Center for Functional Nanomaterials Seminar
"In situ studies of nucleation and growth of nanoparticles under realistic conditions"
Presented by Elena Schevchenko, Argonne National Laboratory
Monday, February 8, 2016, 11:00 am — Conference Room A, Bldg. 735
The progress in colloidal synthesis allowed reaching a high degree of controls in synthesis of nanoparticles. As a result, nanoparticles come in many different shapes, sizes and compositions. Combining multiple components within individual nanoparticles or doping of nanoparticles are simple ways to control chemical and physical properties at nanoscale to obtain efficient catalysts and advanced energy conversion and storage systems. However the successful synthetic protocols are based on empirical rules based on numerous trials and errors and often the mechanism of nucleation and growth of nanoparticles remains unclear. I will present in situ study on the nucleation and growth kinetics and the temporal changes in the crystal structure of the metal dumbbell NPs (e.g. CoPt3/Au, Pt/Au and PtFe/Au). Using synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS) techniques we were able to catch the transient stages of structural and volumetric changes of NPs. We found that in the early stage of the reaction intermediate core/shell heterostructure is formed prior to dumbbells. The transition of the core/shell into the dumbbell occurs via strain relaxation of the pseudomorphic Au shell resulting in the nucleation of a strain-free Au domain. I will discuss the formation and doping process of iron and iron oxide NPs in real time by in situ synchrotron X-ray absorption spectroscopy. In our study we revealed that the mass flow of the metal triggered by oxidation is responsible for the internalization of the dopant (molybdenum) adsorbed at the surface of the host iron NPs. The new oxidation induced doping mechanism allows control over the doping levels by varying the amount of dopant precursor. Our in situ studies also showed that the dopant precursor substantially changes the reaction kinetics of formation of iron and iron oxide NPs.
Hosted by: Oleg Gang
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