Growth of width-controlled nanowires MnO 2 from mesoporous carbon and investigation of their properties
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Xiaolin Wang Spintronic and Electronic Materials Group, Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2522, Australia
Wei Huang, Deyue Yan, Honghua Wang, and Di Zhang Coll. Chem. & Chem. Eng., State Key Lab Met Matrix Composites, Shanghai Jiao Tong University, Shanghai 200030, People’s Republic of China (Received 16 March 2006; accepted 23 June 2006)
One-dimensional ␣-MnO2 nanowires with a controlled width of 10–20 nm have been developed by means of ultrasonic waves from mesoporous carbon using KMnO4 as the precursor. The formation mechanism has been proposed based on the results. A peak around 100 K was detected in the temperature-dependence of magnetization curve, indicating the ferromagnetic state in nanocomposite mesoporous carbon-MnO2, which is in agreement with the transition temperature found from the magnetization versus applied magnetic field curve. The magnetization versus temperature curve of the obtained MnO2 nanowires showed a magnetic transition at about 50 K, illustrating that a parasitic ferromagnetic component is composed on the antiferromagnetic structure of MnO2. The advantage of the method reported here is that phase-controlled synthesis of ␣-MnO2 nanowires was implemented regardless of pH, temperature, and types of ions in the reaction system. A major advantage of this approach is the efficient, fast, and reproducible control of width and the facile strategy to synthesize nanowires MnO2, in addition to the high purity of the resultant material.
I. INTRODUCTION
The controlled syntheses of metal oxides, especially those that are supposed to present some novel properties with a particular dimensionality and size, has attracted intensive attention.1 MnO2 has been the focus of material scientists because of its advanced applications in molecular sieves, catalysts, and lithium batteries.2,3 Synthesis of one-dimensional MnO2 with controlled width is of great interest because the low-dimensional structure results in an improved electrochemical performance, as well as in unique nanomagnetic properties.4 Several successful techniques have been reported in the synthesis of onedimensional nanostructures, such as thermal evaporation,5 nanotube-based synthesis,6–8 solution-based synthesis,9 microemulsion,10 vapor-liquid-solid growth,11 hydrothermal method, 12 and mesoporous confinement.13–17 In comparison with soft chemical processes,18
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0356 J. Mater. Res., Vol. 21, No. 11, Nov 2006
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the hard-templating process is a very different approach that has attracted considerable attention. Direct nanocasting of mesoporous silica has been used widely for the preparation of metal oxide nanowires, including nanocrystallites -MnO2.19,20 Highly ordered mesoporous carbon (CMK-3) with its regular array of uniform mesopores exhibits not only thermal and mechanical stability, but also the capability of enduring various ch
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