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Morphological control of heterostructured nanowires synthesized by sol-flame method.

Luo R, Cho IS, Feng Y, Cai L, Rao PM, Zheng X - Nanoscale Res Lett (2013)

Bottom Line: 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.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.

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Affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA. xlzheng@stanford.edu.

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.

No MeSH data available.


Effects of cobalt salt precursor on the morphology of Co3O4 on CuO NWs. A shell of Co3O4 is formed when cobalt nitrate is used as the cobalt salt precursor. (a) SEM image of CuO/Co3O4 core/shell NWs. The inset shows a single CuO/Co3O4 core/shell NW. (b) TEM image, (c) TEM-EDS spectrum, and (d) HRTEM of the CuO/Co3O4 core/shell NW edge, indicating that the shell is a 9-nm thick polycrystalline Co3O4 film.
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Figure 3: Effects of cobalt salt precursor on the morphology of Co3O4 on CuO NWs. A shell of Co3O4 is formed when cobalt nitrate is used as the cobalt salt precursor. (a) SEM image of CuO/Co3O4 core/shell NWs. The inset shows a single CuO/Co3O4 core/shell NW. (b) TEM image, (c) TEM-EDS spectrum, and (d) HRTEM of the CuO/Co3O4 core/shell NW edge, indicating that the shell is a 9-nm thick polycrystalline Co3O4 film.

Mentions: While the morphology of Co3O4 is significantly affected by the solvent, it will also depend on the properties of the cobalt salt precursors, such as their volatility. To focus on the effect of the cobalt salt precursor, the solvent is fixed to be acetic acid with the same drying condition of 0.4 h at 25°C in air, which leaves a large amount of acetic acid in the precursor coating. We study the effect of cobalt salt precursors on the Co3O4 morphology by comparing volatile cobalt acetate Co(CH3COO)2·4H2O with non-volatile cobalt nitrate Co(NO3)2·6H2O. Volatile cobalt acetate has been used for the above control experiments and leads to the formation of the Co3O4 NP-chain morphology (Figure 1d) when there is sufficient residual solvent. When non-volatile cobalt nitrate is used as the precursor, a shell is formed on the CuO NWs instead of a NP-chain (Figure 3a), despite the presence of a large amount of residual solvent. The shell coating at the surface of the CuO NWs is about 9-nm thick (Figure 3b). The TEM-EDS analysis (Figure 3c) shows the presence of both Cu and Co peaks along with the O peak in the coated NW. Further high-resolution TEM (HRTEM) characterization (Figure 3d) reveals that the final NW consists of a single crystal CuO NW core with a [111] growth direction and a thin polycrystalline shell with an interplanar spacing of 0.25 nm, which corresponds to the spacing of (311) planes of Co3O4.


Morphological control of heterostructured nanowires synthesized by sol-flame method.

Luo R, Cho IS, Feng Y, Cai L, Rao PM, Zheng X - Nanoscale Res Lett (2013)

Effects of cobalt salt precursor on the morphology of Co3O4 on CuO NWs. A shell of Co3O4 is formed when cobalt nitrate is used as the cobalt salt precursor. (a) SEM image of CuO/Co3O4 core/shell NWs. The inset shows a single CuO/Co3O4 core/shell NW. (b) TEM image, (c) TEM-EDS spectrum, and (d) HRTEM of the CuO/Co3O4 core/shell NW edge, indicating that the shell is a 9-nm thick polycrystalline Co3O4 film.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 3: Effects of cobalt salt precursor on the morphology of Co3O4 on CuO NWs. A shell of Co3O4 is formed when cobalt nitrate is used as the cobalt salt precursor. (a) SEM image of CuO/Co3O4 core/shell NWs. The inset shows a single CuO/Co3O4 core/shell NW. (b) TEM image, (c) TEM-EDS spectrum, and (d) HRTEM of the CuO/Co3O4 core/shell NW edge, indicating that the shell is a 9-nm thick polycrystalline Co3O4 film.
Mentions: While the morphology of Co3O4 is significantly affected by the solvent, it will also depend on the properties of the cobalt salt precursors, such as their volatility. To focus on the effect of the cobalt salt precursor, the solvent is fixed to be acetic acid with the same drying condition of 0.4 h at 25°C in air, which leaves a large amount of acetic acid in the precursor coating. We study the effect of cobalt salt precursors on the Co3O4 morphology by comparing volatile cobalt acetate Co(CH3COO)2·4H2O with non-volatile cobalt nitrate Co(NO3)2·6H2O. Volatile cobalt acetate has been used for the above control experiments and leads to the formation of the Co3O4 NP-chain morphology (Figure 1d) when there is sufficient residual solvent. When non-volatile cobalt nitrate is used as the precursor, a shell is formed on the CuO NWs instead of a NP-chain (Figure 3a), despite the presence of a large amount of residual solvent. The shell coating at the surface of the CuO NWs is about 9-nm thick (Figure 3b). The TEM-EDS analysis (Figure 3c) shows the presence of both Cu and Co peaks along with the O peak in the coated NW. Further high-resolution TEM (HRTEM) characterization (Figure 3d) reveals that the final NW consists of a single crystal CuO NW core with a [111] growth direction and a thin polycrystalline shell with an interplanar spacing of 0.25 nm, which corresponds to the spacing of (311) planes of Co3O4.

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA. xlzheng@stanford.edu.

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.

No MeSH data available.