title: Synthesis and detection the oxidization of Co cores of Co@SiO2 core-shell nanoparticles by in situ XRD and EXAFS.
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.
authors: Department of Life Science, Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201204 China.
authors: Kunhao
authors: K
authors: Zhang
authors: Department of Life Science, Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai, 201204 China ; State Key Laboratory of Oil and Gas Reservoir and Exploitation, Southwest Petroleum University, Chengdu, 610500 China ; School of Materials Science and Engineering, Southwest Petroleum University, Chengdu, 610500 China.
authors: Ziyan
authors: Z
authors: Zhao
authors: Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049 China.
authors: Zhonghua
authors: Z
authors: Wu
authors: State Key Laboratory of Oil and Gas Reservoir and Exploitation, Southwest Petroleum University, Chengdu, 610500 China ; School of Materials Science and Engineering, Southwest Petroleum University, Chengdu, 610500 China.
authors: Ying
authors: Y
authors: Zhou
keywords: Co@SiO2; Core-shell nanoparticles; In situ XRD/XAFS; Synchrotron radiation techniques