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Quality and high yield synthesis of Ag nanowires by microwave-assisted hydrothermal method.

Meléndrez MF, Medina C, Solis-Pomar F, Flores P, Paulraj M, Pérez-Tijerina E - Nanoscale Res Lett (2015)

Bottom Line: One of the drawbacks presented so far in the synthesis of nanostructures by polyol path is the high temperature used in the process, which is superior than the boiling point of solvent (ethylene glycol), and also its excessive reaction time.It was found that the reaction time needs to be decreased because of the NWs which start to deform and break up due to significant increase in the pressure's system.Energy-dispersive X-ray spectroscopy and electron diffraction analysis (SAED) did not show corresponding phases of AgO.

View Article: PubMed Central - PubMed

Affiliation: Advanced Nanocomposites Research Group (GINA), Faculty of Engineering, University of Concepcion, 270 Edmundo Larenas, Box 160-C, Concepcion, 4070409 Chile ; Hybrid Materials Laboratory (HML), Faculty of Engineering, University of Concepcion, 270 Edmundo Larenas, Box 160-C, Concepcion, 4070409 Chile ; Department of Materials Engineering (DIMAT), Faculty of Engineering, University of Concepcion, 270 Edmundo Larenas, Box 160-C, Concepcion, 4070409 Chile.

ABSTRACT
Silver nanowires (Ag-NWs) were obtained using microwave-assisted hydrothermal method (MAH). The main advantage of the method is its high NWs production which is greater than 90%. It is also easy, fast, and highly reproducible process. One of the drawbacks presented so far in the synthesis of nanostructures by polyol path is the high temperature used in the process, which is superior than the boiling point of solvent (ethylene glycol), and also its excessive reaction time. Here, Ag-NWs with diameters of 70 to 110 nm were synthesized in 5 min in large quantities. Results showed that dimensions and shape of nanowires were very susceptible to changes with reaction parameters. The reactor power and reactor fill capacity were important for the synthesis. It was found that the reaction time needs to be decreased because of the NWs which start to deform and break up due to significant increase in the pressure's system. Energy-dispersive X-ray spectroscopy and electron diffraction analysis (SAED) did not show corresponding phases of AgO. Some aspects about synthesis parameters which are related to the percent yield and size of nanowires are also discussed.

No MeSH data available.


Proposed mechanism for the synthesis of silver nanowires through microwave-assisted hydrothermal method (MAH).
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Fig6: Proposed mechanism for the synthesis of silver nanowires through microwave-assisted hydrothermal method (MAH).

Mentions: HRTEM analysis of nanowires obtained at 800 W and 5 min was performed in order to determine its structure. These materials tend to grow as penta twinned at {111} planes. Figure 5a shows a FFT of plane area in the HRTEM image. The pattern clearly shows that there is a superposition of more than one diffraction pattern. The FFT corresponds to the diffraction pattern of penta-twinned NWs [32], corresponding to a superposition of [100] and [112] zone axes (double check). The calculated spacing distance was 2.35 and 2.03 Å, which correspond to (111) and (200) planes of metallic silver (JCPDS file No. 04–0783 from ASTM), respectively. Analysis revealed that Ag-NWs have a preferential growth in the [110] direction (along the fivefold axis), shown in Figure 5a. This is confirmed also because EDX analysis revealed that these were only constituted by silver atoms (2.984 keV [Ag (Lα)] and 3.151 keV [Ag (Lβ)]). Phases corresponding to AgO were not found; thereby, possible oxidation of the nanowires was discarded. The growth mechanism of the current MAH method is deduced to be similar to that previously described for the polyol process. It is important to consider that the reaction times with the MAH method are smaller, which prevents that the increment of the hydronium ions concentration degrades the silver seeds and thereby prevent that percentage of nanowires obtained in the process is reduced. In Figure 6, a diagram of possible growth mechanism silver nanowires by the MAH method is shown [33]. The mechanism steps are: i) the reduction of silver ions, ii) the formation of multi-twinned-crystal seeds, and iii) the growth of seeds into nanowires. In the first step, Ag+ ions are reduced to Ag° atoms by ethylene glycol [34]. In the second step, the adsorption of PVP on the Ag passivates the more active {100} plane and also acts as the driving force to form cyclic penta-twinned crystal seeds [23]; the penta-twinned nanocrystals play a key role in the confinement of the diameters of the nanowires and the growth of the longitudinal direction. In the last step, due to much stronger chemical bonding between PVP and {100} compared to that between PVP and {111}, the {111} facet remains active, resulting in longer wire with a pentagonal cross section. As mentioned above, the advantage of the MAH method is based on reducing the growth times to prevent the degradation of the penta-twinned-crystal seeds due to the acid formed in solution. In this method, the system pressure increases rapidly; this variable is closely related to the reactor power, reactor fill capacity, reaction time, and molar ratio. Therefore, the growth is very fast so that the nanowires diameter could be higher compared to other open system wet methods.Figure 6


Quality and high yield synthesis of Ag nanowires by microwave-assisted hydrothermal method.

