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Synthesis of cobalt nanowires in aqueous solution under an external magnetic field

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ABSTRACT

In contrast to the majority of related experiments, which are carried out in organic solvents at high temperatures and pressures, cobalt nanowires were synthesized by chemical reduction in aqueous solution with the assistance of polyvinylpyrrolidone (PVP) as surfactant under moderate conditions for the first time, while an external magnetic field of 40 mT was applied. Uniform linear cobalt nanowires with relatively smooth surfaces and firm structure were obtained and possessed an average diameter of about 100 nm with a coating layer of PVP. By comparison, the external magnetic field and PVP were proven to have a crucial influence on the morphology and the size of the synthesized cobalt nanowires. The prepared cobalt nanowires are crystalline and mainly consist of cobalt as well as a small amount of platinum. Magnetic measurements showed that the resultant cobalt nanowires were ferromagnetic at room temperature. The saturation magnetization (Ms) and the coercivity (Hc) were 112.00 emu/g and 352.87 Oe, respectively.

No MeSH data available.


SEM images of cobalt nanowires prepared under an external magnetic field with PVP (a,b) and without PVP (d,e), and cobalt nanowires prepared without an external magnetic field (g,h). The insets (c, f) show the corresponding TEM images of cobalt nanowires (b,e), respectively.
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Figure 1: SEM images of cobalt nanowires prepared under an external magnetic field with PVP (a,b) and without PVP (d,e), and cobalt nanowires prepared without an external magnetic field (g,h). The insets (c, f) show the corresponding TEM images of cobalt nanowires (b,e), respectively.

Mentions: Fig. 1,b show SEM images of cobalt nanowires prepared with PVP in aqueous solution under an external magnetic field. Uniform linear cobalt nanowires with a mean diameter of about 100 nm were observed, which were much smaller than those prepared in our previous studies in diameter (about 500 nm) [12]. The cobalt nanowires possessed relative smooth surface without apparent aggregation. Fig. 1 shows the TEM image of the PVP-protected cobalt nanowires prepared under an external magnetic field. The nanowires exhibited a firm linear structure without any gap. Furthermore, the diameter of the nanowire shown in the TEM image is about 60 nm, while that in Fig. 1 is about 100 nm. The obvious difference in diameter observed by SEM and TEM indicated that synthesized cobalt nanowires were uniformly coated by a layer of PVP whose thickness was about 20 nm. Fig. 1–f shows SEM and TEM images of cobalt nanowires prepared without PVP in aqueous solution under an external magnetic field. In the absence of PVP, nanowires with a relatively rough surface were obtained, whose size distribution was in the range of 200 to 350 nm. There were also some chain-like structures observed by SEM. It demonstrated that PVP, as a surfactant, had a crucial influence on the morphology and the size of cobalt nanowires synthesized via this method. Fig. 1,h shows SEM images of cobalt nanowires prepared without an external magnetic field. In the absence of an external magnetic field, only spherical particles with the diameter of about 250 nm were obtained, which aggregated without an obvious orientation. Comparing the diameter with that of the nanowires in Fig. 1, it can be inferred that applying an external magnetic field could inhibit the growth of the products. During the experimental process, small cobalt nanoparticles were generated in the solution at first, regardless of the presence of the external magnetic field. Then these small nanoparticles agglomerated and formed larger particles that started to align along the external magnetic field. As the reaction proceeded, Co(II) ions in the solution were reduced and deposited in the gaps between particles, resulting in the formation of cobalt nanowires [11,14].


Synthesis of cobalt nanowires in aqueous solution under an external magnetic field
SEM images of cobalt nanowires prepared under an external magnetic field with PVP (a,b) and without PVP (d,e), and cobalt nanowires prepared without an external magnetic field (g,h). The insets (c, f) show the corresponding TEM images of cobalt nanowires (b,e), respectively.
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Related In: Results  -  Collection

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Figure 1: SEM images of cobalt nanowires prepared under an external magnetic field with PVP (a,b) and without PVP (d,e), and cobalt nanowires prepared without an external magnetic field (g,h). The insets (c, f) show the corresponding TEM images of cobalt nanowires (b,e), respectively.
Mentions: Fig. 1,b show SEM images of cobalt nanowires prepared with PVP in aqueous solution under an external magnetic field. Uniform linear cobalt nanowires with a mean diameter of about 100 nm were observed, which were much smaller than those prepared in our previous studies in diameter (about 500 nm) [12]. The cobalt nanowires possessed relative smooth surface without apparent aggregation. Fig. 1 shows the TEM image of the PVP-protected cobalt nanowires prepared under an external magnetic field. The nanowires exhibited a firm linear structure without any gap. Furthermore, the diameter of the nanowire shown in the TEM image is about 60 nm, while that in Fig. 1 is about 100 nm. The obvious difference in diameter observed by SEM and TEM indicated that synthesized cobalt nanowires were uniformly coated by a layer of PVP whose thickness was about 20 nm. Fig. 1–f shows SEM and TEM images of cobalt nanowires prepared without PVP in aqueous solution under an external magnetic field. In the absence of PVP, nanowires with a relatively rough surface were obtained, whose size distribution was in the range of 200 to 350 nm. There were also some chain-like structures observed by SEM. It demonstrated that PVP, as a surfactant, had a crucial influence on the morphology and the size of cobalt nanowires synthesized via this method. Fig. 1,h shows SEM images of cobalt nanowires prepared without an external magnetic field. In the absence of an external magnetic field, only spherical particles with the diameter of about 250 nm were obtained, which aggregated without an obvious orientation. Comparing the diameter with that of the nanowires in Fig. 1, it can be inferred that applying an external magnetic field could inhibit the growth of the products. During the experimental process, small cobalt nanoparticles were generated in the solution at first, regardless of the presence of the external magnetic field. Then these small nanoparticles agglomerated and formed larger particles that started to align along the external magnetic field. As the reaction proceeded, Co(II) ions in the solution were reduced and deposited in the gaps between particles, resulting in the formation of cobalt nanowires [11,14].

View Article: PubMed Central - HTML - PubMed

ABSTRACT

In contrast to the majority of related experiments, which are carried out in organic solvents at high temperatures and pressures, cobalt nanowires were synthesized by chemical reduction in aqueous solution with the assistance of polyvinylpyrrolidone (PVP) as surfactant under moderate conditions for the first time, while an external magnetic field of 40 mT was applied. Uniform linear cobalt nanowires with relatively smooth surfaces and firm structure were obtained and possessed an average diameter of about 100 nm with a coating layer of PVP. By comparison, the external magnetic field and PVP were proven to have a crucial influence on the morphology and the size of the synthesized cobalt nanowires. The prepared cobalt nanowires are crystalline and mainly consist of cobalt as well as a small amount of platinum. Magnetic measurements showed that the resultant cobalt nanowires were ferromagnetic at room temperature. The saturation magnetization (Ms) and the coercivity (Hc) were 112.00 emu/g and 352.87 Oe, respectively.

No MeSH data available.