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Tracking the restructuring of oxidized silver-indium nanoparticles under a reducing atmosphere by environmental HRTEM

Abstract

Multimetallic nano-alloys display a structure and consequently physicochemical properties evolving under reactive environment. Following and understanding this evolution is therefore crucial for future applications in gas sensing and heterogeneous catalysis. In view hereof, the structural evolution of oxidized Ag25In75 bimetallic nanoparticles under varying H2 partial pressures (PH2) and substrate temperatures (Ts) has been investigated in real-time through environmental transmission microscopy (E-TEM) while keeping atomic resolution. Small Ag25In75 bimetallic nanoparticles, produced by laser vaporization, are found (after air transfer) to consist of an indium-oxide shell surrounding a silver-rich alloyed phase. For large enough PH2 and Ts the direct reduction of the indium oxide shell, immediately followed by the melting or the diffusion onto the carbon substrate or of the reduced indium atoms, is found to be the dominant mechanism. This reduction is concomitant with the growth of the core, indicating a partial diffusion of indium atoms from the shell towards the particle volume. The “surviving” particles therefore consist of a silver-indium alloy, very stable and remarkably resistant against oxidation contrary to native clusters. Interestingly, in the (PH2, Ts) space, the transition from “soft” (core-shell particles for small (PH2, Ts) values) to “strong” reduction conditions (silver-rich alloys for large (PH2, Ts) products) defines an intermediate domain where the preferred formation of Janus structures is detected. These results are discussed in terms of thermodynamic driving forces in relation to alloying and interface energies. This work shows the potential of high-resolution ETEM for unravelling the mechanisms for nanoparticle reorganization under chemical reactivity.

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Publication details

The article was received on 26 Apr 2017, accepted on 31 Jul 2017 and first published on 01 Aug 2017


Article type: Paper
DOI: 10.1039/C7NR02986A
Citation: Nanoscale, 2017, Accepted Manuscript
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    Tracking the restructuring of oxidized silver-indium nanoparticles under a reducing atmosphere by environmental HRTEM

    J. Ramade, C. Langlois, M. Pellarin, L. Piccolo, M. Lebeault, T. Epicier, M. Aouine and E. Cottancin, Nanoscale, 2017, Accepted Manuscript , DOI: 10.1039/C7NR02986A

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