An in situ investigation of the thermal behavior of silver nanocubes with and without a shell of gold Aikaterini Karatzia 1 , K. Loza 1 , O. Prymak 1 , M. Heggen 2 and M. Epple 1 1 Inorganic Chemistry and Center for Nanointegration Duisburg - Essen (CeNIDE), University of Duisburg – Essen, Universitätsstr. 5-7, 45141 Essen, Germany 2 Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany Nanoparticles of noble metals are valuable materials as they exhibit different properties compared to their corresponding bulk material. They present diverse applications in biomedicine, homogeneous and heterogenous catalysis, optics and electronics. 1 Especially faceted nanoparticles, are of great importance in heterogeneous catalysis. However, bimetallic nanoparticles of noble metals have advantages over monometallic ones, not only because they can combine properties of each component, but also due to synergetic effects that can emerge between two different components. 2 In this work monometallic silver and bimetallic core–shell silver–gold nanocubes were synthesized by wet chemical synthesis by a seed–and–growth approach. 3 Both systems were fully characterized by ultraviolet visible spectroscopy (UV-Vis), dynamic light scattering (DLS), scanning (SEM) and transmission electron microscopy (TEM), energy–dispersive X–ray spectroscopy (EDX), atomic absorption spectroscopy (AAS), thermogravimetric analysis (TGA) and X–ray powder diffraction (XRD). Their behavior, stability, and crystallinity were studied at temperatures up to 1000°C by in situ and ex situ heating experiments in SEM, TEM and XRD. For comparison, microcrystalline silver powder and bulk silver were also studied. Microscopy experiments showed that silver nanocubes lost their shape during heating. Due to the comparatively high vapor pressure of silver, sublimation process begins at temperatures above 600 °C under vacuum conditions in SEM, TEM and XRD. The silver–gold core–shell cubes showed almost the same behavior. In situ XRD heating studies confirmed the sublimation of silver nanostructures, in contrast to silver microparticles. Ex situ XRD studies and TGA confirmed that the sublimation of silver nanocubes starts around 650 °C in vacuum due to its high vapor pressure, which is the highest of all noble metals. 4, 5 References 1. Loza, K.; Heggen, M.; Epple, M., Synthesis, Structure, Properties, and Applications of Bimetallic Nanoparticles of Noble Metals. Advanced Functional Materials 2020, 30 (21), 1909260. 2. Zaleska-Medynska, A.; Marchelek, M.; Diak, M.; Grabowska, E., Noble metal-based bimetallic nanoparticles: the effect of the structure on the optical, catalytic and photocatalytic properties. Adv Colloid Interface Sci 2016, 229 , 80-107. 3. Im, S. H.; Lee, Y. T.; Wiley, B.; Xia, Y., Large-Scale Synthesis of Silver Nanocubes: The Role of HCl in Promoting Cube Perfection and Monodispersity. Angewandte Chemie International Edition 2005, 44 (14), 2154-2157. 4. Asoro, M. A.; Kovar, D.; Ferreira, P. J., In situ transmission electron microscopy observations of sublimation in silver nanoparticles. ACS nano 2013, 7 (9), 7844-7852. 5. Ding, Y.; Fan, F.; Tian, Z.; Wang, Z. L., Sublimation‐Induced Shape Evolution of Silver Cubes. small 2009, 5 (24), 2812- 2815.
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