Real-Time Dynamics of Galvanic Replacement Reactions of Silver Nanocubes and Au Studied by Liquid-Cell Transmission Electron Microscopy Shu Fen Tan,† Guanhua Lin,‡,§,∥,⊥ Michel Bosman,#,∇ Utkur Mirsaidov,*,‡,§,∥,⊥ and Christian A. Nijhuis*,†,⊥ †
Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore Centre for Bioimaging Sciences and Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, 117543, Singapore § Department of Physics, National University of Singapore, 2 Science Drive 3, 117551, Singapore ∥ NUSNNI-NanoCore, National University of Singapore, 5A Engineering Drive 1, 117411, Singapore ⊥ Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, 117546, Singapore # Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, 138634, Singapore ∇ Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, 117575, Singapore ‡
S Supporting Information *
ABSTRACT: We study the galvanic replacement reaction of silver nanocubes in dilute, aqueous ethylenediaminetetraacetic acid disodium salt (EDTA)-capped gold aurate solutions using in situ liquid-cell electron microscopy. Au/ Ag etched nanostructures with concave faces are formed via (1) etching that starts from the faces of the nanocubes, followed by (2) the deposition of an Au layer as a result of galvanic replacement, and (3) Au deposition via particle coalescence and monomer attachment where small nanoparticles are formed during the reaction as a result of radiolysis. Analysis of the Ag removal rate and Au deposition rate provides a quantitative picture of the growth process and shows that the morphology and composition of the final product are dependent on the stoichiometric ratio between Au and Ag. KEYWORDS: galvanic replacement, nanoparticle growth, in situ TEM, growth kinetics, reaction dynamics
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evolution, and often it is unclear whether the growth process proceeds via one or multiple pathways10 in parallel. In recent years, in situ liquid-cell electron microscopy has evolved as an emerging technique for elucidating the mechanisms of NP formation in real-time with subnanometer resolution.10−12 This technique makes it possible to monitor dynamics and quantify the structural and morphological changes during NPs growth.13−16
anoparticle (NP) formation and reaction dynamics during chemical synthesis in solution have been widely studied using ex situ methods.1−7 A popular method is the so-called “quench-and-look” approach, where the reaction is stopped at various stages, after which the intermediate reaction products are imaged with transmission electron microscopy (TEM).8,9 This approach yields detailed information regarding the structure of the (intermediate) reaction products, but the dynamics of the reactions, early stages of the reaction, or fast reactions cannot be tracked. Also unknown is the way in which the sample preparation, i.e., quenching, drop-casting, drying, etc., affects the reaction.1,2 These limitations complicate mechanistic studies of structural © 2016 American Chemical Society
Received: May 7, 2016 Accepted: July 7, 2016 Published: July 7, 2016 7689
DOI: 10.1021/acsnano.6b03020 ACS Nano 2016, 10, 7689−7695
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contrast, the Ag nanocubes that react with AuCl4− undergo complete dealloying, resulting in porous nanocages. To understand the dynamic processes of galvanic replacement, Sun et al.21 followed the replacement reaction between Ag nanowires and HAuCl4 using in situ transmission X-ray microscopy (TXM) in combination with a flow cell reactor. They observed three processes: (1) local initiation of pitting process; (2) anisotropic etching of Ag nanowires and uniform coating of Au; and (3) reconstruction of nanowire walls via Ostwald ripening. However, the spatial resolution of the TXM is rather low (10−25 nm) relative to conventional TEM imaging (