Meléndrez MF, Medina C, Solis-Pomar F, Flores P, Paulraj M, Pérez-Tijerina E - Nanoscale Res Lett (2015)

Proposed mechanism for the synthesis of silver nanowires through microwave-assisted hydrothermal method (MAH).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384996&req=5

Fig6: Proposed mechanism for the synthesis of silver nanowires through microwave-assisted hydrothermal method (MAH).
Mentions: HRTEM analysis of nanowires obtained at 800 W and 5 min was performed in order to determine its structure. These materials tend to grow as penta twinned at {111} planes. Figure 5a shows a FFT of plane area in the HRTEM image. The pattern clearly shows that there is a superposition of more than one diffraction pattern. The FFT corresponds to the diffraction pattern of penta-twinned NWs [32], corresponding to a superposition of [100] and [112] zone axes (double check). The calculated spacing distance was 2.35 and 2.03 Å, which correspond to (111) and (200) planes of metallic silver (JCPDS file No. 04–0783 from ASTM), respectively. Analysis revealed that Ag-NWs have a preferential growth in the [110] direction (along the fivefold axis), shown in Figure 5a. This is confirmed also because EDX analysis revealed that these were only constituted by silver atoms (2.984 keV [Ag (Lα)] and 3.151 keV [Ag (Lβ)]). Phases corresponding to AgO were not found; thereby, possible oxidation of the nanowires was discarded. The growth mechanism of the current MAH method is deduced to be similar to that previously described for the polyol process. It is important to consider that the reaction times with the MAH method are smaller, which prevents that the increment of the hydronium ions concentration degrades the silver seeds and thereby prevent that percentage of nanowires obtained in the process is reduced. In Figure 6, a diagram of possible growth mechanism silver nanowires by the MAH method is shown [33]. The mechanism steps are: i) the reduction of silver ions, ii) the formation of multi-twinned-crystal seeds, and iii) the growth of seeds into nanowires. In the first step, Ag+ ions are reduced to Ag° atoms by ethylene glycol [34]. In the second step, the adsorption of PVP on the Ag passivates the more active {100} plane and also acts as the driving force to form cyclic penta-twinned crystal seeds [23]; the penta-twinned nanocrystals play a key role in the confinement of the diameters of the nanowires and the growth of the longitudinal direction. In the last step, due to much stronger chemical bonding between PVP and {100} compared to that between PVP and {111}, the {111} facet remains active, resulting in longer wire with a pentagonal cross section. As mentioned above, the advantage of the MAH method is based on reducing the growth times to prevent the degradation of the penta-twinned-crystal seeds due to the acid formed in solution. In this method, the system pressure increases rapidly; this variable is closely related to the reactor power, reactor fill capacity, reaction time, and molar ratio. Therefore, the growth is very fast so that the nanowires diameter could be higher compared to other open system wet methods.Figure 6

Bottom Line: One of the drawbacks presented so far in the synthesis of nanostructures by polyol path is the high temperature used in the process, which is superior than the boiling point of solvent (ethylene glycol), and also its excessive reaction time.It was found that the reaction time needs to be decreased because of the NWs which start to deform and break up due to significant increase in the pressure's system.Energy-dispersive X-ray spectroscopy and electron diffraction analysis (SAED) did not show corresponding phases of AgO.

View Article: PubMed Central - PubMed

Affiliation: Advanced Nanocomposites Research Group (GINA), Faculty of Engineering, University of Concepcion, 270 Edmundo Larenas, Box 160-C, Concepcion, 4070409 Chile ; Hybrid Materials Laboratory (HML), Faculty of Engineering, University of Concepcion, 270 Edmundo Larenas, Box 160-C, Concepcion, 4070409 Chile ; Department of Materials Engineering (DIMAT), Faculty of Engineering, University of Concepcion, 270 Edmundo Larenas, Box 160-C, Concepcion, 4070409 Chile.

ABSTRACT
Silver nanowires (Ag-NWs) were obtained using microwave-assisted hydrothermal method (MAH). The main advantage of the method is its high NWs production which is greater than 90%. It is also easy, fast, and highly reproducible process. One of the drawbacks presented so far in the synthesis of nanostructures by polyol path is the high temperature used in the process, which is superior than the boiling point of solvent (ethylene glycol), and also its excessive reaction time. Here, Ag-NWs with diameters of 70 to 110 nm were synthesized in 5 min in large quantities. Results showed that dimensions and shape of nanowires were very susceptible to changes with reaction parameters. The reactor power and reactor fill capacity were important for the synthesis. It was found that the reaction time needs to be decreased because of the NWs which start to deform and break up due to significant increase in the pressure's system. Energy-dispersive X-ray spectroscopy and electron diffraction analysis (SAED) did not show corresponding phases of AgO. Some aspects about synthesis parameters which are related to the percent yield and size of nanowires are also discussed.

No MeSH data available.