next generation of microelectronic and optoelectronic devices, nanostructures are expected to play an important role because they can function as both building blocks and interconnections.1,2 Each structure has its own merits that depend on various factors, such as powder size, shape, composition, crystalline structure, or bulk dena)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0091 780 J. Mater. Res., Vol. 23, No. 3, Mar 2008 http://journals.cambridge.org Downloaded: 13 Mar 2015
sity.3–5 For the purpose of property studies and future applications of nanoscaled materials, different synthesis methods such as reflux, coprecipitation, sol-gel, solidstate chemical reaction, template-assisted,6 electrodeposited,7 as well as hydrothermal treatment have been developed to produce new nanostructures with novel shapes. Recently, our group ha
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