Abstract
The solvothermal decomposition of iron complexes using the heat-up process enables monodisperse Fe3O4 nanoparticle synthesis. Here, we demonstrate that the high reduction potential capability of alkaline metal reagents in the reductive environment allows for pure magnetite phase formation at 200 °C, which is lower than that of typical synthetic method and offers highly crystalline superparamagnetic and ferrimagnetic nanostructures with the ability to control uniformity including spherical and cubic morphology with narrow size distributions. Our method involved reduction of the acetylacetonate and acetate anions to aldehyde and alcohol as an oxygen resource for iron oxide nucleation in an inert condition. For confirming the developed pure surface phase of alkaline metal reagent-assisted magnetite nanoparticle, the magnetic field-dependent shifting of blocking temperature was investigated. The degree of the exchange interaction between core spins and disordered surface spins is attributed to the ratio of core spins and disordered surface spins. The decrease in disordered surface spins deviation due to an enhanced pure phase of magnetite nanoparticles exhibited the negligible shift of the blocking temperature under differently applied external field, and it demonstrated that alkaline metal reagent-induced reductive conditions enable less formation of both disordered surface spins and biphasic nanostructures.
Highlights
Monodisperse magnetic nanostructures have attracted significant interest over last decade due to their importance for both fundamental science and technological applications [1,2,3,4]
We found that an alkaline metal acetate reagent involving high reduction potential lead to the burst nucleation of magnetite nanoparticles in the organic solvent phase around 180–200 ◦ C at which an oxygen source can be generated from decomposed acetylacetonate and acetate anions which are working as an oxidizing agent
The higher concentration of alkaline metal reagent produced the amorphous phase formation at the 200 ◦ C and the maghemite phase with alkaline metal doping was obtained under a reflux temperature condition. 3 mmol of iron (III) acetylacetonate was kept in this study
Summary
Monodisperse magnetic nanostructures have attracted significant interest over last decade due to their importance for both fundamental science and technological applications [1,2,3,4]. Among advanced approaches for magnetic nanocrystal synthesis including co-precipitation reactions [8,9], sol-gel [10], hydrothermal/solvothermal [11], and microemulsion or microwave-assisted methods [12], the formation of monodisperse Fe3 O4 nanoparticles has been demonstrated with two typical wet chemical synthetic approaches: (I) solvothermal decomposition of iron (III) oleate complexes; and (2) reductively enhanced reaction using iron (III) acetylacetonate reagents with oleylamine under the reflux condition of high-temperature organic solvents [13,14,15]. Metals 2018, 8, 107 dimensional and phase-controlled synthetic method for magnetite nanostructures, assisted by alkaline metal precursors that show higher reduction potentials than that of iron complexes reagent. In the case of organic phase synthesis, the high-temperature thermal decomposition of iron (III) oleate complexes in alkene hydrocarbon solvent (e.g., 1-octadecene) is a versatile method for monodisperse magnetite nanoparticles [13]
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