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

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 presynthesized metallic a-Fe NPs. Findings indicate that an asymmetric heterostructure emerges from the exchange, which is followed by rapid oxidation to form a NiFe-M 3 O 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 3 O 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 a-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.

Synthetic Approaches to Colloidal Nanocrystal Heterostructures Based on Metal and Metal-Oxide Materials

“…One significant account documented the formation of NiFe-Me x O y (Me = Ni, Fe) hetero-dimer CNHSs upon the reaction of α-Fe CNCs with nickel acetylacetonate in an ODE-diluted mixture of OLAM and hexadecylamine at 180 °C [ 299 ]. Under the specified synthesis conditions, the metal seeds underwent partial galvanic replacement and alloying with Ni, followed by rapid partial oxidation.…”

“…Scheme 3 d) (reproduced with permission from Ref. [ 299 ], Copyright 2015, Royal Society of Chemistry). ( g , h ) TEM and HRTEM images of Fe 3 O 4 –Au–Fe 3 O 4 hetero-trimer CNHSs with a Au domain connecting two Fe 3 O 4 domains, derived from induced welding of preformed Au–Fe 3 O 4 hetero-dimer seeds (cf.…”

Investigation of the Structural Changes and Catalytic Properties of FeNi Nanostructures as a Result of Exposure to Gamma Radiation

“…This application idea is based on the use of nanostructures as a container for binding a drug on the surface of nanostructures and its further transportation in the body by varying the external magnetic field to control the trajectory of the nanostructures and collecting the drug by magnetostriction. Along those lines, permalloy structures with the most suitable structural and magnetic properties, along with oxide forms of iron, are considered as the most promising candidates for this industry [54,55]. At the same time, one of the most significant limitations on the applicability of nanostructures for this area is their resistance to the biological environment of the body in which they will be located during the delivery of drugs.…”

Alloying and Phase Transformation of Fe/FeNi Core/Alloy Nanoparticles at High Temperatures

“…30,31 We have been developed a core/alloy (CA) approach towards crafting alloy nanoparticle interfaces. 2,[32][33][34] By focusing on depositing or forming a nanometer thin alloy at a pre-formed nanoparticle interface, we attempt to overcome challenges often faced when mixing metal salts followed by co-reduction, 6,[35][36][37] electrochemical reduction, 38,39 performing galvanic displacement, 34 or thermal treatment, 40,41 where differences in redox potentials, decompositions, and precursor reactivity makes controlling the final alloy composition, distribution, and phase homogeneity, difficult.…”