Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.
Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.
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DOI：
10.1186/s11671-015-0756-z
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发表时间：
2015
影响因子：
--
通讯作者：
Zhou Y
中科院分区：
文献类型：
--
作者：
Zhang K;Zhao Z;Wu Z;Zhou Y
本文采用溶胶-凝胶法制备了Co@SiO_2核壳纳米粒子。采用同步辐射原位X射线衍射法(XRD)和X射线吸收精细结构法(XAFS)研究了Co核纳米粒子在空气和氮气保护下的氧化行为。结果表明，无论是在空气中还是在氮气保护条件下，钴芯的氧化都经历了三个阶段。在第一步，从室温到200℃，Co核以Co0态为主，同时还有少量的Co2+离子。当温度高于300℃时，Co核与SiO_2壳之间的界面逐渐氧化成Co2+，并观察到CoO层。当温度升高到800℃时，Co核被氧化为Co3O4或Co3O4/CoO。然而，Co@SiO_2在空气和氮气中的氧化动力学是不同的。由于SiO_2壳层的介孔性质，空气中的O2一般可以很容易地通过SiO_2壳层进入Co核表面，诱导Co核的氧化。但在氮气条件下，氧原子只能来自SiO_2壳层，因此O原子在Co核与SiO_2壳层界面的扩散效应起着关键作用。
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 Co0 state as well as small amount of Co2+ ions. When temperature was above 300°C, the interface between Co cores and SiO2 shells was gradually oxidized into Co2+, 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.
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