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      The transformation of α-Fe nanoparticles into multi-domain FeNi–M3O4 (M = Fe, Ni) heterostructures by galvanic exchange

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          Abstract

          Galvanic exchange at metallic Fe-nanoparticles is shown to result in new FeNi–M 3O 4 heterostructures.

          Abstract

          In this work we describe a novel method to prepare multi-domain metal–metal oxide heterostructured nanoparticles (NPs). We investigated the ability of Ni(acac) 2 to undergo galvanic exchange with pre-synthesized metallic α-Fe NPs. Findings indicate that an asymmetric heterostructure emerges from the exchange, which is followed by rapid oxidation to form a NiFe–M 3O 4 (M = Fe, Ni) alloy-oxide microstructure. Nucleation and growth was monitored using UV-vis and TEM, and crystal evolution, composition change, and oxidation states were measured by XRD and XPS respectively. Galvanic exchange and growth was studied by varying Ni : Fe molar feed ratios during synthesis. The findings indicate that at low Ni : Fe ratios, the NP forms multiple domains of oxides, whereas at higher ratios form regions with novel Ni–NiFe–M 3O 4 interfaces. These new heterostructures were highly magnetic, and the extent of magnetization was proportional to composition and morphology, where NPs prepared at high Ni : Fe feed ratios resulted in decreased saturation magnetization and increased magnetic hysteresis. The nickel deposition and NP growth mechanism was considered as a combination of both galvanic exchange and reduction, and the observed rapid oxidation of the remaining α-Fe core was considered in light of electron density change at the heterostructures interfaces. Nanomaterials like these may find use as components in magnetic storage and spintronic devices, probes in biomedicine, additives in corrosion resistant coatings, and even as 3D printing inks.

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          The preparation of magnetic nanoparticles for applications in biomedicine

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            Facile synthesis of Ag nanocubes and Au nanocages.

            This protocol describes a method for the synthesis of Ag nanocubes and their subsequent conversion into Au nanocages via the galvanic replacement reaction. The Ag nanocubes are prepared by a rapid (reaction time < 15 min), sulfide-mediated polyol method in which Ag(I) is reduced to Ag(0) by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Na(2)S. When the concentration of Ag atoms reaches supersaturation, they agglomerate to form seeds that then grow into Ag nanostructures. The presence of both PVP and Na(2)S facilitate the formation of nanocubes. With this method, Ag nanocubes can be prepared and isolated for use within approximately 3 h. The Ag nanocubes can then serve as sacrificial templates for the preparation of Au nanocages, with a method for their preparation also described herein. The procedure for Au nanocage preparation and isolation requires approximately 5 h.
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              Oleylamine in Nanoparticle Synthesis

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                Author and article information

                Journal
                JMCCCX
                Journal of Materials Chemistry C
                J. Mater. Chem. C
                Royal Society of Chemistry (RSC)
                2050-7526
                2050-7534
                2015
                2015
                : 3
                : 24
                : 6367-6375
                Affiliations
                [1 ]Department of Chemistry
                [2 ]Syracuse University
                [3 ]Syracuse
                [4 ]USA
                [5 ]Analytical and Diagnostic Laboratory
                [6 ]Binghamton University
                [7 ]Binghamton
                Article
                10.1039/C5TC00929D
                © 2015
                Product
                Self URI (article page): http://xlink.rsc.org/?DOI=C5TC00929D

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