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 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.
Highlights
In the past years, nanomaterials have been attracted extensive interests due to their unique properties and potential applications in chemistry, physics, biology, and catalysis
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
X-ray diffraction measurements In situ XRD of the Co@SiO2 core-shell nanoparticles was measured at the beamline 4B9A-XRD of Beijing Synchrotron Radiation Facility (BSRF) using an image plate
Summary
Nanomaterials have been attracted extensive interests due to their unique properties and potential applications in chemistry, physics, biology, and catalysis. Magnetic nanoparticles have potential applications in catalyst, resonance imaging, drug targeting, and bio-conjugation. The magnetic nanoparticles can be oxidized in atmosphere and limiting the applications of these nanomaterials [1,2,3]. A series of supported cobalt or cobalt oxide materials such as Co/Al2O3, Co/κ-Al2O3, Co/SiO2, and Co/TiO2 have been studied for catalysis. The most famous application of the Co/SiO2 and Co/Al2O3 catalysts is for the Fischer-Tropsch synthesis [4,5,6,7,8]. Das investigated the influence of support type and cobalt cluster size on the kinetics of Fischer-Tropsch synthesis
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have