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Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.

Zhang K, Zhao Z, Wu Z, Zhou Y - Nanoscale Res Lett (2015)

Bottom Line: As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO.Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells.However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201204 China.

ABSTRACT
In this paper, the Co@SiO2 core-shell nanoparticles were prepared by the sol-gel method. The oxidization of Co core nanoparticles was studied by the synchrotron radiation-based techniques including in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) up to 800°C in air and N2 protection conditions, respectively. It was found that the oxidization of Co cores is undergoing three steps regardless of being in air or in N2 protection condition. In the first step ranging from room temperature to 200°C, the Co cores were dominated by Co(0) state as well as small amount of Co(2+) ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co(2+), and the CoO layer was observed. As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO. Nevertheless, the oxidization kinetics of Co cores is different for the Co@SiO2 in air and N2 gas conditions. Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells. However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

No MeSH data available.


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TEM image of the as-prepared Co@SiO2core-shell nanoparticles.
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Fig1: TEM image of the as-prepared Co@SiO2core-shell nanoparticles.

Mentions: The TEM image of the Co@SiO2 core-shell nanoparticles is shown in Figure 1. Most of the Co@SiO2 nanoparticles with ~50 nm diameter contain multiple Co cores, but the Co cores are separated from each other. According to the TEM image, the average diameter of Co cores is evaluated to be about 20 nm. The obtained Co@SiO2 core-shell nanoparticles are different from the previous work [13,14] which may be due to the different reaction conditions, such as the rate of protect N2 gas and stirring rate.Figure 1


Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.

Zhang K, Zhao Z, Wu Z, Zhou Y - Nanoscale Res Lett (2015)

TEM image of the as-prepared Co@SiO2core-shell nanoparticles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384979&req=5

Fig1: TEM image of the as-prepared Co@SiO2core-shell nanoparticles.
Mentions: The TEM image of the Co@SiO2 core-shell nanoparticles is shown in Figure 1. Most of the Co@SiO2 nanoparticles with ~50 nm diameter contain multiple Co cores, but the Co cores are separated from each other. According to the TEM image, the average diameter of Co cores is evaluated to be about 20 nm. The obtained Co@SiO2 core-shell nanoparticles are different from the previous work [13,14] which may be due to the different reaction conditions, such as the rate of protect N2 gas and stirring rate.Figure 1

Bottom Line: As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO.Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells.However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201204 China.

ABSTRACT
In this paper, the Co@SiO2 core-shell nanoparticles were prepared by the sol-gel method. The oxidization of Co core nanoparticles was studied by the synchrotron radiation-based techniques including in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) up to 800°C in air and N2 protection conditions, respectively. It was found that the oxidization of Co cores is undergoing three steps regardless of being in air or in N2 protection condition. In the first step ranging from room temperature to 200°C, the Co cores were dominated by Co(0) state as well as small amount of Co(2+) ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co(2+), and the CoO layer was observed. As the temperature increasing to 800°C, the Co cores were oxidized to Co3O4 or Co3O4/CoO. Nevertheless, the oxidization kinetics of Co cores is different for the Co@SiO2 in air and N2 gas conditions. Generally, the O2 in the air could get through the SiO2 shells easily onto the Co core surface and induce the oxidization of the Co cores due to the mesoporous nature of the SiO2 shells. However, in N2 gas condition, the O atoms can only be from the SiO2 shells, so the diffusion effect of O atoms in the interface between Co core and SiO2 shell plays a key role.

No MeSH data available.


Related in: MedlinePlus