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Morphological control of heterostructured nanowires synthesized by sol-flame method

Runlai Luo1, In Sun Cho2, Yunzhe Feng1, Lili Cai2, Pratap M Rao2 and Xiaolin Zheng2*

Author Affiliations

1 Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA

2 Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA

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Nanoscale Research Letters 2013, 8:347  doi:10.1186/1556-276X-8-347

Published: 8 August 2013

Abstract

Heterostructured nanowires, such as core/shell nanowires and nanoparticle-decorated nanowires, are versatile building blocks for a wide range of applications because they integrate dissimilar materials at the nanometer scale to achieve unique functionalities. The sol-flame method is a new, rapid, low-cost, versatile, and scalable method for the synthesis of heterostructured nanowires, in which arrays of nanowires are decorated with other materials in the form of shells or chains of nanoparticles. In a typical sol-flame synthesis, nanowires are dip-coated with a solution containing precursors of the materials to be decorated, then dried in air, and subsequently heated in the post-flame region of a flame at high temperature (over 900°C) for only a few seconds. Here, we report the effects of the precursor solution on the final morphology of the heterostructured nanowire using Co3O4 decorated CuO nanowires as a model system. When a volatile cobalt salt precursor is used with sufficient residual solvent, both solvent and cobalt precursor evaporate during the flame annealing step, leading to the formation of Co3O4 nanoparticle chains by a gas-solid transition. The length of the nanoparticle chains is mainly controlled by the temperature of combustion of the solvent. On the other hand, when a non-volatile cobalt salt precursor is used, only the solvent evaporates and the cobalt salt is converted to nanoparticles by a liquid–solid transition, forming a conformal Co3O4 shell. This study facilitates the use of the sol-flame method for synthesizing heterostructured nanowires with controlled morphologies to satisfy the needs of diverse applications.

Keywords:
Heterostructured nanowires; Metal oxide nanowires; Sol-flame; Flame synthesis; CuO nanowires; Co3O4 nanoparticles